Need some help on "Soft field" T/O (Pipers)

[avistudent]

Hey everybody,

These soft field take offs has been costing me a bit of money, and I am frustrated my progress is rather minimal. I have completed all of my training modules and 99% to do my flight test, but I have to master a few flying exercises before the flight test. And this "Soft field" take off is a pain to get it right.

I fly a Piper Warrior PA28.161, so its a low wing. The problem that i am having is the Stall horn that scares me when i am on the soft field t/o roll.

As all of you who flies the Pipers, would know that you will need 2 notches of flaps, controls all the way back, and roll onto the active without braking and then full power. As soon as the plane accerlarate, it get to ground effect and then the STALL HORN goes off and thats where I got scared off and screwed out the t/o.

My instructor told me not to be scared of the stall warning, but it is hard not to. He told me that as soon as the stall horn goes off, apply forward pressure to increase to climb speed.

Anyone here can shed some light to me on my problem?????

Thanks for your time!

Taka care!

[Andy_R]

Your instructor more or less has the right advice. Don't be scared of the stall warner (on this occasion!!!). Most stall warners will go off 5 to 10 knots before you actually stall. Get him to take you up to a safe level and demonstrate this to you. With 2 stages of flap, note the speed at which the 'plane stalls. Then take that speed and multiply by 1.3 and that is a very safe speed you can use for approaches. This is higher than the initial speed you will leave the ground on short field take offs. Then get him to demonstrate slow flight, right on the edge of the drag curve, with the stall warner sounding, but retaining straight and level flight. That way you will see for yourself that you will not fall out the sky.

On a short/soft field take off, the aim is to get yourself off the ground so that you can accelerate to best climb speed. This acceleration is done in ground effect as you say. As you initially drag the 'plane off the ground the stall warner will go off. As you feel the wheels leave the ground, gently nudge the nose forward to remain in ground effect. You will be wanting to keep yourself just a couple of feet off the ground initially. Once you have gained speed, which will happen remarkably quickly, you can then climb away.

Do be careful though to only nudge the controls forward, you don't want to stuff the 'plane back onto the ground nose wheel first!! You will soon get the feel for it. If you are not fast enough and only a couple of feet off the ground, the 'plane will alwys land back on the ground. On a rough field you will find yourself taking off several times across the bumps!!!

Do keep all control movements as gentle as possible whilst the stall warner is sounding and whilst you build up your speed. Large movements of the ailerons cause the stall speed to increase.

For those UK pilots - the CAA do not allow the use of 2 stages of flap on the PA28 :hmm: :rolleyes: ;)

[Genghis the Engineer]

Firstly:-

For those UK pilots - the CAA do not allow the use of 2 stages of flap on the PA28
Really? Where's that? - I fly a -161 in the UK, have done for some years, and have always used 2 stages for soft field take-offs, a practice encouraged by every instructor I know on the type. (Try doing otherwise on a winters day at Popham!, but not in my aeroplane if you'd be so kind).



Anyhow, to the business in hand.

I can see why - quite reasonably - you've developed a nervousness about being too close to the stall. So, in my opinion you need to ask your instructor about doing a bit of stalling practice at a safe altitude. Take the aircraft down to the stall warning and fly it - it flies fine with good control in all three axes. Then pull back slowly until it finally stalls - you'll see that there's a big margin between the warner going off and anything worrying happening - lots of pitch up, lots of pull on the yoke.

With a bit of experience of this, you'll come to realise more comfortably that when the warner sounds it does not mean impending doom - it is simply a timely warning that you need to do something, in this case easing the yoke forward until you have the short-field initial climb speed of 52 kn (and more importantly, the attitude) pegged.

But, I don't think any amount of explanation will do this - you really do need to experience it in the air to really believe it.

G

[Andy_R]

Genghis

My apologies if I am misinformed but I thought the CAA frowned upon the use of 2 stages of flap for take off in the PA28. I may well disagree with this myself hence the use of :hmm: :rolleyes: ;) but thought it to be the case. I wouldn't fancy getting out of Popham with anything less either. Will try and find the relevant text.

Can\'t find exactly what I want at the moment but here are a couple of links discussing this particular issue:

here (http://forums.flyer.co.uk/viewtopic.php?t=8598&highlight=2+stages+flap+pa28)

and

here (http://forums.flyer.co.uk/viewtopic.php?t=7936&highlight=2+stages+flap+pa28)



Would be genuinely interested in your comments Genghis

[TheOddOne]

Here's another thought...

For 'normal' operations, nowadays I always aim to get the stall warner sounding on a PA28 whilst in the flare, just before landing. I would suggest that in addition to all the excellent advice above, you try this out, so that not only is the stall warner no longer a surprise, but you're positively wanting it to sound - make it your friend. That way, you hear it at least once each flight (as well as during your walkround, I hope!). I would even venture to suggest that if you don't hear it before touching, then you're landing too fast! (That should excite further comment!)

We, too, use 2 stages of flap for our soft field practices (Warrior I) As another thread said recently, there's a world of difference between a direct prohibition and the mere absence of an endorsment for a particular activity.

Is it possible that with more powerful machines, the performance is degraded more by additional flap, whereas on the low-power a/c it doesn't make enough difference to affect the figures?

Cheers,
The Odd One

[dublinpilot]

Am I the only one who never had to do this?

Short field t/o was taught to me as flap, and a lower t/o speed, but never heard the stall warner during the t/o.

The above covers a number of types (inc pipers), and different instructors. Was my training somehow lacking? Or is it the more likely case, that the instructors simply didn't want people taking off in aircraft so close to the stall?

As an aside, I was also taught that one should not turn onto a r/w and continue the roll in a Piper....something to do with fuel swishing around the tanks......

dp

[Oscar Juliet]

I believed that the CAA dont allow t/o with two stages of flap for commercial operations only, its somewhere in the flight manual.

[dmjw01]

My instructor told me ... that as soon as the stall horn goes off, apply forward pressure to increase to climb speed.
That's about right, except that you definitely should not push forward on the control column. It's more a case that you should release a bit of the back pressure.

[ontrackfor]

It seems to me the stall warning is a bit like the fuel guages... ok to use sometimes but by no means perfect. It is not always set for 5-10 knots above the stall speed. I flew a plane where the stall warning went off at 65 knots for a 40 knot stall speed! And a fair few with a rather conservative warning (handy for best-glide during an engine failure though). So they can often mis-read.

The stall warning can only indicate an approach to a stall on one part of the wing. Given that they are usually mounted inboard, washout will still ensure the outboard wing is well and truely flying and during takeoff.

Ps: If you are flying with an instructor, im sure they would not let you get dangerously slow. As long as you fly solo like you fly dual, you will be sweet.

PPs: I get stall warnings on moderate^ cross-wind takeoffs when well above short-field rotate speeds so the sensors are prone to all sorts of errors.

[Halfbaked_Boy]

The PA28-161 I fly is guided into the air like so; one stage of flap, onto the runway, full power, rotate at 65 kts, take off at 70, then allow airspeed to increase to 75 :)

I've never experienced the stall warner on the PA28-161 I'm used to... except, obviously, when I learnt HOW to stall :p

Cheers,

Jack.

[Final 3 Greens]

Half Baked Boy

1) - if VR is 65, you don't need flap at all

2) - you will crash through the fence of a short, soft, field using this technique

[Tinstaafl]

Ghengis has good advice: Go do some upper air work flying on the back of the power curve. Develop your skill - and comfort level - flying with the stall warning activating.

Start with S&L, **just** nibbling at the stall warning activating. Progress to very gentle turns & shallow climbs/descents.

Then the same again but aiming to keep the stall warning activated. Not stalling though!

Do this on an early morning without turbulence. Good vis. to the horizon helps too.

Bear in mind that the stall speed is lower for a power on condition than for a power off condition so you can expect a surprisingly low IAS w.r.t. the published stall speeds. Ground effect has a significantly beneficial effect on stall speeds too and this is the period that is concerning you.

The goal is to become comfortable with flying the a/c just about the stall & skilled at controlling the flight path at speeds below 'typical' flight speeds.

[homeguard]

Where has this theory that the soft field take off pitch up is correct when the 'stall warner' sounds?

The main aim durin the soft ground TO is to minimise nose wheel weight/drag in order to increase the rate of acceleration. To do this you cause a down force from the elevator/stabilator. But there is a twist, if you over control you then in fact increase the weight of the aircraft on the ground therefore surface friction increases and also induced drag. Over pitch and all benefit may be lossed. In this scenario you will need to achieve a higher speed before lift off. A longer ground run.

Undertaken correctly you will not hear the stall warner (rigged correctly), if you do then you are probably over pitching.

[Halfbaked_Boy]

Hmm, how short is 'short'? I have applied the above technique to a damp grass runway of 514 metres in length, or are we talking 300 metres minus?

[Final 3 Greens]

Half Baked Boy

I don’t have a number for you, to say how short a short field is, since there are a number of factors that must be considered in making a decision.

Is there any clearway after the runway? Are there obstacles in the climb out area? How soft is soft? Are you the “ace of the base”?

It all comes down to judgement.

The shortest, damp grass field that I’ve operated from was 360M, using a Cessna 172, 2 up, half tanks. I would not have tried that in a Warrior.

I don’t have a Warrior POH to hand, but my handling notes say that, with 2 stages of flaps, the distance to 50 feet is 485M, in 10 deg C, 1013.2hpa, nil headwind, 2325 lbs. That is on a hard runway, no slope, so adding a factor for damp grass (30%) takes the number to 645M.

If there is no obstacle over 50’, this may influence your thinking, but it’s a judgement call.

I’d be okay with 514M with a light aircraft, not okay with a heavy weight aircraft, but I would need to be very clear on where I would reject the take off if not happy with acceleration.

And remember damp runways may be soft, but soft runways aren't always damp - so you need to assess how "soft" the field is ...... the 360M runway above was firm, if it had been soft, I wouldn't have tried, just too risky.

[Tinstaafl]

Homeguard, I wasn't implying the take off should be done with the stall warning on. On re-reading I can see how that could be taken. I meant those flight sequences to be upper air exercises to develop the questioner's skills & comfort at low airspeeds.

[englishal]

Always use the flap setting listed in the POH, regardless of what anyone tells you. 10° of flap in a Warrior will not give you the same performance with regards to S/F T/O, as has no doubt been demonstated by Piper.