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Thrust Line

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Rockiedog2

Well-Known Member
Joined
Dec 11, 2012
Messages
2,652
We had a short discussion a while back about thrust line. As I recall, we didn't go into much depth about it. I know enough about the effects of offset vs zero offset thrust line to meet my needs...I've set my mounts so the crank is plumb with the long axis on all the mounts I've built(Pitts S1, Legal Eagle, SS1). Offset has always looked to be a compromise that I didn't see any need for in my case. I know Pops builds his mounts to zero as well. Here's an excerpt I was recently reading about cubs and mod to zero offset mount

>>>used this Mod last summer and took thirty percent off his TO roll and gained 6-8 mph cruise. Jerry will be able to elaborate on this a bit. In our other testing in Stock Cubs it also showed a thirty percent reduction in TO roll. This is a short field--dump the flaps--get off the ground TO. One person full fuel. Everyone wants to take off short but this is not why this mod was developed. It was developed for landing. The pilots who have flown this mod in fact generally don't even talk about the TO performance after they have flown. It is the landings that are so impressive that you don't do much talking about the TO. We have 180 hp Penn Yan conversions landing better than J3s. I can tell you that we found out that it has never been the weight up front that that spoils the landings on a cub. It has always been that negative ThrustLine<<<

well 30% reduction in TO roll seems like a lot but maybe so. According to redneck engineering the offset will cause drag and reduced thrust at cruise and maybe the handling/performance mentioned above on landing and TO mostly so we don't have to push on the rudder in the TO and climb. That's what it's for is the way I look at that. Well, I know there's more to it than that so maybe we can talk about our experiences both ways and also our scientists can talk about it.
 
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