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Cumulus resurrection

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Shaun Walsh04/06/2019 13:48:00
126 forum posts
12 photos

dsc_0291[1].jpgdsc_0293[1].jpgAlmost finished refurbishing my 45 year old Graupner Cumulus 2800 which hasn't flown for 40 years.

It was stored in its original box in my mother's loft and was in pretty good condition when we found it.

I decided to add the motor pod option and found unused original parts on ebay but with electric power rather than the OS 10 it was originally designed for.

Work completed so far:

New servos fitted (Spektrum 5030) and Spektrum 4 channel receiver, the original equipment was a Sprengbrook 4 channel receiver and two of their full size linear servos.

Old balsa pushrods replaced with carbon fiber tube.

Aerostar 30 watt esc fits nicely under the servos.

Front former had to be cut away to accommodate battery tray.

Turnigy 2217 1050KV motor mounted as a pusher in order to be able to fit a bigger prop, 8x6 pusher.

COG correct with Turnigy Graphene 2200 battery installed.

Just need to test fly before doing the cosmetic stuff, weight 1600g, thrust 900g with motor pulling 17 amps.

Everything worked ok when I did a test run of the motor whilst holding the model, rudder response under power was fine producing plenty of yaw force and down elevator pushed the nose down fine but up elevator was not so good making me think that it will be hard to get it to climb under power. The question is do I need to alter the thrustline of the motor to overcome this?

img-20190604-wa0000[1].jpeg

Torsten Spitzner04/06/2019 16:23:07
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16 forum posts
17 photos

Lovely. Let us know how she flies.

GeeW04/06/2019 21:21:32
109 forum posts
8 photos
2 articles

would try launching with only a low power set and then slowly open up the power. My Cumulus awaits its turn, but very interested in a removable power pod

Shaun Walsh05/06/2019 11:03:30
126 forum posts
12 photos
Posted by GeeW on 04/06/2019 21:21:32:

would try launching with only a low power set and then slowly open up the power. My Cumulus awaits its turn, but very interested in a removable power pod

I was very lucky to get hold of an original unused power pod kit.I could scan the ply motor mount and the aluminium supports if you want to reproduce them for your cumulus. Send me a PM if you are interested.

Charles Smitheman05/06/2019 12:50:16
220 forum posts
18 photos

Wow. I havent seen one of these for about 40 years. It looks in great condition.

That ABS fuselage might have embrittled with age, they were not the strongest when new. I hope your landings are gentle!

Charles

Shaun Walsh05/06/2019 12:59:02
126 forum posts
12 photos
Posted by Charles Smitheman on 05/06/2019 12:50:16:

Wow. I havent seen one of these for about 40 years. It looks in great condition.

That ABS fuselage might have embrittled with age, they were not the strongest when new. I hope your landings are gentle!

Charles

Fortunately it was stored in a cool dark loft in its original box so the fuselage seems ok, no light degradation of the polymer and almost no hanger rash on the wings and tail although I am pretty sure I had to repair the rudder in the 1970s when someone else's model landed on top of it.. Was the fuselage ABS or nylon?

Andrew Ray05/06/2019 13:58:18
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699 forum posts
19 photos

Similar to the Graupner Cirrus fuselage (or were they the same) with a different canopy. A friend was given a kit as a thank you from a good friend of his, very expensive at the time, a typical 100" kit was around £20 this was £100 back in the day.

Shaun Walsh05/06/2019 15:22:13
126 forum posts
12 photos
Posted by Andrew Ray on 05/06/2019 13:58:18:

Similar to the Graupner Cirrus fuselage (or were they the same) with a different canopy. A friend was given a kit as a thank you from a good friend of his, very expensive at the time, a typical 100" kit was around £20 this was £100 back in the day.

That's right, the Cirrus and Cumulus shared the same fuselage (or very similar), I think the Cirrus had built up straight wings as opposed to the foam/obechi veneer swept wings on the Cumulus. Yes it was around £100, almost as much as a 4 channel 27 MHz rc set in the mid 70s, it was an 18th birthday present.

GeeW05/06/2019 17:46:19
109 forum posts
8 photos
2 articles

The back end of the fuselage is different between the Cirrus & Cumulus. The Cirrus has a full height fin, the Cumulus has an area balanced rudder.

Nightflyer07/06/2019 13:02:01
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173 forum posts

Fantastic seeing the Cumulus it looks fantastic. A few years back a mate of mine had a Cirrus that he had originally from the late 70's early 80's that he dug out and overhauled it - complete with his old Futaba M series and with new batteries that model flew superbly off a bungee. Graupner produced some very fine models that were quality definitely in their time of the 70's and 80's - not just in aircraft, but in boats and cars. I loved flying the Cirrus and it smacked of quality.

Speedster08/06/2019 19:10:06
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368 forum posts
163 photos

img_4692.jpg

img_6308.jpg

img_6773.jpgI also got one

Found it very cheap on the web

I gave it a new canopy and made it with ailerons, and with 2 servos so that I can have spoilerons.

And after that, it is a really nice glider to fly.yes

Cheers

Soren

img_6781.jpg

Shaun Walsh19/06/2019 22:33:54
126 forum posts
12 photos

OK, maiden flight after 40 years was this evening, it was a little breezy but decided to give it a go. Motor power was fine, needed a bit of down elevator under power and climbed away nicely. I had forgotten just how much space it takes to land, just keeps going without losing height, had to go around twice to land.

Waited for the wind to drop a bit and flew again, more height this time and just seems to keep on floating, again needed to go around for a landing but 6 feet off the ground the wind dropped and I think I stalled, went in like a javelin, buried up to canopy and tail in the air. ☹️

Expected the worst but after cleaning off the soil, no damage 😅.

So overall reasonably successful but it needs a lot of rudder for directional control and it's not a small rudder! Elevator control was fine COG OK, just need to finish the motor pod to make it cosmetically appealing.

Shaun Walsh20/06/2019 16:18:47
126 forum posts
12 photos

dsc00494_lzn.jpgdsc00490_lzn.jpgdsc00485_lzn.jpgPhoto's from last night courtesy of a fellow club club member.dsc00480_lzn.jpg

Shaun Walsh09/07/2019 16:17:13
126 forum posts
12 photos

Have now tidied up the power pod, put the covers on with an added air scoop made from half a plastic teaspoon for improved cooling and fitted a folding 8x6 pusher prop in place of the fixed one. Measurements show the folding prop draws 14 amps and provides approx 700g thrust whereas the fixed prop draws 17 amps and gives approx 900g thrust. Have ordered a set of 8x7 folding blades to try to improve the thrust. No room for 9 inch blades.dsc_0306[1].jpg

Nightflyer10/07/2019 13:11:18
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173 forum posts

Looks great hope you have many enjoyable flights. From memory with a Cirrus they do float well when looking to land they do seem to glide forever.

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