BaldEagel

Some of the P20 conversions that are happening do not have full flaps or airbrakes to slow down and get into short strips I am thinking of using some of these to get my slippery airframe down quickly and onto the patch: http://www.youtube.com/watch?v=XEGMb1AxzwY anyway anyone used something simmilar?

Mike

Couch Potato

Hi Mike

These things are very popular with the glider fraternity.
In that application they are used to kill lift on a portion of a very high aspect ratio wing.

On a small highly wing loaded jet the effect could be dramatic !
I assume we want to induce drag and not kill lift ?

Where would you stick it on a P-20 powered jet ?

rhklenke

My Feedback: (24)

Couch is right in that they are typically used on gliders and they kill lift more than add drag. I have flown a 16' wingspan glider with them though and they are very effective. They significantly increase the sink rate and do so with no noticeable trim change - which is really nice. They are like a big "down" button. You can modulate the amount of lift that they kill by how far out they extend. I did not see on the video if the ones there were proportional. That is somewhat important - to be easy to use, they need to proportional. On a grass strip, you can use them to get the plane on the ground and then let the grass do the braking. They are also very effective in keeping the aircraft from coming up again - i.e., its *really* hard to bounce with full spoilers out.

If they are not proportional, then I would probably not use them - especially if they cover more than about 30% of the wing span. Deploying them all the way on a setup like that is likely to make the plane fall out of the sky like a rock. However, if they are proportional, then you can play around with how much you deploy them to get the sink rate you desire...

Bob

BaldEagel

Thanks for the feed back guys, but it seems I did not explain myself very well in the original post, I have over 4000hrs in gliders and know a bit about how they work my question was aimed at had anyone used them on jets?

Bob yes they are proportional.

Couch I would conventionally mount them on the wing.

The Sligsby Swallow was only 13M span and had a very broad cord, with the blade brakes deployed they became speed limiting and you could point the thing at the ground and speed would not increase, but boy did you come down and land very short, but on the Libele I used to fly the balde brakes where just not that effective, most of the modern gliders in my day typically used flaps that on second stage deployment extended above the wing with a flexable hinge between the first and second stage, they looked a bit like the flaps on an Elan when fully extended, but operated as normal flaps up to about fifteen degs.

Mike

Boomerang1

They have been used on full size jets.

Does one of these look familiar?

John.

Couch Potato

There must be a difference between popping up a wing fence flush with the top wing skin surface, and a brake well above the surface boundary effect ?

Please try it and post the video.

BaldEagel

In full size a wing fence flush with the wing surface is generally called a spoiler and only disrupts the lift over a limited area of the wing the airflow may even re-attach to the wing section behind the spoiler and decrease its effectiveness, in fact most commercial aircraft use differential spoilers to give a flatter turn, more comfortable for the passengers, putting a brake above the wing surface creates effects beyond its width, the normal position of these is at the thickest part of the wing section, behind the main spar in most wing sections, especially if they are laminar flow sections to disrupt the attached boundary layer at a point that it will not easily re-attach behind the brake, this not only acts as a brake but also decreases the lift of the wing, this in turn will increase the glide slope, consideration has to be given to the effects that this disrupted airflow will have on flaps and also the elevator and even the ailerons if the brake is outboard enough. This is all in simple terms and is not meant to be an exhaustive explanation.

Mike

BaldEagel

The day I posted this thread I ordered some Electric Airbrakes from Galaxy Models in the UK, it has take three e-mails up to yesterday for them to tell me that they are out of stock and do not know when they will get them in, ten days for nothing to happen, I have been in touch with Topmodel in CZ and they have said they will post today I await with antisipation, will detail what happens.

Mike

David Gladwin

What a load of complete and utter rubbish !

BaldEagel

Well that's one persons opinion.

Mike

Henke Torphammar

No, it's fact. A flatter turn will not make a more comfortable ride, fly it clean with the G's pushing stright down. How they use the liftdampers in flight I do not know but they are not used for making flat turns.

BaldEagel

Well, I am repeating what was told to me by a skiing friend of mine who is a commercial heavy pilot, I do not have the experience to argue the fact on these type's of heavy aircraft, like you I don't know why they use the lift dumpers differentially on the wings in flight either, but when I asked the question that is the answer I was given.

Mike

David Gladwin

Michael, you reveal a truly appalling lack of knowledge of the fundamentals of flight. If you REALLY have 4000 hours on gliders its quite amazing that are so utterly and totally ignorant of just how an aircraft flies. May I suggest a read of Kermode ?

Just what IS your experience of flying passengers on aircraft equipped with spoilers ?

You do, at times, spout extraordinary rubbish.

Couch Potato

I hear wing-warping is coming back into vogue

http://pcwww.liv.ac.uk/eweb/fst/WrightBrothers2.htm

BaldEagel

I see we have exactly the same opinion of each other, but I resist the temptation to be rude about it.

Mike

David Gladwin

Your ski-ing friend is pulling your leg and you fell for it !

The spoilers act differentially when the ailerons are used. The first few degrees of aileron do not raise the spoiler panels, after about 5 degrees, the spoilers come into action to prevent adverse aileron yaw and increase roll rate. They act symetrically as speedbrake or differentially when partially raised and aileron is used. Its all done in the mixing box or by FBW. They have absolutely nothing to do with making level turns for passenger (dis) comfort.

I almost fell of my chair when you suggested that diff. spoiler was used to produce flat turns for passenger comfort. I had visions of airliners skidding round turns with pax and crew having a terrible flight ! Max bank upto 30 degrees in airliner ops. and its the rate of roll not the bank angle which makes for smooth flights

The answer you were given is total rubbish and with 4000 hours on gliders you need to watch the yaw string more, I really thought you would fully understand balanced flight ! Try a flat turn in your glider, bootful of rudder with opposite aileron, and see what it feels like, b-dy awful, and DONT try it near the ground or anywhere near stall speed or you may need to start spin recovery !

Of course, if you had a Weatronics receiver you could set up, using Giga Control, you flight controls inc spoilers exactly like a real jet !

David.

BaldEagel

Well David a calm reasoned responce instead of just being rude, perhaps that is how you should have posted before you got your knickers in a twist from laughing.

The Yaw string on a glider was always in the wrong place IMO stuck out in front of the wing on the conopy it showed the cockpit to be in line with the airflow not the wing, think about it before you do yourself a damage again.

Side slipping i.e. boot full of rudder with opposite aileron near the ground is a nomal landing practice for gliders perhaps you need to read up on landing techniques for non powered aircraft.

The advent of me getting a Weatronics or Giga control for my toys is about as likely as you staying on subject.

Mike

David Gladwin

I'm sorry Mike, I just dont know where you are getting this stuff from. You claim to be a gliding instructor with 4000 hours. With which club ?

..............and for which company does your friend fly heavy jets ? Must avoid it.

Now, to keep on thread, anyone who wants to learn about spoilers, flaps and a lift dumpers could do well to read: "Mechanics of Flight"
by A C Kermode and /or "Handling the Big Jets" by D P Davis (former chief test pilot of the UK ARB) in which there is an excellent section on the integration of spoilers, ground spoiler and ailerons on the 747 and which is fairly typical of current large jets.

David.

BaldEagel

You seem to be able to take everything I say out of context, I did not say put the yaw string on the wing, read what I said.

I also said that landing with side slip is a normal landing technique, nothing about below one wing span, where do you get this from.

David you need to take a step back and look at what is written, not what you want to argue about.

By the way when Derek was my CFI he used to rip the piece of wool off the canopy of the Bocian, he said it was too inacurate and missleading to be of any use.

My skiing friend is at the top of the tree, at one time flying only between Heathrow and JFK you should know what that means.

Mike

Boomerang1

Wow David.

From the times I have spoken to you you seemed most reasonable & knowledgable & I always wondered why your fellow Brits had such little time for you.

After this rant I can see why. - John.