Aircraft Quiz #77.

DougRobertson

What all-metal aluminum alloy production real flying powered airplane was designed so simply that its right and left wings were completely interchangeable and all tail surfaces (vertical stabilizer with rudder, and horizontal stabilizer with elevators) were also completely interchangeable? Goals were ease of manufacture, simplicity and low parts count.

1. Designer?

2a. Make and model of aircraft? 2b. Engine and horsepower?

3. Date of prototype flight?

4. How many seats?

5. Year of certification?

6. How many were built?

Not a clue, but I have seen up close a flying example of the quiz aircraft at an airshow around the 1972-73 time frame. It was apparent the interchangeability of the stated flight components.

sparrow9

1. BjÃ¶rn Andreasson

2a. Daetwyler MD-3-160 Swiss Trainer 2b. Lycoming O-320-D2A

3. 1983-08-12

4. 2

5. 1992 (FAR)

6. 5 in Switzerland and 40(?) as Aero Tiga in Malaysia

John

DougRobertson

I took a good look at the Daetwyler MD3-160 Swiss trainer with its description and do not believe it meets any of the quiz aircraft requirements. The MD3-160 description refers to only the moveable flight control components-rudder, elevator, flaps being interchangeable but does not appear to include interchangeability between the fixed vertical stabilizer and the fixed horizontal stabilizers, for example. And, can the entire wing with flap be swapped from one side to the other (this would require absolutely symmetrical airfoils and mating to the fuselage/wing stubs be absolutely identical)?

To further clarify the quiz aircraft attributes-the entire vertical tail with rudder can be swapped for either side of the horizontal stabilizer with elevator as they are completely identical parts. And, the right wing with its aileron can be swapped for the left wing with its aileron as they are completely identical parts.

And, please reread my last paragraph of the quiz and consider those dates precede any MD3-160 production. (Too, the airshow was at Porterville airport KPTV in California).

sparrow9

I am sorry, I did not read your last paragraph.

And of course, you are right.

John

moxy

I'll plump for the following Doug.

1. Jim Bede (as the BD-1 with foldable wings)

2a. American Aviation AA-1 Yankee Clipper

2b. Lycoming 0-235-C2C 108 hp

3. 11 July 1963

4. 2

5. 29 August 1967

6. 461 of the AA-1

DougRobertson

Rob, I somehow lost my extensive response to you why your answers don't qualify. It has to do with the AA-1 NACA 64-415 wing airfoil NOT being truly symmetrical, and wing tank fuel feed issues if wings swapped. I will try again tomorrow to get it posted. Thanks for your input and patience.

DougRobertson

I will try again to explain-the AA-1 has a NACA 64-415 airfoil which is NOT symmetrical. Take a look! This puts the Wikipedia information in doubt about true identical wing for wing substitution. There are fuel feed factors also as the tanks are tubular in each wing and the fuel unports when in a slip to a crosswind landing with fuel starvation leading to a stall with tendency toward a flat spin which is not recoverable. So, the proximal wing stubs if swapped would not be identical either per fuel delivery. This stall/spin tendency condition is aided by the poor streamlining of the fuselage and the short wings. The NTSB fatal accident rate in 1980 published in 1981 shows 4.8 fatal per 100,000 hours for the AA-1 Trainer or Yankee, poorest in its class. (The next and highest fatal rate that year was held by the Luscombe 8 series at 5.1 fatal per 100,000 hours). One wonders whether the AA-1 submitted today would pass the FAR Part 23 flight requirements.

I met Jim Bede, the late designer of the BD-1 (only one prototype built) and the original AA-1 series (before subsequent modifications) at EAA AIRVENTURE 2008.

The Quiz aircraft will be eventually revealed with its NACA airfoil identified which is truly symmetrical. Thanks for your interest in these quizzes.

moxy

Thanks for the information Doug. When I suggested the AA-1 I must admit I did have some doubts about it being correct. I remember a few years ago now, reading about an aeroplane with interchangeable wings etc., but cannot for the life of me recall the aircraft type. When I read about Jim Bede's design it did not jolt my memory hence some doubt.

What interests me particularly is the matter of true symmetry with regard to aerofoils. I have always assumed maybe incorrectly that the top of a wing is in the main slightly convex whilst the lower wing would be concave to enable the air pressure over the wing to be lower than that beneath when the leading edge moves forward. If this is the case and the wings are interchangeable they therefore couldn't be fitted upside down. If not and they can be fitted to the fuselage at either wingtip or end the ailerons would have to be in the middle of the trailing edge. I think I must be missing something in my very basic knowledge of aerodynamics. Perhaps you could clarify this for me Doug.

I'm surprised at the fatal accident rate for the Luscombe 8 series. We have a number in England and I have always thought it quite a handsome aeroplane. The old adage is it it looks right it flies right. I think it looks good. Is there a specific reason why the rate is so high? Finally, I didn't know Jim Bede had passed away, clever chap. I remember seeing his small jet at the Farnborough Air Show a few years ago.

I shall now continue my search for the correct answer.

moxy

Just had a good read up on NACA aerofoil sections. My ideas were certainly somewhat dated if not totally wrong. However I'm still a bit confused how exactly a symmetrical aerofoil provides lift in one direction when one would imagine air pressure would be equal above and below the wing.

DougRobertson

Thanks Rob,

But, far be it for me to expound on the aerodynamics of airfoils, the most of which are certainly NOT symmetrical, as those with absolute symmetry have flight quirks. There is a trade-off between airfoil shapes and aircraft lift and other performance in flight. Some symmetrical airfoil wing aircraft are emphatically restricted from intentional spins, for example. Aircraft with symmetrical airfoil wings may exhibit poor stall recovery performance. Wing "wash-out" is often used by designers so that the wing will not stall out all at once, but by sections based on relative angle of attack, span-wise. This keeps distal ailerons effective, for example, in approach to a stall. Need I write there is no symmetry/interchangeability of wings with washout?

I have recommended Wolfgang Langewiesche's book in this Forum before to a flight student's question, as I recall. It is titled "Stick and Rudder, An explanation of the Art of Flying". It is the first exact analysis of the art of flying, and highly recommended. Written in 1944, it is still in print. Publisher: McGraw-Hill Book Company, New York. 389 pages include a very comprehensive index, and the book is well illustrated.

I don't have any more specific information re the Luscombe 8 series accident rate cause, or theories. A friend learned to fly in one back in the 1960s, and he found it tricky to land consistently well. Meanwhile, this quiz is still out there.

DougRobertson

With this Quiz rapidly zooming to over 600 views and no right answers; my answers follow. I was most surprised that it wasn't answered. After some 250 views I used my search browser (unnamed) to ask "Production aircraft with symmetrical NACA airfoil?" and there were four answers on the first results page referring to the Quiz aircraft. DUH! Here are the answers.

1. Harold E. Emigh (pronounced "AMY").

2a. Emigh TROJAN A-2. 2b. Continental C85-12F 85 Hp, later offered with Continental C90 90 Hp.

3. December 20, 1946.

4. Two seats side by side.

5. A.T.C. #801 was granted December 21, 1948.

6, Fifty-eight total were built. In two plants in California and one in Arizona, successively.

Emigh, after years of study, set out to build a production all-metal aircraft cheaply, by comparison, and with common interchangeable parts. Less drawings and easy assembly. He had earlier in 1929 learned to fly an Alexander "Eaglerock" (Combo-Wing). Unfortunately, a 1948 new light aircraft launch was not the best of timing, as the American market for small two-place aircraft was rapidly disappearing with huge light aircraft builds and sale right after WWII with many general aviation companies folding, or consolidating.

The all metal Emigh Trojan A-2 had interchangeability of all fixed tail structure. Ditto for all moveable tail structure.The fixed vertical stabilizer could interchange with either horizontal stabilizer and the rudder could be interchanged with either elevator. The NACA 0012-63 wing airfoil was symmetrical and either no-flap wing could fit either side of the airplane. The external wing ribs were prominent and "different" from most smooth wing airfoils. That was what initially called my attention to the Trojan A-2 I saw parked at the Porterville, California airshow in the early '70s. The landing gear was short fixed tricycle gear. With the single tail it would never be mistaken for a ERCO Ercoupe of the vintage. Initial price quoted was $2,575 FAF, later average new price was $3,295 FAF. I thank all who pondered this quiz.