Big stik
04-16-2016, 06:09 PM
#1
Big stik
I just bought a very used Great Planes Big Stik.When I checked the firewall to thrust washer distance it is 4 inches. All the old specs I can find say 4 1/4" to 4 3/4". Which is correct and does it make any difference as long as the CG is in the right range?I don't want any surprises on the maiden flight.Also the motor mount is one that has two metal straps to hold in the engine. Specs say 0 degree down and side thrust and this what will be used. I soloed on a Sweet Stick back in 1978 and want to try again.I recovered the plane and fixed some hidden flaws but the motor distance has me worried. Thanks.
04-16-2016, 06:47 PM
#2
You have answered your own question right there. Think Center of Gravity that is what is important. but left out where it balances?? The firewall to thrust washer info is normally important for airplanes with cowlings.
If you have no info one what the 'CG' range should be or the true identity of the airplane may be in doubt then balance at the quarter chord (25%) simply divide the distance from the leading edge to the trailing edge and divide by four, that is the distance back from the leading edge to target for your center of gravity. That is a safe place to start at and can be fine tuned in later flights if desired.
Your are correct most sticks are set up with zero - zero thrust lines. the clamping type engine mount while not my favorite, they can work fine.
John
04-17-2016, 06:15 PM
#4
After looking again at the mount, it will be possible to move the engine ahead about 1/4" so the problem will go away. Thanks for your input. The plane had Great Planes Big Stik decals on it before I recovered it and it was an ARF. All the set-up info is available from the internet including the manual.
04-18-2016, 08:53 PM
#5
After looking again at the mount, it will be possible to move the engine ahead about 1/4" so the problem will go away. Thanks for your input. The plane had Great Planes Big Stik decals on it before I recovered it and it was an ARF. All the set-up info is available from the internet including the manual.
There is quite a bit of force and vibration coming from the engine to the mount... which is fine when the engine and mount are all bolted up, and the mount isn't compromised... but any holes that are unsecured that are between the engine and firewall have a much higher chance of breaking through...
I probably wouldn't do it... and its totally up to you... but this is an FYI to keep an eye on that area of your engine mount... and stay behind the prop at all times regardless. I hope this makes sense..
Good luck with it. I have a Stik also...I've actually had 3 of them... they're a great classic fun plane.
04-19-2016, 04:26 AM
#6
The mount is original I believe. It has the holes drilled and has a metal strap on each side. The engine can be moved front or back and then tightened down.The thing to watch for is right or left thrust as the mount is a bit bigger than the engine so I will use a meter to get the zero thrust called for. I just did not notice the forward movement I had.This 1/4" I have can affect the balance and will be corrected.Thanks but no new holes will be drilled.
04-19-2016, 05:22 AM
#7
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I highly doubt a quarter inch will make any difference. of course it will show up in the location of your CG, but a 1/4 one way or the other of spec'd location, is well within tolerable limits.
if you want to move the engine ahead, you can always epoxy a 1/4 plywood spacer to the firewall and drill new holes. that will also give a weak firewall some strength. with no cowl on the nose it won't look wrong for the front of the engine and/or spinner sticking out that extra distance.
I fully understand the importance of correct balance and i'm not advocating being sloppy about principles, but sometimes we get too excited about small issues that won't make any noticeable difference in how the airplane flies, just for the fact that it isn't perfect. if you run into someone that claims he can tell the difference in a 1/4 inch of CG location, you just met a big BS'er.
use your head before diving into any perminant change,.....1/4 inch on a big stick,....no problem,....1/4 inch on an .020 size plane might be a real problem.....it's all a compromise and all relative to size of plane. when that plane is 50 yards away, are you going to be able to tell that it is flying a half inch tail low ?.
if you want to move the engine ahead, you can always epoxy a 1/4 plywood spacer to the firewall and drill new holes. that will also give a weak firewall some strength. with no cowl on the nose it won't look wrong for the front of the engine and/or spinner sticking out that extra distance.
I fully understand the importance of correct balance and i'm not advocating being sloppy about principles, but sometimes we get too excited about small issues that won't make any noticeable difference in how the airplane flies, just for the fact that it isn't perfect. if you run into someone that claims he can tell the difference in a 1/4 inch of CG location, you just met a big BS'er.
use your head before diving into any perminant change,.....1/4 inch on a big stick,....no problem,....1/4 inch on an .020 size plane might be a real problem.....it's all a compromise and all relative to size of plane. when that plane is 50 yards away, are you going to be able to tell that it is flying a half inch tail low ?.
04-19-2016, 05:35 AM
#8
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The GP Big Stiks tend to come out nose heavy with the recommended engine. I would install all of your radio gear and and then position the engine and battery so that your plane will balance at or near the spar. This will be a safe starting point, then the CG can be moved back up to 1/2" behind the spar without much issue.
On my Stiks, I have the engine shoved as far back as I can get.
On my Stiks, I have the engine shoved as far back as I can get.
