Ground roll take off calculations

6 Answers

1. 
   

   
   

   Mark Kolber on Dec 02, 2018

   I’m not completely sure what you are asking. How is the “ground roll correction” (and I don’t understand what you mean by that) any different than any of the other parameters.

   It would probably help if you gave us a specific calculation question and which tables you are using – calculations using a POH table (like Cessna) are a bit different than using POH graph (like Piper)

   0 Votes 0 Votes  0 Votes

2. 
   

   
   

   usaukel on Dec 02, 2018

   Hi Mark,

   First thank you very much for taking the time to answer. so here was the problem to resolve:
   Calculate the take off ground roll under the following conditions:

   OAT = 30C
   Airport Alt =1248′
   Alt setting = 30.17
   take off weight = 2100lbs
   Dry runway no grass.
   Runway in use = 15
   wind = 110/25

   Table link: https://goo.gl/t91rdf

   So what i am trying to understand is, is there a common procedural approach to always take to calculate, for example:
   1 – calculate Pressure Alt.
   2 – Get wind correction data
   3 – etc…

   Or simply maybe tell me the way you are doing it, would be problably better! 🙂

   Thanks again.

   Ulrich

   0 Votes 0 Votes  0 Votes

3. 
   

   
   

   Mark Kolber on Dec 03, 2018

   The math skill you need in these questions in “interpolation.” I won’t go through the process, but the concept is, if yo don’t have an exact number, find the ones aove and below it. There are plenty of explanation both online and in textbooks. Wes did one on this site some years ago at http://www.askacfi.com/3685/interpolation.htm. There is also one in the Pilot’s Handbook of Aeronautical Knowledge in the Performance Charts section which uses a similartable to the one yo are looking at. I hope this helps, but if those explanations don’t make sense, I sugest a one-on-one with your instructor.

   Here’s how I would approach it.

   1. Use the chart for 2100 lbs
   2. Use the column for 30°C.
   3. Calculate the pressure altitude. In this case it’s 998.
   3. Since the chart doesn’t give a value for 998′, you would interpolate by taking the 1000′ and the SL ground roll numbers and interpolating. But in this case, since it’s 998. I would just take the 1,000′ number. No need to use a micrometer to measure a football field.
   4. In this particular problem, you have a crosswind, so you need to figure out the headwind component and apply the correction in the instructions. Since it is not a grass runway, no need to worry about that one.

   If this is for the knowledge test, there is typically only one answer which makes sense, even if you don’t go through the entire calculation.

   0 Votes 0 Votes  0 Votes

4. 
   

   
   

   usaukel on Dec 03, 2018

   Thanks that helped. As long as i have the correct train of thought i am good. Yes this is for the test and I have to be Ok with not having the precise response but the closest.

   Thanks Mark.

   0 Votes 0 Votes  0 Votes

5. 
   

   
   

   Mark Kolber on Dec 04, 2018

   Let us know how it works in your practice tests.

   0 Votes 0 Votes  0 Votes

6. 
   

   
   

   usaukel on Dec 04, 2018

   Thanks we’ll do!

   0 Votes 0 Votes  0 Votes