Graupner Cirrus 21st Century edition

User avatar
stuart mackay
Posts: 501
Joined: 01 Mar 2018, 10:38
Location: Swaffham, Norfolk
Contact:

Graupner Cirrus 21st Century edition

Post by stuart mackay »

Thought I would share this little project with you.

I have been looking around for an original kit for the Cirrus from the seventies for a while now, (always lusted after one back then, but pocket money wouldnt stretch that far!) But it seems the kit collectors have driven the prices to stratospheric levels these days and also the original plastic fuselages had a reputation for cracking and generally not withstanding the rigours of regular flying.

This semi kit her consists of epoxy fuselage/canopy frame, blue tinted canopy, full size plans, laser cut ribs and decals Produced in Switzerland by a modeller doing his bit for Cottage Industry there.

It is available direct from Xavier Schmidt for all that you see in the pic below, Not cheap at 230 Euro shipped to UK , but where else will you find one?
DSCF8731 cropped reduced.jpg
I bought the 6 mm carbon rod spars from EasyComposites in the UK and have found other items on German ebay such as an aluminium replica of the all moving tail horn and wing retainers.


DSCF8732 cropped and reduced.jpg
A trip just down the road to Watton to the nice people of SLEC, saw me spending £50 for all the wood required for the wings and tail surfaces.

I plan on using an 8mm Carbon rod wing joiner and it will be a full house model with twin aileron servos and fuselage mounted tail servos plus the E Motor ESC.

The plan is to saw off the nose and fit a 3S Electric Drive, I know sacrilege, but don' t forget I live in Norfolk, the land of flat fields and Big Skies!
User avatar
stuart mackay
Posts: 501
Joined: 01 Mar 2018, 10:38
Location: Swaffham, Norfolk
Contact:

Re: Graupner Cirrus 21st Century edition

Post by stuart mackay »

Started on the wings today with cutting the 1/16 wing sheeting for Leading and trailing edges. Took a bit of head scratching as not only are you having to cut the taper which starts just inboard of the aileron, but also having to scarf joint the sheets to make 60 inch long continuous sheets from a 48 inch sheet (max available length from SLEC).
There is also about 1/8 inch washout in the outer panel, so again, had to be mindful of this.
Anyway all sorted and it was a great feeling when all the laser cut ribs slid over the 6mm spar and were glued into place.
I also dry fitted the wing joiner tubes to ensure no nasty surprises later!
DSCF8733 crop.jpg
DSCF8735 crop.jpg
User avatar
stuart mackay
Posts: 501
Joined: 01 Mar 2018, 10:38
Location: Swaffham, Norfolk
Contact:

Re: Graupner Cirrus 21st Century edition

Post by stuart mackay »

Too windy for flying today, so a few hours in the workshop this morning saw the Tail feathers bare structures completed.
The laser cutting is really good and the stab ribs had tabs to compensate for the symmetrical and tapered section, which made building it flat on teh board an absolute breeze.
DSCF8737 crop.jpg
User avatar
stuart mackay
Posts: 501
Joined: 01 Mar 2018, 10:38
Location: Swaffham, Norfolk
Contact:

Re: Graupner Cirrus 21st Century edition

Post by stuart mackay »

After work, attached the leading edge to one wing panel so couldn't do much more on that, so busied myself with the fuselage and drilled the wing joiner tubes using the ply wing root ribs as patterns for where the holes needed to be.
These wont be finally fitted and bonded in place until both wing panels are completed to ensure correct wing/fuselage alignment and incidences.
DSCF8738 crop.jpg
Also epoxied the canopy hatch latch in place on the top of the fuselage.

I am looking for some of this glass tissue on a roll to reinforce the trailing edge inside before adding the top skin, has anyone here seen this stuff for sale in the UK? Think it is called glass fibre fleece as it is non-woven, unlike a glass tape.
254437940_751403282390490_8457590850364833990_n.jpg
254437940_751403282390490_8457590850364833990_n.jpg (10.96 KiB) Viewed 7116 times
Jim
Posts: 40
Joined: 09 Oct 2021, 21:56
Location: Cambridgeshire, England

Re: Graupner Cirrus 21st Century edition

Post by Jim »

Following with interest, should be a nice model when finished. Looks a good kit.
User avatar
stuart mackay
Posts: 501
Joined: 01 Mar 2018, 10:38
Location: Swaffham, Norfolk
Contact:

Re: Graupner Cirrus 21st Century edition

Post by stuart mackay »

Bit more work on the LH wing panel this evening with a mixture of epoxy and micro-balloons added to the roots to bond wing joiner & spar together and reinforce the incidence tube.
DSCF8740crop.jpg
The precut leading edge sheeting was also fitted so the epoxy root reinforcement cures all as one assembly
DSCF8741crop.jpg
User avatar
Wayne_H
Posts: 809
Joined: 17 Feb 2018, 05:26
Location: Temora, NSW. Australia
Contact:

Re: Graupner Cirrus 21st Century edition

Post by Wayne_H »

stuart mackay wrote: 08 Nov 2021, 21:08 ....I am looking for some of this glass tissue on a roll to reinforce the trailing edge inside before adding the top skin, has anyone here seen this stuff for sale in the UK? Think it is called glass fibre fleece as it is non-woven, unlike a glass tape.
Stuart,

It looks very similar to several of the growing variety of jointing "tapes" now available to plasterers/drywall finishers/etc. Might be worth a research trip to one of the bigger DIY stores or speciality building material suppliers. Just watch the weight.

Alternatively, and my preferred option, try a specialist fibreglass supplier, one that stocks cloth, tapes, tow, resins, etc.

You could try a length of carbon or glass fibre tow sandwiched between the TE sheets, but again, watch the weight (i.e. resin). I've had very good results in similar applications with lightweight (180 - 220 g/m2) carbon cloth, preferably pre-applied to the bottom sheet (only because it's easier) with the weave at 45 degrees to the TE.
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
User avatar
stuart mackay
Posts: 501
Joined: 01 Mar 2018, 10:38
Location: Swaffham, Norfolk
Contact:

Re: Graupner Cirrus 21st Century edition

Post by stuart mackay »

Received some of the elusive tape from the Kit supplier in Switzerland and have used it on the other wing half which I built this afternoon.
User avatar
stuart mackay
Posts: 501
Joined: 01 Mar 2018, 10:38
Location: Swaffham, Norfolk
Contact:

Re: Graupner Cirrus 21st Century edition

Post by stuart mackay »

Teaching got in the way of progress this week, but this afternoon, completed the glassing the TE on the other wing panel using the elusive glass tissue tape.
DSCF8832.JPG
I also had a go with the Kontronic Drive that Mike K had kindly sent me for the project and after changing the connector to an XT60 was able to power it up connected to a Lemon 6 ch Rx.
Kontronic 40-42, 5.3:1 Maxon Gearbox
Volts 11.1 V (3S)
Current 30 Amps
Prop 10.5 x 6
RPM 8900
DSCF8828crop.jpg

Encouraged by the breeze created, I made up a 40 mm motor former from 1.5mm Epoxy board, sliced the nose off and epoxied in place with a couple of degrees of down thrust relative to the stabiliser.

I had originally planned on a 40 mm spinner but think I will get a 38 mm Perkins CNC spinner and prop adapter from Pegasus in Norwich tomorrow.
DSCF8829crop.jpg
DSCF8831crop.jpg
As you can see, it all fitted beautifully with the canopy frame instrument panel moulding clearing the motor by a good margin...made for the job, methinks!

More to come
User avatar
Wayne_H
Posts: 809
Joined: 17 Feb 2018, 05:26
Location: Temora, NSW. Australia
Contact:

Re: Graupner Cirrus 21st Century edition

Post by Wayne_H »

stuart mackay wrote: 19 Nov 2021, 22:54 I also had a go with the Kontronic Drive that Mike K had kindly sent me for the project and after changing the connector to an XT60 was able to power it up connected to a Lemon 6 ch Rx.
Kontronic 40-42, 5.3:1 Maxon Gearbox
Volts 11.1 V (3S)
Current 30 Amps
Prop 10.5 x 6
RPM 8900
Hi Stuart,

The current & RPM figures you are getting for this combination are very conservative! Another 10amps could easily be accommodated by the motor & g/box. Suggest you try at least a 12 x 6. You don't need any more pitch unless you want Hotliner performance :shock: Also, I recommend you program in a 0.5-1.0 sec soft-start to reduce initial current draw and protect the g/box from excessive shock loading.
stuart mackay wrote: 19 Nov 2021, 22:54 As you can see, it all fitted beautifully with the canopy frame instrument panel moulding clearing the motor by a good margin...made for the job, methinks!
Yes, it does look a great fit. Beware of heat radiating from the motor case, which will continue after you have shut the motor down, until the motor is cool. If the canopy frame/instrument panel is plastic, it will distort. If glass, it will potentially soften, so could also distort over time. Ensure plenty of flow-through ventilation - a small NASA inlet either side of the nose abeam the g/box and outlets behind the battery will keep everything much cooler.

Speaking from bitter experience, rather than painting the top of the instrument cluster a dark colour, try 1000-2000 grit wet/dry paper glued on - it looks very scale like and helps insulate the underlying surface, further reducing the chance of heat distortion. Just think how warm your car's dashboard gets after sitting in the sun for several hours, even in Pommy Land :P
Admittedly, my large scale sailplanes spend much of their time in temperatures of 30+ deg.C but why risk it?

It should be a great flyer, enjoy.
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
Post Reply