That’s an odd SB writeup in relation to how Bing CV carbs actually work. The design intent of having a vacuum operated slide and tapered needle is to maintain near-constant mixture regardless of the combination of RPM and throttle butterfly position.
Silvaire wrote:
That’s an odd SB writeup in relation to how Bing CV carbs actually work. The design intent of having a vacuum operated slide and tapered needle is to maintain near-constant mixture regardless of the combination of RPM and throttle butterfly position.
Looks to me it’s Bristells way of saying “Sorry, but we made a cooling system that isn’t 100% adequate. Please adjust you engine management accordingly, or you engine will overheat” 
That SB is highly questionable.
How do increased EGTs cause partial loss of power?
How is it possible that merely applying carb heat, or operating the aircraft at approved manifold pressure / RPM combinations causes partial power loss in a certified aircraft?
@aart: could you post a link to the full SB, please?
boscomantico wrote:
The German LBA is now also jumped on the bandwagon. See here.
Has anyone seen a Rotax with carb heating? The reason I’m asking is that link reports a typical failure report as “trying to resolve it by applying carb heat and changing propellor pitch” – I’ve not seen a Rotax with carb heat…..
edited to add: Didn’t realise Bristol had them. Others seem to use a Rotax designed Airbox which avoids carb icing…….unless it’s only the certified versions which require carb heating, non certified use the Rotax designed Airbox….
LeSving wrote:
Looks to me it’s Bristells way of saying “Sorry, but we made a cooling system that isn’t 100% adequate. Please adjust you engine management accordingly, or you engine will overheat”
It could well be that the root cause of whatever unstated issues are occurring is poor airframe cooling design. I think the SB is likely technically incorrect, both factually (on several levels) and in its use of imprecise language. I imagine that nothing they suggest doing in operation will actually have any effect on engine CHT, which is the measurable parameter that would indicate thermally “stressing” the engine in a way that could lead to failure. The other related way that can occur is detonation.
A local friend is currently fighting Rotax 912 overheating problems with a Cub-style Zlin that he recently imported from Europe. It was either never flown in warm weather or the previous owner just let it overheat. It appears to need re-engineering and since he’s put it in FAA Experimental category (versus LSA) that’s probably what it will get unless he unearths some maintenance issue.
boscomantico wrote:
How is it possible that merely applying carb heat, or operating the aircraft at approved manifold pressure / RPM combinations causes partial power loss in a certified aircraft?
Good question.
https://www.bristell.com/bulletins/
It refers to changes made in the AFM, however you need to be a registered user to get access to that doc. Your club must have access, no?
Steve6443 wrote:
Has anyone seen a Rotax with carb heating?
Yes. The P2008 has it, as well as my own Savannah. This is the usual hot air version. Others can have a shroud with cooling liquid heating the carb.
Silvaire wrote:
A local friend is currently fighting Rotax 912 overheating problems with a Cub-style Zlin that he recently imported from Europe. It was either never flown in warm weather or the previous owner just let it overheat.
The only way to get a Rotax working properly here in Norway is to use duct tape (alu tape is what we use). In the summer, most of it is off. In the winter, you can cover most of it. This applies to both the oil cooler and the liquid cooler. Some have thermostats. This helps of course, but I have yet to see a Rotax that is properly hot in -20. Some airplanes are worse than others. The Alphatrainer is terrible. On a warm summer day it WILL overheat on the ground with only a tiny bit of draft from the aft. Turning it into the wind (if it’s only a knot or two) and it will cool just fine. The POH mentions this and what to do (turn the engine off). IME turning up the rpm to 3000-3500 rpm helps a lot. The main problem with this is that when using MOGAS, this will boil in the carburetor, it becomes too hot in there. In the air though, it usually runs on the cool side.
Steve6443 wrote:
I’ve not seen a Rotax with carb heat
These are the water-based heaters on my 912ULS carbs. Because you don’t introduce hot air into the intake, you don’t weaken the mixture.
Steve6443 wrote:
Has anyone seen a Rotax with carb heating?
Yes, the Evektor Sportstar RTC. (At least the night VFR version.)
it’s only the certified versions which require carb heating
Could be. The Sportstar has a certified 912S engine.
