CriCri MC-15 in NZ

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MadRocketScientist

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I tried fresh tempering the seat mount tubes, they still cracked.

The fold is along the grain of the tube and its also a zero bend radius fold. The only solutions I can see are to put and inserts inside the tube (similar to the pushrods in this post) or to file the cracked area away once the flattening is done.

Last night I formed the clamps for around the seat tube. I used the flattened tube I made earlier to test the setup. The plans call for the length of the flattened support tubes to suit. I guess I will wait until I have the seat frame bent and covered before I make them.

Today I cut the thick washers for the landing gear clamps and then started on the pushrods. I had cut the pushrod parts a while back but had to spend some time deburring and smoothing the tooling marks from the edges of all the parts. The smaller bare aluminium pieces fit inside the tubes and the plates go on the outsides to allow for bolting through the spherical bearings on the control arms.
Hopefully I will get back and start flattening and drilling the ends of the tubes tonight.

Shannon.
 

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MadRocketScientist

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Welding would make more work and I don't have a TIG welder handy:dis:. I am after a 'simple' fix if possible. Maybe a drilled hole and slot so the edges don't have to fold over themselves at all?

Tonight's effort continues with the pushrods. I made a couple of aluminium blocks with tapers on the ends to press the flat areas on the ends of the tube. The taper stops the transition from being too sudden (The idea was 'borrowed' from another CriCri builders photos) I folded some 0.020" around one of the blocks to keep them aligned while I clamped it up in the bench vice. I set the length for the larger elevator linkage tubes so I could sit them against the folded end and the flat would be pressed the correct length. I had to insert a small spacer for the flapperon control tubes as the flat areas are slightly shorter. I used the tube inserts to stop the tubes from being squashed too flat. They press slightly oversize but a panel beating hammer sorted that out. Maybe a set of thinner spacers would also work.

I made careful use of the plans as there are two tubes with flats on both ends. One of them has the ends parallel and the other is at 90 degrees. Got them both right first try:).

I still need to pull these apart and de-burr them all. The smaller ends need to have a joggle in the plates to allow for more lclearance on the spherical bearings. I am tempted to flush rivet all the plates just for the looks (flush rivets look good anywhere:gig:) I have spoken to one of the LAME's out at the airfield and they did say the plates are thick enough to flush rivet safely.

Shannon.
 

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Autodidact

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MadSci, just more supposing; don't know if this would actually be stronger than than what you've already got, maybe less prone to the continuance of the crack?:
 

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MadRocketScientist

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That would possibly work with larger tubes but this one is 3/8"diameter and 0.035" wall. It wouldn't leave a lot of room for the bolt and washer. The insert idea may also end up too thick and not wide enough to allow enough room to bolt through too.
There's no real hurry to get it sorted as the seat is a long way from going in. I will ask other CriCri builders about it when I see them at the Tauranga airshow in a couple of weeks time. It may well be one of those things that isn't really an issue at all.

Shannon.
 

MadRocketScientist

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update time... I formed the joggles on the ends of the smaller pushrods. I formed the parts in the vice over a slotted piece of aluminium, seemed to come out reasonable but they did need a tap with the hammer as they had been slightly overbent.

I finally finished forming the hat section for the pedal rails with the help of a custom jig. I had folded the sections into a U channel on the folder a while ago but had not managed to form the center 'hat' part. its hard to see from the photo but it has a slot and a tongue that forms the center part of the hat. With some help from a friend and his 10 ton press it formed reasonably well. It still needs to be curved to match the lower fuselage and the ends joggled to fit over F1 and F3.

Shannon.
 

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vondeliusc

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MadSci, just more supposing; don't know if this would actually be stronger than than what you've already got, maybe less prone to the continuance of the crack?:
Shannon-
I was thinking along the same lines as Autodidact..
Same drawing as he provided; use an interim spacer to compress down to full width (calculated), then use a 1/16" welding rod bent into a cornered 'U' with the legs into the tube (providing a radius on both sides) and using his central compression 'width' form (8mm-fits between the 1/16" welding rods.)



Also, I am starting to work more in earnest on my SolidWorks drawings, and in turn thinking about components I run up against.
I am intending on using imperial tubing for the nose gear.
0.875"x0.049" 4130CrMo Outer
0.75"x0.058" 2024T3 Al
We do not have metric tubing availability. What do you think?
-Christian
 

vondeliusc

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I am intending on using imperial tubing for the nose gear.
0.875"x0.049" 4130CrMo Outer for the 401-04 22mmx1mm
0.75"x0.058" 2024T3 Al Inner for the 401-05 18mmx1.5mm
(gave you the part numbers)
Will have a bit of inner clearance, but I think it will be ok?
-Christian
 

MadRocketScientist

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Hi Christian,

I will give the seat tube forming a go when I get back from Tauranga. Sportavex/Tauranga airshow is on this weekend and I am flying up there in a microlight to see the airshow.
Tauranga City Airshow
The two NZ CriCri's will be there. Sadly ZK-CRI is out of action due to an engine failure but will be there. I suspect the failure is due to loss of prop friction against the hub when the wood prop compresses slightly, causing the bolts to break .

I am going to ask Nev and Wayne about the nose leg tubes as I have the 0.875"x0.058" 4130 and 0.75"x0.065" 2024T3 for the inner. There is an unacceptable amount of free play with those sizes. I am thinking of going to the next wall thickness 4130 outer tube and ream the 2024 inner to suit. The cut will be removing in the order of 0.1mm. Wayne had issues with his gear leg and it appears that he coated it with epoxy to make the sliding fit good enough.

I will post some pics when I get back, hopefully I will get to sit in a CriCri or two.:)

Shannon.
 

vondeliusc

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With stock imperial sizes, I know from hang gliding, that the next size down sleeves well with the outer having an 0.058" wall, but I have calculated the cross-sectional area of the 22x1 vs the 0.875x0.049vs0.058 and I think the weight gain would be excessive with the 0.058. But you gave me a good idea..perhaps use the 7/8ths049 and build a layer of epoxy up on the 3/4 and lathe it to the correct OD. The epoxy would be lighter than the steel and would bond to the Al well, and using a lathe it could be quite precise. The main strength and weight of the nose gear leg is in the outer, so I will be inclined to match it as close to the 22mm as possible.
Have fun at the airshow! and burn up some 'film'. You can post it at Picasa for free.
-Christian
 

MadRocketScientist

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The extra weight of the 0.058" wall tube has is only 34 grams heavier than the 0.049" and the 0.065" is another 26 grams . I may be able to allow that as an extra coat of paint on the exterior adds 500-1000grams. The 0.049 wall tube is around 1.3mm which is thicker than the plan specified 1mm. Lots to think about anyhow.

I would be concerned about the epoxy breaking away if the nose gear hits something hard enough to flex it.


Shannon.
 

MicRuler

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Hi guys, I have a question, I've just downloaded the plans for the Cri MC-15 free from a yahoo group. Is it alright to build and fly without permission from Colomban?
 

MadRocketScientist

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The plans issue is a big one but by all accounts Mr Colomban will still supply plans to anyone outside North America. He does seem to be more interested in his other aircraft designs. He is actively involved with the MCR series of aircraft and also the newer MC-30 Luciole. I think the Zenair/Cricket debacle did a lot to dampen his enthusiasm for more marketing of the design. I would recommend that anyone who is able to purchase the plans as they are only a small part of the time and cost of building a CriCri.

The Trip to Tauranga went very well. Flew direct from Rangiora airfield to Tauranga in an Evektor Sportstar (4 hours) Arrived to lots and lots of sun although the heat took some getting used too. A big thanks to Tauranga Aero Club for use of the excellent facility for all the NZSAA proceedings.

Both Nev and Wayne had their CriCri's there. I hope I didn't drive them both to distraction with all my questions. I got to sit in Nev's CriCri (I fit easily with head room to spare) and they gave me many ideas of small changes to make things better.

Shannon.
 

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MadRocketScientist

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Today I have put into metal some of the ideas that I picked up in Tauranga. I formed a rolled edge on the front of the seat tray by forming it over a 3/4" aluminium round rod. Nev said that the front of his seat was digging into the underside of his legs in turbulence. He rolled the edge on the front of his seat, problem solved.

I also purchased a thicker 4130N nose gear tube (center tube, last pic). Both Nev and Wayne thought the thicker tube would work best when I asked them about it. Thanks to Nev's cat, he had to chrome his nose gear leg (go on ask why;)) . Turns out that it looks really good chromed and gives a hard wearing surface. I will machine the 0.15mm or so off the aluminium inner tube and ream the slider block after mine is chromed.

I also looked at the top seat mounts on the other CriCri's. Nev has used some angle in place of the flattened tube and Wayne used some commercial grade tube as it would flatten without cracking. I may use the commercial grade, 6063 is available locally and should do the trick.

I have also continued forming the pedal rails (no pics though)

Shannon.
 

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MadRocketScientist

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Working on the pedal rails, they are one of the (many?:devious:) items that all builders seem to complain about. I mangled the first two sections (they are two of the ones with the PVC removed) after trying to form them by hand. Cut some more parts on the CNC and folded them on Pat's folder (thanks again Pat).

After a fair amount of trail and error I made up a former for putting the correct curve on them so that they sit nicely against the bottom skin. Its far easier to bend with a former as I just clamp one end and push the rest over the curve. The fit is very good, hopefully drill and cleco them in tomorrow.


Shannon.
 

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litespeed

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I bet the cat pissed on the leg and rusted it big time- cat pee is extremely concentrated and very corrosive.

Keep up the good work- oh save some money and weight and polish the bird, look would be awesome!
 

MadRocketScientist

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Good guess, the nose gear block is phenolic and slightly absorbent so when Nev replaced the front leg it rusted again. The chrome solved the problem and it looks great.

I am planning to polish my CriCri. I am also considering forming the cowls and wheel pants out of aluminium too. I think I will only alodine the interior and leave it at that.

Shannon.
 

MadRocketScientist

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Installed the pedal rails today, clecoed in a few places but I will drill all the holes to size later. The hat sections are clecoed from the underside of the cradle as I made it out of 6mm MDF. The clecos just reach all the way through. I cut a set of alignment blocks to make sure the caps are parallel. A few pieces of PVC tape stop the underside of the pedal tray from getting scratched up during test sliding on the caps.

The pics don't show it very clearly but the PVC coating is removed wherever two aluminium surfaces touch so that all the holes will line up later. When things stack up the thickness of the PVC layers can shift things a bit too far. The lower skin however, still has all its coating as it doesn't affect the alignment when it is removed.

Shannon.
 

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litespeed

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Lookin great Shannon,

How many hours do you expect the build will take?

What engines are you going to use?

Phil
 
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