General rule, a reduction in diameter of 1" (1/2" taken from each blade) will yield an increase in rpm of 100 rpm. So take that original prop down to 50" diameter and you will have your 2900 rpm. That's an easy mod to do, just re balance it and you're done.
On Wed, Dec 23, 2015, 8:04 AM Mark Langford via KRnet <krnet at list.krnet.org> wrote: > Pierre wrote: > > >> It feels as if I've hit a brick wall. I had a 48(pitch) X 52 prop on > my KR2S> (haven't flown yet). The max revs I got was 2,760rpm static.<< > > Depending on the displacement of the VW engine, you likely need less > pitch (as others were quick to point out). The way the prop maker > measures pitch is important also. Having had about 20 different props > on my KR2S and KR2, I can tell you that the pitch numbers vary wildly, > with respect to RPM. Sterba, for example is almost always has higher > pitch numbers for a prop that would turn the same RPM from somebody > else. Tennessee props tends to be nearer to Sterba than others. > > If you haven't seen it already, take a look at the prop vs engine > numbers listed for fifty different KRs at > http://www.krnet.org/kr-info.html . That may help you narrow it down. > > Another issue is are you sure the ignition timing is correct? It's > worth double checking everything involved in making that right (TDC > mark, for example). Ignition timing is everything. Checked at 2700 rpm > or above for full advance to 30 degrees? That eliminates advance issues. > I know it's a real pain to check timing with a a propeller installed, > and very dangerous, so I've started doing it before the prop is even > installed. Given that I do have a flywheel on the back of the engine for > the starter and alternator, it's not going to hurt the engine for a few > minutes, and it allows precise setting of the timing without the > adventure of a prop being there. What a huge difference in pucker factor! > > And you know for a fact that the cam timing is dead on? Have you > considered having the 48x52 repitched to something a little less? At > least that way you have two data points. > > As a data point, I can turn 3200 rpm static and turn it up to 2450 or so > wide open with a 2180cc engine with 8.6:1 compression ratio and 30 > degrees of advance at wide open throttle. I would be reluctant to take > off with only 3000 rpm with my short runway. > > Mark Langford > ML at N56ML.com > http://www.n56ml.com > > > _______________________________________________ > Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. > To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org > please see other KRnet info at http://www.krnet.org/info.html > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > options >
