Comparison of glider classes at Uvalde...

[Steve Koerner]

Considering only the 12 competition days that all three classes were scored...

The average winning speed in 18m class was 148.9kph (92.5mph).

In 15m, the average winner was 4.6% slower than 18m at 142.0kph (88.2mph).

Open class winner was 0.8% faster than 18m on average at 150.1kph (93.3mph).

Isn't it interesting that all of that new technology in open class had so little actual benefit in the final analysis?

[Tim Taylor]

But how do the prices of the gliders compare? We are pricing the
majority of pilots out of the market for a minor gain in performance.

[Dave Nadler]

On Monday, August 20, 2012 10:34:29 AM UTC-4, Steve Koerner wrote:
> Isn't it interesting that all of that new technology in open
> class had so little actual benefit in the final analysis?

Careful, longer wing classes had generally longer
tasks, and longer tasks mean lower speeds.
So, the span benefit is understated in your analysis.

In all classes, higher wing-loadings have really paid
in Uvalde weather. And newer gliders carry higher
wing-loadings MUCH better even in weak weather.

Best Regards, Dave

[Steve Koerner]

Dave - You're right that open class flew further but not by a lot: 575km averaged over the 12 days vs 534km in 18m class. Parity time-on-task would have the open class going 538km to the 18m 534km; the additional 37km puts them out 14.8 minutes longer. I'll agree that there would be a small effect from the open class having to bracket a longer soaring day; but the 15 minutes addition is not enough to make much difference and does not alter my own conclusion on the matter.

[John Cochrane]

The real advantage of open class is not in booming weather, it's when
the weather gets weak and a 60:1 glide takes you over fields full of
landed-out 15 meter gliders. Bigger gliders also can carry motors and
still get light wingloadings when times get tough. The amazing part of
flying in Uvalde is no 2 knot days.

Anyway, "we" aren't pricing pilots out of anything. The manufacturers
have made available a wide variety of contest worthy gliders, from the
PW5, to standard, 15, 18, duo, and open. You can buy fly and compete
at the world level in any of these you'd like. The interesting fact is
that pilots are voting with their wallets for the very best, despite
astronomical cost. PW5 class died from lack of interest, and no new
standard or 15 meter gliders are being produced. This is entirely by
the choice of pilots, not some amorphous "we" behind the scenes.

John Cochrane

[Bob Kuykendall]

On Aug 20, 9:27 am, John Cochrane <john.cochr...@chicagobooth.edu>
wrote:

> ...no new standard or 15 meter gliders are being produced...

Careful there, John, or we'll have to start debating the semantic fine
points of "are" and "produced." In the sense of established
manufacturers, I imagine that that's true. But it bears noting that
amateur builders, taken as a whole, are currently the single greatest
contributor to the US general aviation fleet. So even though
relatively few general aviation airplanes are being "produced" these
days, a heckuva lot of them are popping out of garages and entering
the US fleet. I happen think it is within the realm of possibility to
bring some of that enthusiasm and resourcefulness to bear on soaring
as well as powered flight.

> This is entirely by the choice of pilots, not some amorphous
> "we" behind the scenes.

No disagreement there. One of the primary lessons of the PW5 (for me,
at least) is that it costs about the same to make a pretty glider as
it does to make a not-so-pretty one. One of the other lessons is that
the technologies for making carbon fiber wing spars cost-effectively
are now very mature, and consequently the incremental cost
differential between 13m and 15m has gotten pretty small. It's as if
15m is the new 13m. The differential between 15m and 18m has also
gotten smaller, but is still substantial. The differential between 18m
and 28m is still astronomical, and plays to an audience that is very
picky, so I am grateful I don't play that house.

Thanks, Bob K.
https://www.facebook.com/pages/HP-24-Sailplane-Project/200931354951

[anderson....@gmail.com]

On Monday, August 20, 2012 9:27:12 AM UTC-7, John Cochrane wrote:

Anyway, "we" aren't pricing pilots out of anything. The manufacturers have made available a wide variety of contest worthy gliders, from the PW5, to standard, 15, 18, duo, and open. You can buy fly and compete at the world level in any of these you'd like. The interesting fact is that pilots are voting with their wallets for the very best, despite astronomical cost. PW5 class died from lack of interest, and no new standard or 15 meter gliders are being produced. This is entirely by the choice of pilots, not some amorphous "we" behind the scenes.

John Cochrane

____________________________

In a replacement market where the rate of performance improvement within a fixed span envelope has slowed considerably (you can be very competitive in a 15-year old 15M glider), it's not too surprising that the market for new production is limited. Given that dynamic it's also not too surprising that much of the development and new sales would be in larger spans that can also accomodate motors. It's not so much in my view that pilots want only "the very best", but that the "very best" product categories are ones where there isn't a big resale market yet. 15M is still a bigger market than Open or 18M if you look at it from the perspective of installed base of ships, contest participation, OLC miles, etc. You just don't need to buy new to get into it and if the market isn't growing overall, you don't need a lot of production.

[John Cochrane]

Hear here! Let the 15 meter two-design class live long and prosper!
(ASW27 owner)
John Cochrane

[anderson....@gmail.com]

On Monday, August 20, 2012 5:06:48 PM UTC-7, John Cochrane wrote:

> Hear here! Let the 15 meter two-design class live long and prosper!
>
> (ASW27 owner)
>
> John Cochrane

I don't begrudge the sailplane OEMs the urge to create markets to drive some revenues - I'd hate to see what a new -27B would cost without people buying new -31s and -29s in volume to cover the fixed costs of the business. In a climate where taxing the rich has gotten to be so in vogue here's a situation where the richer folks kinda volunteer to subsidize the rest of the market a bit. Thanks!

9B (another 27 owner)

[Darryl Ramm]

Huh? Subsidizing what market? Is here a market for new ASW-27 AFAIK. Yes they are still on Schleichers web site, but 1. can you still order one and 2. if so how many are being ordered, and 3. At what cost--compered to an ASG-29/15 and ASG-29/18?

With the slightly higher-performance ASG-29/15 available I could only imagine Schleicher keeping around the ASW-27 if there was significant reduced build cost, production capacity to build those gliders and a market willing to buy them new.

What I suspect may be more relevant for terms of making 15m class racers affordable is not existing design 15m gliders being manufacture, but rather new variants like the ASG-29/15 which helps suppress used prices of ASW-27.

The ASW-27 and ASG-29 gliders use basically the same fuselage, the wing in the '29 will be more expensive to manufacture because its multi-part wing and just more complex and a bit stronger, but once tooled up I'd be surprised if the cost to manufacture difference is really that significant (within say a $100k-$150k delivered price range, who cares about another $10k (guessing) higher base price if that gives you the option to also purchase 18m tips.

Once the tooling/moulds are produced they are sunk costs, unless there are other reasons you might as well use the new moulds vs. the old ones. I could imagine production reason for a manufacture to want to push older models if the in-mould work time and mould capacity is is the long tent pole for manufacturing, but with so much finishing and hand work involved in a glider construction my gut field is the moulding/tooling time may not be the main production limit -- anybody have a practical feel for this? And even if it is there a new model in class just basically kills demand of the older model, partially because a manufacturer can't lower the price low-enough to be compelling (esp. vs. a now depressed used market price because the new-toy just created increased supply of the old-toy in the used market).

If there was enough margin, a elastic price/performance demand curve and manufacturers with sufficient production resources then a manufacturer could keep manufacturing an old generation product at an lower price point, but I just don't see that happening. I suspect the manufacturers operate much more in a mode where "this is our latest toy" and orders fill up very fast and the factory goes ape-shit crazy trying to crank out as many of those models as possible--especially for fear of long order lead times killing new orders and to support getting as many glides in the hands of top (and middling racers) to ensure lots of wins for the design. And their competition is all doing the same. And I bet the top manufactures are extremely focused on the very leading edge, especially caring about 18m and now open class race results (e.g. ASG-29 vs. JS1-C, JS1-C vs. SH Quintus, etc -- notice how Jonkers, a small manufacturer, have very effectively positioned themselves in both the key 18m and open class mind-share races here).

The evolution of the 18m vs. 15m class has obviously been a boon for manufactures able to keep up. Now the next effort seems to be modest-open class, gliders that have a hope or running at high wing loadings and flying fast on strong days. I love this stuff even if I may not ever own one. There was a lot to be said for the ASG-29 with 15m and 18m wings, but now the 18m/21m/23m options must look pretty compelling for lots of purchasers. It seems weekly I hear of another JS-1C order....


Darryl

[Brad]

In a climate where taxing the rich has gotten to be so in vogue here's
a situation where the richer folks kinda volunteer to subsidize the
rest of the market a bit. Thanks!
>
> 9B  (another 27 owner)

my heart goes out to those overtaxed rich folks...............anything
I can do to help?

Brad

[Darryl Ramm]

Yep, ofter Andy $50k for his old, tired, ASW-27b....

Darryl

[Brad]

actually, my Tetra is probably just a few points under that
27b..................and I have the distinct honor of being the
builder!

Brad

[Darryl Ramm]

Well demonstrate its performance (and significantly better cost/performance - depends I suspect on how you value personal time/effort ?) vs. an ASW-27 in a few contests and you will be helping the ongoing success of 15m gliders by further deflating the used market price of ASW-27.

Darryl

[Brad]

Darryl,

Bob is planning on finishing up the one he is working on a getting it
into the hands of someone who can make a good comp showing. The really
time consuming part, at least from a kit building perspective will be
the painting and finishing, as far as putting a kit together, it
should take a few hundred hours...............not the 5+ years it took
us to build the Tetra from barrels of resin and rolls of carbon.

My experience has shown it climbs with and has out-climbed several
modern ships, and I'm a crappy pilot!

Brad

[Tim Taylor]

On Aug 20, 10:27 am, John Cochrane <john.cochr...@chicagobooth.edu>
wrote:

John,

I think the variable you are missing in the current purchasing
behavior is uncertainty. I am not sure if it is implicit or explicit
but the IGC has left the Standard and 15M class with an unknown
future. It was assumed that one of the classes would be phased out
with the creation of the 18M class. Without a clear plan why would
anyone buy a new glider for a class that you are not sure will exist
in a few years.

If the IGC would clearly define the future for the classes then both
the manufactures and potential customers could decide to support new
gliders specifically designed for the classes. Right now the only
sure class is the 18M so that is what is being built. The next
generation of 15M specific glider would be under 500 pounds empty (the
Duck Hawk has already shown that) if there was a clear statement that
the class will still exist.

Tim

[anderson....@gmail.com]

On Monday, August 20, 2012 6:20:47 PM UTC-7, Darryl Ramm wrote:
Huh? Subsidizing what market? Is here a market for new ASW-27 AFAIK. Yes they are still on Schleichers web site, but 1. can you still order one and 2. if so how many are being ordered, and 3. At what cost--compered to an ASG-29/15 and ASG-29/18?

Darryl

Last I checked the longer span ships cost up to 2.5x what the span-limited ships do (be that a -29/15 or a -27). and if I look at the pricing versus what the incremental materials and labor likely are it would appear that they are higher gross margin and therefore are covering a lot more of the fixed costs of the overall operation. Some of the pressure on older designs/classes may be an large resale market that keeps the price down. In any event, without the new more expensive models and the slightly less elastic demand for them I would worry what it would cost to allocate the OEM's fixed costs over small volumes for only a replacement market that carries lower margins to start with. I may not have every detail precisely right, but that was what I was thinking.

9B

[tommy...@gmail.com]

The evidence is really undeniable. What has been driving the 18m and open class, is the perception that the bigger spanned classes are far superior than what they in fact are.

The 15m other sailplane builders still have no answer to the Diana-2. Maybe the Duckhawk is an answer - we'll see. Diana-2 has sold poorly IMHO, because of perception.

Maybe we should replace wingspan with wing aspect ratio, when looking at the layout. The Diana-2 and now the Duckhawk, for me, seem to indicate that this is the more important metric. In these two designs, the low weight is used advantageously in an aerodynamic sense to produce a larger aspect ration wing with a smaller wing areas, than would otherwise be practical.

Wing profiles today, show little differences from one to the other.

In the analysis, it should be noted, that the EB29 can be flown in a 25.3M configuration, reaching about 58kg/m wing loading.

On paper the larger ships should have been faster, but they're not. So we are not taking everything into consideration.

Speculating here, does it take longer to accelerate a long spanned ship, due to the higher profile drag, through sink or upon thermal exit? If so, they would be flying slower than the smaller ships through sink.

[Paul Remde]

One point that I think has been missed is that I believe the open class was
tasked with longer tasks than the other classes during the WGC. That would
make their final glide a smaller percentage of their entire flight - which
would make their overall speed a bit slower that it would be if they flew
the same length tasks that the 15m and 18m ships flew.

Also, I image the difference in speeds would be greater at a soaring site
with weaker lift than found in Uvalde. The 21m and 23m ships and their high
wing loadings seem tailor made to Uvalde's very strong soaring conditions.

Paul Remde

[Tom Vallarino]

In the recent edition of AeroKurier, there is an article describing the increasing flight path length associated with a stronger variation of the speed in an ASW-27.

From memory, in the example they gave, increasing the speed from 160KM/h to 180KM/H just through the modeled sink area, increases the flight path by up to 4%. But it is still faster over the horizontal distance, as 180 is the optimal speed for that example.

I assume the same is true in lift (increased flight path due to pull up).

This gets me thinking that in order to vary the speed of a heavier ship, which zooms up 300feet on pull up, that this increases the total flight path over that of a lighter ship which zooms up less and slows down faster.

I have a hunch the higher profile drag requires a stronger push over, over that of a shorter spanned plane, increasing the flight path due to this or causing a slower speed gain.

It would be interesting to compare the effects of 1) longer flight paths,or 2) less speed changes, or 3) slower speed changes - of heavy, long winged ships to a baseline ASW-27.

[Peter F]

Except heavier gliders don't pull up any further than light ones.
(From the same speed)

Otherwise your total energy vario wouldn't work

PF

At 18:01 22 August 2012, Tom Vallarino wrote:
>

>This gets me thinking that in order to vary the speed of a heavier ship,
which zooms up 300feet on pull up, that this increases the total flight
path over that of a lighter ship which zooms up less and slows down

faster.=20
>

[Andy]

On Thursday, August 23, 2012 1:39:37 AM UTC-7, Peter F wrote:
> Except heavier gliders don't pull up any further than light ones.

If both gliders have the same sink rate at the time the pull up is initiated, and if the transition is lossless, then that would be true. However, neither of those conditions is true.

GY

[Peter F]

OK,

So it starts off as a nice day, you're happily dolphining along in your
Discus / Ventus / Nimbus 4 / Quintus (delete as appropriate) full of water
and your TE system is sorted so that pullups don't upset it.

The weather turns to worms so you get low & have to dump water.

You climb away and the weather cycles, so you go back to happily dolphining
along.

Does

1) Your total energy stop working

2) Your vario system that has no idea about the water ballast system
magically works out that something has changed

or

3) Pullups trade Kinetic Energy for Potential Energy and the mass terms
cancel. If you're pulling up from the same speed to the same speed you'll
pull up the same amount. The time taken for the pullup is just a few
seconds so any difference in sink rate at the beginning of the pullup
results in a trivial difference in height gained. (And the light glider can
pull up to a lower speed than the heavy one so will gain benefit there).

TE system doesn't need to know that the ballast has changed 'cos it isn't
affected

PF

[tommy...@gmail.com]

An open class plane has more drag than a modern 15m. Yes, it also has more lift, but lift is irrelevant when trying to use gravity to speed up. Therefore, a larger or draggier plane will accelerate slower.

An open class ship is also heavier, so it slows down slower than a 15m.

The only way to modulate the speed of an open class like a 15m, is to vary the altitude more (dynamic flight) than that of a 15m. This is often seen as a good thing - but it's not. The more dynamic the flight path, the longer the total flight path becomes.

In general, it is harder to vary speeds in larger and heavier gliders. Consequently, they are probably flown at less optimal speeds, than smaller/lighter gliders, and they total flight path length of the larger ones is probably longer over the same horizontal distance, since their dynamic path is more extreme.

As to pull up height: Weight makes a difference as kinetic energy is a function of mass, the higher the mass, the larger the kinetic energy at a given speed. An insect traveling at 100 knots has much lower kinetic energy than a B747 at 100 knots. In other words, it takes more energy to accelerate a B747 to 100 knots than it does to accelerate an insect to 100 knots.

[Dan Marotta]

I have two things to add to this discussion:

First, most of us, when we dump our water, will update the
variometer/computer with that information. This tells the system to change
the speed command for a given MacCready setting.

Second, let's not forget that the kinetic energy of a body in motion
(glider) is equal to one half the mass times the velocity squared. That
means that the heaver glider (water) will be traveling faster (dolphin) so
the conversion from kinetic energy (velocity) to potential energy (altitude)
will be higher.

I hope I said that clearly...


<tommy...@gmail.com> wrote in message
news:9fa32af7-e0b1-4ca9...@googlegroups.com...

[tommy...@gmail.com]

Yes Dan, but even from the same start speed, a heavy glider will climb higher than a lighter one of identical design, when slowing down to a slower target speed - or it will take longer and travel a greater horizontal distance to do so - or both. In other words it will have a more dynamic flight path, unless the pilot chooses to modulate less and keep the speed more constant, regardless of the changing air masses. In the latter case, the plane will fly less optimally than one able to modulate better.

Perhaps these disadvantages are more significant than thought.

In response to Steve's observation that the open class gliders were only marginally faster than 18m and even 15m, I think it is good to have a discussion as to the reason for this.

[Dan Marotta]

I guess I wasn't clear enough. You're correct that given the same start
speed, the heavier glider will climb higher: 1/2mv**2.


<tommy...@gmail.com> wrote in message
news:17e788af-fc32-4611...@googlegroups.com...

[Jan]

When the basic equations of physics are questioned they should be tested by real experimental data.

Having recently worked on the compensation of the vario in my Ventus 2, I just happen to have such data. Several pull ups from 180 km/t to 95 km/t were recorded by the igc-logger (and on film).

Theory first (in SI units):

Potential energy: m * g * h
(m: mass, g: acceleration due to gravity - about 9.8 m/s^2, h: altitude)

Kinetic energy: ½ * m * v^2
(v: speed)

As a result, the theoretical lossless altitude gain by a pull up is:

dh_theory = ½ * (v_start^2-v_final^2) / g

This equation does not depend on the mass of the glider !

Experimental data:

24 pull ups from three different days in relatively calm air.
Average start speed: v_start = 49.8 m/s ± 0.4 m/s
Average final speed: v_final = 26.3 m/s ± 0.7 m/s
Average altitude gain: dh = 90 m ± 3 m

Using the equation above and the average start and final speeds, I find the theoretical altitude gain to be: dh_theory = 91 m ± 4 m

Actually, I was a little surprised to see such a close agreement.

No variation between days or direction of flight is seen (i.e. correct wind correction). The duration of the pull ups is 10 seconds. The quoted uncertainties are the statistical standard error of the average. Further analysis shows that the uncertainties on dH and dH_theory are highly correlated. I could think of several potential error sources but have not investigated their influence.

The mass of the Ventus 2? Well, it doesn’t matter…

Jan

PS! The mass-independent conversion from speed to altitude was actually given as an example in my school physics book when I was 14 years old. At that time I questioned the physics book due to the general (incorrect) understanding of this topic among glider pilots.

[Steve Thompson]

While I agree that the height gain on a pull up is not in principle
dependent on glider mass - being simply an exchange between two forms of
energy less some drag, maybe there is a real difference for the heavier
glider..

I suggest that the heavier glider will probably normally have a greater
initial speed - and thus the G for the pull up can be maintained for a
longer time, albeit small. I think it is the G which is the key thing
here, since it multiplies the effect of the lift. Hard to believe but
apparently true for positive and less practically for negative G...
Reference:- F.G.Irving, the Paths of Soaring Flight, pp86-88, a good
bedtime read.

At 10:07 25 August 2012, Jan wrote:
>When the basic equations of physics are questioned they should be tested

>by=

> real experimental data.
>
>Having recently worked on the compensation of the vario in my Ventus 2, I

>j=

>ust happen to have such data. Several pull ups from 180 km/t to 95 km/t

>wer=

>e recorded by the igc-logger (and on film).
>
>Theory first (in SI units):
>

>Potential energy: m * g * h =20

>(m: mass, g: acceleration due to gravity - about 9.8 m/s^2, h: altitude)
>

>Kinetic energy: =BD * m * v^2 =20

>(v: speed)
>
>As a result, the theoretical lossless altitude gain by a pull up is:
>

>dh_theory =3D =BD * (v_start^2-v_final^2) / g

>
>This equation does not depend on the mass of the glider !
>
>Experimental data:
>

>24 pull ups from three different days in relatively calm air.=20
>Average start speed: v_start =3D 49.8 m/s =B1 0.4 m/s
>Average final speed: v_final =3D 26.3 m/s =B1 0.7 m/s
>Average altitude gain: dh =3D 90 m =B1 3 m

>
>Using the equation above and the average start and final speeds, I find

>the=
> theoretical altitude gain to be: dh_theory =3D 91 m =B1 4 m

>
>Actually, I was a little surprised to see such a close agreement.
>
>No variation between days or direction of flight is seen (i.e. correct

>wind=

> correction). The duration of the pull ups is 10 seconds. The quoted

>uncert=

>ainties are the statistical standard error of the average. Further

>analysis=

> shows that the uncertainties on dH and dH_theory are highly correlated.
I

>=

>could think of several potential error sources but have not investigated

>th=
>eir influence.
>
>The mass of the Ventus 2? Well, it doesn=92t matter=85

>
>Jan
>
>PS! The mass-independent conversion from speed to altitude was actually

>giv=

>en as an example in my school physics book when I was 14 years old. At

>that=

> time I questioned the physics book due to the general (incorrect)

>understa=

[Dan Marotta]

Your analyses are great! I'd been thinking about dH and it's clear that the
mass falls out of the equations, however, the heavier glider will most
likely be flying faster which is, I think, the error most of us, myself
included, make. Given the same entry and exit speeds, the altitude gain
should be the same.

Thanks for the clarification.


"Steve Thompson" <twin...@gmail.com> wrote in message
news:5038be43$0$15656$a826...@newsreader.readnews.com...

[kirk.stant]

What is the optimum G for the pullup?

Or is it more a matter of pulling to ClMax - so an AOA gauge is really needed?

Let's say a generic 15 meter flapped ship, at 8psf and 145 knots - my gut feel is about a 3 g pull while simultaneously setting some flap (0 or +5) is close to optimum. Pull to about 40 degrees nose up, ease off to 1 g, then roll off to let the nose drop to level (no bunt).

How do the rest of you do it?

Kirk
66

[Tom Claffey]

Not like that.
If crosscountry speed is your aim reduce the pushing and pulling.
Tom

At 00:57 26 August 2012, kirk.stant wrote:
>What is the optimum G for the pullup?
>
>Or is it more a matter of pulling to ClMax - so an AOA gauge is really

>need=

>ed?
>
>Let's say a generic 15 meter flapped ship, at 8psf and 145 knots - my gut

>f=

>eel is about a 3 g pull while simultaneously setting some flap (0 or +5)

>is=

> close to optimum. Pull to about 40 degrees nose up, ease off to 1 g,

>then=

[kirk.stant]

Not crosscountry gain - max height gain in a pullup; for example after a low pass.

Kirk
66

[KA6CR Driver]

I wonder; is the heigth loss the same in a push over? Would the energy exchange be the same as in a zoom?

DW

[Dan Marotta]

Not remembering the entire thread, and just responding to this question, a
push over followed by a pull up will always result in an altitude loss (in
still air). We're talking conservation of energy here. Engineers and
scientists will understand. This is not a perfect system and there will be
friction losses (drag). Every time you deflect your control surfaces, you
incur a drag loss. I do this all the time... :(


"KA6CR Driver" <Zen...@live.com> wrote in message
news:707076e1-e50a-436f...@googlegroups.com...

[John Cochrane]

On Sep 2, 10:07 am, "Dan Marotta" <dcmaro...@earthlink.net> wrote:
> Not remembering the entire thread, and just responding to this question, a
> push over followed by a pull up will always result in an altitude loss (in
> still air).  We're talking conservation of energy here.  Engineers and
> scientists will understand.  This is not a perfect system and there will be
> friction losses (drag).  Every time you deflect your control surfaces, you
> incur a drag loss.  I do this all the time...  :(
>

> "KA6CR Driver" <Zen1...@live.com> wrote in message

>
> news:707076e1-e50a-436f...@googlegroups.com...
>
>
>
>
>
>
>
> > On Sunday, August 26, 2012 12:40:46 AM UTC-5, kirk.stant wrote:
> >> Not crosscountry gain - max height gain in a pullup; for example after a
> >> low pass.
>
> >> Kirk
>
> >> 66
>
> > I wonder; is the heigth loss the same in a push over? Would the energy
> > exchange be the same as in a zoom?
>
> > DW

Some basics in my view:

The first thing to get right is not the push or pull, you're doing
this to adjust airspeed. So the most basic issue is when do you want
to speed up and slow down to follow lift and sink. That is primarly a
question of whether the lift or sink will last. There isn't much point
in a huge pull up in east coast punchy isolated thermals, because by
the time you've got the glider slowed down, you're through the thermal
and in to the sink. If the lift is lined up in to the wind, under a
cloud, streeting, clumping, or otherwise giving signs that it will
still be there when you've slowed down, then a pull up and even a
sharp pull up works

The second issue is the dynamic soaring effect. Yes, a pull and push
in still air loses height. But pulling up in lifting air and pushing
over in sinking air gains energy. This is hard to do. Really, you want
to pull when the glider still has momentum from the previous air and
is now in new air. You want to pull when the net lift+drag vector is
pointing forward relative to the path of the glider. Then, increasing
lift+drag speeds up the glider. So a sharp pull when you run in to
sharply increasing lift can gain energy.

A lot of the art of squeezing good glides comes from doing this just
right.

Two good winter projects: Work out the dynamic program of how to
optimally extract energy from a sharp-edged gust, given you don't know
when it's going to come. And create the next generation of "dynamic
soaring" varios that indicates when adding gs adds energy. Its not
that hard to do -- is the lift+drag vector pointing forward relative
to the path of the glider?

John Cochrane

[Roel Baardman]

Related read:
http://home.planet.nl/~kpt9/Hoogtewinst.htm

Should be pretty readable with Google Translate (from Dutch to English).

[and...@gmail.com]

The Dutch study is fun but unrealistic - adopted time 3s means 150m lift diameter for a cruising speed.
For wider lifts and cumulus ways conclusion would be probably reverse