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).