Forward speed of the airplane through the air plays a big part in the calculation. So I hope that website takes that into consideration.
On Tue, Apr 22, 2025 at 10:41?PM Joe Norris via <joepilot13=
[email protected]> wrote:
This is why ¡°seaplane¡± props are always big diameter.? Gives you more acceleration ¡°out of the hole¡± (as the drag racers like to say). Might hurt the top end a little bit, but sure does pull on the low end.
The only thing you want to avoid is the tip speed breaking the speed of sound. ?(And of course you have to consider ground clearance.) ?Pponk Aviation has a prop tip speed calculator on their website.? Go to Pponk.com, click the ¡°props¡± tab, then click the ¡°tip speed calculator" tab.? You can play with various diameters and engine RPM settings to see what might work for ya.
Joe
From a long time (see my sig) RV owner, the C/S prop allowing full power in acceleration and climb obviously helps, but I'll bet it was at least 74" diameter, too. Many of the F/P prop makers sell 68" props for RVs (and likely Tailwinds). That extra 6" of diameter makes a really big difference in acceleration, even with a F/P prop. I've played with various diameter F/P on my RVs I've owned over the years, and the most impressive was a Warnke 72" diameter on a 160 HP RV4. Great takeoff performance, and 170 kt (not mph) cruise.
?
On tire pressure, if the guys at Van's are recommending 25 psi, they're doing it to hide the shimmy issue. I've always run 50+ in mine; if I forget to air them up and they get down to 30 psi or so the plane feels like a '68 Pontiac station wagon on the ground; I hate it.
