Speedy11(at)aol.com
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 Posted: Tue Sep 28, 2010 11:58 am Post subject: RV-8A Numbers |
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Without an aero engineer degree, it’s often difficult to know if the numbers you are getting with your RV are accurate. I have done multiple TAS calculations using GPS triangles and feel confident in my TAS indications. But, I am a fan of IAS – despite it’s well known variations. IAS is something I can see and easily reference in the cockpit and it is indicating how many air molecules are passing the airplane. So long as the pitot-static is properly functioning, I have solid confidence in the IAS. If I lose that confidence, I can drop back and reference other speed or power indications.
I have neither the knowledge nor the desire to determine my exact CAS at various speeds, so one way to check my numbers is to compare them with a like airplane. I flew formation with another RV-8A with the same engine to compare numbers because his IAS was dramatically better than mine. Turns out his IAS was not even close to accurate. That doesn’t really matter so long as he knows the numbers for his particular aircraft. But, when comparing aircraft using textual information, the comparison is more difficult. I have wondered how the numbers I’m getting compare to other RVs across the country. So, for anyone who is wondering about their RV-8A compared to others, I’m posting some numbers that I recently recorded. The Fuel Flow numbers are estimates since my FF readings are not yet accurate.
Altitude MP RPM KIAS KTAS FF (approx) EGT
1000 26 2500 178 182 15.0 Peak
2500 25.2 2500 165 172 12.5 ROP
4500 26 2400 169 184 13.5 40ROP
10500 20.8 2000 na na 9.0 Peak
11500 20.1 2300 142 172 10.5 Peak
11500 20.0 2240 137 166 10.1 Peak
17500 15.4 2400 124 166 7.8 Peak
17500 15.4 2300 120 162 7.8 Peak
20000 13.8 2400 113 160 7.0 Peak
24000 11.5 2500 89 135 7.2 70LOP
24000 11.5 2300 92 139 6.9 40LOP
24000 11.6 2200 88 134 7.0 60ROP
My deduction is that my engine is using far more fuel than other similar engines. I don’t know why, but that seems to be that case. The accuracy of all numbers above have been verified by using other measuring means. The only one that is still inaccurate is the FF. I’ve been making adjustments to the FF values in the engine monitor, but can’t get it narrowed to accuracy.
Based on my numbers thus far, I will plan the following for cross country:
High Altitude to gain a tailwind
FL200 2300RPM 7.0 FF 160 KTAS
Medium Altitude
11500 2200RPM 9.0 FF 160 KTAS
8500 2200RPM 9.2 FF 160 KTAS
Low Altitude
2500 2300RPM 9.5 FF 160 KTAS
What numbers are you using? Stan Sutterfield
www.rv-8a.net
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