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Quote:
5000 RPM will give you about 4.8-5.0 fuel burn and in our aircraft that's about 108kts indicated or around 115kts true at 3,500 feet. |
So, obviously no one is going to be able to go 614 miles at 5,000 RPM. I was curious if it is even possible at the most efficient speed of 85 knots. Any body have a burn rate at that speed?
BTW, I am not negative about the RV-12. At this point I think it is the best option. |
I believe the following is correct. If wrong please correct. The following is based on my memory of "Aerodynamics for Naval Aviators."
Maximum enderance speed equals minimum decent speed, which according to page 6-10 of the POH is 60 kts. It is not maximum range speed. Max glide speed is equal to maximum range speed and minimum lift to drag speed. Again according to page 6-10 of the POH this is 85 kts. Most efficient cruise speed (considers time to get somewhere) is an entirely different question but is usually 1.33 times Lift/Drag speed (85 kts). So 1.33 times 85 kts which is 113 kts. Again this is not maximum range speed. So for max range, set the speed at 85 kts, find the fuel flow at this speed and see how far 20 gallons will take you. Sometimes engine and propeller issues can change these numbers. Hope this helps. Dave Fuselage kit just received. |
To follow up, the math would produce the following, rounded to two places:
Assuming 614 nm, 85 kts is correct, and 20 gallons of gas, no reserve. Flight time: 7.22 hours Fuel flow: 2.77 gal per hour I do not know what the actual fuel flow at 85 knots actually is. |
Dave, what you stated in #13 is pretty much what I was saying in #9. The reason you got a lower fuel burn and a longer time in #14 than I did is that you were assuming 614 nm and I think that Vans RV-12 specs on their web site are speaking of 614 statute miles. (It simple says 'miles.')
In any case what I am wondering is if anyone who is flying an RV-12 can verify the burn rate at 85 knots. |
The RV-12 has a Dynon 180?
Set the power where the MPG, flight time is highest.... Problem solved..... But it has a ground adjustable prop.... So you'd have to do that exercise a number of times with different prop settings....... Oh... and extracting meaningful data out of the vast amount that is generated by the Dynon is more work and effort than one would think... Make you appreciate professional test pilots much more and explains why they need sooooo many test flights to get useful statistical data..... |
FWIW
First, it's Carson's speed, not Compton. Yes, it's 1.32 x L/D max.
Yes, the speed for minimum fuel burn in level flight should be the same as the maximum endurance speed. Yes, the L/D max should be minimum endurance x 1.32. Vy has nothing to do with it. Best MPG on the Dynon should work if it's based on airspeed and you keep a constant altitude. The TAS will vary, but the IAS should be the same at various altitudes. If it's based on GPS, you have to test that way in either zero wind or 90 degrees to a very light wind. Please see all the spreadsheets on my site for how to determine speeds ad how to adjust for wind and a lot more. |
Dave, did you ever refine the drag polar that you were working on a couple of years ago for the RV-12?
By now there ought to be enough people flying to test the reality of the theories about the RV-12 performance. |
No Alan, but I plan to readress it after my 12 is completed.
It will go int a display described here - http://www.ihmc.us/groups/oz/ Dave |
Fortunately or unfortunately, as mentioned...even small changes to the pitch of the prop have a significant effect. Van's recommendation is 4950 to 5000 RPM WOT on the ground/no wind.
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