Light Aircraft Association

I see from the Bulletin issued last week by Rotax that for their four strokes engine full power rev's less than 5,200 rpm must be avoided.

REF: New Rotax Service letter for the 912 & 914 series engines.
SL-912-016 page 4/6 sub point 3.1.2)
"Take off RPM at WOT should not be below 5,200 rpm to avoid overloading the engine."

This requirement rather worried me as I get only approx. 5,000/5,100 indicated rpm.
However Francis D. in the Eurostar review in the Oct. LAA magazine mentions a significantly lower & thus contrary 4,700 at take off & wide open throttle.

So how are we to interpret the situation on our own a/c ?
Especially as this aircraft was built by Conrad Beale the U.K. Rotax distributor. who we assume is bang up to date,

e.g. "I've has always run below 5,200 in the take-off and climb out, so I can safely ignore Rotax ? [Hardly]
Or, Let's fine up the prop to get the specified minimum of 5,200 and then risk overspeeding when flat out, Straight & Level ?

Mike Hallam.

Mike,

The Eurostar SL was assembled by Nigel at Cosmik.

The prop loading on this aircraft is necessary to get the optimum performance, however Nigel and Chris have ensured the engine installation (in particular the cooling) is good. There are a large number of standard Eurostar EV97’s around with a similar installation and prop loading which have not had any of the problems identified in the bulletin you refer to.

SL912-016 is a Service Letter that Rotax issued to advise owners of some recommended operating conditions for the 912 engines. This information is particularly useful to operators of aircraft with VP props fitted so they can operate their engine safely.

It is not mandatory.

After consultation with Rotax, Skydrive sent out the following information to their customers along with the bulletin;

Many engine installations, particularly with the 912UL 80hp engine, do have matching speeds below this recommendation. For production microlights from approved companies, the engine/prop matching will have been chosen on the basis of performance, cooling, noise certification and prevention of engine overspeed in flight. The setups specified by the aircraft manufacturer are the approved ones, and should not be altered by owners, or the Permit to Fly and Noise Certification will be invalidated.
For homebuilt aircraft, owners in any doubt should consult the LAA, BMAA, Aircraft Kit Supplier or Skydrive for information on the recommended setups.

The 912S (100Hp) engine is a little more susceptible to problems caused by over propping, especially when the cooling system is marginal and/or the intake air temperature is high.

Many thanks, Conrad,

That's a relief and sorry if my posting mixed identities of the Beale clan.

Mike Hallam.