Monday, December 29, 2008

ZDesigner snapshot



I created Qt-based UI for the aircraft design program I am writing. The initial version is available from here:

http://www.katix.org/karoliina/packages/zdesigner-current.tar.gz

ChangeLog
COPYING
zdesigner - Ubuntu Intrepid Binary

You need to have Qt 4.5 installed to run the binary.

Friday, December 26, 2008

Advantage of push-pull

I have been thinking what are the advantages and disadvantages of push-pull configuration. Everyone knows that push-pull has both disadvantages of pusher and tractor configuration but also implements a simple to control center line thrust operation for a critical single engine situation. However, there is more than that to it.

If you think one-of-a-kind aircraft, e.g. what Burt Rutan used to do during the early years. You want to build a twin on a shoestring budget. Then you realize that you have to buy two of everything. What if you have two engines already hanging around but they are not exactly the same make, model and horse power.

In case of center line thrust, no problem. Nothing requires the two engines to be the same. Not even weight and balance. Burt Rutan's Voyager is an example. You can find that the front engine is different from the rear engine.

It might not be because of the reason described above, but if you are into auto conversions and designing a twin, how you plan to get two identical engines for not much cost at all (from totalled cars for example). Might prove to be a challenge, especially in a country like Finland where the population and the availability of engines might be poor. With center line thrust you can use different engines in the front and rear.

By the way: Merry Christmas and Happy New Year!

Sunday, December 21, 2008

Nextcraft

I found a quite interesting site:
http://www.nextcraft.com/
There was for example a 1/3 scale Berkut/Long-Ez project. 1/3 scale RC-model is said to be minimum sufficient for modeling the full scale aircraft, so I find this example quite educational. As can be seen though, the airfoils are different than on the full size plane. This is necessary because of the very low Re of the model. It does not thus model it very accurately, so there might be still surprises on the full scale version when scaling up, but I think it would still be good to do 1/3 models of new aircraft designs.

The direct link to the 1/3 scale Berkut can be found here: http://www.nextcraft.com/berkut01.html

Saturday, December 20, 2008

GA aircraft comparison chart

Here is a interesting specification chart which illustrates the differences between different aircraft types:
http://www.flypas.com/images/DA40_comparison_feb_2008_rev_2_022408.pdf

I knew that information already, but this is a chart you can look at if you don't happen to know which is the difference between Diamond DA40, Cessna C182, Cirrus SR20 and Piper Archer. Needless to mention (but I mention anyway), the models utilizing composite high aspect ratio wings with super-accurate surface and laminar flow airfoils are the winners on this chart, namely the Diamond DA40 and Cirrus SR20. On this chart, the DA40 wins also SR20. Indeed, the DA40 is pretty good compromise, but the SR20 is not so bad compromise either. It has for example larger cockpit for larger people. However, bigger size does not come without a penalty and it is evident in the specs, SR20 takes more power to go as fast as the DA40 with 20 hp smaller engine (75% power = 135 hp whereas on Cirrus 75% power = 150 hp). The biggest losers on the chart, obviously, are made of metal (with protruding pop-rivets), and have turbulent flow over the low aspect ratio wing.

The same page also has a comparison made between trainer type aircrafts:
http://www.flypas.com/images/comare_da20.pdf

The comparison chart contains Diamond DA20-C1 Eclipse, Cessna C172, Piper Warrior and Cirrus SRV.
This is not completely fair because some of the planes are 4 seaters and some two seaters, but isn't still too hard to see the difference between the laminar flow planes compared to turbulent flow planes. Both Diamond DA20-C1 Eclipse and Cirrus SRV use laminar flow airfoil, slotted flaps and a high aspect ratio wing. Both are made of composite materials. I have flown myself the Diamond DA20-C1 Eclipse and the SR20 (the IFR version though, but it is no different from the SRV other than in terms of certification and equipment), both are really nice aircraft to fly and they perform pretty well when comparing to the competition. Of these, the DA20 is most pleasant although quite a bit slower in the reality than the Cirrus.

The page also has a performance vs. altitude chart for three aircraft types - 2 Mooney and Cirrus SR22 (normally aspirated version). From this chart, the effect of the turbo is quite evident on the turbo-version of the Mooney. At high altitudes it is the fastest of the compared aircraft. The comparison would get tougher if the SR22 was the turbo-model which cruises well over 200 kts at high altitude.

http://www.flypas.com/images/comparison1.pdf

The comparison chart has some things which I am not in full agreement with. For example the front hinged canopy superiority. It gives good view from the cockpit yes, but it is stating that it makes it easy to get into the cockpit. That is very far from the truth. It is a lot easier to climb to a Cirrus through the door than to a Diamond. Getting into the Diamond is like getting to a sports car. It is not that difficult and I would not consider it personally a problem, but saying that it is superior in easiness compared to the side doors of Cirrus, that is bullsh*t. Cirrus is a lot bigger and easier to get into. Diamond excels elsewhere than on this. And there are other things too on this list, so please have your filter set to on when reading it. In a sense, the comparison chart in the plastic planes is better.

Here is the comparison from plastic airplanes:
http://philip.greenspun.com/flying/plastic-airplanes

And here is a Cirrus SR20 review:
http://philip.greenspun.com/flying/cirrus-sr20

And here is a Diamond DA40 review:
http://philip.greenspun.com/flying/diamond-da40

Wednesday, December 17, 2008

Low pitching moment NLF airfoil with low sensitivity to bugs and dirt

Here is the Honda's tech paper about the SHM-1 airfoil (which was designed for the Honda-Jet). The airfoil includes features which are not important on low speed low Reynolds number flight but it also has features which makes it ideal for lower speed concepts:

http://hondajet.honda.com/pdf/tech_papers/Journal_of_Aircraft_Vol40_No4_P609_P615_SHM_1_NLF.pdf

SHM-1 could be a good starting point for an airfoil for GA-use. The Re area for the SHM-1 is a lot higher than needed by GA, so it may not be directly applicable, but the ideology in the SHM-1 seems just what would be needed for also high speed high efficiency, long endurance GA aircraft, which in addition to having low drag and high Clmax also exhibits good behavior.

Monday, December 8, 2008

Boundary layer suction

I have stated here previously that the boundary layer suction maybe requires jet engine for having enough power to be wasted for the suction. However, a knowledgeable friend just sent me couple of (more) links as he has used to do now for quite some time. (Thanks by the way). Interestingly enough on this ppt: www.aoe.vt.edu/~mason/Mason_f/LaminarFlowS04.ppt on page 17 it has been stated that the example case of Piper Super Cub only required 2.0 hp for suction. Another example was Cessna L-19 with 17 hp used for suction.

This is very interesting since taking 2-17 hp out of e.g. 200 total hp (=2 x Rotax 914) is quite doable. With smaller engine power as the previously discussed 2 x HKS700E, the available excess horse power for suction would be obviously smaller and taking 7 hp out of the available thrust would be unwelcome whereas taking only 2 hp out of it would be clearly still within limits of potentially feasible and that benefit outweights the loss.

The achieved Clmax increase with boundary layer suction is significant. If on the Cessna example the Clmax increased from 2.5 to 5.0, that makes a whole lot of difference in wing sizing and in turn this affects drag and efficiency significantly.

The downside is that if the wing sizing is done with the expectation of Clmax of 5.0, and then because of mechanical failure, the suction is not available, the stall speed in such emergency would be high. Also potential failure modes are that the suction disappears on final approach or shortly after takeoff.

How to mitigate this potential problem? The suction mechanism would need to be very reliable and most likely it should be doubled. In other words, in twin engine aircraft, either engine should alone be able to supply enough suction so that in case of engine failure of one suction pump failure, the aircraft would not crash but could still safely land on the airport (with the remaining engine and remaining suction pump).

Another way to mitigate the problem could be to not count on the achieved Clmax but only take the benefit of the drag reduction caused by the suction. There comes the question then of the justification of the added complexity. One of the unknown issue to me is that how water ingesting through the perforated skin would be dealt with - it would be pretty severe condition to have whole suction slot full of water. In addition to the suction not functioning properly, the wing would weight significantly more.

What the complexity adds to the manufacturing cost? For small commercial general aviation aircraft (which is targeted to masses and which does not try to achieve anything special but be good all-arounder) it could add more than is justified for the benefits gained from market - simplicity and low cost manufacturing drive these rather than the last decimals in the efficiency. However, for experimental prototype aircraft which is built on basis that price of a work hour is not counted, at least then this might be a feasible idea to incorporate. This would require more investigation, and it could depend quite much on the aircraft configuration, how much gains this could add and what kind of tradeoffs there are to be expected in turn.

Sunday, December 7, 2008

Latest version of my aircraft sizing and estimation utility

Here is the latest version of this (currently command line based but later planned to have a Qt UI) utility. The binary is for MacOSX Leopard (Intel binary). You should run it from terminal.

Karoliina's airplane design utility 0.1

Latest source

How to use (shows couple of iterations for a small two place twin engine aircraft using two HKS700E engines):

Example usage

Changes:

http://www.katix.org/karoliina/packages/ChangeLog_head.txt

The program compiles without modifications under Ubuntu Intrepid. Windows version is not available or planned at this time. No support for the usage for the program will be given at this time.

Sunday, November 30, 2008

Link: High altitude still pictures (60000 ft up)



jcoxon77's photostream, Flicr:
http://www.flickr.com/photos/jcoxon77/

They look pretty cool, don't they?

But 76500 ft looks even cooler:



http://www.flickr.com/photos/nebarnix/sets/72157607393699828/

Interestingly though, 42000 ft still looks pretty amazing:

Will it blend?



Seems like, yes it did :)





Created with the latest iRhino alpha.

Changes:
* Placeholder engine nacelles added.
* Rudder added

I was reading today the book "Fluid dynamic drag" a bit and got kind of inspired: canopies and wind shield discontinuity contributes very much to the drag coefficient of the fuselage. Not only the laminar nose seems important, but all kinds of places where something ends and something else continues are sources of waste of engery.

So if the plane is completely faired with no discontinuity of any kind, theoretically the drag coefficient should be very low.
In this picture, the engine nacelle placeholders are just placeholders, because they are not yet accurate airfoil, and it has not been taken into account that in Rotax engines the propeller shaft is not in the middle of the engine, but almost on the top of the engine, this creates a fairing that has the lower side turned up a bit and is therefore not completely symmetrical.

The engine nacelles may need to be moved outwards, otherwise there is not enough clearance between the fuselage and the propeller arc.

I was also reading one day some NASA tech paper about wing tip mounted propellers. I have not drawn such things to this picture, but I may add it later - small brushless DC motor on each wing tip lowers the induced drag quite a bit according to the tech paper (although on high aspect ratio wing the effect is not that radical as on with a low aspect ratio wing that would otherwise be poor).

Potential issues for placing engine nacelles on wings (which seems pretty necessary for a twin, after all, may be the least bad compromise) and blending are the followings:
* the wings take a lot room to build (because they are very long)
* making the mold is difficult, because it has to be done from CNC cut pieces and glued together
* moving the center section to airport or transporting it in a container may be challenging, because if the area up to engine nacelles is continuous part of the center section and not separatable, it means that this is basically wider than the width of the container, shipping the plane to another continent might be a challenge (it seems that it would need to be flown like the design point has been set)

Wednesday, November 26, 2008

Three turbos in Subaru EJ22

Hey watch this out:
http://www.youtube.com/watch?v=bU2elPTJyqA

Pretty interesting system built around the Subaru.

HALE

I have been thinking one idea for better utilizing the HALE concept (HALE = high altitude, long endurance).

Usually nobody flies higher than about 40000 ft. If you look out from a commercial passenger aircraft's window, what you see is blue. You can don't even see clouds very well since you are too high to see them closely and you are too low to see the curvature of the Earth and blackness of space. And the publicly available photography from that altitude is very limited, you don't really get to see even virtually how it looks like up there.

There are some interesting videos about balloon flights to high altitude in Youtube. The balloons go to about 80-100 kilofeets. According to videos, that looks already almost like space. Couple of examples:

Long Trail School High Altitude Balloon at Youtube

Nevada BalloonSat at Youtube

The view is so amazing that I feel it odd that nobody has started to carry people to near space experience with high altitude aircraft. Someone offers MIG-flights, but that is just a ballistic jump there from supersonic flight. Aircraft that can loiter in that altitude would give a whole different experience, it could stay there longer than just minutes.

That kind of aircraft would be impossible someone might say? Not so black and white. There are couple of HALE UAVs around which can go this high. And if you for example look Scaled Composites Proteus which can reach 70000 ft, if you'd replace the telecommunications load from the center section with space grade pressurized passenger cabin, the plane could lift several people at one time to the abovementioned altitude.

According to material I have been seeing from high altitude balloons, it seems like the sky is starting to look like space from about 60000 ft upwards. You need afterburning jet engines to go that high? Not necessarily. Look at for example Burt Rutan's UAV that had twin turbocharged modified Rotax 914 (with fuel injection). It was designed to have positive climb rate at 63000 ft. Seems feasible with piston engines in other words. The company that did the Rotax-conversion for the Scaled Composites UAV, have done triple turbocharged and twin turbocharged versions of the Rotax. The triple turbocharged Rotax is usable to over 80 kft, however, the installation looks really complicated (and the biggest turbo is so huge that must be from a truck).

Tecnam P2006T

Here is a design paper about Tecnam P2006T. I find it quite interesting.
www.aidaa.it/3-2008/P2006_corr.pdf

Interesting detail with the used Rotax 912S is that it provides actually better thrust at takeoff and climb than same horse power with a Lycoming engine (because the engine nacelle has smaller frontal area and the propeller rotation speed is lower).

Friday, November 21, 2008

New variant of the shape I have been thinking about

Here is my today's result from iRhino:



The idea is that the fuselage center section blends into wings like on blended wing body, but it only forms a minor portion of the shape, high aspect ratio wings continue from the blended part and there is a tail in the rear. I have not drawn this as I was thinking because I have been thinking either V-tail or T-tail. This picture doesn't yet have a rudder.

Now the difficulty is that I have hard time on getting the Rhino do what I think. The loft is challenging, because it follows airfoil shape, it follows the configuration and contour from the top I was thinking, but the problem is to vary the airfoil shape in the center section so that the transition from the right side to the left side is smooth and more circular than in this thing where it is pretty sharp (the sharpness there is completely unintentional and will go away as soon as I figure how to loft this thing properly).

The wing tips did not loft as I planned, and also the elevator has wrong airfoil shape in the tip, the scale2D produced results I was not planning to get. There is still something to learn in Rhino. I need to ask from maybe Jani tomorrow how to do this right.

Monday, November 17, 2008

Attended on a composite fabrication course last weekend

I spent the weekend in Nummela. Jarmo Hakala was teaching composite fabrication there. We learned for example vacuum bagging and infusion molding techniques.

The infusion molding is surprisingly easy and doable. And it is not that expensive after all, all the materials needed (almost all) can be obtained from Etola. The only more expensive special thing wasted each time in the process is the sealing tape. That is available from the composite resellers only to my understanding (for example from Kevra in Finland). Of course the vacuum pump is needed and it needs to be very strong (not a lo-vac pump, but quite high vacuum to be powerful enough to make the resin to move in the molded part being wet out).

The infusion molding is especially handy when there are multiple layers on the part, and laying up them by hand would take lots of time. The infusion process is a lot more convenient, everything is placed when the part is dry etc. No sticky stuff involved. And everything happens by itself inside the bag. Biggest time goes to the preparation, e.g. making the bag completely sealed. It can not have any leaks, if it has, the part will fail.

I will try this out with the RC model(s) I am going to fabricate next. We have two vacuum pumps and one venturi tube (that creates vacuum from ordinary compressor) to try this out. Lets see how it works out at home. At the course it felt easy at least. With this process, providing that the bag is completely sealed and the resin is injected from proper places in, the quality of the end product can be very high, virtually almost eliminating sanding process.

Friday, November 7, 2008

Scaled Raptor UAV Rotax 912 modification

I found an article about high altitude UAVs, and the Rotax 912 modification for Raptor UAV is mentioned here:
http://www.cre8tivenergy.com/uav.htm
(Quite interesting two stage turbo installation)

Tuesday, October 28, 2008

Progress on the manufacturing / process side development

As with the aerodynamics, I am also in a continuous learning mode with composite fabrication and also metalwork. We just purchased a TIG welding machine. That seems like a welding machine that have courage to try out, it is almost like using gas-welding but with a little arc. Hmm. like a little tesla-coil? How the arc behaves seems to be adjustable and e.g. it seems possible to avoid the crater when stopping weld by adjusting the time how long it takes for the arc to diminish. There are many adjustments in the machine and there is lot to learn. And we tried yesterday. Welding aluminum is tricky, it suddenly melts without prior warning. And even after that, it continues to melt more, if I didn't pay attention how long I heated it up. Anyway, seems like a fun challenge to master TIG-welding of aluminum. These things may be obvious for professional welders, but you know, they don't teach welding to engineers. One must start from somewhere. I will use the TIG-welding machine for construction of the big CNC machine that we have been planning with Kate for quite some time by now. A big CNC is needed for creating fuselage and wing plugs. Doing it inaccurately manually seems like great waste of time (have been trying and have found that it does not pay off, a better method is worth to be investigated - I don't take any "facts" for granted, unless I agree with the results and have compared the method to alternatives and found it to be the best for that purpose (by the way, different parts may require different kind of construction method, optimal is not always only one method)).

I have been researching also alternative materials since I obtained the Cozy MKIV plans (which I am not building right now). So I have pretty unused 20 kg can of MGS L285. Nothing wrong with the epoxy, but I just found out a better epoxy: The Hybtonite obviously - the carbon nanotube epoxy. The price seems competitive with the MGS (read: the MGS is overpriced because of shipping costs from Germany) and with about the same amount of money I could as well use this "breakthrough material". It does not change the world by itself, but it can add some welcome stiffness to pieces that might be otherwise too flexible. If I hadn't have this 20 kg unused can of MGS, I would be screaming and ordering a 20 kg can of Hybtonite right now. But having this unused epoxy in the garage a kind of slows the process down since I have lots of money invested in that can and the epoxy has limited shelf life. The Amroy representative is saying that the carbon nanotube material should be as safe as any other composite material (read: not more hazardous than epoxy is already, which is hazardous by definition).

I have been discussing off-line with one UAV/RC-plane designer. He has given me lots of valuable links. I may publish some of them sometime later on this blog, so stay tuned. I am not mentioning his name now, because I am not sure if he wants to be mentioned, but anyway, I find the information found this way quite interesting and helpful. As I have been reading these documents, it has also occurred to me sometimes, that what if the configuration layout would have looks and styling as one major parameter. In my opinion, B2 way the coolest publicly known aircraft out there. So I kind of love flying wings. But I have many reasons to not be thinking of designing a flying wing, for aerodynamic and stability standpoint. But one of the configurations (that I have known before of course, but these documents were kind of reminding me about those, that some find them actually useful over the conventional configuration) - the joint wing. What if you take a B2, use no twist - ie. make a normal main wing, and put a inverted V-tail into it in a box wing configuration so that the inverted V-tail starts from the wing tips, and it avoids yet another intersection by not connecting to the fuselage anywhere. This might make the controls a bit tricky, would mean wire in mechanical control rather than push-rods. Or maybe it could be a hybrid of fly-by-wire and manual control: aileron control could be manual and the elevator and rudder (and the mixing of the two) could be handled with electronics and servo motors would drive these surfaces. Would require very powerful servo motors though (needs to be very fast and very strong). But I have been sometimes kind of thinking this kind of fly-by-wire. Before someone screams that fly-by-wire takes hundreds of years to develop, I would like to remind that it is simple RC-plane technology that people are using all the time in the simplest form - fly-by-wire does not need to mean computerized flight controls and a aerodynamically unstable aircraft by definition. A electric wire weights less than a push-rod anyway when the length is very long (e.g. high aspect ratio wing, and in this case, something that starts from the wing tip). This configuration would make the cockpit very wide and not very tall. The looks would be compromised quite quickly if the cockpit part would protrude significantly from the wing. Obviously the cockpit section would be seamlessly blended into the wing. The interesting challenge here would be: how to make that work okay and minimize associated penalties rather than the motivation to choose this would be some parameter obtained from this configuration. At least it is that way until it is proven that this unorthodox configuration could be any good. At least it could be fun to make a RC-plane like that. And I would paint it to black. Full size plane would be trickier with the color, but there is high Tg Hybtonite available too. A realistic process could be infusion moulding with the hybtonite epoxy (I will investigate this at some point in the future, investing in process can pay back in construction phase significantly, instead of spending 20 years for sanding, I rather think first couple of years and try to optimize the actual construction work to not take 20 years). This would be a kind of alternative for carbon/glass prepregs.

Monday, October 27, 2008

Xfoil for Ubuntu Intrepid

You may find out that Xfoil is not in the Ubuntu repositories. For compiling the source package, you need g77 compiler, but that is not included to Ubuntu Intrepid repositories right now and getting it to work from the source seems to be a lot of trouble. Here is what I found, after some digging, a ready made package which installed on Ubuntu Intrepid fine:

http://giuschet.altervista.org/Ubuntu/

Download the file and install with

sudo dpkg -i xfoil_6.97-1_i386.deb

If some of the dependending libraries are missing, just install those from Intrepid repository and it works fine without problems. Have fun!

For more reading about XFoil, please see:
Xfoil manual
Xfoil tutorial with illustrations
Terrabreak.org XFoil tutorial
More on Xfoil at mh-aerotools

Sunday, October 26, 2008

Fuselage cross sections with iRhino

I described earlier on one blog entry how to make fuselage cross sections with iRhino easily. Here is the illustration of the lofted object cut to cross sections:

Cross sections, perspective:



Cross sections from front (simplified):



The source model:



The lofting capabilities of iRhino are awesome, it is easy to create shapes that would be impossible to come up with 2D cad models. I continue to be amazed with the quality of Rhino and I am also more and more convinced that there is no need for a 2D drawing program, I can do everything with Rhino. We are going to model our house next (which will not be discussed on this blog because it is not on-topic), while it is excellent for uniform 3D-shapes, it works so nicely with 2D shapes as well that it would be quite lame to spend all the time for nothing with AutoCAD (I am still getting shivers about the bad user interface, how simple things could take enormous amount of time to do and how innovation could get killed by the tool, we used to use that program when I was doing my studies, it is like completely from different planet than Rhino, and it is not a compliment for AutoCAD) where the work can be completed in matter of minutes in the Rhino..

Thursday, October 23, 2008

Feasibility of air travel on short distances

I, like many others, have been thinking the state of the current air travel system. With all the security checks and check-ins, the travel time becomes long. And easily using car, train or bus wins the passenger plane in the spent time for traveling from place A to B.

In other words, if you fly from Helsinki to Tampere, you can expect the check-in etc. to take at least 1.5 hours prior to the flight and then the flight takes maybe 0.5 hours. It might be also late, cancelled etc., and if this is a connecting flight, you may need to wait for your flight for another 5 hours sitting at the airport. On the other side you are waiting for your luggage to come, and it may take easily 0.5 hours.

So the shortest time with check-in luggage to travel from Helsinki to Tampere is maybe 1.5+0.5+0.5 hours = 2.5 hours. You may have also spent 60-70 euros for taxi from home to the airport, and on the other side the same amount of money to taxi. This makes moving from Helsinki to Tampere to be 180/2.5 = 72 km/h.

What about if this was a connecting flight that you waited for 5 hours and which was one hour late. That makes 5+1+0.5+0.5 = 7 hours. This makes the speed 180/7.0 = 25 km/h. You could beat the plane with a bicycle!

How about if you used a light aircraft to fly by yourself:
- Getting to the airport takes the same time, although it is easier to get to the Malmi airport than to Helsinki-Vantaa with public transportation without paying the large Taxi fee.
- Doing pre-flight check for the plane takes 0.5 hours. If you are quick, you have filed flight plan etc. during this time too. You may be able to speed this up if you are not flying alone.
- If the plane flies 222 km/h on average (includes takeoff and landing), taxi tie down etc. time is accounted with +0.5 hours (includes both airports), the total time to fly to Tampere would be: 0.5 + 0.5 + 180/222.0 = 1.81 hours. This is 99 km/h.

So the slow light general aviation plane is faster than the airliner on this trip. It doesn't win use of car though, getting to the airport and from the another airport takes time. But it wins train, because in case of train, you would have to get to the train station, and get from the train station to your destination with public transportation, which adds easily 0.5 hours on both ends, even Pendolino is therefore slower than the private car on this distance, so it is not better than using the personal aircraft.

How about if the light plane was a bit faster. It would travel 300 km/h. The travel time would become 1.6 hours. This is 112.5 km/h. Actually you can save fuel on Toyota Prius if you travel 112.5 km/h. And you are sooner directly at your destination. Not bad though for the plane. Wins the airliner hands down even in the best case.

If the distance was a bit longer, it would change the other way. The private plane would be a lot faster way to travel than car. And the airline would still have the overhead associated with security checks, package check-ins, package claims etc. For example, already if you would be going to Kuopio or Jyväskylä, the personal aircraft would be faster than the private car. And still the airliner would be the loser in the speed.

If you would go to e.g. Tallinn, Estonia, then the private plane would be excellent choice. That is because you can't go there by car, you have to use some transportation in between (e.g. boat). Even fastest boats are slow compared to even small ultralight aircraft. You could take the airliner, but it would take very long to get to the destination because of the overhead taking place at the airport. Instead if you took off with private plane, the overhead can be made smaller.

This of course requires that the plane could be flown in all weather and it would be simple to operate, with no need to do complicated tasks prior to flight in the pre-flight check. Something that would be for personal travel like a family car rather than for "flying sport". And the plane should be very low drag and very high efficiency design to make it compete in the fuel burn with the car (competing with e.g. Toyota Prius with a plane is very tough - the fuel budget for 100 km would be about 5 liters to be equal). Many current aircraft are not like that. But I feel that there would be use for that kind of planes, and this would not be impossible.

Here is by the way a video I recorded last May in the California trip. This video is about flight from Mojave Space Port to Palo Alto.


Cirrus SR20 flight from Mojave to Palo Alto (raw footage) from Karoliina Salminen on Vimeo.

Tuesday, October 21, 2008

Eclipse ECJ

Here is Gizmag's article about Eclipse EJC:

http://www.gizmag.com/go/7668/

Pictures on Airliners.net:

Airliners.net: Eclipse ECJ

Saturday, October 18, 2008

Suction stabilization for low fineness ratio pusher engine pod

I got an idea how to achieve suction to the read of the engine pod.
* The prop is located just after the laminar-turbulent transition to the pod and the remainings of the pod is a very large spinner which is open from the center.
* The air tunnel inside the pod has venturi-shape.
* There are tunnels that connect the venturi tube and the ring that is supposed to have suction.
* Airflow (which is used to engine cooling) inside the venturi (helped with the propeller part that is inside the pod) causes suction to the rear of the pod. The air exits at the end of the venturi tube, which happens to be the center of the spinner.
* The exhaust in the center makes the cut aft end of the spinner to still maintain low drag, it functions in the same way as the rear cut fuselages in jets

I have not tested this idea and don't know it it would work, but I think it would be pretty easy to try out in the model scale, even with an electric motor. This interests me enough that I think I am going to try it out of someone doesn't tell me (with better knowledge, as a fact that has been proven and tested) that it is not gonna work.

I hereby license this invention under the terms and conditions of GNU General Public License, version 3, or any later version. (C) 2008 Karoliina Salminen. All rights reserved. By reading this text, you aknowledge this and agree with the terms and conditions of the GPL license.

Friday, October 17, 2008

iRhino learnings of Today

Today a colleague (Jani Ylinen, a graphics designer who knows everything about Rhino and Maya) from Nokia helped me out with Rhino a bit. So here is what I learned today.

If there is need to make 2D cross sections of for example of the fuselage, it can be done as follows:

1. Create a rectangular surface.
2. Make rectangular array of it. Adjust proper step to proper direction and use appropriate number of copies. E.g. 100 cross sections, one per each 5 cm for example.
3. Then choose Object intersection. Select all items (the rectangles plus the 3D model that you are going to cut apart)
4. Hit enter and wait that iRhino does the processing. It is slow in the current alpha-version.
5. Move the cross sections to another layer
6. Hide the 3D object layer
7. And you have cross sections. You can export these to in dxf format to for example to Qcad and process them further there. E.g. you can plot them to paper. Printing from Rhino is possible as well, but it prints the zoom level of a view that is currently present, and the scale you get can be about anything (not something that you can repeat for each model and do exactly the same scale drawings on paper each time, does not succeed with Rhino printing capabilities).

Jani also showed how to do radius. Select radius tool, select surfaces and type the radius and hit enter. Magically the radius appears to the piece with amazing accuracy.

There is also a silhouette function that makes a 2D projection out of the wireframe. You can propably utilize that in a 2D Cad, e.g. QCad (or Autocad if you are wealthy enough to have the overpriced licence to that outdated software).

I learned today that actually Rhino can be used for technical drawing without using more traditional technical drawing programs. You need to keep your model history with layers manually (if you change some cross section for example, you need to loft again), but with some work, it seems to be all you need. Also measurements can be handled, but you need to maintain them manually too, if you change some shape, you may need to update your dimension as well. With cutaways with the cross sections and the silhouette function, it seems that all sorts of technical drawing can be done with Rhino. It is different and some things are very manual, but on the other hand, as a bonus, the 3D side is so blazingly good that there is nothing that compares with it in user friendliness and expressivity. You can really create with this tool and about everything is there, you just need to discover all the functions.

Seems like the price-value ratio of Rhino is exceptionally good. With one thousand you can get so nice tool that it actually is better and especially a lot easier to use than overpriced Autodesk tools. This is how the design is done in the future for sure.

I am also downloading the Maya personal edition for Mac now. I plan to try it out for rendering models modeled in iRhino.

Many thanks to Jani for guidance with graphics software. It is very much fun to learn new things.

RC Advisor

Carlos from RCAdvisor commented my one post and I decided to check out his site. I created user account there etc. I was really amazed the RC Calculator, it not only has quite amazing features for model makers, but it also seems to have quite interesting animated UI, I didn't know that this kind of stuff can be nowadays done with Java (or is it flash?). I haven't had time to yet surf what all is on this site, but it looks quite comprehensive and promising and I will for sure look further into it. Indeed, maybe I find some tips for the twin concept RC-scale model I am going to do. Thanks Carlos for your link!

the link to the RCAdvisor

Thursday, October 16, 2008

Trying out different configuration layout for the twin concept


I decided to post here a snapshot of one of my Rhino-models. It has now struts which hold the engines out of the wing surface. The canopy was also replaced with windows.



Monday, October 13, 2008

Modern and even future concepts from over 70 years ago

There are interesting similarities in the old Luftwaffe aircraft concepts to the modern aircraft flying now:

For example:
Similar to Rutan Boomerang
Similar to Adam A700 (Originally designed by Burt Rutan)
Similar to NASA Oblique wing (which was by the way done by Scaled Composites / Burt Rutan)
Almost like the Rutan SpaceShipOne
Some features of Rutan WhiteKnight 1
Wing dihedral and anhedral similar to Rutan Proteus
From up, this could be mistaken to Rutan Long-Ez
Hey I can find similarities to Rutan Vari-Viggen here
Here is the WhiteKnight 2 configuration obviously
Almost like Adam A500 (originally designed by Burt Rutan)

Ok, then what about these:

RAM-jet, back in 1946
First commercial jet aircraft was DeHaviland Comet. But was it invented there? Doesn't this have quite recognizable look. The airliners still have this configuration and look.

And finally, but not least, this one:

Governments are still flying people into orbit with less modern hardware than this, and the idea to this one was from 1929 originally!. Think of it - first flights to space were super-ancient designs (non-aerodynamic rockets) instead of what was thought tens of years earlier already. Even Space Shuttle is quite clumsy compared to what this could have been. I would not be surprised to see someday a rendering on a page of a science magazine, which would look exactly like this and have for example the Northrop-Grumman -logo on it. The sad part was that this was only considered as a bomber, everything was some sort of warplane, it somehow didn't occur to people back then that they could have done the first human space flight earlier than it was done. I wonder why wasn't Dr. Säger utilized in the space programs which followed couple of tens of years later. I am thinking what could be done if the rocket monorail-train was replaced with a MAGLEV-train (and the track would slope upwards inside a mountain to the altitude of couple of kilometers in a tunnel). Wow. If my hair was short, it would be most likely pointing to the ceiling now.

Seems like to design a novel plane, there are examples of about every possible configuration layout, which have been long forgotten already and nobody has maybe utilized it, it just is waiting for someone to find it. The history of unfinished aircraft concepts seems to be an interesting source for inspiration.

So, if there could have been a orbital space plane already in 1930s or so, and ramjets were thought about already back in the 1940s, how much then air travel has advanced in something like 70 years? Not at all, it seems. With modern materials and tools, the feasibility of these designs have increased, but the idea still is very old. And most modern designs are just copies of each other without anything new and creative.

Wednesday, October 8, 2008

Wing droops on laminar flow section

If you have wondered why Cirrus has the discontinuity on the wings. This may answer to that to some extent. I have not found any factual information about the airfoil section used on the Cirrus other than that it is a natural laminar flow section. Cirrus VK-30 used the Jeff Viken NLF414F airfoil. I don't know if the SR20/SR22 uses the same airfoil or a different NLF section.

Anyway in this NASA tech paper it is explained how the stall resistance can be made better with the wing droop. The wing droop on the NASA test C210 actually indeed resembles the discontinuity on the Cirrus SR20/SR22 wing. Please have a look:
Wind tunnel results of the low-speed NLF(1)-0414F airfoil

Notable thing is that the Vmax-probe did not have this wing droop or any other means to prevent tip stall. And it crashed on landing possibly according to NTSB report and Bruce Carmichael's book, because of unfavorable stalling charasteristics at low Re of the airfoil caused a hard landing (which the pilot did not survive). NLF414F is not to be used without some means to prevent tip stall and to soften the otherwise very sharp stall at low Re.

Monday, October 6, 2008

Conceptual design, design requirements, high efficiency twin

Here are set of requirements I have combined for an aircraft suitable for my use case. I have been collecting these things for quite long time now, and have changed them back and forth. However, it seems like they are becoming more stable now:

- Two engines. Rotax 914 (preferably fuel injected) or similar (912 turbo conversion). Alternate engines: HKS700T (the speed may not be achieved with the HKS option). (low power engines which run on autogas are mandatory requirement)
- Range 1000 nm with three on board (mandatory requirement)
- at least 3 places (mandatory requirement, long range flights, third seat is needed for baggage and rescue equipment)
- Designed for IFR flying (mandatory requirement)
- statically stable, dynamically stable behavior (mandatory requirement)
- gentle stall (mandatory requirement (for safety))
- Cruise speed > 200 kts @ 80% power (mandatory requirement for both range and usefulness)
- Stall speed max 55 kts (mandatory requirement, for safety)
- High altitude capable (cruise at 24000 feet) (optional requirement)
- Pressurization as an option (optional requirement)
- Lightning strike protection (mandatory requirement)
- Positive climb rate with one engine out (mandatory requirement)
- Spin recovery possible (mandatory requirement)
- Very high glide ratio and long glide range when both engines out (mandatory requirement)
- BRS system (mandatory requirement, for safety)
- Spin recovery parachute (mandatory requirement, for testing safety)
- Tri-gear possibly with RG, at least the nosegear with RG mechanism (Trigear mandatory, RG optional)
- At least normal category (mandatory requirement)
- Utility category (optional requirement)
- Reasonable cost to build a prototype

Means how to achieve this:
- Selection of efficient NLF airfoils
- By minimizing fuselage and engine pod wetted area
- By minimizing skin friction drag (smooth surface, gelcoat on top of laminate and polyurethane paint on top of gelcoat)
- By utilizing laminar flow over wings and fuselage as much as possible
- By using wing geometry that has higher effective aspect ratio than actual AR
- Turbocharged engines
- Lightweight molded composite structure manufactured from carbon fiber prepregs, foam.
- By minimizing intersections and protruding elements. As clean fuselage and wing as possible. Known limitations - double slotted flaps do require external mechanism.
- By use of double slotted flaps for high Clmax.
- By use of either T-tail or V-tail for good spin recovery.
- Large fuel tanks in engine pods
- For cost effectivity, a pair of midtime Rotax 912ULs equipped with e.g. VEMS fuel injection and Garrett turbocharger is more reasonable cost than pair of stock Rotax 914s. Downside: ease of installation is lost when the engine requires more work than usual for Rotax installations. However, fuel injection is essential for safety.
- Negative sweep on main wings
- Glass cockpit (IFR requirement)

Possible configurations to achieve this:
- Twin with tractor propellers on each wing (known limitation: the propeller causes turbulent flow behind it which increases drag over the engine pod and the wing behind the propeller arc)
- Twin with pusher propellers on each wing (known limitation: the pod on front of propeller decreases the propeller efficiency)
- Push-pull configuration with twin boom tail (known limitation: front propeller disturbs the airflow to the rear propeller and the efficiency of the rear propeller decreases)

How to verify the effectiveness of each parameter:
- Calculate basic parameters for each combination where only one parameter is altered in each.
- This concept generates several different designs and each parameter is justified if it produces verifiable benefit.
- The design points that are proven to produce positive results with large enough margin are incorporated into the design if it does not overly complicate the manufacturing.

Low hanging fruits (design points known to have been succesfull in other designs):
- Double slotted flaps with a mechanism similar to Dynaero. Proven on Dynaero MCR.
- NLF-airfoils. Proven on Cirrus, Lancair and Columbia (Cessna 350 and Cessna 400 nowadays) high performance aircraft.
- Molded composite structures. Industry standard nowadays in most new aircraft designs.
- Tractor twin. Proven on most twins around.
- Pusher twin. Proven on a Polish design called Orca.
- V-tail. Proven on Beech Bonanza and later Cirrus Jet and Eclipse Jet.
- T-tail. Proven on many aircraft designs to date
- High aspect ratio on twin engine propeller driven aircraft. Proven on Diamond DA42.
- Negative sweep (moderate) found on many dual seat gliders. Small amount of negative sweep can also be found from Diamond aircraft.
- Trapezoid on wings. Easy to manufacture from composite materials, the shape is not limited by manufacturing process.
- Prepreg composites. Proven on Cirrus, Lancair, Diamond and Columbia aircraft.
- Rotax 912 series engines. Proven to be highly reliable and simple workhorse on almost all new ultralight and LSA aircraft. HKS is slowly gaining some share, but Rotax rules so far. From personal experience I also know that the Rotax engines meet their TBO, our flying club frequently runs Rotax engines to their TBO without problem without major overhauls. Claims that TBO of Rotax is just marketing and that overhaul is required well before 1000 hours to that is simply not true, this has been proven by experience, the aircraft we used to own has flown about 1000 hours, and the Rotax is the original one and runs nicely without problems and it has been in hard use because the plane was used for the first 683 hours to train student pilots. Rotax can also run on autogas (actually the preferred fuel is autogas, not 100LL).
- Glass cockpit can be made a lot simpler than tradtional gauges. Wiring behind traditional gauges is a mess and takes a lots of handwork to accomplish. Glass cockpit wiring can be made very simple and it can be highly integrated where most of the tasks are done in software rather than mechanics.

Criteria for defining success and failure
- Minimum acceptable range is 800 nm.
- Minimum acceptable payload with full fuel is three persons with no baggage.
- Minimum acceptable cruise speed at 80% is 160...170 kts on Rotax 912/100 hp. However, when comparing to Rotax 912 twins (coming and existing), the speed is no longer in the "top class", but rather below the top.
- Minimum acceptable glide ratio is 1:15. Target is more than that.
- Maximum acceptable stall speed is 55 kts. Design requires changes, if it is more than that.

Tuesday, September 30, 2008

Podrel

A funny idea came into my mind. There are couple of Petrel Amphibians in Finland. It looks like a plane of Donald Duck.

Here is one discussion thread in Finnish about it:
Nyt on suomen kolmas akuankkakone valmis

It has staggered wings (two wings, one on top of each other). What if it was completely different. Not exactly completely, but quite completely. Now on this latest Super Petrel, the engine pod is integrated to the upper wing. How if the upper wing was the only wing on the plane, the lower wing would not exist, the upper wing would be twice as long. The tail would not be angled upwards from the bottom of the fuselage, but it would be rather connected with two booms to the wing, in similar manner than it has been done on Adam A500. And finally, but not least, what if the fuselage was not a traditional fuselage, but a pod in the end of a strut, that fits the occupants, and nothing more. It would end before the prop arc. This would allow moving the propeller a bit downwards.

So the result:
- no aerodynamic penalty normally associated with the amphibian planes.
- center of thrust is at the same level as is the lift (high wing)
- because of the boom tail, the tail does not hit the water unless the plane flips.
- because you would not need to fit the tail to the fuselage, the fuselage-pod could be made a better boat shape

I could not resist, but name this idea as Podrel. Actually this is not a new idea entirely, it is partially borrowed from a NASA tech paper, but the application to amphibian use could be new twist for the configuration.

What do you think about this?

Dynaero MCR-01

I had a chance to see the Dynaero MCR-01 yesterday at Malmi airport. Here are some interesting pictures about it:

Front:


Dynaero smile:


Back:


Double slotted flaps:


Flap mechanism:


Canopy:


Interesting finding: the upper slot is rigid part of the flap. It does not move by itself, and the mechanism is as simple as on plain flap or the single slotted flap found on Cirrus or Diamond. When the flap is retracted, the slot hides under the wing. Very clever design.

Thursday, September 25, 2008

Good NLF airfoil

The SHM-1 airfoil seems quite interesting. It was designed for Honda Jet. There is a patent about it. I need to investigate that further it seems.

Wednesday, September 24, 2008

Toyota General Aviation aircraft

I found an interesting article about the Toyota general aviation aircraft. It looks like it has been flown again.

Read the arcticle from here:
http://mojaveskies.blogspot.com/2008/07/toyota-in-sky.html

Wednesday, September 17, 2008

A Lancair builder has collected a list of links to tech papers, e.g. NLF215F

Link:

Interesting technical papers

There is link to the NLF215F airfoil tech paper. It was particularly interesting. Now I understood the philosophy of the profile - I was always wondering, why this profile has the low drag bucket at so high Cl (around 0.5) rather than what is realized in cruise with small aircraft (up to 0.2). But, it seems, that this airfoil is designed to be used with -10 degrees flaps. With those, the low drag bucket gets into the cruise area. Heureka.

Here is a direct link to the paper:
http://www.n91cz.com/Interesting_Technical_Reports/NASA-81-tp1865.pdf

Monday, September 15, 2008

X-plane 9 flight simulator available for iPod touch / iPhone

I just downloaded the iPod touch version of the X-plane 9. I am quite impressed about it. It is by far the best mobile game I have ever tried. The controls are done with the accelerometers and throttle and flaps are controlled with two simple finger usable sliders on the screen. The landing gear and brakes have translucent buttons on the bottom of the screen. Everything is fully finger usable as it should.

The aircraft selection consists of Cirrus Vision Jet, Piaggio Avanti, Columbia 400 (that was a positive surprise since it wasn't included with X-plane before), and the C172SP. Needless to say that the Cirrus Jet is the most fun of these to fly.

It is possible to set the weather to IMC, but because the instrument panel does not fit into the tiny screen, it is not included with the sim. Therefore flying IFR approaches with the iPod version is not possible. You can keep the attitude though inside a cloud because of the HUD that includes attitude indicator.

Anyway, this is the best iPod touch app you can find from the App store. It only costs 7.99 eur and is worth every cent. You can find it under games category.

What could be cooler than fly virtual Cirrus Jet in bus when going to work tomorrow?!

Saturday, September 13, 2008

Twin engine concept, evolved from the single engine concept

Here is what I lofted today in the iRhino:













To make reasonable place for the rear seat/seats, the wing position had to be moved lowish position. The feet of the rear passengers are below the wing spar of the wing.
The rear window is not necessarily in the best place, it might be too much forward. The idea is that the rear seat ends before the prop arc.

The single engine idea in the previous post had apparent CG issues, how to get CG to correct position other than moving the prop completely on top of the fuselage, which moved the engine pod very high. This twin engine version which places the engine pods to the wings, solves this issue obviously.

Here is how it was drawn (in the case someone is interested in learning iRhino):
- The engine pod is NACA 66-025. It is lofted from couple of cross sections which were set along a helper-line which had the airfoil contour.
- The Fuselage is lofted from 5 elliptical cross sections
- The wings are lofted from two airfoil cross sections each
- The tail surfaces are lofted from two airfoil cross sections each
- The canopy and window utilize the Project to Surface -function of the iRhino
- The picture is drawn with correct dimensions. I used measurement -lines to make the parts correct size. The grid was set to 10 cm spacing.

The fuselage height is 86 cm, length is 6.6 meters. I have not yet measured if one can fit inside or not. But basically it resembles a sail plane fuselage. The fuselage may require some scaling up to fit more than two persons inside.

Friday, September 12, 2008

Single engine concept

Here is yet another concept illustration. The engine pod would contain HKS700T, Rotax 914 or UlPower 260i with pusher propeller.

The idea of the concept is simplicity, low drag and placing the propeller so that the arc does not get under the plane and thus is not vulnerable to flying dirt etc. like it is usually on pusher designs. The high wing is selected just because that way the center of thrust gets closer to the center of lift and the high thrust line does not cause that high nose down pitching moment. The engine pod fits between the V-tail, which makes the concept similar than the Cirrus Jet.



The major idea in this is that the part count is minimal. There are only two tail surfaces, two wing surfaces, and a single fuselage + pod.

I have done an X-plane model like this. In the model, the control sensitivity is low and the plane maneuvers slowly. It is difficult to make the ailerons and elevators effective enough.

Thursday, September 11, 2008

Idea: fowler slotted flapelevators, how to improve the efficiency of a tandem wing aircraft

I have been thinking how the efficiency of a tandem wing aircraft could be improved. In tandem wing aircraft the front wing determines pretty much how high total Clmax the aircraft is going to have which translates then to the required wing area. To maximize the efficiency, because flaps can not be used in the rear wing, the Clmax of the front wing is desirable to be as high as possible. Usually on tandem wing and canard aircraft the Clmax of the front wing is around 2.0 and the elevator is a single slotted flap.

It may not be mechanically very practical, but theoretically it could be possible to increase the Clmax of the front wing by adding more high lift devices into it. There could be a fowler flap implemented so that it increases the wing area substantially while the single slotted elevator flap remains working as usual in the trailing edge. The problem is that how you do that when the whole elevator system moves as consequence when the flaps are lowered or raised (the fowler is either inside the wing or protruded out of the trailing edge). But if this was practical with any other means than using servo motors for the elevator too, it could increase the available lift from the front wing somewhat. A challenging thing in this obviously is that the shear web that connects the spar caps goes through the front wing, and the flap system can not break the integrity of the shear web. More limiting factor also is that the chord length of a tandem wing aircraft front wing is low and there is not that much space for the high lift device.

Anyway, it would be interesting to try this out with a radio controlled model.

I hereby license this invention under the terms and conditions of GNU General Public License, version 3, or any later version. (C) 2008 Karoliina Salminen. All rights reserved. By reading this text, you aknowledge this and agree with the terms and conditions of the GPL license.

Monday, September 8, 2008

NLF airfoil with low pitching moment

I have been searching the web for such airfoil, and it seems like there is no such thing in the public domain. At least I have not found one.

For a canard/tandem configured aircraft, the main wing should have very low pitching moment, preferably zero if possible. The flying wing airfoils generally don't have very extensive laminar flow and they are not that interesting except for some exceptions (found one Wortmann airfoil which has quite high L/D but does not really compare to the drag coefficient of the NLF414F at high reynolds number).

So what I would be looking for would be:
- a thick (16-20%) low reynolds number natural laminar airfoil which has low or zero pitching moment, has design cruise Cl of 0.1-0.2 and which would have comparable drag charasteristics than the NLF414F or not very much higher drag than the NLF414F and which would have design cruise reynolds number around 5 million (not 10 million like the 414F) and which would achieve unflapped Cl of 1.2...1.3 at reynolds number 0.8 million.

So am I looking for an impossible airfoil? If you know that someone has designed and tested in wind tunnel this kind of airfoil, please let me know!

The NLF-414F paper

Here is the link for the design paper about NLF-414F

NLF414 design

Interesting thesis work about NLF airfoil design

Read by yourself from here:

http://www.lib.ncsu.edu/theses/available/etd-09042003-113959/unrestricted/etd.pdf

Interesting NASA ebook: Concept to Reality

Here is a link to the book:

Concept to Reality

I find it quite interesting.

Friday, September 5, 2008

Dynaero MCR structure description

I have been wondering how the Dynaero wing is constructed specifically. It has aluminum skin and composite structure inside. What kind of structure is pretty nicely described in the following document:

LAA TYPE ACCEPTANCE DATA SHEET TADS 301B, Dynaero MCR01 ULC

Friday, August 29, 2008

NACA 66-020, 66-025, 66-030 body drag coefficient

Some numbers from Javafoil using the Drela approximation method (Xfoil after 1991):



NACA 66-020

Parameters: Length 6 meters, diameter from thickest point 1.2 meters:

α Re Cl Cd Cm 0.25 TU TL SU SL L/D A.C.
[°] [-] [-] [-] [-] [-] [-] [-] [-] [-] [-]
0.0 11.60E6 0.000 0.00709 -0.000 0.623 0.623 1.000 1.000 0.000 0.380

So estimated Cd for the fuselage is 0.00709. Doors, antennas, landing gear door, etc. will make it worse.

Bugs and dirt on the fuselage surface and the results becomes:

NACA 66-020

α Re Cl Cd Cm 0.25 TU TL SU SL L/D A.C.
[°] [-] [-] [-] [-] [-] [-] [-] [-] [-] [-]
0.0 11.60E6 0.000 0.01212 -0.000 0.625 0.625 1.000 1.000 0.000 0.380

NACA 66-030 (engine nacelle variant of the laminar body)

m/S = 1
α Re Cl Cd Cm 0.25 TU TL SU SL L/D A.C.
[°] [-] [-] [-] [-] [-] [-] [-] [-] [-] [-]
0.0 11.60E6 0.000 0.00775 -0.000 0.605 0.603 1.000 1.000 0.000 0.456

Cd = 0.00775

With NACA 66-025 the fuselage pod length drops to 4.8 meters.



NACA 66-025

m/S = 1
α Re Cl Cd Cm 0.25 TU TL SU SL L/D A.C.
[°] [-] [-] [-] [-] [-] [-] [-] [-] [-] [-]
0.0 9.28E6 0.000 0.00812 -0.000 0.612 0.612 1.000 1.000 0.000 0.417

Cd = 0.00818

Conclusion: All of these pods provide (according to simulation), a low drag coefficient.

Equivalent drag area for NACA 66-025 assuming body diameter of 1.2 meters:

0.00818*(0.6m*0.6m*3.14159) = 0.00925 m^2 (=0.0823 sq ft)

Hmm. did I calculate correctly? Somehow looks quite small.

Evolved aircraft concept requirements

I have a bit evolved set of requirements for an aircraft concept to present. They are now as follows:

- safe
* 2 engines
* 2 fuel systems
* 2 propellers
* non-stallable
* non-spinnable
* double avionics
* two batteries
* two electrical systems
* moderate stall speed (<=55 kts)
* good brakes
* good tires and landing gear that does not break from few bounces
- economical
* very low fuel consumption
* must run on autogas or diesel oil
- at least 2 places with side by side seating, in comfort (enough space in cockpit, a lot more than in a Cessna)
- very long endurance
- capable to high altitude flight
- best glide ratio speed as high as feasible (enabling cruising at L/D max).
- very high best L/D ratio (>=1:25)
- low minimum sink rate
- relatively low power required to keep in level flight
- low drag utilizing extensive laminar flow in the fuselage and wings
- lightning strike protection (copper mesh installed to the whole aircraft)
- utility category (+4.4/-2.2G)
- positively stable in all flight conditions (suitable for IFR flight)
- speed brakes / spoilers
- ballistic recovery chute
- strong roll cage around the cockpit, exceeding the current FAR23 requirement at least with factor of two
- keeping aircraft CG on correct place do not require using ballast (no matter if there are two or one person sitting on front seats)
- aircraft can be parked without anyone sitting on it on its normal upright position
- aircraft shall look stylish and out-of-this-worldish
- surface finish has to be smooth
- large enough control panel for fitting IFR instruments (Large EFIS screen + analog backup instruments)
- good visibility outside
- rudder trim
- aileron trim
- elevator trim
- using aircraft systems has to be simple and all procedures has to be very simple and easy to memorize (aircraft shall not be a checklist-machine)

Summary: Different-looking composite aircraft that incorporates extensive laminar flow, does not stall or spin and that you can fly from Europe to Oskosh and back with ease and with peace of mind. Complies or exceeds with FAR23.

Wednesday, August 27, 2008

Monday, August 25, 2008

Solar plane makes record flight

A solar UAV utilizing Lithium-Sulphur batteries and amorphous silicon solar arrays has made a record flight. Read the BBC NEWS story: BBC: Solar plane makes record flight

Sunday, August 24, 2008

Illustration for the previously mentioned idea

Here is a rough illustration about the configuration layout. This picture is not drawn into any scale dimensions, it is just "artistic" illustration of the idea. I did not draw taper to wings etc. because I wanted to draw it quickly. Here is the picture:



The drawing program is by the way the Rhino3D for MacOSX, a pre-beta -version of it, I am privileged to be a beta-tester.

Basic locations I had in mind:
Seats are in front of the canard wing. The fuel and baggage is stored between the canard and main wing. The engine nacelles are more forward than in the Long-Ez derivatives. They protrude from the main wing forward in a similar manner like they would be additional fuselages in midwing configuration. The engine nacelles are not necessarily fat enough to look realistic, but they hopefully deliver the basic idea, as this is not a final drawing but a computerized sketch of the configuration layout. The two horizontal stabilizers are in the propeller stream because that way they are more effective than winglet mounted rudders would be on a canard aircraft, and instead of becoming effective at relatively high speed, these can be made to be effective from almost zero speed, similarly than conventionally configured aircraft.

The idea is influenced by this:
http://www.scaled.com/projects/proteus_specifications.pdf

Saturday, August 23, 2008

A configuration idea for a canard aircraft

Canard configuration is usually quite problematic and it has several compromises which decrease the benefits that could be otherwise obtained from the configuration. However, there is one advantage on canard configuration which is better than traditional configuration: stall and spin resistance. If the major design goal is stall and spin resistance, the penalties from the canard configuration can be assumed acceptable. After all very many aircraft accidents are caused by stall/spin.

So how to do a twin engine propeller canard so that the engine pods can be utilized also to other use?

So the idea goes:
1. take a look at Burt Rutan's Proteus.
2. see the booms for the horizontal stabilizers.
3. Instead of placing jet engines to the fuselage, why not put tractor propellers to the front of the booms.
3. The CG on canard aircraft is between the two wings, the long fuselage solves the problem where to place the fuel in
a canard AC, it can be stored between the wings inside the fuselage.

Any comments/arguments why this would not be a good idea in your opinion?

Wednesday, August 20, 2008

Eggenfellner's aircraft project

Eggenfellner seems to be building a new aircraft type:

http://www.eggenfellneraircraft.com/E2B.htm

Interesting design choice - flying wing, no tail. Sounds like no flaps on this machine for increasing Clmax.

Tuesday, August 19, 2008

Drag coefficient for everyone

It seems that Wikipedia explains drag coefficient quite well. Here are two articles:

http://en.wikipedia.org/wiki/Drag_coefficient

http://en.wikipedia.org/wiki/Drag_equation

Here are NASA's study materials about drag:

http://www.grc.nasa.gov/WWW/K-12/airplane/drageq.html

Monday, August 18, 2008

NASA NLF-115-20%

I was changing the parameters in the DesignFoil demo. And got interesting positive change for the NLF-115 airfoil: increasing the thickness to 20%, it does not effect the laminar bucket low Cl area, but it increases the laminar bucket towards higher Cl area. On other airfoils, this change usually moves the low drag bucket upwards to higher Cl, but on this airfoil, the low drag bucket seems to rather extend than move. I was trying it out with Reynolds numbers 2000000, 3000000 and 5000000.

The higher thickness (if the simulation is at all correct) would be favorable for structural reasons. The Burt Rutan's canards also use thick airfoils in the canard wing, the thickness of the original GU25 is 20%. I don't know the exact thickness of Roncz R1145MS and haven't measured (I have the Cozy MKIV plans which have the Roncz airfoil included, so I could measure it if I had time to look at it).

The larger thickness contributes to the strength achieved (only those little glass fiber spar caps are needed instead of very heavy big wing spar or alternatively a wing spar made of carbon fiber).

Thursday, August 14, 2008

Wednesday, August 13, 2008

Finally found a good airfoil program

I have been trying out about all demo versions available of airfoil programs. Best of them so far has been Xfoil and the Javafoil. However, neither seems to accurately simulate the laminar bucket.

I was surprised to try the Designfoil from Dreesecode: it simulates the laminar bucket, and the demo version also run on Ubuntu Hardy Linux with wine. Excellent, the first windows aircraft software that actually runs on Linux so far.

Friday, August 8, 2008

Some calculations for plane which would utilize two HKS 700 turbos

I was flying today (as a passanger) to Brussels and I wasn't doing nothing, I had paper, pen and the HP calculator with me. And of course J.D. Anderson's Aircraft performance & design as a reference.

So I ended up with some numbers, but I know already that they are a bit off - since I calculated AR the other way around and got with the K and e I used AR = 10 even if I had chosen that the AR = 14. Therefore the climb performance may be even quite pessimistic. Besides of that I was reading yet another aerodynamics book which stated that e is as high as 0.9 for clean airplane.

However, numbers are: Trimaran configuration, 2 x HKS 700 turbo, 2 places, fuel 200 liters, S = 99 ft^2, MTOW 1980 lbs (maybe 900 kg would still be within limits, haven't checked), AR = 14. Slotted flaps and flapped ailerons. Taper 0.5. Low drag laminar airfoil and 60% laminar fuselage shape and the plane will be quite fast. RG is assumed, gear stored in the pusher prop engine pods.

Wednesday, August 6, 2008

Another engine, HKS700 turbo - 80 hp turbocharged

Some information about the new 80 hp turbocharged fuel injected HKS 700 can be found from here: 



Ilmailu.org forum HKS700 80 hp turbo thread (in Finnish)

Monday, August 4, 2008

Interesting diesel engine

Tecnam is considering this engine, and it looks very interesting - it is lightweight and runs on diesel. The power output is similar to Rotax 912 and for the turbocharged version (125 hp) even better than any Rotax can do:

http://ppdgemini.com/

The vmax equation

Here is the equation for calculating the estimated maximum speed of the aircraft concept:

The quest for e

Estimating e seems to not be so trivial and causes lots of thinking - it does not seem to be directly applicable by the book:

Daniel Raymer says in his book that e (Oswald's efficiency factor) is normally between 0.7 and 0.85 (the e that is below 1.0 comes from the deviation from the perfect elliptic lift distribution). Jon Anderson Jr. says on his book Aircraft Performance & Design that on general aviation aircraft, the e is normally 0.6. And in one example aircraft design in the book Anderson then goes and uses e that is 0.9. It has quite large impact on the estimation results, so it would be better to estimate it right.

Then there are multiple equations for estimating e, in Raymer's and Anderson's books. All produce different results, and as a result, the K will be different. And the K has effect on L/Dmax. Interesting enough - the L/Dmax, if the e is estimated with any of the equations provided or assumed as 0.6 as Anderson recommends, the Diamond DA42 Twin Star should have L/D ratio around 12 instead of 18 it in reality has. It has been said that these estimation equations apply only to "normal" aspect ratios. It would be interesting to know what is "normal" aspect ratio - DA42 has AR=12 and the LH10 has AR=14. Maybe that is "higher than normal" then and maybe I have had the privilege to fly "not so normal airplane" when flying the Twin Star. Normal or abnormal, it is an excellent aircraft which is very much fun to fly.

So if I am estimating the L/Dmax of aircraft that has AR=14, and has tapered wing, it seems that quite high e value needs to be picked up. The estimation equation is a heavy generalization though, it does not take into account that on which CL the low drag laminar bucked is (it rather seems that the equations assume turbulent flow).

Tuesday, July 8, 2008

Rhino3D for Mac

I am on sick leave and typing this from bed, I have two laptops in the bed right now, my work Linux laptop and Kate's Mac.. I have inner ear inflammation which makes me feel really dizzy if I get up from the bed, so I stay down as much as possible...

I was delighted to notice that there is a MacOSX version of Rhino3D coming. My workmate uses Rhino professionally and he told me about that. I of course straight away went ahead and wanted to become a beta tester. And I got approved as beta tester subsequently. Wow.

Rhino is really interesting piece of software. It took about 30 minutes and I had a NACA 66-018 low drag body modeled.

Tuesday, June 24, 2008

What is wrong with sailplane airfoils for powered planes

Everything might look very obvious at first, but after digging more and more, it becomes clearer and clearer what kind of compromises all aircraft are made of and why.

A known thing is that the more efficient the airfoil the higher L/D ratio it has and vice versa. So one could go and find that sailplane airfoils produce very high L/D ratios. There is a little but on that though: Sailplane airfoils commonly achieve the best L/D ratio at higher Cl than what is optimal for a powered aircraft with reasonable wing loading where the cruise Cl is between 0.15 and 0.20. E.g. NLF 215F seems to achieve its L/D max at around Cl 0.5 which is unusually low compared to some other airfoils that require Cl being close to 1.0. That is acceptable for a sailplane that is thermalling at close to the stall speed. However, that is not where one wants to cruise with a powered aircraft, there is usually a requirement to get somewhere in a reasonable time, thus speed has some importance.

I have previously mentioned that the wing loading and cruise Cl has direct relation. The higher the wing loading, the higher the cruise Cl vice versa. Then the speed where the best L/D ratio occurs has a relation to the previous and it also tends to have relation to the top speed.

Diamond DA40 uses Wortmann FX 63-137 airfoil. It has best L/D ratio higher than the optimal < 0.2 (for light wing loading). Therefore the best L/D speed is the same as the approach speed on the aircraft. Similarly on Diamond DA42 Twin Star the same airfoil was used but the wing loading is as high as it is on Cirrus SR20. The result is that the best L/D speed is higher than on DA40, the top speed is higher (it is not only because of the two engines, the two engines produce also more drag than one). Because of the substantially heavier wing loading, the DA42 cruises at higher Cl than the DA40 and it gets closer to the airfoil optimum resulting better aerodynamic efficiency.

Cirrus SR20 is very similar to the DA40 but it has a different airfoil and higher wing loading. That results best L/D ratio speed being 96 kts. SR22 has that value even higher, it is over 100 kts, but it can be misleading that the best glide speed mentioned in the operating handbook is lower than on SR20. That is the best glide speed, it is not the best L/D ratio speed of the airfoil, it is a compromise of the airfoil + fuselage + propeller and in the SR22 the propeller is braking a lot more than on SR20, which alone is enough to explain the lower best glide speed - because of the propeller braking, the SR22 sinks faster, but if there was no propeller, SR22 could have higher glide speed than the SR20. But what this has to do with the topic? The interesting thing is that the Cirrus has different airfoil and higher wing loading and the optimum glide speed is higher than on DA40 which results potential to faster cruise speed than DA40 (whereas it is not exactly the airfoil's best L/D speed because of the mentioned reasons). Providing that there is enough power available, the Cirrus airframe is faster although the larger fuselage cross section and wetted area most likely pretty much diminishes the benefit from the wing, that is also partly a reason why the best cruise speed performance of DA40-180/XL and SR20 is not that much different, SR20 is just slightly faster - the Diamond has better fuselage shape and it simply is a lot smaller aircraft than the Cirrus and size does not tend to come without penalty when it comes to aerodynamic drag.

However, it would be beneficial for efficiency to have an airfoil which could achieve higher L/D ratio at the cruise Cl of the DA40 already. It does not come without penalties of course, the airfoils which have high L/D ratio at low Cl don't necessarily always produce optimal Clmax (which then has also relation to the required wing area which gets back to the stall speed and wing loading).

And it is not all in that, Daniel Raymer notes in his book that usually only 90% of the theoretical Clmax of the airfoil gets realized in practice. Therefore it is a interesting compromise between the wing sizing, and the best L/D at cruise Cl. Daniel Raymer notes in high book that the Cl is one of the hardest things to estimate without experimental data from test flights, and often test flights result in the need of modifications (e.g. if the Clmax in practise is not as good as was predicted, a larger wing is required to meet the maximum stall speed criteria, which is for single engine aircraft 61 kts).

It would be really interesting if someone would have a batch processing functionality in a airfoil program that would ingest the UIUC airfoil database data and simulate through all airfoils and put them into a correct order for the given specification (cruise Cl below 0.2), as high L/D at cruise Cl for a low wing loading, and at the same time, as high Clmax as possible, and at the same time, gentle stall charasteristics at low Reynolds number. And of course, the pitching moment also has some importance, high pitching moment tends to cause more trim drag which reduces the achievable Clmax (of the total airframe) considerably - if the wing can achieve e.g. Clmax 2.2, the airframe may be left to below 1.5 in total because of the download in the tail that is negative lift.