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Turbine Commander Engines / Re: When do you go to low RPM on landing?
« Last post by donv on March 20, 2023, 05:46:07 pm »
I bring them back once things are stable and I'm on the runway and slowing down.

The Merlin used to have a procedure where you didn't bring them back until turning off the runway, but I think that had something to do with the 4-blade props. The Merlin also had minimal reverse (although didn't need much, because the prop discs were so huge even in Beta!).

If you plan on using reverse, as opposed to just beta, keep the RPM in high until you are done, whenever that is.
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Turbine Commander Engines / Re: When do you go to low RPM on landing?
« Last post by appleseed on March 20, 2023, 02:29:06 pm »
Are you saying You don't go into beta at all sometimes after landing?

On a related note, If I am stopped with nothing behind me to worry about prop blasting I do bring power levers over the gate and out of beta. I was waiting for a clearance one evening, parking brake set underneath a light  that was flickering at a frequency that allowed the prop blades to become visible, and they were oscillating freely through a surprising pitch range that looked like it would wear things out at a higher rate than when we came out of beta and put positive load on the blades. I used to try to minimize wear on brakes. But now I prefer to not be at zero thrust blade angle. Positive thrust, or negative (rarely actually get into reverse) but not floating in between.

And to answer your question Adam, about 40-60 knots. Not in hurry to drop rpm.
dealing with crosswind, or atc is higher priority. But I always go to flight idle and then Beta at touchdown. I got used to lift dump in jets and I feel like flight idle then beta is the next best thing.
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Turbine Commander Engines / When do you go to low RPM on landing?
« Last post by Adam Frisch on March 20, 2023, 02:20:29 am »
This is one of the areas I'm not sure I've been correctly taught in. If I'm not using reverse, I tend to go to low RPM as soon as I can after touchdown, to kill residual thrust. But when I looked at a few older clips on YouTube about operating the TPE, it seems they recommend doing that after clearing the rwy. But in my aircraft, the thrust at high RPM is considerable even at idle power, so I tend to not want to do that. What's correct?
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Classifieds / Commander Seats
« Last post by Ray787 on March 15, 2023, 08:49:28 am »
Does anyone know if someone might have some 500S Commander Seats for sale ?     
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Instructional / Re: Climb Profiles
« Last post by donv on March 14, 2023, 02:40:15 pm »
I think fundamentally that you are correct, it is more or less the same for the same IAS. And that makes sense, since IAS is a measure of how much wind resistance you are facing.

However, as you go up (until you hit the tropopause), each knot of IAS is worth more TAS. So you are spending the same amount of fuel, yes, but getting more knots of TAS for it, and thus becoming more efficient.

It is possible to go too high, though, and get behind the power curve, and now you are not getting more TAS because you don't have enough power to get the IAS that you need, even though you are burning the fuel. In a 980, this is almost never the case, but it certainly can be in jets.
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Instructional / Re: Climb Profiles
« Last post by Adam Frisch on March 14, 2023, 02:28:42 pm »
We've had a long discussion over at the BT forum, and I think the consensus is that the FF is independent of altitude for the same KIAS (which is all we care about when we're talking aerodynamic efficiency), just as it is for pistons. But nobody is quite sure, which is a little alarming as it should be part of our collective knowledge to know that. Because if you're halfway to Hawaii and you don't have enough fuel and you pressurization fails, how do you hypermile/extend a turbines range in the best way? Vg, of course. But if we're under the false assumption that more fuel efficiency can be achieved by staying higher up, when in fact it doesn't matter, then that could have severe operational consequences.

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Instructional / Re: Climb Profiles
« Last post by donv on March 13, 2023, 04:26:24 pm »
I'm not sure, but I can tell you this. In the early 2000s I was flying a Learjet 35 that didn't get RSVM certification for about a year after the RVSM rules took effect. So we were flying at FL280 instead of FL390-410 typically. We elected to operate the airplane at fuel flows giving us 400KTAS, at FL280, instead of the typical 440KTAS that we would see up high.

The result was that the fuel flow per hour was almost exactly the same as at the higher altitude, but the speed was 10% less. And, of course, we were operating way below the EGT limits.

So it was 10% less efficient, operating it down low. Was that because the engines were less efficient or the aerodynamics were less efficient? Not sure.

Nobody has ever been able to verify for me that flying at Vy in a turbine allows the same efficiency as it does in a piston. I would love for it to be true, but some people claim that turbines are only efficient when they have the highest permissible operating temp. If you run them at lower temps, the efficiency drops of a cliff, they say.

So, is that true?

Another thing I'd like answered is the old Carson speed example - how the efficiency is independent of altitude. Well, is it also for turbines? We've been drilled into our head we need altitude for efficiency, but is it really true?
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Instructional / Re: Climb Profiles
« Last post by Adam Frisch on March 13, 2023, 01:37:26 pm »
Nobody has ever been able to verify for me that flying at Vy in a turbine allows the same efficiency as it does in a piston. I would love for it to be true, but some people claim that turbines are only efficient when they have the highest permissible operating temp. If you run them at lower temps, the efficiency drops of a cliff, they say.

So, is that true?

Another thing I'd like answered is the old Carson speed example - how the efficiency is independent of altitude. Well, is it also for turbines? We've been drilled into our head we need altitude for efficiency, but is it really true?
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General Discussion / Re: Twin Commander Fly-In in September 2023!
« Last post by WilsonRiggan on March 13, 2023, 07:51:11 am »
We just put it on our calendar as well.
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Instructional / Re: Climb Profiles
« Last post by donv on March 12, 2023, 11:35:14 pm »
I had a discussion about climb profiles with Barry Lane at my recent recurrent. He also flies King Airs, and he pointed out a couple of things. First of all, the King Air wing is smaller and less efficient than the Commander wing, especially at high altitudes. Secondly, the PT6 is much less efficient at low altitudes than the 331, meaning that getting up high is more important on the PT6 airplanes than on the Commander.

So all in all, the Commander is able to climb at higher indicated airspeeds without the loss of efficiency that you would see in a King Air. He said he climbs around 160-165.
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