All,
Sometime within the last week or so I got a message directly to me
asking some questions about actual speeds vs. RPMs at 2,500 feet. Unfortunately
I
deleted the message (not on purpose) and don't remember who sent it.
However, I did get a chance to run a few numbers on today's flight and the specific
results are below. So whoever asked the question, here is your answer:
N31BZ was at 2,500 feet MSL, density altitude was 3,880', with an OAT of
77 degrees F.
2850 rpm = 150 mph true airspeed and 142 mph indicated. fuel flow = 5.0
gph
2950 rpm = 156 mph true airspeed and 156 mph indicated. fuel flow = 5.6
gph
3050 rpm = 163 mph true airspeed and 153 mph indicated. fuel flow = 6.4
gph
And for "World Record" Earl, 150 mph = approximately 130 kts
156 mph = approximately 136 kts
163 mph = approximately 141 kts
Now some other thoughts:
-Of course, true airspeeds will go higher as altitude increases, but the
person that asked the question wanted some figures at the lower altitudes -
specifically 2,500 feet. When I am on a trip at 10,000 feet or so, I normally
cruise at 165 to 170 true and burn about 6 gph up there. As I have mentioned
before, my cross country technique is to set my fuel flow and accept what ever
rpm and speed that gives me at the altitude I am at.
-For those of you that are still trying to decide if you want fuel flow, I
highly recommend it. Not only for cross country work, but for use as a second
"fuel quantity" system. Tell the EIS how much fuel you have when you fill
up and the fuel flow then subtracts that much as you use it and you always
know how much you have total (you must kind of guess which tank has how much of
the total). This method, at least for me, is much more accurate than the
fuel quantity gauges in the tanks.
-Your Lightnings (not EAB Lightnings that are set up to meet light sport
requirements) should be a little faster once you get the proper prop installed
and we all know that Nick is still working on that. For example the prototype
runs about one or two mph faster than 31BZ the way both are currently
equipped (gear leg farinings and Lightning style wheel pants), but we are waiting
on a 62FK60 for both planes. The prototype currently has a prop that is
marked as a 62FK58 but it measures closer to a 59 inch pitch. N31BZ is still
running a 64ZK55. Now if Sensenich will just send us the two 62FK60s that have
been on order for the past 20 years or so.
-In any case, other than the correct prop, the key to going fast is building
your airplane light and straight, and attention to detail on the airframe
(clean up mods, getting the fairings and pants on straight).
-Perhaps this info will also be helpful to "rimorbod" (_mcpc@wp.pl_
(mailto:mcpc@wp.pl) ) since no one really answered his question from about a week ago.
Blue Skies,
Buz
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