Michael Griffin wrote: > After reading all the comments about stub wing fuel tanks and their > affect on the CG; I decided against them however I have re-read Mark > Langford's page (http://www.n56ml.com/wingtank.html) and he details stub > wing tanks so now I am really confused.
There's nothing inherently wrong with stub wing tanks. They have the advantage of being well protected between the spars, and more importantly, outside of the cockpit. They are very close to the aerodynamic center of the wing, which is essentially the point about which the plane is balanced, although somewhat aft. Keeping the tanks out of the wings eliminates a fuel connection between outer wing and stub wing.
When Larry talks about his outer wing tanks, he's talking about long tanks that are about 10" front to rear, and hug the aft end of the main spar, which is very close to the aerodynamic center. I've heard him say that his CG location might change 1/2" from full to empty. There's nothing wrong with that.
By contrast, the CG in N56ML (with stub wing tanks that are between the front and aft spars) moves about an inch from full fuel to empty. 1/2" CG change is in the noise, unless you're talking about the absolute aft end of the range. When you build your plane, save engine mount and battery location for last, and weigh the airplane on three scales and do the "weight and balance" calculation, with no engine". Then add the pilot, no fuel, engine (along with cowling, prop, spinner, etc) into the spreadsheet to determine where the CG of the engine needs to be installed to get the CG where you want it. Then add fuel to the spreadsheet and see if that and a passenger, baggage, etc still keeps you well away from the aft CG.
If engine isn't mounted, build the engine mount to put the engine where it needs to be (fore and aft) to put the weight and balance where you want it to be (which is biased toward the front end of the range, with light pilot and low or no fuel on board (since the fuel is aft).
If your engine is already installed, you can add spacers (within reason) under the mount to space it out, if needed.
Wing tank shape and location is a choice. Bottom line is keep the tanks as close the the spar location as possible. But really, even with the "plans-built" tank behind the panel, the plane's CG range is clearly working for a lot of folks, and there's a pretty hefty CG shift from full to aft with those things!
Mark Langford m...@n56ml.com http://www.n56ml.com Huntsville, AL _______________________________________________ Search the KRnet Archives at https://www.mail-archive.com/krnet@list.krnet.org/. Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change options. To UNsubscribe from KRnet, send a message to krnet-le...@list.krnet.org
