arvids

Engine right thrust or zero thrust and rudder slaved to throttle?
What's the advantage and disadvantage with either of them?
I have read some pilots build in half of the needed thrust and mix with throttle, why not set the engine neutral and mix the nessesary rudder in?
Does anybody do that in IMAC or 3D planes?

w8ye

My Feedback: (16)

You can do wonderful things with the computer radio

What you can do with the trim physically without the radio is better in the long run.

Howard

My Feedback: (55)

The biggest impact on left yaw, caused by the engine, is at high power and low airspeeds - an example is during take off. As the plane accelerates, picks up speed, the impact is reduced. The answer to your question is that the amount of right rudder needed to keep the ball in the center is continually changing with changes with power and airspeed. Neither approach will be correct all of the time either in combination or alone. If you mixed enough rudder to keep your tracking straight on take off then it would be yawed to the right once in the air with increased airspeed.

Howard

arvids

Do you mean whatever setup (with or without right thrust) will not be correct?
I think I'm going to set the right thrust half of the needed and play with the rudder mix, what do you think about that?

Yes we can do wonderful things with our radios, but we got to be awake when progamming.

Arvid

Carpilot

I'll second that. Everything in this hobby is a trade off.

I'll give you a couple examples.

Topflight p-51 Mustang with a Fuji-64cc 20X12 prop. not a bunch of right thrust. Flies fast and does good straight war bird maneuvers.

During takeoff as soon as the tail comes off the ground get on the right rudder and throttle up to takeoff speed, the amount of right rudder is constantly changing due to many variables.

Aeroworks 1.20 Yak 54, YS110 17X6 APC prop, a LOT of right thrust.

point it down the runway and hammer the throttle, rarely do I have to correct with rudder for takeoff. when doing a flat spin I use the engine right thrust to my advantage, if I try to flat spin with power against the right thrust of the engine it's not a very good flat spin, at least i can't make it look good. If I use the right thrust to my advantage and flat spin with the engine thrust it flattens out nicely and I can develop a nice powered flat spin (or inverted) that looks real good. Point it straight up and do a slow climbing roll, I'm not sure that I could do it without all that right thrust in the engine. maybe a better pilot than me could, but i sure couldn't.

Howard

My Feedback: (55)

Sounds like a good common sense solution. You might find a good explanation of the things (there are several) that cause the left yaw in a pilot training ground school book. Don't get hung up on propeller P effect but do pay attention to the effect of the airstream coming off of the propeller and how it affects yaw when it ultimately hits the vertical stabilizer (rudder). If you mix right rudder with the throttle you might also want to be able to turn off the mix when flying at a constant speed or in the 'cruise' mode.

Howard

mrbigg

My Feedback: (21)

Tried the rudder mix thing after reading Chip Hyde uses it. Didn't care for it. Always seemed like it was either too much or too little rudder in different scenarios. I just add right thrust now with the engine.

arvids

Howard:
Why should it be nessesary to switch off the rudder mix when flying constant speed/cruising mode, you can't switch off the
engine right thrust when flying like this. Is it because the airstream is different? If so, why doesn't the plane track to the
right when flying constant speed/cruising mode with right trust on the engine?
Yes, I have to read the book....

Arvid

Howard

My Feedback: (55)

Good question I don't have a perfect answer but, here goes. Adding some right thrust helps because there is always a left yaw component (except when the prop is not turning) and my guess is that designers likely target typical cruising power and airspeed or possibly some condition where excessive yaw and slow airspeed is risky. If you also add right rudder as the throttle is advanced it seems logical that it is going to be more than you need when you get to cruising speed because you also have the right thrust added to it. While transitioning to cruise speed or during touch and go practice it would be helpful but, once at cruise it is likely to cause a right yaw. Being able to turn it off would leave just the right thrust component. Here is an idea - why not add a gyro that senses the yaw axis and have it in the "normal" mode not the "heading hold" mode and every time you advance the throttle and the plane yaws left the gyro will correct with a momentary right rudder. Here is the best thread I have found on how our RC gyros really work in an airplane http://www.rcuniverse.com/forum/m_6056543/tm.htm. It is important to remember that if you use one of the new Heading Hold gyros you must switch it to the "normal" mode instead of the heading hold mode or you will find it difficult to change directions. This would be an alternative way of adding right rudder with the advantage that it does not engage when you don't need it. I need to add that I have not tried this except for doing loops and Cuban 8's. It could cause more problems than it solves. Great hobby

Howard

Truckracer

My Feedback: (19)

The effects of thrust angle tend to be reduced with airspeed where the effects of a fixed amount of rudder tend to increase with airspeed. The prop is a shorter distance in front of the CG than the rudder is behind the CG so the rudder has a greater mechanical advantage to yaw the airframe. Rudder and thrust really have different functions so they should not be thought of as interchangeable. I know this is a way oversimplified explanation so please don't beat me up over it.

Many years ago, for both models and full scale, I was taught that "rudder always works" at any airspeed and that lesson has never failed me. We can build in thrust angles and we have rudder mixing on our radios and these are good but we always have to remember that the rudder stick always moves and works if we only will use it!

arvids

One more question. How do the airstream affect to the plane when flying straight inverted?
Doesn't it require left rudder to compensate for the right thrust or am I missing something?
I try to learn a little every day, but it's not easy.

Arvid

Howard

My Feedback: (55)

Looking at the plane from the front the propeller is rotating counter clockwise. Picture smoke coming both ends of the propeller and imagine the plane moving forward. You would see a counter clockwise corkscrew shaped smoke trail that looks like a spring with coils with the plane being in the middle of the coiled spring. As the airstream moves around and back along the plane in a counter clockwise direction it is similar in shape to the the spring analogy. The airstream ultimately strikes the port side of the vertical stabilzer, pushing on it (F=MA) and causing the plane to yaw to port (left). This would be true regardless of the attitude of the plane. If you can envision the airstream to be the coiled spring then the faster the plane goes the more stretched the spring becomes and less of it strikes the vertical stab. If the plane slows down or the power increases then the spring coils become tighter and more of it strikes that vertical stab causing a bigger yaw to the left.

Howard

dogshome

Interesting.

For prop-hanging I tend to trim my rudder for vertical stability at zero speed. I also use several degrees of right thrust. That's definitely not ideal for vertical pull-ups though.


What effect engine torque has on this with fixed right-thrust during the hang, I can only guess!

TOYMAKER

My Feedback: (6)

I will trim the airplane (right thrust) to make the plane track striaght in a full power up line. From there learn to use the rudder for the conditions needed. Too many variables that can upset throttle to rudder mix... speed, wind, inverted vs upright.

Wayne

Stickbuilder

Anyone ever considered just flying the plane? I've used my left stick for correcting P factor on take offs and on up lines for years. I don't normally build any offset thrust into planes either. It makes the model look odd to have the engine pointing off to one side or pointing down. Just one man's opinion.

Bill, Waco Brother #1

jaka

Hi!
Have been in this sport/hobby for 34 years and I don't use a mixed throttle /rudder on any of my planes! Be it sport planes, pylon racers, scale or 50cc gassers! At take of all my planes track straight forward!

When newbies complain about a plane not tracking straight they always tend to think about torque /P-factor, but its not!
The reason some planes (mostly belonging to newbies) do not track straight is that the wheels on their planes are not set up correctly!

Stickbuilder

Very true.

Bill, Waco Brother #1

AA5BY

Howard provides a very well worded explanation. Up lines verify what he is saying... the slower the plane gets in the up line, the more rudder needed.

Howard

My Feedback: (55)

I honestly do not want to begin any kind of disagreement but, if someone reads your post and believes it then they will be taking away an incorrect set of facts. So that I don't repeat my previous posts I will simply state that they are accurate and correct. All single engine propeller driven airplanes yaw to the left (for counter clockwise rotating prollers) when you apply power or slow down while keeping the same power - for the reasons that I stated and it has nothing to do with how the wheels are set up. This occurs both on the ground and in the air - always. I respect your 34 years in the hobby. I soloed a Carl Goldberg Senior Falcon powered by a Veco 50 in 1969. Once again, let me suggest that a good pilot training ground school manual/book could be very helpful in providing another source to understand the yawing effects caused by the propeller.

Howard

AA5BY

There is little question that wheel gear need to be set up properly for good ground handling manners and that very often a plane that has bad manners can be tamed by effort to the undercarriage but I agree with Howard, one can't simply dismiss the yaw effects caused by the engine.

w8ye

My Feedback: (16)

As already stated - The greatest effect is with the larger props at the slowest speed.

The same plane at high speed has little left drift compared with the plane on take off

eclipse3g

My Feedback: (5)

Interesting idea. However, I have a question. If we fly inverted, the rudder works in opposite way. I hardly imagine how possible to accomplish that mix with throttle.
Could you explain?

Howard

My Feedback: (55)

Good question when you are inverted you need to use opposite rudder from the turn in order to maintain balanced flight (ball in the center) in order to overcome the effect of adverse yaw caused by increased drag (in this case) on the upward moving aileron. However, yawing caused by changing power levels or changing airspeed remains in the same direction (port or starboard from pilots reference) regardless of whether you are inverted or not for a propeller driven airplane.

Howard

Tony Hallo

When you mix rudder to throttle you have the ability to turn off the mix when not wanted, when the right thrust is built in, it there to stay. The trimming for right thrust is long verticial up lines, the pilot is expected to use rudder during takeoff. My planes have 2 to 3 degrees of right thrust and require the use of the rudder during takeoff.