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Speed Modifications by Roger Hershbein WoodmanRog@aol.com 
Home > Articles > Roger Woodman > Speed Modifications

In writing this article I am probably going to anger some after market manufacturers but in all fairness, the following facts proved true for my airplane.

I took delivery of RV-6 396DS in January of 2000. The plane is VFR equipped with an O-320 150HP engine, fixed pitch wood prop. The method used to determine speeds was unscientific but I believe it reflects the real world. 

I am located Hollywood Florida. The method used for testing was to run the airplane at full throttle, leaned out for maximum rpm, running North to South at 1000 feet. This was done with 2 people and almost full fuel at every occasion.

Anyway, the first few times we ran the plane I was only able to get 136 knots and a maximum of 2600 RPM. Last week my partner and I did a similar run and obtained 165 knots and 2800 rpm. (I did do one run like this by myself and the tach was winding past 2850 before I pulled back power (visions of the prop leaving the aircraft). I still have one more mod to do before I feel I have done everything short of engine modification and that is a new prop this month. I will report on the final outcome. Many people have asked how I achieved this performance increase without doing engine work so the following will explain all I have done to date over the past year. I owe all of the improvement credit to my friend and guru Rich Jankowski who has spent countless hours coaching me.

The first thing I would like to mention is that Van has made a terrific design. It seems that most builders feel that they are smarter and want to improve on a good thing. The result is that you probably will spend a lot of time and money for nothing. “If it ain’t broke, don’t fix it.” Rich has just finished helping another friend build an RV6 with a 180HP/Constant speed and it is doing 220 MPH out of the box.

My mods came as follows:

1.                   I first removed the after market wing root fairings and went back to the original design. 8 knots gained

2.                   My ailerons were hanging below the wing by about ˝” so I bought new brackets and rose the ailerons flush with the bottom of the wing.

3.                   Next came repositioning the horizontal stab to reflect the correct angle of attack. I had to shim 1/8” to get the correct angle. This relieved an excessive amount of down trim. Of course I then had to make a new empennage fairing. When I did this I also eliminated 2.2 extra pounds of excess weight in the tail.

4.                   I then purchased some Tracy Saylor gear leg fairings and replaced the originals.

5.                   Then came new pressure recovery wheel pants by Van’s.

6.                   All of the antennas were removed from the bottom of the plane and installed internally either in the wing tip or the gear leg fairing.

7.                   I have been trying to make new seams wherever two parts come together in order to smooth things up. I am now known as “arts and crafts 101” by my buddies.

8.                   I sealed all openings wherever possible to eliminate excess airflow. Tape over the holes under the empennage fairing, Weather strip under the rear of the sliding canopy, etc.

9.                   The last thing to date was cutting the exhaust pipes off so that the exhaust flowed straight back instead of at a down angle.

10.               My prop is a Sterba wood pitched 68/68. It is going to be replaced with a Catto Prop pitched 68/74. Results to follow.

Even after all that I have done to date, my plane isn’t the prettiest around but it is at least going a lot faster and nicer to fly. I will be building a new RV in the future and this project has given me the knowledge base to get a really good product without redoing everything. I need to Fly, Fly, Fly.

Roger


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