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.