RV speed mods

[GRANT ED]

My dad and I have just started building an RV-7. I was thinking about extracting as much performance from my plane as possible. What "speed mods" have people done and how successful were they? I have been looking at different cowlings and have found the James aircraft site. Has anyone used this cowling? What was the result?

[N523RV]

You might check out this book. I haven't read it myself.. but...

http://www.buildersbooks.com/speed_with_economy.htm

[pierre smith]

A friend of mine is using this cowl on an IO 360 equipped RV8 and has had many many more hours of fitment problems than the stock RV cowl. Nothing seems to fit well as is the case with the RV cowl. They've had to cut the plenum, the cowl and a multitude of other time consuming details in order to make it work. We, on the other hand, have the stock RV cowl fitted to our RV6 and even though this is our first, it has gone a whole lot easier. I see him weekly and for now am very glad that we decided to forego the (claimed) added few MPH.
Pierre

[GRANT ED]

Hmm, that does not sound to good. I have read a story on another site about a guy who used the cowl and plenum on I think an RV-6. His opion was the cowling was great but the plenum was a major PITA.

[Rick6a]

There is no silver bullet with regards to speed mods. You do what you can during construction by paying particular attention to minor details. Hopefully in the aggregate, your efforts will produce some further enhancement in speed. I focused on making the airscoop seal as tight as possible. Mainly for cosmetic reasons I made the gap between the spinner and cowl close....manageble, but close. I used flush, rather than the protruding brazier rivets on the pilot and passenger steps. The steps were then faired to the airframe by beveling and sculpting proseal around them to make as smooth a transition as possible. I installed 2 flush mounted camlock latches to secure the oil access door instead of using the kit supplied parts. All 6 landing gear intersection fairings were installed . Many people omit either the upper or lower intersection fairing on the nose gear...I didn't. The wing root fairing seal is tight and the gap between the retracted flaps and fuselage is close. I hid the GPS, VOR, MB, and ELT antennas within the airframe. I installed the wheel pants as low as I dared. The hinge pins holding the upper and lower cowls together are captured and hidden beneath a triangular shaped aerodynamic adornment rather than the 90 degree bend and screw attach the plans call for. Even the tip fairing is butt sealed to the vertical stab for maximum smoothness. Finally, I installed a Sensenich fixed pitch prop that proved to deliver the fastest cruise speed of all the props Van's tested a few years ago on the same (RV-6?) airframe. Will these varied efforts pay off? I'll know soon enough. First flight will be in the upcoming weeks.

Rick Galati RV-6A "Darla"

[txaviator]

I'm sure Jay Pratt will offer more info on this, however, his recent reports about using a Grove Gear were very intriguing to read. Supposedly it makes a world of difference to use one.

Take care,

[GRANT ED]

Originally Posted by Rick6a

I hid the GPS, VOR, MB, and ELT antennas within the airframe.
Rick Galati RV-6A "Darla"

I'd be interested to see how you did this. Do you have any pic's or info?

[Rick6a]

I have several details shots posted that describe some of the things I've mentioned. Check out my gallery section in http://www.rvaero.com/
Unfortunately, I do not have photographs of the wingtip installed antennas posted there, but are the widely available Bob Archer design. If you do elect to purchase his antennas, I would recommend buying them directly from him rather than a traditional aircraft parts supplier. His customer service is generous, personal and freely offered.

[gmcjetpilot]

[quote=Rick6a] Unfortunately, I do not have photographs of the wingtip installed antennas posted there, but are the widely available Bob Archer design. QUOTE]

My suggestion is there are many places to make speed other than the antennas. I will say with good assurance that all external mounted antennas on a RV will perform much better than any internal wing-tip antenna. From flight test and classic aerodynamic calculations, at 200 MPH external antennas equivelent speed loss is as follows:

Comm antenna = 1/2 mph
Transponder antenna = 1/4 mph
VOR/GS/LOC antenna=1/2 mph
(GPS, ELT I don't mention because they can be placed under the canopy or tail fairing)

So to gain may be 1-1.5 mph you have to sacrifice performance of your Com/Nav radio, plus added weight from long coax and longer building time. If anyone says their wing tip antenna works great, I don't doubt that. However "works great" is relative and many have been very un-happy with their Wing-Tip antenna. Talking to the tower 10 miles away is not like talking to a flight service or an ATC remote transmitter 150 miles away. As far as NAV performance (VOR) I would think the range would also be limited or directional (blind spots). May be NAV is not a problem with GPS and the fact the GS/LOC is for terminal (short range) use.

Builders think nothing of using a 3 blade props (-8 MPH) or steps on their "A" model (-? MPH). You can gain speed with attention to details, rigged well and making small mods, such as fairings and a modified cowl and cooling plenum. The latter mod, cowl & cooling can produce 7-8mph more speed by reducing the cooling inlet area and cooling leakage (loss). This reduced cooling drag is one area where Van's stock design can be improved the most. For those who say this mod is not worth it, I would point to Dave Anders, Tracy Saylor and Dick Martin. All have Sam James style cowls and cooling plenums and race winning RV's. You don't have to use Sam James cowl BTW. You can modify a stock cowl and baffling very cost effectively, but like all mods it takes time, effort and money. It just depends on how bad you want it.

There is speed and then there is speed with economy as the book of the same name suggest (per previous post). One obvious way to go faster is have a pumped up engine with more HP. However to go faster also requires attention to details. First build it light and straight. Remember the fastest RV is Dave Anders highly modified RV-4 with a highly modified IO-360. At 254mph, Dave's RV is only 32-50 MPH than your typical stock RV at (200 - 222) MPH. The point is RV's are already fast and it is quite an achievement to gain any speed over the stock benchmark, much less 30-50mph which is amazing. The faster you go the harder it is to gain each MPH. However, it can be done as Tracy Saylor (+235mph RV-6) and Dave have shown. To see how Dave Anders did some of his magic, see:

http://www.cafefoundation.org/aprs/RV-4.pdf

Dave's 254 MPH RV-4 is still the current Cafe Foundation's Triaviation Champion. I would guess the average builder is not willing to make the effort Dave has, but still there is speed to be had. Except for the cowl and cooling mod most changes are measured in 1 or 2 MPH increments.
Cheers George

PS Suggest you look at the New Hartzell Blended airfoil constant speed prop. I agree with the previous post, if you go with a fixed pitch prop the Sensenich is a good choice all around.

[Rick6a]

So to gain may be 1-1.5 mph you have to sacrifice performance of your Com/Nav radio...........


I tend to agree with this point. I certainly wished to hide all the antennas but in the greater interest of enhanced communication capability, I did mount a Comant bent whip comm antenna and transponder stubby on the belly. I am based under Class B airspace. Sometimes, one must defer an interest in speed enhancement to other more practical considerations. In my case, that means willing to live with an admittedly more draggy and slightly less cosmetic arrangement. I did not mention this in my original post and regret any misunderstanding.