New rotorcraft concepts

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dukkbutt

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Jan 9, 2021
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Spokane, WA
Can't find a reference about stability of a flying wing and pusher props. I'm sure I read it years ago but I'll just withdraw the statement.

If a tractor prop airplane is displaced nose up during flight but still moving in its original direction due to inertia, the thrust vector is above the line of flight, in front of the cg, pulling the nose up which is destabilizing. The pusher prop in the same circumstance has an upward thrust component but it is behind the cg thus pushing the tail up and the airplane back toward level flight.

These are relatively small forces and easily overcome by normal aircraft stability design so they are not typically a consideration.
 

D Hillberg

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very low low low earth orbit
Can't find a reference about stability of a flying wing and pusher props. I'm sure I read it years ago but I'll just withdraw the statement.

If a tractor prop airplane is displaced nose up during flight but still moving in its original direction due to inertia, the thrust vector is above the line of flight, in front of the cg, pulling the nose up which is destabilizing. The pusher prop in the same circumstance has an upward thrust component but it is behind the cg thus pushing the tail up and the airplane back toward level flight.

These are relatively small forces and easily overcome by normal aircraft stability design so they are not typically a consideration.
When thrust/drag & weight/lift are equal it doesn't take much to upset the apple cart.
Add inertia and you get some interesting flights
 

EzyBuildWing

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Sep 23, 2009
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643
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Sydney NSW Australia
Simple "Rat Rod" VW-gyro makes a big statement.........what could be simpler?
Might fly and look better with a dirty/rusty old reliable Rotax 4-stroke with open rusty noisy-pipes, and tundra-tyres.
Love the Rat Rod look......and especially the leather saddle-bag!
Maybe Rat-Rod enthusiasts would go for towing it around on "Rat-Rod trailers" behind their "Rat-Rod cars"?
Mad Max Gyro Silverton Museum.jpg
 

piolenc

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Feb 17, 2013
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Negros Oriental, Philippines
Tractor gyroplanes are much more stable then pushers, PIO PPO are nearly nonexistent in early tractor designs
Flying wings are unstable due to center of pressures and C/G limits being exceeded and not thrust.
Short coupled flaperons and spoilers are not as effective as tail feathers on a stick.
no difference in jet thrust or pusher prop thrust.
Old engineer saying "Easier to pull a rope then push it" pulling is naturally more stable
There may be something about gyroplanes that conceals the stabilizing effect of a propeller behind the center of gravity, but the notion that pulling is just naturally more stable is invalid for all aircraft. A pusher stabilizes in both yaw and pitch.
 

U+fly

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Nov 25, 2021
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There may be something about gyroplanes that conceals the stabilizing effect of a propeller behind the center of gravity, but the notion that pulling is just naturally more stable is invalid for all aircraft. A pusher stabilizes in both yaw and pitch.
Thank you for confirming this fact, explained earlier as good as possible.
 

jazzenjohn

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Oct 22, 2014
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Milan, Mi. U.S.A.
The nature of tractors makes centerline thrust easier to do and a problematic high thrustline difficult. That said, tractors basically suck. You can derive this by the fact that few people have them but anyone could if they really wanted them, you can derive this by the bulk of people that have owned them got rid of them because the visibility totally blows and they are usually difficult to get in them, you can derive this by the dearth of flying examples of tractor gyros, you get the picture. The tractor gyro with tricycle gear that people suggest be electrified was such a lousy performer it was scrapped and im not sure it even flew despite it having a Rotax 582 engine. That engine on a similar weight pusher with the same blades would have had sparkling performance. The only feature tractor gyros have is they are cool looking. The little wing shows that you can make a tractor gyro work, but they are far more difficult and time consuming to build along with the viz issue and entry, exit issues too. Just my opinion. Ive built 4 gyros so I have some experience.
 

Riggerrob

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A pusher prop might help stabilize (in pitch and yaw) if it is on a long tail moment arm. See Taylor IMP.

However, since most gyroplanes mount their pusher props close to the center-of-gravity, their short moment arm means that they contribute little to stability.
It is the same concept as conventional tail surfaces (fin and horizontal stabilizer) on short versus long tail booms.
 

Riggerrob

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"Can't find a reference about stability of a flying wing and pusher props. ... "
Fixed wing deltas - with pusher propellers suffer pitch problems.
The worst example was the 1970s vintage Deltaire mid-wing, pusher Delta with its propeller mounted just aft of the trailing edge and almost in line with the wing chord. That is a good configuration for most flight realms.

But it created serious pitch problems during take-off. Part of the problem was the long landing gear legs needed to prevent the prop from dragging on the runway. The other problem was the need to install main gear legs a long way aft of the center-of-gravity to prevent the airplane from tipping back on its tail when the cockpit was empty.
During its first attempt at flight, the pilot/builder/designer roared down the runway and struggled to lift the nose. Lifting the nose was difficult because of the short distance between the control surfaces (elevons mounted along the trialing edge) and the main landing gear. When the Deltaire finally lifted off, it lost the nose-down moment created by the main wheels. The pilot suddenly found himself applying far to much nose-up elevator input. The Deltaire did the world's smallest inside and crashed, killing the pilot.

The next attempt was Rhor's 2-175 low-wing, pusher delta. Rohr used experimental engines that turned about twice as fast as production Lycomings, so had ducted fans roughly half the diameter of a regular propeller. Mounting the propeller shaft half as high above the center-of-drag and center-0f-gravity halved pitch problems. Rohr 2-175 also had very short landing gear legs. It is a pity that financial problems in Rohr's other divisions forced pre-mature cancellation of the 2-175 project.

Since then most small (1 to 4 seats) deltas have all been tractors (Baker MB-1 Delta Kitten one-off, Dyke Delta, Ver Hees Deltas plus Wainfain Facetmobile). Mounting the prop in the nose has several advantages starting with using mostly Cessna stock parts firewall forward. Mounting the engine in the nose helps a lot with balance. The tractor prop only needs a long nose wheel strut to keep the prop out of the weeds. To that end, several successful small tractor deltas (Dyke Delta and Ver Hees Delta) have their landing gear fixed at the ideal angle for take-off and landing. That angle is critical as deltas only fly well within a narrow range of angles of attack.
Yes Ver Hees Delta flies final approach at a steep angle of attack, but it also has a window - near the rudder pedals - that allows the pilot to keep the runway in sight.
Yes, deltas can generate massive amounts of vortex lift at high angles of attack, but that is only relevant on supersonic jet fighters that have equally massive amounts of thrust to "power" themselves out of that high drag mode. A piston-powered delta will develop a fatal rate of descent int he same scenario, hence the need to fly precise angles-of-attack during landings and take-offs.

If I wanted to make my first million, I would be negotiating with Bart Ver Hees and a CNC shop to pre-cut sheet metal kits for Ver Hees Delata 2.
If I were starting from scrap, I would design a high-wing tractor delta with 1 or 2 seats, again, construction would be mostly pre-prunched sheet aluminum.

Bottom line, when combined with delta wings, pusher problems create plenty of pitch problems. The only successful small deltas all have tractor propellers because tractors have fewer pitch problems and can get by with much shorter and lighter landing gear. Tractors only need long nosewheel struts for soldier-proof landings.
 
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