Gliding.....

[HeadInTheClouds]

Hey,

 

Thought I might post up some things which I have always wondered about gliders and how they work, but which I've never been able to find solid answers for. After Tomo's recent thread and a bit of youtube I've decided it is something I want to learn one day, might wait till I get my RAA cert though.

 

The first thing I'm curious as to know is how on Earth do glider pilots judge how far they can glide? Like in a powered aircraft say you were on approach and were going to undershoot the runway, you just add some power to pull you into the threshold. What happens if this occurs in a glider?

 

I've also seen videos of gliders doing low passes or just flying low in general, how on Earth does this work? Is it just a case of simple physics where you would be carrying a lot of speed flying low then convert that speed back to height when you need a bit of altitude?

 

I've also seen videos of winch launches on youtube, how can so much height be attained from a cable of finite length?

 

Are gliders usually able to do aerobatics too? This is also something that pops up often on youtube...

 

Anyone in the know who could be bothered to even respond to one of my curiosities would be appreciated

 

 

[Tex]

Hey,The first thing I'm curious as to know is how on Earth do glider pilots judge how far they can glide? Like in a powered aircraft say you were on approach and were going to undershoot the runway, you just add some power to pull you into the threshold. What happens if this occurs in a glider?

Instruments and glide calculators help, then pure skill

Do a search on speeds to fly theory... it can all get a bit complicated and then it is also based on what you are attempting... speed over a course - average lift - sink etc.

 

Basically you learn with experience - best glide speeds - best LD are the things you need to know. At its most basic level if it moves up in your field of view you are not going to make it, if it moves down you should be right, if it stays in place it depends on the net lift sink you get on the way.

 

I've also seen videos of gliders doing low passes or just flying low in general, how on Earth does this work? Is it just a case of simple physics where you would be carrying a lot of speed flying low then convert that speed back to height when you need a bit of altitude?

I've also seen videos of winch launches on youtube, how can so much height be attained from a cable of finite length?

 

Are gliders usually able to do aerobatics too? This is also something that pops up often on youtube...

 

Anyone in the know who could be bothered to even respond to one of my curiosities would be appreciated

Yep Speed/energy = altitude, but it is finite of course and knowing what you have in the bank is the skill.

 

I've also seen videos of winch launches on youtube, how can so much height be attained from a cable of finite length?

Are gliders usually able to do aerobatics too? This is also something that pops up often on youtube...

The height you can gain is a factor of the length of the cable and whether it is reflex (run around pulleys) or static (pure tow), you need a pretty long cable for decent altitude. Most gliders can do aerobatics as the have a very broad speed range and retain energy better than most other aircraft...

 

 

[Tomo]

I'm no expert and I think Tex has covered most of it, but it is interesting how far they can glide! I'm still getting the hang of it, usually always playing it safe and being a little bit higher inbound to the airfield, but sometimes you could be on downwind or there abouts and if there is lift around the silly thing won't descend! So you need to pull out air brake etc... It's a great experience, and going from powered planes to gliders is pretty cool because you didn't expect it to glide "that" far! Imagine the surprise a glider pilot gets when converting to powered... But you use the same technique as you would in a powered plane doing a glide descent, which is what Tex has described is simple terms.

 

The difference is if you have a cable break at 250 feet, you just do a 180 and land (depending on the circumstances obviously) but the cable was pulled on me yesterday at around that height... to be honest I didn't look so I don't know, but it was pretty low. Decided on a turn, lined up for a downwind landing (got heaps of runway) and still had to get the air brake out to not overshoot the other end. Totally different kettle of fish to a draggy powered plane hey!

 

Ground effect is awesome, we did some playing around with that - you get some speed on then get into ground effect, and you could sit there for ages! Pull up and get some height, then in my case brake out and land. But I could see how one would be able to do a low level fly past, pull up into a turn and come back the other way.

 

Spot landing with a glider is pretty easy and you almost do have a throttle - you start with a bit of brake out, if you're undershooting, put some away, overshooting get out more... etc, it's a cool experience.

 

 

[Tomo]

Not my video, but gives you a bit of an idea of what you can do, same type I'm flying at the moment.

 

 

 

[HeadInTheClouds]

They must glide a hell of a long way. I bet that any glider pilots converting into powered would find powered aircraft to have the gliding ability of a large rock...

 

Must try this sometime I think.... Looks like a lot of fun!

 

 

[Kyle Communications]

Even gliders of old days had reasonable LD like 20 to 1 but most modern trainers now have 34 to 40 to one LD...some high performance AND very expensive ones can get 60 to one LD. This means for every 1 metre of height you can go 60 metres of distance...taking head winds into account of course. A Savannah has a LD of 11 to 1...so as light aircraft go pretty reasonable and useable Usually you always come in with too much height then bleed what you don't want off with the air brakes which work incredibly well and very easily used. If you are looking a a bit short then you can extend it a lot by dolfining or where you put your nose down then convert that energy into height then stick the nose down again then speed up and do the process again. It is amazing how much further you can go doing this...literally many kilometres...I used to love the fence hopping during my training but its like anything...you need fuel.....fuel is height and speed so when your flying a glider you need to make sure you always have enough fuel to get back to the field.

 

I never did many winch launches...thank god...I hated them 99% of all my glider flying was aerotow

 

Mark

 

 

[kaz3g]

 

 

The first thing I'm curious as to know is how on Earth do glider pilots judge how far they can glide? Like in a powered aircraft say you were on approach and were going to undershoot the runway, you just add some power to pull you into the threshold. What happens if this occurs in a glider?

 

 

 

Experience is a great help but knowing your aircraft and its capabilities will help more. If circuit height is 1000' then, even in an old Blanik 2 seat trainer (28:1) you can glide for more than 5 miles in still conditions before the earth and the mainwheel meet. In a nice single seat competition machine you will do better than 50:1 glide ratio. The aim is to have residual height on approach and then kill the lift by opening the airbrakes/spoilers.

 

 

 

I've also seen videos of gliders doing low passes or just flying low in general, how on Earth does this work? Is it just a case of simple physics where you would be carrying a lot of speed flying low then convert that speed back to height when you need a bit of altitude?

 

 

 

Potential energy (PE) = Kinetic energy (KE)

 

m x g x h = 1/2 m x v^ ( ^ = "squared" )

 

So yes, you can convert height into velocity and vice versa.

 

 

 

I've also seen videos of winch launches on youtube, how can so much height be attained from a cable of finite length?

 

Are gliders usually able to do aerobatics too? This is also something that pops up often on youtube...

 

 

 

I managed over 3000' on the Euroa/Locksley/Wahring Field winch with Peter Johnson driving it. It was a great day with a very brisk wind straight down the strip at Euroa and I went up like a rocket at first. Peter slowed the winch down and let me climb more slowly by pulling up. At around 2000' he stopped the winch altogether and then started to let the cable out. He was playing me as a kite in the wind. I remember it was a very close circuit because I only had around 20 knots of ground speed on final at 55 knots.

 

 

 

Can't remember who the pilot was but a Salto single seat (v-tail) used to do aeros including low passes and stall turns at the big airshows after being towed to 2500'. Think it's got a small jet tacked on now so is self-launching.

 

 

 

kaz

[HeadInTheClouds]

Those wings can take a lot of g's!!

 

 

[facthunter]

It's a pretty clean machine. Couldn't see any twist in the wings. What are they worth? ( Not that I could afford it). Nev