engine thrust angle
 

Hi,
I am trying to check the engine thrust angle on my 90 size pattern ( YS-110FZ )
by measuring the distance from the rudder to both prop tips.

Left = 156.6 mm
Right = 154.8 mm
Prop diameter = 14 inch

do you know how to calculate the angle ? my estimation is that the angle is about 3 degrees

my problem is that i still need right rudder compensation ( 3-4 degrees ) is it make sence that the thrust angle will be greater then 3 degree ? let's say 4 ?

Thanks,

RE: engine thrust angle
 

that is a very small plane for a 110<G>.

RE: engine thrust angle
 

it's Tai Ji 90

175cm x 175cm
8.9lbs

lot of people are using 110 for that size.

RE: engine thrust angle
 

Selnekav,

You will need to take the difference in distance (156.6-154.8) mm = 1.8 mm and convert the 14" prop to mm or 14x25.4 = 355.6 mm. I think there is something wrong in your measurements from the rudder since 156.6 mm is just 6.16". Assuming that your measurements are correct, the formula to calculate the angle is arcsin of 1.8/355.6 or 0.25 degrees. It apperas that you need to increase the right thrust. Check your measurements again and let us know.

Vicente "Vince" Bortone

RE: engine thrust angle
 

I think you have more like 0.29 deg. rather than 3.

Paul

RE: engine thrust angle
 

175 cm = 1750 mm. You need to check your measurements from rudder to prop. I suggest that you use a larger prop. Even better use square aluminum bar that is around 50 cm. Make sure that the prop hole is in the center of the bar. Increasing the prop diameter will make the measurements more accurate.

Vicente "Vince" Bortone

RE: engine thrust angle
 

sorry the measurements are :

Left : 156.6 cm
right : 154.8 cm

RE: engine thrust angle
 

so i guess it should be arcsin 18/355.6 can you tell how to calculate it ?

RE: engine thrust angle
 

asin (156.6 - 154.8) / 14 x 2.54 = asin (1.8 cm / 35.56 cm) = 2.9 degrees. You could mix throttle with right rudder to compensate if you don't want to change the engine.

Vicente "Vince" Bortone

RE: engine thrust angle
 

Thanks, i don't want to use mixer as it cause other problems.
is that make sence that 2.9 degree won't be enough ?

RE: engine thrust angle
 

in addtion is that important that the tip of the engine axis will remain centerlized ? ( i mean every washer that i am adding to the left mount side cause the engine tip axis to move to the right ) do i need to move the engine mount to the left so the engine tip axis will remain centerlized ?

RE: engine thrust angle
 

Yes, you need to move the engine left. Usually I move the engine around 5 mm left to get it centered. Try the mix you will be surprised. You won't noticed other problems since this is small amount (1-3% mix). If you need more than this you will need to adjust the engine.

Vicente "Vince" Bortone

RE: engine thrust angle
 

http://www.rcaerobats.net/trim_chart.htm

This is how Chip Hyde does it.

RE: engine thrust angle
 

Small plane, powerful motor... yeap it makes sense that you'll be needing more than 3deg.
I flew a Hydeout for a couple of years using rudder mix instead of right thrust.
I eventually decided to "F" the mix and build in 3 deg(ish of right thrust. The plane was, in my opinion, revolutionized!
Much happier, less critical and far less fussing about with micro % mixes.
Conclusion, if you ain't as advanced as CH... go the dumb-ass route.

RE: engine thrust angle
 

Thanks for all answers
Is that ok to remain the angle as it is ( 3 degrees ) and add small amount of mix ~1-3% ?
if so do i need to set the mix so it will take affect only from half throttle to idle ( ~ 1-3% linear ) ?

RE: engine thrust angle
 

I didn't understand the following sentence from Chip Hyde trim chart :
"What happens is the fin moves to the opposite side when inverted but the engine and prop don't know it, so the plane starts to yaw really bad due to spiraling slip stream."

is there diffrence how the airplane acting between normal to inverted filght at idle ? i meam of course that if it's normal idle flight then the nose will pull to the right, and if it's inverted then the nose will pull to the left.
but what i have noticed is that when it's inverted the pull to the left is much more significant and i wonder what is the reason of that ?

RE: engine thrust angle
 

in other words is there any diffrence of P-Facor affect between normal and inverted flight ? if P-Factor force is linear to the prop rpm then i whould think using rudder to throttle mix will be much more affective then a constant right thrust angle that will be affective only at high rpm am i missing here something ?

RE: engine thrust angle
 

You got it right. The problem is that you can not do all with mixing. You have to use both and take the advantage of having both to compensate. I think you need to try and let us know how it works for you. It is easier to do the mixing than changing the engine so why not.

Good luck,

Vicente "Vince" Bortone

RE: engine thrust angle
 

P-Factor is a mini effect.

The main effect is caused by the spiralling air stream. ....not at idle throttle though. For the spiralling air stream to be a major problem the model must be in acceleration mode or at least trying to accelerate while another factor (gravity) is keeping it from accelerating. That's why models veer to the left when they are accelerating on ground or when climbing vertically up or turning a corner. When speed is reached, the effect is lessened.

At idle, the spiral stream is much smaller hence the effect is less. One of the main reasons pattern models should always be accelerated slowly

Air moved when the prop is at full rpms has a surprising amount of mass. It's this mass of air that causes the various unwanted effects. Dean Pappas and I have been discussing this phenomenon off and on for a couple years now. Dean wrote a good summary in the latest Model Aviation issue.

Rudder to throttle mix may be effective for some fliers but isn't for everyone....the effect is nonlinear and dependent on model speed. But is easy to do.

Engine offset is still a better solution for many fliers because the result is more linear, dependent on engine thrust rather than model speed. The best solution is to design a model that needs no offsets at all, but that's beyond this discussion. Jet jockeys are laughing!!!

MattK

RE: engine thrust angle
 

Jet jockeys and contra rotating props? Sebastiano Silvestri?

B

RE: engine thrust angle
 

I decided to increase the thrust angle, and it's now 3.8 degree ( before the change it was 2.9 ). i will test it on the comeing days and i hope it will eliminate the need of any rudder trim above of 75% throttle. i hope i won't need to set it someware between 3.8 to 2.9 .....

RE: engine thrust angle
 

Hi All,
Aftre testing it with 3.8 degree it still need right rudder trim to fly straight on the uplines !!!!!
also i didn't notice any real change between 2.8 to 3.9 ! is that make sence ?

Thanks Shlomo.

RE: engine thrust angle
 

... while you're experimenting, you should remember that right thrust is prop sensitive.
One thrust angle doesn't suite all props and vise versa.
What prop are you using?

RE: engine thrust angle
 

Hi,
14x8 APC, i am aware of that but anyhow i am using only 14x8.
i think i will return to the 2.9 degree and add some rudder to throttle mix above ~ 40% throttle

RE: engine thrust angle
 

Hi Shiomo,
it sounds really strange to me that you don't notice any benefit from this amount of right thrust...

How are you evaluating it?

IMHO you should not check if the rudder is aligned or a bit off, this may be due to other factors. I would first trim the rudder in a straight and level flight and be sure that the plane is flying straight. Then check your verticals.

RE: engine thrust angle
 

1) I realise that there is no such diffrece between 2.9 to 3.8 degree since i was needed the same right rudder trim on uplines.
2) The plan dosen't fly straight and level without right rudder trim. it pulls to the left.

any ideas ?

RE: engine thrust angle
 

So the problem here is not right thrust IMHO. As I said previously, I would FIRST trim it in straight and level flight. Trim in this condition, don't worry about rudder trim left or right - just make sure the plane flies straight in this condition. You may end up with a little bit of trim to fly straight, but if you have to put a large amount of trim this means that the plane is crooked.

Trim the plane with at least half throttle, if you are too slow the trim effect will decrease and the thrust effect will increase.

RE: engine thrust angle
 

with 3 degree of right thrust i will need additional of ~ 5-7 degree of right rudder trim in order to fly straight above half throttle , but i want to eliminate it so the airplane will fly staright on low rpm.

RE: engine thrust angle
 

i am not sure if it's 5-7 degree i need to measure it.. but let's say that it's at least 3-4 degrees.

RE: engine thrust angle
 

Ok, first up that doesn't sound like the correct prop for that engine.
Presuming you're using a decent amount of nitro as normal with YS, I'd guess you'd be needing a 14x10-12.

Next, if you're not trimmed to fly straight and level, it's pointless trimming vertical.
You must find out whats needed to maintain level flight.
On a nice still evening, start observing the plane and see how much rudder trim is needed to keep a straight line.
Fly over your head and straight away from you and just leave the plane to fly, hands off.
Don't touch it for several seconds. Keep doing this... adding a little rudder trim until you can fly from horizon to horizon... in a straight line without any input.
Just because you a have an ARTF doesn't mean it's built straight, in fact quite the opposite.
Use rudder trim, not a mix, to sort this out.
Then, trim for vertical using right thrust.
You won't be needing any rudder throttle mix.

RE: engine thrust angle
 

Hello,
right thrust plays a minor role in this case, it's not your problem.

First you have to trim your plane for hand-off flight. Follow the suggestions that David gave you. Forget right thrust now, if you have your rudder off to keep the plane straight, the plane is crooked - right thrust will not help here.

Do what David suggested you and only after go to the uplines & right thrust.

RE: engine thrust angle
 

Hi,
I am not sure i understand that.

since i need ~4 right rudder trim in order to fly straight is that mean that my airplane crooked ? if so is there way to fix it ?

as i said before i am able to fly straight hands off ( above half throttle ) with about 3-4 degrees of right rudder trim, and also the up lines are straight with the exact rudder trim.

my concern is that i still need ~4 degrees of right rudder trim for the up lines although i already have 3.8 degrees of right thrust !

i thought about the rudder throttle mix for the low throttle position.

about the prop issue i can't get the 9500 rpm with 14x10 that's the reason i am using 14x8 ( we have very hot and high humidity climate here )



thanks,

RE: engine thrust angle
 

Hello,
yes you are understanding correctly.

Ideally the rudder should be centered to perform a straight flight, but no plane is perfect - plus there are many disturbing effects of the propeller and so on.

So a little bit off is normal IMHO, I would not be concerned about that - at least if it is a small amount. I don't think you can fix this, perhaps the fuselage is not 100% straight - but again it can have a minor effect.

So if you have straight lines and uplines you are trimmed your plane IMHO - at least regarding the yaw axis.

Check if the plane flies straight even with low throttle: if so your ok, of not you can fix it with a little of mix as you thought.

Let us know how it goes!

But the po

RE: engine thrust angle
 

Thanks this is very helpful.
I will check that and let you know.

RE: engine thrust angle
 

OK, I understand the prop situation.
Yeap, the plane may not be build quite straight, it's as simple as that.
And believe me it doesn't take much to screw things up.

You've got 3degs(ish) on the engine so that a good start.
Now, Just trim (not mix) the rudder for straight flight, what ever it takes and just leave it there.
Then trim/fine tune the vertical with +&- right thrust.
You should be able to solve the problem.

Starting adding a throttle-rudder mix into the equation is going to confuse the issue even more at this point.
Leave that for a different day.
Just stick to the plain simple/obvious fixes first.

RE: engine thrust angle
 

Have you checked lateral balance? Is the left wing heavy? OR, Is there a warp in the wings?

RE: engine thrust angle
 

Hi,
The wings are balanced, about "warp in the wings" i quiet sure it's ok and if there was some then i guess there was other affect then except of rudder trim issue is that so ?

RE: engine thrust angle
 

Yes, a wing warp and balancing would affect roll axis, not yaw one IMHO.

RE: engine thrust angle
 

Unless the warp was causing significantly more drag on one side.