Performance rules of thumb (or rule of thumbs...)
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Performance rules of thumb (or rule of thumbs...)
Could someone please be kind enough to give me the different rule(s) of thumb(s) (delete the right "s" and win £5
) used in adjusting takeoff, landings and other performance for factors e.g head/tailwinds, up/downslopes, grass rwys, temperature , etc...
I also wouldn't mind knowing about other rule(s) of thumb(s) you use for flying
Thanks
Capt. Manuvar
) used in adjusting takeoff, landings and other performance for factors e.g head/tailwinds, up/downslopes, grass rwys, temperature , etc...I also wouldn't mind knowing about other rule(s) of thumb(s) you use for flying
Thanks
Capt. Manuvar
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Look at LASORS HERE
The section in question is "SAFETY SENSE 7C - GENERAL AVIATION PERFORMANCE". There's a table at the end with take-off and landing performance factors.
The section in question is "SAFETY SENSE 7C - GENERAL AVIATION PERFORMANCE". There's a table at the end with take-off and landing performance factors.
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How about this?
According to it:
A 10% change in airspeed will cause a 20% change in in stopping distance.
For each knot of airspeed above Vref over the numbers, the touchdown point will be 100 feet further down the runway.
A 1,000' change in field elevation will cause a 4% change in stopping distance (higher airfield, longer stopping).
A 10deg C deviation from standard temperature will cause a 5% change in stopping distance (higher temp, longer stopping).
According to it:
A 10% change in airspeed will cause a 20% change in in stopping distance.
For each knot of airspeed above Vref over the numbers, the touchdown point will be 100 feet further down the runway.
A 1,000' change in field elevation will cause a 4% change in stopping distance (higher airfield, longer stopping).
A 10deg C deviation from standard temperature will cause a 5% change in stopping distance (higher temp, longer stopping).
One of the stupidist set of questions in the PPL exams are those which seemingly require applicants to memorize the Safety Sense table. To my mind that is highly dangerous; never would a professional pilot try to remember the corrections for perf calculations for contaminated runway ops - they would assess the conditions, then look up the conversion factors from their documents.
Everyone should use the Safety Sense leaflet - and in the PPL exams the applicant should also be allowed to. I want to know that he/she can obtain the correct answer, not merely memorise a table.......
Everyone should use the Safety Sense leaflet - and in the PPL exams the applicant should also be allowed to. I want to know that he/she can obtain the correct answer, not merely memorise a table.......
If you think you're not going to make then you probably aren't. Applies to take offs, landings and judging the distance to the toilet. 
BEagle I agree when operating something chunky and complex but the accepted Rules of Thumb applied to a SEP and based on MAUW should give you a decent margin of error, especially if you are below MAUW.
BEagle I agree when operating something chunky and complex but the accepted Rules of Thumb applied to a SEP and based on MAUW should give you a decent margin of error, especially if you are below MAUW.
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I also wouldn't mind knowing about other rule(s) of thumb(s) you use for flying
If you haven't reached 75% of your Vr by half way down the runway, STOP!
And now I get beaten up.
If you haven't reached 75% of your Vr by half way down the runway, STOP!
And now I get beaten up.
I use 2/3 of Vr by 1/3 down the runway - amounts to about the same thing. Also, if not airborne by 2/3 down the runway, give up and stop.
I agree totally with Beagle - teaching either Engineers or pilots that they should memorising data is a recipe for disaster. Providing the data sheet / safety sense leaflet / formula book and expecting them to show that they can use it properly is much more grown-up.
G
I agree totally with Beagle - teaching either Engineers or pilots that they should memorising data is a recipe for disaster. Providing the data sheet / safety sense leaflet / formula book and expecting them to show that they can use it properly is much more grown-up.
G
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General rule of thumb for SEP.
Each 50 RPM reduction gives about a 100 fpm descent.
For CS prop, 1" manifold pressure reduction achieves the same effect (approx)
General rule of thumb
Dividing ground speed by half and adding a zero to the result gives the descent rate in fpm to maintain a 3 degree approach - please note that I am not an advocate of 3 degree approaches in SEP.
Each 50 RPM reduction gives about a 100 fpm descent.
For CS prop, 1" manifold pressure reduction achieves the same effect (approx)
General rule of thumb
Dividing ground speed by half and adding a zero to the result gives the descent rate in fpm to maintain a 3 degree approach - please note that I am not an advocate of 3 degree approaches in SEP.
Gizajob
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Remember also that as with stopping distances in the highway code, perf data is collected by professionals in new aircraft and may bear little or no resemblence to actual performance!
Use the data, apply the factors as per safety sense leaflets etc but think about things in practical terms too.
As an exmple, did a calc yesterday for a PA 28 into our home airfield and apparently it should have run off the end of the runway - though of course it has landed successfully thousands of times without doing so - explain that one!
BTW - it's ruleS of thumb. It is the rules that are plural and not the thumbs!
Use the data, apply the factors as per safety sense leaflets etc but think about things in practical terms too.
As an exmple, did a calc yesterday for a PA 28 into our home airfield and apparently it should have run off the end of the runway - though of course it has landed successfully thousands of times without doing so - explain that one!
BTW - it's ruleS of thumb. It is the rules that are plural and not the thumbs!
Gizajob
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Yes it is grass. The unfactored data says we just make it, so effectively we are seeing paved level max weight performance on wet downhill grass - what an aircraft!
For some reason I'm still trying to work out, the TO figs are about right once factored, so we do officially get airborne at least...
For some reason I'm still trying to work out, the TO figs are about right once factored, so we do officially get airborne at least...
