Shimming tank to solve lean inverted

[Matt Curtis]

To solve lean inverted can I put shims under the motor because I don't want to cut open the airplane to try to shim the tank.

[Dave_Trible]

To solve lean inverted can I put shims under the motor because I don't want to cut open the airplane to try to shim the tank.
[/quote   If you have an inverted engine setup then no.  That will only make it worse.  When the airplane is inverted you will want the tank a little higher.  You need shims under the tank.  You now see why most don't glue tanks in.  I do-sort of with smallish epoxied blocks to hold the tank in.  If I need to I can cut the blocks  and have the tank out in just a couple minutes.  IF I ever need to adjust the tank its usually only one time and the problem is resolved.  A new ship I test flew today has the engine going just a bit rich inverted.  I could shim the engine up but that will mess up the spinner fit so I will likely just pull the tank and build a new one, relocating the plumbing a little.   Once done it should never change after that.

Dave

[Brett Buck]

To solve lean inverted can I put shims under the motor because I don't want to cut open the airplane to try to shim the tank.

    I think you might have it backwards. You want the tank lower or the engine higher when upright, that will raise the tank when it is inverted. You would want to move the engine higher - meaning you need thinner pads underneath it, or to recess it.

    This is also why almost everyone makes the tank removable, so you can either shim it or alter the uniflow vent to change the upright/inverted speed difference.

     Brett

[Matt Curtis]

Thanks for the info. Looks like I will have to cut open the airplane and and shim the tank. I did not build this airplane. Unless there is another fix maybe motor mounts lower as the engine is upright not inverted. This is on a vampire with a fox .35.

[Brett Buck]

Thanks for the info. Looks like I will have to cut open the airplane and and shim the tank. I did not build this airplane. Unless there is another fix maybe motor mounts lower as the engine is upright not inverted. This is on a vampire with a fox .35.

 If it is upright, you can shim the engine up to get it even.

     Brett

[Dan McEntee]

   did you make the tank, or can you build a tank? One thing I have always wanted to try in a situation like this, if I had to, was build a tank with the  wedge and pick up tube "offset" up or down as required. I still get mixed up on the raise and lower the tank think still after all these years, but I'm thinking that if you are certain about which way to go, make the peak of the wedge and pick up about 1/4 to 3/8" offset up or d own. maybe going a little farther than you need, so if needed to fin tune, you can shim the tank away from the engine bearers a bit at a time as needed. If the engine is upright, you would need to offset the wedge and pick up down. If you do not have any metal plates under the engine, make up three sets of 1/16" thick and try adding one set at a time. If two sets is two much, go to shim stock and fine tune. Who ever built the airplane may have intended for there to be plates under the engine. At least getting it running even, then figure out the cosmetics.
  Type at you later,
    Dan McEntee