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phcpilot
Joined: 24 May 2016
Posts: 16
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 Posted: Tue Oct 05, 2021 3:20 am Post subject: thrustline |
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Re:: 10:48:03 PM PST USSubject: Re: Reducing power on take off versus thrust line.From: "chic" <gcechini(at)msn.com (gcechini(at)msn.com)>Okay, so I am a little confused here..... If I raise (just) the rear of the engineon my Firestar 2 for more prop clearance off the boom tube, am I adding positivelyor negatively to the thrust
Raising just the back motor mount so that the thrustline points lower at the front is down thrust which results in an in flight nose up force..
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Richard Pike
Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee
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| Posted: Tue Oct 05, 2021 6:48 am Post subject: Re: thrustline |
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Correct.
Don't know what you call it, but picture progressively lowering the rear motor mount (pretend that prop length is not a problem) and you can see that eventually your thrust line is going to want to make the airplane just do outside loops. Obvious exaggeration, but you get the idea.
When I went from a 68" prop to a 72" prop, I had to raise the engine to get prop clearance, and also ended up adding two extra washers under the rear motor mounts, working on trim. So the rear of the engine is now about 1/8" higher than the front. But subject to change.
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_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0
Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing. |
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neilsenrm(at)gmail.com
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| Posted: Tue Oct 05, 2021 7:56 am Post subject: thrustline |
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I am concerned people might not understand the negative impact of using thrust to counter power induced pitch changes.
First, your effective thrust will be reduced. The impact is related to total thrust and the amount of change of thrust line.
Second, the down thrust needs to be countered by increasing the angle of attack of the wings which adds drag and increased stall speed.
What is the total impact? Really hard to say but just grabbing an unrealistic number out of the air does a disservice to our readers. There have been a lot of smart people designing and building Kolb airplanes for a lot of years. If it was beneficial and that easy everyone would be flying our planes that way from the very start.
Rick Neilsen
Redrive VW Powered MKIIIC
On Tue, Oct 5, 2021 at 7:22 AM Peter Cowan <cowan.phc(at)gmail.com (cowan.phc(at)gmail.com)> wrote:
| Quote: | Re:: 10:48:03 PM PST USSubject: Kolb-List: Re: Reducing power on take off versus thrust line.From: "chic" <gcechini(at)msn.com (gcechini(at)msn.com)>Okay, so I am a little confused here..... If I raise (just) the rear of the engineon my Firestar 2 for more prop clearance off the boom tube, am I adding positivelyor negatively to the thrust
Raising just the back motor mount so that the thrustline points lower at the front is down thrust which results in an in flight nose up force..
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