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Engine offset Telemaster Senior

Old 01-01-2015, 10:13 PM
  #1  
mikeweber3
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Default Engine offset Telemaster Senior

Hello

I'm converting an old Telemaster Senior to electric


Does anyone know how much engine offset I should use?.

Thanks

Mike
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Old 01-01-2015, 10:25 PM
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rcers
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Three down and two degrees right IIRC.
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Old 01-01-2015, 10:27 PM
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mikeweber3
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Thanks

That was quick

Mike
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Old 01-16-2015, 06:06 PM
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AEAJR
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How did this workout for you? Have you flown it?
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Old 01-16-2015, 07:02 PM
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mikeweber3
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Not yet, probably about a month away, as I have a long vacation coming soon. I'll try to post my results.

Thanks

Mike
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Old 01-16-2015, 08:00 PM
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solentlife
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Most general models end up with ~2 down, ~2 right .... and its' a good place to start.

It can always be adjusted by washers or thin card later. I also use prop shaft adaptor rings when washers are not enough.

You will at times see comments about High wingers requiring more down than a low winger ... to be honest - not something I've ever noticed .. all low, mid and high have been similar for me. At end of day the down resists the tendency to pitch up with engine thrust / wing incidence ... right resists the left yaw caused by air hitting the left side of fin as it spirals around the model from the prop.

I call it the 2+2 rule ...

Nigel
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Old 01-16-2015, 09:03 PM
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Rodneh
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There is a reason that high wings often need more down thrust. Drag is located higher on a high wing plane than a low wing plane and increases faster as speed increases. This tends to make the plane pitch up speed is increased, down thrust counter acts this.
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Old 01-16-2015, 09:22 PM
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solentlife
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Originally Posted by Rodneh View Post
There is a reason that high wings often need more down thrust. Drag is located higher on a high wing plane than a low wing plane and increases faster as speed increases. This tends to make the plane pitch up speed is increased, down thrust counter acts this.
Actually the bigger factor in this is not whether the wing is high set .. it's the distance the wing is from the CoG and CoE ...

The darg and pitch up due to incidence acts on the fuselage based on its distance to the Centre of Effort and Gravity. The MOMENT arm ...

One factor that can influence in favour of the High wing theory is dihedral. Dihedral will raise the wings effective centre as a compromise of its root and tip levels. A low wing dihedral raises that centre and that means it is within the fuselage ... A high wing with dihedral will raise the effective wings centre more away from the fuselage. THAT is why it can be found a difference.

I suggest it is a general misconception that continues the High wing vs Low wing theory as a general unconditional rule.

Nigel
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Old 01-16-2015, 10:18 PM
  #9  
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And... the "Decalage" (diference in incidence between main wing and horizontal tailplane)

As speed increases that will have more tendency to pitch the plane up if it is not zero. That includes the elevator trim effectively altering the incidence of the tailplane.

Since more power is needed for more speed, having more down thrust can effectively compensate for having more decalage.

There are many factors that come into play to determine how much thrust line offset is desirable. Often the only way to get it right such that for level flight no trim changes are needed for different airspeeds is to experiment.
You'll never get it so that there's no reaction to sudden power changes though...
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Old 01-16-2015, 11:12 PM
  #10  
solentlife
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Also if you have TOO much downthrust with a motor that is often more power than needed .... you get a strong pitch UP moment when you close throttle. Reason is that the down thrust of that powerful motor is compensated by trim / set-up of the model ... remove the thrust component and ZOOM up that nose goes.

My Skyleader Biplane with the 15cc gasoline motor did exactly that ... removed the over powered motor .. fitted the 61 (10cc) and she flew like a dream with exact same incidence / decollage / thrust lines.

Here with the 15cc over-power engine ...



At about the 9:40 mark in the video - you will see the violent pitching up she does when power reduced ....... so violent in fact that I had to 'dump' her out with throttle ON !

Now she's here with the 61 as she flies now ... I just love flying her !!



A completely different machine altogether ... with same CoG / thrust lines etc.

Oh and the thrust line figures are .......... wait for it .............

2 + 2 ....

Nigel
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