Hi Colin,

I always use a uniflow tank, but not always muffler pressure, I try both ways to see what works best.  a Standard Vent tank the fuel pressure and flow will change making it leaner and leaner as you fly.

In a profile model, I like to use Sullivan 4.0 OZ  tank plumbed for uniflow, but I guess a 4oz tank will not fit in your model and a 2oz tank may be too small.

I suggest you use a metal uniflow tank that is the narrowest, so the fuel pick-up point is as close as possible to the NVA.

If it is still sagging on top, perhaps you need a bit more power. You can change one thing at a time like more nitro, a larger venturi, or a less restrictive muffler.

Sagging could be related to fuel delivery,  doubt it, but it is worth mentioning.

I never used this Brodak tank, but I understand it is the narrowest one you can get and it was designed specifically for profile models.

https://brodak.com/fuel/fuel-tank/brodak-tanks/uniflow-large-profile.html

For a profile model, you always start with the tank 1/8" higher than the center of the venturi, or better yet of the spray hole, that sometimes is not centered with the venturi. And then make adjustments if necessary after test flying.

Good luck,

Martin

Hi Martin

After some additional run time on my bench, I flew my profile CG Shoestring model today w/ the Enya 29-5224 around 6 times. Engine is running much better.

I also experimented a bit with 5 & 10% nitro, MAS 10-5 and 10-6 props and with and without muffler pressure. What worked best was 10%, 10-6 prop and muffler pressure. Sweet spot seemed to be around 10,000 rpm on the ground. Engine does speed up a bit after it gets in the air on the 1st lap. Was doing close to 6 sec laps with the 10-5 prop, and 5 sec with the 10-6. The Shoestring wing is prone to stall if too much control input, so it needs to fly a bit fast for best performance.

The fuel I was using was 10% nitro and 22% total oil 50/50 castor/syn. (On the bench during initial break-in, I used 25% total oil after adding some castor to the 22% fuel.)