Greetings, just curious as to what others are doing with right thrust or .... lack of on their profiles.

Chatting with a friend confirmed what I'd been thinking, that adding right thrust works against you when inverted, especially high alpha inverted as in harriers.

Don't think I like that!

Thanks,

Ernie

I have used the tethrite thrust plates from OMP on 2 profiles and they seem to be just the trick.

I dont understand why right thrust would make a difference with the plane inverted as opposed to upright. The thrust is being changed horizontally not vertically.

Adding Right thrust is almost MANDATORY, on most Profiles. It zero's out your up lines and cuts down on your rudder input, so I don't understand why you feel it works against you. Left or Right....Upright or Inverted, a straight line is a straight line.....Right??

Right thrust *does* work the wrong way when you're inverted and with most profiles you're faced with either just learning to apply the appropriate amount of (usually) left rudder when inverted or ditch the right-thrust and learn to apply left/right as appropriate.

Since a really good 3D flight will see the model flying inverted for about half the flight I'm starting to switch to zero side-thrust and just using the rudder all the time. It becomes second-nature after a while.

I like to set the side thrust so I don't need rudder in the hang.

However I learned on a Limbo Dancer that needed lots of rudder input in the hang so can fly the rudder stick without having to think about it too much.

I suspect that learning on something that needs lots of correctional input might be of benefit in the long run. It is also like banging your head on the wall great when you stop doing it and get something trimmed out.

Hey guys thanks for the input!

Why does it work against you when inverted? Because when inverted and at high alpha angles of attack, the right side of the prop circle is still getting more bite or pitch as compared to the left side of the prop arc and STILL wanting to pull the plane to your left just as upright.... only NOW (if you installed right thrust) being inverted the right thrust has become left thrust and the plane is also being pulled to the left. A double whammy when inverted and you've shot yourself in the foot. Ouch!

Edit: ... try it for yourself ... pay attention to all the fightin' you have to do to maintain an inverted harrier with right thrust, then remove the right thrust and see how much more enjoyable it is.

Thanks,

Ernie

DUDE.........there ain't no fighting the Hover....I FLY A MOJO!!!

I've become used to adding rudder when doing inverted harriers, but I still think left KE suffers with right thrust.

When inverted, right thrust becomes....... left thrust! (but the prop is still spinning the same direction)

Ernie

I hate to dissappoint you guys but you are not correct with regards to right thrust. Contrary to popular opinions around the RC forums right thrust is not required for engine torque or even P-factor.....which most folks do not fully understand. The only reason you need right thrust is due to the spiralling slipstream caused by the rotating propeller. Becuase most a/c have the vertical stab and rudder above the fuselage versus below, right thrust is required to compensate for more air pressure on the left side of the vertical than the right side. Many factors do come into play like airspeed and prop rpm, as well as angle of attack. Upright or inverted makes no difference whatsoever. There is no perfect solution other than to learn to compensate with the rudder yourself at different speeds and attitudes. 2 1/2 degrees of right thrust is a very good compromise for most prop job planes.

Here is a fantastic article written on P-factor, slipstream, and engine torque. There will be a quiz this Friday! haha

http://www.qmfc.org/school/asym.htm

So what's your suggestion for the OMP 92" hybrid. I did not include right thrust when installing the motor mount. Should I plan on adding washers under the motor mounts or leave it the way it is.

You can certainly add the right thrust with washers under the left side mounts or the more elegant way is to program right rudder with throttle. The more experienced pattern flyers will do this and tailor the curve to the aircraft and setup.

I'm not an experienced pattern flyer, but this is exactly what I started doing about 6 months ago. Took out right-thrust and programmed in a rudder mix. It makes mounting the engine a bit easier and helps prevent (or at least minimize) the crushed-wood syndrome caused by the washers. After a little tweaking of the mix, I can't tell any difference in how the plane responds compared to the when it had right-thrust.

Eric, do you have the mix set up so that it kicks in at higher throttle settings, or?

Thanks,

Ernie

>>> Upright or inverted makes no difference whatsoever. >>>

A question for AFSalmon..... first, thanks for your experienced input and the link.

Now when inverted the vertical fin and rudder are hanging down below as you mentioned, but the propwash that causes pull to the left wouldn't exist anymore would it?

So if you had some right thrust built in for upright, wouldn't inverted be better off without it?

Thanks loads,

Ernie

Sorry Ernie, I guess I could have been a bit more specific, eh? Yes, rudder is slaved to throttle, the more noise the engine makes, the more right rudder is applied.

Erik


Sorry

Hi Erik, thanks for the reply. What's your opinion of the right rudder kicking in when inverted ... any issues at all? Still have your Reactor? I still have mine!

Thanks,

Ernie

That's a good question Ernie. My thumbs aren't really good enough to notice a difference when inverted. I tend to just give it what it needs without really thinking about it. It's possible I'm fighting it more than necessary, but as long as the beast flies, I'm happy.

And yes, I still have the Reactor. It's been out to the field exactly one time this season. I like it, but have gotten addicted to profiles. In fact, I'm thinking about pulling the YS 63 out of the Reactor for another profile. Between my MoJo 60 and Sabre 56, I think I've burn about 12 gallons of fuel so far this year. The might be a drop in the bucket for some, but it's a ton of flying for me.

Ernie, good question but the forces are still the same. Take a look at the spiralling slipstream and just imaging the picture upside down. The vertical fin still sees the same forces regardless of the orientation of the aircraft. The thing that makes this all difficult for us pilots is the fact that so many factors are constantly changing these forces. In straight and level flight all the forces are at equilibrium. Now when we go into high alpha manuevers we now have all kinds of blanking from the wings through the back of the fuselage and tail. This all plays big on the spiralling air and things change. There is no perfect solution like I said and you just need to learn to compensate. Hope this helps Ernie!

I think I will leave the right thrust out and just learn to use the rudder. I don't plan to do much straight and level flight.

I once heard Chip Hyde had a 13 point mix curve for his throttle and rudder on his pattern planes. Having the engine thrust line straight provides for more axial rolls. Still, this takes a lot of trial an error to get it right.

As is often the case with aerodynamics there is no definite answer. Especially not when it comes to compromise solutions such as adjustments of the engine thrust line.
I make decisions about the thrust line only after flying the aircraft several times. If I find that I have to apply right rudder more often than not in different maneuvers I add some right thrust to the engine. For me the correct amount of right thrust is what minimizes the need for right rudder corrections during a typical flight of the aircraft. Typically I seem to end up with 1-2 degrees of right thrust for my 3D aircraft (.40-1.2 cu.in. size).

>>> Ernie, good question but the forces are still the same. Take a look at the spiralling slipstream and just imaging the picture upside down. The vertical fin still sees the same forces regardless of the orientation of the aircraft >>>

Hi Mike, stay with me here and thank you for your patience. I really want to get this! Okay so when inverted the propwash hits the vertical fin in the same way as it does or has the same effect as it does when upright. Right? And that yaws the plane making it want to turn left once again. However our right thrust that we've installed is not the same when inverted, it becomes left thrust. Correct? So why would we want left thrust (or left rudder) when inverted, especially if the propwash is still making it yaw left?

Thanks again,

Ernie

nothing changes when the plane is upside down !.. except gravity, it's pulling toward the canopy but gravity is not the issue here.


an easy way to think about this is with a simple nut and bolt !
no matter what the orientation of the bolt, it's always righty-tighty