Robert Gill wrote: Hi all, does any one have any advise on props, my kr2 has now had its second test flight on it, The prop is a Tonini gt, its a 56*44 and i am only getting 2800 rpm on climb and 2900 at 140 Kts....
160 mph isn't bad at low RPM, but with a CG that far forward, yes, you'll need lots of up trim to compensate. Your tail incidence is probably fine. The first time I flew N891JF the trim tab cable housing was broken, so I immobilized it in line with the elevator. It took a lot of up backstick to keep the nose up, and letting go of the stick would point it right at the ground. After I fixed the trim tab housing it required full nose-up trim from the trim tab to fly level without input. The easy cure is a small (5" tall, 1.5" wide) fixed aluminum tab on the elevator, but the real cure is to get the CG more aft. I've been doing that with it over the course of this rebuild, and right now the ELT, backup battery, and a few other items are located well aft of the seat back....as far as I can reach back there. I've also lightened the battery that hangs on the firewall, which will be moved to the front of the spar if needed, or even behind the seat to join the backup. Having CG biased toward the front is good, but the front limit isn't where you want to fly. CHT temps will likely be 25-50F higher during breakin, but RPM should be pretty close to final RPMs. It does stand to reason that EGTs would be somewhat high with a coating or wrapping that insulated them, but probably no 50F. EGTs are relative, so your probes may be closer than what others are seeing. If you're not into the 1400F range, I wouldn't get too upset about it, but it would make sense to make sure you're not running too lean by checking plugs and making sure you can richen it up to lower them with the mixture knob. Regarding props, you do need to do something to increase RPM. I'd see if you can borrow a couple of other ones before I started shortening yours. It will take a lot to get there, I'd think. Find one that works better, and then commission a copy to be made. I'm no Revmaster expert, but I'd want to be able to turn 3600 RPM on a VW-based engine to get max power out of it on climbout. After that throttle back and enjoy the economy. If it helps, see http://www.krnet.org/kr-info.html for other props for comparison, but nothing works like bolting on somebody else's prop and trying it. I've probably flown 12 different props on my plane, so I have a good feel for what works on a Corvair powered KR2S. Others who've shortened a prop may have some insight. That will certainly get you in the air quickly, but at the risk of making a less-than-efficient prop. I've never done it, so it may be just the ticket though. I know it's the last bit of the prop that does the most work. Most prop makers can repitch the prop some, so that's another option, but not as quick as lopping off a half inch at a time, I'll confess... Mark Langford, Harvest, AL ML at N56ML.com www.N56ML.com -----Original Message----- From: KRnet [mailto:krnet-bounces at list.krnet.org] On Behalf Of robert gill Sent: Tuesday, February 25, 2014 4:32 AM To: krnet at list.krnet.org Subject: KR> kr props _______________________________________________ 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
