Electric-Powered Cross-Country Glider - RC Groups
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Jul 09, 2002, 12:29 AM
around Colombia
ShredAir's Avatar

Electric-Powered Cross-Country Glider

I am assembling a RnR SBXC cross-country glider with an electric drive system. The idea is to have a large glider (170 inches span, 1791 square inches of surface area) for extended thermal and cross-country flights.

The idea is inspired by Scott Reeves (who currently has an SBXC-e built by Jim Thomas), and it is supported by Cross-Country Soaring (http://xcsoaring.com), who is the dealer for RnR's SBXC glider and the Skymelody variometer with total energy compensation.

Shredair's plane will be powered by a Lehner 1940/10D-17S motor with Reisenauer 6:1 Super Chief gear box, BK/LMT 3095 Micro controller, RFM 20x13 carbon prop, and 24 cells. For testing, I'll use the CP1700 packs I have for my F5B planes, but I'll switch to 2400s and would like to test some NiMH cells and the new 3600 NiCads soon. The attached picture shows the drive system and modified fuselage; I'll shoot more photos as I progress.

The idea is to make the big plane climb at an angle of about 45 degrees at a speed of about 35 mph, the speed of best glide for the SBXC. I'd like to have this plane done (unpainted) by next Monday, and test-fly it over Hells Canyon during S&E Modeler's alpine soaring event July 19-21.

Why do this? To promote cross-country soaring! It IS fun!
Please note that "I" said that, I, who is well known to believe that TD stands for tedious dawdling instead of thermal duration, and that HLG means hideously light glider... :o)
Seriously, I'd like to be involved in the movement which shows TD pilots that there is more to life than sandbagging, circling, and dorking, all in the same place (not that there is anything wrong with that...). Let's GO somewhere...

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Jul 09, 2002, 01:43 AM
Registered User
Ranfred Radius's Avatar
Say goodbye to line breaks.. He He He. Plus it opens up more aerobatic opportunities for the SB/XC. I can still remember the first time I did a super slow roll with Dean's. Come to think of it, he never let me fly it again after that..

Jul 09, 2002, 02:51 PM
Electric Airplane Junkie
bhchan's Avatar

Look for some Sanyo Nimh-3000HV. Make sure it is "HV", not just the "V".

A friend told me he tested the HV and the voltage gets higher when it get hotter.
Jul 11, 2002, 11:04 PM
around Colombia
ShredAir's Avatar

tail servo installation

The picture below shows a sand bag holding in place an SBXC fuselage. -- It's SUPPOSED to show a view into the fin of this airplane, clarifying the installation of the elevator and rudder servos (let's hope I'm doing better with a transmitter than a digital video camera).
This airplane is roomy: you're looking at a trusty Airtronics 94141 elevator servo installed ABOVE the bell crank, so that it PULLS for up-elevator (see detail on the left). Below it is a Volz Wingmaxx for rudder control.
These servos are just tacked in for now and won't be final-secured until I'm sure everything functions perfectly; after that, I'll install the rudder post.
It's a real pleasure to assemble such a big plane: standard-sized servos fit into the flap servo bays, 141-sized ones easily fit in the aileron servo bays, and I stuck my whole arm into the nose to install the epoxy/cabasil fillet around the motor mount.
Barring unforeseen problems, I should have this plane ready to go in time for a maiden flight over Hells Canyon at 6700 feet altitude. I'll be there by next Wednesday, July 17.

Jul 24, 2002, 06:41 PM
around Colombia
ShredAir's Avatar

SBXC-electric flight report

The electric SBXC's flight performance exceeds my expectations: The big plane is much more nimble than I expected with excellent 3-axis control response, and the drive system is more powerful than I dared to hope.

The SBXC is a cross-country glider made by RnR with a wingspan of 170 inches, a surface area of 1791 inches and a flying weight (as a pure glider) of 10-11 pounds. The electric version, outfitted with a Lehner 1940/10D-17S motor with Reisenauer 6:1 Super Chief gear box, BK/LMT (Lehner) 3095 Micro controller, RFM 20x13 carbon prop, and 24 CP1700 cells, weighs approximately 16 pounds.

This drive system propels the glider up at approximately 40 to 45 degrees at about 35 mph, which is close to optimal L/D speed for this glider. This is quite an impressive sight, and the real-life performance appears better than theoretical calculations predicted.

Next, I will use a 24-cell pack made from zapped Sanyo CP3600 cells, and I expect current draw with these cells to be just under 50 A (we haven't measured current but calculated about 50 A with the CP1700 pack). Weight with these 3600 cells will increase to about 18 pounds, which is no problem for this glider or this drive system.

With a 24-cell pack of CP3600s and assuming a 50 A current draw, motor run time in the SBXC-Electric is over 4 minutes; this will give 8 to 10 climbs to a 500-foot altitude.

For more information in the SBXC, please see http://xcsoaring.com


Pictures courtesy of Jon Baker
Last edited by ShredAir; Jul 24, 2002 at 06:48 PM.
Jul 24, 2002, 07:36 PM
Scott Summersgill
smsgill's Avatar
Looks great Dieter. You gonna bring this bad boy to the PSSF fly in on the 10th and 11th of August in Olympia? Hint, Hint. Catch you later.

Aug 17, 2002, 01:38 AM
around Colombia
ShredAir's Avatar

Launching off a dolly

This collage shows the SBXC-electric taking off from a launch dolly. This dolly is built by Dan Berry and designed -- I assume -- by Scott Reeves, who also inspired this whole project.

This style of take-off has successfully been completed before, most recently, that I know of, by Tom Rust who built a similar cart to launch his 54-cell Stratos SLe. I'm not kidding; see http://www.aricraft.com/stratos.html

For this test of the SBXC-e, I used the new 24-cell CP3600 pack weighing about 4.4 pounds and bring the flying weight of the SBXC to about 18 pounds. I did two flights at 10 AM and at 2 PM, and despite 100+ degree heat, the Lehner 1940 based system had no problem with that load. Take-off roll was less than 30 feet both times.

I resisted the idea of using a proportional throttle for slow, smooth acceleration, and instead ran the motor on an all-on/all-off switch, just like any LMR or F5B glider. The plane remained rock solid on the dolly and accelerated smoothly and lifted off cleanly.

I'd say this project is a total success:
first, the plane provides excellent flight performance at this weight;
second, the Lehner-based drive system provides more than adequate power;
third, the dolly works smoothly and safely. This dolly provides the perfect attitude, stability, and stance for the SBXC during the take-off run.

Carrying such a huge battery pack (24 x CP3600) is not needed, in my opinion. A pack made from 1700s weighs 1/2 and one made from 2400s 2/3 that of the 3600. Either pack will provide many times more altitude than any winch launch of an 11-lb SBXC glider.

What's next? First, I'll see if I can hand launch this beast with the CP3600s at the sod farm tomorrow (with someone else on the controls). We're supposed to have some wind, which helps, and this thrown-together, assembly-of-blem-parts plane of mine is ideal for this type of R&D; no big deal if I fail, and repairs are needed.
Second, I'm working with Rudi Freudenthaler on a 24x10 prop. This may be a dumb idea, because the existing 20x13 works so well. Still, we believe climb performance, efficiency, and ease of hand-launch will improve with the bigger prop, and at least we'll want to try it.

Aug 17, 2002, 04:08 PM
Registered User
MikeC's Avatar
That is very cool!

I look forward to your X country tales.

It seems that a X country event of even 20 miles out and return would be a great contest format.

Aug 18, 2002, 01:15 AM
around Colombia
ShredAir's Avatar
Originally posted by MikeC
It seems that a X country event of even 20 miles out and return would be a great contest format.

Even off winches, cross-country gliders have flown over 60 miles on a circuit course. For more information on that, please see http://www.xcsoaring.com
This electric system allows multiple climbs many times higher than any winch launch I have seen, so it's reasonable to expect that electric-powered cross-country planes can go farther. Given good air, the power we have available, and a really large receiver pack, pilot fatigue and daylight seem to be the limiting factors on how long or far a flight can last.

Dec 30, 2004, 07:02 PM
Who needs a pilot??
danstrider's Avatar
How much is an SBXC? They have "call" on their website, but was curious how much you payed.

Thanks, neat project too!
Jan 02, 2005, 11:20 PM
Registered User
Wow! A moving transmitter...how do you manage frequency control?

I really like the launching dolly as I am no good at hand launching after biffing one bird.
Jan 03, 2005, 12:28 PM
Ascended Master
Sparky Paul's Avatar
On the dolly, are the wheels locked to the axles?
I've heard this will prevent any wandering for the takeoff roll.
Jan 03, 2005, 04:05 PM
Registered User
Awesome project Dieter!
Thanks for sharing, let us know how it hand launches.

Don't javalin throw, that's prehistoric, put a peg on one tip! :-)

Jan 03, 2005, 07:42 PM
around Colombia
ShredAir's Avatar
Where did you guys dig up THAT one? It's ancient history. This plane still flies today in Santa Cruz, and I have since built a second one with a take-apart fuse. Do a search on large electric glider conversion, that thread also should be on this forum...

Dieter Mahlein, ShredAir
Jan 05, 2005, 04:19 PM
Registered User
ohadvr's Avatar
Awesome project!

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