Climb Profiles

[donv]

In the "5 year items" discussion, we ended up talking about climb profiles.

In the 980, I climb at around 165-170, generally. Down low, this still gets me 2000+ fpm and a reasonable deck angle. The performance charts call for climbing at 130 and decreasing from there, which just seems too slow and too steep. I remember learning from the late John Baldwin, who did my initial Commander training almost 40 years ago, that climbing at the lower speeds didn't seem to result in that much greater of a rate of climb, and the higher speeds got you down range more quickly.

What do others do?

[grantacparks]

I climb at 160 unless I have a reason to reference VSI only (i.e. short step climb, or low cruise altitude). Same speeed I used in the Meridian. I fly a PC-12 as well and the prescribed climb speed is 130 which feels slow.

[Adam Frisch]

POH on the old 680V says Cruise Climb: 135kts. But that's for the original BL engines, so with the Dash 1's, should be a bit better, but haven't gotten any real world numbers.

[JimC]

I understand Vy "feels slow" for powerful turboprops.

But if it lowers your fuel burn and gets you to your destination faster, why not use that profile?

To answer some of Appleseed's questions:

I don't worry about the pax facing backwards. If I have passengers that are nervous I find they self-select to the forward facing seats. My angle of climb is certainly less than an Airbus.

The book profile for max range descent is to fly the profile that results in continuous flight at Vmmo/Vne with power near idle. I think that profile is a little ridiculous and leaves no room for error. Flying a slightly more conservative, but still aggressive, descent profile changes the fuel burn very little. Overall, I delay my descents as long as possible with two exceptions:

If I'm descending from more than FL280 to near sea level, I need to manage the descent to keep cabin altitude descent rates less than 500 ft/min. Descending to my home airport, pressure management is trivial - the cabin finishes the flight at 7,000 ft.

If I expect significant turbulence, I don't want to be near Vmmo or Vne so I'll start descending earlier. I can keep the speed down in a steep descent with the gear out, but I have found that a steep descent in turbulence makes passengers much more nervous than a steep climb.

And, of course, if I'm flying into a B I don't have any say in the matter at all. ATC starts descending me shortly after takeoff.

[donv]

The King Air's angle of climb might be less than an Airbus, but that is not true for a 980 climbing at 130 knots!

Remember, the 980 owned the time to climb and altitude records for turboprops until the Cheyenne 400LS came along.

[JimC]

And as soon as I get one *every* climb will be a Vy climb...

OK, ok....maybe a few Angel flights will have a nice flat climb...but why buy a rocket ship if you're not gonna rocket? 

[JMA]

DonV, time to climb-valid point... we were heavily using the 980 in the 80's and my father couldn't keep up with the flying demands.  Kept a corporate pilot on retainer to help handle the load, he once was showing off doing max takeoff and scraped off the tail lock holder (metal piece)...   Crazy guy.

[donv]

I've heard of people scraping the tail on takeoff-- on the 690A with some antennas back there, it used to happen pretty easily. But on a 980, it takes some work.

The truly crazy thing is, I remember one guy boasting about doing it more than once! He was proud of it! It takes all kinds, I guess...

[JMA]

Im sure there are some crazy stories out there.  Not sure who's 980, but youtube shows this max takeoff

https://www.youtube.com/watch?v=eEF_KdyKSyA

[donv]

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.

[Adam Frisch]

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?

[donv]

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?

[Adam Frisch]

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.

[donv]

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.