Trends in Sailplane design

In my studies of various gliders I have noticed we seem to have a lot of what I call racing gliders being produced today. There really do not seem many alternatives in the market today. When I look at the specifications I note that the Min sink is about 55 mph and the best glide about 60 mph. Wing loadings vary from 6 psf to about 10. If you do the math for the circling diameters you realize that these gliders do very large circles and have relatively high sink rates for a 15 meter.

Most of the gliders built today seem to be built for high speed cruise and in general more useful on the west coast where large thermals seem to abound.

I was very surprised in my studies of the Genesis to discover a theoretical sink rate of only 135 fpm... and the LS8 15 meter of about 120 fpm. The airfoils and subsequent wing loading, are all optimized mostly for high speed!

In our area of Ohio we need gliders with a sink rate of about 100 occuring at an airspeed of about 40 mph to capture light lift and the best L/d occuring at about 50.

What is the best East coast glider and what are its requirements? And what is really the needs of a soaring pilot? Are we just to emulate the racing pilots aqnd fly only on super days?

Hang on a minute. I am sure that the weather conditions in Ohio can not be worse than the UK for gliding and we still manage to do decent long cross country flights. Lift of more 6knots is quite rare here, more common is 2 to 3 knots. Wing loadings in the range you mentioned allow decent glide angles to reach the next thermal. Low wing loadings climb beautifully which is fine as you do not want to go anywhere. Compare K8 with say a PW5 and you will see what I mean.

Specifications for what? If you've got a specific line of inquiry or argument, you're going to have to provide specifics.

Since you mention the LS-8 in other parts of your post, let's have a look at its numbers. According to this graph, in 15m trim it has a min sink rate of about 118 fpm at 51 mph:
http://www.neukom-composite.ch/ls/d/products/ls8/ polareLs8.gif

When I extend that graph to the origin and draw a tangent to the polar, I get a best glide of .65 m/sek (98 fpm) at 100 kph (62 mph); that works out to a best L/D of 42.7 to 1. And, having flown against the LS-8, I have no doubt that 43:1 is a realistic best glide for that ship. Also, the polar is real, real flat on top; that means that even below the min sink speed the sink rate has no substantial increase. And pilot reports say that the controls are still crisp and responsive down at those speeds. A combination like that is hard to beat.

Most of the gliders built today are optimised to provide ownership value in line with what it costs to produce them in an effective if only mildly profitable manner. Ya pays yer money and ya takes yer choice.

And besides, I only wish that thermals 'abounded' out here.

That is a pretty strange paragraph. You're surprised that the LS-8 has a lower sink rate than the Genesis? Are you surprised that the sink rates are so modest despite being 'optimised for high speed?'

But, you have a point that there is much to be surprised about when it comes to the LS-8. It is basically an LS-6 with a fixed trailing edge corresponding to something like the LS-6's 0-degree flap setting. Conventional wisdom, backed by one or two similar attempts that failed miserably, says that if you try that you'll get a dogmeat glider. But Felix's FX-81 seems to have the kind of dynamic range it takes to make that particular shenannigan come up roses. I'm going to try that with the HP-24, and see if I can get Standard class sport/racers out of the same molds as the flapped ships. But I won't be very surprised or disappointed if it doesn't work out.

If you're judging by contest scores, I'd guess from the 2002 Perry SC contest that the best East Coast sailplane is the LS-8 in Standard class and the ASW-27 in 15-meter. And the speeds were all in the 50s and 60s, so you can't say that the weather was booming.

Which soaring pilot are you thinking of?

Mat, we all love your little flying lawn chairs. They're cute. I'd like to have one myself for an afternoon or three of just wafting around. And I think that it's great that you're extending the scope and range of what constitutes soaring flight. There is definitely much to be enjoyed when it comes to slow, low-energy soaring. I just happen to believe that you would do well to target the people to whom that kind of soaring is proven to appeal.

As I've said in person to both you and Jim Marske, I think that you guys should do a part-count-reduction and cost-reduction program on the Monarch G. Then market it heavily to aging baby-boomer hang glider pilots tired of driving up hills and tired of broken bones. I bet you'd have units just flying out the door in no time.

The problem here is that soaring pilots generally have room in their lives for only one major toy, and perhaps one or two secondary and tertiary toys. So they have to choose their toys wisely, and get ones that will suit them over a fairly wide variety of conditions. The problem with the Monarch and similar low-energy ships is that they still cost a ton of money to buy, or take a ton of time to build. If you can bring the price tag down to where established soaring and racing pilots will buy them just for the three or five days per year when it will stay up and their LS-8 won't, you'll be golden.

And besides, when it comes to 'emulating the racing pilots,' all the best wannabes practice on weak days as well as the good days. Contests are conducted over all kinds of terrain, in all sorts of weather.

Thanks, and best regards to all

Bob K.

Hmm... how do you come to this conclusion?

'Racing' is not running along cloud speeds at 100 mph+... racing is often the simple task of staying airborne AND covering as much distance as possible (at least here in Europe... where any lift over 600 fpm is considered to be very good). No idea why you think that 'racing pilots' only fly on super days.

History shows clearly that the greater range of a glider with superior L/D is far more important than slightly lower sink rate or turning radius. In reality you rather need the possibility to reach the next lift with minimum loss of height.

BTW: The first example of a glider matching exactly (!) your numbers was built 40 years ago. It was the first glass glider, the MBB Phoenix with a minimum sink of slightly under 100 fpm at 40 mph, a best L/D of 37 at 47 mph. Compared to the Ka-6E with an L/D of only 34 and a significantly higher sink rate, it was not better... because the highspeed performance of the Ka-6E was better. In other words - the Phoenix was optimized for too-low speeds. It's successor, the Phoebus, was optimized for higher speeds - it had a significantly higher sink rate, but about the same L/D.. and performed a lot better overall.

The example of the day that allows light Ka-6's to stay airborne while the 'heavy' glass gliders need to land (because only the light Ka-6's can actually climb in the wek lift) is a fairy tale - it helps a lot more if you have two or three times more range to check for possible lift than having 25 fpm more climb rate in a weak lift.

Sure... with a lot of knowledge you could build a very light glider that could fullfill your numbers (100 fpm min sink at 40 mph, best LD at 50 mph). The sink rate can be done... of course this glider will have lousy maximum L/D as well as highspeed performance.

This glider needs to be *very* light. It will be able to climb even in the slightest lift... but will be a lot worse than any glider with a conventional wing loading when it comes up to running for the next lift. On 95 percent of the soarable days the conditions are good enough that any 'conventional glider' will have a huge performance advantage over your proposed wek-lift concept.

Bye

Since this hasn't popped up on r.a.s. yet:

From the OZ report http://www.davisstraub.com/OZ/Ozv6n150.htm

' Gary Osoba set two new world records today in Big Spring , Texas , flying the SparrowHawk over a 500 kilometer (300 mile) triangle. This is the longest triangle every flown by an ultralight glider. He also set the speed record for the 500 km triangle.

The distance around the triangle was 502.2 kilometers. His average speed was 50 mph, which just happens to be approximately 30 percent faster than the world record speed of the Apis WR when it was flown around the 300 kilometer triangle (shorter triangles are usually flown faster).

Gary 's average lift was only 320 fpm over an area that had received rain a couple of days ago. He had to struggle through about 80 miles of blue late to get back to the clouds.

The sky was full of cummies today over Big Spring and for much of the surrounding area. Gary just picked a triangle to the southeast of Big Spring because he thought that there was a chance that it would blow up to the west. Northeast would have been the ticket. He flew over some areas that weren't landable - it is quite nice to the north and west.

He got stuck in a small valley going to and coming from the second turnpoint and struggled with blue conditions, while there were cu's every where around us. 500 kilometers is a big distance.

The racing gliders of today are desgned in Germany were the conditions are similar to the US east coast. The evolution of a racing glider har brought it to the point where it is today. They are optimized for all kinds of weather Empty they work fine in weak conditions and then you can almost double the wing loading by adding water.

Gliders like the K-8 are great on weak conditions when it comes to thermalling. But as soon as the conditions rise above weak (and allow some cross country) the advantage is gone. Then you need L/D to get to the next thermal.

I think that one of the gliders of today that is optimized for weak conditions is actually the Eta. It can glide for miles and miles and make use of the few good thermals that can be found.

Staffan

Mat, you need to re-think this.

Over the years I have noticed that each soaring day usually starts weak, gets strong and then gets weak again. The heavy, slick gliders take off first and return last - staying up the longest. The light wing loading gliders almost never do this.

Now this is partly due to the fact that better pilots tend to own racing gliders, but is also true that these gliders give them an advantage in just staying in the air in weak conditions. Making slow tight circles in lift is just part of the reason, covering lots of ground looking for the best lift is the really important part.

The ultra light gliders work in Ohio because, while the thermals aren't strong or go very high, they're close together. When the thermals are strong and go high, they are often more than 10 miles apart. L/D then becomes the most important parameter for just staying aloft. 100 FPM min sink just isn't important if you can't find a thermal. Even in Ohio, there are some strong thermals but you will never find them at 25:1.

In strong western conditions, high L/D 'reach' is just part of it - high speed 'dash' is what will get you to a building cumulus before it dissipates giving you assured lift along a course.

Jim Marske's designs have the potential to join the high speed game and maybe win at it but that won't happen if you keep emphasizing the low and slow end of the spectrum.

Bill Daniels

Part the drift from the core topic however ...

It was recently pointed out to me that in order of personal priority my toys appear to be

1. Glider 2. Car to tow glider 3. Girlfriend to drive car to tow glider

fortunately I did manage to string an agrement together that reversed the order

Maybe from simple observation on most days at any midwest airport? Since the start of our season, the 2-33, the 1-26 and the L-13 have flown on every weekend that the wind would allow. The Slingsby Vega has flown once. None of the other 'super ships' have even bothered to come out to the field. This should tell you something.

In what context and to what end? There is no such thing as one concept of design that fits all purposes perfectly, if there were, we would only have one design available, but it would be fantastically successful.

And again, this depends on the purpose and desire of the one sitting in the cockpit. If one is content with circling for hours in the house thermal, anything that will keep him up there is good. If one has to bomb across country at high rates of speed, a 2-33 probably wouldn't be a good choice, but it is still important ONLY to the one in the pilot seat. There is no bigger waste than buying performance that you don't need, more so if you never learned the capability of what one already has. Both ends of the spectrum need to be explored, unfortunately the low and slow end is being largely ignored.

If the eta is so great why is there no performance data on the website?? - maybe I missed it.

there was no point in going for longer wingspan than currently.

George Emsden

Are we just to emulate the

No, we are just to emulate the racing pilots and fly on good, bad, sunny, raining, windy, hot, cold, strong, and weak days. And we want to see what's over the next hill, and the next hill beyond that, and make it back for a cold beer and some lie-swapping.

My Ls-6 does just fine on weak days - dry, I have no trouble out-climbing the local 1-26s and 2-33s (so much for lower wing loading). On strong days, I fill it up and blast off trying to catch my friends (who fly their glass much faster than me!). And when I get back with some altitude to spare, it sure does loop and barrel roll nice (heh-heh just kidding...).

If you think the missing link between hang-gliders and current glass is the way to go, great! Build it, then go have fun. But don't be surprised if you go by yourself! On the other hand, if you want to be retro, make sure you keep the cockpit open, and use a pellet variometer, just to make it a challenge...

Me, I want a paraglider and a winch setup for those really weak days - then when I landout I just pack it up and hike back across the field and try again. I spent a pleasant afternoon at Tiger Mountain near Issaquah, WA last week watching those guys blossom off the Puu-Puu Point launch - counted 18 wings up at one point - and they were having a blast with nice little Cu's everywhere. And some of them were hiking up the mountain (about a 2 mile uphill) with their wings, then going off downwind crosscountry. Way cool. And not a rigid or flex wing insight (or any gliders - they shut down that nice gliderport long ago).

That may be the future, and where we might get the next generation of pilots (although most seemed to be my age - those wings and harnesses aren't cheap!)

Kirk LS6-b '66'