PROFILE TANK LOCATION

I know this question has probably come up before, but I came accross this problem this morning and would like some input from anyone who might of had the same problem. I have built a lot of profile planes over the years and have installed my tanks (regular and uniflo) dead center of the engine and have always had good runs uprite and inverted. This plane I'm finishing now (Brodak Russian Lagg) the plans show the tank 1/4 inch higher from center. My question is I've installed a Super Tigre G21-46 on it with the offset venturi. Is it necessary to install it a 1/4 inch higher and do I use the crankshaft for a center of the engine or the Venturi. I know I could test it out after it's done but I would like to get my tank bracket mounts close. I will have some adjustment on the tank. Thanks for any help.

It has been my experience that the C/L of the tank needs to be slightly higher than the Crankshaft C/L to get a run on a profile that is not richer inverted. I like to have a 1/4" adjustment available above the thrust C/L. I have never needed to adjust the tank below the thrust C/L.
Bill <><

When in doubt follow the plans. Leave some room for adjustment in both directions. Most of my building is scratch and I set mine in the center. I leave at least 1/8" top and bottom and use balsa shims and rubber bands. Once the best location is found I go to a more permanent mounting.

I'm convinced that there is an effect here that we don't understand. For my Fox 35, the tank needs to be about 3/16" above engine centerline. On the same airplane, a Thunder Tiger 36 wants the tank offset to be 1/4" above C/L. On a different airplane, the OS Max S seems to like about the same offset as the Fox, but the Brodak 40 runs best with the tank center 1/16 below the engine C/L! Trial and error to find what works, and allow enough adjustment to make it work.
Steve Holt

Hey, CR.

Do you have any pictures of that LaGG to send north yet?

Don't you have a flying buddy in Reno who flies a Super Tigre .46 on a profile plane? How is his tank set? That might be a place to start.

PME

P.S. CR also likes Ringmasters. There two in the shot below. At one time, he had all three of the profile, built-up winged versions all in the same paint scheme. Let's see.....Mutt, Jeff, and ??????!

OK Old SD,
As you know I still have my Baby Ring (Little Mutt). The Ringmaster I'm holding I built in 64 and I still fly it on a regular basis, still powered with K&B 35 GH. My super Ring is getting the same paint scheme. I should have the Lagg finished in the next 2 day's and I'll send you Pix. I'm covering it with chrome Monokote, it's like using tin foil. I did check on the local flyer with his profile and he centered his tank on the crank, and his ran good till he stuffed it. I think what threw me was the plans showing the tank higher. I should have enough adjustment to try both. I'll let you know how it works. I've bench run this engine with a 12-5 Rev up prop and it runs so good I'm going to try that on the Lagg. I don't know how long to have my lines but I'll start with 70's and work down. Thanks for the suggestion Paul and every one else.