REFLECTOR: Takeoff roll - fuel burn

[Chuck]

Al, would moving the CG forward shift additional load onto the front of the plane (canard) which would need to be overcome by generating more lift with a higher t/o speed? IOW did you happen to notice the t/o speeds for the last 2 tests? Were they the same, or was the last test a higher speed? Also as we know, the canard is pointed downward slightly which creates more pressure on the nose wheel increasing rolling resistance which decreases acceleration resulting in a longer t/o roll. 

What's your analysis of these results?

Chuck H


From: Al Gietzen 
Sent: Thursday, May 21, 2009 11:47 PM
To: reflector 
Subject: REFLECTOR: Takeoff roll - fuel burn


Here's a bit of data from today's measurements.

The question came up here awhile back about fuel economy vs CG.  I did flights today in my SE RG with CG at 120", total weight about 2060; and at 116", total weight about 2270.  The CG was shifted by adding a person in the right seat. Surprising; within the accuracy of the measurements, both cases were the same: 160 KTAS burning 9.5 gph at 2500 rpm on a fixed pitch prop (rotary 20B, lean cruise). At pattern speed of about 100 KIAS I noted the heavier, forward CG took more power; but I didn't take any data.



Takeoff roll - 85F; 1400' field elevation, roughly 8-10kt wind component down the runway, fixed pitch cruise prop.



Weight - 2100; CG - 120"; about 1630 ft

Weight - 2300; CG - 120"; about 1730 ft

Weight - 2300; CG - 116"; about 2300 ft



These are all single run measurements, taken by spotting relative to taxiway exits and edge lights, and taken from a rolling start - rolling on to the runway, getting it straight and adding power. Moving the CG forward made a more dramatic difference than adding weight, and I didn't like the way it handled at pattern speed, or landing.



The first case above was repeated using so-called 'Short field takeoff' procedure - getting lined up near the end of the runway, and applying power while holding brakes; then release.  Takeoff roll was the same as the rolling start. My rotary spools up very quickly when I push in the throttle; things may be a bit different with a Lyc.



Al







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