High Density Altitude Operations

[Comet]

On 8/22/2020 at 10:25 AM, jaylw314 said:

Nice!  Thanks for the description of your procedure!

The highest DA I've taken off in was about 7000', from a 4000' runway, with 4 people and near max gross weight.  It took almost no runway to get off the ground with a 32 knot headwind (luckily not much of a crosswind, but a pretty exciting parking job!), but it seemed like it took forever to climb.  Luckily it was in a pretty flat area (Tulelake CA)

About the same time that I bought the airplane, there was a fatal accident at a nearby airport (higher altitude)...makes you think (and learn from others).

A couple of months after I bought the plane, there was a fatal accident at my airport.  The local flight instructors put together a good resource for the airport.  Always, a licence to learn.
 

https://f8fcd52a-a-62cb3a1a-s-sites.googlegroups.com/site/lamairport/airport-info/KLAM_Pilot_Warning.pdf?attachauth=ANoY7covjD11zC5M6-s0faEhn4vat8zQ7ZHITI6D2OF9LxazDLqhiqJVeDR1v9BcdL1biL3YVkBK9JclSCGkciv3zh-JhHszrXR59IF2eXErA5rxdI8FEDh_T6uSbG45LJdRln1ezeUDUbjK8HGKOvOAbxYQw_R5YW_eoQqBIwcqbq4nufJXKP7CJYGRP8nfpv7q9sNAKe4PTscD60sW9SQsuAI9wtG5f4aBG1O-AFoDT41wx-eteyk%3D&attredirects=0

 

 

[Hank]

40 minutes ago, Comet said:

About the same time that I bought the airplane, there was a fatal accident at a nearby airport (higher altitude)...makes you think (and learn from others).

A couple of months after I bought the plane, there was a fatal accident at my airport.  The local flight instructors put together a good resource for the airport.  Always, a licence to learn.
 

https://f8fcd52a-a-62cb3a1a-s-sites.googlegroups.com/site/lamairport/airport-info/KLAM_Pilot_Warning.pdf?attachauth=ANoY7covjD11zC5M6-s0faEhn4vat8zQ7ZHITI6D2OF9LxazDLqhiqJVeDR1v9BcdL1biL3YVkBK9JclSCGkciv3zh-JhHszrXR59IF2eXErA5rxdI8FEDh_T6uSbG45LJdRln1ezeUDUbjK8HGKOvOAbxYQw_R5YW_eoQqBIwcqbq4nufJXKP7CJYGRP8nfpv7q9sNAKe4PTscD60sW9SQsuAI9wtG5f4aBG1O-AFoDT41wx-eteyk%3D&attredirects=0

 

 

Holy cow! Guess I won't pop in for lunch in my C . . . . .

[Shadrach]

On 8/22/2020 at 7:16 PM, Ragsf15e said:

Any idea how high you were able to climb?  This would be nice info to have. 

I would assume at a much slower airspeed. Mid body Mooneys climb just fine with the gear out unless you try to use normal climb speeds...if you’re pitching for 120 or even 100 fugetaboutit. Need to be ~80-85mias. Would be pucker worthy at high DA’s but on a hot day and a DA ~3000 our lightly loaded, stock F will  do 1000fpm with the gear out. However, the cooling is suboptimal at those speeds. Would likely be rough on a parallel valve 4cyl. 

Edited August 25, 2020 by Shadrach

[cliffy]

KFLG (7000"msl)  has very large electric signs at the ends of the runway showing the current density altitude  

Did many summer T/Os out of DEN in an old 737-200 and they all were right at max tire speed at lift off (flaps 1 improved IIRC a long time ago)   An engine failure at T/O wasn't going to be fun at all.

On the inverse a 757-200 out of LAX with ferry fuel and pilot crew only to LAS will climb better than an old Lear 23!!!!!!!           80,000 lbs of thrust on a light weight airplane the size of a 757 was spectacular.      

I gotta say there are some smart folks hanging around this forum with all the figures and formulas etc WOW

 

[flyer338]

Cheryl and I flew from Las Vegas to Fortuna CA this morning for a week’s stay. The smoke and the baggage volume I will save for another post.

My ‘83J was at gross weight, the pressure altitude was close to the field elevation of 2205’. The temperature was 91 degrees, and I calculated the density altitude to be 4833’. The ground roll was about 1300’. Time to 12,500 was 32 minutes. Density altitude was 15,560 and TAS 143 knots.

The ground roll was 30% more at gross weight than for he previous flight where the weight was about 2475 lbs., albeit this flight started at 10% higher density altitude.

I think that keeping a real world performance log for an individual airplane offers some advantages over time.

Edited August 25, 2020 by flyer338
Clarity

[Ibra]

9 hours ago, carusoam said:

I was wondering... helicopter and high DA...

I flew with a friend who did his "helicopter BFR" in Ecureuil B3 flying near the Alps going up to 10kft-12kft
My friend was hesitant to invite 2 extra SOB that day but the instructor was "don't worry kind" which was not reassuring at all 
Turns out the instructor did land a heli on top of Everest at 34kft DA in 2005 with a similar machine !

His main concern was limited fuel endurance (as light on weight) and high 70kts-100kts winds, that meant few landing attempts but he managed to find wave lift and climb at idle, second concern he was getting questioned by authorities on the way back on the validity of his flying permit (apparently 1/ he broke a Nepalese military colonel record over there and 2/ he did an unauthorised rescue mission by picking two climbers that were stuck ) 

Edited August 25, 2020 by Ibra

[Ibra]

8 hours ago, Shadrach said:

Would be pucker worthy at high DA’s but on a hot day and a DA ~3000 our lightly loaded, stock F will  do 1000fpm with the gear out

I get the same impression on M20J, I twice "forget to raise the gear" as 1SOB climb rate at slow speeds 70-80kias is always in +1000fpm at sea level
But to @Ragsf15e question I am also wondering how high it would climb with gear down at slow speeds? same +18kft ceiling just ROC will be sluggish? or I will get stuck 9kft? I did not test but may do one day !

Obviously for cruise fuel burn the gear down matters a lot, I recall getting 10GPH for 120kias (cable gear extension got unlatched while we loaded some baggage in backseat but I had 4h to read that bit in the POH, I found it after 2h of slow cruise) but I doubt much on climb performance at slow 70kts speeds one need it up to accelerate to cruise speeds

In Arrow I used to fly, it was hard to pitch up or accelerate without rising the gear even at slow speeds 

Edited August 25, 2020 by Ibra

[cliffy]

I suspect the drag of the retractable gear is somewhat more than that of a D model fixed gear due to the doors being more draggy than the fairings on the original D. 

Had the last flying fixed gear Mooney pass through here a few weeks ago. I think it is the only one of the 3 left, flying. The density altitude that day was around of 8,000'

Just as an  aside IIRC-  An MU-2 on one engine gear down will be hitting the ground somewhere if a go around is started at or below 300 AGL.  On the old 727-200 with 2 engines inop #1 & #2  having the hyd's (with #3 running, single engine approach. no hyd's) once the leading edges are driven out electrically (they can't be raised) you WILL be on the ground somewhere, permanently. No go around is possible. 

Horse power to drag affects all classes of airplanes whether high DA or just high drag. Its still drag vs HP.  

Might be an interesting exercise to see how high one might climb in a C model with the wheels out. May have to give it a try. 

[Ross Taylor]

11 hours ago, cliffy said:

KFLG (7000"msl)  has very large electric signs at the ends of the runway showing the current density altitude

And there's a reason that sign has 5 digits on it! 

[EricJ]

4 hours ago, cliffy said:

I suspect the drag of the retractable gear is somewhat more than that of a D model fixed gear due to the doors being more draggy than the fairings on the original D. 

Another difference, that was pointed out to me when I had the experience of flying home with the gear down, is that the bottom of the wing has big, draggy, non-lifting slots in it when the gear is down, and that area is smooth lifting surface when the gear is up.   I suspect this is a big part of where the difference in climb performance comes from.   I think this is also why some airplanes, like Beechcraft, close up some of that area even when the gear is down.

 

[cliffy]

9 hours ago, Ross Taylor said:

And there's a reason that sign has 5 digits on it! 

and I've seen all 5 lit!!!!!!!!!!!

[cliffy]

14 hours ago, cliffy said:

and I've seen all 5 lit!!!!!!!!!!!

If anyone hasn't caught on yet- 5 digits means that the density altitude is over 10.000' for T/O

As mentioned earlier  Big Bear CA is another "gotcha" airport for this in the summer. Many low landers from Los Angeles have been abruptly notified of this fact as they impact the trees trying to takeoff. 

[gsxrpilot]

1 hour ago, cliffy said:

If anyone hasn't caught on yet- 5 digits means that the density altitude is over 10.000' for T/O

As mentioned earlier  Big Bear CA is another "gotcha" airport for this in the summer. Many low landers from Los Angeles have been abruptly notified of this fact as they impact the trees trying to takeoff. 

I've seen 5 digits on the sign at Centennial here in the Denver area. As I recall it was 11,600 or something over 11K. The 252 didn't seem to pay any attention to it and just took off and climbed out 

[larryb]

High density altitude will affect runway length in a turbo as well. One needs to accelerate to a higher GS to achieve the desired IAS. At 10K feet, 20% higher GS is required. Climb gradient is also affected for the same reason, going faster horizontally but climbing at the same rate. Even in a turbo, high density altitude is not exactly the same as sea level operation.

[Ibra]

22 minutes ago, larryb said:

High density altitude will affect runway length in a turbo as well. One needs to accelerate to a higher GS to achieve the desired IAS. At 10K feet, 20% higher GS is required. Climb gradient is also affected for the same reason, going faster horizontally but climbing at the same rate. Even in a turbo, high density altitude is not exactly the same as sea level operation.

While indicated stall speed does not change with DA, the aircraft has to accelerate like 3-wheels car to the associated GS
Yes the same story for climb gradient for obstacles, it goes down as GS goes up...

But it is worse than that, even ignoring propeller efficiency, the ground roll is still proportional to Stall_GS^3/Power, you may cheat on power with turbo but not on GS, so make that 60% ground roll increase at 10kft assuming (even with no temp correction to GS vs IAS) or 172.8% to be more accurate 

The elephant in the room is still the loss of power on normally aspirated engines, at 10kft the max I get even with proper leaning on M20J is 70%, so let's make that (1+0.2)^3/(0.7) = 250% ground roll at 10kft, I never tried that in Mooney and I certainly failed to notice 200ft vs 500ft ground roll in Cubs 

[gsxrpilot]

3 hours ago, larryb said:

High density altitude will affect runway length in a turbo as well. One needs to accelerate to a higher GS to achieve the desired IAS. At 10K feet, 20% higher GS is required. Climb gradient is also affected for the same reason, going faster horizontally but climbing at the same rate. Even in a turbo, high density altitude is not exactly the same as sea level operation.

Of course there is an effect. But on 17L at KAPA with 10,000 ft of runway, it's not enough a difference to get out the charts. I'm certain I've never seen my 252 take 3000 feet to get off the ground. Even at KLXV sitting at 9934 MSL, we were off the ground at about 1900 ft. And once in the air, 800 ft/min is standard for me and 1000+ ft/min is available if needed.

I've flow an M20C around these mountains, and I've been flying with @Matt Ward around these mountains in his M20E. And both are very capable airplanes that will get you into and out of any airport here in the Rockies. Really, any Mooney is more than capable enough for these elevations.

[Matt Ward]

Indeed.  My home airport is almost 5700 and we routinely see DA of +8.5-9K in the summer.  We have 5000 feet minimum and it's a non-event.  I honestly don't ever recall taking over 1500 feet to get off the ground.  I don't get the same climb rate as @gsxrpilot but I do see 500 FPM without any issue.  I probably wouldn't do touch and gos at 18V (3500 x 60, I think) in those sort of elements but for normal operations I've not experienced any adverse effects.

[0TreeLemur]

On 8/25/2020 at 5:41 AM, Ibra said:

I flew with a friend who did his "helicopter BFR" in Ecureuil B3 flying near the Alps going up to 10kft-12kft
My friend was hesitant to invite 2 extra SOB that day but the instructor was "don't worry kind" which was not reassuring at all 
Turns out the instructor did land a heli on top of Everest at 34kft DA in 2005 with a similar machine !
 

I remember seeing the video of that "ascent" of Everest.  The B3 is a hell of a machine.   He had trouble with control sensitivity at the top of Everest- the difference between static (hovering) blade AoA and stall AoA on the collective was about 1 degree.  He didn't "land" as much as he "moved some snow with a skid" and got out of there.  Gutsy move nonetheless!   Screw up with a 1-degree collective margin that close to the snow and that pilot wasn't gettin' rescued.  He's freezing to death.