Tuesday, May 1, 2007

Plastic engine performance

I must say something here before starting discussing plastic performance. I did not had the opportunity to fly the same aircraft with classical and plastic engine, so I can not compare pure engine performance. It is obvious that performance does not depend of engine only, but I will give here some engine performance figures.

As mentionned earlier, the FADEC gives some engine indications that are quite unusual compared to classical engine.

The classical injected engine with variable pitch prop is managed unsing Manifold Pressure (MP), Prop RPM, and Fuel Flow (FF). A diesel engine is managed using Load (in %). The instruments also indicate RPM and FF, but the pilot has no direct impact on those parameters. RMP and FF are indicative only to help monitoring.

RPM is clearly not a performance indicator, but FF is interesting. The example I will base my comment on is using a DA40D (classical instruments), with three mid-weight persons on board, on a quite normal summer day. Departure from Sion (LSGS), 1500ft AMSL, 20 °C.

Until 7000ft AMSL, flying at about 85 kts, VSI remains above 700fpm. Regarding engine parameters, the power is maintained to 100%, and remains so until 7000ft AMSL, then it slowly decreases. FF is slightly above 6 USG / H until to about 5.8 when reaching 13'000ft.

The climb stopped there to circle the local mountain peak. En route we set power to 70-75%, and FF remains arround 5 to 5.5 USG/H.

This is not a performance issue, but remind that during the whole climb, the power lever was left untouched. No RPM to set, no MP to re-increase in climb, and no mixture to set.

In terms of flight planning, the value of 6 USG/H is a safe standard. Anyway, most of plastic engine planes have huge tanks.

To close this pose, here is a picture of the standard AED / CED displays coming with Thielert engines.

More on these displays in a next post