Jealous airplane - a la Herbie?

CJones

CJones

Final Approach
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uHaveNoIdea
I've logged somewhere around 300 hrs in the RV-7A that my dad and I built about 5 years ago. In that time, I've gotten pretty comfortable with the plane and its performance. I know that 10.1-10.2 GPH / 75* ROP / 2350 RPM / 23.5" MP will yield 160 KTAS - yes it is 'slow' by RV standards, mostly due to the older style 3-blade prop we're running.

Over Memorial Day weekend, we had the first flight of the RV-10 that my dad has built over the past few years. After we felt comfortable to take the -10 out of the pattern, I flew chase plane in the -7A as we checked out the 'test flight area'. We were checking speed numbers between the two planes in flight and I noticed that I was getting slightly better performance from the -7A. Interesting. Oh well, it must be because I'm not operating in 'normal' cruise setup and I'm a little rusty with my numbers.

I brought the -7A back to Georgia with me after Memorial Day. On the flight down here, I noticed again that I was getting better performance out of the -7A. What would normally be a 160 - 165 KTAS trip was now getting a consistent 170 KTAS. WTH!? Check my numbers again... and again... and again. Cross reference RPM / MP / EGT / fuel flow... everything checks. Cross reference winds aloft / heading indicators / course indicators / airspeed indicators / groundspeed indicators... everything checks. Weird.

Flying to-and-from Alabama this past weekend, once again I was getting 170 KTAS out of the -7A.

We haven't changed anything mechanically on the plane! Other than an oil change right before coming down to Georgia, nothing has changed on the plane.

I'm starting to think that the plane has started to feel abandoned since so much attention has been placed on the -10 -- it's been banished to a buddy's drafty, dirty hangar at the home base and everyone always talks about how good the -10 will be when it's done. I think the -7A is trying to prove itself to us all over again!
 
id suspect the accuracy of your engine instruments and/or airspeed indicator has changed.
 
tonycondon said:
id suspect the accuracy of your engine instruments and/or airspeed indicator has changed.
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You're probably right - the airspeed is what has jumped about 5 KIAS, but I like to pretend that the airplane is willing itself to be faster. ;)
 
I had the same thing happen to me in the PA28. Next static check, ASI wasn't indicating correctly. New one put it, and I was back to normal. I was disappoint.
 
CJones said:
You're probably right - the airspeed is what has jumped about 5 KIAS, but I like to pretend that the airplane is willing itself to be faster. ;)
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It's also possible that conditions have changed enough to generate most of the improvement. Higher DA at the same altitude will yield faster performance up to a point and with the ground heating up there's plenty of rising air around which can raise TAS significantly.
 
gismo said:
It's also possible that conditions have changed enough to generate most of the improvement. Higher DA at the same altitude will yield faster performance up to a point and with the ground heating up there's plenty of rising air around which can raise TAS significantly.
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That's my thought. I'll notice a difference in the Aztec between winter and summer performance in cruise. I'll especially notice it if I'm loaded up. The thing gets pretty doggy when it's filled (usually with dogs ;)), and I can lose 10 mph in cruise from that. But I also operate at economy cruise. I've not tried it at power cruise in a while since I initially ran it a couple of different ways and found that the economy cruise was about 10 mph slower for far less fuel burn, so I just keep running it that way.

Now if only I could get the IO-540-K1G5 STC for 300 hp engines... :D
 
vontresc said:
Then you'd just burn even more gas :D
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Actually, it depends on how you use them. I could make more power up higher where my engines start to become inefficient and lack power. I believe Lance saw an improvement in TAS on same fuel burn when going up to 13,000 ft instead of 7,000 with his bigger engines.

It's a lot easier to throttle back than it is to go beyond full throttle. :)
 
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