larrysogla

How do engineless slope soaring gliders attain 150+ mph on a hilly slope with the wind blowing just 30+ mph? What is the physics behind such a multiplier over the 30+ mph wind velocity? It is kind of mind boggling that such a benign windspeed could be harnessed to produce blazing flying speeds all without engines or motors. Thanks for your valuable replay.
larry

da Rock

Fairly simple.

They gain more energy on the "downhill" side of the flight than they lose on the uphill. The flight path is intelligently flown to gain the max where gains can be made and to not waste that where it might be wasted.

Control Line flyers can fly quite a bit of their pattern without their engines. No lie. They don't even have to have the engine for takeoff. That is, if they've got some wind blowing. It's called wind flying and is almost exactly the same deal. Wind is potential energy basically. For slope gliders and CL planes and.... whatever we're smart enough to use it for.

Scar

My Feedback: (3)

To be clear, that 30 mph wind gives the glider Lift. The Lift is used to acquire altitude. The altitude then is traded for speed, in a dive. Best wishes, Dave Olson
(edited to correct amisspelled word)

larrysogla

My next question is why do powered airplane flyers not harness the same 30 mph wind blowing in our flying sites to fly with our engines cut off and go 100 mph without engines turned on just like the slope soarers??
Thanks
larry

Skratchbilt

My Feedback: (6)

As with all aircraft, powered or not, there is an upwind force, and a downwind force, relative to the direction of flight. Naturally, the aircraft will slow, or lose speed, in an upwind situation, but can use this to gain altitude, then trade altitude for speed... and an aircraft will gain speed without exerting energy, or losing altitude, in a downwind situation... much like a boat on a river. However, soaring is as reliant on heat as wind... they are called thermals. These thermals are indicated in a soaring plane (full-size) by the chirper, and can set a soaring plane at 20,000 ft very quickly, and efficiently. Mountain soaring utilizes updrafts, and loops, so to speak, to multiply the speed as the craft repeats its coarse. Once at an altitude, the craft will descend, building speed, and as it reaches its climb point, is pulled up gradually, and the Gs it experiences at the base of the loop will in turn multiply the speed when they are relieved. Piloting is the main factor in this phenominon... everything gradual and smooth. The more times a pattern is used, to gain speed, the more speed is gained. Particular attention should also be paid to the design of soaring birds... very slim, very long surfaces.

Dsegal

See the discussion of dynamic soaring at http://en.wikipedia.org/wiki/Dynamic_soaring

rmh

almost sounds like purr pet shoe all moshin-

Jim Thomerson

For some time the world record speeds for model gliders where higher than for powered models. Problem was twofold: at speed the propeller was actually slowing the airplane down because the engine could not turn it fast enough to give positive thrust; and, there were questions about how the Russians timed speed runs. I think all that has been sorted out. Model Aviation gives all the world records once or twice a year. There are a number of world records not held by USA folks.

Scar

My Feedback: (3)

I'm going to assume you haven't flown yet. Some of us are quite happy to have control of a plane at speeds under 50 mph, and have no incentive to go faster.

I suggest you visit slope flying places, and visit a place out on the prairie (no slope.) You'll find differences. You will notice a lot of people making no effort to reach high speed. You will also find people making a LOT of noise getting to speeds much less than 100 mph. To each his own.

Good luck,
Dave Olson

Lnewqban

It is similar to the flywheel principle, where a little amount of energy is accumulated in each rotation.
In each loop, the model absorbs the differential of energy between the rising stream of air next to the hill, and the slower stream far from the hill, as it accelerates.

Power flyers could do the same, getting energy from the wind, but the drag is higher and the results less spectacular.
Power fields are mainly flat, but still could do the trick by alternating flying low where the wind is slower and flying high where it is faster.

BMatthews

Larry, dynamic soaring is sort of like a kid in a swing being pushed by a parent with a sore arm. He can't push hard but the second push adds to the first, the third adds to the other two, etc, etc and pretty soon the kid is up where he's either yelling in high altitude glee or is yelling to slow down. Dynamic soaring involved the model circling around to where it can be pushed on again and again. Also the model is not seeing a steady wind. Instead it is using the wind shear caused by a wind break or back rotor and the pilot is timing it just right to catch the shear line where the wind speed suddenly increase to get this push. The first few times through the shear line the model isn't going all that fast at all. The videos you see about this are taken once the glider is up to speed for the most part.

Pure slope soaring high speed comes from the wind blowing up the hill to lift the model. The speed from that comes from ballasting the model and then putting it into a shallow dive so that the descent speed is no more than the updraft speed. But by that time the 30 mph upward speed and the effective 30 mph downward glide path equals a hellish forward speed with no apparent change in altitude.

Why can't power models do this at a regular flat field? Simple, the wind has niether an upward component or a shear effect to work with. Just a steady flat direction. So there's no way to work it so as to gain lift.

Actually there's accounts of smaller gliders dynamic soaring from the shear effect off a tree line. And I've personally slope soared off a tree line and seen it done on many occasions by others. But this requires a rather solid line of trees to do and only works over a small area that is fairly close to the trees. But in both cases the trees have formed the required wind effects. Without the wind being affected this way there's no soaring ability due to just the wind's velocity.

larrysogla

BMatthews,
Thanks for your reply. Of course we have heard or seen these land sailing buggies running in the dry lake beds of the west with no engines but able to go up to 40-50 mph on a 25 mph wind.....................so can we also take these wind side force and utilize it to sustain engineless flight? I see on the internet videos these model airplanes with flat sided fuselages that generate a side force effect for side manuevering....................can we also use this flat sided fuselages to generate side force from prevailing winds and create a sort of tacking motion as in land sailing and in sailboat sailing? Of course I have no engineering/aerodynamics degree so it is all conjecture...............but hey!!!! if the sailboat guys and the landsailing guys can do it on a horizontal side wind to create forward motion..................we airplane guys should be able to do it also provided we design a sail area on the fuselage. Yes.....No......Maybe?
larry

RosscoW

Larry,

I'm afraid there has been some flat-out wrong physics quoted here, and it has left you with some mis-conceptions.

An aircraft, once it is off the ground, cannot harness energy from a constant, horizontal wind. The reason yachts and land sailers can is becuse they interact BOTH with the wind and the land or water. A wind from the side produces a force i that direction, but is opposed by the drag of either the hull in the water, or the wheels on the ground. This in turn means that the air flows over the sail which can be turned into a force in the direction of motion.

An aircraft has no other medium to act against. If an aircraft encounters a side- wind, it simply accelerates in that direction and very quickly rreaches the speed of that wind. If an aircraft is flyinf forwards at 100MPH with a 30MPH side=wind, it's grond vector will be the result of 100mph in direction of flight and 30mph at right angles to that. There will be no airflow over aircraft from the side, and therefore nothing to convert into motin.

Slope soarers can maintain altitude and speed because of the slope!! The hill directs the wind VERTCALLY. No unpowered, heavier than air aircraft can maintain altitude unless it utilises a VERTICAL flow of air- in the case of slopesoarers, ridge lift. In the case of Thermal soarers, differential heating produces regions of less dense air that rise relative to the surface, and a glider can hitch a lift in these.

It is counter-intuative to model flyers, but the fact is the aircraft doesn't "Know" which way the wind is coming from, or even if there IS a wind. The aircraft interacts with the air. If that air is moving relative to the ground, it makes no difference to the aircrafts perforfance. It LOOKS like it does to us, because we are judging it's path relative to the ground, but the only thing the aircraft reacts to is the air moving over it.

RosscoW

Just an added note to say, the wrong physics DIDN'T come from BM!

HIS synopsis is basically the same as mine, just worded a little more accessibly!

larrysogla

RosscoW,
Thanks. I see now that there has to be resistance from the ground or the water to stop wind drift to produce a "tacking" motion on a landsail buggy or a sailboat.
larry

BMatthews

Exactly Larry,

I didn't want to mention it before because I thought it would cloud the issues.But IF, and this is a mighty big "if", you can sense sudden speed variations in the wind on highly turbulent daysyou can use those variations along with your airplane's inertia to gain energy the gusts. Watch gulls and other soaring birds and they will show that it can be done. Years ago I was out with a glider on a day that started fine and turned VERY stormy. Myself and one other were out in this mess because we were basically stubborn. For some reason the wind was extremely gusty with sudden shifts from moderate to gale force winds. I was able to play these dynamic increases and turn in a 20 minute flight that never got above the launch altitude. But this is a very unique situation and normally I would say it can't be done. It had its effect on me as well. I was totally nerve wrecked and drenched with sweat from the adrenaline involved in this rare experience. In fact it was well over 20 years ago but it still ranks as one of my all time biggest moments of my model flying. So IF you have a wind that is highly variable in both velocity and perhaps direction you CAN pluck some of the energy from the sudden increases. But it's nerve wracking, defies any reasonable ability to program how to use it and is not useful for actually getting from A to B since it involves a lot of back and forth crabbing in the wind with sudden turns into the wind when the model signals a sudden wind increase by usually trying to turn to downwind. When that happens you force the turn into the wind and ease back on the stick to use the sudden and highly temporary speed increase to climb to gain altitude. In effect this is the flat land version of what the shear line dynamic soaring pilots do but without the knowledge of exactly where the shear line is or when it'll be there.

But from steady or only slightly varying wind? Nope, can't be done unless you want to tie a string to the ground and use that for the second factor. We call those "kites".....

larrysogla

BMatthews and all the aerodynamics gurus,
.............If there is a STEADY 25 mph horizontal wind and the glider has a 20 mph take-off speed.................there should be a way to provide forward momentum and lift WITHOUT thermals, updrafts, uphill wind currents and other vertical winds.,,,,,,,,,,,,,,,,,given the advances in high lift/low drag airfoils, slab/flat sided fuselages with a sail area for side force manuevering, super lightweight radios, servos and airframe foam structural materials..
The elevator control surface is a drag inducing control surface when deployed for climbing/diving......so why not a glider with variable CG for climbing/diving manuevers without deploying drag inducing elevators. This will conserve what little energy was recovered from the 25 mph horizontal wind ............and then the resistance to wind drift so as to induce a "tacking motion" is the inertia of the airframe during climbing turns. Again the ailerons are drag inducing control surfaces when deployed for banking manuevers, so again a variable lateral balance design to induce banking without drag inducing ailerons should be the way to go.......again to conserve what little speed/energy recouped from the " tacking motion".
I am not into kit building so somebody else with kit building talents should be able to explore the possibility of engineless flight with no thermals or updrafts.......just a steady horizontal wind.
Of course..............we must remember what somebody said about crazy idealists............................."People who are crazy enough to think that they can change the world are the ones who actually do!".
God Bless, always
larry

topspeed

I think ( IMHO ) the slope soarers and sailplanes use pretty much same way wind energy as sail boats but in different direction.

Also the cleaniness of the sailplanes and large low drag lifting area contribute to the speed.

RosscoW

Larry,

The short answer is no, as you are still missing the basic physics of the situation.

Try it this way- If you towed a glider up to 25mph on a day with nil wind, would you expect any amount of advanced materials or aerofoils to allow it to remain airborne indefinatley without thermals or ridge lift? The answer is no as there is no way for the glider to extract energy from the air around it.

Now consider the same glider on a day with a wind of 25MPH. What is wind? It's movement of air relative to the ground. What effect does it have to an aircraft that is not ATTACHED to the ground? NONE! An aircraft above the ground has no interaction WITH the ground. It reacts to the air flowing over it's surfaces. It does not "feel" the fact that the air is moving over the ground.

You are still getting confused because you are ground based, feel the wind flowing past you, and assume you must be able to use that flow to power an aircraft. Imagine you are IN your glider, above a perfectly featurless fog bank, such that you can't detect you movement relative to the ground. how will you even know if or in what direction the wind is blowing? the fact is, relative to you and your glider, it ISN'T moving- and whether it is or is not ralative to the ground doesn't effect your glider at all.

Scar

My Feedback: (3)

And continues to "miss". I suspect a troll. He's just trying to see how many people he can get to waste time responding.
Dave Olson

larrysogla

RosscoW,
Yessssir, you are correct...............but allow me to pose another question....................if we have an airfoil with more lift than drag in a 25 mph horizontal wind......................will it climb while losing little of it's geographical position in a slight nose down position?......................thereby gaining altitude...............oh well I give up. My last post I hope................fighting windmills like that famous Don Quixote.
larry

RosscoW

Hmmm...

It does seem like you say I'm right, then pose a question which shows you didn't understand what I said.

I'll just state ot once more- The presence or absense of wind makes no difference to the aerodynamic performance of an aircraft not in contact with the ground.

BMatthews

Larry, what you'reasking above is just not possible. There is no magic airfoil that can glide uphill.Since all airfoils produce drag the wing has to generate someamount of forward force to achieve this. And to do so the airfoil has to constantly be in a very slight dive. Go to the followinglink and about 1/4 way down the page is a nice explanation with vector diagrams that shows why you can't glide uphillregardless of what the airfoil looks like. Your misconception is based on the idea that you can get lift without drag or MORE lift without more drag.But that is like perpetual motion or lifting yourself upby your ownbootstraps. When you divert the air hard enough to get the lift you're after you generate drag. The more diversion for more lift the more drag you generate. Modern full sizesailplanes are pretty good at getting quite close to a flat line glide but even the best of them is slowly coming down if they can't find some lift.

And it doesn't matter what wind the model is flying in be it 25 mph or 0 or even a 25 mph tailwind the airfoil will work the exact same since it will only see the airflow over the wing from the leading edge that the model is trimmed to glide at. The rest is just window dressing. Consider this situation to describe this point. A man is walking along the aisle of a railcar from front to back. To him he's walking at his normal speed. As they pass a station at a slow speed butwithout stopping it appears to folks on the platform that the man in the car is moving faster than the train. Similarly if he turns around to walk back he still sees the same walking speed and it takes the exact same time to return to his seat. But again from the rail platform it seems like he's passing slower than the train is moving. And just like the man on the train your model sees the same airspeed regardless of what the wind is doing around it.. The body of moving air the model is flying in is like the train and you're on the rail platform (the ground) watching both the windwith the model inside the moving air move past and seeingthis exact odd seeming behaviour. But it's not odd at all from the man's or the model's perspective. Both are reacting with their respective environments of the moment with no issues about what the "outside" world sees.

larrysogla

BMatthews,
Thanks......me thinks we can lay this post to rest.
larry

CloudyIFR

You may wish to take a heart mediction pill prior to watching this!

http://www.youtube.com/watch?v=WaQB16ZaNI4

Curtis
Montana
www.TailwindGliders.com