Raptor Composite Aircraft

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dave wolfe

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I cant get it straight in my head where the elevator is going to center aerodynamically. At low deflections I see the airflow thru the gap holding the elevator in a mostly nose down position. At full nose up deflections I see the elevator being held in the full nose up position due to the drag on the elev relative to the hinge position. Trying to imagine the flutter modes makes my head explode.
 

pictsidhe

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Peter's 'Frise elevator' may not be fully aerodynamically balanced. But it will lighten up a lot as the stick is pushed forward. This may not feel very nice to fly. After seeing the multiple attempts to make his ailerons not work, it's a safe bet that he does absolutely no calculations on control forces for the elevator. An aircraft with poor controls is rarely easy to fly well.
 

Venom

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I take it that the single channel, auto power reducing, ECU is no longer a problem....interesting how that was the primary reason for Len's not flying the airplane but now it is apparently not an issue. What say you Marc?
 

Marc Zeitlin

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I take it that the single channel, auto power reducing, ECU is no longer a problem....interesting how that was the primary reason for Len's not flying the airplane but now it is apparently not an issue. What say you Marc?
I'm not anything resembling an engine expert, so I don't think my opinion on this matter is worth a whole hell of a lot, but people are willing to do things in prototypes, to prove an idea, that they wouldn't do in a production unit. I would not consider going on cross-country jaunts without some indication either of redundancy or extreme reliability in the engine, but for test flights in the vicinity of an airport, the risk level is relatively low. And IMO, there are far higher risk items with regard to flying this aircraft than the single channel ECU. Each test pilot gets to choose their own level of risk acceptance when hard #'s aren't available from a System Safety Analysis / Fault Tree Analysis. For Len, that was one of many things he noted in his report, but hardly the only one, or even the main one.

Justin and I were on the same page with the 23 items I indicated needed to be remediated prior to flight - the single ECU was noted as a "this will eventually need attention, but won't stop a first flight" item. Peter is working his way, sometimes directly, sometimes less so, through the 23 items, some of which were easy to fix, some not so much. I will give him a lot of credit for substantially reducing (although I don't know if it's at an acceptable level, but it's clearly a lot less) the compliance in the roll system, as well as dealing with the pitch trim in a reasonable manner. Elevator counterbalancing is moving in a direction I'm not particularly pleased with, but his engineer, Mark B., seems insistent that it will work. We'll see if it's deemed acceptable by the test pilot.
 

pictsidhe

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I take it that the single channel, auto power reducing, ECU is no longer a problem....interesting how that was the primary reason for Len's not flying the airplane but now it is apparently not an issue. What say you Marc?
I wouldn't be worrying too much about the ECU as a potential thrust loss right now. The engine, however, is seeing temperatures and pressures way, way past design values and the redrive is downright scary.
 

BBerson

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Almost all airplanes have one fuel system. But they have dual ignition and carb heat, which he doesn't need.
 

pictsidhe

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Watched it. Solid steel pushrofds as he has NFC what needs beefing and how to do it! I don't like his elevator counterbalance one bit. IMHO, somebody should do a flutter analysis to OK that. I briefly wondered why he didn't ask someone to do a quiick calculation on what size trim strip he needs, but without knowing the forces in the system, that can't be done. I'm not impressed with the single offset clamp hole for the servo linkage. If he'd drilled a new centre hole in the bracket, then drilled the spring to suit, it would have been much better.
 

BoKu

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Is the really? What about elevator it self? I think it's deflection UP to small and why he made it slotted like a flap? Isn't canard should stall first? But this setup possibly will make canard "flying" at slower speed then main wing.
Yes, those are curious aspects of this airplane. Peter appears not to have a solid grasp of the Cl relationships that protect a canard from deep stall.
 

Doggzilla

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That limited elevator deflection angle is extremely dangerous. If the upward angle of attack exceeds the maximum downward angle of the elevator, it’s AoA becomes stuck positive in relation to the incoming air and cannot be pushed down.

Extreme divergence risk.

I would suggest physically limiting the opposite elevator limit so it cannot easily push the nose high enough to exceed the downward range of motion, but that could possibly cause other handling issues.
 

wsimpso1

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Is the really? What about elevator it self? I think it's deflection UP to small and why he made it slotted like a flap? Isn't canard should stall first? But this setup possibly will make canard "flying" at slower speed then main wing.
Well, a slotted flap elevator has been fairly standard in canards. This has been needed because the canard is necessarily more heavily loaded than the main wing for reasons of stability. In fact in all airplanes with more than one lifting foil, the forward most is most heavily loaded, with successive foils less loaded as you go aft. Likewise with stall being first on the forwardmost foil, but that is a stall behaviour requirement, not stability. Stall behaviour and pitch stability are different things, and the Wrights figured that out too. They had the canard stalling a little early at Kittyhawk, but the human in the loop was where stability came from. It was not until Huffman Prairie that they shifted the CG forward, loading up the canard and confirmed inherent stability was available.

Stability needs drive higher Cl's on the canard than on the main wing under any flight mode. The canard must also have some reserve lift remaining to flair and land while already at high Cl for approach. So the slotted flap elevator makes a ton of sense - it allows a direct linear pitch control with modest control forces and somewhat extends the Cl of the canard for flair and landing. IIRC, Burt Rutan used them in all of his two-surface craft.

Burt Rutan did not go with as large a vertical offset of his slotted flap elevators as Peter has with the Raptor - even at his most radical, Rutan was interested in well working airplanes. Some of us suspect that Peter has too much vertical offset to the hinge line. He may end up having to limit travel or rebuild the system with smaller offsets based upon flight test results.

Now to not enough up deflection, again the canard is heavily loaded in all flight. All positive g operation should be easily managed by reducing Cl with modest up elevator movement. A little elevator up will drop canard lift for just about any upright maneuver your could want, including getting the nose down right now during an engine failure.

Get into sustained negative g, and while it should be possible, I do not know if the Rutan ships and derivatives can hold it - I doubt the Raptor has inverted oil and fuel on board... So, maybe it has enough up travel, maybe not. Many conventional tailed ships have less nose down elevator travel than nose up as well, indicating reduced capability in nose down pitch than in nose up.

Once the very capable and exceptionally skilled flight test team thinks it will fly, we shall see how it behaves and where its limits lie.

Billski
 
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