I'm Building my first full fuselage model (Legacy 40)

How much room should I have in the tank bay for height adjustment?

Thanks

Steve

As much as you need? As much as will fit?

I have no fear of tearing a tank open and relocating the uniflow vent. 

If you have the uniflow vent close to the right spot, then you don't need to move the tank more than plus or minus 1/16 of an inch.

That means that I'm going to aim for about an eighth of an inch up and down movement of the tank. If I fly the thing and moving the tank all the way to the top or the bottom of the compartment isn't enough, then I will take a guess at how much the uniflow vent needs to be moved, I will take out the tank, and I will move the vent.

Once the vent position is settled, then the remaining space to move the tank up and down will pretty much take care of any further adjustment.

Thanks Tim, just the information I was after.

I'll be making my own tank so any surgery shouldn't be a problem.

Steve

Quote from: Steve Glass on August 04, 2026, 07:04:15 AMI'm Building my first full fuselage model (Legacy 40)

How much room should I have in the tank bay for height adjustment?

    If you have absolutely no idea, then make it reasonably big (1/4"-3/8"). But once you have some idea, then, the shims are typically around 1/64 just to fine tune it.

   What engine do you have? someone probably already knows a reasonable starting point.

    Brett

Quote from: Brett Buck on August 04, 2026, 12:18:55 PMWhat engine do you have? someone probably already knows a reasonable starting point.

    Brett

Brett,
I want to use an Enya 45 fitted with a Brian Gardner ABC p/l. The Enya is powering a Fancherised Twister at the moment, mounted sidewinder, so that doesn't help much?

With a 1" thick tank I'll only have 1/16" of up adjustment before the tank hits the crutch that I've made. Down adjustment of the tank is not a problem as I've yet to fit the tank floor.

Steve

 

I don't fly stunt, so what do I know. But if it was me, I would start with the tank positioned so that the uniflow point inside the tank was at the same level as the needle valve of the engine. Then move from there as flying would dictate.

On a profile like a Twister, my favorite rig is to mount the tank on a small platform.  The platform has elongated holes to bolt it to the fuse.  A starting point is about 1/8" higher than the spray bar, but the elongated holes allow 1/5" freedom in each direction, field adjustable.  Also, the platform has a stop at the front to prevent tank movement in a crash.

Peter

You may be approaching this with a predetermined idea as to tank THICKNESS.  Nothing says it has to be 1" or whatever.  As long as you have the length and width to work with a little you can make the tank a little thinner and give yourself the 'space' to shim it up or down.  Having said that I make my tanks 1 3/8" thick for my RO Jett engines, then start out from building with aluminum shims -around 1/32"- under the engine that would allow me shim the tank closer to the mounts if need be. 

Dave

Keep in mind OP is building a  full fuselage model, so profile mounting doesn't really mean much.

Thanks for that correction.  Yes, I'm now seeing that the above reference to the Twister referred to the existing plane, not the one under development. 

Regarding tank shimming, my experience is that the typical limitation is the the tank needs to be able to be higher than the design allowed for.  In practice, engines run rich inverted.

Peter

Excellent suggestions here.

Shim the engine 1/16" and a 7/8" tank will give me 3/16" up adjustment before hitting the bearers.

Thanks

Steve

Quote from: Steve Glass on August 05, 2026, 12:26:59 PMShim the engine 1/16" and a 7/8" tank will give me 3/16" up adjustment before hitting the bearers.

I don't normally fly IC motors anymore, but when I did I made the tank box 1 1/4" tall and used an old set of playing cards for filler.  Move it up: Take cards out of the top and put them in the bottom.  Move it down: Take cards out of the bottom, and put them in the top. Always have the right number of shims with you.

Ken

And when the engine won't run right, you switch out your full house for a straight flush?

Quote from: Dave Hull on August 05, 2026, 05:59:45 PMAnd when the engine won't run right, you switch out your full house for a straight flush?

Ace high! 

Ken