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Trying to wrap my head around tractor vs pusher when it comes to High Thrust Line ...

Say you have 2 gyros ... everything equal , both have a 12'' high Thrust Line

Except one uses a Pusher Prop and one has a Tractor prop

Would the Tractor be equally susceptible to PPO (Power Pull Over) ... compared to PPO (Power Push Over) with a rear mounted prop ????

My guess is the the answer is YES , both are equal .... but my head wants to say the Tractor would be better

Anyone know ?

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Arnie- Chuck Beaty has touched on this several times, and will say it makes no difference. It seems to me a tractor would be better, but I know Chuck can prove that assumption wrong .

The TL is a line, and it makes no difference where its sorce is along that line, its effect on the frame is the same.

The main diff is usualy the tractor needs a higher nose to keep the prop off the ground, which puts the rotor head higher, which means you have more room out back for a longer HS arm.
And its easier to line all the mass bits up with the TL.

A pusher behind the CofG can make a machine want to swap ends (depending on tail) and want to push over if anywhere near negative, where as a tractor will always try to pull itself straight, so in that sense, the tractor is more stable..... however, tractors have their own issues including all of what Birdy said and also that the pilot has less forward view and sits in the prop blast so screen is quite handy.... the pilot tends to block the tail, so although a bare bones frame can work, a more streamlined rear fuselage is more desirable. Tail dragger tractor gyros can have issues with prop strikes if fitted with to effective brakes (Jam on the brakes and it stands on its nose)... that's why some have a nose wheel or skid even tho they are tail draggers. Plenty of them around, which is great to see, but I doubt if they will ever come close to scratching the market for pushers. I have seen 4 myself, and videos of others, but the only one I have seen fly is our little wing over here.... one time. either they are less fun to fly, or more difficult to fly.... I don't know?

I think you would find if tractor was a better 'all round' machine, then all of the musterers would be using them. Birdy, how many musterers use tractors to muster all day every day? I doubt many at all?

Madmuz- What you say seems correct....or the analogy you can't push a rope
..but only pull it. Chuck has clearly explained it makes no difference....a thrustline is as Birdy said...just a line and doesn't matter where the thrust on that line is pushin or pullin.

It is a harder concept to grasp......and it takes an engineer to better explain it.

How I look at it is, in a tractor just above the bottom of the power curve, the motor will just keep pulling and be fairly stable even if you travelled out of a nasty updraught, into a sudden nasty down draught.... even if the tail jammed or fell off (exaggeration) whereas a pusher, depending on the tail design, you would need to work on keeping it pointing how you want it.... yes Stan, like you cant push a rope... but also like balancing a pool cue on your finger takes a lot more work/movement than just holding the tip of the cue and hanging the rest below....

In my opinion, a tractor is naturally strung out ....the engine being much further in front of the rotor, than a pusher is behind.....this makes its moment of inertia much higher. Like how a tandem is less maneuverable than a side by side.

I think you mean tandem is less manouveurable than a single? but I know what you mean

Edit: I polished my glass eye and swapped it with my good eye and read it again, Dead right Stan after the edit, my bad

No Stan is correct. A tandem is never as agile as a side by side.

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Hellified .... that is where my mind wanted to go .... pulling a rope vs pushing a rope

Good point about a tractor prop being farther forward , plus the longer tail would delay pitching moments a bit.

1. mass distribution will affect rates of movement even if the c/g will remain the same. so stability will be way different.

2. try pushing a rope. think pulling on one will be more satisfying.

The thrust line is nuthn like a rope.
Its fixed, ridged, to the props axis, so it follows the frame just like it dose ina pusher.
Take the rotor drag away from a HTL tractor and the effect is zactly the same asa pusher.
Wether you push or pull on one side of a mass, itll rotate at the same rate.

The thrust moment will be different add side slip & P factor , You will have your ass handed to you by the same beast you hacked together,

a tractor and a pusher will have the same degree of stability if all things are the same but most times on a tractor the tail feathers will be much further back so it will be less affected by thrust line offset and by being longer it will feel less sensetive in both pitch and yaw. I have a 85% finished tractor in the shop and the only reason that I am building it is for use on floats, with the prop up front it gets much less spray through it, being a tractor it will need a bigger engine than my pushers for the same performance.
The old tractors had a low thrust line due to their large heavy rotor systems.

Norm

The rope analysis is nothing more than a comparison of the tensile vs compressive strength of the rope itself and is not comparable to the analysis of forces acting on an aircraft.

The stability of an aircraft is determined by the summation of all of the forces acting on the aircraft at a single instance in time. To properly analyze these forces each force (thrust, gravity, drag, torque, etc) is expressed as a three dimensional vector or rotational force (torque). Once all of the forces are known then the analysis is mathematical (which can become quite intricate and complicated). The analysis is further complicated by the fact that many of the forces acting on an aircraft are dynamic (continually changing).

In an attempt to clarify some of the confusion, a vector force can be fully described as the amount of force and the direction of force relative to a fixed point. Therefore, the thrust-line from the prop is a direction or a straight line (at a single instance in time) regardless of where along that line the force is applied.

However, that is only the thrust-line force. Other forces may definitely be different based upon where along the prop thrust-line the particular force is applied (remember there are gravity, drag, torque, etc. forces in addition to the thrust from the propeller).

So, while it is true that if all of the other forces acting on the aircraft are exactly the same and the propeller thrust is exactly the same then a pusher vs a tractor will have the exact same stability.
The catch to that statement, however, is that the design must be different between a tractor and a pusher so it is not possible for all of the other forces to be exactly the same.

Gordon- Well Put. I think we finally have a new never ending argument to replace the downwind turn argument that will never be understood by some.

Balance a broom handle on your finger..... you have to constantly move your finger/hand around to keep the broom handle upright..... if you dangle the broom handle from your finger (if the handle was tied/glued to your finger) the broom handle will just stay upright/downright without moving your hand.... more stable when pulled from the front, than pushed from the rear

Another analogy, a water skier could be towed behind a boat with an imaginary steel rod, or a car can be towed by another with an actual steel rod/pipe..... if there was no difference, then the skier could be in front of the boat, being pushed by the boat thru the steel rod..... or the car being 'towed' could be pushed by a vehicle behind with a steel rod..... nowhere near as stable as when being towed..... instead of pushed.... Even front wheel drive cars tend to be more stable, usually wanting to stay straighter pulled by the front wheels and tend to resist turning (understeer) than a rear wheel drive like a Porsche, which are pushed from the rear wheels and tend to want to oversteer or even swap ends on the lift of the throttle mid corner....

What about, why are the rotors on a helicopter on the top of the chopper.... (in tractor/pull) if pusher was more efficient/better. the rotors could be on the bottom of a helicopter? Something hanging/pulling is always more predictable and therefore IMO, more stable than something being pushed.... We have all seen model fw aircraft hanging off the prop, often for long periods of time.... I would like to see a BD5 with the pusher prop behind the rudder try that....

Having a pusher prop/thrust just suits us and various other aircraft/airboats/rockets/arrows so we balance the instability with various rudders/stabilizers/fins/feathers to achieve our required goal.... which in our case is to not be sitting in the propwash and high pressure area behind the prop, better forward visibility, light weight and just to continue where Benson left off...

Tractors are inheritantly more stable, but we don't only want stability, we want controllable and predictably unstable machines..... I think a tractor gyro might be a little too stable for people liking the controlled instability of our pusher type gyros

Think bout your annalergys Muz, theres a huge difference between your skier and a prop.
Ok , ill give a hint, the pole pulln/ pushn the skier is NOT ridged, it can hinge at both ends.
If, OTOH, the pole was ridgedly fixed to the boat, and the skier couldnt hinge on the other end, it wouldnt matter if the skier was pushed or pulled.
The prop cant hinge and the engine is fixed.

Birdy- EXACTLY! You boil it down better than Chuck.

Would you like to go skiing and be on a pole fixed out of the front of a boat? I don't think so? why does a train pull the carriages? if you had two loco's pushing 20 carriages up a hill from the back, what do you think will happen? The same 2 loco's can pull 40 carriages up the same hill no worries.... but hey, I could care less, if you want so badly to be right, go for it.... it doesn't worry me at all.... everyone is free to believe what they like..... until I see something like the flying bedstead fly with the thrust underneath (pushing) without flipping over and destroying itself, see them make parachutes with rods up to the parachutist above the canopy, when they perfect the stand on hovering platform (like a heli/multicopter with the rotors below the pilot, or any other flying vehicle where the load is above the thrust (pusher) and it becomes a main stay of aviation..........until then, I am happy to be completely wrong and believe what I do