landing

[Zack C]

My understanding, which might be entirely wrong...

For any given load factor, a fixed-wing aircraft's speed is determined by its angle of attack. Increasing drag decreases its L/D and thus its glide ratio. So if for a given angle of attack (set by bar position on a hang glider) drag is increased, the vertical component of the aircraft's velocity (i.e., sink rate) will increase and the horizontal will decrease (as will the aircraft's pitch attitude), but the magnitude will be the same. Thus, deploying a drogue on a hang glider will result in a steeper descent angle (especially at higher speeds), but the glider's speed will still be the same for any given angle of attack/bar position. After all, do people with draggy harnesses trim or stall slower than those with race harnesses? And if drogue chutes allowed hang glider pilots to touch down with less speed, I'm pretty sure they'd be a lot more popular.

In powered aircraft, speed is also determined by angle of attack, which is set by the elevators. The engine determines climb/sink rate. In the case of the B-47, the chute used in flight is not decreasing the magnitude of its velocity...as with the hang glider, it's increasing its sink rate and decreasing its horizontal speed. This allows it to descend with power at the same slope as it would with no power and no chute. But its speed is the same, determined (as always) by angle of attack (again, for a given load factor).

All of this assumes the plane is not accelerating. Changes in thrust (for example) can momentarily affect speed.

Zack

[Tad Eareckson]

And here's what I was working on before Zack posted...

Nope.

You showed me a photo of a B-52 on a runway with a drag chute deployed after all the wheels were on the pavement being used to conserve runway and brake pads.

In hang gliding - with rather rare exceptions - we don't eat up enough runway to be worth talking about once we're on the ground.

They were used to limit the speed of the aircraft while the engines were at a certain power level.

To accomplish what?

They did final with these chutes to limit descent speed.

1. They will:
-- INCREASE the descent speed (feet per minute)
-- NOT allow the plane to safely fly at a lower airspeed. The stall speed remains THE SAME
2. To increase your descent speed AND lower your stall speed lower your flaps.

remember these?

Maybe. Extremely dimly at best.

Seen one of these before?

Yes.

The name of the game for landing B-47s and hang gliders is energy management.

Don't forget directional control. Anything with wings that'll carry us into the atmosphere is gonna land - with or without our help.

Going upright, while not as effective as a chute or the chaps creates drag and the drag is a useful tool for speed control during descents.

It is NOT for SPEED control.

If your glider stalls at eighteen and you want to arrive at the ground at two miles per hour over it won't matter whether you're proned out and zipped up in your racing pod or upright with your legs out and your Flap Chaps spread and your drag chute deployed. Your gonna arrive at the ground at twenty. And if you slow to eighteen before you get to the ground in either configuration things are gonna get ugly fast.

Furthermore...

It's not a great idea to come into fields so restricted that we need to degrade our glides by going upright or using drag chutes. And statistically people aren't doing it and we're not having problems in that area.

We're having problems...

http://www.hanggliding.org/viewtopic.php?t=22176
Paragliding Collapses

Jim Rooney - 2011/06/12 13:57:58 UTC

Most common HG injury... spiral fracture of the humerus.

...with the control and danger issues associated with having hands on the downtubes.

I fly one hand up and one down because my harness and the way it hangs does not allow for good pitch control from the downtubes.

I wouldn't worry about it too much. NOBODY has good pitch control from the downtubes.

Works great for crosswind landings.

Super. So do the techniques employed by Dave Seib, Steve Pearson, and Bob Grant.

[miguel]

OK

I will try again.

From wiki:

Dive Brake

Dive brakes or dive flaps are deployed to slow down an aircraft when in a dive. They usually consist of a metal flap that is raised against the air flow, thus creating drag and reducing dive speed.

In the past dive brakes were mostly used on dive bombers, which needed to dive very steeply, but not exceed their red line speed in order to drop their bombs accurately. Dive brakes are often fitted to the bottom surfaces of glider wings as companion controls to top-surface-mounted spoilers. Most modern combat aircraft are equipped with air brakes, which perform the same function as dive brakes.

http://upload.wikimedia.org/wikipedia/commons/thumb/b/b6/Dauntless_bomb_drop.jpg/300px-Dauntless_bomb_drop.jpg


The dive brakes are the perforated metal strip on the bottom trailing edge of the wing.

Are you with me so far?

The dive brakes lower the speed of the aircraft during the dive.

The B-52 picture with the drogue chute was because I was unable to find a drogue chute pic for the B-47



More Wiki: taken from the wiki on the B-47

Drag chutes

A related problem was that the aircraft's engines would have to be throttled down on landing approach. Since it could take as long as 20 seconds to throttle them back up to full power, the big bomber could not easily do a "touch and go" momentary landing. A small "approach chute" (drogue parachute) provided drag so that the aircraft could be flown at approach speeds with the engines throttled at ready-to-spool-up medium power. Training typically included an hour of dragging this chute around the landing pattern for multiple practice landings.

The aircraft was so aerodynamically slick that rapid descent ("penetration") from high cruise altitude to the landing pattern required dragging the deployed rear landing gear.

Unusually high wing loading (weight/wing area) required a high landing speed of 180 knots (330 km/h). To shorten the landing roll, Air Force test pilot Major Guy Townsend promoted the addition of a 32 ft (9.75 m) German-designed "ribbon" drag chute. (Jet engine thrust reversers were still a "far-future" concept.) As a consequence, the B-47 was the first mass-produced aircraft to be equipped with an anti-skid braking system.

Are you getting it now, drag systems to control speed?

Hang gliders.

Lets start with the latest ATOS cruising at 5000ft agl. Our pilot pulls in the bar to about waist level and keeps it there. The speed will build and build until Vne is exceeded and bad things will begin to happen. Our pilot realizes this so he slowly lets the bar out untill he is in a mild climb. Once he reaches the apogee of the climb, he deploys a Mike Sandlin drogue chute. He then pulls in to his waist.

What happens now?

The glider will nose over and begin to pick up speed. It will stabilize at a speed somewhat porportional to the drag that the chute is producing. The glider will not continue accelarating to Vne and beyond.

The chute is being used to control speed!

For the millionth time, consider the upright hang glider pilot. The glider can be dove at a steeper angle than a prone pilot can without picking up additional speed.

Got it?

[Zack C]

Are you getting it now, drag systems to control speed?

Miguel, where Tad, Nobody, and I are at issue with this concept is that airspeed is determined by bar/elevator position and drag systems will not affect stall speed. Saying that drag systems control speed implies otherwise (to me, anyway). Increasing drag (whether through dive brakes, drogue chutes, or getting upright) only reduces glide angle, allowing you to descend faster for the same airspeed and thrust.

Drag systems' effect on airspeed is indirect...they allow you to descend at sink rates that otherwise would require higher airspeed. If this is what you mean by 'controlling speed', than yes, drag systems can be used to control speed, but I find that usage misleading.

For the millionth time, consider the upright hang glider pilot. The glider can be dove at a steeper angle than a prone pilot can without picking up additional speed.

Yes, a glider will descend at a steeper angle with the pilot upright for any given airspeed. Tad hasn't said anything that contradicted that, nor has he said anything inaccurate (as far as my understanding goes).

It will stabilize at a speed somewhat porportional to the drag that the chute is producing.

The glider will not continue accelarating to Vne and beyond.

The airspeed will be the same for any given bar position regardless of drag. Thus, the Vne can still be exceeded just as easily/in the same way with a drogue chute as without. It will just be descending a lot faster when you do it.

Zack

[miguel]

Zack

I have never ever, ever mentioned stall speed. It has nothing to do with the argument. Stall speed is totally independent of external drag producing devices. Airspeed is not

Add more drag to a stable flying aircraft and it will loose air speed. It will then dive to pick up air speed and reach a new equilibrium. Take away drag and the aircraft will increase air speed. It will climb to reach a new equilibrium.

[Zack C]

I have never ever, ever mentioned stall speed.

No, and I never said you did...only that what you said implied stall speed was affected. You spoke a lot about using drag devices to slow down. Since the aircraft could be slowed to any speed above stall without a drag device, one could infer you meant that with a drag device a slower speed was possible.

Add more drag to a stable flying aircraft and it will loose air speed. It will then dive to pick up air speed and reach a new equilibrium. Take away drag and the aircraft will increase air speed. It will climb to reach a new equilibrium.

Yes, but I thought we were discussing the equilibrium state. Once the aircraft has stabilized (assuming no change in bar/elevator position), its speed will be the same as before the drag change, no?

Zack

[Tad Eareckson]

Wills Wing - 2007/02
T2 144, 154 Owner / Service Manual

Using drag devices during landing

It is becoming more popular on high performance gliders for pilots to utilize a small parachute or "drogue chute" during landing approach. The proper function of such a device is to increase drag on the glider, and as a result reduce the glide ratio. Please note that a drogue chute, because it produces only drag and not lift, does not "slow the glider down" or allow it fly at a slower speed, or reduce the landing speed. What it does do is to allow the pilot to fly a steeper approach at a higher speed, have much less "float" after round out, and thus make it much easier for the pilot to plan his approach, to time the flare, and to accurately "hit the spot" and land close to the intended landing point. It restores the ability, which used to be present on lower performing gliders, to use adjustments in speed to control the steepness of the descent.

Comments...
- If you've ever NEEDED to fly a steeper approach at a higher speed, have much less "float" after round out, better time the flare, accurately "hit the spot", and/or land close to the intended landing point please tell me.
- Please also include a description of the prior stupid mistake(s) you made which necessitated any or all of the above.
- The ability, which used to be present on lower performing gliders, to use adjustments in speed to control the steepness of the descent doesn't need to be restored - it didn't suddenly disappear when we hit some critical lift to drag ratio.
- Assuming no wind, if you wanna eat up as much runway as possible, come in on final at best L/D.
- If you:
-- wanna use less runway fly slower or faster
-- REALLY wanna conserve runway fly just above stall speed - but don't expect to land right side up too many times in a row
-- wanna conserve runway AND land right side up lotsa times in a row come in a lot faster than best L/D
- I lied before. You can eat up more runway by speeding up above best L/D as you near the surface and getting a ground effect boost but that requires extra numbers and calculus so I'm not gonna worry about it.
- And unless you're really good at plugging in the variables and running the equation in your head at twenty-five feet either don't land in fields so tight that somebody who sucks at math is apt to get worried or use the goddam drag chute.

[miguel]

I have never ever, ever mentioned stall speed.

No, and I never said you did...only that what you said implied stall speed was affected. You spoke a lot about using drag devices to slow down. Since the aircraft could be slowed to any speed above stall without a drag device, one could infer you meant that with a drag device a slower speed was possible.

Please point out and post, Tad style, where I have implied that drag or going upright affects stall speed.

I am fully aware that external drag devices do not affect the stall speed of an aircraft. I do hope my words have not said or implied otherwise.

I have gone upright in a hg right around stall speed and stalled the glider. It spun into a tree. I hit wit a glancing blow on the wing tip and it spun the glider the other way. It spun into the wind and I landed it uneventfully.

Add more drag to a stable flying aircraft and it will loose air speed. It will then dive to pick up air speed and reach a new equilibrium. Take away drag and the aircraft will increase air speed. It will climb to reach a new equilibrium.

Yes, but I thought we were discussing the equilibrium state. Once the aircraft has stabilized (assuming no change in bar/elevator position), its speed will be the same as before the drag change, no?

Check the vector diagram below



For a drag addition to a powered aircraft with elevator position fixed, some thrust must be added to maintain speed and altitude. For an unpowered aircraft with a drag addition, it will have to dive slightly to maintain speed. Its l/d will be less and it will not glide as far.

Hope this makes unambiguous sense.

And Tad, I will be back. I do not do internet on weekends.

[miguel]

Please note that a drogue chute, because it produces only drag and not lift, does not "slow the glider down" or allow it fly at a slower speed, or reduce the landing speed.

It is NOT for SPEED control.

If your glider stalls at eighteen and you want to arrive at the ground at two miles per hour over it won't matter whether you're proned out and zipped up in your racing pod or upright with your legs out and your Flap Chaps spread and your drag chute deployed. Your gonna arrive at the ground at twenty. And if you slow to eighteen before you get to the ground in either configuration things are gonna get ugly fast.

For any given load factor, a fixed-wing aircraft's speed is determined by its angle of attack. Increasing drag decreases its L/D and thus its glide ratio. So if for a given angle of attack (set by bar position on a hang glider) drag is increased, the vertical component of the aircraft's velocity (i.e., sink rate) will increase and the horizontal will decrease (as will the aircraft's pitch attitude), but the magnitude will be the same. Thus, deploying a drogue on a hang glider will result in a steeper descent angle (especially at higher speeds), but the glider's speed will still be the same for any given angle of attack/bar position. After all, do people with draggy harnesses trim or stall slower than those with race harnesses? And if drogue chutes allowed hang glider pilots to touch down with less speed, I'm pretty sure they'd be a lot more popular.

Time for a true story:

I had just taken ownership of a brand new, crispy, crinkly sail, TRX. I made my normal aircraft approach for landing. The TRX carried a lot more energy into final than my old glider. Plus there was no wind. I flew over the spot at about 20 feet and 35 mph. Once you get past the spot, the lz goes down hill for about 75 yard, ending in brush. I settled into ground effect still going about 35 mph. The brush was getting closer. The glider was not sinking. I had no wheels. I did the quick mental calculations and figured the best spot the crash in the brush. I passed by the peanut gallery in the lz. The looks on the faces say they were salivating for a good crash. Wait a minute though. I have a brand new, never been used, Mike Sandlin drogue chute out back. Nothing to loose, I pull the cord. I feel a force holding the glider back. I did a mellow flare and did a 2 step landing way before the brush. The peanut gallery had saucer eyes of astonishment.

Question for Tad and company.

WTF happened?

No rhetoric, personal pronoucements or bull. I would like accepted theory and accepted concepts.

[Tad Eareckson]

I have gone upright in a hg right around stall speed and stalled the glider. It spun into a tree. I hit wit a glancing blow on the wing tip and it spun the glider the other way. It spun into the wind and I landed it uneventfully.

Wouldn't the landing have been even more uneventful if you had stayed prone? Or were you landing in a narrow dry riverbed with large rocks strewn all over the place in which bellying in would've been suicide?

Hope this makes unambiguous sense.

Yes.

I flew over the spot at about 20 feet and 35 mph.

1. How high did you fly over whatever it was that was obstructing your final approach to the field?

2. Would it have been unduly difficult or dangerous to land prior to the spot?

http://www.hanggliding.org/viewtopic.php?t=21088
What you wish you'd known then?

Doug Doerfler - 2011/03/02 05:24:44 UTC

Nothing creates carnage like declaring a spot landing contest.

3. What was the importance or significance of this particular spot?

Once you get past the spot, the lz goes down hill for about 75 yard, ending in brush.

How good an idea is it to aim for a spot at a point on a field after which the terrain slopes down for about 75 yards to brush?

I had no wheels.

1. Meaning the surface WAS suitable for wheel landing - one of those Happy Acres putting greens in which one comes down on only the rarest of occasions.

2. How come?

3. Did you have a helmet?

4. Two gliders - one has a helmet but no wheels, the other wheels but no helmet. Who's more likely to make it through the flying season?

The looks on the faces say they were salivating for a good crash.

Did one of those faces belong to the person who placed the traffic cone at the top of the slope and look anything like Jason Boehm's?

WTF happened?

http://www.hanggliding.org/viewtopic.php?t=22176
Paragliding Collapses

Jim Rooney - 2011/06/12 13:57:58 UTC

Most common HG injury... spiral fracture of the humerus.

1. You decided to fly without the equipment most likely to protect you from crashing, damage, and injury.

There is nothing more useless than runway behind you.

2. You ignored one of the most fundamental rules of aviation and elected to eliminate the first half of the runway as a landing option.

3. You prioritized a dangerous spot landing over a safe runway landing.

4. You came in too high and fast to even hit the far end of the runway.

5. You didn't consider the option of landing uphill - which is so brain dead easy that it's not worth the battery power to video record the event even when people without wheels are foot landing and shooting for a spot.

6. You were flying with a bunch of testosterone poisoned douchebags who manage LZs and landing protocols to be as dangerous as possible 'cause they get their kicks by watching gliders crash.

7. You had a crutch with which you were able to successfully compensate for a long list of bad decisions and shortcomings in execution and land at the same speed you would have if you had done one or two things right.

No rhetoric, personal pronouncements or bull. I would like accepted theory and accepted concepts.

How did I do?