Kitfox 4 + HKS, the saga continues

[Mnflyer]

Hi why do you want such a low static RPM?? My static RPM setting is 5900 +/_ 50 rpms. You want at least 6000 RPM's for take off and a 2 blade prop will not decrease performance if fact it will improve TO / climb performance.

[rwaltman]

Hi why do you want such a low static RPM?? My static RPM setting is 5900 +/_ 50 rpms.

Fear of overreving the engine in straight and level flight. Was aiming for 5400.
The baseline I'm using is the prop testing shown in Green Sky Adventures web site: 15 props combinations on two airplanes, 9 on a Zippy Sport and a 6 Kitfox II. (Both with HKS-700's, 2.58:1) The Kitfox II static RPM range from 5200 to 5800, average is 5533. The Zippy Sport static RPM range from 3820 to 5840. Average is 4987. The average of the whole lot is 5205.

On the other hand, just searched for static to max RPM ratios for several other planes & engines, and found a range from 86% to 95% For the HKS, 90% of 6200 Max would be a static 5580 RPM, right where I was before.

You want at least 6000 RPM's for take off

How much additional RPM do you get from static to take-off and climb-out speeds?

a 2 blade prop will not decrease performance if fact it will improve TO / climb performance.

If the prop is chosen correctly. The advice received is to go to 70" or more. For a 68", max prop tip speed would be ~0.63 Mach. (2400 RPM with the 2.58:1 reduction. I do not have the 3.47 unit as I originally thought)
That means there is a lot of room to increase speed and/or diameter. Cannot do either.

As usual, trying to make sense of what I learn while drinking from a firehose.

Roberto.

[Mnflyer]

As I posted my static RPM is 5900 and I have never come close to over reving the engine, when I release the brakes and push the throttle to full throttle the R's go to 5900 and stay there thur roll out and climp when I get to the altitude I want I pull the throttle back to 5500 and cruise, the engine has a 2.58 GB and I have a 2 blade 68" Warp Drive which far out preformed the 3 balde 66" GSC I started with.
If you check the Operators manual you see that at 5400 R's the HKS will be producing only 52 hp that is not enough for decent to roll and climb you'll need 2000' of runway and climb will be about 250 FPM, you have already noted that the increased pitch cause more idle vibes.
Once again there is little or no Rpm increase from static thur TO roll and climb only time would be in straight and level and that's when you pull the throttle back, you will aslo want the higher Rpm capabilities in the event you should need to make an emergency go around.

[rwaltman]

Gary, thanks for all the information. Will re-pitch for 5900 static.

[napierm]

Static balance, yes. Use a tube and good parallels. Pair of level chairs backs will work. Pretty sensitive too.

Dynamic balance... Has anyone done a dynamic balance on the HKS?

The balance master would be a better use of your dollars. It sounds like junk but they are using a similar system in tires now - a bunch of loose balls inside the tire. The balls will shift to balance the wheel. It is counter intuitive (to me, at least) until you've seen a demonstration - it works. The balance master uses mercury as the balancing medium.

[Dave F]

looking at the HKs chart -- you max power is 5800 to 6200 rpm .
I would set static RPM 6000 to start
you better off with a too fine then courser the pitch 1/4 degree at a time.
Static below 5800 would not be an option.

Running at 5400 static would likely give you 80 to 90% power so about 50 HP only
plus you be lugging the engine and using more fuel.


You can statically balance your prop well. This should be pretty close.

[rwaltman]

Went to the airport once earlier in the week and repitched the propeller to 9.1 degrees. Went back today to try it, slightly delayed by having to replace the band clamps holding the muffler.
The new setting gave exactly 6000 RPM static. The idle rpm went up with the lower propeller load, so another Carbmate session is due to bring it back below 2000 RPM. And still need to chase that CHT ...

Roberto.


Another static flight into the sunset ...