Bobby CAU Posted August 12, 2012 Author Report Share Posted August 12, 2012 dear Roger and Tim, BIG THANKs to you both for guiding me. im just quite new comer and willing to learn from you, and again thanks !!. it is GOOD discussion for me, i would go out now and start to try and made some adjustment as well. i made a phone call to my instructor this evening and told him about what i had thru this forum and it was surprising him too. just a GOOD new knowledge to us here. all the way my training always at 4000 to get 85 knot but now it could be different. sometimes, 85 knots quite fast to me to enjoy the great scenes but sometimes as well i need 120 knot as you said !!. NO HARM at all hahaha ... btw, what is the maximal rpm in CT when we open for full throttle?. Jakarta always high humidity as always, visibility not that good as last time but still ok for VFR. you will be here soon, then you will be know Roger !!. regards from Jakarta to Tim and Roger, Bobby CAU Link to comment Share on other sites More sharing options...
Roger Lee Posted August 12, 2012 Report Share Posted August 12, 2012 Hi Bobby, I look forward to meeting. Let me know. It's a shame you won't be here for the Page, AZ Fly-In then you would gets lots of great scenery and good CT and Rotax information right from the people. It's some of the best scenery in the US. Don't take offense guys in the other parts of the US I think that scenery is really great too. I like it all. It's just the Grand Canyon, Lake Powell, Zion & Bryce Canyon and last, but not least Monument Valley is very different. Now that I think about it, Bobby why not fly over and join us at Page, AZ Fly-In? There is always an open seat some where. Link to comment Share on other sites More sharing options...
Bobby CAU Posted August 12, 2012 Author Report Share Posted August 12, 2012 hello Roger, WOW to me ... the scenes there INCREDIBLE for me for sure. thanks for the new info and will consider if still got seat of course ... i already checked out the US FD site and put in our group now, lets see and will info to you. regards, Bobby CAU Link to comment Share on other sites More sharing options...
CT4ME Posted August 12, 2012 Report Share Posted August 12, 2012 BTW, not that we haven't beat this horse to death... but in the Sept 2012 Plane&Pilot magazine (sport pilot special), they suggest a minimum of 5,000 cruise for Rotax, 4,000 for descent. Typical 75% cruise is 5,200. Other interesting tips and an otherwise good article - although they don't mention the CT much. Tim Link to comment Share on other sites More sharing options...
chanik Posted August 12, 2012 Report Share Posted August 12, 2012 Best endurance would be an rpm that will maintain altitude without any loss and this may be down around 4000 rpm. Speeds will be down around 50 knots. I have a friend that has been up in the CT for over 9 hours on a tank. Best endurance and range will always be something close to Vy, about 78kts. Below that, the plane has a higher induced drag profile from inefficient lift generation and above, the drag climbs with (very roughly) velocity ^2 due to form drag and skin friction. After all, I can fly nose high that requires full power just to maintain altitude at 40kts Link to comment Share on other sites More sharing options...
Doug G. Posted August 12, 2012 Report Share Posted August 12, 2012 BTW, not that we haven't beat this horse to death... but in the Sept 2012 Plane&Pilot magazine (sport pilot special), they suggest a minimum of 5,000 cruise for Rotax, 4,000 for descent. Typical 75% cruise is 5,200. Other interesting tips and an otherwise good article - although they don't mention the CT much. Tim Tim, not sure what that means since the CTLS Performance Addendum puts 75% at 5010 to 5050 except at 12,000 ft.where it goes up to 5100. I guess if I split the difference I need to hold it at 5005 rpm! Doug Link to comment Share on other sites More sharing options...
Roger Lee Posted August 12, 2012 Report Share Posted August 12, 2012 Hi Doug, The CTLS manual is based on the Rotax manual and many of those figures are based on a constant speed prop and not a ground adjustable. These figures are also based on a 5800 WOT setting both for take off and for 5800 WOT flat and level. When you look at these manual numbers keep this in mind and some may need a little interpolation. Set your prop pitch to get 5550-5700 rpm WOT flat and level at your average altitude. Then cruise over 5000 rpm and I would say many 912 owners seem to cruise between 5100-5300. Easy on the engine and fuel economy. We can beat these numbers up all day and everyone will have a little difference in preference, but so long as your some where in those numbers your good and it will make absolutely no difference one way or the other. Since we don't have a constant speed prop we need to balance our flight characteristics for the best all around. Link to comment Share on other sites More sharing options...
Howardnmn Posted August 13, 2012 Report Share Posted August 13, 2012 FWIW my Remos GX POH says economy cruise is 4400 - 4800 rpm. Link to comment Share on other sites More sharing options...
Roger Lee Posted August 13, 2012 Report Share Posted August 13, 2012 The problem has been with some of the LSA Mfg's is they never read the Rotax manuals and they have been wrong numerous times. I have helped correct almost a dozen mistakes that have been in print by LSA Mfg's and that just the tip of the iceberg. This has been happening not only with the engines (Rotax, Jabiru, Hirth ect...), but with other components from other Mfg's that the LSA Mfg's are using. One of the big problems which is slowly working itself out is the way Mfg's have written their regs in their manuals and has over stepped or left things out on a fairly frequent basis. Like I said the LSA industry is fairly new compared to the other categories and don't forget where many LSA's come from, Europe and they don't understand many of our regs so things will take a while to work themselves out. I remember when Remos had a mistake in the manual about who could do an inspection. It originally said only an A&P and completely left out an LSRM-A. That was one I called about and they had it change in the manual within 24 hrs. Link to comment Share on other sites More sharing options...
CT4ME Posted August 13, 2012 Report Share Posted August 13, 2012 FWIW my Remos GX POH says economy cruise is 4400 - 4800 rpm. I'm sure the economy cruise spec'd by most manufacturers is similar... what they don't tell you is that while it may save fuel, it's not necessarily saving your engine. At that RPM, if you are burning 100LL, you are definitely gumming things up with lead. I think Jeremy or Roger had some great pics of the innards of a flight school engine, where they ran mostly 100LL... lead was caked all over. Tim Link to comment Share on other sites More sharing options...
Howardnmn Posted August 15, 2012 Report Share Posted August 15, 2012 Besides the lead build up (I'm using mogas) what harm is done cruising at 4500? Link to comment Share on other sites More sharing options...
Jim Meade Posted August 15, 2012 Report Share Posted August 15, 2012 It is interesting that the 912 manual lists operating at 55% 4300 rpm and 65% 4800 rpm. One would think if it was unsuitable that the manual would be changed. Link to comment Share on other sites More sharing options...
CT4ME Posted August 15, 2012 Report Share Posted August 15, 2012 Same answer... you can cruise whatever speed you want, it's just that you aren't doing your Rotax 912 engine a favor by throttling back. It's not that it is unsuitable, it just might cause a bit more wear. Nothing serious, probably not notable, but perhaps measurable with a nanometer. It's kind of like lugging/revving a automobile engine... you're not going to see it seize-up just because you shift into 3rd gear too early (or late), but you can feel the engine's pain. Tim Link to comment Share on other sites More sharing options...
CT4ME Posted August 15, 2012 Report Share Posted August 15, 2012 Besides the lead build up (I'm using mogas) what harm is done cruising at 4500? I don't know I would use the word "harm"... it's just that there is actually more wear on the engine at that speed than 5400. It's counter-intuitive. Back in post #15, it mentions more piston wear and general drive-train stress is increased. I'm sure there is a best air temperature to run the Rotax, too, but we all fly at various temperatures. Sure, there's probably more stress/wear on the engine because I fly at 100 degrees, but that doesn't stop me from flying. Tim Link to comment Share on other sites More sharing options...
Bobby CAU Posted August 16, 2012 Author Report Share Posted August 16, 2012 dear Roger and Tim, yesterday i just flew and found if maximal rpm i had is 4700 and during idle or taxi rpm is 2100. is there any problem with my engine setting?. regards, Robert CAU Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted August 16, 2012 Report Share Posted August 16, 2012 Bobby, What type of prop do you have? Is it adjustable in flight? When you found your max RPM to be 4,700 is that on the ground or in flight? Link to comment Share on other sites More sharing options...
Bobby CAU Posted August 16, 2012 Author Report Share Posted August 16, 2012 hi Charlie Tanggo, thanks for the quick response, 1. im using neuform 2. max rpm gets during take off (maximal power) 3. during taxi or idle is rpm 2100 4. i dont know the prop could be adjust during flight regards, Bobby CAU Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted August 16, 2012 Report Share Posted August 16, 2012 Your idle sounds a bit high, is that because of your carbs or because of your prop pitch being flat? You can probably get better economy, more speed and at the same time be kinder to your engine if your prop pitch is optimized. What qualifications does your mechanic have? Can he adjust your prop pitch? #1 all 3 blades need to be the same pitch within a close tolerance. #2 you want to be able to achieve 5,500RPM in level flight, at WOT ( wide open throttle ) at your normal cruising altitude. 7,500' is a good altitude for many because there is where you will receive your best performance. ( perhaps your missions are always close to the ground ) You can only realize maximum power if you can achieve 5,800RPM at WOT but that only benefits you for 3 minutes and the CT climbs well so it makes more sense to optimize for cruise. In order to realize maximum cruise power you need to fly at 5,500RPM at WOT, your prop pitch will determine at which altitude you can realize max power for that altitude. After you pick the altitude to optimize for and see what your current, level flight WOT RPM is, you can compare that to your static ( on the ground max ) and Roger Lee can tell you how many degrees to change the prop blades. Your plane should fly 125 knots give or take. Link to comment Share on other sites More sharing options...
Bobby CAU Posted August 16, 2012 Author Report Share Posted August 16, 2012 thanks for the reply. 1. total population CT in indonesia about 8 aircraft 2. we do not have QUALIFICATION mechanical here in indonesia 3. normal cruising to us here about 3000 to 6000 but mostly 1200 during the flight 4. long journey only will be climb and cruise at 6000 regards, Bobby CAU Link to comment Share on other sites More sharing options...
sandpiper Posted August 16, 2012 Report Share Posted August 16, 2012 Bobby, If you have a fixed pitch prop and you can only get 4700 RPM WOT in climb then you need to repitch. Set it for 5500 in level flight with WOT at an altitude you frequently use. That, in turn, should give you 5000-5050 on climb out. 4700 RPM with WOT is much too low. Link to comment Share on other sites More sharing options...
Bobby CAU Posted August 16, 2012 Author Report Share Posted August 16, 2012 dear John and Charlie, thanks a lot, really open my mind now ... learning everyday. so ... 1. max WOT should be in 5700 right? 2. idle is 2000 still ok? 3. to get above 2 then i should repitch, am i right? regards, Bobby CAU Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted August 16, 2012 Report Share Posted August 16, 2012 1. max WOT should be in 5700 right? If your mission was to tow gliders, then yes otherwise limit to 5,500 at cruising altitude, maybe 6,000' 2. idle is 2000 still ok? I'm assuming its your carb set up, I would get your prop pitched for cruise then set your carbs to idle at lower idle, maybe 1,700. 2,000 will increase your float / landing distance. 3. to get above 2 then i should repitch, am i right? You should repitch to get above 4,700 use 5,500 at level, cruise flight with wide open throttle, at 6,000' as a target. You can then fly at higher power settings without giving up the lower power settings that you currently have. You can also have all power settings at higher RPM to be easier on your engine. Link to comment Share on other sites More sharing options...
Bobby CAU Posted August 16, 2012 Author Report Share Posted August 16, 2012 Wow ... THANKS John ... now, clear to me ... will do the setting later. again, THANKS !! regards, Bobby CAU Link to comment Share on other sites More sharing options...
Howardnmn Posted August 25, 2012 Report Share Posted August 25, 2012 It seems to me that answers to the simple questions regarding airplane criuse operation asked at the start of this thread should be available in the POH or published by Rotax Inc. What is a good cruise rpm setting for: hi speed; most economical/ best endurance; and low speed for neighborhood touring? Doesn't the tach with 'rotax' logo have green, yellow and red zones? Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted August 25, 2012 Report Share Posted August 25, 2012 It seems to me that answers to the simple questions regarding airplane criuse operation asked at the start of this thread should be available in the POH or published by Rotax Inc. What is a good cruise rpm setting for: hi speed; most economical/ best endurance; and low speed for neighborhood touring? Doesn't the tach with 'rotax' logo have green, yellow and red zones? The best cruising RPM for me is 5,500 ( WOT @ 10,000' ) that way I can realize at least 70hp while cruising high in the mountains. Most CTSWs that I have seen were not capable of this because of their prop settings. The answers to these simple questions have some complexity. I might descend at 4,700RPM ( in the green ) with a partially open throttle and the descent won't damage anything due to its duration and lack of load on the engine. Cruising at 4,700 ( still in the green ) can present problems due to lead build up or vibration or over-stress due to a coarse prop setting or even just wasting fuel. What is a good cruise rpm setting for: hi speed; most economical/ best endurance; and low speed for neighborhood touring? There are lots of answers, if I lived in the Bay Area I would pitch for 5,500RPM @ WOT @ 7,500'DA and that would be your high speed setting. Most economical would be to throttle back to something like 55% but you might find 70% or 65% to be a nicer compromise. For neighborhood touring just throttle back to a setting that gives you adequate speed. If flying for best economy be sure to use unleaded fuel. Link to comment Share on other sites More sharing options...
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