Engine Down Thrust

Engine Down Thrust

Post by Dani » Sun, 05 May 2002 04:37:08



Hello friends,

I had trimmed my RCM on mid throttle.
When I am opening the throttle to full power it dives.
Do I have to lower the engine thrust angle or to rase it up?

My common sence tells me that the engine thrust angle
was to high,and therefore a down trimm was required
on mid throttle.
when the throttle is opened to full,
the down trimm takes a larger affect and the RCM gets pitch down
and dive-> the angle must be lowered and a new trim is required.

What do think?
just remmember,the throttle is being opened from mid to high

Thanks
Daniel

 
 
 

Engine Down Thrust

Post by john al » Sun, 05 May 2002 04:43:08



stated...

Quote:
> Hello friends,

> I had trimmed my RCM on mid throttle.
> When I am opening the throttle to full power it dives.
> Do I have to lower the engine thrust angle or to rase it up?

> My common sence tells me that the engine thrust angle
> was to high,and therefore a down trimm was required
> on mid throttle.
> when the throttle is opened to full,
> the down trimm takes a larger affect and the RCM gets pitch down
> and dive-> the angle must be lowered and a new trim is required.

Have you changed the angle of the engine, or wing, or tail, from the
plans? From your description, you are flying with down trim at mid
throttle. It should be slightly up. The symptom you are describing is
that of a tail heavy plane. Where is you balance?

If your balance checks good, I would be more inclined to think the
wing or tail incidence is wrong. It's hard to build the engine in with
that much downthrust (way too much) on that kit. Is it stalling with
the engine at idle?

 
 
 

Engine Down Thrust

Post by Pe Reiver » Sun, 05 May 2002 18:08:01


The down trim is needed, to alter the absolute angle between the wing and
the stabilizer, which is the effective wing incidence. Don't worry about
that too much, You might decrease wing incidence, but it is not absolutely
necessary.
When the plane dives on more power, there are two things to watch for.
1) does it do so immediately, and before the plane speeds up?
2) does it do so <AFTER> the plane speeds up?

case 1): reduce down thrust of the engine
Case 2): your CG is way aft, which also to some extent explains the needed
drooped elevator.

I hope this helps you out

--
P, from Arcen, south-east Netherlands

www.mvvs-nl.com/index.html



Quote:
> Hello friends,

> I had trimmed my RCM on mid throttle.
> When I am opening the throttle to full power it dives.
> Do I have to lower the engine thrust angle or to rase it up?

> My common sence tells me that the engine thrust angle
> was to high,and therefore a down trimm was required
> on mid throttle.
> when the throttle is opened to full,
> the down trimm takes a larger affect and the RCM gets pitch down
> and dive-> the angle must be lowered and a new trim is required.

> What do think?
> just remmember,the throttle is being opened from mid to high

> Thanks
> Daniel

 
 
 

Engine Down Thrust

Post by Mike Slaughte » Mon, 06 May 2002 00:44:18


Take the plane up high, mid throttle and trimmed for level flight.  Increase
speed by diving at a 30 -45 degree angle.  If it tucks under as the speed
increases (throttle still at mid) then it is the trim that is the problem.
If it stays on course, it is the engine.  If it climbs out of the dive, then
it is tail heavy.  This way you can test the response of the plane to speed
increase without increasing the throttle.
Mike

Quote:
> Hello friends,

> I had trimmed my RCM on mid throttle.
> When I am opening the throttle to full power it dives.
> Do I have to lower the engine thrust angle or to rase it up?

> My common sence tells me that the engine thrust angle
> was to high,and therefore a down trimm was required
> on mid throttle.
> when the throttle is opened to full,
> the down trimm takes a larger affect and the RCM gets pitch down
> and dive-> the angle must be lowered and a new trim is required.

> What do think?
> just remmember,the throttle is being opened from mid to high

> Thanks
> Daniel