New tandem tractor design and build

[Jean Claude]

110 HP (82000 watts) at 2300rpm (240 rd/s) is a torque of 82000/240 = 340 mN
With no torque compensation by the tail, the weight (4500 N) will shift lateraly of 340 / 4500 = 0.075 meter or 3". If the gravity center is 1.65 meter below the rotor, then the tilt of the mast will change 2.6° from idle to full throttle.

 

[C. Beaty]

Here’s what JC is saying; I’ve exaggerated the angles for clarity.

Using rotor thrust to balance propeller torque, as Cierva points out in his patent literature, has its problems.

Rotor thrust varies with rotor load; gusts, attitude change, etc. This produces a rolling motion about the longitudinal axis. A sudden reduction of rotor thrust, as could be the case when encountering a violent downdraft, can invert the machine in an instant.

Offsetting the rotorhead to one side changes nothing except aesthetics.

Aviomania is the only gyro from across the pond to have gotten this right.

 

[okikuma]

I know I'm late in the conversation and repeating the same idea.

This is what Ron Heron told me how he compensated for his Rotac 2800 engine torque on his LW-3.

After tying down his tail on his LW-3, Ron placed his main wheels on individual scales. Then Ron adjusted each horizontal trim tab up and down accordingly to achieve the same weight on each wheel when the engine was running at full power. Ron reasoned that if each wheel had the same weight when the engine is running at full power, then differential setting of his trim tabs would effectively cancel out the torque while in flight. Simple and ingenious. Ron's method is simpler and easier than designing and building in asymmetrical airfoils or variable angles of incidence on each side of the horizontal stab like Cierva and Kellett did on their autogyros.

Wayne

 

[C. Beaty]

Pitcairn played with several ways of compensating propeller torque in the AC-35 Autogiro.

The first try was counter-rotating props; too noisy, too heavy and too expensive.

The second try was via the “catfish whiskers” designed by NACA. These fins removed swirl from the propeller slip stream and perhaps recovered some of the power wasted in rotating the slip stream.

The final and most satisfactory solution was via tailplane differential.

 

[Jean Claude]

Ron's method is simpler and easier than designing and building in asymmetrical airfoils or variable angles of incidence on each side of the horizontal stab like Cierva and Kellett did on their autogyros.

Wayne, The Ron's method works well, but in my opinion the rigorous roll compensation is not the most important. Mast tilt change three degrees and even less with a symétrical horizontal tail is little. The most important is the yaw compensation thanks the vertical tail centered in the propeller slip stream.

 

[Phenix5]

As you can see, in the Phenix we have a big horizontal stabiliser with 2 fin/rudders on it´s extremes. We spent a lot of time investigating aerodynamic solutions and finally went for a symmetrical HS and no offset on the rotorhead.

We have never encountered any torque related issue either in roll or yaw.

Like Jean Claude says, mast tilt is small and we can fine tune it with the trim. It is hardly noticeable on the stick.

Michael, you´re doing a great job and heading in the right direction. Congratulations!

Carlos

 

[C. Beaty]

A wide chord horizontal or vertical stabilizer surface that is centered in and spans the propeller slipstream provides a considerable amount of propeller torque compensation, even without differential incidence.

Without such aerodynamic torque compensation, a gyro can flip in a hurry in the event rotor thrust is lost. Admittedly a rare event but it does happen during a violent downdraft or a hard pushover.

A typical gyro has a moment of inertia about the roll axis of ~75 slug-ft² and 100 hp delivered to a propeller turning 2600 rpm provides a torque of ~200 ft-lb.

The roll axis acceleration in radians/sec² is equal to torque/MOI = 200/75 = 2.66 rad/sec². 1 radian ~57.3º

The distance traveled in radians = ½at² = 1.33 radians after the first second or 76º

Look out below.

 

[Jean Claude]

Without such aerodynamic torque compensation, a gyro can flip in a hurry in the event rotor thrust is lost. Admittedly a rare event but it does happen during a violent downdraft.

I agree, Chuck. However a rotor 29 'x 8' lifts 1100 lbs to 60 mph with an angle of +11°. To suddenly get 0g require an angle of attack of -13°, ie a instant input in a descending area of: 60 mph Sin (24°) = 2100 ft/min. Admittedly possible but very rare event, and
still not catastrophic in my opinion: Just a horizontal tail with a CTL will restore a positive g as quickly as it disappeared.

 

[C. Beaty]

I agree, JC that torque roll over is not likely on a CLT tractor with tail centered in the propeller slipstream.

However, it is a concern with HTL pushers having a keel mounted horizontal stabilizer.

Many of the eyewitness accounts of RAF-2000s tumbling out of the sky report torque roll over combined with pushover. The forward pushover insures a period of minimum rotor thrust that allows propeller torque to roll the machine.

Here’s one that had a keel mounted horizontal stabilizer:
“The pilot was practicing an air show routine. After making a number of low passes, then landing, he took off again. The gyroplane then made another approach, paralleled the runway, and made a shallow descent to about 60 to 75 feet. The pilot maintained that altitude and heading for a few seconds, then initiated a 45-degree climb followed by an "immediate" right turn. During the turn, the rotor blade sound changed from a high pitch, to a "Bell Huey" sound. The gyroplane then made a "pronounced roll" to the right and descended to the ground. Postaccident examination of the gyroplane revealed no evidence of any preimpact failure, and there was no evidence of the rotor blades having struck the rudder, horizontal stabilizer or winglets. The rotor hub and rotor blades exhibited evidence of upward coning, consistent with the rotor blades having lost rigidity due to low rpm.”

https://www.ntsb.gov/_layouts/ntsb....-b267-4939-9626-5e348db84b6c&pgno=1&pgsize=50

Why ignore propeller torque when it’s so simple to correct and doesn’t cost anything?

 

[Gman]

Chuck,
What is the simple way to diagnose prop torque and correct it? I have read 10° leading edge tail offset???
Thanks,
Jerry

 

[C. Beaty]

That 10º vertical fin offset is a form of rudder trim, Gman. If set right, it permits cruise speed without rudder pedal pressure.

Torque and yaw are something else:

Yaw occurs because the vertical tail is dipping in the lower half of the whirlwind coming off the prop; it pushes the vertical tail sideways in the same direction as the lower half of the prop is moving by an amount that depends on throttle setting. The only way throttle/yaw coupling can be eliminated is by a vertical tail centered in the propeller slipstream so that it gets an equal push from both the upper and lower portions of the prop. A Dominator type tall tail does just that, eliminating throttle/yaw coupling.

Torque roll results from torque applied to the prop; if you could hold the prop still, the engine and airframe would spin in the opposite direction. But without doing that, the prop rotates the air in the same direction as the prop is turning, still producing a torque reaction that tries to rotate the airframe in the opposite direction of prop rotation.

You can measure prop torque by tying the tail to a tree and placing the main wheels on bathroom scales with the engine going full blast. If the prop, viewed from the rear spins CCW, the right wheel will have a higher reading than the left wheel. The difference between the two readings x wheel track is the resultant torque.

A full span tail surface centered in the propeller’s whirling slipstream is given a rotational force in the opposite direction from the torque reaction acting on the airframe. Such a surface will reduce the inequality of readings on the bathroom scales, whether it’s a vertical or horizontal tail. The Dominator tall tail provides partial torque compensation so that torque roll isn’t noticeable except with the more powerful engines.

Cierva used differential incidence between horizontal tail halves to balance propeller torque; the old radial engines turning props at 1600 rpm produced a bunch of torque. Ron Heron did the same with his LW gyros using scales to determine correct setting and I suppose Giorgos does the same with his Aviomania gyros.

Part of the problem is the result of following the Bensen layout by “designers” not skilled in the technical aspects of gyro design. Bensen didn’t bother with aerodynamic torque correction because a Mac engine spinning a 4’ prop doesn’t produce enough torque to bother. The Bensen did, however, have very strong throttle/yaw coupling that required some skill with the necessary rudder pedal toe dance during the takeoff run. But once the reflexes are acquired, most pilots aren’t consciously aware of their footwork.

 

[Gman]

Thanks so much Chuck! I appreciate your time. This will help me a bunch.
Jerry

 

[Jean Claude]

Cierva used differential incidence between horizontal tail halves to balance propeller torque; the old radial engines turning props at 1600 rpm produced a bunch of torque. .

Just for info.
Cierva C30 built for France (Leo C301) weighed 1950 lbs AUW. It was equipped with a Salmson 9NE engine developing nominal 175 HP at 2050 rpm weighing 357 lbs
Mechanical output for rotor prélanceur: max 25 HP at 1350 rpm on propeller

https://aerophile.over-blog.com/art...utogire-leo-c-30-c-301-et-c-302-45750859.html

Cierva C30 built for England (Rota) weighed 1900 lbs AUW. It was equipped with a Armstrong Siddeley Genet Major1A developing nominal 140 HP at 2200 rpm

So, in proportion to the roll inertia, propeller torque had no more effect than now. But as Chuck said: it's simple to correct and doesn’t cost anything.

 

[ILikeJetsToo]

Thanks for the comments everyone. As always, I appreciate the discussion and input.

Twisting the horizontal makes me think of problems after a high speed throttle chop... But again, what is high speed for a gyro and I've never done it!!

Dennis, I’m not sure what to think of high speed throttle chop with a differential horizontal stab. I wonder if the prop slipstream reduces just as fast as the torque subsides. “If” the dynamic pressure over the horizontal is primarily dominated by prop-wash, maybe that is why high speed throttle chop typically seems somewhat benign?

A wide cord horizontal or vertical stabilizer surface that is centered in and spans the propeller slipstream provides a considerable amount of propeller torque compensation, even without differential incidence.

Chuck, that is what I have been thinking. I have a wide horizontal with good area, but it is pretty far away from the prop compared to a pusher. I do like the Ron Heron technique for measuring torque. It’s tempting to add an adjustable surface to the horizontal, so I could just “tune” out the torque on scales. I guess I could always proceed with a fixed/passive horizontal and see how it performs during ground engine runs and modify it later if torque seems problematic before first flight.

I agree, JC that torque roll over is not likely on a CLT tractor with tail centered in the propeller slipstream.

Chuck, I’ve been hoping that is the case. I think I agree with you that offsetting the rotor only changes aesthetics.

Engine torque compensation can only come from the detwisting of the flow. In my opinion, a wide horizontal tail passing through the prop wash can reduce, even with no asymmetry.
JC

Jean Claude, I think a well thought out horizontal design is my preference for torque compensation. That being said, it’s nice to know that a few degrees of rotor bias to one side is enough to compensate.

Just for info.
Cierva C30 built for France (Leo C301) weighed 1950 lbs AUW. It was equipped with a Salmson 9NE engine developing nominal 175 HP at 2050 rpm weighing 357 lbs
Mechanical output for rotor prélanceur: max 25 HP at 1350 rpm on propeller

Cierva C30 built for England (Rota) weighed 1900 lbs AUW. It was equipped with a Armstrong Siddeley Genet Major1A developing nominal 140 HP at 2200 rpm

So, in proportion to the roll inertia, propeller torque had no more effect than now. But as Chuck said: it's simple to correct and doesn’t cost anything.

Jean Claude, interesting comparison. Thanks.

As you can see, in the Phenix we have a big horizontal stabiliser with 2 fin/rudders on it´s extremes. We spent a lot of time investigating aerodynamic solutions and finally went for a symmetrical HS and no offset on the rotorhead.

We have never encountered any torque related issue either in roll or yaw.

Like Jean Claude says, mast tilt is small and we can fine tune it with the trim. It is hardly noticeable on the stick.

Michael, you´re doing a great job and heading in the right direction. Congratulations!

Carlos

Carlos, thanks for the data point on the torque handling of the Phenix.

Wayne, thanks for the Ron Heron technique description and the great photos of differential horizontal stabs. I had not seen several of those.

Thanks everyone,
Michael

 

[Jean Claude]

I have a wide horizontal with good area, but it is pretty far away from the prop compared to a pusher.

Michael, Far or close to the prop does not change the effectiveness of the untwisting. The difficulty is to stay byline despite the different angle of the flight

 

[JAL]

Chuck, that is what I have been thinking. I have a wide horizontal with good area, but it is pretty far away from the prop compared to a pusher. I do like the Ron Heron technique for measuring torque. It’s tempting to add an adjustable surface to the horizontal, so I could just “tune” out the torque on scales. I guess I could always proceed with a fixed/passive horizontal and see how it performs during ground engine runs and modify it later if torque seems problematic before first flight.

I don't know whether this works because the HS is fixed but a Cessna 152 has a small fixed trim tab on the rudder that is adjusted on the ground (just a piece of metal that can be easily bent)

I wonder if something a little bigger on the trailing edge of the HS will work. It would allow the HS to be built and then the torque compensated by trial and error on the scales later.

One of the downsides though is that people walk past and say what's this and give it wiggle and then you have to reset it.

 

[Jean Claude]

Jordan,
Small tab of your Cessna just cancels the effort orienting the rudder. It does not replace the yaw force produced by the rudder. If the rudder was fixed then the tab would have no detectable effect.

 

[500e]

C30
https://www.rotaryforum.com/forum/showthread.php?t=43804

 

[DennisFetters]

Dennis, I’m not sure what to think of high speed throttle chop with a differential horizontal stab. I wonder if the prop slipstream reduces just as fast as the torque subsides. “If” the dynamic pressure over the horizontal is primarily dominated by prop-wash, maybe that is why high speed throttle chop typically seems somewhat benign?
Michael

Since I have no actual experience in this matter, I can only tell you how I think it may work out while working it out in my head;

You have both propwash and forward airspeed going over the HS. If you twist the flow just enough to counteract the propwash while on the ground, then in forward flight it will counteract the engine torque, but you also have the forward airspeed reacting on the twisted HS, and the higher the airspeed, the more reaction of the HS to the point where it will actually over twist the airframe to the point where you are having to add and hold cyclic to counteract the over torque, and this amount will all very throughout the airspeed range.

Now my concern would be in the event of sudden power loss at a high speed, you are going to be wound up like a rubber band. That means you lose the added airflow over the HS from the propwash instantly, but still have the forward airspeed now adding counter torque, but you still have to adjust cyclic during deceleration.

It boils down in my mind that if you are going to have to be adjusting cyclic in any matter, why have all the drag of a twisted HS and unwanted counter torque after loss of power, when by just tilting the rotor disk to the side to counteract the engine torque offers the most manically simplest, lightest and stable solution and no need to hold hand pressure until you have a power loss?

No matter how you add it, twisting the rudder will add increased drag with increased airspeed, in any matter.

Just me thinking out loud....

 

[DennisFetters]

I just want to clarify a few points in your post:
Counter the engine torque requires no pressure on the stick. The rotor thrust is still on the roll pivot, even when the head is tilted to the side. It requires just a position of the stick, without any pressure.


If the twist of the propeller flow is rectified par le HS, then the rotational kinetic energy is recovered. This means that the drag of the horizontal tail is reduced instead of being increased. Here's how:

To hold the stick in position requires pressure, or you would not need to manually hold the stick to the side, or hold the stick to correct when loosing engine torque. Admittedly, it is a low pressure, but the annoyance of having to hold it to counteract is the main point I'm making.

For the HL to counteract torque in Michael's application, it must produce lift on opposite sides of the opposite ends and equal to the torque. If not, then it's not counteracting torque. My point is that lift creates drag.