Newton, Runways and Rules
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Ah, yes but....
I have read this thread with great interest, both for the entertainment value and for the more important purpose of understanding the mathematics and physics involved in flying.
However as a PPL(A) I line up, apply full throttle and then check that the static rpm is at the correct level and constant, the airspeed in building in line with expectation, apply slight back pressure and finally check the “feel” of the a/c. At say 65-70knts depending on type I rotate.
I was not taught not do I feel the need to necessarily worry about what speed I should have achieved at various points along the runway. I am more concerned with the weather conditions, the take-off weight and take-off configuration.
May I just say again however, that notwithstanding the above, this thread of very interesting and informative and while it may not change the way I fly, one of the fundamental joys of learning to fly in the first place was the learning curve.
Please, before anybody shoots me down, I am incredibly safety conscious, aware of my limitations and certainly not arrogant enough to accept that I have learnt something from this thread.
However as a PPL(A) I line up, apply full throttle and then check that the static rpm is at the correct level and constant, the airspeed in building in line with expectation, apply slight back pressure and finally check the “feel” of the a/c. At say 65-70knts depending on type I rotate.
I was not taught not do I feel the need to necessarily worry about what speed I should have achieved at various points along the runway. I am more concerned with the weather conditions, the take-off weight and take-off configuration.
May I just say again however, that notwithstanding the above, this thread of very interesting and informative and while it may not change the way I fly, one of the fundamental joys of learning to fly in the first place was the learning curve.
Please, before anybody shoots me down, I am incredibly safety conscious, aware of my limitations and certainly not arrogant enough to accept that I have learnt something from this thread.
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Chimbu,
I apologise for offending you, and I certainly defer to your vast experience of bush-flying which is more than I will ever log. However, even if you dislike and dismiss my approach, you cannot do the same with physics. Physics works the same in PNG as in SE England, and therefore so do airplanes.
You give an example where you do not climb from the runway, but you push down! Hair-raising and an entertaining tale, but not relevant to what most of us do, or this example either.
Why didn't you crash? I suspect you used the benefit of experience so your Vr was actually a lot lower than what the books said (39knts example). It was still a Vr, and if you weren't at 71% of it by half way down the runway, and if you were accelerating at a constant rate, you would not make that Vr by the end. That's not a rule I made up, and that's the rule I am pushing.
More interestingly. I also suspect you hopped off the ground well prior to published Vr, used ground effect to increase lift and reduce drag, and accelerated faster than you would have done on the ground. This is a very effective way of getting off a field which is shorter than you like. Of course, you have to get out of ground effect at some stage. You obviously do this with great effect by diving off a cliff. It doesn't always work that way, most runways don't end like that, and sometimes you cannot climb out and you hit something. Better to stop
Hey, just trying to throw out some numbers here as a safety guide. Take it or leave it.
bookworm,
Show me a light aircraft where the stopping distance is greater than the starting distance. POH figures will show that you need less runway to stop than go. So if start at zero, and you brake properly at 50% of the runway length, you will always reach zero before the end.
If somebody wants to think about ground effect then that's cool. I do not recommend you plan to use ground effect anywhere except above a runway, unless you know what you are doing and are bush-flying in PNG, where you might have no choice.
F3G,
Strap a decent airspeed indicator on it, but remember it will stop your bulldog going into warp drive. You just have one less piece of data to assist you in safe decision making. You increase your risk of running off the end of the runway if you fly a plane with an ASI not calibrated at takeoff roll speeds.
I apologise for offending you, and I certainly defer to your vast experience of bush-flying which is more than I will ever log. However, even if you dislike and dismiss my approach, you cannot do the same with physics. Physics works the same in PNG as in SE England, and therefore so do airplanes.
You give an example where you do not climb from the runway, but you push down! Hair-raising and an entertaining tale, but not relevant to what most of us do, or this example either.
Why didn't you crash? I suspect you used the benefit of experience so your Vr was actually a lot lower than what the books said (39knts example). It was still a Vr, and if you weren't at 71% of it by half way down the runway, and if you were accelerating at a constant rate, you would not make that Vr by the end. That's not a rule I made up, and that's the rule I am pushing.
More interestingly. I also suspect you hopped off the ground well prior to published Vr, used ground effect to increase lift and reduce drag, and accelerated faster than you would have done on the ground. This is a very effective way of getting off a field which is shorter than you like. Of course, you have to get out of ground effect at some stage. You obviously do this with great effect by diving off a cliff. It doesn't always work that way, most runways don't end like that, and sometimes you cannot climb out and you hit something. Better to stop
Hey, just trying to throw out some numbers here as a safety guide. Take it or leave it.
bookworm,
Show me a light aircraft where the stopping distance is greater than the starting distance. POH figures will show that you need less runway to stop than go. So if start at zero, and you brake properly at 50% of the runway length, you will always reach zero before the end.
If somebody wants to think about ground effect then that's cool. I do not recommend you plan to use ground effect anywhere except above a runway, unless you know what you are doing and are bush-flying in PNG, where you might have no choice.
F3G,
Strap a decent airspeed indicator on it, but remember it will stop your bulldog going into warp drive. You just have one less piece of data to assist you in safe decision making. You increase your risk of running off the end of the runway if you fly a plane with an ASI not calibrated at takeoff roll speeds.
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Hi Bookworm
Indeedy it shows that trust decreases with airspeed. But how about the assertion that you stop accelerating.
If I just may take you back to your AvWeb quote (interesting reading)
http://www.avweb.com/news/airman/182410-1.html
in figure 6 Thrust vs drag you can see that the Thrust vector is greater than the drag vector until 69 KTS so until that point for this particular mount (a C172) the resulting factor will be acceleration.
You will agree that at 69 KTS a 172 will be flying.
Over to you.
FD
Indeedy it shows that trust decreases with airspeed. But how about the assertion that you stop accelerating.
If I just may take you back to your AvWeb quote (interesting reading)
http://www.avweb.com/news/airman/182410-1.html
in figure 6 Thrust vs drag you can see that the Thrust vector is greater than the drag vector until 69 KTS so until that point for this particular mount (a C172) the resulting factor will be acceleration.
You will agree that at 69 KTS a 172 will be flying.
Over to you.
FD
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Aussie,
Yep, I think people should consider the theory. There are many old wives tales out there with no basis in fact, and individual experiences mean nothing.
What you are doing in your pacing out is calibrating a specific airplane for specific conditions. This can be useful because you can determine true braking distance for that runway. So start by brakeing at half way. You WILL stop, measure distance to end, divide by two, and add to half way point of runway. Perform roll again, brake at position determined by previous run. Continue until you calibrate that plane for that runway.
That will give you a better figure of speed and distance along a runway you can brake and still stop. JUST.
Using this method, you will take off when I would not. I will never kill myself, but I will have to face the ridicule of fellow pilots at the airport restaurant for turning back because I want to stay unkilled. I think I can handle that (being the arrogant git I am). I also have NEVER been ridiculed by any pilot in the high country for erring on the side of caution.
If you cannot think of a reason not to teach my method, why not consider it?
It might save somebody when their engine is not performing as it should. We should use ALL means at our disposal to evaluate engine performance at such a crucial phase of flight.
QDM,
You mentioned you flew on backcountry strips in Idaho. Never notice the markings on the side of the runway on some of them, half way along. What do you think they are for? Quick look down, takes fraction of a second, stop or continue with butt clenched On high altitude strips round here I ALWAYS know where half way down is. This can either be an intersection, or sometimes they have numbers on the side of the runway with distances to the end. White on black background.
Down low where the runways are long, I don't make such an effort. That is wrong of me, I should.
Flying Dutch
Cheers!
Yep, I think people should consider the theory. There are many old wives tales out there with no basis in fact, and individual experiences mean nothing.
What you are doing in your pacing out is calibrating a specific airplane for specific conditions. This can be useful because you can determine true braking distance for that runway. So start by brakeing at half way. You WILL stop, measure distance to end, divide by two, and add to half way point of runway. Perform roll again, brake at position determined by previous run. Continue until you calibrate that plane for that runway.
That will give you a better figure of speed and distance along a runway you can brake and still stop. JUST.
Using this method, you will take off when I would not. I will never kill myself, but I will have to face the ridicule of fellow pilots at the airport restaurant for turning back because I want to stay unkilled. I think I can handle that (being the arrogant git I am). I also have NEVER been ridiculed by any pilot in the high country for erring on the side of caution.
If you cannot think of a reason not to teach my method, why not consider it?
It might save somebody when their engine is not performing as it should. We should use ALL means at our disposal to evaluate engine performance at such a crucial phase of flight.
QDM,
You mentioned you flew on backcountry strips in Idaho. Never notice the markings on the side of the runway on some of them, half way along. What do you think they are for? Quick look down, takes fraction of a second, stop or continue with butt clenched
On high altitude strips round here I ALWAYS know where half way down is. This can either be an intersection, or sometimes they have numbers on the side of the runway with distances to the end. White on black background.Down low where the runways are long, I don't make such an effort. That is wrong of me, I should.
Flying Dutch
Cheers!
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Strap a decent airspeed indicator on it ...... You increase your risk of running off the end of the runway if you fly a plane with an ASI not calibrated at takeoff roll speeds.
Anyone out there know of a Bulldog which has run off the end of the runway???? I've just done a search and can't find any, but would be interested in anyone else's experience.
Lets assume, for the sake of argument, that the fleet of about 300 'dogs has flown 50 hrs each per year for 25 years (average lifespan over the fleet) - which makes 375,000 hours, which I would argue would involve a landing on average at least every hour (given that she is a trainer.)
So that would also mean 375,000 take offs .... so how many Bulldogs have run off the end of the runway out of an estimated 375,000 attempts? (Having flown a few hours in 'em, I reckon not too many, since they take off like rockets
) In fact, the very reason that the Bulldog does not meet Slim Slag's 'rule'is that it has extremely good take off performance and requires a Vr of 45kias at about the same weight as a 4 seat PA28-181 requiring 65kias.
The examples of both types that I have flown have ASIs with a bottom stop of 40kias, so the latter can meet Slim Slag's 'rule' as 75% of Vr is 48kias, but the former cannot, because it's Vr is 20kias LESS meaning that 75% of Vr is an unmeasurable (if very healthy) 34kias, but this ASI calibration 'defect' apparently increases the risk of running off the end????
So, I think there's a bit of a logic problem here somewhere.
Now for another beauty.....
So if start at zero, and you brake properly at 50% of the runway length, you will always reach zero before the end.
Please let me know where I can get these for the PA28/PA32/B121/SA120 as I would gladly invest in them tomorrow.
I have to say, Slag, that your posts have given me much more entertainment that Coronation Street going to 5 days a week, please keep it up as I can't wait for the next episode
Last edited by Final, 3 Greens; 26th Jan 2003 at 22:08.
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accelerate v stop distance
Only just got brave enough to stick my nose into this thread, as I am still trying to understand the opening post 
Anyhow, I am with Final, 3 Greens on the matter of accelerate/stop distances.
For instance, what about an SEP with a magnificent power/weight ratio, but only the bog standard brakes, that are fitted to most light aircraft. If it accelerates like s@#t down the runway, why is it guaranteed to stop in the same distance?
Anyhow, I am with Final, 3 Greens on the matter of accelerate/stop distances.
For instance, what about an SEP with a magnificent power/weight ratio, but only the bog standard brakes, that are fitted to most light aircraft. If it accelerates like s@#t down the runway, why is it guaranteed to stop in the same distance?
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distaff_beancounter
For instance, what about an SEP with a magnificent power/weight ratio, but only the bog standard brakes, that are fitted to most light aircraft. If it accelerates like s@#t down the runway, why is it guaranteed to stop in the same distance?
Where can I find one of these?
I think you can take it as read that on a dry, paved runway the brakes will out-perform the thrust. Were that not the case your power-checks and short-field takeoff (full power before brake release) would be "interesting" to say the least
Where this balance shifts is where the friction is reduced such as on ice or wet grass - here the thrust (unaffected by such things) may be greater than the braking ability.
These circumstances may lead to a situation where you need less distance to accelerate than you do to stop (NB remember we are talking about speeds less than "flying speed") - but that would be the exception rather than the rule.
=========================================
I found this an interesting thread, but can we play the ball, and not the man?
For instance, what about an SEP with a magnificent power/weight ratio, but only the bog standard brakes, that are fitted to most light aircraft. If it accelerates like s@#t down the runway, why is it guaranteed to stop in the same distance?
Where can I find one of these?
I think you can take it as read that on a dry, paved runway the brakes will out-perform the thrust. Were that not the case your power-checks and short-field takeoff (full power before brake release) would be "interesting" to say the least
Where this balance shifts is where the friction is reduced such as on ice or wet grass - here the thrust (unaffected by such things) may be greater than the braking ability.
These circumstances may lead to a situation where you need less distance to accelerate than you do to stop (NB remember we are talking about speeds less than "flying speed") - but that would be the exception rather than the rule.
=========================================
I found this an interesting thread, but can we play the ball, and not the man?
Last edited by rustle; 27th Jan 2003 at 09:06.
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Rustle
I see where you are coming from, but what about the kinetic energy already in the airframe?
AFAIK, there aren't any accelerate/stop distances published fror SEPs, which could be factored to account for the variables you mention.
So there must be an element of uncertainty about stopping performance, although practically speaking I've rejected three take offs and never had a problem stopping - with one being a decision made at 50knots in a PA28 on a 700m dry grass runway with a slight downslope.
I think you can take it as read that on a dry, paved runway the brakes will out-perform the thrust. Were that not the case your power-checks and short-field takeoff (full power before brake release) would be "interesting" to say the least
AFAIK, there aren't any accelerate/stop distances published fror SEPs, which could be factored to account for the variables you mention.
So there must be an element of uncertainty about stopping performance, although practically speaking I've rejected three take offs and never had a problem stopping - with one being a decision made at 50knots in a PA28 on a 700m dry grass runway with a slight downslope.
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Final, 3 Greens
"...but what about the kinetic energy already in the airframe"
Yikes, haven't thought about stuff like this for far too long
Whilst I concede that (kinetic energy) would be additional if our intrepid pilot decided to leave full power on whilst aborting, if we assume he/she doesn't 
the loss of thrust should at least compensate for the inertia/kinetic energy of movement.
Without, hopefully, confusing things here's an example of accelerate-stop distances - albeit for a twin where such things are in the P.O.H.
Turbo Cessna 310R, 5500lbs (MTOW), pressure alt. 2000', temp +10C, nil wind, Vr = 92KIAS.
Accelerate distance (ground roll) = 1790'
Accelerate-stop distance = 3460'
So stopping, under these conditions, requires 120' less than accelerating. No tricks - at this speed (92KIAS) the wings are producing sufficient lift to fly. (Stall speed, this config, is 80KIAS)
So does this illustrate that you need less space to brake than accelerate? (Okay, in this aircraft, under these conditions)
So if by 50% TORA you abort there should be sufficient space remaining ahead to brake and stop, within the TORA. (In the context of this discussion, which was that if you are not at 75% Vr by 50% distance)
If you now add-in the other variables - ice, wet grass, - which we agree (I think) don't affect thrust but do affect braking, we end up where Bookworm started:
The "50% rule" isn't conservative enough.
slim_slag said the same thing too: "Actually I am far more cautious than that, because I don't want to use all available runway"
"...but what about the kinetic energy already in the airframe"
Yikes, haven't thought about stuff like this for far too long
Whilst I concede that (kinetic energy) would be additional if our intrepid pilot decided to leave full power on whilst aborting
, if we assume he/she doesn't the loss of thrust should at least compensate for the inertia/kinetic energy of movement.Without, hopefully, confusing things here's an example of accelerate-stop distances - albeit for a twin where such things are in the P.O.H.
Turbo Cessna 310R, 5500lbs (MTOW), pressure alt. 2000', temp +10C, nil wind, Vr = 92KIAS.
Accelerate distance (ground roll) = 1790'
Accelerate-stop distance = 3460'
So stopping, under these conditions, requires 120' less than accelerating. No tricks
- at this speed (92KIAS) the wings are producing sufficient lift to fly. (Stall speed, this config, is 80KIAS)So does this illustrate that you need less space to brake than accelerate? (Okay, in this aircraft, under these conditions)
So if by 50% TORA you abort there should be sufficient space remaining ahead to brake and stop, within the TORA. (In the context of this discussion, which was that if you are not at 75% Vr by 50% distance)
If you now add-in the other variables - ice, wet grass, - which we agree (I think
) don't affect thrust but do affect braking, we end up where Bookworm started: The "50% rule" isn't conservative enough.
slim_slag said the same thing too: "Actually I am far more cautious than that, because I don't want to use all available runway"
Last edited by rustle; 27th Jan 2003 at 11:05.
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Rustle
I wasn't thinking of such a horror scenario Just uncertain about how well SEP brakes deal with the non linear nature of kinetic energy in extreme cases.
As I said I had no problem stopping from 50kias (1 above VS1) on a 700m runway, dry grass, very slight downslope, with a PA28 that was ready to start flying.
Absolutely and I would accept that the aircraft could stop under different conditions with the appropriate factors being applied to the distances you quote.
My problem was with the original statement "I'm just guaranteeing that you will be able to stop", which I don't think can be true as an absolute assertion.
The lack of accelerate/stop performance tables for SEPs does leave a bit of uncertainty in my opinion though, because what do you apply safety factors to? Say short wet grass, 2% downslope, no headwind, ISA +15.... I can calculate the TORA and distance to 50' and apply the CAA safety factors, but have to hope for the best that I could stop in the event of a rejection being needed.
Whilst I concede that (kinetic energy) would be additional if our intrepid pilot decided to leave full power on whilst aborting
Just uncertain about how well SEP brakes deal with the non linear nature of kinetic energy in extreme cases. As I said I had no problem stopping from 50kias (1 above VS1) on a 700m runway, dry grass, very slight downslope, with a PA28 that was ready to start flying.
So does this illustrate that you need less space to brake than accelerate? (Okay, in this aircraft, under these conditions)
My problem was with the original statement "I'm just guaranteeing that you will be able to stop", which I don't think can be true as an absolute assertion.
The lack of accelerate/stop performance tables for SEPs does leave a bit of uncertainty in my opinion though, because what do you apply safety factors to? Say short wet grass, 2% downslope, no headwind, ISA +15.... I can calculate the TORA and distance to 50' and apply the CAA safety factors, but have to hope for the best that I could stop in the event of a rejection being needed.
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Sorry for dragging this to the top kiddies, but aussie andy said he had never seen this in print, and last night while perusing the latest FAR/AIM (which everybody should do every now and again, even though it is a nasty US rag) I found this little beauty.
7-5-6. Use of Runway Half-way Signs at Unimproved Airports
Don't expect anymore from me on this, as I actually think my presence is clouding the issue and I don't want to be responsible for your blood pressure blowing your head off. Some on this thread understand, but unfortunately not most. I refer to my original post bemoaning the standard of education nowadays 
7-5-6. Use of Runway Half-way Signs at Unimproved Airports
Don't expect anymore from me on this, as I actually think my presence is clouding the issue and I don't want to be responsible for your blood pressure blowing your head off
. Some on this thread understand, but unfortunately not most. I refer to my original post bemoaning the standard of education nowadays
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Yes rustle, it does seem a bit of a suspicious coincidence, but I promise that if I had thought about it earlier, I would have cited it then. Honest, guv! I would have missed out some fun though.
Thanks dutch, but was there ever a doubt
Thanks dutch, but was there ever a doubt
