I'm just about finished but need to verify the correct fuel system plumbing. I have the two 50oz. tanks, one in front of the other. The rear tank vents to the atmosphere while the clunk feeds the front tank. The front tank vent is used to fill the front tank by the rear tank clunk while the front tank clunk feeds the UAT. UAT feeds the fuel filter. Did I get it right? The engine runs good but I'm just concerned about fuel burn vs. CG during flight.

thanx

Why don't you vent both to the atmosphere and use a Tee to feed the hopper? Make sure the lines coming from the tanks to the Tee are the same length. They should drain at the same rate and not change the CG during flight.

Bob

I thought about that but the rear tank requires about 10" of line just to get to the front. To use a tee I think I would have to coil excess tubing from the front tank to keep the lines equal length. I tried to mount the tanks side by side but they are a little too tall when placed on their side. Unless I'm missing something somewhere.
-al

You're right. Coiling is OK. The lines just need to be the same length. The pump won't care where the tanks are as long as the lines are the same the effort to pump each tank will be equal. The only time what you are doing will work and nort affect CG is if the tanks are stacked or right beside each other. Even side by side you would still have a slight change in Lateral balance.

Al,

Our DV8R is plumbed as you describe and I haven't really noticed any issues with CG change during flight. I'm sure it does change, but I don't really notice a trim change with the CG shift...

Bob

Ok good thanx! It will save me some work. I'm getting anxious!

brg,
-al

Al,

The airplane flys very nicely and tracks well. Our's lands quite easily. One person on RCU claimed that his buddy has one that always bounces on landing - sometimes badly. I have not noticed that problem but I will admit that the CG on ours is probably an inch foward of the recommended point (we have a bunch of flight electronics in the nose - its a test UAV in our program), and I'm always careful to make sure its as slow as possible before touching down. IMHO, its easier to land than the KingCats I've flown.

Have fun with it!

Bob

Hi Bob,
I kinda figured it has a large CG envelope. I saw here on the Universe there was a CG change that has not been corrected in the manual. I sent PCM an email questioning that and they verified the new CG location to be 10 5/8". With the new location I was able to remove a significant amount of weight needed to balance at the old location. So, like you said earlier, the fuel burn is probably not as big a factor as I was guarding against but I'm just trying to cover all bases, if ya know what I mean. Sounds like yours is really high-tech! I guess that really speaks volumes for the airframe.
-al

I just received an email from PCM. They said theirs is plumbed the same as I described above and it works fine. So I guess we are on the same track. Thanks for all the help and suggestions!
-al