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incidence/thrust line/engine offset - 1/5/2013 3:08 AM   
Leroy Gardner


 

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From: Coeurd'''''''''''''''''''''''''''''''' ALENE,
Status: offline 		On my latest bash build, Tiger 60, I raised the thrust line 1" to accommodate the instlation of a DLE 20cc engine, I also raised the wing 3/4" and kept the incidence at O as well as the horizonal stablizer at 0. engine is mounted with 2 degrees down and right as per plan. when you make these kinds of changes is it nessessary to change engine off set because of the difference in the thrust and air movement in comparison to the reccommended engine size of .60 to.91 ? Also should changing the thrust line have any adverse effects in the control of the plane.

I hope I asked that in the right way, thank you, Leroy

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Eagle 2'' bashed Tiger 60

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RE: incidence/thrust line/engine offset - 1/5/2013 12:02 PM   
AA5BY


 

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Status: offline 		The simple answer would be that everything has an affect. Predicting your changes to better or hinder flight is tough. The simple truth is that most times we don't know until after the experiment. Even so, we each have such varied desires that what might please you the most, won't me.

It's fun and interesting to bash... tell us the outcome for better or worse.




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RE: incidence/thrust line/engine offset - 1/5/2013 1:40 PM   
charlie111


 

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Status: offline 		Back in the days of my control line Flying.We used to use right  Rudder and or shim the Engine.To keep Tension on the Lines while doing Wingovers and loops.Theres a Fine Line Between Tension and Drag.R/C does not need this. You still need right rudder But only for takeoff and recovering from a stall.When Engine is Throttled up? I have flown both Full size aircraft and Models.And that was my experience! Hope it helped some? Checkout my Electric Rotowing charlie111 I'm planning on Building a Full Size version that a Small Electric could be Driven into.Something like a Bird cage comb. Roll Bar.The unit would then use the Auto's power supply and be flown by Wire from inside the Vehicle.I would imagine you could get by with a Map,Tom Tom,Altimeter and Airspped to Navigate. And more Practical than trying to fold up wings the size of Glider and the control surfaces.I have a Bad Neck that limits my upper body strength.The Concept works it has been proven.There is a video of a self rotating wing that had no wings.Just 2 squares of paper and balsa I think.And that actually Flew with electric motors turning props at the wingtips.I wish I knew how to get it? Good Luck!

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RE: incidence/thrust line/engine offset - 1/5/2013 6:04 PM   
speedracerntrixie


 

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Status: offline 		Leroy, I doubt that you will notice any difference. I'm not all that familliar with the Tiger but due to it having some down thrust I am going to assume it has a semi-symmetrical airfoil. If it was symmetrical I would question the need for downthrust.


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RE: incidence/thrust line/engine offset - 1/5/2013 7:05 PM   
Leroy Gardner


 

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From: Coeurd'''''''''''''''''''''''''''''''' ALENE,
Status: offline 		Yes bashing is fun, it's the gray areas that raise the questions and the lack of aerodynamics knowledge and thats where you guys come in. It's a been there, done that road I'm yet to travel. Trying to get assurances is a comfort when it comes to what I have done.

Good to have your experiences in the areas I lack and I am learning a thing or two here. In asking the question it may also help others get there answers too.

Thanks alot, Leroy

< Message edited by da Rock -- 1/9/2013 10:36 PM >

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RE: incidence/thrust line/engine offset - 1/14/2013 4:36 PM   
dksnyder


 

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From: s. windsor, CT, USA
Status: offline 		I am assembling an Oasis electric pattern-type plane (from Value Hobby)
The firewall is tapered to provide some right thrust, but I don't measure and right thrust when the
motor is mounted. I think the factory assembly is sloppy and the firewall is out of alignment.

What is a "normal" amount of right thrust?
I installed shims to provide 2 deg, but this "looks" excessive....

This is a 3 1/2 lb electric, not in the F3A size class.... but I expect the thrust line adjustments
may be similar.

I will do final adjustment after first flights, but the right thrust does affect how the cowl is installed.
I would like to be close when I install the cowl....

Thanks for any help

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RE: incidence/thrust line/engine offset - 1/20/2013 6:51 AM   
Leroy Gardner


 

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From: Coeurd'''''''''''''''''''''''''''''''' ALENE,
Status: offline
quote:

ORIGINAL: speedracerntrixie

Leroy, I doubt that you will notice any difference. I'm not all that familliar with the Tiger but due to it having some down thrust I am going to assume it has a semi-symmetrical airfoil. If it was symmetrical I would question the need for downthrust.



Down and right engine off sets, what determines the # of degrees in the first place. I'm going to check again, I think the wing is said to have a symmetrical shape and the plans show a 2 degree down thrust and the same for right thrust. If you change one or the other a degree what are the effects going to be ? I would like to better understand these things should I decide to design and scratch build a plane possibly taking info. from other planes. I have collected alot of info. but have nothing on thrusts.

Thanks, Leroy

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RE: incidence/thrust line/engine offset - 1/20/2013 11:12 AM   
da Rock



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quote:

ORIGINAL: dksnyder

I am assembling an Oasis electric pattern-type plane (from Value Hobby)
The firewall is tapered to provide some right thrust, but I don't measure and right thrust when the
motor is mounted. I think the factory assembly is sloppy and the firewall is out of alignment.

What is a ''normal'' amount of right thrust?
I installed shims to provide 2 deg, but this ''looks'' excessive....

This is a 3 1/2 lb electric, not in the F3A size class.... but I expect the thrust line adjustments
may be similar.

I will do final adjustment after first flights, but the right thrust does affect how the cowl is installed.
I would like to be close when I install the cowl....

Thanks for any help


Cowled models that have down or right thrust place the engine mount so that the drive shaft is centered just beyond the cowl where it exits.

There isn't a certain amount of thrust that's used. Why? Things like wing position for example affect how much is needed. Designers usually guess whether or not they need it and how much to try on their prototype model. Fly and adjust, then decide what to put on the production models.

2 degrees right is a good start.

Cowls should be straight on a model, btw. If you're wanting right thrust, placing the rear of the motor mount to the left makes that easier. Down thrust? Place the rear higher on the firewall. Drawing centerlines on the firewall help. You'll notice that some motor mounts have marks on their base showing where their centerlines are just for this placement.

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RE: incidence/thrust line/engine offset - 1/20/2013 7:21 PM   
BMatthews



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Status: offline 		dksnyder, if you think the angle looks excessive double check it by measuring from the fuselage center line at the tail to the tips of the prop with the prop level. With a bit of trigonometry, drawing the triangle in CAD or some other method you should be able to double check the angle.

In the end we set our thrust lines to what we think is needed. But nothing stops us from shimming in a little more or a little less depending on what the model does in flight. So try the model as it comes and if the model seems to roll or pull too strongly to the right then try shims to remove some of the side thrust.

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RE: incidence/thrust line/engine offset - 1/21/2013 4:59 AM   
Leroy Gardner


 

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From: Coeurd'''''''''''''''''''''''''''''''' ALENE,
Status: offline 		From what you all say thrust angles are guess work, 2 degrees is a good start and adjust by shimming if it reacts a certain way., does that apply to a symmetrical wing foil on a low wing plane, why would that negate down thrust if in fact it does ?

Leroy

< Message edited by Leroy Gardner -- 1/21/2013 5:45 PM >

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Eagle 2'' bashed Tiger 60

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RE: incidence/thrust line/engine offset - 1/31/2013 8:52 AM   
David Bathe



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From: Oslo, NORWAY
Status: online 		Leroy, I've been looking at your Tiger Bash... looks like it's going well.

By raising your engine and wing, what you've done is effectively lower the stab!
Which in th case of the Tiger, may not be a bad thing.
Regarding the thrust angles (2deg down and right)...
you may have over cooked the down thurst alittle and underestimated the right thrust. You'll just have to see.
Just build in the possiblity to adjust the engine mount/firewall for an extra 1deg right/minus 1deg down now while it's on the board.

Regarding the "why down trust " conversation.
An areofoil (yes even a symetrical one) requires possitive incidence to create lift. Not much, but some.
Even if you set up an aircraft at the mythical 0-0-0 setting on the bench... the moment you get airborn you'll have to at some up trim to maintain level flight.
This lowers the stab, put's  the wing at the positive angle hat it needs.
What it all so does it is put a positive angle on the stab and engine... which isn't necessarily what you want.
What they end up flying isn't a 0-0-0 model, it's a say  "+0.5 - +1 - +1.5 configuration... if you understand what I mean.

If you set the wing at 0... knowing it will be +1 when flying... you'll set the engine at -1deg down thrust to compensate.
It's a great deal more complex than that but that the basic idea.

When we set up a pattern model... the wing will be set at +0.5 -1.5 (depending on your CG preference) while on the bench.
The engine would be set a with -0.5 - 1 down thurst and the stab set a 0.
Hope this helps.




< Message edited by David Bathe -- 1/31/2013 9:13 AM >

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RE: incidence/thrust line/engine offset - 2/1/2013 4:50 AM   
Leroy Gardner


 

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From: Coeurd'''''''''''''''''''''''''''''''' ALENE,
Status: offline 		David I think you said to raise down thrust to 1 deg. I think I got something out of that, aerodynamics can be very confuseing to some one thats knows little about it. Thanks for your effort to explain it in a way that I can make some sense of it. Should I leave the side thrust at 2 deg, ?

Leroy

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Eagle 2'' bashed Tiger 60

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