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mdnanwelch7(at)hotmail.co
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 Posted: Mon Oct 25, 2010 5:56 am Post subject: proper thrustline |
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Thom,
(I changed the subject line to correctly reflect the topic)
One year ago, our fellow comrade John Ratcliffe and I had several private messages
regarding his wing's incidences on his MkIII Xtra. John drew up a nice computer generated
stick figure Xtra with ALL the appropriate digital angles that the Xtra is supposed to have.
(tailfeathers, boomtube, motor mount, etc)
One thing he and I were NOT completely sure of is; if you rotate that stick drawing for
say...the tailfeathers to be zero degrees, this will give you a certain new reading for the
rest of the planes angles.
Now, what if you rotate that stick figure instead from the main wing's as you pivot point,
to where the main wings incidence is now zero? Will that give you an exact change in the
[i]tailfeather's incidence as you got with the main wings?[/i] I am NOT sure.
What I'm getting at is that it MAY not be as simple as adding or subtracting one angle setting
from another by simple mathematics. Frankly, I'd need proof that by simply rotating the airplane
from the wheels as a pivot point that ALL other angles change in an equal amount compared to
if you rotated the plane by the main wings.
Between John and I, we never really did figure out if it mattered. Maybe it doesn't matter whether
you pivot the plane by the wheels, or the tail, or the main wings (to get all the different incidence
readings).
What I'm getting at is unless I saw for my own eyes that by simple addition and subtraction
you could figure out one reading compared to another, I would have to physically reposition
the plane, and take a reading, before I'd accept that that were true! Maybe it's just me, but I
want proof!!
Your example of;
Tail Boom = 5 degrees (front higher)
Horizontal Stabilizer = 5 deg. (front higher) parallel to boom
Wing Bottom = 12 degrees
Engine Thrust Line = 15.5 degrees
Therefore, relative to the Horizontal Stabilizer....
Wing Bottom has a 7 degrees incidence (12 - 5)
Engine Thrust line has 10.5 degrees incidence (15.5 -5)
Unless I saw this was the case, I wouldn't automatically and necessarily believe it.
One thing I can guarantee I'd do, if it were me, I'd go with the factory recommendations on
how to set up your planes angles. On the MkIII, you set the motor mount to zero, and all other
angles go from there. I imagine the SlingShot does too.
After all, unless you first establish that the motor mount is zero, and then take all your reading,
for all you know, maybe the engine thrust line is correct and the main wing's incidence is wrong!
The photos supplied by Chris show his plane in the initial factory recommended position, where
all other incidences are to be set. I'd do that first, and then determine where to proceed. (You
probably were going to do this anyway)
I could be completely in the dark on this, but that's how I see it. ( you appear to have a digital
level) I also wouldn't change a thin washer without taking precise (!!) readings of where
everything is at the moment!!
This is a good topic, with lots of experiences pilots weighing in. Proper Kolb flying surface settings
are always an important topic for me.
Mike Welch
MkIIICX
[quote][b]
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Mon Oct 25, 2010 8:13 am Post subject: proper thrustline |
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Mike W/Gang:
I agree with the statement below, build the Kolb according to plans and instructions. Test fly it, get some hours on it, get the feel of the airplane, then make minute changes. However, make one change at a time, then test fly to verify what you changed.
Many of you all are building Kolbs, have never flown one, and, for sure, have never flown the airplane you are building. Making a lot of changes based on what someone else did to their airplane, especially another model Kolb, is not wise, in my humble opinion.
You will not know how your particular Kolb will fly until you fly it. However, if built to plans, it will fly well. Maybe need a tiny bit of tweaking, but not much to please the builder/pilot.
When experimenting with angles of thrust, don't forget the attitude of the engine on the ground, with the engine stopped, will not be the same as the angle of thrust when the engine is flying at and producing cruise power. Depending on the engine, Rotax two or four stroke, or other engines, the prop will be turning either clockwise or counter clockwise. The thrust will cause the rear of the engine to rise and depress the front of the engine, more left front or right front, depending on which way the prop turns. Depending on the desity of the Lord Mount (on a standard Kolb configured engine mount) the change in angle of thrust will be significant. If you doubt me, then tie down your Kolb, while observing the engine, go to full power and watch the engine change position on the mounts as you change power settings.
Recommend you insure you have the most dense Lord Mounts on your airplane no matter what engine you are flying with.
Take care,
john h
mkIII
Rock House, Oregon
[quote] One thing I can guarantee I'd do, if it were me, I'd go with the factory recommendations on
how to set up your planes angles.
Mike Welch
[b]
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_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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