lol.... now there is a great experiment. Simple.... to the point..... any idiot ought to be able to see and feel the results.

I'd like to suggest and even simpler takeoff of the same setup.
I have a box fan in my shop that runs 24/7. I've held little foamies in front of it many a time. Fans are perfect substitutes for RMH's clever experiment. Except of course their blades aren't usually airfoiled, so if you're one of the crowd that fears flat surfaces....... you've got a detail to use to in your argument the experiment isn't appropriate.

So far, this discussion has been heartwarming in that nobody has tried to argue that our models don't hook a left on takeoff, that it's just theory that they do. But there's still time.......

Perfect example!

[quote] [Consider the case of the F4U, it did not get its carrier wings due to the massive torque effect of the engine/prop at 'go-around',/quote]

The reason for the gullwing on the F4U is the 13'4"diameterHamilton-Standard prop required to absorb the 2,000+HP (and torque) of the P&W R-2800 Double Wasp, at that time the most powerful engine on any fighter. On its maiden, the flight ended prematurely when the elevator trim tabs failed and the test pilot wrestled it to a successful landing.

Everyone knows that the real purpose of thrust offsets is to counteract our building errors. Fine tuning is then done by adding weight and more warps.

jess

LOL Seriously?

Wow, guys this is amazing!

Now we’re bringing in issues that are far outside the scope of my original post.

Just to be clear; the intent of my OP was to point out that adding right thrust to a model, does not and can not, by any law of physics, do anything to counter or reduce the torque on an airplane. Notice I did not say the effects of torque, just the torque itself.

Right thrust can only directly counter the effects of “P-factor�.

That is the only purpose to my post to stop you guys from saying “Right thrust is added to counter torque.�

Jet Plane, your comments in post 34, only go to prove that many folks, even with the highest credential repeat what they have been taught as “truth� without question. I found this most evident in one of the dozens of aerodynamic text books I mentioned earlier. One gentleman starts his document with “question everything you read here to make sure it is correct and to advance the science.� Then he proceeded just rattled off the spiral causes yaw on the fin, without question.

To answer your statement in post #34: My opinion is based on the fact that there are NO equations in all of aerodynamics to account for the slipstream swirl. There is ONE mention of a value for it and it was from empirical wind tunnel data. No one has mathematically modeled the effect. Furthermore, as pimmnz pointed out in several of his posts, show us ONE PHOTOGRAPH of an aerobatic airplane (in straight and level slow flight, yeah I can find one in the middle of a snap roll too) where the smoke from the smoke system is wrapping around the fuselage, shoot just show us one where the smoke is doing ANYTHING but flowing straight back parallel to the centerline of the fuselage.

And the way it is taught TOTALLY IGNORES what the teacher is saying!

If you will please examine my three attachments.

The first image is how Spiraling slipstream is taught.

The swirl of air, induced by the propeller, wraps around the fuselage, striking the vertical fin from the left, causing a higher angle of attack on the right side of the fin, causing the aircraft to yaw to the right. Note that this is taught as a CONSTANT not just at take off on a tail dragger where this yaw, OR as dabigboy pointed out in post 46 under high power and low airspeed.

The second image is how Spiraling slipstream would be in reality, and what is conveniently overlooked.
IF the spiral is real, and constant, this shows what should be really happening to the aircraft. The same force that is causing the massive yaw to the left should uniformly affect the wings and stabilizer causing a MASSIVE ROLL to the RIGHT. Yet this is NEVER taught or even mentioned in ANY aerodynamics or pilotage text books.

My theory.

No one seems to have a problem with the “P-factor� explanation; i.e. the propeller at higher aircraft AOA produces more thrust off the right side than the left side due to a combination of relative airspeed and angle of attack on the propeller disc. Actually the illustration in Lnewqban’s post #45 is a great place to start; it shows there is more force or thrust coming off the propeller blade at the 3 o’clock position.

Dabigboy (Matt) pointed out another item to add to the confusion in post #46, he threw in the yet to have been used term “Gyroscopic precession�. IF no one has a problem with P-factor, then no one should have a problem with the statement: At high angles of attack, where P-factor is greatest, the resultant force from the P-factor, acting through the propeller, transmitting the force to the airframe will cause the aircraft to PITCH UP. In Matt’s example, the aircraft pitching down applied a force on the prop at the 12 o’clock; this resulted in the aircraft yawing to the left because of the reaction of that force at the 3 o’clock position AND the P-factor of his full thrust-low airspeed condition.

We have two forces to consider here; the actual thrust from the prop, the increased airspeed is acting at the 3 o’clock position of the propellers rotation. This high speed air is flowing faster down the right side of the fuselage than it is flowing down the left side of the fuselage. BUT…the resultant force on the propeller, applied at the 3 o’clock position, MUST by gyroscopic precession react at the 6 o’clock position of the propeller’s rotation. The FORCE from the P-Factor thrust again cannot cause the plane to yaw right; it causes it to pitch up!

Finally have a look at figure three, the alternate explanation.

So what could be another possible explanation? We still have one item we haven’t looked at, what happens to the P-factor air when it flows aft? Contrary to the spiral theory shown in the second figure the P-Factor high speed air increases the AOA of the right wing and right horizontal stab, adding a LEFT ROLL. This matches the behavior we see from the aircraft. It also does exactly what the spiral theory is trying to say; it causes high speed air on the right side of the fin, increasing the AOA of the fin and causes a LEFT YAW!

And that’s about all I have to say on that.

My point, please learn the correct terminology to use with the hobby and use it.

Thank you,

I think a well known poet once wrote " A rose by any other name ". I understand what your point is but if for decades the force that drags our models to the left when power is applied has been called " Torque " and the fix is to apply right thrust why over complicate the whole thing?


One thing that I simply can't fully understand as well is why people want to apply full scale theory and think it will 100% directly relate to our models. I't just dosent work that way. Sure Physics still apply in the same manner but when was the last time some real data was taken from an aircraft with our wing and power laoadings? These two things make it a whole different ball game.

Take any serious Pattern or IMAC pilot and I promise you they are doing things to get their airplanes to trim out correctly that disproves some of what is said here. That dosent make any of it wrong, just that it's applied in a different senario.

It probably goes beyond the scope and intent of this discussion, but Reynolds numbers will be far different for a model even if it otherwise precisely duplicates a full scale counterpart.

jess

"That is the only purpose to my post to stop you guys from saying “Right thrust is added to counter torque.� "

I don't think it is known exactly the percentages of the several possible effects of left yaw and to prohibit the use of torque as one of the possibilities sounds a bit presumptuous.

In the past, it has been pointed out that the left main wheel might contribute... it being loaded far heavier than the right main. That would be a product of engine torque.

What percentage does this issue bring to the yaw issue... who knows. And... to quantify, one would have to do so for every variation of runway surface condition and tire combination.... an improbable task of any formula.

From what I gather here, your main focus is at take off. Being that I am an aerobatics pilot I tend to set up right thrust as needed for proper tracking during an upline. My goal is to have an airplane track strait up on a vertical hands off for 150' to 200' depending on the size of airplane. As speed falls off and the prop load increases it will strt to drift to the left unless right rudder is applied. It shouldn't come as any surprise that the model with the deepest pitch prop requires the most right thrust ( electric pattern airplane with a 20X15 APC ). Having this dialed in correctly greatly simplifies take offs though.

When we did TOC and IMAC stuff - we cured the P problems pretty easily
Low weight and enough power to accelerate straight up works
The problem is much of the off the rack stuff just won't do that
Ditto on pattern stuff
Lowering weight and increasing power cures just about anything
The full scale guys always knew this but doing it was quite another thing
NONE of th warbirds could do it -
The Red Bull contestants really work at it
Those things are almost as good as a flat 3D foamie
My last EDGE- a H9 with clipped wings , end plates and a ZDZ80 piped would accelerate vertically from a dead stop hover

The free flight guys were doing VTOs fifty years ago.

jess

From a hover?

So basically your argument is based on the 'evidence' that'MajorTomskiright andthe recognised experts in the field of propeller propulsion are all wrong'....... Sorry if i don't find that a convincing argument. It's the case that the burden of evidencemust laywith the person trying to overturn accepted wisdom, so you need to come up with proof that the experts are all wrong, not just rhetoric.

As for your diagrams.. #2 is how it is (though the spiral angle is massiveness exaggerated, it's more likely to be only a couple of degrees). Of course the spiral slipstream effects any surface it encounters, including the wing and horizontal stab (both Hepperle and Stackhouse said so much in the quotes i included in my last post). The effectof the interaction with all surfaces is,as you pointed out, to produce a rolling torque to the right butbear in mindthatthese surfaces don't take all the energy out of the slipstream so this right rolling torque will always be much less powerfulthat the left motor reaction torque produced directly by the engine, so the overall torque remains to the left.

You can see evidence of spiral slipstream in the design of stators in a EDF fan or in the compressor statorsin an axial flow turbine. As further proof there is the use of right thrust to trim aerobatic model in the up-line as discussed a few posts ago. In a vertical climb then there is no P-factor because the prop disk is perfectly perpendicular to the direction of travel. Also as you point out, torque would not produce a left yaw.. <u>So why is it that most if not all planes yaw left in a vertical climb unless right thrust is added?</u> (my latest aerobatic model needed 4.5Deg of right thrustto straighten the up-line)

Steve

4.5 degrees offset?
That is a BUNCH!
We do some right trim-but only when it is shown to be required on a particular model.
Down thrust -basically a design patch- required on quite a few designs
Everyone has their own fix for things they don't like .
Every "offset" comes with some penalty-
Personally -I start at 0-0-0 then dial in or adjust for whatever causes a problem.
Simply adding some arbitrary incidence or offset ,starts you out with no clear understanding of what offsets and angles are really required.
.shoving the CG around will often fix or screwup a design
overweight -will also screw the pooch
ditto for trying to fly a design in a speed envelope for which it is not suited.
Tho it is not often seen of larger models - the added drag plates used on latest indoor aerobatic stuff ,really does have value.
If our big models had to hold very tight speed parameters -you would likely see these additions on them.
As it is - most don't have the reserve power to allow em.

On the contrary sir, I did not say they are wrong. I repeat again, spiraling slipstream is the ONLY aerodynamic phenomina that has not been quantified. There are no mathematical models to prove or deny that it exists. Yet it persists as hard, unarguable fact. I'm offering another point of view with another possible explanation that accounts for the same behavior. I intend to someday in my retirement look into generating the "proof" you so desire.

I have just built and flown a lightweight delta/flying wing hybrid. It has no up or down thrust, nor any left or right thrust, and even more surprising no reflex. It flies straight and true with no trim needed a type of result that RMH was talking about. The first flight had an issue with torque pulling the plane left, but launching it with a catapult eliminated that problem. Once in flight the spiral slipstream or P-Factor does not seem to be an issue at all. I think that any real problem is caused by the torque of the motor, not the spiral slipstream.

I just drop it and hit the power

Lots of the pattern guys are adding what they call " Cantalizers ". This is nothing more then a stub wing placed right behind the canopy. It is intended to straiten out the spiral slipstream before it reaches the tail. I would have to think that if it didn't work then it would not be so commonly used. Then again this is R/C and I have seen lots of fads come and go.

I see the main problem with understanding is as Speed said, all of these forces create "torque effects." Most model flyer's are more familiar with cars and therefore when torque effects are mentioned they assume they mean engine torque. Yes they all play a part and design is a huge factor.

[quote]ORIGINAL: speedracerntrixie


[quote]ORIGINAL: MajorTomski


Ah the Cantilizer -
What it CAN do is stop air from spilling over the top of the fuselage in knife or extreme yaw-and that can be a good thing-
the spiral correction - I seriously doubt but an improvement from trapping flow - I will buy
As for "follow the leader " in Pattern - it is quite common.

Rub it in...

Now the reason I mentioned my plane is; if this spiral effect was so pronounced, with the leading edge being between 1/8 an 3/4 of an inch behind the prop, this plane should want to heel to the right and it doesn't. Now on the flip side of all this (which lead me to think motor torque is more of an issue) is that she will roll left a lot faster than she will roll right.

What?? and you haven't fixed that yet? LOL You just stumbled on to another thing I see many many times. When I am asked by a pilot why his airplane does not roll as well as mine. I ask if he has equal throw on his ailerons. The answer is always YES! Then we get into his TX and sure enough his end points on aileron and flap channels are all set to 100% ( Aileron and flap are JR, Spektrum dual aileron servo setup ) Then when we actually measure the ailerons they are way off due to bad linkage geometry ( ARFs). So all I do is set the ailerons so both move exactly the same up and down, throw in a few points of ail diff and the airplane rolls much better. After that the door is open and they see the light and realize there is more to trimming an airplane then strait and level at full throttle.

Another thing to consider about Pattern Flyers: They are after such small degrees of improvement that if they even THINK they have a hint of improvement, then they are happy. If they think the extra control surface helps, then they'll be more confident and fly a touch better. Being just a touch better wins contests at the top levels. Improvement is improvement, even if it's only mental.

Some are not quite large enough to make the airplane be considered a reverse-stagger biplane, but I've seen some large ones.