Starck AS.37 - one engine, two propellers

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cluttonfred

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I am spinning this off from the Nenadović biplane thread to avoid mixing the streams between the aerodynamics of the wing on one hand and the pros and cons of the engine installation on the other. On that engine installation, I think its definitely an idea worth exploring as it provides great visibility and allows shorter landing gear, though there are certainly issues of safety to address in the tractor incarnation with the props just outside the doors. There is definitely a weigh penalty compared with direct drive, but perhaps not too much when compared with other PSRU installations. Here again are those AS.37 pics and specs.

starck as 37 pusher 1.jpg starck as 37 pusher 2.jpg starck as 37 engine installation.png starck as 37 tractor.jpg

Specifications (AS-37A)
Data from Jane's All the World's Aircraft 1980/81[2]

General characteristics
  • Crew: 2
  • Length: 6.00 m (19 ft 8 in)
  • Wingspan: 6.30 m (20 ft 8 in)
  • Height: 1.60 m (5 ft 3 in)
  • Wing area: 13.60 m2 (146.4 sq ft)
  • Empty weight: 400 kg (882 lb)
  • Max takeoff weight: 620 kg (1,367 lb)
  • Powerplant: 1 × Citroën GS 1220 4-cylinder air-cooled, 48 kW (65 hp)
  • Propellers: 2-bladed
Performance
  • Maximum speed: 185 km/h (115 mph, 100 kn) at sea level
  • Cruise speed: 170 km/h (110 mph, 92 kn) at sea level
  • Range: 1,500 km (930 mi, 810 nmi) with 90 L (24 US gal; 20 Imp gal) fuel
  • Service ceiling: 4,500 m (14,800 ft)
  • Rate of climb: 3.5 m/s (690 ft/min) at sea level
  • Take-off run: 200 m (655 ft)
  • Landing run: 140 m (460 ft)
 

Vigilant1

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The best thing about one engine, two fans is the large amount of disc area that can be made available compared to direct drive from one prop, so low disc loading and high prop efficiency (esp at low airspeeds).
With the AS-37A, I suspect the props operating very near the TE of the front wing and also the LE of the rear wing would be noisy, and not as efficient as ones in cleaner air.
 

cluttonfred

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Personally I think it would be very desirable to develop something like this as a drop-in, self-contained unit including the projecting masts with two pusher props driven off the rear of the engine to keep the weight as far forward but the props as far back as possible. With propeller hubs 200 cm/6' 6" on center you could easily fit two 150 cm/60" props to double the disc area compared to a typical direct-drive VW with resulting gains in efficiency and reduction in noise. A basic frame could be adapted to different engines and installations as needed. The effect would be something like the Airbus E-Fan but with props on small masts rather than the electric ducted fans and it could be adapted to various wing and landing gear and cockpit layouts as desired. This idea of a centrally-mounted engine driving multiple propellers has been tried before (see Parnall Possum or Boulton Paul Bodmin) but I think the low power and short distances involved in the AS.37 approach would be more successful.

68100631_An_Airbus_3370568b.jpg
 
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dog

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The engine cooling apears to be very unusual and slightly different in each version,
with the aft facing ducts bieng the inlets feeding an engine driven fan and the outlet
bieng the entirely missing aft fueselage bottom.
Any development would benifit from easy to perform belt maintinance and changes.
Its interesting that,at least first glance, that the
basic design worked as a tractor or a pusher,or
did it? and were there issues with power on /off pitch changes as a tractor?
 

cluttonfred

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Duplicating this post from the Nenadović biplane thread:
Martin R. said:
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.
 

Lendo

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The Starck name reminded me of the New Zealand Snark, nice little design with good rear pilot vision, mid-wing, pusher.. I'd want to know that boom is well and truly strong enough and the only odd thing is you needed to swing the landing gear forward on take-off. As you know main landing gear legs further behind the CG than necessary, makes it harder to take-off.
George
 

Martin W

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I am a helicopter pilot who is spoiled rotten by the unobstructed vision of the Bell47 plexiglass bubble ....... the single biggest reason I have never had a desire to fly fixed wing is the horrible forward vision .... some aircraft let you see the sky above and nothing else unless you bank and do a faceplant on a side window

My first thought (was) going to be along the lines of angle drive gearboxes and driveshafts splitting to two props .... no way !!! ... not practical.

However after reading the OP and looking at the drawings I think the two belt drive is excellent , it is simple , belt drives are a proven concept , and many re-drive systems already use a belt and separate jackshaft (propshaft) .... this concept only requires one more belt and shaft .

Again , I say excellent .... and especially for visibility to be gained.

.
 

blane.c

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One engine driven generator to supply power sufficient for normal cruise to two electric motors supplemented by batteries for additional power for takeoff. The engine would then be 60% to 75% of the power otherwise required although required to make that power continuously (not unusual for generators). 25% to 40% battery power could also be emergency power. This would additionally make the location of the propellers more flexible.
 

cluttonfred

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I don't think that is likely to be a very significant effect with those small props and just 65 hp for a plane that's too heavy for LSA. AdrianS is absolutely right about the need to keep it simple.

with propwash probably significant contribution to spanwise lift distribution on both airfoils, I would think it COULD help.
 

rotax618

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It probably would be a good plan to build a model to test the effect of rotation/counter-rotation, you don't need a belt drive you could use two brushless motors. In any case the original was reported to fly OK so, as you say, it probably has little effect.
 

rotax618

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The angle of the longitudinal/transverse airflow on the underside of the wings would definitely be effected by inflow to the props so close to the trailing edge, how much it effects the lift one side more than the other is a moot point.
 

dog

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There are a lot of factors to harmonize with the twin pusher props,how far aft of the trailing edge,how is the airfoil treated in the zone effected by the prop,what angle of incidence
are the props set at,what are the considerations in choosing/designing a prop for this application and what can be done to mitigate the oft cited noise generated from the
prop operating in the wing wake?

Or is it prop shaft parallel to the wing cord on
a tapered wing,with the prop from a pusher canard of the same hp,as close to the wing as practicable.
The bi plane design alows flaps on the other wing,in a mono plane flaps are a big ask.
Useing a single larger prop centraly mounted ,
could work in a seaplane to get the c of g down,as pictured in a belt driven ,rotory power coot Welcome to Rotary Coot
best looking coot ever.
and with work a burried engine install could yield a performance advantagepossibly easier to do with a water cooled motor.
AND if you realy want contra rotating props there is the awsome gizmo that Heynrick(sorry spelling) and his buddys built.
 
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