New design for a long range aircraft

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watt

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I finished this concept for a long range 4 seater, and I would like to push the design further, and even, maybe, one day build it.
I know a bit about aircraft design, but I am not an engineer and not very good yet with computers as a design tool. I would greatly appreciate comments, help and suggestions.
I have a million questions ready to fire, so here are the first three:

My wing is flying at 3 million reynolds, do you think that it is leaving pure laminar flow regime, and does it makes sense to use a laminar flow wing?

I am planing to make this aircraft as silent as possible, any suggestions?

I would like to use the long AR wing for range and economy, Is there any drawback from it other than structural, (Stall, behavior, passenger comfort.)

Best regards everyone, great forums!
 

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SVSUSteve

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do you think that it is leaving pure laminar flow regime
In all practical application, there's no wing that maintains completely "pure" laminar flow.

I would also point out that for most small aircraft, the range should be limited by the capacity of the human bladder. Not to mention that even the most comfortable seat after three or four hours starts to become a prison.
 

Jan Carlsson

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I like the design, 12 h range at 55% 1425 NM

one q. how is head room in the circular fuselage?

Laminar or turbulent airfoil is also a question of building material.
 

cluttonfred

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Neat design, very reminiscent of the White Lightning WLAC-1 and I agree that the cabin arrangement looks very comfortable. I am not so sure that a retractable tailwheel is worth the complexity when you have fixed main gear. I also wonder if you might want to go with a 7' or so center section to allow the plane to keep it's feet wings removed for transport or storage. I also agree with Steve that unless you looking to make record long distance flights, anything more than 3-4 hours per leg or maybe 6-8 hours round trip to a remote area without fuel is really too much time in the air.
 

dcstrng

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Interesting; I don’t speak metric so I washed your numbers through my favorite propeller software (Jan’s) that allows input either way and your numbers appear well within the ballpark – a bit more optimistic than I could make work, but I don't know the software like the writer, but certainly close enough… looks like an acceptable climb rate at full gross (something around 900fpm – 5.1m/s). Didn’t show quite the range, but I think the software is conservative, because it usually comes in a tad lower than some of my alternatives…

Assuming the 55% cruise comes in close to your 220kph, you may be able to sell more than you can build…

All in all I like it… fixed gear, wheels faired and outside the propeller steam… hmmmm… works for me… When I win the lottery... :)

I agree -- I immediatly thought "White Lightening"
 

Jan Carlsson

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Interesting; I don’t speak metric so I washed your numbers through my favorite propeller software (Jan’s) that allows input either way and your numbers appear well within the ballpark – a bit more optimistic than I could make work, but I don't know the software like the writer, but certainly close enough… looks like an acceptable climb rate at full gross (something around 900fpm – 5.1m/s). Didn’t show quite the range, but I think the software is conservative, because it usually comes in a tad lower than some of my alternatives…

Assuming the 55% cruise comes in close to your 220kph, you may be able to sell more than you can build…

All in all I like it… fixed gear, wheels faired and outside the propeller steam… hmmmm… works for me… When I win the lottery... :)

I agree -- I immediatly thought "White Lightening"
Larry, lately I adjusted the drag on sleek airplanes, with less cooling drag and antennas and ...
 

dcstrng

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lately I adjusted the drag on sleek airplanes, with less cooling drag...
I'd be happy if I can build to approach the performance of the version I have :ponder:-- the "sleek" is maybe like for the Mike Arnolds in the world, which I can only admire...
 

watt

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Thank you everyone for the comments and answers, I'll try to explain a bit better what I am trying to do here, First the Specifications calling for a true transatlantic aircraft: I did it for the mythical idea of Atlantic crossing but also because a real travel aircraft must be able to do at least a Gander- Azores with reserves. Might never do it but it must be able to. Second because this long range specification brings out certain qualities out of an aircraft: robustness, economy, comfort and simplicity. And these are important to me.

I have been working on it for 6 months and the design changed a lot: I got rid of a lot of complications (retract, tricycle gear, Constant speed, large engine) I am trying to use any trick in the book to improve aerodynamics, and slowly the design emerged as it is now: First I wanted a very quiet aircraft, (If we all get tired after 2-3 hours of flight it is because of noise!) so a long swiss muffler is installed in a tunnel in the center of the fuselage (Thank you Tony Bingelis for the idea), that tunnel is insulated and extends the firewall all the way to the trailing edge of the wing where cooling and exhaust exit. That tunnel is taking some space and pushes the wing up to its median position, it also makes the installation of a front gear problematic, so off with the front wheel too. I wanted a wide spar to go thru the fuselage, so it forced the back to back seating. Yes it looks a bit like a white lightning, but it is all in the nose and windshield (a hard area to be creative). personally, I think it looks more like a modern 1935 Caudron Simoun.
I started to play with range and fuel requirements and it was clear that a "thin" aircraft uses very little power in cruise: here I plan on 78kg of thrust for a 220 km/h IAS or 270 km/h TAS at 4000 meters. So a reasonable engine was chosen o-320 at 160hp.
I am planing a full scale mock-up of the fuselage to see about comfort, and what space I have to work with. The fuselage is completely circular and very wide (130 cm).
For the wing I am contemplating the use of a semi laminar airfoil The Hawker Tempest semispan (14.5%) at the root and Eppler 231 (12.5%) at mid wing, Both have very low drag from Cl 0.3 to 0.6 with low moment. (If anyone can help me run them in X-foil at R 3 million I would be very happy because I can't seem to be able to do it.)

As for performances, they are calculated for a zero lift friction of 0,0053, the white lightning reached 0,0032 (probably the record) P-51 is 0,004 and a C-172 is about 0.009
 

Birdman100

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View attachment e231-polar.txt
(If anyone can help me run them in X-foil at R 3 million I would be very happy because I can't seem to be able to do it.)
I did it, see the attached file (.dat), this is polar in numbers for E231 at 3M Re. Send me coordinates for "Hawker Tempest" airfoil.The reason you are unable to run analisys in XFoil for e231 is probably that you used UIUC database coordinates, and they are inaccurate sometimes (like in this case, in the nose region, which is very sharp, BTW) so you have to refine the airfoil and use more points (160). Sometimes you need to make another airfoil with the same contour using spline just to smooth some critical areas.It would be much better to do airfoil analysis for Re*SQRT(CL)=const instead of Re=const, as it fits to constant mass case which is what we mainly have. For that, 1. wing loading, 2. flying height, and 3. chord (MAC) is needed.
 

Birdman100

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Hi Watt (james? hehe),

i will attach polar, lift and moment diagrams, and polar "table" for your (tempest) foil.

the given coordinates were in wrong form so I had to modify order to fit Xfoils way of reading them...

For a given WL, chord and height (standard atmosphere) we have Re*SQRT(CL)=1.88*E6. That stands for your aircraft at that height.

Take any numerical results with reserves! I would add 10% more drag to digital polar just to be safe and to count in manufacturing imperfections, bugs, dirt at the airfoil surface, aileron/flap gaps etc.. Lift curve is ovestimated as this airfoil cant be effective above 15 degs; XFoil is known that it gives higher lift gradients and maximum CL compared to experimental data.View attachment tempest-polar-1.txt

Appart from the xfoil results; Tempest airfoil is nearly symmetrical one (c=1%!), you would be better with more curvy airfoils, c=3-4%. You could use less wing area (if fix span, you will have more AR), so less friction (profile) drag. Sailplane foils are your friend here.

tempest-foil-1.jpglift curve-1.jpgpolar-1.jpgmoment-1.jpg
 

TFF

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Looks good. I think you will need to reconsider the constant speed prop. Long takeoff runs, bad climb, and not being able to taylor engine loads for different conditions, will really hurt your clean design.
 

Jan Carlsson

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Instead of the H 37.5-14 the more modern Ribblet GA 37 will be a good candidate
Have to look at Cl at climb and cruise, high speed situation not so important in a long range wing.
 

bmcj

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Nice design, looks realistic.

The only thing I'd have a good look at is the circular fuselage XC. Works great for a single or tandem, but side-by-side it costs a lot of head room. Maybe try a superellipse:
Superellipse - Wikipedia, the free encyclopedia

Same aerodynamic qualities as a round XC, but with lots more head room.
But how does the superellpse compare structurally?
 

bmcj

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Looks good. I think you will need to reconsider the constant speed prop. Long takeoff runs, bad climb, and not being able to taylor engine loads for different conditions, will really hurt your clean design.
Or an Aeromatic prop.
 

watt

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Thank you bird for the tests, 1.8million R would be for the stall speed, in cruise we are looking at 3M. But that's not the point, I have been contemplating those "old" Tempest airfoils for a while and I am amazed at their good performances at Cl 0.2 to 0.6, they are actually better than the Naca laminar serie and even the NLF and with lower moments. Am I missing something, why are they not used any more? any other suggestions for airfoils?
I am looking for low camber low drag at low alpha types, to try to push the best L/D speed as high as possible. With the Tempest and at 87kg/m2 I expect a L/D of 22 at 176 km/h and 15 at 220 km/h
If I get really serious about this aircraft I will have to test the airfoil in a wind tunnel.
the fuselage will probably get a tad more square at the cabin but I am waiting to see how the mock-up will feel and adjust accordingly.
 
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