ayavner Posted November 8, 2012 Share Posted November 8, 2012 Hi there, Hoping someone can jog my memory as to where to get started figuring this out. I have tried googling it, but so far have only come up with some very complicated articles using maths symbols I have never seen, or links to apps to do it for me - I seem to remember having learned this at some point, something to do with calculating pressure and density altitude, but having trouble remembering the connective tissue that ties it into the takeoff and landing distance. POH just shows the distances at ICAO std atmosphere, but say I want to know what it is at 30* and 2500' AMSL? thanks, all help gratefully received :) Link to comment Share on other sites More sharing options...
Guest Howard Hughes Posted November 8, 2012 Share Posted November 8, 2012 Can you post a picture of your POH page? Then I can give you some pointers on how to read it! Link to comment Share on other sites More sharing options...
ayavner Posted November 8, 2012 Author Share Posted November 8, 2012 Sure thing HH, thanks! there isn't anything in the POH other than this info, so a bit stuck, though I did find something called a Koch chart on the FAA site... Cheers! adam Link to comment Share on other sites More sharing options...
facthunter Posted November 8, 2012 Share Posted November 8, 2012 Think you will have trouble deriving figures. Larger planes like a Beaver would probably have a very adequate Graph/chart which will give you a trend but beware of engines that are supercharged that can compensate for power loss due to altitude. You can run into a length limit due to low power and the need to accelerate to a higher actual speed, and a performance (climb) limit due to density altitude. Pretty difficult job I reckon. Nev Link to comment Share on other sites More sharing options...
Guest Howard Hughes Posted November 8, 2012 Share Posted November 8, 2012 Not a lot to go on there! Link to comment Share on other sites More sharing options...
ayavner Posted November 8, 2012 Author Share Posted November 8, 2012 Nope, see what i mean? So what would one reasonably do in this situation, if there is no way to calculate it? I presume "hope for the best" isn't an option Link to comment Share on other sites More sharing options...
JUSTNUZZA Posted November 8, 2012 Share Posted November 8, 2012 Buy yourself a take of distance calculator from Sporty's pilot shop for $23 see image attached . 2 Link to comment Share on other sites More sharing options...
Guest Howard Hughes Posted November 8, 2012 Share Posted November 8, 2012 Koch chart looks like the way to go. I would be adding at least a 20% buffer to any figure extrapolated from the Koch chart and exercise extreme caution when taking off in hot/high conditions. Do you have the instructions on how to use the chart? You could also employ the 80/50 rule. That is if you have not achieved 80% of your flight speed in 50% of your available take off distance, then abort! PS: Did some searching and found a number of different Jab 17o POH's, with different figures in the performance section!! Link to comment Share on other sites More sharing options...
ayavner Posted November 8, 2012 Author Share Posted November 8, 2012 I am thinking that Sporty's rig looks like the go, as it also factors in slope and wind and surface etc... Thanks everyone! Link to comment Share on other sites More sharing options...
facthunter Posted November 8, 2012 Share Posted November 8, 2012 I know that the Mooney has comprehensive data and you are not getting to the "high" altitude limit situation. You might study the chart for that aircraft and ovserve the magnititude of the effect of density altitude on THAT aircraft. This will give you some idea of what "order " of effect you might be dealing with. I would try to compare yours with an aircraft that has a ssimilar service ceiling and power/weight ratio. You are only going to get an evaluation of what might be the effect but at least it is something. Any time I am doing a limiting take -off with a high altitude and temperature I evaluate the take-off performance and have a point on the runway where I abort the take-off if the plane is not performing . Nev Link to comment Share on other sites More sharing options...
ave8rr Posted November 8, 2012 Share Posted November 8, 2012 Ayavner, have a look at the NZCAA publication GAP (Good Aviation Practice) on Takeoff / landing performance. Some very good info in that publication on this subject. http://www.caa.govt.nz/safety_info/GAPs/Takeoff_Landing.pdf Cheers 1 Link to comment Share on other sites More sharing options...
ayavner Posted November 8, 2012 Author Share Posted November 8, 2012 wow thanks for that Mike, I wish all aviation docs were this clearly written. So in absence of a computer or chart, i could probably start with the following from this document: An increase in density altitude, therefore, has a two-fold effect on the takeoff: • An increased takeoff speed (TAS) is required. • Engine power and propeller efficiency are reduced. • The approximate effect of these two components on takeoff and landing performance are: • The takeoff distance is increased by one percent for every 100 feet of aerodrome pressure altitude above sea level, and the landing distance by one percent for every 400 feet. • The takeoff distance is increased by one percent for every 1˚C above the standard temperature for the aerodrome elevation. • Rate-of-climb and angle-of-climb are noticeably reduced, as is obstacle clearance after takeoff. Link to comment Share on other sites More sharing options...
djpacro Posted December 18, 2012 Share Posted December 18, 2012 ... I did find something called a Koch chart on the FAA site... Koch chart is good. Also need to comply with CASA rules I guess - see CAO 20.7.4 from memory. Link to comment Share on other sites More sharing options...
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