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.