Short field takeoff climb speed?

[bjornhall]

On a short field takeoff, does anyone actually use the POH initial climb speed?

For example, in a C172S with just the pilot and a splash of fuel, lift off with flaps 10 should be at 44 KIAS and initial climb at 50 KIAS... Everyone I speak with, including my former instructors, say that is unsafe bordering on crazy. And having tried simulating an engine failure in a 50 KIAS flaps 10 climb at a safe altitude, I rather agree. Yet everyone is quite happy to use the POH figures for takeoff distance... To me it makes little sense to use the POH distances while disregarding the speeds that those distances are based upon?

I understand what people end up doing is to use higher climb speeds (65 KIAS or so), thereby sacrificing obstacle clearance at the departure end, on the grounds that there is no 50 ft obstacle there... But my understanding of the 50 ft obstacle clearance requirement is that you should be 50 ft above any obstacles, which includes being at least 50 ft up when passing the far threshold; not that there's a 48 ft pine tree growing right on the runway end.

What do you think?

[SNS3Guppy]

You may be confusing the takeoff speed with the climb speed. You see, it really doesn't matter what speed you're climbing after you've left the ground...because the ground roll is over.

A best angle speed is there to get you over an obstacle. You're not intended to fly that speed until you break out of the atmosphere.

If you've predicated your takeoff distance on chart values, then you should use the criteria spelled out in the chart. Use your given speeds until you're clear of obstacles. If you're told to lift off at 44 knots for a short field takeoff maximum performance run, then that's the number you use.

The real problem lies in the fact that much of the time, truly short fields are also soft fields, and soft fields seldom have unlimited runway, and are therefore not uncommonly short.

Pilots are often taught, and given procedures which differ, and indeed are too often nearly diametrically opposed in practical application, between short and soft field. Therein lies the problem; in the real world, such as most back country operations where it's truly a rough field, short and soft is the same procedure...and often involves a brief delay in ground effect to get speed after the wheels are clear of the surface before attempting to outclimb obstacles.

I've departed truly soft surfaces in 172's and the like where large quantities of mud or slush covers the underside of the wing, the struts, and even the leading edges, thrown up by wheels and even the propeller. Imagine climbing at the ragged performance edges with an altered wing covered in mud. Not only is the performance data invalid (it's going to take longer to get off the ground due to the excessive coefficient of drag on the wheels in the mud), longer to accelerate, and the airplane is heavier, dirtier, and with reduced airflow and a higher coefficient of drag in flight, than what the book may describe...and the book has no way of knowing the density or depth of the mud, sluch, wet grass, rocks, etc.

I say that to make two points; one is that you should never plan to operate at the ragged edges of performance, and the other is that you should follow the book as closely as possible...but only so long as the conditions match what's in the book. If the book says use 44 knots and then 50 knots, then do so...but only if you're departing in the same conditions provided. If you're operating in other conditions, then the book numbers and values no longer apply. In the case of the mud covered wing, for example, one might justifiably expect the stall speed to be higher, and the climb numbers to be higher. Additionally, if one isn't actually outclimbing an obstacle (it's not uncommon for short fields to be short because they're surrounded by obstacles), then striving for the max angle of climb isn't nearly so critical...but keeping the airplane flying certainly is.

If you're departing a dry, hard surface runway and following the procedure outlined in the book, fly it like you see it in the book.

[dont overfil]

I suppose it depends on the defination of initial climb. If it was a couple of seconds OK but I would not be happy about climbing to 200 feet at 50kts.
Probably these figures should be taken as limitations rather than normal proceedures.
A C172S is a very capable aeroplane but you would be pushing your luck flying into a place which would require such extreme manoevers to get out again unless you were a bush pilot.

[SNS3Guppy]

I suppose it depends on the defination of initial climb. If it was a couple of seconds OK but I would not be happy about climbing to 200 feet at 50kts


When did you last see a 200' tree? Or powerline? The obstacle clearance speed is there to...clear obstacles.

That said, is there something about operating the airplane at 200' that makes it less safe than operating it in that condition at 50'? Certainly not...altitude is your friend.

Generally you're not going to need to climb higher than 50' or so before allowing the airplane to accelerate slightly...but per the previous comments, you do what you must according to the conditions under which you're operating.

As an ag pilot I climbed over tall 100' or higher trees every 30 seconds all day long...to do a steep turn at tree top level and drop right back to the ground again...over and over. The airpalne never magically quit flying simply because I was 100' above the ground, nor should it. This is why you, as the pilot are there...to fly the airplane, rather than let it do what it wants.

Today in my regular job, we hold our climb speed all the way to 3,000' before we start cleaning up the airplane...and it doesn't fall out of the sky, either. Sometimes it feels ridiculously slow, but it's the procedure, it's taken from the performance data, and it's what we use.

Remember too, that there's no regulation preventing you from being more conservative. If the book says you can get off the ground in 600', there's no reason why you can't set a personal minimum of 2,500' for a runway. See what I mean? No law says you have to fall back to the ragged edges of performance.

Probably these figures should be taken as limitations rather than normal proceedures.


No, the figures the manufacturer gives you for performance tables and for their procedures are just that...normal procedures. They're meant to be followed, subject to some of the previous discussion.

[bjornhall]

That all makes a lot of sense!

As a freshly minted PPL holder, my focus is still on 'ordinary' short fields; your typical 500 - 700 m dry & firm grass strip with perhaps a fence and some low bushes at the departure end... I'd feel decidedly uncomfortable at 50 KIAS at anything more than 10 ft or so off the ground. But I also know that if the POH distance to 50 ft is (say) 500 meters, the only way I can be at 50 ft after 500 meters is to climb initially at 50 KIAS; a higher climb speed means I will be lower (or the POH would not use the lower speed). And I'd feel decidedly uncomfortable at 30 ft or less with anything other than an airstrip beneath me.

The way I see it, there's no safe way to use the POH takeoff figures; you're either climbing too slow, or climbing out too low. Is that right, or am I being overly cautious? I know that view is unusually cautious, at least where I fly...

[dont overfil]

Bjornhall,
You are right to be careful. Limited clearance and low speed both have dangers

SNS3Guppy.
I think you are sort of agreeing with me. In Scotlandshire we also have some terrain to deal with. The 50kt bit should be kept to a minimum as days with no gusty winds are rare.
DO

[Them thar hills]

Well, FWIW I was looking at several 200ft + transmission towers this afternoon.
Halifax Gliding Club and a private strip not many miles east (at Northowram) were both put out of use by just such an "obstacle" !! (The trans-Pennine 400 kV grid line)
Don't they count then ?!:bored:

[Gertrude the Wombat]

Pilots are often taught, and given procedures which differ, and indeed are too often nearly diametrically opposed in practical application, between short and soft field.
The only difference I was taught was that for a short field take-off you stop at the beginning of the runway and run up to full power against the brakes, whereas for a soft field take-off you don't stop as you might never start again.

The thing I've still never found in a POH ... is any indication of how long the runway has to be before you can stop worrying about doing a "short field" take-off and do a "normal" take-off instead.

[Gertrude the Wombat]

The way I see it, there's no safe way to use the POH takeoff figures
POH figures, as I'm sure you know, are what the company test pilot could achieve in a specially tuned brand new aeroplane with no paint on it on a carefully selected day at sea level (and then only if he couldn't find an airfield below sea level).

The safe way to use several of the POH figures is to apply a fudge factor. For take-off and landing distances there's an AIC containing recommended fudge factors, which I'm sure we all refer to when doing our sums. For fuel burn your club's flying order book may contain the fudge factor they expect you to use.

Dunno what fudge factor you apply to the 172 POH's "climb at 50", though, but I'm sure I wouldn't do it. If you're short of space and the trees are looming up at you it will climb at less than your usual 80 (or whatever you normally use), but you won't catch me trying 50.

[SNS3Guppy]

Well, FWIW I was looking at several 200ft + transmission towers this afternoon.


Generally one goes around those, rather than attempting to climb directly over them. If one's smart. One also avoids them by a wide margin, as the guy wires that support them extend out a lot farther than one might think and can cause a lot of grief. They're invisible too, for all intents and purposes, from the air.

In Scotlandshire we also have some terrain to deal with.


Yes, I'm familiar and the flying techniques I've been discussing have that in mind. I grew up with small hills too...12,000' to 15,000' ones. The flying techniques and the ability of the airplane to fly doesn't change, however. Ordinarily one isn't trying to maintain 50 knots to clear the 12,000' mountain. Just the objects at the end of the runway.

And I'd feel decidedly uncomfortable at 30 ft or less with anything other than an airstrip beneath me.


That's somewhat akin to feeling comfortable swimming only in water in which you can stand...but being afraid to go swim in the ocean or the deep end. So long as you float...the water can be fathoms deep and it just doesn't matter...because you're floating on top of it.

If you're 50 knots at 10' or 50 knots at 50' does that make any difference? Does the airplane know the difference? If you closed your eyes, would you? If you are at 50 knots over the runway, does this make any difference from 50 knots when not over the runway? Does the airplane know the difference? If you closed your eyes, would you?

The answer to all of the above is no, it makes no difference, and you'd know no difference, either. With one big exception, which we'll talk about.

The way I see it, there's no safe way to use the POH takeoff figures; you're either climbing too slow, or climbing out too low. Is that right, or am I being overly cautious? I know that view is unusually cautious, at least where I fly...


You're not being overly cautious; you're being prudent, and prudent is right. Like I said before, there's no law which forbids you acting more conservatively. Generally speaking, it's a very good thing. However, is there a safe way to use the takeoff figures? Yes. So long as you understand how they apply.

First, you have to understand that the takeoff figures were using a clean airplane in demonstration conditions with an experienced, demonstration pilot on board...and were done under the specified conditions. Apply that to your situation: do you have a new airplane with a new propeller and a new engine and a clean, unblemished wing that's in trim per the factory specifications? Probably not. Are you launching under identical conditions of runway surface, etc? Probably not. How does this apply to you, then?

If you're departing grass you'd need to know about the soil condition under the grass that was used in the demo, to make a comparison. You'd need to know the grass type,the moisture (wet grass can be like taking off on ice; it's slick...a big issue on landing, too), the height of the grass, etc. Taken t0 the extreme, take it from a guy who's had his wheels in tall corn and crops on more than a few occasion...tall grass and plants produce a LOT of drag (which can actually suck you in, if you touch it while flying over...). What your field conditions are may not replicate the conditions that the factory used to demonstrate and formulate the takeoff data.

Next consider that you're flying an airplane that's not certificated under transport category requirements. It doesn't have hard and fast performance requirements, and much of the data has been interpolated. It's calculated, based not what you can rely upon the airplane to do each time it goes out, but on what it did once long ago before it was certificated for production and public use. A transport category airplane's performance is sometimes referred to as "guaranteed," whereas light airplanes performance is decidedly NOT.

Again, back to how it applies to you; being conservative is always a very good rule of thumb. Yes, the airplane can takeoff in XXX distance, but you decide you'll never fly it unless you have XXXXXX to use. You see the point.

However, if you intend to replicate the book figures, or use those procedures, then you should use the numbers. At a minimum, you should be able to use them.

I said there's an exception, and there is. If you're climbing off a short field at a maximum performance airspeed, which in a light airplane usually means minimum speed or close to it, then you don't have much margin for error...really the point of this whole discussion. Where it will eat your lunch is ground effect. You can get off the ground at a much lower speed than the airplane will really fly in ground effect. You can break ground, in the example in use, at 44 knots, but shouldn't be climbing out of ground effect until 50 knots. That's fine in calm conditions. But as other posters have noted, what if it's not calm.

Windshear. It's everywhere you want to be, as the commercial likes to say. The surface of the earth is a giant wind modifying device; it's all about friction. Get away from the surface as you know, and the wind may be goign a different direction or speed. If you're flying on a day when there's an inversion or simply a day when the wind speed increases with altitude (when doesn't that happen?), then as you climb out, you're getting a different wind than when you started your roll. It's possible to takeoff in relatively calm surface conditions, but run into a tailwind as you begin to climb. If this occurs suddenly, as it can do in an inversion, you're in a windshear and the airplane will not simply with the wind; you lose airspeed and now you have a problem.

This is where airmanship comes in. Knowing the winds, knowing the conditions, and using judgement to make the decision as to where to go and what to do.

It's part of deciding and planning the takeoff, too. What are you going to do if you get off the ground and find you can't climb. Waiting until that happens isn't the time to make that decision. You must plan for it, believe it WILL happen, and plan your takeoff accordingly. It may mean taking off the other direction. It may mean taking off earlier or later in the day. It may mean taking off lighter, flying somewhere else for fuel and passengers. It may mean a lot of things, but it's up to you as the PIC to determine exactly what it means and how it applies to you. If you ever have to ask yourself if you feel okay with, then you have a big red flag right there...don't do it.

Too often we ask ourselves if we can. Too frequently we fail to ask ourselves if we should.

Use the performance data to help you make your plans...and if you do plan based on the numbers given, then fly the numbers given. Just realize that they are based on a set of criteria that must match your operating conditions in order to be valid.

Don't they count then ?!


They most certainly do count, especially if you hit them.

Climbing over an obstacle should only be done when it's necessary. A big obstacle at one end of a strip may effectively make it a one-way airstrip. You takeoff one direction and land the other, with no go-around options available when landing. Sometimes fields aren't easily recognizable as one-way; we think it looks okay, but it really isn't. That's where analyzing the performance data that's published by the manufacturer can help you make what may become the most important decision of your life (because if you make it incorrectly, it may be the last decision of your life). Simply looking at the data may be enough to tell you to depart the opposite direction, away from the powerlines.

A good rule of thumb, especially where obstacles and terrain are concerned, is the water principle. Water flows down hill, and so should you. That's where your escape path goes. Avoid having to outclimb obstacles if you can help it. In many cases, obstacles will outclimb you, and that's never a good thing.

I flew from one field when doing ag work that required departing under the powerlines, rather than over them. Another location had a large cliff at the end, necessitating taking off one way, landing another. And so on.

I flew from a mountain airstrip that requried an approach down the face of a volcano at the same descent angle as the slope of the volcano...often not very high above it, either. The strip was a steeply angled dirt runway and as one approached it one went to nearly full power, landed uphill, taxied to the top and spun around...and left the engine running on one mag with rocks under the wheels for chocks. This in a Cessna 206 or 207, while loading passengers and gear. The departure was always the opposite direction, no matter what the wind conditions, because the runway was in a box canyon. The takeoff involved preventing the airplane to fly when it hit the first hump in the runway (too soon), preventing it from touching down at the second hump. Then maintaining about 10' while following a flashflood drainage past the base of the volcano where it spit out into a 2,000' drop and rising air.

Some pilots and passengers were killed there, attempting a go-around while landing. The field didn't really look like a one way strip when approaching from the mouth of the canyon, but failure to respect it as such proved a killer. Doing the math using the performance charts would easily bear this out, and for anyone who took the time to do so, it might have proven a lifesaver, too.

That field, like many others, incidentally, required both short and soft field techniques, and judicious use of ground effect, as well as other soft field techniques such as doing airborne mag checks and applying flaps well into the takeoff to avoid rock damage and allow a faster acceleration. Some of those are more advanced techniques, but work very, very well...and shouldn't be attempted without adequate supervision and instruction. Nor should even flying into such a place be attempted without being taken there by one experienced in that particular operation, at least a few times before doing it on your own.

Never the less, if you're going to use the book numbers, use all of them. Definitely don't apply the ground roll or obstacle distance figures unless you use the climb figures to match, and don't use any of them unless your operating conditions match those in the takeoff data.

The thing I've still never found in a POH ... is any indication of how long the runway has to be before you can stop worrying about doing a "short field" take-off and do a "normal" take-off instead.


That's precisely why one should calculate one's takeoff performance...in order to know the answer to that question. The numbers will tell you.

[bjornhall]

Thanks a lot, this all seems much clearer now!

[Gertrude the Wombat]

Quote:
The thing I've still never found in a POH ... is any indication of how long the runway has to be before you can stop worrying about doing a "short field" take-off and do a "normal" take-off instead.
That's precisely why one should calculate one's takeoff performance...in order to know the answer to that question. The numbers will tell you.
What numbers??? - that's my point!! If the POH only contains tables for short field take-off, and contains no data for "normal" take-off, how are you to know when a runway is long enough to be safe trying to take off with no flaps??

[SNS3Guppy]

Your aircraft manual has no takeoff data describing the takeoff length for a normal takeoff? Or you're saying a normal takeoff in your aircraft involves flaps?

Is the only takeoff data published called "short field takeoff" data, or is your manual missing data? Which aircraft?

Not really enough information here.

Some aircraft aren't to be taken off with flaps up. Presently the airplane I'm flying gives us a choice; flaps 10, or flaps 20. We generally prefer 10 because while the greater flap setting gets us of the ground a little sooner, we don't climb as well...and we always plan for an engine failure...so we plan for the best climb with a failed engine...and that means flaps 10 where ever we can.

I'm not sure I understand your question...perhaps you can be a little more specific.

[Chuck Ellsworth]

Interesting read here.

I must be really hamhanded because I'm damned if I can fly at 44 knots right on the knot.....how do you do that when the airspeed needle is wider than what a knot would look like if it was graduated with marks for every knot?

[john_tullamarine]

The thing I've still never found in a POH ... is any indication of how long the runway has to be before you can stop worrying about doing a "short field" take-off and do a "normal" take-off instead.

Accepting that I don't have in front of me whatever POH you are viewing .. in general, it is reasonable to presume that the manufacturer's POH will be based on certification standards minimum speed schedules (= most marketable distance data). "Normal" takeoff may not have any distance data in the POH and may just represent a convenient and more conservative school/club technique than the min speed schedule. That is to say, "normal" takeoff may be appropriate for a longer runway at an established aerodrome .. but possibly/probably not at all appropriate for a paddock departure.

POH figures, as I'm sure you know, are what the company test pilot could achieve

I wouldn't be excessively cynical .. it is reasonable to presume that the regulator approved parts of the POH, at least, will be reasonably repeatable. Other parts may need to be viewed as "indicative"

The safe way to use several of the POH figures is to apply a fudge factor

That's entirely appropriate and, in some jurisdictions, mandated for some or all operations. The manufacturer can be expected to publish what the rules require and no more .. unless there be an OEM risk management decision to publish more conservative data.

Dunno what fudge factor you apply to the 172 POH's "climb at 50",

The fudge factor is applied to the TOD .. not the speed. I have no concern operating a 172 (or any other Type) at the AFM speed schedule ... although I might chose not to do so in gusty conditions. If you choose to put a conservative margin on the speed .. then don't believe the distances as the speed and distance schedule is glued tightly together.

Above all, be wary of operating lighties in critical distance conditions as the POH data certainly does not have the level of rigour one would see normally in a heavy aircraft AFM .. it's a bit late as you plow into the crown of the tree (powerlines, whatever) to second guess your exhuberance ...

SNS3Guppy tells the story with a lot of wisdom born of experience .. worth re-reading and absorbing the detail ...

[Big Pistons Forever]

I will add a few points to this important discussion.

1) I think it is also important to note that C 172's are not designed to be STOL aircraft. They are optimized to be easy to fly economical touring/training aircraft. I think it is important to respect the the fact that they have relatively low performance and IMO cessna never intended they be operated off very short strips

2) Where did the 44 kts rotate and 50 kts climb theh original poster asked about come from ? I do not have a C172 S handbook but these numbers seem very low. The only POH I have handy is for the C152. It gives a gross weight sea level rotate speed of 50kts and an initial climb (at 50ft AGL) of 54kts IAS (57 kts CAS). It is important to note that in this configuration the power on stall speed is approximetely 43 kts CAS. I think a 14 kt margin is not unreasonable provided the air is not excessively turbulent and the airplane is acurately flown.

3) When I teach the manoever I expect the book numbers to be flown in order to achieve the best performance from the aircraft. But and it is a big "But" , flying the book numbers will result in a very nose high attitude. If the engine were to fail the nose must be instantly and forcefully lowered. This should be practiced at altitude and the pilot must be mentaly primed for this eventuality before commencing the takeoff.

4) The book runway distance required numbers are for level paved runways. Short fields are usually not paved and rarely perfectly level. For that reason I told all my students to take the book figure and add 50% to the book takeoff distances. This probably a bit too conservative but I think it is better to pass up a field that may be OK than to try to operate from a field that turns out to be a little too short... Also when operating from a short field it is vital to have identified a physical marker next to the field that is your go no go point. If the airplane is not airborne by this point the takeoff must be immediately aborted.

[RatherBeFlying]

As a newly minted pilot with a shiny new license, adding 50% to the required runway length after factoring in surface condition, wind and density altitude as suggested is smart practice, even for the more experienced pilot.

If you want to try short fields, gliders come highly recommended -- if the towpilot does not accept the field, you can get the trailer:}

[IO540]

The book runway distance required numbers are for level paved runways. Short fields are usually not paved and rarely perfectly level. For that reason I told all my students to take the book figure and add 50% to the book takeoff distances.

This is an area where a better understanding is worth having, but the data is rarely in the handbooks.

The extra for grass depends hugely on the kind of grass. Short dry grass is perhaps 20% extra. After that, all bets are off. My TB20 gets off the ground in about 300m tarmac (MTOW). I have also verified 350m on short dry grass. I once went into a 1200m grass strip where the grass was about 8" and it used up at least 800m. The other thing is that the whole plane got covered in green crap because the bottom of the prop arc cut into the top of the grass.... cost me £200 to get it cleaned off.

Slope is another one. I think every 1% UP slope is worth about 10% off the runway length - much more than most would believe. Recently I looked at a 750m strip with a 1.4% slope and it worked out that one would be better off landing downwind unless the wind was more than about 7kt or something like that. In the end I didn't go for that one because of trees at the ends...

Many many planes are flown overloaded and there is another big factor to take into account. Every 1% extra weight is about 2-3% extra runway needed.
Plus a higher Vr value.

Finally, worth realising that (except in extreme obstacle clearance scenarios rarely present in Europe) the feet/minute climb rate is not very dependent on the climb speed. For example my Vy is 95kt but the climb rate is no more than 5% worse at 120kt, but 120kt gives vastly better engine cooling and aircraft control, as well as forward visibility. A Vx climb is a really extreme thing to do which is rarely needed - except for passing checkrides.

[Big Pistons Forever]

IO540

Quote> Finally, worth realising that (except in extreme obstacle clearance scenarios rarely present in Europe) the feet/minute climb rate is not very dependent on the climb speed. For example my Vy is 95kt but the climb rate is no more than 5% worse at 120kt, but 120kt gives vastly better engine cooling and aircraft control, as well as forward visibility. A Vx climb is a really extreme thing to do which is rarely needed - except for passing checkrides

I think you have to be carefull about not attributing specific performance characteristics across the whole GA fleet. The TB 20 has a relatively powerfull engine and a IAS speed range of approx 80-160 kts thus it has more fexibilty in terms of how it is flown. For low performance aircraft like the C 172 flying the book climb speed is very important to achieve reasonable performance particularly at gross weight and/or hot temps. Under these conditions just keeping the ball in the centre is good for an extra 100 fpm. Also for take off it is Vx (best angle of climb) that is the most important speed. This speed is usually quite low which is important to maximize the effect of the not very high climb rate implicit in low powered aircraft.

[bjornhall]

2) Where did the 44 kts rotate and 50 kts climb theh original poster asked about come from ? I do not have a C172 S handbook but these numbers seem very low. The only POH I have handy is for the C152. It gives a gross weight sea level rotate speed of 50kts and an initial climb (at 50ft AGL) of 54kts IAS (57 kts CAS). It is important to note that in this configuration the power on stall speed is approximetely 43 kts CAS. I think a 14 kt margin is not unreasonable provided the air is not excessively turbulent and the airplane is acurately flown.

It is indeed that slow... The 44/50 kts is at 2,200 lbs; an average size pilot and fuel to the tabs puts us a little bit below that weight. At MTOW (2,550 lbs), speeds are a slightly more 'normal' 51 KIAS to lift off and 56 KIAS initial climb.

But it sounds a lot slower than it is due to the ASI misreading quite a bit at such speeds... 44 KIAS at flaps 10 is really 53 KCAS, and 50 KIAS is 57 KCAS. Stall speed at 2,200 lbs and flaps 10 is about 47 KCAS power off, which would be well below 40 KIAS, but the power on stall speed is not in the book...

[SNS3Guppy]

Many many planes are flown overloaded and there is another big factor to take into account. Every 1% extra weight is about 2-3% extra runway needed.
Plus a higher Vr value.


It absolutely should NOT be taken into account. There is no reason to believe, nor to employ performance values outside those published for maximum weights. It's not legal, should never be considered safe or acceptable. "Everybody's doing it" is not an acceptable reason to fly overweight, or to make light of it. Don't take it into account...don't do it. Period. Certainly don't assume a linear increase in numbers based on an increase in weight over that for which the aircraft is certificated.

Finally, worth realising that (except in extreme obstacle clearance scenarios rarely present in Europe) the feet/minute climb rate is not very dependent on the climb speed.


Actually it is. That would be aerodynamics 101.

[EdButler]

44/50 sounds dangerous to me. Im a student at Netherthorpe in 130hp C-150A's so please dont take my word as gospel, but instructors teach to pull the nosewheel off at 45kts and start to bring the rear undercarriage off the ground at 50kts.

Immediately after takeoff, nose level (or almost level) and accellerate to 55kts and slowly pitch back a 60-65kt climb.

I remember once an instructor took control after a touch and go; in takeoff configuration the stall warner was sounding when attempting a 50kt climb... Lets just say i was a tad scared that the port wing was suddenly going to take a liking to the ground! :)

[scooter boy]

I had a restless night last Sunday lying in bed worrying about departure from Lausanne in my Mooney.

Three 200lb + males plus bags plus fuel, OAT +26C, 2000ft amsl with an 850m runway with a significant bowl shape to it - 2.5% downslope initially and a 5kt headwind component.
I was regretting having left the POH in the aircraft but the hotel had free internet downstairs so I crept down in the middle of the night and downloaded what performance charts I could from the web, these allayed most of my fears.

Before we took off I also went through the POH performance charts which confirmed we would be OK for the prevailing conditions and added 120L of avgas which kept us well within the comfort zone both for takeoff and cruise back to the UK + diversion (our destination was 200m vis in FG when we departed Lausanne with an optimistic TAF to clear by our arrival time - which it duly did) .

As it happened we were fine, I ran the engine up to max power on the displaced threshold while just holding it with the brakes, released the brakes and used only 70% of the available runway, taking off on rwy18 helped with the acceleration being brisk and we lifted off with the stall warner bleating at 65kt into ground effect whilst still on the downhill segment of the bowl.
Lower the nose a tad, stall warner goes, touch of brakes, wheels up, more lift, less drag, leave 10 deg flaps down to help the initial climb and we were on our way.

The POH is pretty accurate, there are performance charts for just about every phase of flight and I find it reassuring to use them when hot, high and heavy.

SB

[SNS3Guppy]

I flew some Forest Service officials to an airport with a relatively short field length, in a Shrike Twin Commander. We were part of a large fire in Southern California, and they wanted this field because it was near the main fire camp, where they had a meeting. As they were waiting for their ride, I quickly reviewed the performance, looked at the temperatures for the day, and told them we'd have to leave by 11:00, or couldn't leave until evening. That cut short their meeting time. They weren't happy.

They tried bargaining. They wanted to see the numbers. They tried demanding. Said they'd report me to my employer; pressure was applied. I held firm. The numbers said we could go; we could get off the ground in the required distance...but I also noted powerlines all around the field. It just became a lot shorter. Yes, on paper, it looked okay. But what if we lost power, or an engine, on takeoff. What if the gear didn't retract? What if we had any number of problems that meant we couldn't meet that criteria? If we were just on the edge of making it out, then it left insufficient margin for something to go wrong...and we never plan for things to go right.

Everything should be planned with the worse case scenario in mind. Not what could go wrong, but what will go wrong. Not what if, but instead, when.

I offered them choices. I gave them departure deadlines based on the temperature increase for the day. I offered to reposition the airplane to a different airport, farther away, to pick them up. Or leave some behind. Or I could depart and burn fuel, and return. At length they agreed. My sole concern was their safety and the safety of flight, with all else being far in second place. So it needs to be with every takeoff.

As others have rightly said several times now...being conservative is a good thing. If you're going to depend on the book distances, then you're going to have to fly the book airspeeds to make it work. When you do calculate it, though, do it for the worse case scenario.

Something we often do to build in a margin of safety is use "assumed temperatures." This isn't assumed as in guessed, but assumed as in planning the takeoff based on a theoretical higher temperature (and therefore, density altitude). If the airplane could make the takeoff safely at the greater temperature, then we know it could certainly do so at the present temperature. If it's 15 degrees at the time of takeoff, but we determine it can be safely done at 30 degrees outside air temp, then we've got a safety performance factor built in. We'll sometimes use this to apply a power reduction factor to still safely make the takeoff, something that's not necessary or done in light piston airplanes...but the point is that being conservative and allowing more distance and allowing for reduced performance is a prudent and even a professional thing to do. It's standard procedure in most professional cockpits; acting conservatively should be standard procedure in any cockpit.

Good job pulling the performance charts and using them, Scooter Boy. That's exactly why the charts are there. Your example is one everyone can take heed, and follow.

[Tinstaafl]

Scooter Boy, "...leave 10 deg flaps down to help the initial climb..."? Unless my understanding of aerodynamics & performance is wrong, leaving any flap down will adversely affect climb performance although the shorter take-off run compensates for some of this loss by allowing the climb to commence earlier. Even so, at some point there will be a crossover point where leaving flap down results in reduced net climb performance.

[SNS3Guppy]

That depends on the airplane. Some airplanes experience better performance with a little flap, some with none, and some with a reflexed flap.

I've flown airplanes that not only benefited from flap for takeoff, but also for climb...several, in fact.

[Chuck Ellsworth]

I have flown an aircraft that flys better with some flap down in level flight when loaded to the max allowable..

[Mikehotel152]

I think SNS3Guppy's explanation is clear and sensible. You should never accept given performance figures without properly considering whether your environmental and runway figures match those used to create the performance table. And remember too, that those figures were calculated by a test pilot in a new aircraft with new engine and propellor and probably without the usual aviation related junk lurking behind the seats! I doubt you'll quite match those performance figures even on a good day, hence the need for a safety factor!

But in any case I can't think of any airfield in England where you would perform a short field take off in order to get off the ground in the shortest possible ground roll, then have no option but to climb at Vx until over a hill, mountain, power line or anything else at any significant distance from the departure end of the runway. In reality, if faced with such a restrictive and dangerous airfield, I wouldn't go there and neither would anyone else!

Isn't the reality that we use a shortfield take off to get off the ground in the shortest distance, climb to 50 ft at Vx, level off in order to collect a few knots of airspeed, before climbing at Vy?

[SNS3Guppy]

Mikehotel152,

I believe you've got the correct idea.

[scooter boy]

Tinstaafl,
It is counter-intuitive but 10 deg flap helps the initial segment of a steep climb in my aircraft.
All to do with angle of attack and relative wind.
There is a clear explanation of the reasons for this in "piloting for maximum performance" by Lewis Bjork.
Amazon.com have it for $6 - it really is a great read, well written, relevant and full of get-you-out-of-trouble wisdom.

SB