NC Bill Posted February 6, 2011 Report Share Posted February 6, 2011 MY 912ULS sees 4850 ~ 4900rpms on T/O and climb out at Vy WOT. The ROTAX Service Letter says 5200 WOT and I plan to have it adjusted. Question is how difficult is that to do by a ROTAX certified A&E and about how long will it take? I need to plan the shop visit and hope to do it without RON. Thanks! Link to comment Share on other sites More sharing options...
CT4ME Posted February 6, 2011 Report Share Posted February 6, 2011 Hi Bill, I'm sure there will be more comment on this but, in a CT, I don't think 5200 is possible without going too high at WOT cruise. In other words, if you were to adjust for 5200 on climb, your straight and level WOT in cruise would likely be 5750+ or higher... I think most of us are probably getting around 5K on climb. I'm not sure what the book time is for adjusting the prop... but I've seen it done in less than an hour. Tim Link to comment Share on other sites More sharing options...
Roger Lee Posted February 6, 2011 Report Share Posted February 6, 2011 Hi Bill, If you are only turning 4850 rpm on take off then I bet you do not get 5500 rpm WOT flat and level? To get 5500 rpm WOT flat and level then you will usually see 4950-5050 rpm on take off. The reason for the spread above will depend on a few factors like density altitude for that particular day, climb angle, flap setting and OAT that day, ect.. My plane sees right at 5000+ take off rpm in a zero flap 75-80 knot climb. It might be a tad less at 15 flaps and a 60 knot climb. This puts me right at 5525-5550 rpm at WOT at about 3000' 3200' MSL. My field is 2417' MSL. Everyone with a CT is slightly different and you don't need to be on exact numbers, just in the ballpark. To reset the prop takes me about 30 minutes (ask Sandpiper , inside joke). It may take you a little longer like 40 minutes if you have never done one. If you tell me what WOT rpm you are set at and do it at your normal cruise altitude and I can tell you about how many prop pitch degrees it will take for the adjustment. If we set our ground adjustable only props to see 5200 rpm on take off then you will be very close to 5750-5800 rpm WOT flat and level. That is a loss for fuel economy and cruise to start with, but killer climb. The other issue here is if you ever break a throttle cable or one comes lose and you have a WOT setting like 5600-5800 you could only fly like that for 5 minutes. Remember if a cable breaks or comes lose you throttle lever spring is set to pull that carb to wide open. If you have the throttle setting to be a max of 5500 WOT flat and level and you break a cable then you could advance the throttle to allow the other carb to be wide open and you could fly any where for any length of time at 5500 rpm to an airport and that equates to a better safety margin for you. Everything we do should have a safety margin in it and being too close to the edge on the high side or low side decreases any safety margin. Link to comment Share on other sites More sharing options...
N89WD Posted February 6, 2011 Report Share Posted February 6, 2011 I'm seeing 4950-5100 on a Vy climb with DA's from 6000-9000'. Field elevation is 6201, WOT from 7500-11000 is 5500@11K to 5600@7500. Cruising at 5300 at pretty much those altitudes I consistantly see 4.8gph. I feel like my prop is set perfectly for my CT. I WANT AN INFLIGHT ADJUSTABLE PROP AND ONE OF THOSE BELLY PODS! Iguess we can s#%t in one hand and want in the other and see which one fills up faster. Link to comment Share on other sites More sharing options...
coppercity Posted February 7, 2011 Report Share Posted February 7, 2011 My airport is at 4780 ft above sea level, with density altitudes from 5000 to 10000 ft throughout the year. I see about 4850 at the start of the takeoff and about 4950 at 73kias Vy climb. Cruise at WOT at 7500ft is about 5600 and at 14500 WOT I get about 5300. I cruise at 10k to 12k most the time and 5400rpm, throttled back slightly with a fuel flow of 5.3-5.5gph. Link to comment Share on other sites More sharing options...
207WF Posted February 7, 2011 Report Share Posted February 7, 2011 I see 5050-5100 rpm on takeoff at Vy flaps -6, and my prop setting yields 5650-5700 rpm WOT at a similar altitude, operating from a sea level 'port. I would go 100 rpm coarser to optimize cruise if things were perfect, maybe some day, I would probably get 2-3 knots more at 5200 rpm. Now I get 112 knots true in cruise at 5200 rpm in my CTSW. WF Link to comment Share on other sites More sharing options...
GlennM Posted February 8, 2011 Report Share Posted February 8, 2011 I get about 4800 rpm in a climb. The CTSW manual mentions 4800 rpm for a normal climb on page 6-1, so it is right on. They even have a blade incidence angle for a 2 bladed prop, which does not help anyone with a three bladed prop. Link to comment Share on other sites More sharing options...
Roger Lee Posted February 8, 2011 Report Share Posted February 8, 2011 Hi Glenn, There are typos in the manuals. Like the one I pointed out earlier in the Operators Manual, that the compression ratio is listed as 11:1 when it is only 10.5:1. We all need to read the SB's as they have corrections. Your 4800 rpm on climb has been corrected in an SB. The idle rpm is taught by Eric Tucker of Rotax and has been for many years. We need to get our info for all sources and not just one. I teach for Home Land Security and we teach "Best Practices" and that's what should always be taken into consideration. 20 years of 912 use has taught us and Rotax what the best practices are. Link to comment Share on other sites More sharing options...
GlennM Posted February 11, 2011 Report Share Posted February 11, 2011 I don't want to be operating against a service bulletin or left out. I looked on the Flight Design website and there is no mention of a pitch change to the propeller and their latest CTSW manual (Rev 7) still lists 4800 rpm. Do you have a copy of the Service Bulletin that changes the normal takeoff rpm to something above 4800 rpm? I would like to take it to Lockwood to get the prop repitched. Thanks, Glenn Link to comment Share on other sites More sharing options...
Roger Lee Posted February 11, 2011 Report Share Posted February 11, 2011 Hi Glenn, People aren't always jolly on the spot on bringing up certain areas in manuals. Rest assured it is ok. FD themselves now bring in all CT's with the max rpm set at 5500 WOT flat and level. Rotax told them and it has been documented that over stressing the gearbox and crankcase with a max WOT setting of only at 5200 can and has cracked crankcases. FD has been setting WOT rpm to 5500 for at least 2 years and maybe a little longer. Lockwood will have no problem setting the rpm to the proper 5500 rpm. Don't wait, every flight with a 5200 WOT rpm can cause harm. Link to comment Share on other sites More sharing options...
GlennM Posted February 11, 2011 Report Share Posted February 11, 2011 I must be ok then. I have never been to WOT in cruise, so I don't know what RPM I would get. I got caught up on the 4800 rpm during a normal climb being a proxy for the WOT engine speed. I have been to 5300 and have had throttle left, so it is definitely not set to 5200. Thanks. Link to comment Share on other sites More sharing options...
Tom Baker Posted February 11, 2011 Report Share Posted February 11, 2011 I don't want to be operating against a service bulletin or left out. I looked on the Flight Design website and there is no mention of a pitch change to the propeller and their latest CTSW manual (Rev 7) still lists 4800 rpm. Do you have a copy of the Service Bulletin that changes the normal takeoff rpm to something above 4800 rpm? I would like to take it to Lockwood to get the prop repitched. Thanks, Glenn Glenn, the SB is from Rotax not Flight Design. I ask about this last year at Sebring at the Rotax booth. There were several factors that Rotax considered when making this recomendation. The one thing that the CT has going for it is the light weight Nueform prop. The Rotax rep said they had not seen any problems with the CT. That being said there other advantages to repitching the prop. You will see increased performance with reduced fuel burn. All of this at the same cruise speed. IMO those advantages along with less stress on the engine it is the right thing to do. Tom Link to comment Share on other sites More sharing options...
CT4ME Posted February 11, 2011 Report Share Posted February 11, 2011 I must be ok then. I have never been to WOT in cruise, so I don't know what RPM I would get. I got caught up on the 4800 rpm during a normal climb being a proxy for the WOT engine speed. I have been to 5300 and have had throttle left, so it is definitely not set to 5200. Thanks. The physical throttle position/location may not be a good indication of WOT. Mine seems to be about 70% of physical travel space is actual WOT. You can even open the little cover at the bottom and see that, from that point forward, the cable is actually no longer advancing and just bunching up. You could also open the cowling and see at what point the lever on the carb is no longer moving. Tim Link to comment Share on other sites More sharing options...
207WF Posted February 13, 2011 Report Share Posted February 13, 2011 Roger's broken cable scenario is a great argument for 5500 WOT, or even a tad less, that I had not considered. Maybe I will try to coarsen mine by 100-150 rpm to hit that! WF Link to comment Share on other sites More sharing options...
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