Airbourne prematurely
 

A hell of a lot better than keeping the nose high, though

New PPL so hardly the voice of experience, however the grass strip I learnt at has a displaced threshold on 24, which starts with an upslope and then a bump just before the runway levels out at the threshold, and you usually hit that at around 45kts when two up in the Robin, when you actually want to be rotating at around 55kts.

The technique I was taught was to accelerate with gentle back pressure to take the weight off the nose - assuming you don't have too much back pressure when you hit the bump you grab a bit of air but it settles back down again quite quickly, then you can rotate as desired.

You certainly don't push the nose down at any point, just manage the level of back pressure to maintain the right attitude. If you're solo and get a good run up the slope you can just get launched off the bump :D

Its quite a common issue with some C172 airframes.

I used to just let her fly and accelerate in ground effect as per a short field takeoff.

Don't try and keep her on the deck and don't lower the nose.

That main gear can soak a whole heap punishment the nose wheel can't. I have seen folk drop them from 6ft up onto the deck with spectacular rebounds afterwards no harm apart from pride occured.

Thanks so far.

So the correct approach is light back pressure and then maintain the attitude on the ground or in ground effect until rotation speed...

MJ what about when the stall warner sounds? A few weeks back at I was three up flying out of the grass strip at Shoreham which is very bumpy. We hit a bump and jumped a good few feet in the air and the stall warner sounded. I lowered the nose instinctively and must have come quite close to impacting the nose wheel back on the runway. I guess it's a balance between not stalling and not shoving the nose forward so aggressively that you bump the nose wheel.

I was never really taught these techniques as I learned at Biggin which has miles of tarmac, and have joined a club with an even longer tarmac runway.

obviously it varies from aircraft to aircraft, but the stall warner usually goes off a bit before the wing is fully stalled.

172 short feild takeoff is 10 of flap holding on the brakes full power, release brakes and hold weight off the nose wheel.
one strip i fly out of has a seal taxi way 1/3 from the threshold and will bump you off at 40 odd kts but a slight check forward ( not below horizon ) gather speed and away you go.

1. Well to be honest on a C172 they are pretty crap anyway.

2. If it goes off your not actually stalled yet its just a warning your getting close.

3. Ground effect is a bit different to normal clean air. Trick is don't get out of it until you have enough energy.

You don't push the nose forward just hold your current attitude and as you speed up gently reduce the back pressure to maintain your height and when your up to your normal speeds pitch for your climb attitude.

The plane may settle back down but don't worry about it.

If you have never been taught soft fields and perfomance departures its good fun. You can use more flap and then clean up in ground effect as well. Read your POH and see if you can use another stage of flap.

Anyway I think you could have a very enjoyable and productive hour with an instructor doing this sort of thing. As usual go and find an auld fart to do it that have done a bit of flying.

Even that varies, in the POH for the 172K and M it says no flaps, just full power on the brakes. Soft field is 10.

Think about why the stall warner is sounding and what it's measuring. It's not airspeed, it's angle of attack. Until the AOA is reduced, the warner will continue to sound. But, the warning will usually start 5-10 knots above the stall, so if you're actually flying, the airspeed is increasing and the AOA isn't excessively high, you're moving away from stall conditions, not into them. Just don't pull back any harder, a slight release of pressure should be enough.

Fair point didnt state for N R models as thats what ive used

holding weight off of the nose wheel for trikes I would think would be a standard for a short feild (allways an exception, glad to hear of some)

I like starting the takeoff roll without flaps and then selecting 10° during the run. This reduces drag and gets you to speed faster.

All good advice thanks. An hour with an instructor might well be a good idea.

For the 172p the POH just says 10 degrees for short field (although the club I fly with like you to use 10 degrees of flap on a 1.8km runway in order to reduce wear on the wheels!). I tend not to as I'd rather have more height, quicker in case of an engine failure where the runway is smooth and length isn't limiting.

It also says the aircraft should cruise at 120kts which is news to me :ugh:

All good fun (used it many times operating from 'questionable' strips) until only one side deploys and you're lying broken amongst hot metal and burning bumble bees!

Or one wheel falls off, or the engine blows up at 50ft, or a wing tank bursts into flames.:ugh:

I use that no flaps till 40kts method. But my flaps are manual & a solid bar between them both.

I used to find the C172 N & P would take forever to accelerate between 45 and 50 kts IAS on grass with flap 10 without lifting the nose wheel. In a way if you get bounced off it's a good thing because it means less drag!

I recently flew a C172 SP and it seemed easier to fly to me than the older models. I don't know if there is any significant difference apart from the fuel injected engine and a lower maximum flap setting?

The SP is really capable and goes better than an extra 20-30 HP would suggest. Genuine cruise is 115kts tas at 8usgph Maybe not carrying 40 years worth of crud makes the difference.

As for the cruise on the old ones. More like 120mph. Cessna are a bit more truthful these days.


D.O.

Hmmm, some poor advice here in my opinion...

Grass runway, possibly not as smooth as the pavement you're used to - keep the nosewheel light the whole takeoff run. As you start your takeoff run with 10 flaps, note the amount of horizon you see above the cowl. Full stick back, add power (don't worry about brakes). After a few feet of ground roll, the nose will come up a bit (generally just meets horizon). When you detect this, release a little back pressure, and just hold it in that attitude no matter what. If you're going over undulating ground, just hold that attitude no matter what. The aircraft is accelerating, and will fly when it is ready. If you get a stall warning, just don't pull any more! You're very slowly releasing back pressure anyway right? - the plane is accelerating, so it is moving away from stall "speed" and critical angle of attack. If it's in the air - great, is that not what you were intending? Give it time. If you try to correct by pushing, you're more likely to bounce the nosewheel off the ground, and it all gets really bad after that. I have watched it.

As for fiddling with flaps during the takeoff roll, if they are electric, forget it, it's a waste of time, and dangerous distraction. A C150/152/172/182/206 will have more favourable pitch control on the ground during takeoff with "takeoff" flap rather than no flap, just do what the flight manual says. Drag increases as a square of the speed, so the drag difference between zero and ten flaps on a 172 in the first 20 knots of the takeoff, is negligible, and, you have lost the positive pitch control those ten flaps give you, when you need it most on rough ground.

There are pilots who reposition manual flaps to augment lift during takeoff. I can't say that it does not work. I can say that the Cessna and Piper flight manuals don't tell you to do that. If you need to ask if you should do it - you should not. That technique will optimize takeoff performance under certain circumstances for a very skilled pilot. 95% of pilots never fly in those circumstances. Doing this has serious downsides if you get it wrong, which you'll have real trouble explaining to your insurance adjuster.

Seneca twins are terrors at getting airborne early off bumpy fields. You have to take the weight off the nose to avoid the nose impacting the bumps and you are stuck with the fact that some of those bumps act as launch pads.
I had a Seneca up and flying at 60kts IAS which is a tiny margin especially if the winds are strong and there is wind shear to add to the equation.
I believe the Jockey Seneca which crashed killing the pilot was out of a horse racing track and dropped a wing.
As MJ says its about letting the speed build while not descending back onto the turf and making small movements with the column.
As speed builds then start pitching again but it is about feel and coaxing the aircraft in the initial stages.
Make sure you are trimmed right too!

Pace

10 degrees of flap will cause so little extra drag at the low speeds you are doing at the start of a takeoff run that doing this will make no noticeable difference whatsoever. I'd think that all it does it cause extra distraction on the takeoff run, and give you the risk of going through the hedge if you set them wrong or they don't operate.