Nenadović biplane

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Bigshu

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I am much more interested in the potential of the Nenadovitch biplane wing to be an attractive option for light planes (with or without the endplate ailerons)
I was just wondering what kind of weight penalty there would be to have both wings cantilevered, rather than joined by the end plates, or struts. Having each wing attached only to the fuselage allows for optimal placement of the wings to maximize slot effect, or CG range, or size and shape of each wing (like Sockmonkey's straight wing/delta wing tandem designs. Using struts or end plates to join the wings allows for really light but rigid wings, right?
 

cluttonfred

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Yes, I did think of the wing folding bit, and took another look at the Luciole specs (just 50 sq ft of wing) and I don't see how you could do it without putting the spars through the pilot using shorter span wings of the original chord. If you halve the wing chord, then you could have a semi-reclined seat and the front wing spar under the pilot's knees.

Screenshot 2021-06-16 10.20.41 PM.png

Something still small but a little bigger like a Sonerai 1 might work better. The Sonerai pilot is already used to having the midwing spar in an awkward place. Another option might be putting the lower wing at shoulder height and having the upper wing completely in clear air, with faired cabane struts if needed.

At the scale of a small single-seater, there is actually a lot of benefit to a low aspect ratio as it gets the wing spars further apart vertically and horizontally. Starck was no dummy in choosing a racer-like design for his AS.27 tractor, and dealing with the spar locations may have inspired the central engine of the AS.37.
 
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Martin R.

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Here you will find some considerations from Rudy Nickel - a very experienced builder and pilot - who built and flew an AS-37 at the end of the seventies:

André Starck Archives - Passion pour l'aviation

The article was published in the RSA magazine no 100-101. It is written in French and the president of the RSA has allowed me yesterday to publish it in this HBA forum.

Here my attempt of a translation ;)
 

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cluttonfred

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Here you will find some considerations from Rudy Nickel - a very experienced builder and pilot - who built and flew an AS-37 at the end of the seventies:

André Starck Archives - Passion pour l'aviation
Thanks, Martin, for this article! I didn't realize you had done a translation, and the attachment is not working for me, so here is mine. Square brackets [ ] are my editorial additions. I'll go ahead and duplicate this post in the A.S. 37 thread so we have it in both places.

THE STARCK A.S. 37 BY R.NICKEL
[Les cahiers du R.SA.100-101 May June July August 1978]

With the approval of the president of the RSA, I publish the report by R.Nickel from issues 100-101 of Les Cahiers du RSA on the A.S 37 that he built according to the plans designed by André Starck.

"I thought that an objective and real-life report on the flights of my A.S.37 might interest your readers.

The 37 that I built conforms strictly to the original plans package, GS 65 HP engine, electric starter, classic tube landing gear, angled endplates, upholstered cockpit, radio, fully fabric-covered (in my case) which resulted in a significant weight increase.

Since the first flight in January 1977 until October, I totaled nearly 72 hours and more than 250 landings, flights divided into testing, engine tuning and cooling, airframe adjustments, propeller tests, exploration of weight and balance and especially flight demonstrations to visitors.
  • Total safety aircraft, does not stall, sinks flat with slight buffeting. With full action side stick still no tendency to spin.
  • Turns can be executed correctly, either with the rudder or the stick without any problem. No adverse yaw.
  • Relatively short take-off at medium load (160-180 m). [525-591 ft]
  • Very short landings, less than 150 m [492 ft], in the worst conditions. It is possible to land the 37 on a strip 3 m wide and 50 m [164 ft] long (tests carried out), and in certain cases, in 35 m [115 ft] (measured) into the wind.
  • Excellent visibility at all flight angles. - Very easy cabin access.
  • Safety on the ground: the propellers are placed in such a way that it is possible to go around the aircraft with the engine running, without risk of accident.
  • Uncompromising solidity (10g ultimate load). Reduced space requirement.
  • I executed loops, hammerheads and very tight turns.
  • Precise piloting, always responds to the controls.
Some extracts from the flight log.
  • CG adopted between 27-30%, tests until 36%.
  • 5,400 RPM at takeoff
  • 5,800 RPM maximum level flight
  • 150 km (93 mph) maximum speed at 5,700 RPM
  • Climb to 1,400 meters : 0.45 ' [4,600 ft in 27 minutes]
  • Propeller pitch 0 m 85 : climb speed 1 m 80/s [33.5 in pitch for 354 ft/min]
  • Propeller pitch of 0 m90: climb speed 1 m 50/s. [35.4 in pitch for 295 ft/min]
  • Ascent to 900 m in 9 ' - pitch of 0.85 (1 m 60/s.) engine 5,600 RPM. [2953 ft in 9 min with 33.5 in pitch for 315 ft/min]
  • Climb to 300 m in 2′, 5 - step of 0,85 (2 m/s.) engine 5,600 RPM. [984 ft in 2 min with 33.5 in pitch for 394 ft/min]
Presentation in flight to Mr SALAÜN of the SFACT. Meeting R. S.A. of Romans.
Presentation in flight at the meeting of Brienne-le-Château on Monday and Tuesday only (because of bad weather).

The CITROEN GS 65 HP engine is an excellent engine, robust and reliable. It was very tempting at the beginning because of its low purchase price (2,500 Francs) [about US$500 at the time], on the other hand its maximum torque (8,9 kg) [62 ft-lb] which is produced at low engine speed (3,240 RPM) does not leave any more than 41 hp, that is to say with the output of the propellers of 80 %, 33 hp usable for takeoff and climb.

This maximum torque at low rpm, which is a good quality for acceleration on a car, becomes a handicap in airplane use, which requires its maximum power and torque at takeoff and in climb, not having a gearbox.

It is however remarkable that this aircraft flies with so little power (16 1/2 HP on each propeller).

All these flights were done without wheel fairings.

I routinely climb to 2,000 meters above the terrain, but the climb speed in these conditions of power is insufficient (one does not make miracles with 1200cc).

In the last year, still waiting for the GS 1500cc engine to come out, STARCK has turned to engines with more torque, and recommends the adoption of the PORSCHE 2 liters - 100 CV that Mr. KNOEPFLI, other manufacturers, and myself are currently assembling.

On the other hand, RENAULT put at the disposal of STARCK an R. 20 engine of 90 HP. This engine is being assembled on the 37 of Mr. BOUCHER of St MARCELLIN.

Another 37 built by Mr. BOURDREUX of CADARACHE will be equipped with the new SACMA engine of Mr. NEGRE.

In all these cases, the power will be at least doubled, which lets us foresee beautiful performances at climb speeds.

In order to facilitate the adoption of the best pitch, I built propellers with two blades with ground-adjustable pitch. On the same process, I made three-blade propellers for 90-100 HP engines.

The POWERGRIP toothed belt drives from UNIROYAL have a very good behavior, without any problem.

For the new level of power, I use the new HTD belt of the same brand, which is rated for 120 HP per propeller.

In conclusion, apart from some personalized adaptations and a sufficient power (currently in progress), the aircraft confirms the safety qualities of the formula, already tested for a long time on the AS 20 and more recently on the AS 27 by nearly 30 pilots.

However, building in amateur time, development is necessarily longer than that of industrial production. "

R . NICKEL 1978

This A.S. 37 is now in the collection of the Espace Air Passion d’Angers museum.
 

cluttonfred

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Could you get away with making a tailless version? A double plank so to speak.
It could be done but I don't think it would be a good application. The two wings acting as one big slotted wing have quite a bit of camber as a combination, which means a lot of nose-down pitching moment which has to be balanced somehow. A plank needs nose-up pitching moment to be stable, either from the use of a reflexed airfoil or from trailing edge control surfaces deflected upwards (which amounts to the same thing).

The Nenadović biplane also gets interesting at smaller chords where it gets easier to package the combination as one thick wing. It would be neat to see something along the lines of the Braunschweig LF-1 Zaunkönig adapted as a slotted biplane.

Let's say you replace the Zaunkönig's 8.02 m (26 ft 4 in) span and 8.5 m2 (91 sq ft) wing with one of equal span and area along the lines of the AS.27 or AS.37. Each biplane wing would be a little more than 50% of the monoplane wing's chord to make up for the area lost from the lower wing because of the 45-degree end plates. The combination would still be less than 4' overall chord and less than 1.5' overall height and the wings themselves would be clean and smooth.

1623960464063.png
 
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Sockmonkey

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It could be done but I don't think it would be a good application. The two wings acting as one big slotted wing have quite a bit of camber as a combination, which means a lot of nose-down pitching moment which has to be balanced somehow. A plank needs nose-up pitching moment to be stable, either from the use of a reflexed airfoil or from trailing edge control surfaces deflected upwards (which amounts to the same thing).

The Nenadović biplane also gets interesting at smaller chords where it gets easier to package the combination as one thick wing. It would be neat to see something along the lines of the Braunschweig LF-1 Zaunkönig adapted as a slotted biplane.

Let's say you replace the Zaunkönig's 8.02 m (26 ft 4 in) span and 8.5 m2 (91 sq ft) wing with one of equal span and area along the lines of the AS.27 or AS.37. Each biplane wing would be a little more than 50% of the monoplane wing's chord to make up for the area lost from the lower wing because of the 45-degree end plates. The combination would still be less than 4' overall chord and less than 1.5' overall height and the wings themselves would be clean and smooth.

View attachment 112031
I was thinking one might add a third wing with a slight negative AOA.

Anyhow, one could have the main spar of the lower wing of a Nenadovic' setup right behind the pilot's shoulders if you wanted something akin to a high wing. Should be slightly less draggy than having the lower wing at the bottom of the fuselage.
 

cluttonfred

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The Nenavodić biplane and the box wing are clearly related but not the same. The Sunny ultralight comes close but the others give up any favorable, drag-reducing interaction between the wings in favor of a tandem-wing approach.
 

Bill-Higdon

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It could be done but I don't think it would be a good application. The two wings acting as one big slotted wing have quite a bit of camber as a combination, which means a lot of nose-down pitching moment which has to be balanced somehow. A plank needs nose-up pitching moment to be stable, either from the use of a reflexed airfoil or from trailing edge control surfaces deflected upwards (which amounts to the same thing).

The Nenadović biplane also gets interesting at smaller chords where it gets easier to package the combination as one thick wing. It would be neat to see something along the lines of the Braunschweig LF-1 Zaunkönig adapted as a slotted biplane.

Let's say you replace the Zaunkönig's 8.02 m (26 ft 4 in) span and 8.5 m2 (91 sq ft) wing with one of equal span and area along the lines of the AS.27 or AS.37. Each biplane wing would be a little more than 50% of the monoplane wing's chord to make up for the area lost from the lower wing because of the 45-degree end plates. The combination would still be less than 4' overall chord and less than 1.5' overall height and the wings themselves would be clean and smooth.

View attachment 112031
Looks almost like a Bf 163
 

Martin R.

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Here you will find some considerations from Rudy Nickel - a very experienced builder and pilot - who built and flew an AS-37 at the end of the seventies:

André Starck Archives - Passion pour l'aviation

The article was published in the RSA magazine no 100-101. It is written in French and the president of the RSA has allowed me yesterday to publish it in this HBA forum.

Here my attempt of a translation ;)
Here is a better translation with which the French RSA helped me.

Unfortunately, my query about the whereabouts of the other AS-37 mentioned in the article did not reveal anything. It is quite possible that only the F-WYBG was flown for a longer time.
 

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cluttonfred

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So no one gets frustrated trying to read that screen capture.... ;-) It was a design for a 95 hp three-place touring aircraft (staggered side-by-side seating up front plus one seat in back) based on Starck's earlier A.S. 20. Sketch and projected performance published in l'Air Revue in 1943.

Starck AS50 1.png
Starck AS50 2.png
 

Magisterol

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I wander if those numbers are valid. With a prop efficiency of 0.8 you get 52hp available. At 185km/h or 100kts you get an equivalent flat area of lest than 1sqft which is same as an AR-5. Kind of doubtful for me. That would translate in a lift to drag ratio of over 11 at max speed. At max speed, the lift coefficient would be 0.081, so a drag coefficient of less than 0.007 would imply for the whole airplane. That drag coefficient is less that some of the NACA 6 series airfoils. I don’t know what to say. I would like to believe it, but ....
 

Magisterol

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Thanks, Martin, for this article! I didn't realize you had done a translation, and the attachment is not working for me, so here is mine. Square brackets [ ] are my editorial additions. I'll go ahead and duplicate this post in the A.S. 37 thread so we have it in both places.

THE STARCK A.S. 37 BY R.NICKEL
[Les cahiers du R.SA.100-101 May June July August 1978]

With the approval of the president of the RSA, I publish the report by R.Nickel from issues 100-101 of Les Cahiers du RSA on the A.S 37 that he built according to the plans designed by André Starck.

"I thought that an objective and real-life report on the flights of my A.S.37 might interest your readers.

The 37 that I built conforms strictly to the original plans package, GS 65 HP engine, electric starter, classic tube landing gear, angled endplates, upholstered cockpit, radio, fully fabric-covered (in my case) which resulted in a significant weight increase.

Since the first flight in January 1977 until October, I totaled nearly 72 hours and more than 250 landings, flights divided into testing, engine tuning and cooling, airframe adjustments, propeller tests, exploration of weight and balance and especially flight demonstrations to visitors.
  • Total safety aircraft, does not stall, sinks flat with slight buffeting. With full action side stick still no tendency to spin.
  • Turns can be executed correctly, either with the rudder or the stick without any problem. No adverse yaw.
  • Relatively short take-off at medium load (160-180 m). [525-591 ft]
  • Very short landings, less than 150 m [492 ft], in the worst conditions. It is possible to land the 37 on a strip 3 m wide and 50 m [164 ft] long (tests carried out), and in certain cases, in 35 m [115 ft] (measured) into the wind.
  • Excellent visibility at all flight angles. - Very easy cabin access.
  • Safety on the ground: the propellers are placed in such a way that it is possible to go around the aircraft with the engine running, without risk of accident.
  • Uncompromising solidity (10g ultimate load). Reduced space requirement.
  • I executed loops, hammerheads and very tight turns.
  • Precise piloting, always responds to the controls.
Some extracts from the flight log.
  • CG adopted between 27-30%, tests until 36%.
  • 5,400 RPM at takeoff
  • 5,800 RPM maximum level flight
  • 150 km (93 mph) maximum speed at 5,700 RPM
  • Climb to 1,400 meters : 0.45 ' [4,600 ft in 27 minutes]
  • Propeller pitch 0 m 85 : climb speed 1 m 80/s [33.5 in pitch for 354 ft/min]
  • Propeller pitch of 0 m90: climb speed 1 m 50/s. [35.4 in pitch for 295 ft/min]
  • Ascent to 900 m in 9 ' - pitch of 0.85 (1 m 60/s.) engine 5,600 RPM. [2953 ft in 9 min with 33.5 in pitch for 315 ft/min]
  • Climb to 300 m in 2′, 5 - step of 0,85 (2 m/s.) engine 5,600 RPM. [984 ft in 2 min with 33.5 in pitch for 394 ft/min]
Presentation in flight to Mr SALAÜN of the SFACT. Meeting R. S.A. of Romans.
Presentation in flight at the meeting of Brienne-le-Château on Monday and Tuesday only (because of bad weather).

The CITROEN GS 65 HP engine is an excellent engine, robust and reliable. It was very tempting at the beginning because of its low purchase price (2,500 Francs) [about US$500 at the time], on the other hand its maximum torque (8,9 kg) [62 ft-lb] which is produced at low engine speed (3,240 RPM) does not leave any more than 41 hp, that is to say with the output of the propellers of 80 %, 33 hp usable for takeoff and climb.

This maximum torque at low rpm, which is a good quality for acceleration on a car, becomes a handicap in airplane use, which requires its maximum power and torque at takeoff and in climb, not having a gearbox.

It is however remarkable that this aircraft flies with so little power (16 1/2 HP on each propeller).

All these flights were done without wheel fairings.

I routinely climb to 2,000 meters above the terrain, but the climb speed in these conditions of power is insufficient (one does not make miracles with 1200cc).

In the last year, still waiting for the GS 1500cc engine to come out, STARCK has turned to engines with more torque, and recommends the adoption of the PORSCHE 2 liters - 100 CV that Mr. KNOEPFLI, other manufacturers, and myself are currently assembling.

On the other hand, RENAULT put at the disposal of STARCK an R. 20 engine of 90 HP. This engine is being assembled on the 37 of Mr. BOUCHER of St MARCELLIN.

Another 37 built by Mr. BOURDREUX of CADARACHE will be equipped with the new SACMA engine of Mr. NEGRE.

In all these cases, the power will be at least doubled, which lets us foresee beautiful performances at climb speeds.

In order to facilitate the adoption of the best pitch, I built propellers with two blades with ground-adjustable pitch. On the same process, I made three-blade propellers for 90-100 HP engines.

The POWERGRIP toothed belt drives from UNIROYAL have a very good behavior, without any problem.

For the new level of power, I use the new HTD belt of the same brand, which is rated for 120 HP per propeller.

In conclusion, apart from some personalized adaptations and a sufficient power (currently in progress), the aircraft confirms the safety qualities of the formula, already tested for a long time on the AS 20 and more recently on the AS 27 by nearly 30 pilots.

However, building in amateur time, development is necessarily longer than that of industrial production. "

R . NICKEL 1978

This A.S. 37 is now in the collection of the Espace Air Passion d’Angers museum.
These numbers are more realistic than Wikipedia...
 

blane.c

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How is the mean air chord established? On normal bi-plane's the method is straight forward but for the Nenadovic bi-plane the front wing (?) gains additional lift because of the air through the slot so how is that extra lift factored into the mean air chord? Or how is the CL determined in relation to the mean air chord?

How is angle of incidence determined? There is obviously six degrees of angle different between the front and rear wing but how is the relationship established regarding placement on the airplane? For example if you had a monoplane with angle of incidence of four degrees would you put the front wing of the Nenadovic at four degrees and the rear wing at ten degrees or .... ?
 

Magisterol

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How is the mean air chord established? On normal bi-plane's the method is straight forward but for the Nenadovic bi-plane the front wing (?) gains additional lift because of the air through the slot so how is that extra lift factored into the mean air chord? Or how is the CL determined in relation to the mean air chord?

How is angle of incidence determined? There is obviously six degrees of angle different between the front and rear wing but how is the relationship established regarding placement on the airplane? For example if you had a monoplane with angle of incidence of four degrees would you put the front wing of the Nenadovic at four degrees and the rear wing at ten degrees or .... ?
Nobody determines mean aerodynamic chord - MAC. It can only be determined in aerodynamic tunnel or with a very powerful software. It is very easy to determine mean geometric chord - MGC and it is close enough for homebuilt or general aviation airplanes. For this case I guess the further away you move from something established, the more “experimental” it gets. Take it for a flight and see how it works, tweak it as you go…
 
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