Anticept Posted June 18 Report Share Posted June 18 Best glide is an indicated based airspeed, and so is L/D. Thus, so is the Carson Number. In no wind condition, it will give you the greatest distance to fuel consumed. Of course, if you can still develop the power, higher is better in no wind, and standard lapse rates. Also remember that travel time is a little funny... going faster doesn't always make it worth it. Example: It takes 60 minutes to go 60 nautical miles at 60 knots. If you double your speed, you will arrive in thirty minutes. If you then double your speed AGAIN (120 -> 240) you don't go to 0 minutes of travel... you now need 15 minutes. Double again to 480, and it takes 7.5 minutes. Now imagine your exploding fuel consumption if your aircraft could perform these speeds... Now on our smaller scale with our little aircraft... adding an extra 10-15 knots is going to consume a lot more fuel, but it is not going to save you much time unless it's a LONG journey. Quote Link to comment Share on other sites More sharing options...
Towner Posted June 18 Report Share Posted June 18 2 hours ago, FlyingMonkey said: Hmm...according to that article, the number is found by best glide x 1.316. Best glide at -6° flaps is 78kt. So that number for the CT is 78 x 1.316 = 102.6kt. That is awfully slow...102kt indicated might be a good number at 10,000ft to give a good TAS cruise speed, but at lower altitudes it would not be ideal or even good. 102kt indicated at 4000ft would have me chugging along at something like 4500rpm. Maybe I'm missing something? I’m not sure where you got 78 knots at -6 for best glide. I know my SW shows 63 at 15 degrees. I believe the LS has 78 at 0 degrees. Where did you find the -6 best glide speed at? The POH on mine is definitely weak on information. Quote Link to comment Share on other sites More sharing options...
Jim Meade Posted June 19 Report Share Posted June 19 15 hours ago, FlyingMonkey said: Assuming you're measuring by the reciprocal of others' measurements, you are right at 27° (63 + 27 = 90). Andy, who cares? All that matters is the RPM at WOT at cruise (or whatever your criteria is). Other than an initial "get it close" setting, pitch is utterly and completely irrelevant. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 20 Report Share Posted June 20 On 6/18/2024 at 6:13 PM, Towner said: I’m not sure where you got 78 knots at -6 for best glide. I know my SW shows 63 at 15 degrees. I believe the LS has 78 at 0 degrees. Where did you find the -6 best glide speed at? The POH on mine is definitely weak on information. I correlated the POH and other source information with my own real-world testing to get 78kt. Unless you cruise at 15° flaps the best glide at that setting makes no difference. I'm sure the Carson number at that setting is something like 80kt (if not higher), right at max speed for the flaps. Nobody's going to cruise any distance at 80kt and 4000rpm in a CT, no matter how much fuel it saves. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 20 Report Share Posted June 20 On 6/18/2024 at 11:20 PM, Jim Meade said: Andy, who cares? All that matters is the RPM at WOT at cruise (or whatever your criteria is). Other than an initial "get it close" setting, pitch is utterly and completely irrelevant. Uh, ok. I'm just pointing out that it sounds like your pitch is similar to others' E-Prop pitch numbers. It wasn't a personal attack or anything, just a bit of napkin math to discuss. Maybe switch to decaf. Quote Link to comment Share on other sites More sharing options...
Towner Posted June 20 Report Share Posted June 20 49 minutes ago, FlyingMonkey said: I correlated the POH and other source information with my own real-world testing to get 78kt. Unless you cruise at 15° flaps the best glide at that setting makes no difference. I'm sure the Carson number at that setting is something like 80kt (if not higher), right at max speed for the flaps. Nobody's going to cruise any distance at 80kt and 4000rpm in a CT, no matter how much fuel it saves. The Carson number is something I’ve never heard of, so I’m guessing I should be figuring out my best glide at -6 to make it work for cruise. I was just wondering where you got the speed. I thought maybe I had missed something or something new had come out giving the best glide for other flap settings. I’ve played a little to compare best glide at 0 degrees vs the 15 degree speed in the POH, but never at -6. I guess I should do the same for -6 now too. I was just hoping something with this speed was put out by the factory, but I guess it’s back to doing experiments and calculations to find the best glide for me at -6. I might just cheat and use your number and call it close enough for my plane too. I think the planes are probably close enough that the best glide would be no more than a knot or two different from each other in the same configuration. Quote Link to comment Share on other sites More sharing options...
Roger Lee Posted June 20 Report Share Posted June 20 Since people / pilots and instruments are that accurate then I would worry about splitting hairs. Quote Link to comment Share on other sites More sharing options...
Anticept Posted June 21 Report Share Posted June 21 It wouldn't make any sense to fly in a dirty configuration while trying to aim for the Carson Number. Unless you're in something really exotic. As far as pitch is concerned, e-props has the recommendations with their instructions. If you deviate from their recommendations, the stalled portion of the prop will either kick in too soon or too late, which means prone to overspeeding or loss of take off and climb performance. The whole reason for the e-prop's design is so that the engine can spin at high RPM at launch. Power = torque x RPM. This is why variable pitch props and their siblings exist, maximize RPM, as the torque is set by engine geometry, then drop RPM down so that leaner mixes can be used without detonating. E-props figured out a way to do it by stalling part of the prop until enough forward airspeed is attained instead of complex mechanical movement systems. Quote Link to comment Share on other sites More sharing options...
Jim Meade Posted June 21 Report Share Posted June 21 11 hours ago, FlyingMonkey said: Uh, ok. I'm just pointing out that it sounds like your pitch is similar to others' E-Prop pitch numbers. It wasn't a personal attack or anything, just a bit of napkin math to discuss. Maybe switch to decaf. I guess I didn't get my point across. (And, by the way, I do not take caffein in any form - thanks for your concern about my health.) Here's what E-PROPS says: 12.1. ROTAX 4-stroke engines PROCEDURE: 1/ Adjust the pitch as recommended on your E-Props Propeller Identification Sheet. 2/ On the ground, put full power on brakes or chocks. - If you have between 5.000 and 5.800 rpm, you can go on with the flight tests. - If this is not the case, adjust the blade pitch to have between 5.000 and 5.800 rpm on the ground. Increasing the pitch by 0,6° reduces the rpm by 100 rpm (and vice versa). No mention of a given pitch, only that the pitch yields the desired result. Quote Link to comment Share on other sites More sharing options...
Anticept Posted June 21 Report Share Posted June 21 Big point to jim's post: by specifying performance and not pitch, you eliminate having to worry about field conditions. If pitch were set by a number, a table would be needed to list out conditions especially for altitude. Different conditions means different power curves, and someone operating regularly out of denver will have a different pitch than someone in seward, alaska. Since a big selling point to these props is their variable pitch like performance with a ground adjustable propeller, it requires more than just a number for setting their pitch. Constant speed and variable pitch props can adapt to any conditions for max performance, e-props cannot, they have to be tuned to their typical operating conditions just like any other fixed pitch prop. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 21 Report Share Posted June 21 17 hours ago, Towner said: The Carson number is something I’ve never heard of, so I’m guessing I should be figuring out my best glide at -6 to make it work for cruise. I was just wondering where you got the speed. I thought maybe I had missed something or something new had come out giving the best glide for other flap settings. I’ve played a little to compare best glide at 0 degrees vs the 15 degree speed in the POH, but never at -6. I guess I should do the same for -6 now too. I was just hoping something with this speed was put out by the factory, but I guess it’s back to doing experiments and calculations to find the best glide for me at -6. I might just cheat and use your number and call it close enough for my plane too. I think the planes are probably close enough that the best glide would be no more than a knot or two different from each other in the same configuration. I did my testing because I realized that the -6° configuration has the lowest drag, and thus will give best glide distance. You can glide a LONG way in a CT at -6° from anything above 3000ft AGL, but you are pretty fast. Since my testing my plan in engine out has been to leave the flaps in reflex for the glide and then progressively dump them once my chosen landing spot is made. As I said the number I came up with is 78kt, which is best climb at -6° (I read that number somewhere but I'm not sure where without digging into it again...maybe the CTLS POH?) and *should* be very close to best glide and my testing validated this. As Roger said don't split hairs...anything in the 77-82kt range it going to give you close to the same glide. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 21 Report Share Posted June 21 7 hours ago, Jim Meade said: I guess I didn't get my point across. (And, by the way, I do not take caffein in any form - thanks for your concern about my health.) Here's what E-PROPS says: 12.1. ROTAX 4-stroke engines PROCEDURE: 1/ Adjust the pitch as recommended on your E-Props Propeller Identification Sheet. 2/ On the ground, put full power on brakes or chocks. - If you have between 5.000 and 5.800 rpm, you can go on with the flight tests. - If this is not the case, adjust the blade pitch to have between 5.000 and 5.800 rpm on the ground. Increasing the pitch by 0,6° reduces the rpm by 100 rpm (and vice versa). No mention of a given pitch, only that the pitch yields the desired result. I agree they give recommendations in terms of rpm and not pitch, but one of their docs or videos does mention starting at 27° and fine tuning from there. Most folks with the E-Prop on the CT seem to land between 26.5° to 27.5°. I guess I don't see why you resist having a starting pitch to try...it's not like you can know where to pitch the blade for the correct RPM by guessing. I certainly never said pitch to 27° and forget it...you have to get the rpm correct through testing, as with any fixed pitch prop change. But you have to start somewhere. Quote Link to comment Share on other sites More sharing options...
Jim Meade Posted June 21 Report Share Posted June 21 Yeah, I think that is what I said several messages ago. "Andy, who cares? All that matters is the RPM at WOT at cruise (or whatever your criteria is). Other than an initial "get it close" setting, pitch is utterly and completely irrelevant." The "get it close" initial or "start" setting on my FDCTSW is about 27 degrees. ON my Rans S-7S it was 23. Quote Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 21 Report Share Posted June 21 4 hours ago, Jim Meade said: Yeah, I think that is what I said several messages ago. "Andy, who cares? All that matters is the RPM at WOT at cruise (or whatever your criteria is). Other than an initial "get it close" setting, pitch is utterly and completely irrelevant." The "get it close" initial or "start" setting on my FDCTSW is about 27 degrees. ON my Rans S-7S it was 23. We are in agreement. Quote Link to comment Share on other sites More sharing options...
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