I ran the speed comparisons to Van's numbers for a RV7A with a 180 hp engine with a CS prop. At 55% and 75% power at 8,000 feet, I used several different combinations, check in 2 directions, leaned to between 75 and 100 degrees ROP, used several different MP and RPM combinations that will give you the percent of power, and averaged the numbers.
What I learned:
My plane is about 8-9 mph slower than Van's numbers at these power settings. Hmmm....I looked at the Van's website and blew up the 7A photos. The difference. I have things hanging on the plane they don't unless I can't see them). Steps, a VOR/GS antenna, ELT antenna, GPS puck, MB antenna, wing tie down rings, and second comm antenna. Since I built a cross country traveler IFR traveler, I'm satsified with the numbers.
For those that are asking how to build a faster plane, everything you have hanging out will cost you about 1 mph. Perhaps this would be a fairly decent rule of thumb.
The second thing I learned. Higher RPM for the same power setting will cost you more in fuel for the same speed. Want to run 55% on economy cruise - then crank the prop back and add more MP. The prop set at 2,100 rpm gave me about 24 miles per gallon, when set at 2,400, I was burning more gas. This doesn't make sense to me since you are producing 55% power, however the fuel flow meter says different. I'll check this one out again. And of course, YMMV.
Last thing, because of examining the Mothership's pictures of their 7A, an experience tip comes from this. For you nose draggers, always leave the tail tie down ring in. Van's had theirs in but I could not see the one for the wings. Back in my 172 days during a flair, not once but twice I managed to barely touch the rear tie down ring on the runway due to wind shear. Had it not been there, the tail would not have survived quite as well.
What I learned:
My plane is about 8-9 mph slower than Van's numbers at these power settings. Hmmm....I looked at the Van's website and blew up the 7A photos. The difference. I have things hanging on the plane they don't unless I can't see them). Steps, a VOR/GS antenna, ELT antenna, GPS puck, MB antenna, wing tie down rings, and second comm antenna. Since I built a cross country traveler IFR traveler, I'm satsified with the numbers.
For those that are asking how to build a faster plane, everything you have hanging out will cost you about 1 mph. Perhaps this would be a fairly decent rule of thumb.
The second thing I learned. Higher RPM for the same power setting will cost you more in fuel for the same speed. Want to run 55% on economy cruise - then crank the prop back and add more MP. The prop set at 2,100 rpm gave me about 24 miles per gallon, when set at 2,400, I was burning more gas. This doesn't make sense to me since you are producing 55% power, however the fuel flow meter says different. I'll check this one out again. And of course, YMMV.
Last thing, because of examining the Mothership's pictures of their 7A, an experience tip comes from this. For you nose draggers, always leave the tail tie down ring in. Van's had theirs in but I could not see the one for the wings. Back in my 172 days during a flair, not once but twice I managed to barely touch the rear tie down ring on the runway due to wind shear. Had it not been there, the tail would not have survived quite as well.
