There is lots of strong feelings about tractor vs. pusher propeller configuration but no exact generic answer. Here is one article about the topic. Does not make definitive answer, but gives some background for the topic:
http://www.flyingmag.com/technicalities/1582/pusher-pusher.html
Here is another article:
http://dic.academic.ru/dic.nsf/enwiki/514042
Forum discussion
Another forum discussion
http://www.aiaa.org/content.cfm?pageid=406&gTable=mtgpaper&gID=50663
Tractor (prop forward of laminar flow wing):
http://www.aiaa.org/content.cfm?pageid=406&gTable=Paper&gID=1248
Tuesday, August 25, 2009
Monday, August 24, 2009
Hypotenuse and catheti and how blending makes wetted area not larger but actually smaller!
Most aircraft have larger than necessary wetted area and not so optimal body shape. One could think without thinking in more detail that wetted area is saved by lofting the plane so that the engine cowling is part of the main fairing and then there is a minimum canopy added on top of that.
However, a little thinking further: which one is the shortest route always, hypotenuse or catheti? Unlike the first thing which comes to mind when looking at planes and saving wetted area, instead of having this complicated shape, actually having more volume and fairing everything in the single form actually produces not only easiest path to the airflow, but also it produces lowest possible wetted area. So making the fuselage larger by removing canopy and putting the cockpit inside the main shape decreases wetted area and drag instead of increasing it. The shallower angle for windows does not decrease the visibility - the visibility can remain still the same. The only problem comes from the optical quality of the windows - as you are looking them from angled direction, you are looking through more plexiglass than you otherwise would and it can degrade the visibility. However - the visibility directly forwards is usually not so good in single engine aircraft which have engine in the front and it is neither better on planes without engine on front since somehow designers seem to not think that people would like to see straight forward very well too. Some twin engine planes have very high panels and poor visibility forwards despite of the fact not having the engine in front would make it possible to make the forward visibility a lot better than that.
So the design on CAD system becomes easy when the shape is not complicated but super simple. And in turn the super simple shape (convex to all directions though, in that sense not so simple, but I mean it is a single loft) has the best drag coefficient and the best wetted area too. At times it feels unbelievable that the solution can be so simple (and I have difficulty to believe it myself when looking e.g. our shared ownership Diamond DA40, it has many shapes, parts and forms), but who says that it has to have so many shapes. Nobody. So it will not have so many different shapes and forms if one shape can do it all. And who says the instrument panel needs to be panel and everything laid out to the panel? Nobody again. A bit more creativity and a lot better forward visibility is achieved despite of not having a bubble canopy and despite of having a pressurized fuselage.
Blending the fuselage to the wings increases frontal area. But who cares about the frontal area. It has very little effect to the drag in airplanes. It is all about wetted area and saving in the wetted area (in addition to maximizing the laminar flow). So blending the wing decreases wetted area - hypotenuse again, it is not a good idea to follow catheti. And the air likes that too - in fuselage wing joint the airflow can not sustain laminar flow. But what if you eliminate the joint and at the same time save in the wetted area. Great stuff.
One could say that it is hard to make a door to a such fuselage. Yes it is hard to make a door. But the solution for the door is to eliminate the door. A hatch that has no hinges and that is larger than the hole is the most light weight door one can imagine. It does not require complicated mechanism to hold it on place and it does not require lots of latches. It holds on place by itself because of the air pressure differential. It can be locked with a lot lesser heavy duty mechanics from inside to the fuselage. And how to ensure the hatch does not ever get out of the hole? That is super easy too: the hole and hatch can be circular and there is no way to put a larger circle out of a smaller circular hole. Not even magicians can do that!
Now then the window problem:
- to glue windows on pressurized fuselage, how to make sure the windows don't rip themselves out - how to glue them on place. Keep it simple and stupid solution: glue them to the inside so that they are larger than the hole in the fuselage. Now what, we have a problem that there is a dent outside of the fuselage on the window area which is really bad for the airflow. No problem again, there can be a simple non-pressurized window that is glued to the outside and faired level with the fuselage around it. It is also a fail-safe: if the windows that are exposed to outside get scratches, no problem, it does not affect the pressurized fuselage - these windows can be replaced fairly easily. And guess what, no bolts are needed, no rivets are needed, very simple.
Then how to get the blended fuselage to work with pressurization. Again super simple: the blend can be fairing on the outside and the pressure vessel can be tubular with completely circular cross section inside.
However, a little thinking further: which one is the shortest route always, hypotenuse or catheti? Unlike the first thing which comes to mind when looking at planes and saving wetted area, instead of having this complicated shape, actually having more volume and fairing everything in the single form actually produces not only easiest path to the airflow, but also it produces lowest possible wetted area. So making the fuselage larger by removing canopy and putting the cockpit inside the main shape decreases wetted area and drag instead of increasing it. The shallower angle for windows does not decrease the visibility - the visibility can remain still the same. The only problem comes from the optical quality of the windows - as you are looking them from angled direction, you are looking through more plexiglass than you otherwise would and it can degrade the visibility. However - the visibility directly forwards is usually not so good in single engine aircraft which have engine in the front and it is neither better on planes without engine on front since somehow designers seem to not think that people would like to see straight forward very well too. Some twin engine planes have very high panels and poor visibility forwards despite of the fact not having the engine in front would make it possible to make the forward visibility a lot better than that.
So the design on CAD system becomes easy when the shape is not complicated but super simple. And in turn the super simple shape (convex to all directions though, in that sense not so simple, but I mean it is a single loft) has the best drag coefficient and the best wetted area too. At times it feels unbelievable that the solution can be so simple (and I have difficulty to believe it myself when looking e.g. our shared ownership Diamond DA40, it has many shapes, parts and forms), but who says that it has to have so many shapes. Nobody. So it will not have so many different shapes and forms if one shape can do it all. And who says the instrument panel needs to be panel and everything laid out to the panel? Nobody again. A bit more creativity and a lot better forward visibility is achieved despite of not having a bubble canopy and despite of having a pressurized fuselage.
Blending the fuselage to the wings increases frontal area. But who cares about the frontal area. It has very little effect to the drag in airplanes. It is all about wetted area and saving in the wetted area (in addition to maximizing the laminar flow). So blending the wing decreases wetted area - hypotenuse again, it is not a good idea to follow catheti. And the air likes that too - in fuselage wing joint the airflow can not sustain laminar flow. But what if you eliminate the joint and at the same time save in the wetted area. Great stuff.
One could say that it is hard to make a door to a such fuselage. Yes it is hard to make a door. But the solution for the door is to eliminate the door. A hatch that has no hinges and that is larger than the hole is the most light weight door one can imagine. It does not require complicated mechanism to hold it on place and it does not require lots of latches. It holds on place by itself because of the air pressure differential. It can be locked with a lot lesser heavy duty mechanics from inside to the fuselage. And how to ensure the hatch does not ever get out of the hole? That is super easy too: the hole and hatch can be circular and there is no way to put a larger circle out of a smaller circular hole. Not even magicians can do that!
Now then the window problem:
- to glue windows on pressurized fuselage, how to make sure the windows don't rip themselves out - how to glue them on place. Keep it simple and stupid solution: glue them to the inside so that they are larger than the hole in the fuselage. Now what, we have a problem that there is a dent outside of the fuselage on the window area which is really bad for the airflow. No problem again, there can be a simple non-pressurized window that is glued to the outside and faired level with the fuselage around it. It is also a fail-safe: if the windows that are exposed to outside get scratches, no problem, it does not affect the pressurized fuselage - these windows can be replaced fairly easily. And guess what, no bolts are needed, no rivets are needed, very simple.
Then how to get the blended fuselage to work with pressurization. Again super simple: the blend can be fairing on the outside and the pressure vessel can be tubular with completely circular cross section inside.
Saturday, August 22, 2009
First atlantic crossing completed
We completed the first atlantic crossing in the N756DS (Diamond DA40) on Wednesday and arrived to Helsinki-Malmi. There will be a presentation about the trip in SIL-luokka Helsinki-Malmi later. I will let you know more about it when I know more details and have prepared the presentation. If you are a reporter in a newspaper or magazine and want to write a story about our not so ordinary adventure, feel free to contact me karoliina dot t dot salminen at gmail dot com.
We received the ferry flight training from Edward Carlson.
We want to do the trip again also, if you are looking for inexpensive ferrying from USA to Finlandm or to any other European country via Denmark/Opmas, I am glad to inform that the Danish VAT will work still to next summer as followings: if you buy aircraft this year before the end of the year and complete all the agreements, according to Opmas, the plane can still benefit from the Danish VAT if it is ferried on the first half of 2010. We would be glad to help for free (no ferry flight fee) at the price of the expenses (gasoline, hotel (we choose cheapest options always), maintenance needed for the plane, airport fees). If you are interested in inexpensive ferry (or should I say delivery) flight, please contact me to the abovementioned address. You can not fly the North Atlantic for first time by yourself, but you need someone that has flown it before to get insurance (which is mandatory for the flight). We have now flown it once and are willing to help people who haven't flown it yet and/or who do not want to fly it by themselves. The summer time is the best time for ferrying an aircraft because of weather. We will spend our summer vacation for flying your plane for free, you can not get better deal from anybody. We agree to fly the following aircraft make and models: Diamond DA40-180/G1000, Diamond DA40XL/G1000, Diamond DA40-CS/G1000, Diamond DA40-180/Avidyne, Cirrus SR20/Avidyne, Cirrus SR22/Avidyne, Cirrus SR22/Garmin Perspective or Diamond or Cirrus with any other comparable glass cockpit avionics - this list is based on our prior flying experience - we have flown Diamonds and Cirruses before. We can consider also other aircraft, but that will rise the expenses a bit since we need to get checked out to these prior flying the trip. I could estimate that most familiar of those would be Columbia 350, Columbia 400, Cessna 350 Corvalis, Cessna 400 Corvalis and these we would be glad to fly providing that we would get proper check-out before starting the trip to feel comfortable enough flying the plane in not so ideal conditions. We may not agree to fly steam-gauge IFR planes and surely will not agree to fly VFR-only equipped planes. Also we will not fly C172, because that is not suitable for the trip. We are not interested in taking unnecessary risks, we want to deliver.
We received the ferry flight training from Edward Carlson.
We want to do the trip again also, if you are looking for inexpensive ferrying from USA to Finlandm or to any other European country via Denmark/Opmas, I am glad to inform that the Danish VAT will work still to next summer as followings: if you buy aircraft this year before the end of the year and complete all the agreements, according to Opmas, the plane can still benefit from the Danish VAT if it is ferried on the first half of 2010. We would be glad to help for free (no ferry flight fee) at the price of the expenses (gasoline, hotel (we choose cheapest options always), maintenance needed for the plane, airport fees). If you are interested in inexpensive ferry (or should I say delivery) flight, please contact me to the abovementioned address. You can not fly the North Atlantic for first time by yourself, but you need someone that has flown it before to get insurance (which is mandatory for the flight). We have now flown it once and are willing to help people who haven't flown it yet and/or who do not want to fly it by themselves. The summer time is the best time for ferrying an aircraft because of weather. We will spend our summer vacation for flying your plane for free, you can not get better deal from anybody. We agree to fly the following aircraft make and models: Diamond DA40-180/G1000, Diamond DA40XL/G1000, Diamond DA40-CS/G1000, Diamond DA40-180/Avidyne, Cirrus SR20/Avidyne, Cirrus SR22/Avidyne, Cirrus SR22/Garmin Perspective or Diamond or Cirrus with any other comparable glass cockpit avionics - this list is based on our prior flying experience - we have flown Diamonds and Cirruses before. We can consider also other aircraft, but that will rise the expenses a bit since we need to get checked out to these prior flying the trip. I could estimate that most familiar of those would be Columbia 350, Columbia 400, Cessna 350 Corvalis, Cessna 400 Corvalis and these we would be glad to fly providing that we would get proper check-out before starting the trip to feel comfortable enough flying the plane in not so ideal conditions. We may not agree to fly steam-gauge IFR planes and surely will not agree to fly VFR-only equipped planes. Also we will not fly C172, because that is not suitable for the trip. We are not interested in taking unnecessary risks, we want to deliver.
Sunday, August 16, 2009
First Northern Atlantic Crossing
I have been recently a bit silent on this blog. The reason have been that I have been too busy and out of Internet most of the time. In other words, I have been flying.
I am typing this from Iceland. Our trip has been so far quite incredible:
1. from Helsinki to Miami with airliner
2. from Miami to Jacksonville with car
3. from Jacksonville to St. Louis with plane, N756DS
4. from St. Louis to Pueblo with N756DS
5. from Pueblo to Palo Alto with N756DS
6. IFR training in San Francisco Bay Area with N756DS
7. from Palo Alto to Sioux Falls with N756DS
8. from Sioux Falls to Oshkosh with N756DS
9. spent couple of days in Oskosh/Airventure 2009. Camp with Cozygirrrls.
10. from Oshkosh to Rhode Island with N756DS
11. from Rhode Island to Wabush (Canada) with N756DS. First Northern Atlantic Crossing in a small airplane was started for us. We are flying with Ed Carlson (he is a ferry flight instructor specialized in Northern Atlantic crossing).
12. from Wabush to Kuujjaq (Canada) with N756DS
13. from Kuujjaq (Canada) to Iqaluit (Canada) with N756DS
14. from Iqaluit (Canada) to Kangerlussuaq (Greenland) with N756DS
15. from Kangerlussuaq (Greenland) to Kulusuk (Greenland) with N756DS
16. from Kulusuk (Greenland) to Reykjavik (Iceland) with N756DS
17. from Reykjavik (Iceland) to EGILSSTADIR with N756DS
We will continue to Faroe Island / Vagar next. After that is either Bergen or Stavanger in Norway.
Kate has been keeping a blog about the adventure here:
http://n756ds.blogspot.com
I am typing this from Iceland. Our trip has been so far quite incredible:
1. from Helsinki to Miami with airliner
2. from Miami to Jacksonville with car
3. from Jacksonville to St. Louis with plane, N756DS
4. from St. Louis to Pueblo with N756DS
5. from Pueblo to Palo Alto with N756DS
6. IFR training in San Francisco Bay Area with N756DS
7. from Palo Alto to Sioux Falls with N756DS
8. from Sioux Falls to Oshkosh with N756DS
9. spent couple of days in Oskosh/Airventure 2009. Camp with Cozygirrrls.
10. from Oshkosh to Rhode Island with N756DS
11. from Rhode Island to Wabush (Canada) with N756DS. First Northern Atlantic Crossing in a small airplane was started for us. We are flying with Ed Carlson (he is a ferry flight instructor specialized in Northern Atlantic crossing).
12. from Wabush to Kuujjaq (Canada) with N756DS
13. from Kuujjaq (Canada) to Iqaluit (Canada) with N756DS
14. from Iqaluit (Canada) to Kangerlussuaq (Greenland) with N756DS
15. from Kangerlussuaq (Greenland) to Kulusuk (Greenland) with N756DS
16. from Kulusuk (Greenland) to Reykjavik (Iceland) with N756DS
17. from Reykjavik (Iceland) to EGILSSTADIR with N756DS
We will continue to Faroe Island / Vagar next. After that is either Bergen or Stavanger in Norway.
Kate has been keeping a blog about the adventure here:
http://n756ds.blogspot.com
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