Characteristics of a straight-wing, tailless model in the Langley free-flight tunnel

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nickec

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Determination of the stability and control characteristics of a straight-wing, tailless fighter-airplane model in the Langley free-flight tunnel

Inspired by the above document, I plan to use this thread to describe a very light, very small, all metal aircraft.

The design will attempt to emulate the Davis DA-11 in size and performance - while being very slightly less heavy.

I will use a spreadsheet to check weight and balance.

My initial assumption is that since the DA-11 "worked" a flying wing derivation can "work". The NACA study seems to support this conjecture.
 
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nickec

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

Three view of the NACA model.

Scaling the three view shown in the link above for a MAC of 30 inches and a wing span of 154 inches results in a surprising result: 65 inch long cockpit approximately 22 inches wide.

I believe a slightly wider cockpit, and thus slightly wider fuselage, would not negatively affect the spin tunnel testing results outlined in the NACA report above.
 

nickec

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

Preliminary spreadsheet weight and balance indicates that assuming a 40 pound engine and a 160 pound pilot will result in an appropriate Center of Gravity and will also respect the scale of the NACA model. This is ideal because the DA-11 used a heavier engine which means the proposed design can serve heavier pilots by using an engine like the DA-11 used.

I used a lighter engine weight to investigate if an oversize paraplane engine might "work" - inspired by a video. And another video. This lighter engine weighs 2/3rds what the engine Leeon Davis used in the DA-11. However, it is very speculative that this smaller engine will suffice. It depends on how much HP the DA-11 used on take-off.

It might work though vibration might be unacceptable. Without a redrive, which I am avoiding in my analysis, the smaller engine is marginal at best.

I am using DeltaCAD to quickly scale overlaid drawings atop screenshots of the NACA report.

Repurposing commodity engines will only appeal to a minority of forum members, though many likely scoffed at Leeon Davis when he embarked on creating "Mower Power for the People" with the Briggs v-twin. Experimenting with Harbor Freight engines is a fringe effort in the same direction. The engine mentioned costs about $100, before modification.
 
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nickec

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

Interesting stuff, see my attempt at a straight wing flying wing, much less high tech, Hughie.

Thanks Hugh.

You may find THIS interesting also. When the link opens you click the button "Open in 3D viewer" to view a fairly accurate model of Scott Winston's Facet Opal.

Imagine that the Opal and the DA-11 married and had a child. The child was metal and DA-11 size with the planform of the Opal. That is what I will later more thoroughly describe and analyze.

Your design is very similar in planform to the Facet Opal. Did they allow you to fly it? I remember the authorities restricting your efforts.
 
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danmoser

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

Repurposing commodity engines will only appeal to a minority of forum members, though many likely scoffed at Leeon Davis when he embarked on creating "Mower Power for the People" with the Briggs v-twin. Experimenting with Harbor Freight engines is a fringe effort in the same direction. The engine mentioned costs about $100, before modification.

Nickec,
I'm doing something very similar .. the HFT Predator 212cc engine will power my Bright Star SWIFT ultralight glider.
I've got the Ecotrons EFI system to be installed on it, along with shaving down the heads & removing the governor .. planning to direct drive to small prop @ ~5000 RPM max ..
This should put out a max. power of ~14 hp .. perhaps a bit more.
One guy has done similar mods on his paramotor setup.. an American fella named Dan Bachelor .. you can see a bit on his work posted on the "Eggmotor" Yahoogroup.

Anyway, I think you are on the right track to make a screamin' flying plank design.
I imagine Scotty Winton would be very pleased by your efforts!
Mower power to the people! ;)
 

nickec

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

Thanks Dan.

Here is the spar cross section at root.

Spar cross section at root.jpg

6061T6 caps cut down from 1.25"x1.25"x0.125" angles.

All dimensions in inches. No interstitials shown.

Inspired by the Colomban MC15 Cri Cri spar.
 

cluttonfred

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

Neat stuff, I had not seen such a Fauvel-like "plank" flying wing before from that period in the USA.

A straight leading edge and tapered trailing edge would give you more leverage for your elevators, though that would also exacerbate the problem of a relatively low maximum coefficient of lift because the raised elevators are lowering the effective angle of attack of the center section at low speed.

While not quite as sexy, a straight constant-chord plank wing with outboard elevons might better suit a lightplane along the lines of the Davis DA-11--it would be easier to build and likely have better low-speed performance and stall behavior. I am sure you already know that, but it might worth be taking another look at the work of Fauvel, Backstrom, Marske, etc.

Good luck with your project.

Cheers,

Matthew
 

autoreply

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

Repurposing commodity engines will only appeal to a minority of forum members, though many likely scoffed at Leeon Davis when he embarked on creating "Mower Power for the People" with the Briggs v-twin. Experimenting with Harbor Freight engines is a fringe effort in the same direction. The engine mentioned costs about $100, before modification.
Please baseline for a much heavier engine. Many that have gone before you, eventually had to move to a much heavier engine and could shelve/rebuild their design. If you baseline for 90 lbs (engine mount, running engine, prop, battery) there's a huge list of proven engines (half VW, Parazoom, the Luciole and Spacek offerings) to choose from. Adding lead is cheap and you might yourself gain a few pounds in the future too ;)
 

nickec

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

Please baseline for a much heavier engine... ;)

My previous post regarding the engine was misleading.

I have already baselined for an engine heavier than the exact installation used by Leeon Davis.

The lighter engine can be positioned further back - thus respecting the moments used in the NACA model.

An even heavier engine, like those you mention require short prop extensions to respect the scaling of the NACA model.

My goal is to scale the NACA model, since they thoroughly tested the flight characteristics.
 

nickec

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

DA-11 vs. FWDA-11.jpg

Just to give an idea of scale the above picture compares the original DA-11 to a chopped up DA-11.

Note shorter landing gear, shorter fuselage nose, cockpit moved forward relative to wing, and wing enters fuselage higher (compared to DA-11).

Vertical surfaces not shown. Pusher prop not shown.

Scale of both aircraft is identical.
 

cluttonfred

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

It would be very interesting to see the NACA design modeled as a full-size aircraft in X-Plane to see what sort of handling that might display.
 

nickec

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

It would be interesting Matthew.

There are two things x-plane cannot provide:

control stick feedback
seat of the pants feel


In flight a pilot must move the stick. The stick pushes back - differently in different aircraft. You cannot feel this when "piloting" in x-plane.

Nor do you feel pressure on your body in x-plane. So the flight experience is much different than real flight in an actual aircraft.

When aircraft designs are investigated using Radio Control models stick feedback and "seat of the pants" are also invisible.

For these reasons, and others, x-plane and RC models do not suffice to assess an aircraft design. The only way to really test: full size with a pilot aboard - very carefully.

Sometimes designs become deadends because the "feel" was judged unacceptable.

It still would be fun to fly an x-plane model of the aircraft described in the NACA report. You could scale it to the size they had in mind - which was quite large (40 foot span, over 8000 pounds, and 30 pounds per square foot wingloading). Or you could scale it to the size of a DA-11. Or any size in between. ;)
 
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cluttonfred

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

Everything you said is quite true, nickec, but simulations like X-Plane and RC model tests can be useful in validating basic stability and control before proceeding to a full-size aircraft. Both simulations and models can reveal major problems so that they can be avoided in the full-size design, or even demonstrate why a full-size design may not be worth the effort. Personally, I would not tackle a project like this with a little used configuration without first trying it out in a simulation and on a fairly large model of at least 1/4 scale, better yet 1/3 or 1/2. But, it's your project and your life. ;-)
 

nickec

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

Hey Matthew.

If I gave the impression that I would not use x-plane, or build models, it was not my intent. I have already built several models - not as large as the NACA model.

That NACA model is very close to 1/3rd scale of a DA-11 and they tested it in ways I cannot - lacking a wind tunnel and a spin tunnel.
 

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

My previous post regarding the engine was misleading.

I have already baselined for an engine heavier than the exact installation used by Leeon Davis.

The lighter engine can be positioned further back - thus respecting the moments used in the NACA model.

An even heavier engine, like those you mention require short prop extensions to respect the scaling of the NACA model.

My goal is to scale the NACA model, since they thoroughly tested the flight characteristics.

Good to hear.

Metal is a personal preference I presume?

I'd have a critical look upon your canopy shape. Pretty expensive to make one. Check whether you can use an existing one (motorglider, sailplane) and save a hell of a lot of trouble.
 

Aircar

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

Nickec - try captive testing on a car top 'windtunnel' ("If the mountain will not come to Mohammed then Mohammed must go to the mountain ") it is sometimes easier to move the model rather than the air .
 

nickec

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

Regarding canopy:

Leeon Davis, and many others, have made very economical "canopies" using inexpensive flat wrap materials. I lean toward this option.

DA-9: DA-9.jpg DA-11: mh8.jpg

The PIK-26 also achieves a low cost "canopy" with flat commodity material. This might work well if the design remains very boxy - with sharp fuselage edges.

PIK-26 Mini-Sytky: PIK%u002520-26%204a.jpg

Right now I am reviewing bulkhead positions and control mechanism interference.
 

nickec

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

Good to hear.

Metal is a personal preference I presume? ...

It is a bit quicker to use metal as a level of confidence generates from the success of the DA-11.

Knowing some of the weights of Leeon's machine allows some reasonable extrapolations:

He included 6 gallons of fuel which provided over 5 hours operation and possibly 6 hours. I will go with 3 to 3.5 gallons.

Since the DA-11 had an engine weight of 61 pounds we know the rest of the airplane weighed about 114 pounds. A first pass analysis of the wing, as designed by me, with near identical area and spar height, weighs about 45 pounds - for a three-piece wing with three equal area panels. Of course the central panel weighs more than a single outer panel. Such a wing cannot weigh as little as Leeon's, and be equally strong, unless made as a one-piece wing.

15 to 18 pounds are saved by reducing fuel capacity. If the 40 pound engine succeeds, which is very speculative, another 20 pounds is saved.

The gross weight of the DA-11 was reported by several sources to be 375 pounds. So a pusher mashup of the Winton Facet Opal and the Davis DA-11 with a lightweight pilot of 160 pounds might have a gross weight of perhaps 330 pounds or less. This is optimistic. If the mashup used the same engine Leeon would still result in a gross under 360 pounds worst case - assuming no weight saving despite a much smaller fuselage - and shorter moment arms on the engine and the fuselage.
 

autoreply

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Re: Characteristics of a straight-wing, tailless model in the Langley free-flight tu

15 to 18 pounds are saved by reducing fuel capacity. If the 40 pound engine succeeds, which is very speculative, another 20 pounds is saved.
Just lost a long post, so in short:
Reducing fuel capacity doesn't reduce structural weight. Plan for as much fuel as possible.

I'd be surprised if - even with a 90 lbs engine - a good design, either composite or alu would end up weighing over 300 lbs empty. 250 lbs or so seems reasonable (without instruments, upholstery and a BRS)
 
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