Performance Degradation

Jaybird180

Jaybird180

Final Approach
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Jaybird180
How much margin do you add to your take-off, landing and 50 foot obstacle clearance calculations?
 
A significant margin - I'm a wimp and sloppy pilot. I like 50% more then the book says is possible. Even then, I approach it very carefully.

If the book said I needed 1500 ft to depart, there is simply no way I'd even consider it without a 2250 ft runway. Even then I'm going to be trying to account for the variables the book didn't - surface, etc.

I generally slowly work my way up to whatever I'm trying to determine. The book for the Debonair indicated you could operate it at Gastons at gross no problem this year. I did the first takeoff there solo, with everything removed, and light fuel. I then had a metric to work with and added weight as the weekend went on. Even then I never got anywhere near gross as it wouldn't have been safe. The temperatures were soaring, the winds shifting, etc.
 
There are so many variables in this equation that any answer is almost meaningless. (Surface condition and material, grade, DA, load, experience on that particular field, yada yada yada. But in reality the question really comes down to: Would you land here?

My wife is fond of saying a good attorney never asks a question they don't know the answer to. I would never land any place I wasn't sure I could get out of. (Barring emergencies of course.) But I would need a specific data set to categorically state the safety factor applied.
 
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Threefingeredjack said:
There are so many variables in this equation that any answer is almost meaningless. (Surface condition and material, grade, DA, load, experience on that particular field, yada yada yada. But in reality the question really comes down to: Would you land here?

My wife is fond of saying a good attorney never asks a question they don't know the answer to. I would never land any place I wasn't sure I could get out of. (Barring emergencies of course.) But I would need a specific data set to categorically state the safety factor applied.
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Interesting that your answer conflicts with your signature, sir.
 
Interesting question. I can't say that I ever made it a quantifiable percentage like The CFIs have.

I just know better than to expect book performance from a Cessna or to expect 100% performance out of myself every single time.

As Jesse mentioned, I work up to it in controlled conditions to see what I and the aircraft can do.

Usually I fail to have flawless technique somewhat before the aircraft can't perform.
 
My answer is it depends. In an airplane I am unfamiliar with I add at least 100% safety margin. I have flown some that it stays at 100%. As I get to know the airplane I might eventually reduce that to 25%. Most airplanes end up around a 50% safety margin.

Brian
CFIIG/aSEL
 
I know some folks that should have added a much bigger margin on a recent and very short flight. Warm summer day, 3k ft grass field surrounded by forest, C-172 with 4 adult passengers, gear, and gas. Departed on take-off and went into some tall (>100') cedar trees inverted. Killed my sister-in-law's childhood friend, along with the 3 other folks (including the pilot). IMHO, adding a few extra hundreds/thousands of ft of runway never hurt anyone, but the annals of aviation tragedies have been written by folks who tried to get by with what they thought was the minimum required.
 
steingar said:
Surprised they made it there in the first place, with that load.
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Agreed. I'm not sure how much gas they had, but obviously they had enough to get back out of the field (no FBO/gas where they landed).
 
Depends...I'll usually double any figure on a new to me airplane, but I only added 20% in the 150 I used to be part owner of as I was comfortable with that airplane and have a few hundred hours in it.
 
I use 150% of the book 50-foot obstacle takeoff distance based on actual conditions as the minimum runway length I will accept in light planes. Yes, it's very conservative, but it's kept me out of trouble for over 40 years.
 
I use the grannies underwear rule. It depends
 
I found Koch chart to be way conservative. Not being a test pilot of Piper or Remos, I beat it every time when temperatures start climbing. If you just use the Koch chart, you aren't going to be flying a lot back-country strips.

However, I learned not to be complacent about DA. Use what the book says and add a bit of margin. Jessie's 50% is as good as anything.

Another super important thing which everyone forget is the climb performance. So many people do due dilligence on takeoff run, take off, fly out of ground effect without issue, and then crash into a benign climbing terrain, because look how much distance you need to climb! I once departed Angel Fire and had to cut zig-zags over the lake before I was able to fly out of the valley.

POH for Remos GX says to add 10% for "bugs on the wings" (no joke), and 10% for grass aerodromes.
 
I currently fly an old piper, I'm fairly certain the numbers were written by the marketing department and not the engineering. I went to an airport with 10,000' density altitude and plenty of asphalt. I started with an hours worth of fuel and added stuff here and there, filled up made mental notes and measurements. (My wife was riding a 162 mile bike ride, what else was I going to do in the middle of nowhere montana) You'll get a good respect for your planes performance or lack thereof.
 
bartmc said:
I currently fly an old piper, I'm fairly certain the numbers were written by the marketing department and not the engineering. I went to an airport with 10,000' density altitude and plenty of asphalt. I started with an hours worth of fuel and added stuff here and there, filled up made mental notes and measurements. (My wife was riding a 162 mile bike ride, what else was I going to do in the middle of nowhere montana) You'll get a good respect for your planes performance or lack thereof.
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The charts in the '67 Cherokee 180 I instruct in are an absolute joke. Same in the Debonair.

OTOH I've found Cessna charts to be much more realistic.

I'm sure it's all in my head though.
 
None, I've got 40 more horsepower than the book numbers were predicated on at about the same weight. I regularly beat the book numbers.
 
jesse said:
OTOH I've found Cessna charts to be much more realistic.
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If my Cardinal is any guide, I wouldn't be so sure about that.

Then again, I really DO need to clean those bugs off the wings. :redface:
 
jesse said:
The charts in the '67 Cherokee 180 I instruct in are an absolute joke. Same in the Debonair.

OTOH I've found Cessna charts to be much more realistic.

I'm sure it's all in my head though.
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Probably. I remember the C-206, 210 and 320's charts being wildly optimistic, especially for service ceiling. But these were 1960s airplanes when the charts were only a few pages and written by the marketing department, I think.
 
Everskyward said:
Probably. I remember the C-206, 210 and 320's charts being wildly optimistic, especially for service ceiling. But these were 1960s airplanes when the charts were only a few pages and written by the marketing department, I think.
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Interesting. I've found the restart numbers pretty easy to achieve using only 1/4-1/3 on the Henning pilot skill level chart.
 
Alexb2000 said:
Interesting. I've found the restart numbers pretty easy to achieve using only 1/4-1/3 on the Henning pilot skill level chart.
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:confused:

It seems to me I remember you having a newer airplane. I was talking about airplanes from the 1960s with very skimpy documentation.
 
Everskyward said:
:confused:

It seems to me I remember you having a newer airplane. I was talking about airplanes from the 1960s with very skimpy documentation.
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I know, that's what I thought was interesting, Cessna has changed all that to conservative numbers. Age of litigation trumping marketing I suspect.
 
Alexb2000 said:
I know, that's what I thought was interesting, Cessna has changed all that to conservative numbers. Age of litigation trumping marketing I suspect.
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Oh, when you wrote "restart numbers" you meant after production restarted. For whatever reason I was thinking about restarting the engine. :redface:
 
azure said:
If my Cardinal is any guide, I wouldn't be so sure about that.

Then again, I really DO need to clean those bugs off the wings. :redface:
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All the Cardinals were built before Cessna started publishing a more detailed POH. The "newer" post 1980 cessna POH's are actually pretty useful.
 
If any of you watch me get into Diana's Far....the book says I can do it but I went 1,000 undergross.

I like having margins.
 
steingar said:
If I have to worry about it at all I usually don't go.
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More or less. I only run the numbers for unfamiliar conditions. If I feel I have to worry I can work on the procedures before I go. I can get very close to book performance out of myself but I have found the ability to do so is VERY perishable.
 
steingar said:
If I have to worry about it at all I usually don't go.
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Respectfully sir....:raspberry:

You at least have some way of knowing if you need to worry about it. I'm not going to mention the regs either

Establish a baseline and know where it ceases to function...but I'm sure you have enough time in type to have it already even if you don't articulate.
 
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