CriCri MC-15 in NZ

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MadRocketScientist

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Now that I have the heads all painted black, I only have a few more machining operations to finish them. Firstly I need to cut the sparkplug seats and holes and then thread them.
I spent some time today making a cutter for the threads from what I think is a boring head tool from a mill? It has a new job now and works for cutting threads on the CNC.

I ran a few tests on some scrap acrylic to get the fit pretty close to ideal. I do have the right size taps, but they cut the threads a bit too loose for my tastes. One thing I do come across fairly frequently on forums about engines of this style is the plugs coming loose and wrecking the threads. If I make the threads in the heads a close fit the the sparkplug along with correct toque settings, it should reduce the chances of this happening.

We shall see how much paint I end up removing in the process of completing them!
 

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TFF

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MadRocketScientist

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I tacked the new headers together a week or so ago and finally had them welded this weekend. Thanks Rory!

Since the exhaust flanges are so thin where they bolt onto the head, they tend to melt away during welding so I made them wider and cut them to size after welding. This makes it easier to weld and gives a neater final edge. The CNC'd groove on the underside gives me a final size to file to.
DSC00784 (Medium).JPGDSC00786 (Medium).JPGDSC00788 (Medium).JPGDSC00790 (Medium).JPG
The bolt holes are really close tolerance to keep the ports lined up, and since the welding shrinks as it cools, it was enough to pull the two holes closer to each other by 0.4mm (0.016"). I needed to slot the holes outwards with a round file to get everything to fit perfectly. I have already slotted the holes in the CAD drawings in case I ever need to make these again.
DSC00779 (Medium).JPG
A scuff up with some sandpaper and a light coat of matt black makes them look the part. I still have yet to get the ball ends welded on.
DSC00791 (Medium).JPGDSC00795 (Medium).JPG
 

MadRocketScientist

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What engines are you using? I have only seen pics of Cri-Cri's with single cylinder and jet engines, plus electric motors.
They are a now highly modified ZDZ210 B2RV-J but I would recommend that others use the ZDZ250 with twin spark heads. Same crankcase but less modification needed. There are a few pictures around of CriCri with boxer twin engines.
 

MadRocketScientist

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A bit pricey and overpowered for me, but good looking.
I spent a lot of time on the RC large scale forums searching for the various types of engines and how many failures they had. ZDZ tended towards the lower end in number of reports of engine failures AND many of those failures were overheating related. The thing that really sold me on ZDZ was that the large scale RC pylon racers are running them on methanol and revving them to over 9000rpm, getting in excess of 40hp in doing so.

I did look at the cheaper engines such as EME, DLA etc but they didn't have anywhere near the reliability or any extra hp in case of an engine failure.
 

MadRocketScientist

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Canterbury, New Zealand, Earth, Milky Way Galaxy.
Quick update of the last weeks progress.

The new spark plugs arrived, I ordered enough to have two full sets. Better to have spares on hand.
DSC00796 (Medium).JPG
from slightly longer ago, I have made some wing covers from some cheap sheets. I was finding that the polished aluminium scratches really easily and needed something to keep the dust off.
My mother sewed them up for me, thanks Mum! I could have sewn them myself but it has been so long since I used the machine that I am really out of practice. Better to get the expert onto them instead. I am still waiting for the chief seamstress to complete the elevator covers.
DSC00798 (Medium).JPG
I am also looking at getting some infusion resin to make some fuel tanks and landing gear bows so I have been doing some filling on the fuel tank male mold. I think I mentioned earlier in the thread but I intend to mold this so the smooth side is on the inside of the tank to limit any loose fibers getting into the fuel lines.
DSC00800 (Medium).JPG
And I continued some more work on the plug for the new and improved landing gear bow mold. I have designed this to be for infusion from the outset. The bow will be made from rovings placed under a slight tension, seemed to work really well on my first one and it hasn't sagged at all over the past years with the weight on it. Prestressed fiberglass anyone?
DSC00802 (Medium).JPG
I have also been spending more time flying the bright orange Karatoo, nicknamed the "flying road cone" and have over 27 hours, 3.6 hours solo. :pilot::cool:
 

Sraight'nlevel

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Quick update of the last weeks progress.

The new spark plugs arrived, I ordered enough to have two full sets. Better to have spares on hand.
View attachment 121537
from slightly longer ago, I have made some wing covers from some cheap sheets. I was finding that the polished aluminium scratches really easily and needed something to keep the dust off.
My mother sewed them up for me, thanks Mum! I could have sewn them myself but it has been so long since I used the machine that I am really out of practice. Better to get the expert onto them instead. I am still waiting for the chief seamstress to complete the elevator covers.
View attachment 121538
I am also looking at getting some infusion resin to make some fuel tanks and landing gear bows so I have been doing some filling on the fuel tank male mold. I think I mentioned earlier in the thread but I intend to mold this so the smooth side is on the inside of the tank to limit any loose fibers getting into the fuel lines.
View attachment 121539
And I continued some more work on the plug for the new and improved landing gear bow mold. I have designed this to be for infusion from the outset. The bow will be made from rovings placed under a slight tension, seemed to work really well on my first one and it hasn't sagged at all over the past years with the weight on it. Prestressed fiberglass anyone?
View attachment 121540
I have also been spending more time flying the bright orange Karatoo, nicknamed the "flying road cone" and have over 27 hours, 3.6 hours solo. :pilot::cool:

How much would you say that LG bow weighs ?
 

MadRocketScientist

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Canterbury, New Zealand, Earth, Milky Way Galaxy.
How much would you say that LG bow weighs ?
I was thinking exactly the same thing last night to work out how much resin is needed! I don't really want to pull the one I have already off the plane since it a a fair amount of work.

I sat down and calculated that it should be between 1.8 and 2kg, or 2.4-2.7% of the aircraft empty weight.
 

MadRocketScientist

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Canterbury, New Zealand, Earth, Milky Way Galaxy.
what made you decide to design/build new ones?
The first mold I made was a real pain to pay up as wet roving tends to pull down really flat around the corners and them bulge outward along the straight sections in the middle of the bow s cue to all the resin. Also with the first landing bow, I had to file a lot of the glass away in the center section to get the glass cut down to the correct thickness. Along with the handling the wetted out rovings it wans't really my idea of fun.

With infusion I can lay all the rovings dry and close out the mold before pulling the resin through. The taper in the ends of the legs means that I will have to use some shaped uni cloth sections internally to fill out the profile through the center section but the vast majority of the core will be a single piece of rovings looped back and forth. Setting everything up dry means I can play around with the layup until I get the thickness consistent right across the bow without dealing with the mess of resin. There might be a slight loss of some rovings but they aren't too expensive, in fact I have a couple of bales available that didn't cost me anything.

I will make sure to get pictures of the process eventually.
 
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Feb 6, 2022
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Now to the spar construction, CNC is great for things like the web reinforcements, hundreds of holes without any fuss.

Mdf is great for spar jigs, offcuts from paying work:) cut on the CNC (of course).

The last pic is the wing and elevator spar (nissan serena for scale)

Shannon.
I love the Cri Cri. Thanks for the great build picks. Especialy the spars; always intersting.
 

JonMiller284

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Apr 5, 2021
Messages
30
I tacked the new headers together a week or so ago and finally had them welded this weekend. Thanks Rory!

Since the exhaust flanges are so thin where they bolt onto the head, they tend to melt away during welding so I made them wider and cut them to size after welding. This makes it easier to weld and gives a neater final edge. The CNC'd groove on the underside gives me a final size to file to.
View attachment 121000View attachment 121001View attachment 121002View attachment 121003
The bolt holes are really close tolerance to keep the ports lined up, and since the welding shrinks as it cools, it was enough to pull the two holes closer to each other by 0.4mm (0.016"). I needed to slot the holes outwards with a round file to get everything to fit perfectly. I have already slotted the holes in the CAD drawings in case I ever need to make these again.
View attachment 120999
A scuff up with some sandpaper and a light coat of matt black makes them look the part. I still have yet to get the ball ends welded on.
View attachment 121004View attachment 121005
shannon, do you have a 3d model of these pipes you made?
 
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