TLS/Bravo Takeoff performance at high density altitude

[Rick Junkin]

Does your airplane make the book numbers for takeoff distance at higher altitudes?

I got surprised at Big Bear (L35) last spring when my takeoff roll was far in excess of what I calculated from the POH charts. The same thing would have happened later that month on departure from Spanish Peaks (4V1) if I hadn't reference my Koch chart for a conservative backup set of numbers.

Are you seeing book numbers, or close to them, for your takeoffs at higher altitude airports? The charts say that the no wind takeoff roll shouldn't exceed 1500' at 10,000' pressure altitude and 30 degrees C, does that fit with what you are seeing?

Cheers,
Rick

[carusoam]

Rick,

What do you see for SL departures?

Have you used the MSFS flight sim Bravo? Not technically accurate, but it shows some long T/O runs at sea level... 1800' or so.

Are you measuring the actual T/O run using a WAAS source like CloudAhoy?

Comparing T/O runs between the O's 280 and 310 hp engines...

I went from 1200' to 800' ground rolls at light weights...

The Bravo has less HP and can drag the T/O run even longer...

Is the Turbo lag very noticeable in your plane?

The NA IO550 has full power as the MP is firewalled...

Best regards,

-a-

Edited March 27, 2017 by carusoam

[Rick Junkin]

My full gross takeoff roll is routinely 1,100' at my home airport (KSUS) at 463' MSL. The takeoff roll at 9-10,000' density altitude on two separate occasions was about 3,500', more than twice what the POH says it should take (1,500'), but right in line with what a Koch chart shows, using 1,000' feet for my SL baseline.

I used my Stratus track log data to get the distances. All power indications were nominal in all cases, and winds were minimal. I currently have no confidence in the takeoff charts in the POH, and use the Koch chart to determine my runway requirements. It's been working well for landing distances too.

Has anyone else seen this on a TLS/Bravo?

Cheers,

Rick

[Hoeschen]

Are you leaning for best takeoff power at altitude?

 

This as common as a mag check during my flight instruction in CO. However all my flat land flying ever since is always full rich for takeoff and when I do go to a high altitude airport I'm now uncomfortable pulling the mixture out for takeoff.

 

 

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[midlifeflyer]

11 minutes ago, Hoeschen said:

Are you leaning for best takeoff power at altitude?

 

This as common as a mag check during my flight instruction in CO. However all my flat land flying ever since is always full rich for takeoff and when I do go to a high altitude airport I'm now uncomfortable pulling the mixture out for takeoff.

 

 

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If I'm correct, the TLS Bravo is turbocharged. I'm not familiar with the model but with the turbos I have flown,  you do not lean for takeoff.

[Rick Junkin]

Good question, and no, I always take off full rich. My understanding is that I should always use full rich on takeoff with a turbocharged engine, but I'm always open to education!

Cheers,
Rick


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[JohnB]

33 minutes ago, Junkman said:

Good question, and no, I always take off full rich. My understanding is that I should always use full rich on takeoff with a turbocharged engine, but I'm always open to education!

Cheers,
Rick


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Rick, Your understanding is correct. You should Always take off full rich if you have a TLS/ Bravo engine. Your density controller will control fuel flow at altitude.

I haven't noticed a takeoff ground roll more than usual at high elevations in my plane but I will start keeping more exact track of it to see out of curiosity.

jb

[mike_elliott]

You didn't accidentally take off on one mag after doing your runup, did you, or not have the prop full forward? 

[Rick Junkin]

37 minutes ago, mike_elliott said:

You didn't accidentally take off on one mag after doing your runup, did you, or not have the prop full forward? 

Nope, I'm a checklist zealot, and didn't have anything out of place going in to cruise in either case. Everything looked nominal, except for how close I got to the end of the runway before liftoff...

Cheers,
Rick

[donkaye]

Rick, I'm responding here instead of your email to me of several days ago.  I've taken off at full gross from Leadville at DA of over 13,000'.  Leadville marks their 6,000' runway every 25%.  I was off  before the 1st line.  What was your MP at takeoff?  How many hours on your engine?  I have found that above 6,000' DA the Mooney does not really like to get book climb until about 100 knots.  I leave the ground at high DA and keep the plane in ground effect until I reach near 100 knots, then climb at Vy.  The plane immediately goes to 1,000 ft/min.

[Rick Junkin]

 

9 minutes ago, donkaye said:

Rick, I'm responding here instead of your email to me of several days ago.  I've taken off at full gross from Leadville at DA of over 13,000.  Leadville marks their 6,000 ft runway every 25%.  I was off  before the 1st line.  What was your MP at takeoff?  How many hours on your engine?

Engine parameters at takeoff were 2570RPM and just shy of the 38"MP redline. The engine is ~100 hours STOH with flow balanced cylinders done by Lycon in 2014, and ~700 hours SMOH in 2006. The prop was overhauled when the top was done. The engine was disassembled for inspection in 2014 when the previous owner reconditioned the whole airplane, and was in great shape internally. The airplane produces better than book performance in cruise (185KTAS at 16K', 2200/30, 16GPH).

I'm beginning to think that I need to gather some more data to make sense of this. Could be that I was a little weak/late on my rotation? I was new to the airplane, less than 15 hours, but I remember that the acceleration seemed less than I was used to at that point and attributed it to the altitude.

Don, you've answered the major question that I had, and that is that I should be able to get the book performance numbers on takeoff.

I'm getting the book numbers here at home at ~460MSL, and all other performance parameters have been nominal.

Sitting here thinking about it, the only other thing I can imagine is a no-flap takeoff, or not-enough-flap takeoff, which would extend the roll. I'm sure that I had the flaps set for takeoff, but maybe I need to measure the flap angle with the indicator showing takeoff flaps to make sure I'm getting a full 10 degrees with the setting I use.

Any other thoughts?

Cheers,
Rick

[donkaye]

22 minutes ago, Junkman said:

 

Engine parameters at takeoff were 2570RPM and just shy of the 38"MP redline. The engine is ~100 hours STOH with flow balanced cylinders done by Lycon in 2014, and ~700 hours SMOH in 2006. The prop was overhauled when the top was done. The engine was disassembled for inspection in 2014 when the previous owner reconditioned the whole airplane, and was in great shape internally. The airplane produces better than book performance in cruise (185KTAS at 16K', 2200/30, 16GPH).

I'm beginning to think that I need to gather some more data to make sense of this. Could be that I was a little weak/late on my rotation? I was new to the airplane, less than 15 hours, but I remember that the acceleration seemed less than I was used to at that point and attributed it to the altitude.

Don, you've answered the major question that I had, and that is that I should be able to get the book performance numbers on takeoff.

I'm getting the book numbers here at home at ~460MSL, and all other performance parameters have been nominal.

Sitting here thinking about it, the only other thing I can imagine is a no-flap takeoff, or not-enough-flap takeoff, which would extend the roll. I'm sure that I had the flaps set for takeoff, but maybe I need to measure the flap angle with the indicator showing takeoff flaps to make sure I'm getting a full 10 degrees with the setting I use.

Any other thoughts?

Cheers,
Rick

Yes.  At gross see if you are getting book rate of climb at Vy.  That will tell all.

[midlifeflyer]

2 hours ago, donkaye said:

Rick, I'm responding here instead of your email to me of several days ago.  I've taken off at full gross from Leadville at DA of over 13,000'.  Leadville marks their 6,000' runway every 25%.  I was off  before the 1st line.  What was your MP at takeoff?  How many hours on your engine?  I have found that above 6,000' DA the Mooney does not really like to get book climb until about 100 knots.  I leave the ground at high DA and keep the plane in ground effect until I reach near 100 knots, then climb at Vy.  The plane immediately goes to 1,000 ft/min.

...and that, btw, is a very common takeoff procedure at very high density altitudes in piston aircraft.

[Rick Junkin]

Ok, for some reason I didn't get the last part of Don's original post as quoted by midlifeflyer...:

 "I have found that above 6,000' DA the Mooney does not really like to get book climb until about 100 knots.  I leave the ground at high DA and keep the plane in ground effect until I reach near 100 knots, then climb at Vy.  The plane immediately goes to 1,000 ft/min."

I believe it was my technique that was lacking and prolonged my takeoff roll. My Vy climb rates meet or exceed the book values at all altitudes, so I think I was using the same rotate-to-Vx technique that I was using at lower altitudes at that time, and kept the airplane essentially stalled on the ground at high DA until I powered through to a climb speed. That translates to an excessively long time on the ground.

I've since developed a technique of rotating at 65 knots and accelerating in a shallow climb to 120 knots before getting serious about establishing my climb, where the runway length and obstacle departure procedure allows, and consistently get a comfortable 700+ FPM climb rate. This is a little different from the recommended accelerating in ground effect to Vy, but that transition will be easy for me now. I haven't operated at high DA since getting smarter with my takeoff technique, but will be headed west in August (hence my interest in asking questions now) and wanted to get this figured out well in advance.

Thanks for the quick responses to my questions. I have a couple of trips to the east coast and the gulf planned over the next few months and will be practicing my technique before heading back to the Mojave Desert (KWJF) in August for my annual. I'm very loyal to the good folks at MH Aviation at William J Fox Field where I bought the airplane.

Cheers,
Rick

[midlifeflyer]

8 hours ago, Junkman said:

Ok, for some reason I didn't get the last part of Don's original post as quoted by midlifeflyer...:

 "I have found that above 6,000' DA the Mooney does not really like to get book climb until about 100 knots.  I leave the ground at high DA and keep the plane in ground effect until I reach near 100 knots, then climb at Vy.  The plane immediately goes to 1,000 ft/min."
Rick

Then I'm especially glad to have quoted it.

Just for reference, an expansion on that point. You have a number of things going on at high density altitude. Turbocharging helps with power but that's just one of them. The other big one is loss of airfoil efficiency - think of trying to drive a screw through whipped cream rather than a block of wood. So, even with a turbo, you have less thrust at high DAlt to overcome even simple things we don't usually worry about, like ground friction on your tires.

So you can do something similar to what you do on a soft field or water takeoff. Use a modified soft field technique where you get into the air and away from "ground drag" and into ground effect, level off, and accelerate to climb speed. 

Works in everything from LSAs to turbocharged pistons when the DAlt gets too high.

 

[gsxrpilot]

I read something the other day that Rotate is something jets do. And it's really not applicable, or shouldn't be, for the piston singles that we fly. With the plane properly trimmed for take-off, it should fly off the runway when ready. We shouldn't tell it when to fly by "rotating" at a specific speed.

In the thin air at high DH, the prop, wings, control surfaces, all take more time/speed to bite.

[midlifeflyer]

1 hour ago, gsxrpilot said:

I read something the other day that Rotate is something jets do. And it's really not applicable, or shouldn't be, for the piston singles that we fly. With the plane properly trimmed for take-off, it should fly off the runway when ready. We shouldn't tell it when to fly by "rotating" at a specific speed.

In the thin air at high DH, the prop, wings, control surfaces, all take more time/speed to bite.

It's a nice idea. It's value is in telling pilots that we don't have to do as much work as many of us do during takeoff. But it has some serious limitations, including at very high density altitudes. Just two example based on standard piston procedures:

1. Soft field takeoffs involve rotating to get the airplane off the ground and into ground effect before it is "ready" in order to minimize the takeoff roll.  I doubt simple trimming for takeoff will result in the airplane flying itself off some time before it crashes through the fence at the end of the runway.

2. Takeoffs in strong crosswinds typically involve keeping the airplane on the ground until after it is "ready"  and then pulling it off to avoid the  transition period when the wings are biting enough to lighten the aircraft but there is insufficient control authority to keep it from drifting across the runway and into the weeds.

Sure, a standard takeoff for a properly trimmed airplane on a hard paved runway in standard conditions with winds either zero or straight down the runway doesn't really require rotation. But as far as I can tell, we don't always get that. 

 

[DAVIDWH]

"I read something the other day that Rotate is something jets do. And it's really not applicable, or shouldn't be, for the piston singles that we fly. With the plane properly trimmed for take-off, it should fly off the runway when ready. We shouldn't tell it when to fly by "rotating" at a specific speed."

Like everything else in life, it depends:

A Mooney with its laminar flow wing and a standard takeoff,  I agree.

That being said, my previous,  Bellanca Super Viking,  would nose first, wheelbarrow you into the ground if you failed  to rotate.

[carqwik]

IMHO the Bravo is a dog with high/hot takeoffs...until you get to 120 kts.  So ground effect acceleration is the one trick to use to get to the speed needed.  Bob Kromer explained to me that it was the prop used on the Bravo.  A better climb prop cost some knots in cruise so they went with the "cruise" prop instead which is what we have.

[Rick Junkin]

Interesting point, Paul. Jets have a rotation speed where control power is available to raise the nose and set the angle of attack for takeoff, and then the airplane starts flying at takeoff speed.

I'm sure I'll get some educational inputs on this statement, but being properly trimmed for takeoff has a lot to do with your personal takeoff and climb technique and preference. For instance, my personal technique is to set trim at takeoff to give me 85KIAS on initial climb. That requires me to apply back pressure (rotate) at 65KIAS to raise the nose so that the mains don't come of the ground first. Once I'm away from the ground with a climb rate, I trim as I accelerate, clean the airplane up and and continue trimming to attain 120KIAS for my climb to altitude. 

I've learned from this thread that I need to modify that technique for high DA operations, and trim for a higher initial climb speed and stay in ground effect until I get there. The bottom line for me is that I want to be putting pressure on the yoke in only one direction during takeoff, and modulate that pressure to get the speeds where I want them and then trim as required to keep them there.

Ok, I'm ready to learn more...

Cheers,
Rick


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[jlunseth]

3 hours ago, carqwik said:

IMHO the Bravo is a dog with high/hot takeoffs...until you get to 120 kts.  So ground effect acceleration is the one trick to use to get to the speed needed.  Bob Kromer explained to me that it was the prop used on the Bravo.  A better climb prop cost some knots in cruise so they went with the "cruise" prop instead which is what we have.

I think that is true of all models - that the prop was chosen for cruise speed and efficiency and not for power on takeoff, but then we spend hours at cruise and minutes taking off so I like it that way.

[thinwing]

On 3/27/2017 at 0:34 PM, Junkman said:

My full gross takeoff roll is routinely 1,100' at my home airport (KSUS) at 463' MSL. The takeoff roll at 9-10,000' density altitude on two separate occasions was about 3,500', more than twice what the POH says it should take (1,500'), but right in line with what a Koch chart shows, using 1,000' feet for my SL baseline.

I used my Stratus track log data to get the distances. All power indications were nominal in all cases, and winds were minimal. I currently have no confidence in the takeoff charts in the POH, and use the Koch chart to determine my runway requirements. It's been working well for landing distances too.

Has anyone else seen this on a TLS/Bravo?

Cheers,

Rick

That is too long!At Evansville 7000 msl runway,warm morning say 78 about 2000 ft lift off..

[thinwing]

 Never  seen this at all...carqwik I am doing a WTF over your experience ...I realize in Scottsdale departing when asphalt temps are 135 f...but I have never experienced your "dog"performance..I usually like a 130 kt climb in hot air but that is temp controll...

[carqwik]

Just to clarify...my Bravo's INITIAL climb is doggy in high and hot conditions (as compared to cooler weather near sea level).  The differences (to me) are astounding. And by initial climb for high and hot, I mean from takeoff roll through climb until reaching 120 kts...then it gets with the program and seems to perform better.   

[donkaye]

Again, What is your Vy at sea level?  Do you perform a short field takeoff at high altitude?