"burp" on manoevers

I have 2 different diesel powered stunters and having problems with the engine cutting out or burping on sharp pullups. Seems to me i remember a magazine article that this was due to the location of the end of the pickup in the tank. One tank was a homemeade, the other a "profile" uniflow. Can anyone help me with this?

I assume from this that the motor is mounted inverted. Diesels like to be side-mounted. Assuming the above assumption is correct, the problem is most likely due to fuel accumulating in the crankcase and then rushing up the transfer port This can be lessened by careful adjustment of the needle (as lean as possible) and compression (as low as possible). When the motor misfires instead of burping, you're just about there.

>I assume from this that the motor is mounted inverted.
>Diesels like to be side-mounted. Assuming the above
>assumption is correct, the problem is most likely due to
>fuel accumulating in the crankcase and then rushing up the
>transfer port This can be lessened by careful adjustment of
>the needle (as lean as possible) and compression (as low as
>possible). When the motor misfires instead of burping,
>you're just about there.

Can you try to describe the difference between "misfires" and "burping"?

Actually one motor is side mounted on a profile and the other is upright. the side mounted engine is the worst offender. I do not have the difference between a "burp" and a "misfire". Adjustment-wise I have been all over the place; rich, lean, lower compression, higher compression. generally flat out; higher compression and leaned out fully is better but not trouble free. This is what has led me to thinKing I have fuel feed/tank problems.
Other pertinent data:
upright motor: MPJet 1cc BB. backplate NVA, homemade tank immediately inboard
Profile mount: MVVS 2cc , I have tried 3 commercial tanks: standard 1" high wedge VECO tank, uniflow profile tank, and uniflow 1" high wedge
regards bill

>I have 2 different diesel powered stunters and having
>problems with the engine cutting out or burping on sharp
>pullups. Seems to me i remember a magazine article that
>this was due to the location of the end of the pickup in the
>tank. One tank was a homemeade, the other a "profile"
>uniflow. Can anyone help me with this?

OK, let's try something else. You say on sharp pullups. I am assuming from level flight. What happens when you are inverted and do a sharp pulldown (well, you know what I mean. We don't want you to hit the ground.) If it does it one way, but not the other, then I would think it has something to do with the engine internally. If not...

What size venturi do you have. This may be a fuel draw problem. When you do a sharp "G" maneuver, you need more draw. Diesel engines need small venturis. How far is the tank from the engine? What size prop are you turning? What type of fuel?

Leonard has asked the right questions. I was fighting the same problem with a PAW 40 mounted on its side (as recommended by PAW). Eventually, going to a smaller and thinner prop (11X6 Power Point of all things!) and spinning up the rpm's enough to ensure a good fuel draw was what seemed to help the most. There was a price to be paid in fuel efficiency, however. Good luck, Dzl

>Leonard has asked the right questions. I was fighting the
>same problem with a PAW 40 mounted on its side (as
>recommended by PAW). Eventually, going to a smaller and
>thinner prop (11X6 Power Point of all things!) and spinning
>up the rpm's enough to ensure a good fuel draw was what
>seemed to help the most. There was a price to be paid in
>fuel efficiency, however. Good luck, Dzl

I flew two different Blue Pants. Both had upright diesels, one was an AM .15 the other was a PAW TBR .15. Both planes burped when doing a bunt despite having two different tanks, one a uniflow, the other as per plan.

I had to learn to live with the 'burp' even though I found every instance a buttock clenching one. I learned to reduce the burp wiht the PAW by using higher reves and a finer pitched prop. I was never totally satisfied with the experience though.

Chats with other modellers indicated that this was typical behaviour for upright mounted diesels. I have not had the experience with side mounted planes.

I believe the problem was one of the reasons why Tony Eifflander of PAW, redesigned his stunter to be a side mounted one.

LAST EDITED ON Mar-02-04 AT 09:41 AM (CDT)
 
"I believe the problem was one of the reasons why Tony Eifflander of PAW, redesigned his stunter to be a side mounted one."

Actually, my last two planes were sidewinders (one of them--Freebird IV--designed by Tony E.) because of the PAW recommendation. They also recommended a chicken-hopper tank.

LAST EDITED ON Mar-01-04 AT 08:56 PM (CDT)
 
I really hate it when I do that, as it tends to give away my position to my opponent(s)...

Jake