This is my first attempt at a uniflow tank. I have an LA .25 mounted on a Shark 402 with a 3oz. uniflow tank. I guess my question is do I use the muffler pressure or do I leave the uniflow vent open. I am curious as to what is working for other people.

Thanks,
John

John, it works well both ways for me , i have a mix of tube mufflers and tongue mufflers. Some seem to run better on suction and some better on pressure. I would say the run on muffler pressure may be a little more consistent but sometimes with a slight lean out towards the end of the tank. My advice is to try it both ways and see which one you like the best, the needle will need to be leaned a little when you switch to pressure from suction.

Really dumb question time... Prepare yourself.... When one says to raise or lower a tank on a profile plane do they mean to raise it in relation to the ground or raise it in relation to the profile fuselage?   


John

John, There are no really dumb questions, and this is the place to ask.  For everyone who asks a "dumb" question, there are plenty of others reading the forum who may have the same question, or may realize they misunderstood how something works until you asked.  So you do a service by asking. 

How are we doing on the tank height question?  Is that enough for now or do you want to go into it more?  And of course you can always come back to a question later.

Kim

OK, let's skip theory for now and move right to the practical.  Let's say you have the needle set where you like it for level flight--the engine is running steadily, the lap times are good (around 4.6 to 5.1 sec per lap for the 402), you have good line tension, everything seems OK.  Then if you go inverted or do an outside loop and the engine speeds up, it probably means that you need to adjust tank height.  With the plane standing upright on its wheels, try lowering the tank about 1/8", fly again and see what happens.  If the engine slows down during outsides/inverted, try raising the tank 1/8" (again with the plane standing upright on it's wheels), fly again and see what happens.  (We'll leave the "why" for later).  If 1/8" helps but isn't enough, try another 1/8" until you get a reasonably steady run everywhere. 

I notice you have a nonadjustable tank mount strap, which is why I brought it up.  Foam double-stick tape along with rubber bands or tie wraps make adjustment possible.  There are also solder-on slotted metal tank brackets that go on the front and back of the tank and allow a 4-40 bolt in each slot to be loosened while the tank height is adjusted.  (Brodak has them).  I just took a look at my S-402 and there isn't a lot of room for slotted brackets.  I would suggest flying it first.  Maybe you will get lucky and no height adjustment will be needed!     (We need a four leaf clover happy face for luck.

Also, speaking of my S-402, the controls are very sensitive.  The elevator is large, and not a lot of control movement is required.  Mine balances at 1/4" in front of the spar, has about 20 degrees of Up, 20 degrees Down, and it turns fast.  I would recommend that you start with the pushrod in the lowest hole on the control horn for your first flights to make sure it isn't difficult to fly due to oversensitive controls.  And keep us posted on your progress.

Kim

This is my first attempt at a uniflow tank. I have an LA .25 mounted on a Shark 402 with a 3oz. uniflow tank. I guess my question is do I use the muffler pressure or do I leave the uniflow vent open. I am curious as to what is working for other people.

  I haven't run the LA, but I got more consistent results on the 20/25FP running no muffler pressure into the uniflow. Pressure would work, but about 10% of the time, it would take off lean about the time of the square 8, and stay that way. This was with several different engines and several different tanks. Without pressure, it was pretty much bulletproof.

      Brett