Here are my (very brief) test notes and some background comments.

 

04-27-04   Flight Tests w/ old 13B & RD-1C drive.

 

1 min Timed climb from 1000 agl to 3650 agl   at 130 mph , 2650 fpm   OAT = 76 F, high humidity ?%.

 

Was a little disapointed as I thought it was in excess of 3000.  It will be higher at lower airspeeds and under standard day conditions.  I used my old Vy speed with the B drive and short prop.  Vy is now lower because the engine is up in its power band even at lower speeds and prop efficiency is much better at lower speeds compared to old prop.   Will do a test at lower speeds next time.

 

What I really like is the effortless feeling the plane has during climbs at lower throttle settings.  Don't have any past bench marks but here is a number you can bounce off your own performance numbers.   

 

Climb rate while holding fuel burn at a constant 10.0 GPH = 1600 fpm climb @ 140 mph.   Was able to sustain this number from SL to 10,000 feet which is where I stoped the test.

 

Cruise @ 11,300, OAT 37 F, IAS 140, TAS 171  @ 6.0 gph  5600 rpm

 

This is only slightly better performance than before.  RPM was a little higher and MAP a little lower.

This was supposed to be done at 12,500 but I had drifted a bit lower while staring at instruments and re-dialing the EC2 map table in (needed changing due to the different loading on engine with C drive).   Good thing the sky is not crowded, I don't think I looked outside the cockpit for 20 minutes. 

 

Cruise @ 12,500, OAT 36 F, IAS 163, TAS 203  @ 8.6 gph 6460 rpm  (WOT, mixture leaned for best economy)

 

This is respectable performance for an RV but it is not significantly different than with the old prop (except the rpm was lower with B drive)

Very low speed (110 mph) sight-seeing fuel burn is also lower.   Was around 4 gph and now about 3.5.

 

Conclusions:  The C drive gives significantly better takeoff & climb performance but only a slight advantage in economy cruise.  I do like the fuel savings that show up when looking at the fuel burned during cruise-climb phase of flight.  On a long cross country, I would typically set a fuel burn of 8.5 gph during climb to cruise altitude but now I can get the same climb rate at 7.0 gph.

 

The other thing I like is that the engine vibration signature is now changed just enough that the airframe resonances are almost all gone.  Beer-can airplanes are a bunch of aluminum skinned drums flying in close formation looking for any excuse to start drumming.

 

Tracy