The walbro-type carburetter is the commonly used type with model gas engines.
I believe there is a major problem with these carburetters that nobody realy
seems to master.
The definition of the problem is:
A good setup on the ground, full power ok, idle ok, transistions ok...on the ground.
Once in the air the setup changes
Those who haven't experienced this problem probably will say
I'm nagging and the rest will know what I'm talking about.
The problem is the apparent sensitivity for airpressure variations and /or
turbulence in flight. Some set-ups won't, others will, and from those who
do, some succeed in resolving it totally or partly by experimenting with all kinds of tubes and scoops
and others just keep struggling, I think that's about the size of it for the moment
I had a ZDZ50 in a CAP232 that changed RPM in every other flight position. All kinds
of changes under the cowl, tubing and enrichting and leaning of the mixture minimised
it at a certain moment but it never went completely away and after all these changes I cannot put my finger on what
exactly did the trick.
I have a DL50 in an EXTRA260 which virtually doesn't has the problem.
I have a GF45I in a ZLIN526 with the carb sticking out of the cowl which runs
very well on the ground only if I use an airfilter or a scoop but always
backs off in flight (cfr Rusty Tumbles in the GR45I thread).
I know guys with DA50 which do it in some models and don't in others.
I think this is something that is related with the system used with this carburetters
and that's it. Next step for gasser industry should be to deal with this by developing
a new kind of carburetter that is airworthy. Nice theory but probably industrial rubbish
cause someone will copy and offer it at a lower price.
So it's up to the hobby scientist I guess.
I was thinking about electronic mixture control using a few sensors and controllable needles as it
is(was?) used by OS in their high end 140, I don't know if it was a success though I don't see it listed
in their catalog today, maybe a sign.
It's a problem we don't know of in the nitro branche, why? Is it because they use different type's of carbs
or because the nitro/air mixture is totally different (1/6 versus 1/15 for gas) and therefor not so
sensitive for variations.
Anyway, it would be nice if someone could come up with at least some guide line to minimise this effect
so we don't have to unscrew the cowl a dozen times to try another setup.