Colomban, Cri-Cri MC15

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Colomban, Cri-Cri MC15

Somewhat behind schedule I have restarted work building my Cri-Cri MC15 Aeroplane, the worlds smallest twin engine aircraft.

This page is dedicated to the construction of my Columban CrCri MC-15, originally planned as a two year build (Started 2003!) it is a little behind schedule. After a break of just over two years I have started again in earnest, the new glue has arrived and has an expiry date of November 2017, I am not planning on buying any more and so that is the new deadline.

08/08/2017

A few images of the rear fuselage, the skins and bulkheads are made from 2024 T3 0.5mm sheet, the bulkheads were folded on a box and pan folder and then the corners 'joggled' using an MDF form, the flanges around the two holes which will eventually carry the rudder cables were formed using a piece of piece of nylon 20mm x 10mm with a small cut 0.5mm x 5mm, the tool was then run around the hole whilst 'easing' the material out, the tool was about wrecked at the end, but it full filled its duty.

11/01/2016

A little work today on the right hand main spar, a few tweaks with the rubber mallet straighten out the forked part, riveting hand caused it to distort so that the ends where around 1mm out of true. I can honestly say I have hated every moment of working on the spar and will be glad when it is finally finished.

A few historical pictures again I'm afraid, I ordered the Aluminium angle from Aircraftspruce, it arrived promptly 3 days after ordering it. The spar is made from 3.2mm 2024 angle riveted to a 0.8mm 2024 web to form a capital 'I' shape, the caps taper from 3.2mm at the tip to 20.9mm at the root (I think those numbers are correct), I cut the caps down in the band saw and then filed to the final size, Mr Colomban gives a tolerance of +0.5mm and -0mm from the dimensions specified. The web side of the cap is cut to 15.0mm with the rivets dead centre, this produced a rather serious issue, the internal radius if the angle is far larger than the angle in the plans, the rivet heads will not sit flat due to the proximity of the radius, bu**er! A number of discussions with my inspector and eventually a letter to Mr Colomban solved the issue, the solution is to cut the caps 15.5mm and drill the holes 8.5mm from the corner, this still caused the rivet heads to sit proud but they can be easily 'leaned' into the radius with a rivet squeezer. End of problem? not quite, I had cut the caps almost to there final size, two of them had been cut to 15.1mm and were therefore undersize by 0.4mm. By this point around 18 months had passed and Aircraftspruce are no longer able to ship the angle full length, luckily they have a Euro hub which shipped the following week. By the time the caps were down to size almost two years had passed!

Next it was time to spot bend the caps, a folder was fashioned from 2014 Aluminium from the local supplier, hey presto it works, and really well if I do say so myself, collection/machining/threading/polishing e.t.c took maybe 30 hours, the bending took less than an hour, folding was very easy and care was necessary to avoid over folding. The righthand caps are folded twice, it was therefore necessary to machine two clearances either side of centre to accommodate the first folds, all in all a success. Hooray!

08/01/2016

A few pictures from before I went away, Mr Colomban left a little trap for me! When fitted, the lower cap reinforcers foul the rivets of the opposing longhorn, I was left with a choice - either cut away half of each rivet or machine a chamfer on the edge of the reinforcer. A few calculations revealed that the chamfer would remove between zero and 1.8mm square of material depending upon location, this equates to 5.8% of the reinforcers CSA. The reinforcer is optional and increases the fatigue life of the spar from 200 to just over 2000 hours, 200 x 9.42 = 1884 hours, I would rather increase the life less than weaken the opposing spar and so I machine the chamfer off using an 8mm ball head end mill as below. I remember seeing a large chamfer when I was saw a Cri-Cri and now i know why.

01/01/2016

Rather randomly I decided to make the corner reinforcers for frame 5, well why not aye. Made from 1mm 2024 they are cut to shape before being folded in the magnum bender with a bend radius of 2mm. As a word of note if you are folding metal it will 'grow' perpendicular to the fold line by an amount equal to the fold radius, for example the upper portion is 100mm and the lower portion needs to be 12mm, the developed length was 110mm which when folded produces the correct overall dimensions.
The 20mm hole was marked by producing a quick jig to ensure accuracy, I don't want any nasty surprises when I come to fit the control rods. The 20mm hole was cut using a trepan mounted in an ER32 chunk in the milling machine, I cannot recommend using collets highly enough, they are so superior to a chuck in every way - well almost every way, they do take longer to swop. Next job is back to the mains spar.

27/12/2015

Christmas is thankfully over and it is back to the Cri-Cri, I have to work in Germany next week for a few days and so I have 7 days to learn German, two days in and the going is slow!

After work today my evening task on the Cri-Cri has been on frame 4 once again. I have secured the wing pin doubler plates to the front and rear halves of Frame 4, they are bonded and then riveted with countersunk 1/8" rivets. The plates were located on the front frame by measuring the edge distances from each end and the lower web, the assembly was pinned and initially secured with 3/32" clecos before enlarging to the final size, the rear frame was then centred on the front frame with 1.4mm overhang each end before being drilled through with a 2mm bit and the whole process repeated for the rear frame.
Just as with every other task so far it took a lot longer than estimated, in total it took 4 hours tonight and two hours on Christmas Eve, 6 hours to drill and rivet 4 plates! Unfortunately there are still rather a few parts left to secure.

That will do for tonight, I have 90 minutes of German lessons to do.

22/12/2015

Still up in Scotland, but I will be coming home tomorrow, a few historical pictures again i'm afraid.
The rudder this time, a really easy a relatively large piece considering the time involved, the ribs are all different but are very easy to make once you have the cutting tool described earlier, the ribs are rough cut and baked before having a 15mm hole cut in the leading edge, the ribs cam then be 'swung' on a peg set the correct distance from the cutter, the edges can then be cut using a sharp blade and a straight edge. The ribs and same 15mm tube is then fitted into a suitably manufactured comb made from 12mm MDF. The skin is cut to the correct dimensions before being scoured and painted, once dry the sheet is folded around a steel bar (I forget the diameter) the sheet is then bonded along the first 50% of the ribs 'on jig' secured with elastic bands and clamps. Once the from is dry the assembly is removed and then the rear half bonded (don't forget to break the trailing edge 5mm in).
The upper and lower bearing plates were swung in the lathe and machined from 2024 60mm diameter. Trying to remember all of the steps is bringing back some rather unwelcome memories that I had suppressed for many years, if I can give you any advice it would be this: Do not try to cut corners, it is better to make one form out of Alu than 2 out of MDF, make it right - make it once, if Mr Colombian recommends you do something then do it!

19/12/2015

Another wet and windy day, amazingly warm though for the time of year, 36C warmer than the same day 4 years ago! I have remade wind pin reinforcers 202 09 as the edge distance was a little small on the ones I made a few years ago, I will paint them tomorrow and fit them some time next week, I have a couple of jobs in Scotland next week and won't be back until Christmas Eve, not much work will be completed before Christmas I suspect.

Bonded the front lower spar doubler to the left hand spar, tomorrow I will attack the rear doubler.

Dropped the Girlfriend off at the pub last night, on the way back the oil light came on the Volvo and it promptly seized!! Looks like some Cri-Cri time will be spent looking for a replacement engine - and then putting it in. The last vehicle I had that seized was a motor crosser back in the 90s, I thought those days were behind me.

16/12/2015

Removed the front and rear halves of frame 4 from the jigs, all looks good so far, next I need to locate the wing pin centres and bond the wing pin reinforcers in place.

The Left main spar lower cap doublers have dried and are ready for bonding, tomorrow I will spend some time and bond them in place before baking in the oven, they need to be fitted perfectly to ensure the fatigue life is maintained and the spar plates fit correctly - so no rushing!

14/12/2015

F-PYYJ le 26/12/2012 en tour de piste à LFMV. Pilote : Philippe MAZELLIER

13/12/2015

This weekend has consisted of bonding and riveting the front components of Frame 4, the cross member, corner webs and vertical components were first bonded before being riveted, two jigs were made to locate the uprights during bonding. The jigs took a little time as they have to be exactly right, the final accuracy was +/- 0.2mm. Using the old 3-4-5 method to square the uprights produces amazing accuracy.

All components are packed to the correct heights using scrap offcuts of sheet with Aluminium foil lightly waxed to prevent the components sticking in the corners of the jig.

I need to work away tomorrow so no Cri-Cri work, but the next task will be to bond the rear section of frame 4 in the same manner as the front, and then on to completing the main spar.

08/12/2015

A couple of hours squeezing rivets this afternoon, actually quite relaxing once you get into the rhythm, especially the 3/32" ones.
The front tunnel box lower section is riveted and bonded ready to accept the uprights, I will finish painting the rear parts tomorrow and build the jig necessary to hold the uprights during bonding.

Talking of glue, the stuff used is Araldite 420A/B - formally called Redux 420A/B, I use a high sensitivity scale to mix the small quantities to the accuracies needed, the front section used 1.4g of glue mixed in the ratio of: 1 Base to 0.4 Hardener, the scales I have measure up to 200g in 0.01g increments.

07/12/2015

A few more bits painted, and work has begun bonding the front half of Frame 4 (Spar Tunnel), all bonded parts fixed with Clecos dipped in WD40 to ease disassembly. Baked at 75C for two hours cures the parts sufficient to allow riveting without 'Swelling' between rivets, elevated bond temperatures produce stronger joints and increases heat resistance.

Riveted the pedal pivots in place and loosely bolted the 15CDV6 pedals that had been prepared earlier.

All in all a successful few sessions, I really had forgotten just how long everything CriCri related takes, the prepping alone took best part of 8 hours with the painting another 4, fortunately everything else in life is great, with nothing else to do.....

Address

Bewdley
Worcestershire

Website

http://www.aerial-imaging.co.uk/

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