My RV4 was built in 1986. It had the original Van's cowling, wheelpants, rubber wingroot fairings, and had the rectangular air intakes. I used to fly along side my father's RV6, which cruises at 190 mph, and was usually about the same speed.
Then I brought the plane in for a major refurbishment. I changed the cowling out for a Sam James Holy Cowl, which was significantly lighter, and had the round air intake openings. Sam James, who is a friend of mine, told me he had done significant studied showing that round inlets provide less drag that rectangular inlets. I then installed a Sam James fiberglass plenum chamber. I really liked the plenum chamber, but I did have some over heating problems at first. The reason for the overheating was not the plenum chamber however, it was because there was too much leakage around the plenum. After fixing the leakage, the temps were constant around 180 degrees.
I then attached the Sam James fiberglass wingroot fairings. This was an easy install, and super slick. I would highly recommend this for everyone. I installed the Van's pressure recovery wheel pants, then made really slick upper and lower gear root fairings along with fiberglass gear fairings. I followed this by a new paintjob. The decrease in weight was really significant. The next time that I flew along side my father's RV6, I had to throttle back considerably, because I was leaving him in the dust! My -4 now cruised at 205 mph, and faster at full throttle.
I attribute the major speed difference to the Sam James cowl and plenum chamber, along with the significant weight loss because of the new installation. Thanks Sammy!
If you want to outfit your RV with some really nice fiberglass Holy Cowl, plenum chamber, or wingroot fairings, contact Sam James Aircraft at
(863) 234-1096. Tell him Scott "Buzz" Brown sent you!
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