Short-field takeoff technique
Joined: Dec 1998
Posts: 4,282
Likes: 6
From: Escapee from Ultima Thule
Unless I misread J.D's article there's a point I disagree with. For obstacle clearance he seems to be advocating that - given more runway than the ground roll requires - the a/c be kept on the ground until some speed higher than Vx (or maybe accelerated after lift-off to some speed >Vx) THEN the a/c is zoom climbed, trading speed for height.
If that's the case then there's an error in his method: Any speed greater than Vx is wasteful of energy due to the greater proportion of drag reducing the excess available for climb. Think of the power & thrust required/available curves.
Have I misread something in his article? Or am reading more into it than he intended?
If that's the case then there's an error in his method: Any speed greater than Vx is wasteful of energy due to the greater proportion of drag reducing the excess available for climb. Think of the power & thrust required/available curves.
Have I misread something in his article? Or am reading more into it than he intended?
Joined: Jan 2004
Posts: 74
Likes: 0
From: East Coast of Oz
I havent read JD's article but that does sound odd Tinstaafl....the only thing i can think of similiar to that would be a V2 overspeed giving us better performance from the 2nd segment on.
In smaller aircraft this zoom climb technique gets u thinking, why would you want to be remaining on the runway chewing it up for emergency use and then zoom climbing when you could take off as usual and have gear up already ad be climbing and accelerating away.
hmmmmm
In smaller aircraft this zoom climb technique gets u thinking, why would you want to be remaining on the runway chewing it up for emergency use and then zoom climbing when you could take off as usual and have gear up already ad be climbing and accelerating away.
hmmmmm
Joined: Jun 2001
Posts: 509
Likes: 28
From: Albany, West Australia
John Deakin's Article
Have to agree with Tinstaafl that this article is more than a bit wobbly.
He seems to be confused about a few things.
Firstly, a rolling start will give you quicker acceleration than the training method of stand on the brakes and feed in full power. On reasonably wide strips, you should start these from the 'downwind' corner, heading slightly toward the upwind side of the runway. You'll be 10kts ahead of the traditional method at any given distance.
He never mentions load anywhere. Why not dump some weight if the strip is so short?
His suggestions for full flap t/o, followed by a gradual change in configuration and acceleration at 6 inches height - leaves one thinking it's again test pilot stuff. One change in the wind gradient and JD is history!
As for leaving the aircraft on the ground beyond when it will fly - this is contrary to all we know about drag and also u/c damage. It will accelerate faster if airborne, all other things being equal. If the strip is at all rough, the less time the wheels are rolling - the better.
All in all - the article does more to confuse than clarify, and I can't say that I'd be recommending it to any student as background reading on short field operations. About the best thing he suggests is to find yourself an experienced bush instructor to learn this sort of stuff.
happy days,
Have to agree with Tinstaafl that this article is more than a bit wobbly.
He seems to be confused about a few things.
Firstly, a rolling start will give you quicker acceleration than the training method of stand on the brakes and feed in full power. On reasonably wide strips, you should start these from the 'downwind' corner, heading slightly toward the upwind side of the runway. You'll be 10kts ahead of the traditional method at any given distance.
He never mentions load anywhere. Why not dump some weight if the strip is so short?
His suggestions for full flap t/o, followed by a gradual change in configuration and acceleration at 6 inches height - leaves one thinking it's again test pilot stuff. One change in the wind gradient and JD is history!
As for leaving the aircraft on the ground beyond when it will fly - this is contrary to all we know about drag and also u/c damage. It will accelerate faster if airborne, all other things being equal. If the strip is at all rough, the less time the wheels are rolling - the better.
All in all - the article does more to confuse than clarify, and I can't say that I'd be recommending it to any student as background reading on short field operations. About the best thing he suggests is to find yourself an experienced bush instructor to learn this sort of stuff.
happy days,
Joined: Dec 1998
Posts: 4,282
Likes: 6
From: Escapee from Ultima Thule
V2 overspeed still doesn't take you past Vx. That method is used in jets (where Rwy length is available) to get closer to Vx for the climb.
I use the rolling start from downwind taxi a lot ie power applied as I turn the corner from one side of the airstrip.
The goal is to accelerate & rotate to achieve Vx then flap & gear as soon as possible. Maintain Vx & full power until clear of the obstacle. Some strips I go into require a turn almost as soon as airborne.
If a soft, boggy or rough field then that will adverserely affect distance required. No getting around that. Get the thing airborne in ground affect as soon as you can - but not below Vmc - then accelerate to Vx & as per before.
I use the rolling start from downwind taxi a lot ie power applied as I turn the corner from one side of the airstrip.
The goal is to accelerate & rotate to achieve Vx then flap & gear as soon as possible. Maintain Vx & full power until clear of the obstacle. Some strips I go into require a turn almost as soon as airborne.
If a soft, boggy or rough field then that will adverserely affect distance required. No getting around that. Get the thing airborne in ground affect as soon as you can - but not below Vmc - then accelerate to Vx & as per before.
