Take off with stall warning horn
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Take off with stall warning horn
I recently flew a light sport aircraft off a grass runway.
The regular take off procedure according to POH:
During check out of this type I was told to simply accelerate to 55-60 before doing rotation.
Because of the grass runway I didn't feel comfortable keeping the nose down at those speeds. While flying the C172 I learned to lift the nosewheel while gaining speed on the grass to reduce drag and to save the nosewheel from getting a beating.
So I followed the same procedure, and rotation occurred at around 40 knots indicated, which also happened to be the stall speed (yeah yeah, AoA etc, but let's continue). As soon as the nose left the ground the stall warning horn sounded, and instinctively I put the nose down a bit. It accelerated a bit more, but at around 45-50 knots the aircraft lifted off and immediately the stall warning came on again. I then accelerated in ground effect until the horn stopped.
So while everything went OK, it still didn't feel comfortable. A friend of mine who was flying with me put it all on tape. Looking back at it, the stall warning only sounded for 3-4 seconds, but in my experience it was beeping for 20 seconds... time is relative.
So my question really is: is it normal for stall warnings to go off at take off? What could I have done differently?
The regular take off procedure according to POH:
During take-off run smoothly lighten up the nose landing gear until airplane take-off occurs. After take-off accelerate airplane to............... 57 KIAS (106 km/h IAS)
Because of the grass runway I didn't feel comfortable keeping the nose down at those speeds. While flying the C172 I learned to lift the nosewheel while gaining speed on the grass to reduce drag and to save the nosewheel from getting a beating.
So I followed the same procedure, and rotation occurred at around 40 knots indicated, which also happened to be the stall speed (yeah yeah, AoA etc, but let's continue). As soon as the nose left the ground the stall warning horn sounded, and instinctively I put the nose down a bit. It accelerated a bit more, but at around 45-50 knots the aircraft lifted off and immediately the stall warning came on again. I then accelerated in ground effect until the horn stopped.
So while everything went OK, it still didn't feel comfortable. A friend of mine who was flying with me put it all on tape. Looking back at it, the stall warning only sounded for 3-4 seconds, but in my experience it was beeping for 20 seconds... time is relative.
So my question really is: is it normal for stall warnings to go off at take off? What could I have done differently?
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The 172 is heavier in its control forces than some - it may be that the aircraft you were flying had lighter controls leading to a bit of over-control.
You can keep the strain off the nosewheel whilst not actually rotating the aircraft. (In a 152 you can lift the nosewheel pretty much at any speed)
If the PoH says not to lift off until 57, then it's not really that surprising that the stall warner sounded when you tried to fly at 40.
You can keep the strain off the nosewheel whilst not actually rotating the aircraft. (In a 152 you can lift the nosewheel pretty much at any speed)
If the PoH says not to lift off until 57, then it's not really that surprising that the stall warner sounded when you tried to fly at 40.
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A few thoughts
If the stall speed really is 40 kts, then 57 kts seems on the high side for entering the climb.
If the stall speed really is 40 kts and the warner is beeping at as much as 50 kts it probably needs adjusting. Have you checked the stall speed?
If you have taken off and are flying a few inches above the ground gaining speed, then you aren't going to come to much harm if the stall warner beeps.
In aircraft I have flown, I have experienced the odd beep in the very early stages of the climb if the air is turbulent, but I don't think it is normal to experience continuous warnings during the ground run or initial climb.
If the stall speed really is 40 kts and the warner is beeping at as much as 50 kts it probably needs adjusting. Have you checked the stall speed?
If you have taken off and are flying a few inches above the ground gaining speed, then you aren't going to come to much harm if the stall warner beeps.
In aircraft I have flown, I have experienced the odd beep in the very early stages of the climb if the air is turbulent, but I don't think it is normal to experience continuous warnings during the ground run or initial climb.
I did some real soft field work at X58 in Florida, in a C172. 7000' of grass, very wet with lots of puddles. Water was flinging off the wheels and hitting the wing. I found I could not get it off unless I had the stall horn going. Else, I could never get enough speed to get airborne before the next big puddle sucked the life out of the takeoff roll.
In the same conditions I was able to get the J3 off easily, no special technique and no stall horn.
In the same conditions I was able to get the J3 off easily, no special technique and no stall horn.
Seems to me that you used the POH procedure almost exactly for your T/O.
You may have had a more rapid response to your control movements than you expected, due to the very light control forces, and raised the nose a bit suddenly, initially trigering the stall warner.
Also, on many light aircraft, the stall waner is set a little on the sensitive side. This may be why the operators are recommending the non-standard T/O technique.
If this is the case here, they would be better to have it adjusted to the correct setting.
What type of aircraft was it?
MJ
You may have had a more rapid response to your control movements than you expected, due to the very light control forces, and raised the nose a bit suddenly, initially trigering the stall warner.
Also, on many light aircraft, the stall waner is set a little on the sensitive side. This may be why the operators are recommending the non-standard T/O technique.
If this is the case here, they would be better to have it adjusted to the correct setting.
What type of aircraft was it?
MJ
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What aircraft were you flying? My aircraft (Jabiru) regularly has the stall warner go off upon rotation. The POH even states that the stall warner may sound. My POH states to lift the nose at 35kts and let the aircraft fly itself off the ground usually between 40 and 45kts. It does have a note saying stall warner may sound. It then goes on to say accelerate in ground effect before climbing at 65kts.
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There is no harm flying the aircraft in 1G straight, ball in the middle flight with the stall warning sounding - it's a stall warning. If the plane is actually stalling, it'll probably stop flying soon, so if you're flying, and indeed accelerating, you're fine. Staying in ground effect is wise, if you can.
Think of this entirely differently, a wing would like to lift the aircraft when the AoA is just right, then increase airspeed at that same AoA, and it's going to climb happily. So, as early as possible, lift the nose. As early as you can after that establish that ideal AoA. In a normal C150, you can get to that AoA after about 100 feet of ground roll.
So you're rolling down the runway with the nose held a few degrees up, and the plane is accelerating. Hold that attitude no matter what. It is very likely that you'll get a stall warning - keep the ball in the middle, and hold that attitude. When it's ready, it'll fly. Hold that attitude! You'll find that the stall warning has ended, and the plane is accelerating more into a climb. Likely now, you'll have to lower the nose a bit.
Would you have believed that you could takeoff without "rotating"!?! I think I have just described a Cessna POH soft field takeoff.
Don't worry about hearing a stall warning, if you have the aircraft under control, and you're headed toward somewhere safe, in controlled flight. During "Vref - 5" testing, I have had to fly entire circuits with all speeds flown 5 knots slower than the specified speed for that phase of flight. I heard the stall warning quite a bit - cautious, but no problem - unless the engine quits!!! THEN, you would like bags of speed, unless you're 6" off the runway, with lots ahead of you.
Think of this entirely differently, a wing would like to lift the aircraft when the AoA is just right, then increase airspeed at that same AoA, and it's going to climb happily. So, as early as possible, lift the nose. As early as you can after that establish that ideal AoA. In a normal C150, you can get to that AoA after about 100 feet of ground roll.
So you're rolling down the runway with the nose held a few degrees up, and the plane is accelerating. Hold that attitude no matter what. It is very likely that you'll get a stall warning - keep the ball in the middle, and hold that attitude. When it's ready, it'll fly. Hold that attitude! You'll find that the stall warning has ended, and the plane is accelerating more into a climb. Likely now, you'll have to lower the nose a bit.
Would you have believed that you could takeoff without "rotating"!?! I think I have just described a Cessna POH soft field takeoff.
Don't worry about hearing a stall warning, if you have the aircraft under control, and you're headed toward somewhere safe, in controlled flight. During "Vref - 5" testing, I have had to fly entire circuits with all speeds flown 5 knots slower than the specified speed for that phase of flight. I heard the stall warning quite a bit - cautious, but no problem - unless the engine quits!!! THEN, you would like bags of speed, unless you're 6" off the runway, with lots ahead of you.
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Sport aircraft are not my forte but I suspect that PEC work is not to the standard of certificated Types. All sorts of funny things happen around the stall to ASIs - errors can get significant.
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Thanks for all the replies. If it wasn't for the stall horn I would also say I did it by the book. I'm just not used to hearing that horn on take off. Usually it only comes on when I start the flare. We were well within M&B limits and the aircraft was an Evektor SportStar RTC. It flew fine and wanted to accelerate and climb, so from a performance point of view everything was as usual.
It could indeed be as simple as the horn being a bit sensitive, or the ASI might be misreading. The POH doesn't mention stall horn can happen on take off, but if that's common for this aircraft than that could also be why the instructor said to accelerate to 55-60 before bringing the nose up.
On my next flight in this aircraft I will do some slow flying and stalls, just to see how much margin there is once the horn starts beeping. During the checkout we did some stalls, but I simply didn't pay attention to the speeds as my focus was keeping the aircraft steady and looking outside.
It could indeed be as simple as the horn being a bit sensitive, or the ASI might be misreading. The POH doesn't mention stall horn can happen on take off, but if that's common for this aircraft than that could also be why the instructor said to accelerate to 55-60 before bringing the nose up.
On my next flight in this aircraft I will do some slow flying and stalls, just to see how much margin there is once the horn starts beeping. During the checkout we did some stalls, but I simply didn't pay attention to the speeds as my focus was keeping the aircraft steady and looking outside.
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Pirke, I think your T/O is generally fine for the conditions of the field and the day. In an LSA the operating speeds are of course quite low, and the acceleration is brisk. The other thing is that the nosewheels are typically quite fragile - some would say particularly so in the SportStar.
The stall warning horn/vane is easily checked at altitude. In my P2202JF VLA, it's set very conservatively indeed. I suppose I could tweak it but I've never bothered. (The LSA version doesn't even have one, so I don't feel especially threatened).
Many GA pilots do require a bit of re-training with the LSAs in terms of getting the weight off the nosewheel and never holding the wheel on the runway, even a little bit. As someone previously said, you can take the weight without resorting to that. In gusty conditions, at low speeds, you do need to make sure that you have sufficient directional authority, either via the nosewheel or the rudder. These are very light aircraft and, although experience leads to very good capabilities, a bit of prudence in the early stages is not a bad thing. The saving grace is that the acceleration is very brisk indeed, so by firewalling the Rotax throttle in line with normal practice, you minimize the time you are vulnerable. Nothing at all different in principle to any light aircraft, just a slightly different set of emphases.
Happy flying!
The stall warning horn/vane is easily checked at altitude. In my P2202JF VLA, it's set very conservatively indeed. I suppose I could tweak it but I've never bothered. (The LSA version doesn't even have one, so I don't feel especially threatened).
Many GA pilots do require a bit of re-training with the LSAs in terms of getting the weight off the nosewheel and never holding the wheel on the runway, even a little bit. As someone previously said, you can take the weight without resorting to that. In gusty conditions, at low speeds, you do need to make sure that you have sufficient directional authority, either via the nosewheel or the rudder. These are very light aircraft and, although experience leads to very good capabilities, a bit of prudence in the early stages is not a bad thing. The saving grace is that the acceleration is very brisk indeed, so by firewalling the Rotax throttle in line with normal practice, you minimize the time you are vulnerable. Nothing at all different in principle to any light aircraft, just a slightly different set of emphases.
Happy flying!
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why the instructor said to accelerate to 55-60 before bringing the nose up.
Though I have not flown the type you mention, I imagine, that like other light aircraft, it responds to be being "flown" even before reaching flying speed. Therefore, you should fly it. If you would think to correctly position ailerons and elevator while taxing in a cross or tailwind, then when flying that type you would also want to apply flight controls at the beginning of the takeoff roll, which would have the effect to promote flying.
If the elevator effectiveness is adequate to lighten the nosewheel, the rudder will be effective enough to steer with the nosewheel having little effect.
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ST, you're right about correct control positioning etc. But in my experience there are LSAs around without particularly good rudder authority. It is possible to get airborne and then be disappointed in the ability to check the weathercock effect in a strong wind. This can be compounded by the powerful slipstream effects in these generously powered little machines, typically making e.g. a take-off with a strong left crosswind that much more challenging.
Remember that many LSA types exist outside the certification system, so approaching with an open mind is prudent. There are of course several types, such as some Tecnams, which have parallel lives in the LSA and certified worlds.
Remember that many LSA types exist outside the certification system, so approaching with an open mind is prudent. There are of course several types, such as some Tecnams, which have parallel lives in the LSA and certified worlds.
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I would be interested to climb to a safe altitude and check the IAS (in all configurations) at stall warning and actual stall against the book. The stall warning tab is a crude mechanical device and, as such, easily damaged. But barring such damage, it's not likely to give consistent false indications. If, however, the stall warning sounded the requisite interval above the actual stall, but both were occurring at different IAS to those in the book, it could indicate damage/obstruction/calibration issues in the PITOT system/ASI?
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@IMFU
"In the same conditions I was able to get the J3 off easily, no special technique and no stall horn"
Yep - fly by feel. I'm just learning the delights of the L4 Cub
"In the same conditions I was able to get the J3 off easily, no special technique and no stall horn"
Yep - fly by feel. I'm just learning the delights of the L4 Cub
During check out of this type I was told to simply accelerate to 55-60 before doing rotation.
until airplane take-off occurs
Last edited by Jan Olieslagers; 5th Nov 2014 at 16:55.
Totally agree Jan.
I've around 700 hours on LSA's, and holding the nose up till the aircraft takes flight is the technique I have successfully used for at least 699 of those hours!
I've around 700 hours on LSA's, and holding the nose up till the aircraft takes flight is the technique I have successfully used for at least 699 of those hours!
Slap a bit of sticky tape over the vane if it bothers you.
The Pawnees I have towed with generally had the breaker for the stall warning light pulled. Otherwise it is a distraction. It is fun, though, to split-S after release and pull a couple G's all the way through with it in. Lights up and if you keep it lit all the way you are only doing 120 out the bottom.
The super cub, like its little brother, was unencumbered by any such nonsense.
The super cub, like its little brother, was unencumbered by any such nonsense.