Fudge Factors

cocolos

cocolos

Pre-takeoff checklist
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cocolos
What fudge factors do you use for safety? That is how much below gross do you usually stay? 5%,10%,15%? or do you just add a fudge factor to your performance numbers? if so how much?


Thanks!
 
I have no problem flying right at gross.

Performance is rarely an issue at sea level airports, but I know that if I have 900 feet to the FAA standard 50 foot obstacle, I'm good to go.

It might be different in a different kind of airplane - what are you flying?
 
The answer at KSAC will be dramatically different from the answer at KTRK on a warm summer afternoon.

Right at max gross on the hairy edge of CG limits is fine at KSAC. But I do like to allow a 50% margin on the 50 foot length to allow for less than perfect technique.

Don't extrapolate the tables. This is much less of a problem than you might think -- a 172 can handle South Lake Tahoe at max gross at 90 deg F. But it will take a lot of runway (a lot IS available -- over 8000 feet), won't tolerate overloading, and may climb really slowly up to Echo Summit (circle, or climb over the lakeshore).

And do your density altitude calculations in the Sierra. Flying over Tioga Pass on a hot summer day in a tired 172 may be problematic. The service limit may be over 14000, but they get less than 100 FPM climb over 12000 feet...
 
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My airport is 5500ft MSL, and it's been a while since my plane was weighed. I keep a 10% gross weight reserve in my calcs (don't go over 90% of useful load).
When doing TO/Landing performance calcs, I build in a 50% safety factor.
When doing fuel calcs, I use 10gph, but average about 9 (11% safety factor), plus plan on 1 hour in the tanks at landing.
 
PilotAlan said:
My airport is 5500ft MSL, and it's been a while since my plane was weighed. I keep a 10% gross weight reserve in my calcs (don't go over 90% of useful load).
When doing TO/Landing performance calcs, I build in a 50% safety factor.
When doing fuel calcs, I use 10gph, but average about 9 (11% safety factor), plus plan on 1 hour in the tanks at landing.
Click to expand...

Keep doing what you are doing.

Bob Gardner
 
i usually don't count on being able to acheive more than half the published L/D
 
My world is a legal / not legal one resulting in a go / no go decision. If I say 'no' to a flight I need to be able to say why and 'because we're only 5% below gross' isn't going to cut it.

I get thats not the way it is for others.
 
0, bought the plane for its load carrying capability, I plan to use it.

I fudge air speeds down and fuel burns up for planning considerations however. Well unless I am trying to figure if I am going to violate my landing weight, then for THAT calculation I fudge the fuel burn down.

Perhaps I should also note that flying the plane I was for my primary my first X-C was made at 4lbs under gross, about .2% of a fudge factor.

Downloading for DA and runway length and obstacle clearance is case by case.
 
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bobmrg said:
Keep doing what you are doing.
Click to expand...
Thanks Bob.
Here's my thinking... I don't have a crew to backstop my calculations and judgments, it's just me. We all make errors, best to leave yourself room for error. If you're running at the edge of the envelope, it doesn't take much to end up past the edge.
I'm not commercial, so I don't have to answer for my no go decisions.

Second, out here in the high country, people run off runways all the time. I don't want to be that guy.

Third, I will NEVER be a fuel starvation statistic (the ones we shake our heads at and say 'how could that happen?').
 
Any anticipated airplane related expense under $500 I round up to $500. Anything expected to be more than that I add 30%
 
Simple. Really no different than factors with numbers.

(Sorry, this is where my mind went when I saw the title of the thread. Carry on...)

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I have zero issue flying at gross. I do keep in mind the DA though and add 50% or more on very warm days, especially at gross. The airplane is heavy, but will fly at gross at a high DA. Just be smart about it, do your leaning.

As far as fuel goes for a 1hr flight I estimate 14gph and during long XC's I estimate 12.5. They're closer to 12.5 and 11, respectively. Fuel I won't mess with, which is why I fly at gross fairly frequently.
 
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