Flying wing for high efficiency

[Norman]

which is better, partial span drooped leading edge or automatic slats?

Moving parts can jamb

 

[Hugh Lorimer]

This thread is too too deep theoretically for me. But as I have actually designed and built a flying wing a/c, I have a great interest In this layout. I have considered some of the points discussed when I was designing it.

 

[captarmour]

the designers of the superstol actually highlighted that they pop out as needed, some times just one of the 4 pops out and they seem to like that. i thought the opposite would be true. i guess lets say the right wing experiences a gust and starts to stall the slat(s) opens and restores lift preventing a wing drop. as soon as the flow is restored it retracts so it can probably act as a wing leveler more so than if both wings slats popped out.
their system is so simple it would be hard for them to jam, as far as i can see.
re laminar flow maybe wing twist would work better. does not the twist work with the increased vertical flow of a swept wing to tilt the lift vector forward?

 

[captarmour]

very nice!

with a rear mounted engine and such a short forebody how easy was it to balance?

 

[captarmour]

View attachment 24205View attachment 24206This thread is too too deep theoretically for me. But as I have actually designed and built a flying wing a/c, I have a great interest In this layout. I have considered some of the points discussed when I was designing it.

sorry fat finger, pressed the wrong reply!

very nice!

with a rear mounted engine and such a short forebody how easy was it to balance?

 

[John Newton]

Moving parts can jamb

True, was thinking more along the lines of which yields higher cruise drag, drooped le or automatic slat?

 

[John Newton]

the designers of the superstol actually highlighted that they pop out as needed, some times just one of the 4 pops out and they seem to like that. i thought the opposite would be true. i guess lets say the right wing experiences a gust and starts to stall the slat(s) opens and restores lift preventing a wing drop. as soon as the flow is restored it retracts so it can probably act as a wing leveler more so than if both wings slats popped out.
their system is so simple it would be hard for them to jam, as far as i can see.
re laminar flow maybe wing twist would work better. does not the twist work with the increased vertical flow of a swept wing to tilt the lift vector forward?

Twst alone is not very effective at preventing tip stall unless you use a very large amount (greater than that required for trim on a moderately swept flying wing) it may tilt the lift vector froward giving induced thrust and reducing adverse yaw, this is the Horten aproach, they used very large twist so although they had a strong taper the plane would not tip stall, the downside of course is a large static margin and higher induced drag, not to say that their designs are "wrong" just a different approach. The hortens did try a laminar flow wing but unfortunately chose an unsuitable airfoil (mustang wing I believe?) and it gave very poor stall performance.

 

[Hugh Lorimer]

The first consideration re balance was to establish aero centre of layout and then applied simple moments to balance an 86kg pilot with the engine weight to establish AC- engine distance. Finer balance by lead weights in nose to compensate for pilot weight variations. Hughie,,,,,,,,,,,

 

[captarmour]

The first consideration re balance was to establish aero centre of layout and then applied simple moments to balance an 86kg pilot with the engine weight to establish AC- engine distance. Finer balance by lead weights in nose to compensate for pilot weight variations. Hughie,,,,,,,,,,,

gr8, just looks a bit short, but on second look the square extended center wing will lift a lot of the engine weight.

 

[captarmour]

another look at the slats

The Highlander (Super STOL) Smackdown :: Ohio Bush Planes - YouTube

 

[karoliina.t.salminen]

I believe that the tip stall must be solved without any moving parts (except drag rudders could be used for stall recovery).

Actually the X8 stalls quite straight and quite ok if stalled carefully and not too high aoa. At high angle of attack it becomes a like falling leaf, the winglet gets blanketed so that it virtually has no winglet at all, and it autorotates to the ground spinning furiously. I don't know if drag rudders could be used to straighten it. Or maybe there should be additional verticals nearer to the center of the wing to mitigate the winglet blanketing. It is very easy to get to such aoa with very good power to weight ratio, these problems generally occur when the nose points straight up and airspeed becomes zero, so the nose straight up situation needs to be made recoverable (and not preventing nose going straight up eg by limiting controls or the like, because it will go straight up). Software stabilization seems to even further aggravate the situation because it deflects elevons to counter wing drop at stall if wing drops. Stall recovery may need to be programmed on it too, not only stabilization.

So I am predicting that geometric twist of at least 5 degrees will be needeed as a baseline. I think Horten used even more than that. Excessive twist reduces efficiency obviously on a craft that cruises at low angle of attack because the tips may therefore be on negative angle of attack on cruise flight and will produce downforce, in other words, negative lift. And induced drag increases as there will be drag due to lift for keeping the craft in air, drag due to lift for countering the negative lift on tips, and then drag due to negative lift on tips, it could translate into poor efficiency in the worst case, and this is where my question about high efficiency flying wing got started originally. Of course in conventional layout, there is the tail, that does the same than the tips on flying wing, so that layout also has similar losses.

 

[henryk]

I believe that the tip stall must be solved without any moving parts (except drag rudders could be used for stall recovery).


and this is where my question about high efficiency flying wing got started originally.

.

-do you know tailless KASPERwing philosophy=technology?

\no problems with stall,practically no twist!\

 

[John Newton]

I believe that the tip stall must be solved without any moving parts (except drag rudders could be used for stall recovery).

Actually the X8 stalls quite straight and quite ok if stalled carefully and not too high aoa. At high angle of attack it becomes a like falling leaf, the winglet gets blanketed so that it virtually has no winglet at all, and it autorotates to the ground spinning furiously. I don't know if drag rudders could be used to straighten it. Or maybe there should be additional verticals nearer to the center of the wing to mitigate the winglet blanketing. It is very easy to get to such aoa with very good power to weight ratio, these problems generally occur when the nose points straight up and airspeed becomes zero, so the nose straight up situation needs to be made recoverable (and not preventing nose going straight up eg by limiting controls or the like, because it will go straight up). Software stabilization seems to even further aggravate the situation because it deflects elevons to counter wing drop at stall if wing drops. Stall recovery may need to be programmed on it too, not only stabilization.

So I am predicting that geometric twist of at least 5 degrees will be needeed as a baseline. I think Horten used even more than that. Excessive twist reduces efficiency obviously on a craft that cruises at low angle of attack because the tips may therefore be on negative angle of attack on cruise flight and will produce downforce, in other words, negative lift. And induced drag increases as there will be drag due to lift for keeping the craft in air, drag due to lift for countering the negative lift on tips, and then drag due to negative lift on tips, it could translate into poor efficiency in the worst case, and this is where my question about high efficiency flying wing got started originally. Of course in conventional layout, there is the tail, that does the same than the tips on flying wing, so that layout also has similar losses.

Just got back off my holls, so here goes...

I think using a partial span drooped leading edge will prevent tip stall/ spinning problems on the X8 with very little increase in drag during cruising flight. The problem with using twist alone to cure tip stall is that the twist required increases with sweepback angle whereas the twist needed to trim for level flight for a given static margin actually decreases. Therefore for a highly swept, strongly tapered wing you end up with a large static margin as per horten designs, I suspect large twist may yield a desing that is a "one speed" model i.e. it is only stable and relaively efficient at one speed?

Using partial span drooped leading edges enables you to reduce the twist required to only that needed for trimmed level flight at the design Cl. I hope the above makes some sense!

On my design with a sweepback of 20 degrees and a constant chord and partial span drooped leading edge I'm looking at a geometric twist of only 2 degrees

 

[pictsidhe]

I think an early question before this thread got derailed was about economy.
Mpg is dependant on the BSFC, the propulsive efficiency, and the aircraft drag. If you drag 1000N 1km, it's 1MJ, whatever speed you do it at.
Drag depends on L/D and weight. A sailplane L/D is no good if the useful load % of gross weight is small. The facetmobile is a good illustration of how a light plane of mediocre L/D can compete economy wise with 'higher performance' aircraft.
If you haven't read 'the simple science of flight you should it's now online: https://www.google.com/url?sa=t&source=web&rct=j&url=https://mitpress.mit.edu/sites/default/files/titles/content/9780262513135_sch_0001.pdf&ved=0ahUKEwjfhMOSldTPAhVn1oMKHYbNDCMQFggbMAA&usg=AFQjCNGdJRy0_d_LdpOqjtCpkaprl7n44A&sig2=6sxMAYFz8I65CgkYFCVELg

 

[WonderousMountain]

Very good points to remember, very few planes are light, stingy on fuel and smooth. Problem is probably people and their pesky desires.

 

[Jay Kempf]

Wow, just read back through this thread. Has some of TS100's classics. Great laugh this AM. Thanks for digging it back up.

 

[pictsidhe]

I've had topspeed on ignore for a long time...

 

[clanon]

"Ohhh ...those flying men on their pedaling machines..."