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Old 10-18-2017, 06:22 PM   #1
Billie
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Default Engine mounts

Hi

I recently bought another Skybolt and after 6 months of paperwork I have finally been allowed to fly it.
One snag though is the engine mount. The engine is an IO360 CIC with a rear throttle body and the mount is exactly as shown in the build newsletter, ie just straight tubes to a Dynafocal ring without any diagonal cross bracing tubes. Also the bottom tubes are not connected as is shown in the latest plans from Steen. Whilst I do have an old set of plans a few pages are missing and one must be the drawing for the mount. It seems that the mount design has been improved / beefed up along the way and this aircraft is from 1990 and must predate that.
I have been told that the setup I have is OK with a fixed pitch prop but not substantial enough for use with a CS prop, which I do plan to add at some point. Could anyone tell me the history of the mount design and what the implications are of the old design?

Thanks

Jason


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Old 10-19-2017, 12:41 AM   #2
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Default mount changes

I have three complete sets of plans. One set is pre 1990 i.e. no Hale Wallace updates, one set is mid 1990's with the HFW updates and one set I purchased in Oct 2016. All three have the exact same mount design. Sorry I don't have something to support your design.

Dale


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Old 10-19-2017, 05:56 AM   #3
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Jason, there are some engine mount drawings and pictures in Skybolt News that Mac McKenzie published. But are similar to the plans, I suspect that the cross brace tube on your mount was deleted because of the rear injector as it probably interfered with the fuel servo? Most engine installations with a rear injector servo require that the mount be modified to accommodate this feature, at least that has been my experience. Dave
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Old 10-20-2017, 12:29 PM   #4
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Thanks for the info. I actually have two Skybolts and neither of them has a mount that looks like the plans!
In the latest Steen plans the bottom most tubes are cranked so that they meet in the middle, just where the throttle body is on the "new" (it's 25 years old) Skybolt and the 4 into 1 exhaust is on the one I have had for 20 years.("old" Skybolt)
The "new" Skybolt mount looks exactly like the drawing and photos in the Skybolt News instructions on how to build the mount.
The "old" Skybolt has the same arrangement but short diagonal cross braces connecting between the tubes at the engine end, much as they are on the latest plans that I have.
There must have been a reason to change from the original instrucyions to the current plans and I am trying to get to the bottom of why.

Thanks
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Old 10-20-2017, 02:27 PM   #5
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Quote:
Originally Posted by Billie View Post
Thanks for the info. I actually have two Skybolts and neither of them has a mount that looks like the plans!
In the latest Steen plans the bottom most tubes are cranked so that they meet in the middle, just where the throttle body is on the "new" (it's 25 years old) Skybolt and the 4 into 1 exhaust is on the one I have had for 20 years.("old" Skybolt)
The "new" Skybolt mount looks exactly like the drawing and photos in the Skybolt News instructions on how to build the mount.
The "old" Skybolt has the same arrangement but short diagonal cross braces connecting between the tubes at the engine end, much as they are on the latest plans that I have.
There must have been a reason to change from the original instrucyions to the current plans and I am trying to get to the bottom of why.

Thanks
Maybe?

Some aircraft plans leave the engine mount out or publish "typical" mount with caveat that many engine accessories will make changes necessary.

Typical homebuilt mount is pretty straight forward. Four points on airframe/four on engine. Usually two tubes will bracket each engine mount position and go back to single point @ the firewall for a total of eight. Do the best you can to miss stuff.

I wonder about the caveat that mount is ok for FP prop and not CS. Probably weight. Same reason for mention on some plans that their "nominal" design with certain tube dia./thickness is good for a certain length mount and no longer. I see some of these 30" or more Starduster mounts and have to wonder, might placard something like,

"No Snap Rolls above 20 MPH IAS"

Or look for an engine with enough power to do a 2 G loop?

Jack
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Old 10-20-2017, 04:57 PM   #6
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One other thing, builders make changes for what ever reason, mostly because they can to improve? Or at least in their minds it is! Sometimes there is a valid reason, and other times it is just wishful thinking? I have seen several things over the yrs, where the question was, "WHY WOULD SOMEONE DO THAT" A builder installed a very expensive Subaru engine conversion in a Starduster Too, it had W&B issues was set up to fly from the front cockpit, and was wrecked during the first several flights, by a test pilot that told me he would not fly the airplane again after it was repaired! And another where the builder installed a 10 Gallon main tank with a C-125 six cylinder Continental! My point is there may be no valid reason? Dave
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Old 10-20-2017, 05:31 PM   #7
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"WHY WOULD SOMEONE DO THAT"

Yup, seen a few of those and one or two on my present airplane. Didn't make it better and probably not worse so WT * do it?

It does make you want to look at the rest of the airplane very closely.
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Old 10-20-2017, 05:39 PM   #8
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Tried to build the mount with the cross bracing per original plans for my Bolt, could not get the oil screen in/out (4 cyl. angle valve). Parallel valves I think have the screen more toward the center.



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