TarDevil
Well-Known Member
So if the plane catches fire he'll have longer to barbeque.
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I think when the chute is needed there will be very little horsepower.
I've seen video of a pusher aircraft deploying a BRS in flight test. It did tangle in the prop a bit, but deployed fine, the only consequence of the entanglement was that the aircraft descended in an unplanned attitude.
Why a free wheeling prop has no aerodynamic drag? shut off your engine and play with your pitch and you will notice a difference in drag so drag exists. Beside compare it to a wing of a glider which is "freewheeling" all the time, and even how laminair and smooth the wings are they have drag.
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Flyfalcons
Well-Known Member
Trust me, there's a reason heli pilots keep their headspeed up when they have an engine failure.
Malish
Well-Known Member
Free wind wheeling prop producing more aerodynamic drag then prop is not turning at all!
None of that invalidates what I said.
Engine being turned by a windmilling prop has a significant sink rate - you are cranking the engine along at a few hundred rpm - that takes a bunch of energy;
Engine and prop stopped, has a substantially flatter glide angle than with a windmilling prop and engine - the prop is a pretty small frontal area dragging straight through the air;
A free wheeling prop not connected to anything else has no net torque at its hub like the above cases. Yes, it is an inverted airfoil and its helix angle is too small, so we can expect it to be an inefficient wind turbine. And it does take energy to make the lift times the rotation speed, but do we really believe that the unloaded prop drag torque times its rotation speed is more energy than the windmilling engine and prop? I gotta think it is inbetween. Maybe it is time for some engineering and math...
Billski
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Marc Zeitlin
Exalted Grand Poobah
And this thesis, from 1936 (Caltech), says pretty much that, and has some references to other documents that say similar things.
It is interesting, however, to see that it's very dependent upon the blade angles of the prop.
Way too lazy - I'll just take other folks' word for it, if they've got the evidence
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flywheel1935
Well-Known Member
Isn't all this talk of windmilling props academic ? With Raptors PRU 'design'!!! if the belts fail, then it windmills, (S or B). If the engine fails to operate, ie temporary fuel cut off/electrical failure, then the chance of airstarting, with a compression ratio of 2-3 times greater than a petrol engine ( diesel comp ratio being 14 to 22 to 1)
is probably nil ? And really at the end of the day, if the Raptor comes to market( which is highly unlikely) then the Kit builder is free to fit his own engine anyway.To be honest if these so called west coast investors really want to build a canard SUV, then why not go direct to people like Jeff Kerlo, the only thing to learn from PM is how NOT to build an aircraft, there I've said it !!!!
is probably nil ? And really at the end of the day, if the Raptor comes to market( which is highly unlikely) then the Kit builder is free to fit his own engine anyway.To be honest if these so called west coast investors really want to build a canard SUV, then why not go direct to people like Jeff Kerlo, the only thing to learn from PM is how NOT to build an aircraft, there I've said it !!!!
Aesquire
Well-Known Member
In simple terms, a wind-milling prop driving an engine has a lot of drag, but a freewheeling prop can have more or less than one still coupled to the engine, depending on how much pitch & how fast it is spinning. ( in both cases ) See Table III on page 33 of the above report.
Personal experience with Ultralight types with a clutched, freewheeling propeller ( unfortunately for this purpose, fixed pitch so I can't comment on pitch change ) on a 20hp range engine, is there is a huge increase in drag between stopped and spinning freely. A non-freewheeling prop spinning a small ( 12 hp range ) single cylinder 2 stroke ( thus much lower pumping drag than a 4 stroke ) was also large, but since it was a smaller propeller, I can't compare directly.
In both cases, the spinning prop was a real drag. ( pun intended ) In the direct drive 12hp case ( Quicksilver Very Early model 2 axis ) at slow airspeed the prop stopped, and drag was noticeably reduced, then at higher speed would restart spinning, and again, noticeably throw on the air brakes. In practical terms, it can make the difference between clearing a tree line to a nice field, and landing in the brush in the closer, ( almost straight down ) one.
Personal experience with Ultralight types with a clutched, freewheeling propeller ( unfortunately for this purpose, fixed pitch so I can't comment on pitch change ) on a 20hp range engine, is there is a huge increase in drag between stopped and spinning freely. A non-freewheeling prop spinning a small ( 12 hp range ) single cylinder 2 stroke ( thus much lower pumping drag than a 4 stroke ) was also large, but since it was a smaller propeller, I can't compare directly.
In both cases, the spinning prop was a real drag. ( pun intended ) In the direct drive 12hp case ( Quicksilver Very Early model 2 axis ) at slow airspeed the prop stopped, and drag was noticeably reduced, then at higher speed would restart spinning, and again, noticeably throw on the air brakes. In practical terms, it can make the difference between clearing a tree line to a nice field, and landing in the brush in the closer, ( almost straight down ) one.
Wake me up when all this engine stuff is finished and testflying the plane it self started. I'm not an engine man , but was interesting and learn full thanks to the many comments of HBA members But I have more questions about the canard. If I look to the Raptor it has a very thick long wing root and very large winglets or rudders. So what is the advantage? I assume at cruise speed your stabilator in a normal configuration could be trimmed to almost zero (downward) lift with minimum drag , one rudder instead of two winglets seems to me also less drag , beside those large winglets seems to me very complex both the external aerodynamic forces and internal which effects each other combined with the bending of the wings. Why not as combination pectoral fins under the fuselage and smaller winglets?
But I have more questions about the canard. If I look to the Raptor it has a very thick long wing root and very large winglets or rudders. So what is the advantage? I assume at cruise speed your stabilator in a normal configuration could be trimmed to almost zero (downward) lift with minimum drag , one rudder instead of two winglets seems to me also less drag , beside those large winglets seems to me very complex both the external aerodynamic forces and internal which effects each other combined with the bending of the wings. Why not as combination pectoral fins under the fuselage and smaller winglets?
I think Malish was agreeing with you.
Richard Schubert
Well-Known Member
None. The canard configuration is a compromise to allow more effective packaging/styling, at the cost of higher "stall" speed and some other quirks.
Three Surface vs Canard (Two Surface) Discussion
Has this ever been done on any production or kit aircraft? I'm pretty sure the Avanti has some kind of syncronized flap system on both the main wing and it's front lifting surface.
www.homebuiltairplanes.com
The LongEz and its derivatives (all the way to the Raptor) are about the best way to configure a two lifting surface light plane.
There are other ways, like tandem wings (from Mignet to Quickie, Q2, Q200, Dargonfly) but this arrangement gets high effective aspect ratio on both wings (the winglets make the effective aspect ratio of the big wing larger) while getting enough vertical tail volume at minimum wetted area and having a decent range of loading available. Want more performance? Well, you could go Catbird or Piaggio-Gates Avanti, but the best of all seems to be the Boomerang. Have fun!
Billski
Tough to tell what he meant...
...For a relatively narrow range of Cl and commensurate speeds. Marc Z can probably describe it better than I, but as I understand it you can tailor the main wing to accommodate the downwash of the foreplane well at some specific Cl, but not very far away from that design point you'd be better off with a conventional tail.
The prime example of this is the Rutan Solitaire canard sailplane. You couldn't crank the Cl up enough to make it thermal well, and its polar dropped off so fast at the high end that it wouldn't run. A sailplane that won't do either of those well is just a glider.
TarDevil
Well-Known Member
My perception of canards is they are ok for extended travel for no more than two souls who can live without short, unpaved runways. I think I would enjoy a Velocity V Twin for that purpose. For a non-professionally flown twin, that airplane makes a lot of sense with it's low vmc. Not sure you can make a conventional twin that docile.
?? Wouldn't a centerline thrust twin (push-pull) conventional design with a Vmc above Vs be as docile? It is easier to make that configuration have a lower approach/landing speed than we'd typically find in a canard configuration .
Might be nice for extended water crossing. A bit of hull adjustments would allow reasonable ditching but not takeoff.
TarDevil
Well-Known Member
Oh yeah. I've long lusted after Rutan's M-309; compact, ~200 HP engines.
(Edit: Since I'm one of the old pharts who can remember this coming out of Rutan's barn, I remember it having IO-360's, yet anything I find online now says they were 550's. Anyone know?)
I'd prefer it to the Velocity. But Adams turned it into a bloated pig.
And, the Velocity is available... the M-309 is not.
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