Build your own HO229 WW2 German Jet Fighter!!

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Speedboat100

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12% past theoretically possible?

Somebody has screwed up somewhere, I somewhow doubt that it was Betz. His limit has been around a long time, and nobody has shown it to be wrong yet.

Ye cannae change the laws of physics, Jim!

Betz was right about propellers...please read the paper.
 
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Victor Bravo

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Red, I believe you might be in a good position to address some of the questions raised earlier in this thread, pertaining to whether Al's Prandtl twist is only valid for one Cl, or one fight condition? Knowing Al I would bet that he considered this during his research, but I think you're closer to being able to verify that factually than myself and most of the others here. I hope to see you in Tehachapi,

Bill / VB
 

Richard Schubert

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To piggyback on this question a little, maybe the problem should be attacked from the other direction. What kind of configuration and mission profile would result in the least amount of Cl change during flight?
 

Aerowerx

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To piggyback on this question a little, maybe the problem should be attacked from the other direction. What kind of configuration and mission profile would result in the least amount of Cl change during flight?
Do you mean Coefficient of lift (lower case letters) or Coefficient of Lift (upper case letters)????

Coefficient of lift (lower case) depends only on the AoA at each wing station, and the airfoil used.

Coefficient of Lift (upper case) depends on the gross weight of the aircraft and the wing area.
 

Richard Schubert

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To clarify, in the context of the discussion, if there is a large penalty for the off design condition, what kinds of configurations and missions could this be practically applied to.
 

Aerowerx

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To clarify, in the context of the discussion, if there is a large penalty for the off design condition, what kinds of configurations and missions could this be practically applied to.
Not sure I have a good answer for that, except for a touring/sight seeing/cross country mission you would be spending 90% of your time in cruise.

Also, in the book "Tailless Aircraft" they give the example of a sailplane. Low speed/high Cl when in thermals, and high speed/low Cl between thermals.

If any of you are REALLY interested in flying wings, buy, borrow, or steal a copy of Nickel's "Tailless Aircraft in Theory and Practice". It covers many of these topics. Although they treat elliptical as the ideal, IMHO the same arguments could be applied to the Prandtl-D bell shape.
 

pictsidhe

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To clarify, in the context of the discussion, if there is a large penalty for the off design condition, what kinds of configurations and missions could this be practically applied to.
Well, you either work out how to use a point design, or work out how to minimise the penalty.
For a long distance mile eater, flying really high keeps the Cl high and increases ground speed. The bad is that you need a engine that can put out enough power while breathing a partial vacuum. After that, the Armstrong limit gets in the way. A lot of additional weight is needed to safely get past that one...
 

Urquiola

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In Northrop bomber and reconnaisance flying wings, engine shaft nacelles of propeller versions had vertical fins effect.
Images exist of Northrop Flying wing dropping bombs successfully; as it were able to land in an airstrip, their flight was for sure precise enough as for a bombing or photography tasks; mr Northrop always denied his flying wing accidents being caused by structural failures.
The Horten brothers (do not confuse with US born: 'Horton', designer also of flying wings) were reported being basically glider designers, and even if Aerodynamics of their flying wings was advanced, structure was not, coming from the 20s.
A general drawing of Horten Ho-IX/ Gotha Go-229; Me-163 and other airplanes can be purchased at: 'Al Bentley Drawings'. Salut +
 

Aesquire

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My personal preference for rigid swept flying wings is vertical tip rudders. ( out only drag effect rudders ) As used in many Rutan designs.

Partly because it's easier to build than Northrop style clamshell drag rudders. And if designed as part of a winglet, offers reduced drag. Even the unsophisticated versions I've flown seem to be decent "end plate" tip vortex reducers.

The Easy Riser biplane uses weight shift for pitch & tip rudders for yaw. So a 2 axis craft. ( No ailerons ) I haven't calculated what shape the lift distribution is. Flies great, though.

The Pterodactyl ( and the Fledgling hang glider it's a modification of ) use weight shift or a canard ( unweighted, ideally ) for pitch, tip rudders for yaw. 2 axis.

Both are swept, twisted flying wings. ( The biplane also has stagger, & the lower, rear, wing is set at a lower AOA. ) Both were originally gliders and later ultralights with 10hp & up. ( one glider tug version I've seen uses a Rotax 503. Climbs like a homesick angel. )

OTOH, I've got hundreds of hours with swept flex wing gliders with no rudders at all. Some had variable geometry, changing the twist ( washout ) in flight for reduced drag at different speeds.

Could those flex wings slip to increase drag? Nope. But the fuselage/pilot can change his drag by changing body position. The pilot is the drag brake.

Hammerheads? Nope. Never tried a snap roll, either. ;)

Don't usually roll & yaw independently... Not on purpose, anyway.

Scimitar shaped flying wings are an elegant, bad, idea. :)
 

thjakits

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Hi all,

fascinating discussion! Most is way beyond my aerdynamics knowledge...

- I wonder why people frequently come back to "bird like" - birds have very little to do with stable flight. Their wings are constantly adjusted - as are their tails. If you look at detailled studies - especially of various predator birds - you find they are more like the equivalent of a B2 or F16 or similar - highly unstable (but efficient!) flyers.
And like the B2 or F16 they need a very sofisticated control system - that in the end, does not correspond with classic logic to flight control...
Fly-by-wire enables the pilot/controller to tell the computer what kind of response we would like/expect from our input (based on the usual classic inputs - elevator, ailerons, rudder, throttle - in a usually somewhat stable airplane) - but usually the computer then actuates a complete mix of controls - which we would be totally unable to "compute" and apply by ourselves.
Same as the birds - birds fly - they are hardwired to subconscious/automatic flight control and mix match input means at will (look up youtube on eagle or falcon wingtip feathers, observe complete cross-control between the rotating tail feathers and wing tip feathers - WHEN they have their wings locked in place - change AOA and AOI at will, subconsciously...).
So - I think comparing Flying Wings to birds as a means to understand a FW is seriously useless. Also comparing a B2 to the kind of aircraft discussed here is useless. Alright - a B2 IS a FW, by the obvious lack of a controls bearing tail, but the B2 was designed with way different priorities in mind than what is looked for here....

- Question to the masters: Horten/Prandtl BSLD is always taken from a sin function formula. 2.5 seems to be the do-it-all. Diverge from that and things get interesting fast. Did anyone ever try to merge different exponents for different parts of the wing?? Obviously the distribution would not be a "clean bell" anymore, but if it helps, who cares?
The overall design would still be slick looking!
Obviously not much of a genius stretch here, so I assume someone tried it long time ago and found it has no practical use.... does anyone know?

- Obviosly for the size aircraft we are discussing here (1,2,4, maybe 6-seater) a PURE Flying Wing is about impossible, at the very least - very impractical.
Systems space and pilot space and visibility kind of demand protrusions that would make the Wing into somewhat a BWB... - what about adjusting the crossections of the required protrusions to still conform with the desired BSLD - a bit like the ATLANTICA of years ago, but without the winglets. http://www.wingco.com/atlantica_bwb.htm

- I think I would be willing to compromise on the exact flawless FW to optimize for actual use.
It seems we are pretty clear that a FW is not the preferable machine to do extreme aerobatics, but rather a high-efficiency glider or a high-efficiency-high-speed long distance traveller.
So- obviously we want to design for max-efficency at the target environment (high speed high altitude for the latter).
Negative wingtip lift is not wanted there. So how about rotating the wing tip up above a given speed - at a designed point along the wingspan.....
Rotate up at let's say 100 kts and rotate back down at 90 kts - all automatically done - with manual over-ride...

Possibly I am just driveling here ..... - Horten like FW always held a great fascination for me and IF ever I could build a plane myself I always would look at the FW first. (Would it make any good racing machine?)

I get my frequent flying-fixes by making a living flying helicopters (....a totally different can of worms!) - so I keep the need to build a flying machine in check for now!

Cheers,

thjakits
 

Aerowerx

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- Question to the masters: Horten/Prandtl BSLD is always taken from a sin function formula. 2.5 seems to be the do-it-all. Diverge from that and things get interesting fast. Did anyone ever try to merge different exponents for different parts of the wing?? Obviously the distribution would not be a "clean bell" anymore, but if it helps, who cares?
The overall design would still be slick looking!
Obviously not much of a genius stretch here, so I assume someone tried it long time ago and found it has no practical use.... does anyone know?
Take a look at Al Bowers paper on his PRANDTL-D design. I also see that he has patented the design, which can be seen here. He ended up with something that is not quite a BLSD. His lift distribution is double-humped. There are two maxima located at about 1/3rd half span on each side, and the lift vector is tilted forward near the wing tips producing induced thrust (negative drag, if you prefer) which helps with yaw stability.

My viewpoint is to design for where you spend most of your time (cruise, for example), then live with the compromises on the other flight modes.
 

Aesquire

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My viewpoint is to design for where you spend most of your time (cruise, for example), then live with the compromises on the other flight modes.
Yep. Unless you design a wing you can change the washout on in flight, you're going to be optimized for a narrow range of flight. Just like every other aircraft.

A segmented flap system ( or flexible... Oh my aching head on flutter calculations ) can simulate wing twist, at a cost in drag. Which means in your computer model you can look at flap deflection then twist the wing to minimize deflection to optimize at that speed/density.

Keep in mind that a hang glider with variable geometry has to still be stable at both ends of the washout range. ( unstable craft like the F-16 not applicable in a homebuilt context, IMHO )

As to purity of flying wings... I'm a heretic. Hang a pod underneath, BWB ( HO229 ), or big fuselage tailless, ( Northrop SM-62 Snark ), it's all good. It's just not "pure". Where you draw the line between taillless & flying wings is a bit arguable, but we should design to requirements and desires, not purity.
 

Riggerrob

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....
A segmented flap system ( or flexible... Oh my aching head on flutter calculations ) can simulate wing twist, at a cost in drag. ...is.
Flexible trailing edges, ailerons and flaps are currently being wind-tunnel tested by NASA and the big factories. They say that their primary goal is to reduce noise during final approach.

Have you ever noticed the strong vortices growing from flap tips during humid days?

To minimize flutter, look at a suggestion made more than a decade ago for inflatable wings. Install a series of bent “carrots” along the rear spar. The “carrots” long axis is parallel to the wing chord and you could extend the “carrot” axle all the way to the front spar. Flaps
Or ailerons are deflected by pulling on control cables wrapped around the “carrots.” Turning “carrots” changes the direction of the bend, ergo changing curvature of top and bottom skins. You can install as many “carrots” as you want ... until you run out of “carrots” or run out of weight!
These days you could simplify control runs by making them electrical so you only have to worry about distance from the rear spar to the “carrots.”
 

Urquiola

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I did a virtual test of one once, in XFLR5.

Absolutely no yaw stability, since the wing looks the same to the relative wind regardless of the yaw angle.
Nice! You tested which one? Again, a design I like a lot is the facetmobile derivative PAV, for 4 passengers, if winglets and a single vertical fin will improve it, I don't know.. Thanks. salut +
 
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