CriCri MC-15 in NZ

[MadRocketScientist]

More progress today.
First up I purchased a brand new towball for pressing these ball joints. Can't go to wrong for $21NZD. I tested it out by making another pressed flange, the hole in the middle giving an idea of how much the mild steel stretches.

Stretches a long way without cracking. The outside sometimes wrinkles where the steel is getting pulled into the hole from the outside.

I marked around the outline with a sharpie and roughed the shape out with some tin snips.

Then cleaned up the perimeter with a flapper disk on the angle grinder. The flange was formed the same way as the earlier post, with a panel beating hammer...

Having completed the flange I then took to the lathe and turned up a couple of the 'ball' parts. The ball is really a ring with a spherical outside shape.

If you look closely there is a recessed step to fit over the exit of the header pipes. I think these may only need to tilt a couple of degrees each way, I will video the joint with the engine running to check how much movement is really needed.

The ball fits quite well on the headers.

I taped the flange to the tuned pipe to do a trial fit of the coupler...

 

[MadRocketScientist]

Welded the exhaust fittings to the tuned pipe and headers today. I used the MIG and it is rough as so don't look too close, doens't really matter to mush as it is a prototype.
First I cut some acrylic templates for the mounting 'ears' that the bolts to thread into. I also turned some aluminium spacers to hold the ears in alignment with the holes in the ball socket.

I cut some ears from 5mm thick mild steel but I was on a mission to get it assembled and didn't get any photos of the actual parts.

In the photo below, the acrylic cutouts do a stand-in for the steel parts and show how they hold the ears in alignment. This fits neatly over the outlet pipe on the headers and is welded in place. Then I removed the bolts and welded the ball flange onto one of the tuned pipes.

And here are a couple of photos of the finished setup. I just grabbed some random springs from out of a junk box. I think I will make some springs from some K&S music wire, they certainly need to be stronger than the current springs. The bolts are 10-32 and will eventually have locking nuts on the frontside to lock them in place. Testing will show if I need to go to the next larger bolt size. I like the minimalist look of the setup and I think I can save a little more weight on the V2 model.

 

[Jay Kempf]

That just won't do. Too much drag. Those tubes all need to be aero contoured and that coupling junction needs to be machined out of billet with cooling fins and fully contoured. Disappointed. And I can see the fasteners! Sheesh! <facepalm>

 

[MadRocketScientist]

Haha! I have to offset the extra hp somehow

 

[MadRocketScientist]

More random progress today, I have removed the engine mounts and alodined them. I used some fresh alodine and they ended up a bit darker than I intended. No matter at least they won't corrode now.

I also cleaned up all the music wire holders and alodined them as well.

I had some stop sleeves for the 1/16" brake cables but they are quite short and weren't available in the tin plated variety needed for use on stainless steel cable. I also wanted to ,make them longer for a stronger grip, so I decided to have a go at making my own.
My first mistake was to make some from 6mm diameter copper rod, only to realise later that the stop sleeves I had were 5mm diameter I tinned them with lead free solder (99.3% pure tin)

But since those were not going to work I then made some from some 5mm copper rod instead.. The tinning is a bit thick on the outside of these so I may reheat them and wipe off the excess. I removed any excess tin from the internals by running a piece of cable through the inside while the tin is hot and molten. There is a way to do a chemical Tin plate process but I don't happen to have the right acids around.

I think a cable pull test is in order once I have some of these swaged in place.

 

[Kenneth Higdon]

Thanks - for showing your handy work. Good work ! Keep em' coming !

Kenneth Higdon
Alabama Gulf Coast Beach builder

 

[plncraze]

Nooo Kenneth, don't watch him. You'll never finish! LOL.

 

[Jay Kempf]

It's like watching some Swiss jeweler build a tiny airplane. Riveting. Wish I could go hang out and help but that commute would bite.

 

[MadRocketScientist]

It's like watching some Swiss jeweler build a tiny airplane. Riveting. Wish I could go hang out and help but that commute would bite.

And not to mention the two weeks in isolation when you enter the country....

 

[flyunder]

My cri cri engines

 

[MadRocketScientist]

Another little job done today, slowly getting closer to being able to test the engines again..

I cut some of the igntion sensor brackets from phenolic. The PLA of the 3D printed ones gets a bit soft and rubbery around 60°C but the linen phenolic should be good to around 120°C continuous.
I used double sided tape to hold some offcuts of phenolic on the CNC and let it rip.

The linen phenolic furrs up quite badly so I had to use some 120 grit sandpaper to clean them up. I could have cut the small undercut on the CNC but I was too lazy to make the custom cutter needed. I made a custom cutter for the lathe instead. I CNC cut a backing plate from some 10mm acrylic and turned the opening as close as I could to fit the freshly cut sensor brackets. Over tightening the 3 Jaw chuck held the brackets in place for machining, the slight distortion shouldn't matter. I machined the front face down from 13mm to the final thickness of 11mm and then flipped then around and then bored the recess to final size along with the small groove.

Looking the part but still more machining operations to go yet!

I have some slots and holes around the perimeter, the pair slots are for the two screws that lock the brackets in place and the holes are for adjusting the timing. Much easier to insert a 1/8" rod and use the leverage for fine adjustments. I have been thinking about how to cut the slots for quite a while, I don't have a 4th axis, mill or a divining head. What I came up with is 3 patterns cut from 10mm acrylic. I set these up against a V block clamped to the drill press. The sensor bracket sits on top and can be rotated around against each stop to drill the two 3.3mm (#30?) holes on one jig. Pictures tell the story..

The slots I cut a similar way but the sensor brackets are slightly unsymmetrical, so another jig was needed for each slot. I can't remember why I didn't make them completely symmetrical, there must be some reason?
I also did these on the same setup on the drill press, after adjusting the Vee block forward a slight amount as teh slots are close to the rear of the brackets. I drilled a series of holes and then carefully rocked the bracket back and forward using the drill press as a mill. The drill press spindle has a lot of play but if used carefully it make a reasonably straight slot. After testing these on the engine I then decided to widen the slots with a 4mm drill bit to give the screws more clearance.

Pile o' brackets ready for the next processes...

 

[MadRocketScientist]

Too many pictures for the last post,

How the sensor brackets fit on the engine, also showing some of the previously alodined parts with plenty more still to alodine.

The last machining step was to cut the recess on the front for the hall effect sensor. I cut the start of the hole for the wires bigger and then cut the 4x3mm recess with a 1.5mm cutter. The sensors themselves are really tiny!

I need to solder and heatshrink the wiring onto the sensor leads but here is how the sensor fits with the wiring coming out the back. I think I will pot the sensor and wires in place with epoxy of some sort, it needs to handle a reasonable amount of heat, JBweld may work as a potting compound.

 

[MadRocketScientist]

My cri cri engines

Have you had any interest in the sale of them?

 

[flyunder]

Yes for a price

 

[TFF]

That’s so nice. Are building in adjustment to fine tune the timing or do you have it where you are happy with timing.

 

[MadRocketScientist]

That’s so nice. Are building in adjustment to fine tune the timing or do you have it where you are happy with timing.

Making it adjustable to fine tune things. Since I am adding tuned pipes it may need to be retarded slightly compared to the typical 28° or so. From my reading the idea is to run the least amount of timing for the power needed, I guess to keep as far away from detonation as possible. I haven't shifted the timing at all when using the club prop dyno, I set it at 28° and left it there. I hope to run some tests with various timing settings and see how it affects the power and the engine temperatures.

 

[TFF]

All my tuned pipe experience is glow model, less variables. I would want it adjustable too even if it ended up in the original spot.

 

[Yellowhammer]

I haven't decided about releasing the CAD files yet, once they get out into the wild of the internet there is no getting them back. I estimate that I have over 1000 hours in them or more so I think you will understand why I am cautious about letting them loose.

I will share the files for the parts that I have changed from the plans to make the build go smoother, some have already been posted on this thread but I can send them to you all at once saving you hunting for them.

Are you going to do a build thread when you finally start?

I appreciate your kindness. I thought I would probably do a build thread for the Cri Cri since it is such a complex little airplane; What do you think?

 

[Yellowhammer]

Also, I totally understand you not wanting to release the files into the wild of the internet!!

 

[proppastie]

I set it at 28° and left it there.

It has been a while since I ran my engine......I put a timing lght on it and I think it was variable , or maybe it jumped to 30 and stayed there from TDC for starting. I thought the model ignitions were pretty similar. My trigger is just past TDC so it does not run backwards......Can you vary your ignition?