First Encounter With Density Altitude

5000 ft runway and 3000 ft DA isn't bad, but it's great you knew to check. Lots of "experienced" pilots are listed in NTSB reports because they didn't.
 
CTLSi said:
From the Flight Design CTLS POH:
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Thanks for that - I learned something!!!

I think it really is the first time I've seen altitude limitations expressed as DA.

In my Cirrus manual, the altitude limitations are listed as "msl".

In my Sky Arrow manual, it just gives the service ceiling as 13,500', not specifying further.

But expressing it as DA does make more sense, so if there's been a recent trend to do so I applaud it.
 
FastEddieB said:
Thanks for that - I learned something!!!

I think it really is the first time I've seen altitude limitations expressed as DA.

In my Cirrus manual, the altitude limitations are listed as "msl".

In my Sky Arrow manual, it just gives the service ceiling as 13,500', not specifying further.

But expressing it as DA does make more sense, so if there's been a recent trend to do so I applaud it.
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I agree FastEddie. When I saw it I thought, hey it makes a lot of sense to do it in DA since all the performance tables are in DA, and lets face it, if you are staring at your altimeter and your plane stops climbing at 9k when you think it should go well past 12k it would be a bad surprise.
 
The reason performance should be indicated in DA is because your plane operates in DA. Aerodynamically and engine wise, DA is the only altitude that counts.
 
Henning said:
The reason performance should be indicated in DA is because your plane operates in DA. Aerodynamically and engine wise, DA is the only altitude that counts.
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The service ceiling is in DA.

Just because it says 14,100 in a 172N POH doesn't mean 14,100 true altitude. It's DA. Always. Even if it's labeled "MSL."

To be honest, I'm a bit surprised this is so poorly understood. Comparing service ceilings to expected density altitudes and requiring a specific margin is a really important thing to do before a high mountain flight.

The only aircraft performance issue where true altitude is relevant is terrain/obstacle clearance. Even dodging other aircraft is not true altitude unless you are both on the ground at the reporting station or it's an exactly standard day.
 
itsjames2011 said:
Hey everyone,

I earned my PPL in Oct 2013 and have about 80 hours total time. I'm spoiled and am always into and out of airports at sea level but today's trip was not usual. Below is a summary of the situation and any advice would be appreciated. I know this is probably not out of the ordinary for some of the folks here but I still have LOTS of learning to do. :)

Today I departing Pittsfield KPSF in my Warrior II PA-28-161. Field elevation is 1188 and temp was 26c which gave me a density altitude of about 2555ft. I have never dealt with an elevated airport let alone in hot weather so I pulled out the POH, did all of my calculations, and determined I had enough runway not only to take off but also to abort at rotation should something go wrong. That 5700 foot runway was a godsend. I held off on my rotation to 60 kts, accelerated in ground effect to 79 kts, and then brought up the nose to hold 79kts and sure enough I had a 400ish ft per min climb as the manual predicted.

Anything else a new pilot can learn from this? Did I miss anything important?

James
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You did it right. No fault there.

Coming from Denver, I tend to think of any airport w/ an elevation below about 2000 ft as being pert' near sea level. :D
 
Henning said:
The reason performance should be indicated in DA is because your plane operates in DA. Aerodynamically and engine wise, DA is the only altitude that counts.
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Yes.

Which is exactly why I just said it "does make more sense".

My point was simply that I don't think it has traditionally been expressed as such for small GA aircraft.
 
FastEddieB said:
Yes.

Which is exactly why I just said it "does make more sense".

My point was simply that I don't think it has traditionally been expressed as such for small GA aircraft.
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It doesn't use the words "density altitude," but it is density altitude, and it always has been.

Were it not density altitude, you would need a service ceiling chart showing the effect of temperature.

The ceiling expressed as MSL on a standard day is exactly density altitude.
 
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MAKG1 said:
It doesn't use the words "density altitude," but it is density altitude, and it always has been.

Were it not density altitude, you would need a service ceiling chart showing the effect of temperature.

The ceiling expressed as MSL on a standard day is exactly density altitude.
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Actually, it is aircraft performance based on ISA. DA is just correcting actual conditions to ISA.

Yes, we are all saying the same thing.
 
FastEddieB said:
... it still seems that for any given IAS climb speed, the pitch would be the same.

Right?
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It's typical for me to depart from 7,100' and sea-level is typical return flight departure.

At sea level I climb at over 1,000'/min and a high deck angel, power to spare.

At 7,100' my climb might be more like 500'/min and my deck angle is flat.

both climbing at Vy.

Note: I keep my nose down in mtn departures for margin from stall and also for dealing with wind shear.
 
FastEddieB said:
Thanks for that - I learned something!!!

I think it really is the first time I've seen altitude limitations expressed as DA.

In my Cirrus manual, the altitude limitations are listed as "msl".

In my Sky Arrow manual, it just gives the service ceiling as 13,500', not specifying further.

But expressing it as DA does make more sense, so if there's been a recent trend to do so I applaud it.
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Again, a performance altitude listed as MSL will almost always be measured under or corrected for standard atmospheric conditions. And that means that the published MSL altitude is indeed a density altitude.
 
MAKG1 said:
The difference in Vy over a few thousand feet DA is a couple of knots at most, so I find it hard to believe the pitch change is perceptible.
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Your pitch attitude is the sum of your AoA and your climb gradient. The AoA should be virtually the same (IIRC there's a slight change in that due to the reduction in thrust generated lift) but the climb gradient varies considerably in any airplane capable of a fairly steep climb at sea level DA. For a simple example consider an airplane climbing 1200 FPM at 60 Kt. That's a climb gradient of almost 12°. The same airplane clawing upwards at 120 FPM nearing it's service ceiling will have a climb gradient of a little over 1°.

A change in pitch attitude of 11° should be hard to miss.
 
gismo said:
Your pitch attitude is the sum of your AoA and your climb gradient. The AoA should be virtually the same (IIRC there's a slight change in that due to the reduction in thrust generated lift) but the climb gradient varies considerably in any airplane capable of a fairly steep climb at sea level DA. For a simple example consider an airplane climbing 1200 FPM at 60 Kt. That's a climb gradient of almost 12°. The same airplane clawing upwards at 120 FPM nearing it's service ceiling will have a climb gradient of a little over 1°.

A change in pitch attitude of 11° should be hard to miss.
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Yup, the climb gradient, that splains it Lucy.
 
gismo said:
Your pitch attitude is the sum of your AoA and your climb gradient.
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Maybe I'm just being dense, but...

...if I'm climbing at 60k into a 60k headwind, my climb gradient would be vertical. But my pitch angle would not be affected.

Argumentum ad absurdum to be sure, but I can't quite grasp how climb gradient affects pitch attitude.

Sorry.
 
FastEddieB said:
Maybe I'm just being dense, but...

...if I'm climbing at 60k into a 60k headwind, my climb gradient would be vertical. But my pitch angle would not be affected.

Argumentum ad absurdum to be sure, but I can't quite grasp how climb gradient affects pitch attitude.

Sorry.
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Pitch attitude is relative to the level ground but your plane flies relative to the relative wind. In a steep climb the relative wind would have a downward component causing a high pitch attitude even with a consistent climb speed of say Vy.

Edit: Your 60kt climb into a 60kt headwind would effect your pitch attitude because your are limiting your speed to 60kts assuming WOT.
 
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gismo said:
Your pitch attitude is the sum of your AoA and your climb gradient. The AoA should be virtually the same (IIRC there's a slight change in that due to the reduction in thrust generated lift) but the climb gradient varies considerably in any airplane capable of a fairly steep climb at sea level DA. For a simple example consider an airplane climbing 1200 FPM at 60 Kt. That's a climb gradient of almost 12°. The same airplane clawing upwards at 120 FPM nearing it's service ceiling will have a climb gradient of a little over 1°.

A change in pitch attitude of 11° should be hard to miss.
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OK, now let's use some numbers in the same galaxy as the OP.

It's a Warrior. Climb rate is 700 FPM at sea level DA. And it's done at Vy=75 KCAS. That's just over 5 deg climb angle.

Now, let's assume 2500 DA like the OP said. According to the POH for a 172N, the climb rate is now 500 FPM, and Vy is maybe 73 KCAS. That's 4 deg.

A 1 deg difference is not at all hard to miss.
 
MAKG1 said:
Not to rain on your parade, but 2500 DA is nothing. You did almost all the right stuff for higher DA, and identifying abort points is important. If the DA were above 5000, you would have needed to lean for takeoff.

The big takeoff risks at high DA are excessive pitch trying to get sea level climb performance, wrong Vy (it is indicated SLOWER at high altitude), overloading, taking off full rich, and failure to identify a short field. Winds and rising terrain are dominant risks at altitude.

The highest DA I've taken off in in a Warrior is 8500. Highest DA overall in a Warrior is nearly 12000 (using ridge lift to get over a 10500 ridge).

A Warrior (or even an Archer or Arrow) isn't the best platform for real high DA. Even a 172 can do better. Cessna retracts can do a lot better.

You would benefit substantially from some mountain training. It's quite a lot of fun.
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I know it's off topic but who or where can I call to get some mountain training in the Midwest or north west states?? I'm in ND.
 
The Colorado Pilots Association offers mountain flying classes. You can find their web site here http://coloradopilots.org/

There are some interesting info points on that site too, even if you don't take the course. Interesting info on the various passes, accident history, etc.

As one more data point, I flew last night after it cooled off a bit, just before sunset from Meadow Lake in Colorado Springs. They were still reporting DA well above 8000 feet. In my Gobosh LSA with a 100 HP engine I was still seeing over 500-700 FPM climbs without pushing it. I was quite happy with that performance.

Carl
 
A person probably couldn't do much better than taking mountain flying training in western Colorado!
 
Palmpilot said:
A person probably couldn't do much better than taking mountain flying training in western Colorado!
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Sure you can, you can take lessons in Carson City, NV KCXP and fly over the Sierra crest to Lake Tahoe and back and all around Reno...

Some of the best mountain wave flying is in the Carson valley, Minden, NV KMEV is one of the biggest glider facilities in the world.

In the summer, DA can reach 10 to 11k easily over the crest. And the winds will make you see God...
 
CTLSi said:
Sure you can, you can take lessons in Carson City, NV KCXP and fly over the Sierra crest to Lake Tahoe and back and all around Reno...

Some of the best mountain wave flying is in the Carson valley, Minden, NV KMEV is one of the biggest glider facilities in the world.

In the summer, DA can reach 10 to 11k easily over the crest. And the winds will make you see God...
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Is it "much better" than doing it in western Colorado, which has similar terrain heights?
 
Palmpilot said:
Is it "much better" than doing it in western Colorado, which has similar terrain heights?
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It probably similar. CO is said to be more treacherous due to the deep canyons and crazy uplifts while flying in the middle of high terrain.

In Nevada, you get to experience the same dynamics, but you can get off the mountain crest must easier and faster if you get scared.
 
2500 ft is not much, but yes you get a decrease in performance especially with a marginal 160 hp power plant.
 
CTLSi said:
It probably similar. CO is said to be more treacherous due to the deep canyons and crazy uplifts while flying in the middle of high terrain.

In Nevada, you get to experience the same dynamics, but you can get off the mountain crest must easier and faster if you get scared.
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It sounds like I was correct to say that you can't do much better than to learn it in Colorado, then (at least as far as the contiguous United States is concerned).
 
Palmpilot said:
It sounds like I was correct to say that you can't do much better than to learn it in Colorado, then.
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Sure you can. Both places give you mountain flying, mountain wave winds, and the skill you need to manage that...

Frankly, if I had not learned to fly in the mountains, I would surely not want to gain those skills in Colorado.

Colorado may scare and kill you before you have the chance to experience and learn fully how to deal with high DA, fierce up/down drafts of wind, dealing with crest uplifts, and shooting a canyon turn with no where to get down... And that kinda defeats the purpose, doesn't it?
 
CTLSi said:
Sure you can. Both places give you mountain flying, mountain wave winds, and the skill you need to manage that...

Frankly, if I had not learned to fly in the mountains, I would surely not want to gain those skills in Colorado.

Colorado may scare and kill you before you have the chance to experience and learn fully how to deal with high DA, fierce up/down drafts of wind, dealing with crest uplifts, and shooting a canyon turn with no where to get down... And that kinda defeats the purpose, doesn't it?
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If it's much better to learn mountain flying in the Tahoe area than in Colorado, then why did you say that it's probably similar? :confused:
 
Palmpilot said:
If it's much better to learn mountain flying in the Tahoe area than in Colorado, then why did you say that it's probably similar? :confused:
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It is similar because both offer mountain wave winds, mountains, crest updrafts, and high DA.

It is different because in CO you may not always be over a good place to do an emergency landing or be able to get out of the mountains as quickly as you can in NV/Carson/Minden.
 
I take the view that with a sufficiently experienced instructor, learning in a more challenging environment is better.
 
Palmpilot said:
I take the view that with a sufficiently experienced instructor, learning in a more challenging environment is better.
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I tend to agree. Tahoe is a bit too easy. Though it isn't a very good idea, you can top Squaw Peak in a 172 in summer. Just barely. Altitudes in CO are 1/2 mile higher, and it makes a huge difference when climbing above all the terrain is not possible.

There are places further south in the Sierra that are much better than Tahoe.
 
MAKG1 said:
I tend to agree. Tahoe is a bit too easy. Though it isn't a very good idea, you can top Squaw Peak in a 172 in summer. Just barely. Altitudes in CO are 1/2 mile higher, and it makes a huge difference when climbing above all the terrain is not possible.

There are places further south in the Sierra that are much better than Tahoe.
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Tahoe itself is a yawn, but the smaller airports like Alpine County, Bridgeport and Lee Vining can be pretty challenging. Especially Alpine since it's carved in to the side of a mountain. I spent most of my mountain training flying in and out of those.
 
Palmpilot said:
It sounds like I was correct to say that you can't do much better than to learn it in Colorado, then (at least as far as the contiguous United States is concerned).
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I agree. Others may be just as good, but you won't do any better than CO - at least not outside AK. In CO you will learn DA and serious mountain flying.

The Colorado Pilots Association's mountain flying course is very highly regarded. The class in June had over 30 pilots.
 
FastEddieB said:
Maybe I'm just being dense, but...

...if I'm climbing at 60k into a 60k headwind, my climb gradient would be vertical. But my pitch angle would not be affected.

Argumentum ad absurdum to be sure, but I can't quite grasp how climb gradient affects pitch attitude.

Sorry.
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My bad, I should have stated that this was in still air (no wind, no vertical air movement).
 
Someone asked about where to get training...

Bill Standerfer gave a nice presentation on Mountain Flying at OSH in the FAA hangar and I got an email today that they published videos of the safety seminars.

His slides were the CPA slides.

Only possible problem is they made him pause mid-presentation for computer problems with the live stream. Whether that trashed their recording, I can't say.

Worth a peek through the seminar listings and recordings if you're interested. I haven't had time to look.
 
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