A new tractor design

Vance

Gyroplane CFI
Joined
Oct 30, 2003
Messages
16,310
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2400+ in rotorcraft
I am going after stability in thrust and airframe design. I feel the tractor has some advantages there. The expense is certainly some forward visibility.
What are the stability advantages of a tractor gyroplane over a pusher gyroplane with the same empennage volume John?

In my experience a properly designed pusher gyroplane is very stable.

I feel you will be giving up ground handling stability with a conventional landing gear.

I feel based on my experience the RAF you will be training in is less stable in pitch than most of the gyroplanes I have flown and not because it is a pusher.
 

Attachments

Supermotive

Member
Joined
Sep 13, 2019
Messages
168
Location
Greenville
What are the stability advantages of a tractor gyroplane over a pusher gyroplane with the same empennage volume John?

In my experience a properly designed pusher gyroplane is very stable.

I feel you will be giving up ground handling stability with a conventional landing gear.

I feel based on my experience the RAF you will be training in is less stable in pitch than most of the gyroplanes I have flown and not because it is a pusher.
I see that you are a CFI, so I am guessing that you know this answer. Therefore my assumption is that you are quizzing me to see if there may be some area that you may help me to understand better; which I certainly do welcome. So here it goes... All things held equal, the puller will be more stable due to thrust being in front of the longitudinal center of gravity. I know there have been advancements in thrust vector placement, but the thrust stability can't trump the thrust stability of a tractor, due to not being CLT at 100% of the time, and when the thrust is exceedingly high, or the CG, RTV, of Rotor drag variables become a stack up of unfavorable states.

As for the ground stability, I don't think I will be giving up anything in my particular case. Could a ground loop happen?? Sure, but I think my speeds will be low, and I have another trick up my sleeve for tail wheel stability during ground operations that I will share as it unfolds.

Last, though this does not directly address your question, I want to be in an enclosed cabin. Center of drag, in the typical pusher side by sides could increase the likelihood of a bunt over at higher speeds under certain rotor loading conditions. A tractor can handle this better, again, all things held equal.

That's the best I can do for right now.
 

Alan_Cheatham

Member
Joined
Nov 14, 2003
Messages
1,972
Location
Dallas, Texas
All things held equal, the puller will be more stable due to thrust being in front of the longitudinal center of gravity.
You may want to read Doug Riley's comments here about puller vs pusher:
https://www.rotaryforum.com/threads/food-for-thought.6863/post-165683

As for the ground stability, I don't think I will be giving up anything in my particular case.
While the tail-dragger gyro is workable there are a few ground handling quirks compared to other designs.

For one, because the rotor is a given distance behind the main gear (lever arm) pilots have found that when the rotor is producing lift a roll input will cause an opposite yaw. A right roll will pull the fuselage right causing a left yaw.

Another is for every degree the tail-dragger sits on it's tail an extra degree of forward rotor head tilt will be needed to level the rotor to the horizontal.
Being able to level the rotor to kill lift aids or is essential to rotor management, especially in windy conditions. Many of the old winged tractor gyros, which didn't have tilting heads, succumbed to ground accidents because they couldn't level the rotor to kill lift after a landing only to be blown over.

Another caution with a tractor configuration due to it's longer length is rotor to tail clearance, at low rpm the rotor can strike the tail so centrifugal teeter limiters and a stick lock are considered a must on many designs.
 
Joined
Jan 11, 2013
Messages
307
Location
Eureka,Illinois
Aircraft
Challenger ll
Total Flight Time
2100
Just because the engine is in the front, doesn’t mean it has to be a taildragger. Arliss Riggs built several nice tractor tricycle gear gyros that performed very well. In fact, he built one taildragger and immediately changed to a nosegear. Jim Eich built a 2 seat tandem tractor trigear that handled well on the ground, but had some flying issues (tail too small?). Tervamaki has some neat tricycle designs with at least the prop in front. I would think, if starting with a clean sheet of paper in the 21st century, a tractor tricycle gear gyro would be a no-brainer. A quick check of the Tractor Designs Section here on this forum will show some interesting attempts.
 
Last edited:

Supermotive

Member
Joined
Sep 13, 2019
Messages
168
Location
Greenville
Thanks for the input. I will check into these options. My thoughts are I need an off-road type suspension that can handle a 10 mph plop to the ground and tail dragger configurations accommodate the suspension architecture that I need for the 10mph drops better.
 
Last edited:

Supermotive

Member
Joined
Sep 13, 2019
Messages
168
Location
Greenville
Just because the engine is in the front, doesn’t mean it has to be a taildragger. Arlisa Riggs built several nice tractor tricycle gear gyros that performed very well. In fact, he built one taildragger and immediately changed to a nosegear. Jim Eich built a 2 seat tandem tractor trigear that handled well on the ground, but had some flying issues (tail too small?). Tervamaki has some neat tricycle designs with at least the prop in front. I would think, if starting with a clean sheet of paper in the 21st century, a tractor tricycle gear gyro would be a no-brainer. A quick check of the Tractor Designs Section here on this forum will show some interesting attempts.
I am strongly considering an on the fly lockable tailwheel for times when a strong yaw moment could move the fuselage easily.
 
Joined
Jan 11, 2013
Messages
307
Location
Eureka,Illinois
Aircraft
Challenger ll
Total Flight Time
2100
One of the other problems a taildragger tractor gyro has is that it can lift the tail during landing resulting in the prop striking the ground. A Pitbull builder (with a heavier, more powerful engine plus larger prop than recommended) encountered this when trying to level the still spinning rotor after touchdown. If he kept the rotor tilted back, then the machine would stop, then try to roll backwards. If tilted forward, the tail would lift. So there was a delicate balance where rotor rpm, rotor tilt, cg, main gear placement, relative wind, even rough ground were variables that could cause difficulties making a safe landing. If you look at many of the ‘30’s autogyros, the long main gear is placed well forward, so any forward rotation would be restricted. This also required the tail structure and tail wheel to be very beefy to survive the landing loads, Might as well put some of that beef in the main gear, move it back, then can put a (lighter) nosegear up front to prevent forward rotation pranging the prop. I’m an old fixed wing taildragger pilot, so have experience with the excitement that configuration can provide. Adding a spinning rotor in the mix, especially for a new pilot, seems unnecessary. Highly recommend looking at Arliss Riggs designs.
 
Last edited:

Supermotive

Member
Joined
Sep 13, 2019
Messages
168
Location
Greenville
One of the other problems a taildragger tractor gyro has is that it can lift the tail during landing resulting in the prop striking the ground. A Pitbull builder (with a heavier, more powerful engine plus larger prop than recommended) encountered this when trying to level the still spinning rotor after touchdown. If he kept the rotor tilted back, then the machine would stop, then try to roll backwards. If tilted forward, the tail would lift. So there was a delicate balance where rotor rpm, rotor tilt, cg, main gear placement, relative wind, even rough ground were variables that could cause difficulties making a safe landing. If you look at many of the ‘30’s autogyros, the long main gear is placed well forward, so any forward rotation would be restricted. This also required the tail structure and tail wheel to be very beefy to survive the landing loads, Might as well put some of that beef in the main gear, move it back, then can put a (lighter) nosegear up front to prevent forward rotation pranging the prop. I’m an old fixed wing taildragger pilot, so have experience with the excitement that configuration can provide. Adding a spinning rotor in the mix, especially for a new pilot, seems unnecessary. Highly recommend looking at Arliss Riggs designs.
Thank you. I do intend on having the main gear close to the firewall. I will look at Riggs’s design.
Update: I looked at Arilss’s designs. They look really simple. I actually like that. My attraction to tail dragger is mainly the plop down landing at about 8-10 mph. That needs a good suspension. I am imagining I will be landing at a low forward speed. I will have a rotor brake. I do believe these 2 factors can help minimize prop strikes; especially the rotor brake. I also intend to have a lockable tail wheel for use during landing (or take off if need be).
 
Last edited:

Jean Claude

Junior Member
Joined
Jan 2, 2009
Messages
2,113
Location
Centre FRANCE
Aircraft
I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
Why could a tail dragger land more slowly than a pusher?
 
Joined
Jan 11, 2013
Messages
307
Location
Eureka,Illinois
Aircraft
Challenger ll
Total Flight Time
2100
Jukka Tervamaki has some interesting concept side by side tractor gyros on his website. Frankly, I would like a simple single place enclosed tractor. Sat in the Pitbull and really liked it, visibility was quite good, especially compared to my old Luscombe, but the designer ran into business difficulties before completely solving some of its construction and handling problems. Will be the first to admit I am not an engineer, so still waiting for you knowledgeable types to produce what I want ( and can afford). Good luck.
 

Supermotive

Member
Joined
Sep 13, 2019
Messages
168
Location
Greenville
Jukka Tervamaki has some interesting concept side by side tractor gyros on his website. Frankly, I would like a simple single place enclosed tractor. Sat in the Pitbull and really liked it, visibility was quite good, especially compared to my old Luscombe, but the designer ran into business difficulties before completely solving some of its construction and handling problems. Will be the first to admit I am not an engineer, so still waiting for you knowledgeable types to produce what I want ( and can afford). Good luck.
Neat stuff! There are a lot of great pioneers in aviation. That is for sure
 

Jean Claude

Junior Member
Joined
Jan 2, 2009
Messages
2,113
Location
Centre FRANCE
Aircraft
I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
I do not believe landing speed Is affected much by landing gear configuration.
Why you writed : "My attraction to tail dragger is mainly the plop down landing at about 8-10 mph." ?
 

Supermotive

Member
Joined
Sep 13, 2019
Messages
168
Location
Greenville
Why you writed : "My attraction to tail dragger is mainly the plop down landing at about 8-10 mph." ?
Jean Claude. I see my statement was misleading. What I really meant was that I wanted a suspension system that would handle the 8-10 mph plop down. I feel the tail dragger is a good platform for that type of suspension. Sorry for the confusion.
 

Supermotive

Member
Joined
Sep 13, 2019
Messages
168
Location
Greenville
What are the stability advantages of a tractor gyroplane over a pusher gyroplane with the same empennage volume John?

In my experience a properly designed pusher gyroplane is very stable.

I feel you will be giving up ground handling stability with a conventional landing gear.

I feel based on my experience the RAF you will be training in is less stable in pitch than most of the gyroplanes I have flown and not because it is a pusher.
By the way, I love your gyro. It looks like a well made machine.
 

Jean Claude

Junior Member
Joined
Jan 2, 2009
Messages
2,113
Location
Centre FRANCE
Aircraft
I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
All things held equal, the puller will be more stable due to thrust being in front of the longitudinal center of gravity.
In front or behind the center of gravity does not change anything if the thrust continues to aim this center.
But this is rather the opposite, because of the radial thrust of a yaw propeller.
On a pusher, this radial prop. thrust helps to decrease yaw and pitch attitude

Sans titre.png

The advantage of a tractor is elsewhere:
- Facility of putting the GC on the propeller thrust line
- Facility of effectively reducing airflow detachment on the long rear walls


Directional stability by the wheels is another story
 
Last edited:

Supermotive

Member
Joined
Sep 13, 2019
Messages
168
Location
Greenville
"In front or behind the center of gravity does not change anything if the thrust continues to aim this center."
Respectfully, this is only true in all cases if the thrust is perfectly centerline in all cases. We both know that can't occur.

Your post is interesting though.
 

Jean Claude

Junior Member
Joined
Jan 2, 2009
Messages
2,113
Location
Centre FRANCE
Aircraft
I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
Of course, the aim is imperfect, but since the gap is constant, the pusher is not more unstable that the tractor
In addition, the pushing mode is more stable than the tractor mode: As showed my drawing, propeller that does not move axially produces a slight radial thrust.
If the propeller is located behind the center of gravity, this radial thrust produces a torque on the airframe which tends to reduce the sliping
If the propeller is located in front of the center of gravity, this radial thrust produces a torque on the airframe which tends to aggravate the sliping

Sans titre.png
 
Last edited:

Supermotive

Member
Joined
Sep 13, 2019
Messages
168
Location
Greenville
"Of course, the aim is imperfect, but since the gap is constant, the pusher is not unstable."

I agree with this if the center of gravity never moved. Center of drag may be another issue. The pusher will also be pushing against the cg and the center of drag which will always be dynamically moving and not in the center of thrust. It certainly is true that a large stabilizer moment can help, but the fact does remain.


"In addition, the pushing mode is more stable than the tractor mode: As showed my drawing, propeller that does not move axially produces a slight radial thrust.
If the propeller is located behind the center of gravity, this radial thrust produces a torque on the airframe which tends to reduce the sliping
If the propeller is located in front of the center of gravity, this radial thrust produces a torque on the airframe which tends to aggravate the sliping"

I do not agree that the pusher is more stable than the tractor, but there certainly is a slipstreaming effect on the fuse of the tractor. We must also note that this slipstreaming affect is also putting moments on the tail control surface. However, this in either configuration the effect is not really that much and easily countered with rudder of control surface trims.

I think the net is that if all other principles are held equal, the tractor is by design a more stable configuration. It is similar to accelerating hard and loosing traction of the tires on a rear wheel drive car vs a the same on a front wheel drive car. The rear wheel drive will want to rotate when everything is not lined up perfectly, which is almost always.

Though, to be fair, I do think pushers have come a long way, and a good HS covers where they an not so perfect.

The real price for the tractor will be the forward view. This will be better on the pusher.
 
Last edited:
Top