It is obvious that using the short runway takeoff method(hold the brake till engine get full power) could get the aircraft in air within a shorter runway distance.Then why it is not used for every takeoff for all different runways? My understanding is that occupying less runway should always be a better option, isn't it? What are the disadvantages for using short runway takeoff method?
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$\begingroup$ Related: Could an aircraft be tied down, then throttle up and release for takeoff in order to use a shorter runway? $\endgroup$– Manu HCommented Dec 9, 2019 at 7:43
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1$\begingroup$ A rolling take off may also save some runway as you star using the runway with some speed you don't need to acquire at the beginning of the take off role. $\endgroup$– Manu HCommented Dec 9, 2019 at 9:27
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$\begingroup$ In my RV-8 if I apply full power with brakes, I'll get a prop strike. $\endgroup$– Kirk WollCommented Dec 10, 2019 at 18:15
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2 Answers
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Three main things:
- There is a little bit of increased brake wear because you apply them to stop, they usually creep a bit at full power, and when releasing them, there is also that short period where they are slipping while under pressure. More wear than not using them at all anyway. Of the three this is pretty trivial however.
- Sitting stationary at full throttle has the engine at maximum heating rate and minimum cooling flow. The area of the exhaust valve on the head heats up very quickly. During maintenance, full power engine runs except for very short bursts are to be avoided without a special cooling box shroud, to catch large amounts of air and force it down between the cylinders, installed in place of the cowling.
- The full power condition while sitting stationary turns the prop into a pretty powerful vacuum cleaner and it will suck up just about every pebble and bit of grit on the pavement (and even clean looking pavement is full of that sort of FOD). Or water if you are over a puddle (and water erodes aluminum). It will leave you wondering why you have to constantly have your propeller dressed out to clean up all the little stone nicks (this is why I always do run-ups over a patch of grass whenever possible). Of the three, this is probably the biggest item in my experience.
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$\begingroup$ Good points. I had forgotten 2 & 3 which are both significant. $\endgroup$– Jamiec ♦Commented Dec 9, 2019 at 13:25
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$\begingroup$ Sliding slightly OT: As I understand it, the grass is usually left a bit longer at airports and (potentially) lots of debris could blow in and get stuck in longer grass. Is there not a worry about sucking things up out of the grass? $\endgroup$– FreeManCommented Dec 9, 2019 at 14:35
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3$\begingroup$ @John K: A better example might be the difference between vacuuming a hardwood floor vs a carpet. Carpet traps a lot of dirt, which is why vacuums often have a special carpet-beater attachment. $\endgroup$– jamesqfCommented Dec 9, 2019 at 18:48
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2$\begingroup$ Yeah that works too. The other thing is that the base of grass blades is mostly soil so you have way less of the nasty objects like pebbles or small chunks of limestone in the first place. $\endgroup$– John KCommented Dec 9, 2019 at 18:55
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2$\begingroup$ You'll also burn more fuel, because you're sitting there running the engine without going anywhere. $\endgroup$ Commented Dec 10, 2019 at 11:21
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What are the disadvantages for using short runway takeoff method?
About the most tangible I can think is additional brake wear. However that is negligible, just holding brakes isn't going to wear them that much faster.
What I actually dispute is this:
[...] occupying less runway should always be a better option
I would ask yourself why you think this. More runway gives you more time to
- scan engine instruments
- Check airspeed increasing as appropriate
Those 2 things are the primary checks on the take off roll. By rushing to get off the ground you might miss something that with an extra second or 2 you might have otherwise caught.
When genuinely attempting to take off from a short field, we might sacrifice an acceptable level of safety margin, but as a general rule on a mile long stretch of tarmac - it's just not worth it!
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$\begingroup$ Does the use of more flaps also impact the climb gradient as it does for the big jets, or is it negligible for the small planes, which I guess is what is being asked about? $\endgroup$– user14897Commented Dec 9, 2019 at 11:05