Pusher vs Tractor - The old debate

Twinstarr

Twinstarr

Ron A. Any chance that you have looked at or flown the Twinstarr ?

Interested in this aircrafts performance comparied to the other birds you've listed. THANKS

Spaans
 
Jean, your half rite.
I didnt mention roll, coz theyd be identical, but in pitch, there would be a noticable difference.
Wot youd call " much the same" is wot id call " noticable difference".

As for the yaw, the same applise.
You say "I do not know if it is really necessary to have a powerful rudder."
Well, maybe so, but its essemtial for wot im do'n.
And its not just the distance from prop to rudder and the length of the machine, but also, if you stomp on the rudder of a long tractor, the tail will very quickly be out of the prop blast, coz the prop blast wont instantly follow the yaw of the machine. The fastest a tracter could yaw is dependant on how fast the prop blast catches up.
The pusher OTOH will have the rudder in the prop blast no matter how fast you yaw the machine.
 
Jean, your half rite.
I didnt mention roll, coz theyd be identical, but in pitch, there would be a noticable difference.
Wot youd call " much the same" is wot id call " noticable difference"...
Birdy, Forgive me if I say perhaps beside the point. Google translates sometimes in unexpected ways
I calculated the inertia, in pitch, of a pusher and of my tractor project (single seat, Rotax 503). With identical masses for the 42-Main objects arranged according to the two hypotheses: difference: less than 5%.

As for the yaw, the same applise.
... if you stomp on the rudder of a long tractor, the tail will very quickly be out of the prop blast, .
In yaw, it is true that the rudder can out of the propeller flow. I think he would a voluntary action which is outside the context of rapid changes alone, but a asymmetry exceptional desired by the driver.
In these conditions, two rudder can push away the inconvenience? So, It seems that the effectiveness of the rudder is a very secondary concern of manufacturers, when you see the thin profiles used
 
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Understand wot your sayn Jean.
Horses for courses mate.

difference: less than 5%.
Wen your on the limit, that 5% is wot itd take for a wrecked machine.
 
The two primary masses are the pilot’s body and the engine.

With front engine, the pilot needs ~40” from seatback to firewall for legroom. The CG of a seated pilot is typically at his belly button, perhaps 6” from seatback. The engine CG is perhaps 6” in front of the firewall.

With pusher engine, the distance from belly button to engine CG is perhaps 15”. Reducing MOI by a factor of 7; (40/15)².
.
Chuk,
Allow me to choose more realistic dimensions.
Tractor
Center Rotax 503) / firewall: 12 inches forward
Firewall / seat (back): 44 inches behind.
Center pilot / seat (back): 15 inches forward.
Pilot Center / firewall: 44 -15 = 29 inches behind
Pilot Center to the center of the engine: 12 + 29= 41 inches

Pusher
Engine Center (503) / firewall: 12 inches behind
Firewall / seat (back): 3 inches behind.
Pilot Center / seat (back): 15 inches forward
Pilot Center / engine center: 12 + 3 + 15 = 30 inches

So, the reduction MOI is only (41/30)2= 1,8 for these two objects (no factor of 7). And when I count the 35 main items ( Rotor excepted) , the reduction is only 20%. We can not say that a tractor is handicapped by the inertia in yaw.
Jean Claude
 
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Lines do not make the gyro. The pit bull has issues not enough vertical stabilizers. And it is really squarely on the ground. It is hard to get the balance right and it has a tendency to ground loop on takeoff.
 
Pitbull

Pitbull

John, you've mentioned before about vertical stabilizers-------what about a longer fuselage length such as th SS verion? Two (2) feet longer I believe it is. "pbool" also mentioned in one of his earlier posts that toeing in helped, however, I have also read toeing out would help in some cases, not specific to the Pitbull. It would seem on rollout if it were toed in and not lifted off cleanly, that is , bearing the load to one side of the front wheels, it would have a tendency to pivot on the grounded wheel if only for a short time. Don't know. You were also considering lengthening the mast by six inches. How has that worked out? Jim.
 
Birdy mentions yawing a tractor so fast that the rudder "outruns" the airflow off the propeller, and I've seen this mentioned on the forum in other discussions. Has anyone ever experienced this, or is this just something theoretical that "might" happen? My Little Wing is almost exactly 16 feet from the prop to the rudder. If the air coming off the prop is moving at 100 knots, or 166 feet/second, it will arrive at the rudder 1/10th of a second after it leaves the prop, even with absolutely zero airspeed, which is not likely. I'm finding it hard to visualize a rate of yaw sufficient to get the rudder out of the prop wash, especially since the airflow KEEPS flowing off the prop all the time the fuselage is yawing. How about a "there I was at 30,000 feet with nothing between me and the ground but a thin blonde" story to add some actual experience to make this either a fact or a myth.

Dr. Rob
 
"outrunning the rudder" ???? be sure to consider the type of fuselage in this claim, a open frame or "single tube" type will give a very different resistance to yaw than a "covered " fuselage with sufficient length. While the Cierva formula is debated sometime, I think here is where it is a quite valid factor. Also the main landing gear on the Pitbull was wire braced fore and aft and this may have been a problem along with the "very " tall tail wheel on a leaf spring arm that may have been a contributing factor to iniating a "weaving" in ground handling and I think the original Pitbull did not have stearable tail wheel to provide stearing when below rudder control speed. If I am wrong on any of these factor please correct me, as I have never owned a Pittbull

Tony
 
I have another theory that the picaren had winglets at the tips of the horizontal stabilizer that were at an angle about 45*. One of the things this did in a ground loop the winglet would twist the horizontal stabilizer slightly up making the horizontal stabilizer a vertical stabilizer and stop the ground loop.

I too have wondered about the leinght of the pitbull. would longer be better.
 
John you have asked a good quesstion, but I don't know the answer for sure, I have wondered if the "wasp waist" design of the body may have resulted in some turbulence back there rather than smoothing the airflow like intended. I have always felt that the Pitbull was a little short on both vertical and Horizontal stab.

Tony
 
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