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Author Topic: NEW DYNAMIC SOARING RECORD 545mph  (Read 543 times)
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OZPAF
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« on: June 11, 2018, 10:44:36 PM »

As an interesting side light and a testimony to miniature aircraft design and piloting skill, Spenser Lisenby of the USA  has raised his previous Dynamic Soaring (DS) record to 545 mph. This was flown in winds of round 80mph - some gusts were recorded at 90mph, at 5,500ft at bird Springs Pass.

Although the recorded speed translates to an average Mach No of 0.73 this would not have been the top airspeed of the aircraft as for safety reasons the speed recording (with a custom radar gun) is taken as the plane comes back up the slope near the pilot generally and this is the slowest part of the circuit!

Also obviously there are areas along the chord of the wing where the airspeed is higher than the mean and thus the true max. Mach no is more than likely 0.8+

The aircraft is a custom designed and built glider of AR approx. 20:1 and uses specially developed transonic airfoils by one of Germany's top modelling aero engineers - Dirk Phlug. Stutgart Uni were also involved.

The high AR is required to most efficiently glean energy from the shear layer boundary at the top of the slope(the secret of DS) and the high taper of the modified elliptical wings is necessary to optimise strength of the spars. The aircraft is stressed for 100g+.

Truly an outstanding bit of flying and design.

Here is a link to the video of the flight - you won't see it in flight but you will hear it going through the shear layer.

https://www.youtube.com/watch?v=MoaWlKC3wIM

John
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« Reply #1 on: June 12, 2018, 06:32:08 AM »

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testimony to miniature aircraft design and piloting skill

You ain't kidding.  Strordinary spectacle John. I DL'd the video in 720p and you can clearly see the glider. I don't  have a clue what's happening. It somehow gains airspeed with each circuit - I'm happy with diving and zooming, slope soaring and wind gradient and boundary layer but can you explain how it gains impetus?

Stephen.
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« Reply #2 on: June 12, 2018, 11:23:05 AM »

Stephen, It's quite an amazing use of energy and is the mechanism used by the great wandering Albatross to fly long distances with next to no flapping of his wings.
The idea of applying it to slope soaring gliders was discovered by Joe Wurts another aero modelling aero engineer who was/is a top glider flyer - both thermal and slope.
I'll try to explain it as I understand it. The system of energy exchange relies on a hill or wave facing the oncoming wing with a sharp crest or ridge. It's this ridge and the sharpness which leads to the airflow breaking away from the hill instead of rolling down into the lee of the hill as would be likely to happen with a more rounded ridge. This separated stream of air is referred to as the shear layer as the air above it is at free stream velocity but the interesting thing is that the air under it for some distance is almost still. The shear layer slows as it loses energy and some distance down the lee side of hill it rolls back into the hill forming a rotor. The distance between the hill and the rotor is determined by the hill shape characteristics, including the height, sharpness of the ridge and of course the wind strength.
To use the energy the DS pilot takes of conventionally into the wind on the front side of the hill gains height and when ready dives down into the lee or back side of the hill. The object then is as you saw on the video to fly a circular course underneath the shear layer on the back of the hill and close to parallel to the back hill slope, turning at the bottom before reaching the powerful bottom rotor to coming back up the hill. On reaching the top , the pilot takes the plane through the shear layer in a vertical bank turning to go back down the hill.
It’s this crossing at the top where the transfer takes place and is similar to a yacht sailing into the wind as the aircraft sees a massive jump in freestream direction and speed and angle of attack which generates tremendous lift accelerating the plane which then goes into the still air on the lee side of the hill, and returns again to the ridge with very little loss(needs good piloting as well) to repeat the energy boost. It’s basically as I see it a matter of vector addition at the top which increases the lift vector and inclines it in the direction of flight – accelerating the plane, aided by min drag loss behind the hill. Providing the pilot can keep the model in the groove, the vector angles remain constant at the shear crossing providing acceleration at each crossing. The plane will continue to accelerate until it reaches an equilibrium speed where the energy used per lap is equal to the input at the crest from the shear layer crossing. The pilot may not be able to maintain the groove for this long however – it depends a lot on the design and of course the conditions and pilot skill.
The loads on the plane are enormous and the planes are quite heavy as they need high stalling speeds to be able to fly and land in these wind strengths. Spenser’s model is 3.3m WS and would possibly be ballasted to around to 8-9kg.No details yet but this is based on previous efforts. You’ll notice on the video that the flapped landing, using crow bakes is almost a hover in the 80+ winds at the crest, which would be close to the stall speed, as otherwise it would not sink.
The enthusiasts have been doing this for something like 30 years and while it started in America there is now strong support in England, Germany, Australia and New Zealand with many of these enthusiasts designing and building their own models.
Spenser is producing limited versions of his “Kinetic” models (not this one yet) and is a very serious, practical innovator with a strong theory approach to the subject and has been doing it for over 20years.
The models need special care in setting up the controls to handle the high speeds – particularly to avoid flutter on the control surfaces. The flaps particularly have linkages designed to provide over centre locking when in the up position. All the surfaces are controlled by good quality digital servos and the surfaces are fitted with longer control horns to eliminate the effects of any slop as far as possible with servo arms being sized to provide full servo movement for the required surface deflection. All the wing servo arms have additional outrigger bearings to complement those in the servo itself.
Finally here is a link to a presentation by Spenser himself. I prefer the Vector explanation I have used which is basically that of Mathieu Scherrer to Spenser’s airmass/ground speed explanation.
http://events.techcast.com/bigtechday10/Sydney-1345/?q=Sydney-1345.
Hope this is interesting.
John
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Konrad
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« Reply #3 on: June 12, 2018, 11:46:39 AM »

Great talk! I find that the You Tube link loads faster.
https://www.youtube.com/watch?v=nv7-YM4wno8

While I do DS I can tell you 200 mph is more than enough for me. Still haven't reach that speed. After listening to his talk I may re-evaluate my DS models and set ups. I really like the idea of mass dampening.  My models from the turn of the millennium, are way out of date!

All the best,
Konrad
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« Reply #4 on: June 12, 2018, 01:36:53 PM »

Thanks John and for the quick link Konrad. As soon as I read 'rotor' I was halfway there. I'd thought of that but the camera angle in the vid made me think they were operating right at the front edge of a big ridge. Another viewing after reading your post makes it look as if they're dipping right into the lee side of a small hillock. To get more than halfway there, I'll have to read your post again and then look at the YouTube presentation (55 min) when I've time.

Stephen.
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strat-o
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« Reply #5 on: June 12, 2018, 01:52:05 PM »

This reminds me of something I read about where, if a wind is blowing, you can fly a control-line glider.  Half of the flight is flown level but as you approach downwind, you pitch up and go nearly vertical, then as you approach upwind you dive down back to level flight.  It sounds like nearly identical forces are at play.  The control lines create an artificial windshear.  Interesting stuff.

Marlin
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« Reply #6 on: June 12, 2018, 07:22:44 PM »

     Very interesting topic and videos, this Dynamic Soaring Category.
This reminds me of a guy I knew who researched Golden Eagles.  He found the migration corridor, where there was a narrowing canyon at the end of some mountains, where the narrow was the cliffs of the neck of a gap of a pass.  The Eagles were going south in the Fall,  and they were shooting through, one at a time, downwind,   ( wind blows a lot faster through a restriction ),  with wings almost tucked in, just folded out a little bit.    They measured the speed at over  200 mph.    Peregrine falcons can "stoop" dive at speeds 200 mph (  320 km/  ).
     But those Eagles were just shooting through ( not diving ) at 200  mph.
A  couple of pics of the Mongolian Eagle Hunters  (Falconers or Austringers).   And a couple of Dynamic Soaring Gliders.
In the Diagram below:

MEER   =    SEA
WILNDSTILLE   =    CALM
BERGRUKEN   =    ?
TRENNSCHICH   =     TRANSITION LAYER 
                                   the WHITE SHEAR LAYER in the pic
OPTIMALE FLUGBAUN      =      TRAJECTORY

Man, can those gliders ever go fast !!!!!

LASTWOODSMAN
Richard
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« Reply #7 on: June 12, 2018, 09:05:49 PM »

Stephen although the rotor defining the end of the quiet zone is also sometimes used to gain speed to come back up the rear of the hill - it is the shear layer crossing at the top that appears to provide the major input of energy. The rotor is very turbulent and if the model overshoots and goes to far into it then it is likely to be rolled into the hill.

From what I understand once the speed has reached a certain level - it is no longer necessary to use the bottom rotor.

Mark Drela has come up with a programme to select optimum weights, orbit diameters etc for the plane for various wind strengths and Spenser uses this and I believe refers to it in his presentation.

Marlin - yes that is a similar and utilizes the wind gradient and also the boundary layer at ground level. It would be most noticeable I imagine on  windy day in open country.

Interesting comments Richard - birds discovered it long ago - the great wandering albatross is a master - I believe it sleeps on the wing!

Thanks for the better link Lincoln.

There is a fair bit of discussion on the web for anyone interested in finding out more.

I have attached a multiple exposure of a glider in a DS orbit in Australia (Newcastle)

John
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« Reply #8 on: June 13, 2018, 04:25:59 AM »

The key to dynamic soaring is the shear layer. Think of this like an eddy line in a river - on one side there is moving air (above in the airflow of the wind) and the other still air (below and behind the hill.) As John has described you need the right topography for this to form on the downwind side of the ridge (not on the front face as with conventional slope soaring.)

If you cross the shear layer in the right direction the model gains energy. When flying from the still air up into oncoming breeze, the model experiences an increase in airspeed. Flying downwind and back down into the still air also gives an increase in airspeed. By the way the reverse is true - fly through the shear layer the wrong way and you get a big reduction of airspeed, which may cause you to stall. This is why wind shear can be a problem for full size aircraft as they descend (upwind) into slower moving air (wind gradient) on approach and landing.

The circles flown by DS models are half in the still air and half in the main wind flow, crossing the shear layer twice in each circuit and gaining energy each time. In theory there is no limit to the energy gained, but at some point the drag of the airframe, engineering challenges, pilot skill and conditions (and presumably mach number!?) start to provide an upper limit.
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« Reply #9 on: June 13, 2018, 10:34:29 AM »

How far can pilot skill  and reflexes take it I wonder? 
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« Reply #10 on: June 13, 2018, 01:22:11 PM »

Cognitive human reaction time is about 0.45sec. It now seems that at the current speeds this is the limiting factor. Augmented stabilization will allow for higher speeds. But then we need to start to ask where is the line between radio control and autonomous flight. 

If this is not a concern then there are no theoretical reasons, than I'm aware of, that the speed of sound couldn't be reached.
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« Reply #11 on: June 13, 2018, 01:38:07 PM »

Cognitive human reaction time is about 0.45sec.  ......

Is it still 0.45 seconds if there's a rhythm and flow to the events? The pilot's inputs are, I assume, sensibly cyclic.

Wing sweep will presumably become necessary as the transonic drag rise takes effect....
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« Reply #12 on: June 13, 2018, 01:45:41 PM »

Yes, most humans are limited to this 0.45 reaction timing for cognitive reaction time. This isn't to say that we can't move faster from outside influences. But if having to make a decision as to which way to make a correction (movement) 0.45 sec is about the limit.

I recall Spencer covered this a bit in his talk.
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« Reply #13 on: June 13, 2018, 04:36:56 PM »

 Bergruken with an umlaut over the u is Mountain ridge per Google translate..
Hugh
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« Reply #14 on: June 13, 2018, 09:13:18 PM »

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Is it still 0.45 seconds if there's a rhythm and flow to the events? The pilot's inputs are, I assume, sensibly cyclic.
I think rhythm has a lot to do with the control of the plane under normal circumstances and it is a learned response from the hours of flying these fellows have done.
However turbulence can always be unpredictable - especially at the bottom turn, due to slight changes in wind strength and direction which would then seem to need a considered response. However there is also a bit of learned awareness associated with this as well and thus the response could be faster than expected.
Flying F3B, F3F and pylon racing to a degree have similar issues - but not as extreme.

Quote
Wing sweep will presumably become necessary as the transonic drag rise takes effect
Spenser has a fair bit to say about the problems of transonic flight in the presentation mentioned earlier. He had tried sweep before his current design but decided it did not offer enough advantages.

It's interesting to note that the design speed of the current Transonic DP130 is 575mph and he is already close to that.

John
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« Reply #15 on: June 13, 2018, 09:45:13 PM »

Speed limit keeps going up  Good on them.
Only takeaway is that the pilot (s?) are Not ...Geezers.. are they ?
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« Reply #16 on: June 14, 2018, 09:13:19 AM »

Ah! -  not that I know of Fred.  Smiley

Spenser is probably closer to 40 but there are some slightly older flyers. It's mainly a young man's game as it takes a fair bit of energy to take part and a great amount of perseverance and determination.

John
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« Reply #17 on: June 14, 2018, 09:31:08 AM »

Spenser Lisenby has just put in a post on RCGroups of the new Record flight. It indicates how skilful and determined you need to be

Quote
I've been meaning to do a little write up on the day but have been a little too busy.

 So as most of you know, this is pretty late in the season for Socal to get good winds. So when I saw the forecast,
 I figured I needed to make it happen since it might be the last decent day of the year. I met Bruce, Alan (and his friend Wally),
 and Josh at Weldon and the wind was really good. We had average in upper 30s - low 40s and a max gust of 51mph (more than forecasted).
 Our top speed was 456mph with the Transonic DP and Bruce got 227mph with his RT-30 (within 1mph of his best). We had been watching the BSP sensor all day but even by 4:30, it still hadn't quite broken the threshold for being good enough
 to make us leave Weldon. When the 5:30 reading came up with gusts to 75, we quickly packed up and hit the road.

 We didn't even check the windspeed upon arriving, I just heard alot of wind and decided to put the heavy Transonic together.
 Bruce ran on up with his JW48 to see how the air was. Josh, Alan, and Wally were still en route. Bruce had already flown a few minutes by the time I hiked up and it was clearly cranking.
 I gunned him for a bit and got a 210mph reading but I could tell he was fighting the turbulence. Soon he started having more and more trouble
 sticking the line and it became aparent something wasn't right with the plane. After a few more circuits, the poor JW taco'd mid air and came down softly
 by the road. We threw out the Transonic and got right into it. I had forgotten to charge the Gopro so when I put it on, it only showed 14% battery. Luckily my whole flight
 was under 7 minutes and it captured everything.

 On diving in, I could tell the power was there but alot of the early laps were sort of 'safety' laps, trying to figure out where the power was and how the backside was acting.
 Even without digging early, the speeds got up into the mid 400s. Thats when I started to get the hang of the turbulence and felt ready to stick the line a little better.
 I did get a couple strong suckdowns, one of which had me worried, but the plane behaved well and was able to get back on track. Getting a good line on the gun was tricky because of the
 constant fluctuation between bounce-out and suck-down on the bottom turn. After getting some good laps in, but not aimed well at the gun, the speed climbed quickly. You can seen in the video that the 545 seems to come out of nowhere
 but that was just because the previous laps weren't lined up well with the gun. The Transonic was really flying well and making some of the coolest thunder I've ever heard! I was really impressed
 sense of huge power being unleahed... Afer a nice string of 500+ laps, Bruce heard something that sounded different. I was pretty happy with things so I decided to land to check it out
 After landing we found the left middle flap surface was totally stuck in a slightly reflexed position with stripped/jammed servo gears. On this early model, I didn't have the spar, drag spar, and servo recess locations coordinated well enough
 and had to use the 10mm HV6130 instead of the HV747 I intended for that spot. All subsequent models have things correct and use the HV747 there. After studying it a bit, I think I'll be able remove the little guy and shoehorn in the HV747. I was
 really just glad to have landed the model safely after such an adrenaline filled flight. All I can say is that the Transonic DP flew GREAT! It never showed any signs of stress and always went right where I pointed it. I couldn't be happier.
 If I had been able to continue flying and the conditions held up, I would be suprised if we couldn't get readings over 550. I just can't wait to get another chance to try for more speed...

 Alan went up next with his K2mDP and found a really turbulent backside even with the stability system. It was so bad, he almost didn't make it back from the initial dive-in. A testament to how quickly conditions can change. Despite the turbulence,
 Alan managed to get a 498mph airspeed before he decided to land. Not bad for a 2m ;o)

 Next up was Bruce with the RT30. It looked like it was a real handful in the big rough air but he was flying it hard and managed 218mph. Bruce then threw out the Orbit wanting to get a 400+mph speed. He had installed stoppers on the root of the flaps
 to prevent flutter but still got a very tight flutter on 2 different laps at a top speed of 371mph. Not 100% sure what surface was doing it but my guess would still be the flaps with the outboard end doing most of the movement. Bruce wanted to give the Stormchaser
 a go but decided to call it a day. With the rocks and barbed wire fence, the landing at BSP isn't really well suited for setting down a heavy plank.

 All in all it was a day of flying I won't soon forget. Thanks Bruce, Alan, Josh, and Wally for all of the help, thoughts, camaraderie, and an all around awesome day in the wind!

 Ian, I tend to sell my gun and update every few years so my current gun is only a few months old. I'm really happy as it seems to perform very well! There's nothing special about the plane to help with RCS. As mentioned above, factor in that Bruce seems to be good at most things he does (including radar).

There were a few questions raised about the accuracy of the radar gunning and that's the reason for the reference to the radar gun and operator.

John
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