Density altitude, slope and TO/Land distances

[MikeJ 7A]

Does anyone have any hard data on the change in runway required for T/O & Landing when going from sea level to 6000' elevation?

I'm toying with the idea of a private runway. I've got room for 1500' but I'm at 6000' elevation. I'm also not sure what the runway's slope would be, but it's probably close to a limit. I assume that some slope would help (always t/o downhill and land uphill, winds permitting) as long as it's not too extreme. Does anyone know if a "max slope" is even defined anywhere? (I'm guessing more than 5% and it's going to be too much?)

Mike

[the_other_dougreeves]

Originally Posted by MikeJ 7A

Does anyone have any hard data on the change in runway required for T/O & Landing when going from sea level to 6000' elevation?

A Koch Chart may be of help here:



This is a generic chart for light aircraft. It will not be spot on for all aircraft, but it should give you an idea of what to expect.

So, per the chart, 70F and 6000' (warmish day) would add about 150% to your takeoff distance and reduce ROC by about 70%. So, if your SL, ISA performance is TO distance of 1000' over a 50' obstacle and ROC of 2000fpm, you would need 2500' and have a climb of 600 fpm.

I don't know how well this chart will apply to the low lb/hp loadings that most RVs have, but the implication is pretty clear.

[Kevin Horton]

Originally Posted by the_other_dougreeves

A Koch Chart may be of help here:

I don't know how well this chart will apply to the low lb/hp loadings that most RVs have, but the implication is pretty clear.

Take-off distance will vary with the square of the lift-off TAS, divided by power available. TAS and power available vs altitude will vary on RVs the same way they do for any other normally aspirated light aircraft, so the Koch chart should be as valid for RVs as it is for any light aircraft.

If the Koch chart was optimized for typical type-certificated light aircraft, it will be pessimistic on the rate of climb for RVs. I.e. the reduction in rate of climb that is actually experienced won't be as bad as the Koch chart predicts. This is because the rate of climb is proportional to the excess power (the power available minus the power required for level flight at the climb speed). RVs have a lot less power required than typical light aircraft, so the excess power won't go down as quickly when the altitude increases.

[frankh]

Go find a runway at 6000' in the Summer and try it out. It would be ideal if it was grass but even paved you should get a pretty good idea of the preformance decrease.

Then add a multiplier to this for operating off of whatever surface you plan.

To me 1500' is about the minimum I would want at close to sea level. Of course the RV has fabulous performance but there are winds and the biggest variable is our own screw up potential. I mean can you be sure you will NEVER come in too hot too fast?

Maybe you can learn to do precision landings 100% of the time (I guess carrier pilots do?) but my own annecdotal evidence points to the contrary...especially when I have an audience!

Frank

[MikeJ 7A]

Thanks for the replies. While I love the idea of a private strip here in the hills, I don't like the idea of zero margin for error. My nearest airport is only a 40 minute drive away, which is plenty close for now.

[videobobk]

Interesting thought! I have video of a C-185 landing on a 22 DEGREE(!) slope in the Philippines. Approach is done climbing. It is 540' long and he has no problem getting stopped. I have landed on a strip that requires full power (at least in a C-150) to get to the end, although it gets steeper the farther you go. It is 1000' and a Cherokee 140 lifts off in about half that. I think slope limit is a mater of training. Of course all of these are one way in, one way out.

Bob Kelly

[MikeJ 7A]

Originally Posted by videobobk

Interesting thought! I have video of a C-185 landing on a 22 DEGREE(!) slope in the Philippines.

Wow, 22 degrees?! (not 22 percent?) A 540' runway with a slope of 22 degrees would mean a drop of 202' from one end to the other. Yikes! Even 22% would mean a drop of 119'. I'd love to see that video!

Mike

[Ron Lee]

I take off from a 6000' paved runway and this time of year am airborne is about 1500' using FP prop and 180 HP engine. It gets worse in the summer and with a passenger so 1500' seems way too short. I would estimate that you would want 3000' (plus/minus).

[donahuedc]

True a short strip can be marginal, but if it is steep too this can make up for the length. A pilot here has a short steep private strip and he flies his C182 out of. I know of a mooney that has been in and out of it too. The best thing would be to test fly on another sloped strip that is longer before you commit to building your own. I'm sure an engineer here could be more precise, but I would thing a 50 ft. drop would just about get you over 50 ft. trees at the end.

[RV7ator]

Come on over to Idaho. Try Deadwood north of Boise: 5400 MSL, 1800 ft, 5% (looks vertical), non-standard 100' obstacles. Too rough for RVs (will tear off your wheel fairings) but aircraft with 1/2 an RV's performance easily handle it. Such a slope has its own problem - erosion. Be mindful of weathering effects if you're looking at installing such an airstrip. Also, is the up-slope characteristically into the wind? A steep slope can compensate for high ground speeds with tailwinds, but taildraggers can get touchy in such a landing. I believe siting trumps slope as the sole consideration.

If Deadwood is too easy, we have others! Plenty of others, too, that are flatter/longer/shorter/higher/lower, etc. Try before you buy.

John Siebold
Boise, ID