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On 01/01/2013 08:52 AM, Tracy wrote:
Mark S. had asked me for some performance numbers on my RV-8 at more typical power settings than I normally use since I usually fly at economy settings. Being an efficiency nut as well as the psychological effect of imagining a $50.00 bill going out the exhaust every hour is the reason, not any concern about the health of the engine. I usually average only 5 - 6 GPH on a local area recreational flight at speeds around 130. Thought I'd share the results of the trial run I did for Mark with the group.
Went on a New Year's Eve flight and tried higher power settings at close to the conditions you gave me. I have a fixed pitch prop and don't like to cruise at engine speeds more than about 6000 so had to modify the settings to keep them in that range. (Mark had asked about performance at around 15 gph) One other interesting thing I noticed was that the OAT kept increasing the faster I went. When I slowed down (at same altitude) the OAT measured 6 degrees lower. My OAT sensor is located in the diffuser for the radiator but not in line of sight of the core. I don't know if the change was due to rad heat finding it's way to the sensor or the result of compressing the air in front of the rad.
Altitude 6500
OAT 64
IAS 191 MPH
TAS (calculated) 214 MPH
GPS 4 way average - 212 MPH
MP 18.7" Hg
GPH 12.7
Engine RPM 6100
Tracy
Thanks Tracy. I'm always interested in direct comparisons between traditional a/c engines & alternative engines, & the rotary seems to be pretty consistent in its ~10% efficiency penalty (more than offset by the ability to run low octane mogas & save from 20-40% in fuel cost).
For those who aren't familiar with RV-8s & their performance using Lycs: a 200 hp -8, properly leaned, burns ~11gph at *8,000* feet & 212mph (Van's 75%/8k ft numbers, which are met by many builders). When you factor in Tracy's lower altitude, and his extra wing area (which might have actually hurt his drag numbers at that low altitude), his -8 seems to be in that 10% range. If he was running ethanol laced mogas, then he's almost an exact match for Lyc efficiency (e-mogas gets about 10% poorer mileage than straight mogas).
I'd love to see the numbers at that speed up at 8000 ft (corrected for 'FAA 'standard day'. Then the only difference would be wing area.
Charlie
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