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Down thrust, Right thrust and Thrust line

 
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Starduster History



Joined: 30 Nov 2006
Posts: 735
Location: St. Helens, Oregon

PostPosted: Wed Mar 12, 2008 1:26 pm    Post subject: Down thrust, Right thrust and Thrust line Reply with quote

Down thrust ,Right thrust and thrust line on the Starduster Too

I just had a private message asking about these items re: the installation of an O-540 on the Starduster Too, and thought it would be of some interest to the current members on this board .As it also brings up some other questions. So please feel free to make additional comments that may be useful or helpful to a new builder.
The down thrust and right thrust of 1 1/2 degrees makes for a well behaved airplane on the ground and in the air, as this is what we did with my son Dans airplane. We also used the thrust line of 6" below the upper longeron (these are the specs that Lou Stolp recommended on the original engine mount drawings) and seem to work just as well with the big engine as it does with the four cylinder lycoming ,as my son Dans airplane has the IO-540-G1B5 290 HP Lycoming. Most engine mounts that are built today have no down or right thrust and are zero zero especially if they are to be used for( other than) basic aerobatics. Furthermore a zero zero mount is much easier to build. The down side of the bigger engine is a lower "G" rating which would require a new limit load factor to be calculated unless the airplane was built from the get go as an aerobatic mount and paying close attention to weight. I might remind all of you that the Starduster Too was designed as a week end sport biplane and was never intended for anything other than mild aerobatics it is however a 6 G airplane plus or minus but that is at a GW of 1704# it does not take a rocket scientist to determine very quickly that with anything other than fuel in the main tank two 170# pilots with chutes and nothing else in the airplane it could easily be more than the 1704#, and furthermore another 100# or more with the six cylinder engine and a C/S prop could further reduce the "G" load rating to 5 Gs or less. One other thing to consider is horizontal stabilizer incidence, what should it be set at with the four cylinder, or the six cylinder engine? So whats your opinion or experience with all these factors Dave
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Dave Baxter
Starduster History
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Alan Williams



Joined: 04 Dec 2005
Posts: 444
Location: Chipley, FL

PostPosted: Wed Mar 12, 2008 6:03 pm    Post subject: Reply with quote

I'm not an engineer but it seems that stabilizer incidence can be set so that at your normal (what ever that is) weight and c/g location that the elevator will be neutral at normal cruise flight. I'm sure this would be a trial and error process and of course the leading edge must be adjustable with shims. I've never done this as my birds have been close enough not to fool with it (I've adopted projects and have never built one, a disclaimer).
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cmeek



Joined: 09 Nov 2005
Posts: 114
Location: Aurora, CO

PostPosted: Fri Mar 14, 2008 9:48 pm    Post subject: Reply with quote

Dave,

Do you happen to know the thrust line information for the Acroduster? I have never seen this anywhere.

Thanks
Cam
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Cam Meek
www.acroduster.net
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Starduster History



Joined: 30 Nov 2006
Posts: 735
Location: St. Helens, Oregon

PostPosted: Sat Mar 15, 2008 6:08 pm    Post subject: Thrust Line SA-750 Reply with quote

Cam When I was building engine mounts while working for starduster I never really tried to figure out the thrust line as we built the mounts for either engine using the correct fixture. However several years ago I was involved with an acroduster too that had been powered with the IO-360 Lyc and the new owner wanted to put the IO-540 on ,we like you tried to come up with some published numbers but were unable to do so. But during my search, looking at an existing 540 powered acro too and using the original four cylinder engine mount. With it mounted on my fixture the number I came up with was about 2 1/4 " below the upper longeron C/L. Keep in mind that the angle valve cylinders stick up several inches higher than do the parallel valve cylinders which can make building the engine nose cowl and doors quite a pain. Furthermore with the 540 installation the engine has to go as high and as far back as possible for C/G issues and still be able to remove the mags. It is further my understanding that on several 540 powered acro toos the upper wing has been moved several inches farther forward. this has been my experience for what ever its worth Dave
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