Nenadović biplane

[Vigilant1]

I wonder if putting the props on airfoil-shaped masts projecting left and right from the fuselage above the rear wing might be more effective? You could have a removable, self-contained unit of engine, mount, and a T-shaped structure with the props on the ends of the T. The wing installation would then be much simpler and folding or removable wings could be an option. Better yet, put one large prop on a single vertical mast and give it a T-tail in the propeller stream rigged to counteract the nose-down tendency with power like many amphibians.

In 20-30 years, if batteries are cheap and light, this would be the type of application where electric power might shine. Put three 10kw electric motors pusher style in each top wing, each turning a 36" prop. For storage or transport on a trailer, leave the wings alone and hinge the empennage to one side or up-and-over. Pull three pins to allow all the wheels to castor so it can be pushed wherever it needs to go. Very low disk loading allows for good prop efficiency, and failure of one engine doesn't create crazy amounts of asymmetric thrust.

 

[Sockmonkey]

Is this another one of those things where it's good but doesn't get used much because people don't know about it, or does it have some significant downside?

 

[cluttonfred]

I don't think it will be that long until something like this is viable with electric power, perhaps much sooner if you go with a series hybrid option. Design a plane to cruise efficiently at 50% max power, keeping the rest in reserve for takeoff and climb only. Now size an internal combustion-driven generator to provide, say 75% max power, and give it a battery capacity of 50% max power for 15 minutes. So now you have a plane that can takeoff and climb at 100% power for 15 minutes and cruise at 50% power for as long as you have fuel while also recharging the battery reserve in 30 minutes. As battery technology improves you could drop the generator capacity and increase the battery capacity.

In 20-30 years, if batteries are cheap and light, this would be the type of application where electric power might shine. Put three 10kw electric motors pusher style in each top wing, each turning a 36" prop. For storage or transport on a trailer, leave the wings alone and hinge the empennage to one side or up-and-over. Pull three pins to allow all the wheels to castor so it can be pushed wherever it needs to go. Very low disk loading allows for good prop efficiency, and failure of one engine doesn't create crazy amounts of asymmetric thrust.

If you mean the Nenadović biplane wing, I honestly don't know. It could be something that just didn't get traction because it was discovered at a time that biplanes were being supplanted by monoplanes anyway. I do think it's worth investigation for light planes if only because it should provide a lighter wing structure in a category where weight is paramount.

Is this another one of those things where it's good but doesn't get used much because people don't know about it, or does it have some significant downside?

 

[Vigilant1]

Cheap, simple route: Mount a 30HP B&S engine on each side in pusher mode. But, all bets are off in case of an engine failure.

If the MTOW was kept low (single place, modern construction), if a lot of rudder was available, and if the claimed Nenadovich benefits of low drag and better lift are accurate, maybe safe single engine climb could be possible despite the asymmetric thrust and the dead-prop drag on the other wing. But, if single engine minimum controllable airspeed is above the aircraft's stall speed, we know there's a very good chance that, in the real world, bad things will happen.

It seems to me it would be a pain in the neck to work on a pusher engine mounted in that front wing. Due to the location of the rear wing, you'd probably need to build a scaffold/platform to do any engine maintenance.

 

[cluttonfred]

In addition to the single-engine handling issues you mentioned, you’ve now left the realm of LSA or microlight because of the two engines and you will likely need a multiengine rating always or at least to carry a passenger depending on the country and category. One engine driving two props is far more appealing in my book.

Cheap, simple route: Mount a 30HP B&S engine on each side in pusher mode.

 

[Sockmonkey]

If you mean the Nenadović biplane wing, I honestly don't know. It could be something that just didn't get traction because it was discovered at a time that biplanes were being supplanted by monoplanes anyway. I do think it's worth investigation for light planes if only because it should provide a lighter wing structure in a category where weight is paramount.

Yeah, that was my thinking as well. You're getting the compactness and strength of a low-aspect wing apparently without the induced drag penalty.

 

[karmarepair]

There is a lot I don't like about the configuration of the AS.37. Maintenance access has already been mentioned. It looks like the weight fraction for propulsion would be off the charts of Raymer or Roskam - all those pulleys, bearings and shafts add up. But it's the crashworthiness, or lack thereof, that really bothers me. The Citroen engine wants to smash the occupants to a pulp in any sort of sudden stop. And there is no crush zone in front of the passengers.

The earlier tractor configurations look much more sensible to my eye. Although visibility looks dreadful. Perhaps that's the problem the AS.37 configuration set out to solve?

I had thought that Negative Stagger was aerodynamically superior, due to the Beech Staggerwing, and an all aluminum (bonded!) negative stagger sport biplane of the early 1970's I read about in "Air Progress" when I was a kid (Looks like "Sorceress" is the plane I was thinking of). "Superior" I guess depends on what characteristics you're optimizing, and it looks like both these examples were after something other than impressive Polars.

 

[cluttonfred]

Yes, I can see those criticisms, and I don't want to get sidetracked by pros and cons of the AS.37 and I'm already guilty of that. ;-)

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) especially in the very light categories (Part 103/SSDR/microlight/LSA) in which the weight savings could pay dividends.

I don't have the math skills, and I don't think we yet have enough clear data in any case, but it would be interesting to run the numbers on something like a Sonex to see what switching out the existing monoplane wing for a setup like the AS.27 would get you.

 

[Martin R.]

In 20-30 years, if batteries are cheap and light, this would be the type of application where electric power might shine.

I don't think it will be that long until something like this is viable with electric power, perhaps much sooner if you go with a series hybrid option.

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[blane.c]

I am curious about the propellers between the wings wouldn't that just mix the airflow trying to be achieved? It seems either tractor or pusher would be more advantageous? It is assumed the tractor engine configuration are later models?

 

[Sockmonkey]

When commenting on the plane, for clarity's sake one should specify if it's about the wing or the prop configuration because those are two separate things that may or may not be applicable to specific applications.

 

[cluttonfred]

***THREAD SPLIT***

I have created a new thread, Starck AS.37 - one engine, two propellers, so we can keep the conversations about the pros and cons of the engine and propeller installation separate from the aerodynamics of the biplane wing.

 

[karmarepair]

Just some spitball numbers, using the proposed Sonex comparison, and the top-line percentage numbers from the original paper. Using the SONEX B-Model book numbers:

	stall	Cruise at sea level
As-is	40	130
Biplane	35?	170?

IF those aerodynamic results can be achieved, it strikes me that finding a prop to suit that speed range will be very challenging. Saber shaped blades? In flight variable pitch?

 

[Vigilant1]

Just some spitball numbers, using the proposed Sonex comparison, and the top-line percentage numbers from the original paper. Using the SONEX B-Model book numbers:

	stall	Cruise at sea level
As-is	40	130
Biplane	35?	170?

IF those aerodynamic results can be achieved, it strikes me that finding a prop to suit that speed range will be very challenging. Saber shaped blades? In flight variable pitch?

In the transmogrification to the biplane, what are we keeping constant? Stall speed, wing area, HP, useful load at some specified ROC, something else?

If the wing area is kept constant, it would seem unlikely that cruise would be faster than the Sonex monoplane because:
1)The claimed advantage for the slotted wing biplane (lower drag for a stated amount of lift) is least significant at high speed (since induced drag is a very small portion of total drag at high speed).
2) The intersection drag of those connecting endplates will be substantial (again, with little to show for it at speeds where induced drag is low)
3) Likewise for two additional wing/fuselage intersections.
4) If the slot speeds up airflow over the lower wing, then skin friction drag over that surface will be higher.

 

[karmarepair]

In the transmogrification to the biplane, what are we keeping constant? Stall speed, wing area, HP, useful load at some specified ROC, something else?

In this VERY crude example, I was keeping the HP and the weight the same. Since the Cl max was advertised as being better, I used some of that improvement to lower the stall speed, and then applied the Advertised improvement in speed range.

Your points about induced and interference drag are well taken. I think the assumption is that the wing area is going to drop,

 

[cluttonfred]

Thanks, I appreciate the practical example. I am not sure that the speed range improvement is a 1:1 correlation since the article states that the relationship Cz max/Cx min correlates to the speed range of the wing, which I believe is maximum load (so gross weight the wing must support) divided by minimum drag. That's just going to cover the induced drag from the wing, not any of the rest of the drag from the fuselage, gear, tail, etc. As I said before, I don't have the math skills at this point (35+ years since I've done much more than basic arithmetic and geometry) to do this quantitatively. My gut tells me that a reduction in induced drag all other things being equal will improve speed slightly and climb a little more.

One thing we haven't discussed is the behavior of the Nenadović biplane at high angles of attack. It appears to me that the Nenadovic biplane continues flying at angles of attack beyond the monoplane's stall, which could be useful in providing low-speed safety and perhaps eliminate the need for landing flaps, which would partially make up for the complication of building two wings not one.

 

[karmarepair]

This configuration MAY be useful for the single seat aluminum tube and gusset two cylinder industrial engine flivver we've been kicking around forever. Low induced drag in a relatively short span sounds like a good recipe for decent climb performance with relatively low HP.

I'm still puzzling what the configuration would make sense. Maybe a single seat, open cockpit version of the AS.37 planform? A biplane Kolb Ultrastar? The leading edges of the lower, rear wings would be about at your elbows? See attached doodle.

 

[cluttonfred]

That’s a neat concept but I wonder if any benefit of the Nenadović wing would be lost in all that parasitic drag. What about a small slick single-seater with an industrial V-twin? Think Colombian Luciole, Špaček SD-1, PIK-26 Mini-Sytky, etc.

 

[Vigilant1]

What about a small slick single-seater with an industrial V-twin? Think Colombian Luciole, Špaček SD-1, PIK-26 Mini-Sytky, etc.

Aerodynamically, I think the claimed attributes of the Nenadović wing would be a good fit for a little plane of that type. Two challenges:
1) In real world use, a lot of the owners of these planes really do remove the wings after each flight for trailering or storage. Some way to make the a plane with Nenadović wings similarly compact for storage would be a big plus.
2) If there are plans to use an especially high AoA capability provided by this wing for steep approaches (or climbs), the limited power of a small industrial engine is going to be a limiting factor. Regardless of any magic the configuration may offer in reducing induced drag, just the parasite drag of wings at 15 deg AoA is going to present a high drag bill that will become important in a go-around, etc.

 

[karmarepair]

That’s a neat concept but I wonder if any benefit of the Nenadović wing would be lost in all that parasitic drag. What about a small slick single-seater with an industrial V-twin? Think Colombian Luciole, Špaček SD-1, PIK-26 Mini-Sytky, etc.

You'd end up with a smaller AS.27, and that upper wing blocks out ANY view of the ground unless you're inverted. I'd have to be convinced that was a good idea. Thus, my thinking about a configuration I really don't like, pilot forward pusher, I.E. Ultrastar.

But maybe we can convince BoKu to try a biplane CarbonMax....