Engine up and down thrust  
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Engine up and down thrust - 1/6/2008 2:38:41 PM   
hulio516


 

Posts: 47
Joined: 12/30/2007
From: toledo, OH, USA
Status: offline 		my plane needs down trim from the neutral position on the elevator to fly level. Does it have too much up thrust or down thrust on the engine?

hulio
       Post #: 1

RE: Engine up and down thrust - 1/6/2008 3:25:42 PM   
DavidAgar



Posts: 2829
Joined: 12/5/2001
From: Battle Ground, WA, USA
Status: offline 		Your problem may not be the engine. It could be the the wing incidence or the stabalizer is not mounted correctly. As for the engine, it could be mounted with some up in it, which would cause the plane to climb. You might want to get an incidence meter and check everything. If you are only dialing in a little down trim, you may just want to not worry about it and fly. Good Luck, Dave


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If the screw ain't loose then things ain't normal.

Dave Agar
AMA#97144

(in reply to hulio516)
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RE: Engine up and down thrust - 1/6/2008 3:32:42 PM   
safeTwire


 

Posts: 171
Joined: 3/3/2003
From: Rye Brook, NY, USA
Status: offline 		Is the CG (Center of Gravity) within the suggested range?

Check it with the plane fully equipped, ready to go...EXCEPT...no fuel/tank empty.

(in reply to DavidAgar)
       Post #: 3

RE: Engine up and down thrust - 1/6/2008 3:51:40 PM   
rwright142



Posts: 1785
Joined: 9/2/2004
From: Beech Grove, IN, USA
Status: offline 		What plane is this?
Many kits, ARFs, etc have the correct thrust angle already built into the design so as the others have mentioned it may not be the engine.

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In the works: 1/6 Scale F4U Corsair

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RE: Engine up and down thrust - 1/6/2008 4:32:00 PM   
hulio516


 

Posts: 47
Joined: 12/30/2007
From: toledo, OH, USA
Status: offline 		CG is in the center of the recommended range.

astro hog

if everything is correct except for the engine up or down thrust and the engine has up thrust in it, will that make a plane climb or decend is what I really want to know.

hulio

(in reply to rwright142)
       Post #: 5

RE: Engine up and down thrust - 1/6/2008 4:36:03 PM   
hulio516


 

Posts: 47
Joined: 12/30/2007
From: toledo, OH, USA
Status: offline
quote:

ORIGINAL: DavidAgar

Your problem may not be the engine. It could be the the wing incidence or the stabalizer is not mounted correctly. As for the engine, it could be mounted with some up in it, which would cause the plane to climb. You might want to get an incidence meter and check everything. If you are only dialing in a little down trim, you may just want to not worry about it and fly. Good Luck, Dave


thats where i am confused....i thought someone once told me that an engine with upthrust in it will make it decend, not climb.

sure wish i knew!

hulio

(in reply to DavidAgar)
       Post #: 6

RE: Engine up and down thrust - 1/6/2008 4:49:34 PM   
DavidAgar



Posts: 2829
Joined: 12/5/2001
From: Battle Ground, WA, USA
Status: offline 		With up in it, it should climb. Dave


_____________________________

If the screw ain't loose then things ain't normal.

Dave Agar
AMA#97144

(in reply to hulio516)
       Post #: 7

RE: Engine up and down thrust - 1/6/2008 5:05:00 PM   
Stickbuilder



Posts: 5404
Joined: 11/20/2005
From: leesburg, FL, USA
Status: online 		If the model has a flat bottom wing, then it will climb under throttle even if you have added down thrust. If the wingplan is symmetrical or semi-symmetrical, it won't do this. If you have a laminar flow airfoil (only Pica used this on their P-51) all bets are off.

I use no down or right thrust on my planes. I use the flight controls, and throttle management to fly the plane, not let the plane fly itself.

Bill, AMA 4720
WACO Brotherhood #1

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RE: Engine up and down thrust - 1/6/2008 5:18:49 PM   
hulio516


 

Posts: 47
Joined: 12/30/2007
From: toledo, OH, USA
Status: offline 		I figured if i kept it the way it is with the elevator being down about 1/4 inch from the neutral position, in flight, what it is actually doing is putting a load or stress on my elevator servo.

right or wrong?

hulio

(in reply to Stickbuilder)
       Post #: 9

RE: Engine up and down thrust - 1/6/2008 5:27:45 PM   
safeTwire


 

Posts: 171
Joined: 3/3/2003
From: Rye Brook, NY, USA
Status: offline 		Upthrust will make an airplane climb.

Things to consider:

If the airplane's design calls for zero thrust or possibly down thrust, and your plane has up thrust, when we say "the airplane will climb", this "climb" will be fairly drastic whenever full power is applied. Almost like you are beginning to perform a loop.

What thrust does your airplane call for? This is important to know.

Most planes, after properly constructed and trimmed for straight and level flight, will actually climb slightly when you are making a full speed pass. We are talking a very shallow climb here, perhaps only several feet higher in altitude over the entire length of the field. This is normal.

Pattern aircraft, scale, and other special designs can act in different ways also.

I am no expert for sure. This is just what I have found out from sport flying.

Quick basic check:
( The plans will identify if the horizontal stabilizer has any positive or negative incidence, or degrees tilted up or down in respect to the centerline of the fuselage )

With incidence, if any, factored in:

Level your horizontal stabilizer using a small bubble level. Then place the level against your engines mounting flange. What you see...is what it is!

(in reply to hulio516)
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RE: Engine up and down thrust - 1/6/2008 6:55:03 PM   
clouddancer



Posts: 120
Joined: 5/23/2006
From: Salina, KS, USA
Status: offline 		Sure sounds a little tail heavy to me. 1/4 inch of down trim is quite a bit.
Try moving any movable weight such as receiver battery, forward and see if it improves.

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(What goes up must come down)
The landing is up to you

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RE: Engine up and down thrust - 1/7/2008 3:57:15 AM   
hulio516


 

Posts: 47
Joined: 12/30/2007
From: toledo, OH, USA
Status: offline 		upon further inspection the +2 1/2 degress incidence in the wing and +1 1/2 degrees in the stabilizer are correct. the plane calls for 0 degrees on both engine thrust angles. I think I found the problem. it has about 1 inch of up thrust in it. well, the top of the prop is about 1/2 inch back from 0 degrees and the bottom is about 1/2 inch forward of 0 degrees. i guess i forgot to add washers when i changed the engine on it last.

i'll take it off and set it at zero degrees thrust angle. that should do the trick

the CG is in the middle of the recommended range

thanks for all the help everyone

hulio

< Message edited by hulio516 -- 1/7/2008 3:58:46 AM >

(in reply to clouddancer)
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RE: Engine up and down thrust - 1/7/2008 10:59:15 PM   
safeTwire


 

Posts: 171
Joined: 3/3/2003
From: Rye Brook, NY, USA
Status: offline 		Good to hear that Hulio!

Let us know how you made out.

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RE: Engine up and down thrust - 1/8/2008 11:58:15 AM   
ED STEFAN


 

Posts: 1262
Joined: 11/12/2002
From: BONAIRE, GA, USA
Status: offline
quote:

ORIGINAL: hulio516




thats where i am confused....i thought someone once told me that an engine with upthrust in it will make it decend, not climb.

sure wish i knew!

hulio



The only time this comes into play is when you're checking engine thrust while flying. To do this, you fly WOT in a straight line and then cut throttle to idle and watch if the plane goes up, or down.

If the plane goes down at idle, you have too much up thrust, and vs. if the plane goes up at idle, you have too much down thrust.

This may sound backwards to a lot of folks but what is happening is the engine is the main factor at WOT and the plane has a little up or down trimmed into the elevator to allow for level flight. Once the engine goes to idle, the main control factor shifts to the elevator for flight characteristics. (up and down) If down trim was used to compensate for too much up thrust, you'll see the plane descend at idle due to this down trim. The reverse is true for up trim at WOT.


_____________________________

ED -- AMA 20464 -- A plane is 1000+ different parts all flying in very close formation.

(in reply to hulio516)
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RE: Engine up and down thrust - 6/26/2008 7:22:37 PM   
Garthwood


 

Posts: 472
Joined: 5/2/2003
From: mississauga, ON, CANADA
Status: offline 		Hello Stefan........................came across this thread from doing research. I have a Seagull Harrier 46, a nightmare of a plane.
CG recommendation is between 140mm-150mm, I'm mid way 145mm. Climbs when throttle is increased, when throttle is reduced it almost hovers if wind is about 20kmh. down elevator is almost constant. I have not checked the wing and stab incidence. This is an ARF. On another thread, someone said that ARFs hardly have their incidence incorrect. But I'm not betting on that.

I was planning to add some downthrust, about 3 degs.. There is probably too much upthrust, if I understand you correctly. Your help is appreciated.

Charles.

(in reply to ED STEFAN)