# Has anyone be thinking of designing a more modern, light weight powered sailplane ?

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#### Victor Bravo

##### Well-Known Member
Because then you would have to wear one of those silly looking hats ...

View attachment 90677
I resemble that remark ! I still have one or two of my old soaring hats, and I think they make a fine statement of fashion.

Regarding another post, a retired United Airlines pilot told me that their DC-8's had a L/D of 20-1 in the clean cruise configuration.

#### stanislavz

##### Well-Known Member
HBA Supporter
My small contribution about in flight starts "helper" autogyro in far 103 class as a rotor - prerotator do use just an big cordless drill. Small shaft with hex end.. It helps to stay in 254 empty lbs category.

Same could be sued here if needed..

#### Pops

##### Well-Known Member
Log Member
So I put in those numbers and calculated Cdi and Cdp to get best glide at 45 kts and 33 hp required for 80 mph cruise (80% prop efficiency) with my motorglider power required spreadsheet (see attached). It came out to 8.6 glide ratio and min sink of 456 ft/min.

If I then take those same Cdi and Cdp and put in a 38 ft span and 134 area, then it goes up to 10.9 glide ratio and 327 ft/min sink. Cruise on the same 33hp only goes up to 82 mph.

My spreadsheet isn't that sophisticated, but I find it usually works out power for speed and min sink speeds within 10-15% if I calculate the Cdi and Cdp to match listed best glide performance.
The glide ratio is far better than that. At about 45 knots it wants to just hang in and floats. Get about 40 or 42 you can tell the sink rate goes up. What is the glide ratio of a T-Craft? Its about like that at least.

Did a ROC chart, wished I had done a rate of sink.

#### bifft

##### Well-Known Member
The glide ratio is far better than that. At about 45 knots it wants to just hang in and floats. Get about 40 or 42 you can tell the sink rate goes up. What is the glide ratio of a T-Craft? Its about like that at least.
I find 10:1 for a Taylorcraft (https://www.aopa.org/news-and-media/all-news/1996/march/pilot/new-pilot-(2)).
Putting in Cdi and Cdp for 10:1 @ 45 kts says only 28 hp needed for 80 mph, 399 fpm min sink.

Expanding to 38 span kicks that up to 12.7:1 @ 40 kts, 82 mph on 28 hp and 283 min sink.

So, by my crude calcs the glide ratio wouldn't go up much without considerable attention paid to cleaning up profile drag, but just increasing the span really helps with the sink rate.

#### BBerson

##### Well-Known Member
HBA Supporter
Well, glide ratio and sink vary together. (Double glide ratio will cut sink rate in half)
But that's only at constant speed.
Cut the speed (as in post 124) and now the minimum sink may improve more than the glide ratio.
The problem is real airplanes get heavier with span increase and may not get a slower glide speed.

Hang gliders have a low sink speed with rather poor glide, with very low wing loading.
And that DC-8 in post 121 with a L/D- 20:1 has a horrible sink rate.

#### Topaz

##### Super Moderator
Staff member
Log Member
Sailplane pilots obsess about L/D because that's what wins sailplane races - getting as far as possible between thermals, as fast as possible. Recreational glider pilots (and hang-glider pilots) are much more concerned about the minimum sink rate, since that determines how weak a thermal will keep them aloft. If your minimum sink rate is -200 fpm, you need to find a thermal or ridge lift that's going up at +200 fpm, just to sustain level flight. If you're just hanging around locally, L/D is, within limits, far less important.

From his description so far, I seriously doubt Pops is going to be doing any "distance" soaring in his new design, and instead will be catching local thermals and ridge lift, staying in the local area. As such, reducing minimum sink is going to be the dominant soaring performance goal. That means reducing induced drag is the most important concern, and that means span. Since the minimum sink airspeed is usually just a little above the stall speed, parasite drag reduction is going to be less important, and whatever effort is made there will primarily be for powered cruise, not soaring. Span will be considerable, compared to a normal tube-and-rag airplane, as will be aspect ratio. For a two-seater, you'll be looking in the 45-50 foot span range. Either struts or a carbon-rod capped wing spar would keep the weight down.

I would consider -200 fpm the very worst minimum sink rate you could tolerate and still have some fun soaring on reasonable days. The SGS 2-33 training glider has about this minimum sink rate, and if your area has a good ridge that works often, or local "house" thermals that will work that hard, you can do some decent soaring. A better minimum sink rate means you can stay up in weaker lift, and therefore will be able to stay up more often, and for longer. A good sailplane will have a minimum sink in the -140 fpm range or less. You probably won't achieve that in this airplane, but somewhere in-between the two values would make for a decent-performing "local fun" motorglider.

#### Pops

##### Well-Known Member
Log Member
I like this. Weathered in at my place for 2 weeks.

283 min sink sounds good. Build light and clean. On the SSSC I put all the control cables inside including the elevator horn. Used 500 x 5" wheels and tires for several years ( 800 x 6" cost 2 knot of cruise. Flying with open windows and door folded down cost about 3 knots of cruise. The cruise of 80 mph is at 2650 rpm burning about 2.9-3.0 gph.

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#### BBerson

##### Well-Known Member
HBA Supporter
2-33 specs above. Note: the L/D is same for both 1 person or two.
But minimum sink is much less with one person. Weight has no effect on L/D but a huge effect on minimum sink.

So the motorglider problem is that engines and the extra wheels add much weight. So how can a motorglider compete with a glider on minimum sink?
The upside of motorgliders is the option to look for better thermals. Or like I do, just glide down in still air for fun.

#### leifarm

##### Well-Known Member
I have a Pipistrel Sinus like the one that weathered in by you, but with the tailwheel in the proper place. It's got the soaring performance you want, but visibility when circling isn't great. Compared to the higher wing loading TMGs like the Super Dimona I think it`s much better in marginal lift. Build a U2, not a Starfighter!

Also used to have a Super Koala. Fun little airplane.

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#### billyvray

Whisper motorglider. Started as a kit. Now evolved to a fast sport plane, Whisper x-360 or something. On Facebook the original builder has started a scratch build and will sell plans for about $500. 2 place, sbs, all foam, rotax 912 power typically. #### Pops ##### Well-Known Member Log Member View attachment 90783 2-33 specs above. Note: the L/D is same for both 1 person or two. But minimum sink is much less with one person. Weight has no effect on L/D but a huge effect on minimum sink. So the motorglider problem is that engines and the extra wheels add much weight. So how can a motorglider compete with a glider on minimum sink? The upside of motorgliders is the option to look for better thermals. Or like I do, just glide down in still air for fun. I will never forget the 42 mph on the 2-33. Sort of special for me. In my instruction in the 2-33, if I went 41 mph the instructor would lean forward and say with a loud voice, " why are you going to stall , get the speed back to 42" and if I went to 43 mph he would be saying " get it out of the dive". He died about 30 years ago, like to hear him again. Very nice person and a great pilot. Been an instructor in powered, gliders, float planes since 1937. We went to OSH together many years and he would take me to sailplane contest with him where he was flying. Lot of fun. #### Dillpickle ##### Well-Known Member Sailplane pilots obsess about L/D because that's what wins sailplane races - getting as far as possible between thermals, as fast as possible. Recreational glider pilots (and hang-glider pilots) are much more concerned about the minimum sink rate, since that determines how weak a thermal will keep them aloft. ..... Man, this post made sense. Glider purists are so focused on efficiency, they forget about fun. You made this make more sense to me in this whole post, and I enjoyed the education. Thanks. #### Dillpickle ##### Well-Known Member Pops, is your VW a Hoover style rear drive, or a front drive? I’m picturing a hollow chrome molly tube shaft on sintered bushings going through the fire wall, with a gear on the end that engages a automatic VW ring gear, with a spring to kick it out and a 3/8 socket drive receptor on the cockpit end. A single light shaft. When the engine is stopped, press a drill driver against the shaft, push in to overcome the kick out spring, and pull the trigger, as soon as it starts, pop it free. The spring disengages the start shaft. #### Pops ##### Well-Known Member Log Member Flywheel drive, using Hoover plans for the prop spool and his plans for cutting out the center of a flywheel with the spool bolt to it. There is a stc for a similar starter for the Cont- A 65 engine, powered by a drill driver in the cockpit. Been done before. #### Dillpickle ##### Well-Known Member Flywheel drive, using Hoover plans for the prop spool and his plans for cutting out the center of a flywheel with the spool bolt to it. There is a stc for a similar starter for the Cont- A 65 engine, powered by a drill driver in the cockpit. Been done before. So someone was smarter and faster than me, lol. No surprise there. I also thought about sand casting buggy style valve covered with bushing bosses as part of the casting, but then thought that a hollow shaft starter might be lighter and less complicated—except for the drill driver of course. I also had in mind, since you were quoting weights for the VW that seemed rear drive probable, the old WWII hinged crank that flopped down over the pulley and only engaged in one direction, since your engine would be pointed the right way, but it would take a geared drive for most drill drivers. #### cheapracer ##### Well-Known Member Log Member One of the topics that came up in the discussion portion of that lecture is that a conventional high-wing design has really terrible visibility in a thermal, in that the wing is blocking almost all the view up and inward in a continuous turn, such as you'd consistently encounter circling in a thermal. Several glider pilots expressed some pretty strong concerns about the safety issues this would present. Cheap cameras and screen are available. A bit cheaper than changing a whole plane. Should be mandatory in a high nose tail dragger too. #### User27 ##### Member For decompresser valves look a Schempp-Hirth glider with a 2-stroke "turbo" get-you-home engine. They use a Solo engine that is dive started and use a manually activated decompresser valve. If the cylinder heads were drilled for 2 plugs these valve could be used instead of one set of plugs. The modern electric self-sustainer gliders (http://www.front-electric-sustainer.com/) use a 22kW (around 30hp) motor and can achieve around 400fpm climb, but the batteries only last 15 minutes. Flying level at 60kt uses only 20% power, the batteries last an hour. The take away is that keeping the motor running at low power in a low drag airframe greatly improves the L/D and means the airframe doesn't need to be so finely tuned. For a homebuilt motorglider that means the airframe doesn't need nearly so much time spent on it if the motor can be run at low power all the time. #### Pops ##### Well-Known Member Log Member My SSSC would fly level at 50 knots at about 1900 rpm with the 1835 cc, 60 hp engine. The VW engines idles at 900 rpm. Just thinking out loud-- IF I extended the wings and cut more drag, etc, etc. Flying in formation with my neighbors 2 Piets with 65 HP conts, I would have to be back to 2450 rpm. But then, the oil temp and CHT's would start dropping and getting to cold, so at any more RPM, I would have to turn around and circle back and get back in formation. Last edited: #### 103 ##### Well-Known Member My SSSC would fly level at 50 knots at about 1900 rpm with the 1835 cc, 60 hp engine. The VW engines idles at 900 rpm. Just thinking out loud-- IF I extended the wings and cut more drag, etc, etc. Flying in formation with my neighbors 2 Piets with 65 HP conts, I would have to be back to 2450 rpm. Every story about this plane draws me back to the SSSC concept for pure fun flight that does not wreck the family budget. The 1834CC should easily pull 12-1500 hours with this load <2700 rpm and still only cost$500 to refresh new bearings, new pistons and a valve job.
Simply Brilliant!

#### plncraze

##### Well-Known Member
HBA Supporter
There is very little new under the sun when it comes to aviation. Pops put all the good parts on one plane and called it the SSSC. I am glad that he can share his experience here where it is appreciated!

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