Rotax 912 High Temp/Vibration Issues

Food for thought if other things don't pan out.

I know Rotax won't like what I'm about to say, but it has worked. For my clients we have all wrapped the exhaust pipes. The wrap MFG says it cuts up to 70% of the heat. Now I don't always believe MFG's, but even if it cuts the radiated and convected heat by 50% on all you wiring, hoses, VR and ignition modules that is substantial. When I did a research project (temp stripped lots of parts and in different planes) using header wrap on my Flight Design  CTSW and later on a few RV12's  temps on parts dropped 20F-40F. My parts temps never ever got over 140F on a hot day in Tucson, AZ. For the RV12 guys it also saved their VR because Vans mounts the VR within inches of the #4 exhaust pipe on a hot metal shelf.

p.s.

They then allowed you to move the VR. They now mounted the 912iS fuse box within inches of the #4 exhaust pipe so I'm waiting to see how that turns out. 

With an earlier discussion here on the forum on header wrap it must be applied correctly and never over wrapped because it can cause too much heat retention in the pipes and cause issues. Some aircraft MFG's use wrap right from the factory. I bet I know of a hundred plus US LSA aircraft with wrapped pipes and some are well over 2K-3K hours without any issues or ruined parts or vapor lock.

This certainly sounds like fuel vaporisation/vapour lock.

Whatever happened to basic pilot training in risk management particularity in relation to weather?

I live/fly in Australia. Summer temperatures routinely rise to 45 C. I have experienced this problem, as have most Rotax 9 pilots in Australia.

Rotax drivers should all understand that the 9 engines have a particular weak point, in that the fuel lines pass over the engine. This makes the fuel contained within the lines vulnerable to vaporisation/vapour lock.

The problem almost always occurs on a hot day (most often 30C and above), after the engine has been run (flown or prolonged taxi), shut down and then re started before completely cooled. On shutdown, the still hot engine heats the fuel lines/ boiling the fuel. The minimal  air movement inside the cowl exacerbates the problem.

There are several strategies that may help reduce the problem;

AvGas, as mentioned, has a higher vaporisation point - may assist a little 

Insulation of all fuel lines - absolutely essential for Rotax 9's flown in hot weather.

Fuel return line assists in clearing vaporised fuel.

Pointing the engine air inlets into the breeze to assist in cooling.

Opening any inspection doors/hatches to improve hot air exhausting

Upper cowling vents (as above).

(I dont use AvGas or have upper cowling vents but employ all the other "fixes".)

Ultimately the only reliable solution is management; 

I obtain a weather forecast (don't all pilots?) - if high temperatures are forecast;

I scheduling flying to start very erly in the morning (usually first light). This will allow for several take-offs before the day gets above 30C.

It doesnt often suit me but I could equally fly in the late afternoon/evening for the same reason.

If I must fly at or above 30C, I assume fuel vaporization will occur after each landing/shut down.

I extend my "run up" watching for fluctuations in fuel pressure and listening for engine roughness - when indications dictate that vapour cleared/not present, I line up for take-off.

I assume I will have a problem at full power/fuel flow/burn and am prepared to abort the take off and return to the holding point. I will also have a plan for an engine out on climb out.

Climb out should be conducted at a lower angle and higher speed (consistent with terrain clearance) than normal, to maximise engine cooling and give some degree of reserve energy if partial or total engine failure occurs.

Its a good idea to stay within easy return to the field, for at least one standard or high level circuit, to asses engine condition.

I hope I have covered all the main points

I fly in Tucson, Az in the US and see temps of 100F -110F (37C - 43C) during the summer. Coming up as we speak. Flying a Flight Design CTSW. I only see 240F during climb and around 218F 221F during cruise. All the LSA aircraft in our desert climate (and we have many) are in the same boat. Some do see higher temps. What I truly believe to be the difference is good air flow through the cowl, proper relationship of coolers to the airflow, all oil and fuel hoses in fire sleeve, no reduced flow of any liquid due to too sharp a bend in a hose (we use springs if there are excessive bends in hose reducing flow. This keeps the hose wide open), header wrap for many to reduce under cowl heat and finally shallowing out the climb to increase speed and air flow through the cowl and reduce engine workload.

Hi Roger L - I think we may be on two slight differing (related) subjects;

You seem to be talking in flight temperatures. Important to be sure and certainly need to be considered when ambient temperatures are high.

Roger K would seem to be asking about an issue of high ambient temperature, resulting in rough running while on ground and/or during take-off/climb out - this would seem likely to be fuel vaporisation/vapour lock.

Though related, I would suggest the two have differing mitigation strategies.

Quick comparison on your CTSW temps & my ATEC Zephyr temps; My climb out would be similar 110-120C depending on ambient, climb angle & load. Cruise at altitude (5-8,000ft) about 90C

Hi James,

You're right I may have misread his comments. As he explains it it does sound like vapor lock, but taxiing and running the engine cooler fuel should have taken care of the vapor lock.

In my Flight Design I could have low fuel pressure and some vapor in my fuel lines after a flight and then come back 45 minutes later to fuel pressure down to 1.8 psi, but after taxiing down to the eyebrow enough cooler fuel would have replaced the warmer fuel and pressure would come back to normal, but I never had any rough running. 

Looks like it's in an RV12 and their electric pumps run all the time in the factory built plane.

So after reading his post 3-4 times (LOL) my question would be did this happen after a flight and the engine was already hot or was it cold? If it was a first flight of the day seems like it would have been vapor lock too soon and the hoses didn't have time to absorb heat. What was his fuel pressure when this happened? That should have been below normal if it had that much vapor lock. Why did just his right side EGT's drop and not the left if it was systemic vapor lock? 

"Had to abort take off due to vibration with engine just after fueling up on a hot/humid day 91 non-ethanal"

230F - 245F oil temp on take off is very normal here in the west US this time of year and that by itself shouldn't cause vapor lock. All of us have those oil temps on take off including many RV12's and none have vapor lock on take off or at 230F.

Out here 230F is a low take off climb temp this time of year. Usually the fuel hoses need to heat soak to cause the fuel to vaporize.

I think we may need a tad more info.