Van's Air Force
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Landing Distance grid calculation
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Mark Albery
Well Known Member
Vans published landing distances are, I believe, just the ground roll distance and should be scaleable as proportional to the square of the touch down ground speed. For still air and sea level that will be a little above your stall speed in most cases. It assumes deceleration at about 0.25g or 5-6mph per second.
Density altitude correction will be about 3% per 1000' of DA.
But if you want to calculate runway length requirement, you need to add the distance from threshold to touch down point. For commercial operations, that will add about 1000'+ to the distance as they assume you arrive at the threshold at about 50' and on a 20:1 glide slope. The actual amount will depend upon your aiming point on the runway and your threshold speed which is usually 20-30% higher than touchdown speed.
So no simple answer, but an approximate method would be to use Van's numbers scaled as above for touchdown speed and add a fixed distance from threshold to touchdown point - a 1000' should be pretty conservative if you regularly touch down before the TDZ markings on the runway.
Density altitude correction will be about 3% per 1000' of DA.
But if you want to calculate runway length requirement, you need to add the distance from threshold to touch down point. For commercial operations, that will add about 1000'+ to the distance as they assume you arrive at the threshold at about 50' and on a 20:1 glide slope. The actual amount will depend upon your aiming point on the runway and your threshold speed which is usually 20-30% higher than touchdown speed.
So no simple answer, but an approximate method would be to use Van's numbers scaled as above for touchdown speed and add a fixed distance from threshold to touchdown point - a 1000' should be pretty conservative if you regularly touch down before the TDZ markings on the runway.
Mark Albery
Well Known Member
Still air take-off distances increase at about 5-6% per 1000' of D.A. for a normally aspirated engine or 3-4% for a turbo-normalised one.
Establishing your sea-level datum will depend on the propeller type (FP or CS), power output and prop efficiency, so difficult to generalise. If your configuration and weight is similar to the Van's example then their distance should be fairly close.
Some approximate rules of thumb:
Headwinds and tailwinds: Divide by take off safety speed, subtract from 1 for headwinds, add to 1 for tailwinds, square that number for TOD /LD factor
Weight - adjust by weight squared for take-off, but linearly for landing distance (i.e 10% weight increase= 20% on TOD and 10% on LD
Density altitude - 6% per 1000' for TOD, 4% per 1000' for LD
Gradient - 5% per 1% gradient for TOD and LD
Snow, long grass, standing water etc. add lots or stay at home
Establishing your sea-level datum will depend on the propeller type (FP or CS), power output and prop efficiency, so difficult to generalise. If your configuration and weight is similar to the Van's example then their distance should be fairly close.
Some approximate rules of thumb:
Headwinds and tailwinds: Divide by take off safety speed, subtract from 1 for headwinds, add to 1 for tailwinds, square that number for TOD /LD factor
Weight - adjust by weight squared for take-off, but linearly for landing distance (i.e 10% weight increase= 20% on TOD and 10% on LD
Density altitude - 6% per 1000' for TOD, 4% per 1000' for LD
Gradient - 5% per 1% gradient for TOD and LD
Snow, long grass, standing water etc. add lots or stay at home
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Aircraft performance predictions
The Jeppesen Flight Theory for Pilots has a lot of equations in it for calculating performance as a function of weight, density altitude, etc. It's a cheap book and I believe has all the information you need to estimate the performance of you're airplane.
There is another method that works off of data gathered from you test flying your airplane. It's call the "Bootstrap Approach to Predicting Aircraft Performance". It's much more involved but you also get much more information from it. Google it and you'll get a bunch of links on the subject.
I hope this helps.
Jeff
The Jeppesen Flight Theory for Pilots has a lot of equations in it for calculating performance as a function of weight, density altitude, etc. It's a cheap book and I believe has all the information you need to estimate the performance of you're airplane.
There is another method that works off of data gathered from you test flying your airplane. It's call the "Bootstrap Approach to Predicting Aircraft Performance". It's much more involved but you also get much more information from it. Google it and you'll get a bunch of links on the subject.
I hope this helps.
Jeff
az_gila
Well Known Member
PDF Page 20 of the AC has a good chart to use based percentages of approach speed.
http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_91-79A.pdf
Page 21 has a more specific example.
http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_91-79A.pdf
Page 21 has a more specific example.
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