Ok, I thought it was about time I reported back on 396 hrs of flying in the 4 1/2 years that we have had our RV9a in the air with some numbers etc.
The Rotec TBI we had on the 0-235 for the first 100 hours was out of the first batch that Rotec produced, since then we have replaced it with a later model (instead of having the old model upgraded) and have learnt to fine tune it to get the most out of the small 0-235. I also replaced the original exhaust that was fitted when I built the aircraft with the new lighter smaller tubed exhaust that was designed for Lycomings new 0-233 LSA engines.
To help keep running costs down I designed the fuel system when I was building the plane to run on mogas without having to worry about vapour-lock. our 9a has an electric "push" pump mounted next to the fuel tank in each wing root and does not have an engine mounted mechanical fuel pump. A small "dyno" type alternator was mounted on the accessory case along with a tiny battery to supply electrical back-up for the fuel pumps (if the need arose). But with testing we have found the TBI is happy to keep supplying the engine with fuel by gravity feed only (no pumps), not only for normal cruising but also for 500'-600' a minute climbs and this is with minimum fuel in tanks. Because of this I removed the back-up alternator and battery and along with this weight saving and the lighter exhaust system I fitted earlier I was able to fit wheel pants and leg fairings and still keep our aircraft under the minimum weight required by RAA. Fitting the leg fairing and wheel pants resulted in a win win situation, not only did the 9a cruise at a 10 knot higher airspeed at the same rpm but it also did it using 1-2 litres less fuel per hour. This means we are now able to travel further on the same amount of fuel or, carry less fuel to travel the same distance.
Ok, now some figures. Please keep in mind this may be a RV but it was built to be able to register it RAA and to achieve this a small light low compression, air cooled Lycoming 0-235 CTC engine was chosen. This engine is plated @ 108hp and according to Lycoming has a t/o hp of 115,
Take off and climb out with two up is around 1000' a minute to circuit height then the nose needs to be lowered slightly to allow speed to build up to around 110kts to keep the air cooled engine temps down while climbing further.
Short local flights with take off and a cruise between 2500' and 4500' at around 2300 RPM will give us 120 IAS and a 22 LPH ROP average fuel consumption. Cruising at altitude above 5000', we can expect at the same RPM and IAS a 138-142kt TAS and a 20LPH fuel flow. 55% power ROP gives us 110kts and 18 litres per hour while 55% power LOP still at 110kts will shrink the consumption to 16 LPH.
Pushing the 9a over 130 kts IAS will push the fuel consumption up around 30 LPH or more.
Cheers.
Bob