I have a Dave Patrick 26% Edge 540 with a Saito 180 and a APC 17x4W prop.. It flys like a DREAM.. It will hardly tip stall and all seams fine. When I pull to hover I have to put full Right Aileron in it to keep it straight. This in turn makes it harder to controll the hover.. If I let it torque roll then It rolls out of it.. I am just not good enough to TR YET!! I have been thinking of changing the trust line but the plane flys SO good like it is..

INPUTS PLEASE>> ALL ARE WELCOME!!


LATER

Umm iv herd of this happeneing on gassers that when different props were tried it solved the problem, just an idea....

btw iv herd of good thigns with the "vess" props for hovering and other 3d things

I did think of that. I will try another style prop. Maybe it's too much drag on the 17x4W..

LATER

Hmmmm. Not sure I understand the Q, are you contemplating changing the thrust line to compensate for the T-roll in hover?

If that is your Q then my 2 cents is no, absolutely categorically no. Don't chg the thrust line. That will alter your pitch or yaw moments (depending on the change) and CREATE problems without having any effect at all on the torque roll issue !! Cutting open an orange with an apple slicer...just a big mess.

I agree w/ Freak. Swap out props. Experiment. I love my APCs. Try an 18-4 if they even make one as the S-180 can swing it just fine. Then a 17-6.

let us know how it turned out!!

I tend to agree with highhorse. Torque rolling is due to the reaction to the amount of power you are having to use to support the model. Switching to a prop that lets you use less power to maintain the hover will help. Adding more aileron throw would also help. Especially if you are using a reduced travel on the ailerons until you get a feel for this style of flying. But adding right thrust for example will NOT reduce the torque roll effect and would add in some yawing force during your hovering attemps. A lighter model would also torque roll less because it needs less power to hold it up. A lower pitch prop would help because it gets a better bite.

Now there's also the drag produced by the prop as it performs it's lifting duties. When operating in a static thrust mode as we have on the ground or in a motionless hover if the pitch of the blade is high enough the blades will stall. They still produce the lift needed to hold the model up but the stalled condition of the blades requires a lot more power from the engine to maintain the RPM needed to produce the lift. Switching to a prop that doesn't stall under this static condition will greatly reduce the power level needed to maintain the hover RPM's. This could be from a prop with a more stall resistant airfoil or it is usually done using a lower pitch prop so the blade's angle of attack is less.

Ya got me on that one !
to hover takes a given amount of work and the reaction for that amount of work will be the same irrespective of the prop selected

Try it

I closed your quote there Dick.

I stand by my post.... well, actually I sit in front of the monitor by my post...

Some playing with props will/may find one that provides the same thrust but with less power going into the prop. In particular if the prop has a significant amount of front/upper surface stall or pre stall separation drag. That drag has to be overcome by the engine to provide the thrust needed to hold the model up. If a different prop can provide the same amount of thrust but without the need to input as much torque because the air flowing over the prop blades does so in a cleaner manner then the engine won't be generating the same amount of torque.

You may have heard this with some of your electric models. Some props produce a sort of frying bacon zzzzzzzz sound while others, usually with a higher pitch, produce a deeper and "fluffy" sound. I can't describe it any better than that but I know it when I hear it. If you're using an ampmeter at the time you'll see a big jump in current (torque is directly related to current in electrics) with this new prop and a huge drop in thrust per amp. SInce this seems to occur quite regularly at around the 5 to 7 inch pitch range I sort of came to the idea that it's related to the blades operating in the stalled region or with some separation taking place.

I agree that for the model to hover it needs to generate the same amount of thrust from the prop disc. But nothing says that the prop disc can't do this with very littl eor a lot of drag. But if the prop has a lot of drag while doing it then the torque needed to overcome that drag and produce the needed 1:1 thrust will require more power than one that does this with very little drag.

Respectfully disagree. Some props will do the job more efficiently. A prop that has lots of drag for only just enuff thrust in HOVER ( a high pitch prop like an x-8 ) will force the engine to WORK much harder to generate the req'd thrust for hover.

Don't confuse the work done by the engine with the thrust. That ratio will vary GREATLY with the variables of pitch and speed.

OK-- try this:
I did a lot of testing with electric motor and a thrust stand andfound this situation to be very repeatable :
when a given amount of energy (watts ) were absorbed by the motor --the thrust was always -always - almost identical
Irrespective of the prop size/shape number of blades - I even placed two two blade props on the motor shaft-same results
I was surprised but the test was validated over and over .
remember this is a STATIC THRUST demonstration-- NOT a test of prop efficiency.
So If you can disprove this -please demonstrate how.
The reason for the test ?
I was trying to find the "prop"best for a static thrust of 8 ounces at the time .
there was ZERO data I could find which was applicable and the "calculated info" was just plain incorrect.
Prop efficiency in moving flight is a completely different matter - but in the original question -the problem was re hover (static flight).

In actual practice with larger models the results were very hard to qualify. (and I used up to, including, my 160 cc , 40 lb EXTRA
Why?
each different prop put the prop at a different rpm which was at a different point in the power curve of the engine .
the actual torque reaction at stationary hover tho -was the same -IRRESPECTIVE of prop
not surprising as the work (load)was the same .
also no matter how hard the engine appears to be "working"-- the stationary hover will require the same amount of "WORK" if the weight to be hovered is the same.
This is basic physics

Again, I respectfully disagree.

While I can't dispute or disprove your "data" because I have neither the equipment or inclination I would like to address the topic from a perspective of, as you put it, "basic physics".

If I set the brake on my truck and drive up a hill the same "work" is done as done as when brakes are released except for the EXTRA work to overcome the DRAG of the brakes.

If I hover a model with a low (at zero airspeed) lift/drag x/12 prop then the engine does the same "work" as when using a more efficient (at zero airspeed) y/6 or even z/4 prop except for the work to overcome the extra DRAG of an x/12 prop operating way, way off the peak of it's l/d-vs- AOA curve.

We can go around and around on this topic and probably never convert each other to another point of view. But I, for one, am grateful for the brain-teasing exchange. I wish I had the equipment and time to really test all of this under controlled lab conditions. Does anyone reading this have a connection to the Myth Busters TV show?

Well.. I opened a can of worms.. But.. It's good info so thanks to all.. I do see what Dick is saying. If the model is one weight then the same thrust will hover it.. I know that some props are more efficient than others.. I have the 4W on there now.. I will try one of the 18x6 Evolution props and see what happens..

Thanks guys

LATER

energy expended and work are not the same thing
one can take a lever and pull on a load till they collapse from exhaustion -but if the load does not move - no work has been done.
The electric motor and the watt meter experiment -tho simple - showed the relationship of thrust and watts (energy)

An inefficient prop did notchange load appreciably.However, rpm changed all over the place
a drag brake -instead of the prop would have produced a different result -obviously -

Comparing apples and oranges? or electric motors and internal combustion engines?

When the electric motor is loaded more and more, it simply pulls more and more electricity until it reaches some equilibrium or burns out the battery, esc, or itself. When the glow engine is loaded more and more it will reach it's max chamber pressures and if the load continues to increase, start to lose rpm from higher heat/friction/whatever.

So what stops the electric motor from increasing the thrust of that mass of props, all of which produce exactly the same thrust? It stops itself from producing more thrust, just as it does when there is less load. It has reached a load it can handle and does so.

So the electric motor isn't actually proving anything about the props, it's proving it can overcome whatever aero problems all the tested props have to produce identical work from all, to produce it's max work.

My take on the electric motor test is that it's not telling the efficiency of the props at all, but that it's telling you how strong the motor was designed to be, and that you have a sufficient battery for that motor. If I wanted to test the efficiency of the props, I'd run them all through a series of rpms and record the thrust at selected rpms. And I'd use a sufficiently large motor for the test. Basically, I can see the motor test as a test designed for comparing the efficiency of a bunch of electric motors.

But then, I consider almost all static test results for props of little value. It's more efficient to fly them puppies to see how they're going to fly.

Not to be contrary - but you missed the point
the electric motor in the test was not fully loaded - it merely was showing that X amount of watts would equal Y amount of thrust
in the tests all th props were basically about the same size and about (reasonably same in blade type - using APC And GWS props)
why dont--you make a thrust stand and try it yourself ?
I was surprised when I did the tests .
efficiency nor rpm was the issue - it done to find how much power was needed to get a static thrust of a given number --equal to the model in question.
using WATTS and an electric motor simply took out the power curves of a IC engine-- which apparantly ,easily confuses the issue.

wow.... who needs Physics...any ways....


interesting posts....

I will leave the discussion with this thought
If it takes 10 lbs of thrust -to hold in stationary hover a 10 lb model -using a simple single propeller - - the prop will need a given amount of power (hp) to do that job . not more or less
the reaction of the applied power at the prop will be equal to the force turning it..
swapping props -as long as the setup will still just hover the model -- will result in same "torque rolling effect".

So in turn If I do swith to a 18x6 prop and it's going to take the same amount of power from the motor to hover the plane then It will torque the same.. I see that point..
SO.. What can I do if anything..?? !! Thanks for all the inputs guys.!!


LATER

Dick, we're on the same wavelength but perhaps you and I tested different props.

Way back when a couple of buddy's and I were just getting into the whole electric thing we made up a rig to test thrust vs amp draw and played with a wide range of motors and props. At the time these were brushed motors and gearboxes as well as direct drive.

For lower pitch props our results were the same as you found and for a given motor the thrust and current climbed in step up to a point. As we used props with higher pitches things suddenly changed at around the 6 to 8 inch pitch range. At that point the thrust would still go up with the higher pitch but the current went up far more than the prop change would indicate. The thrust/amp at that point didn't climb in a linear fashion anymore. We all noticed a marked change in the sound at this point also. Hence we chalked it up to the idea that the prop was running in a stalled condition. The sudden drop in the "efficiency" as shown by the thrust to current ratio seemed to confirm this. The key here was that the motor was suddenly drawing a LOT more watts of power but the thrust went up only a small % or in a couple of cases didn't go up at all.

Since you were after hovering props I'm going to guess that you didn't try any that were higher in pitch and would be considered as more a higher speed prop?

correct - no reason for me to use high pitched props which would simply be stirring air - I do know a little about prop efficiency-- that little bit is that the pitch used needs to somewhat matched to the speed of the craft - in this case ZERO airspeed
and max thrust is at zero airspeed .
back to original query -the man wants to hover - and so he is not likely to use a 12x12 prop -tho I used that kind of prop for fast models years ago also 14x14 on four stroke emgine (YS 120/140-in pattern planes )- BUT- for the case at hand - the results I got - seem quite applicable - N/Y?

Ponder this:

A small prop requires more power (watts) to produce the same thrust as a larger one.

For instance, a 12x7 Aeronaut prop at 6000 RPM takes about 85W to produce 27 oz of thrust.
To produce the same thrust a 6x5 prop needs 18000 RPM and takes about 195W.

Another detail is that power is not energy.

Electric Power = V*I (watts)
Electric Energy = Power*time (Wh) or (Joule - Ws)

Look DUDE!! YOU JUST WENT WAAAAYYY OVER MY HEAD!! But it sounded good.. So.. redneck talk please.. New prop or get a new plane.. LOL

LATER

You're right. I didn't see where you said you controlled the motor to get a set wattage reading.

As for doing the same test for myself..... you kidding? You just gave away the discovery. I trust your testimony. And see no real value in repeating the test.

I would recommend you changing to a prop with smaller diameter, but you'll need more RPM and more power to get the same thrust as the bigger one.

OOOOK---
Now--do you ever fly the so called 3D stuf - have you ever tested the various props used for THAT type flying .
and - what is the nit picking about Joules for?
Are you simply bored?

Dick,

I just thought it shouldn't hurt with some definitions in order to keep the things tidy…

And believe me, a smaller prop requires more power than a larger one to produce the same thrust.
It's written on the stars…