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CriCri MC-15 in NZ

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PIK-21

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Apr 21, 2015
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Switzerland
Sometimes there is a method to the madness and sometimes there is just the madness..

I really wanted to have a look inside my airspeed indicator due to it being solid state rather than purely mechanical. There are plenty of pictures of the insides of traditional airspeed indicators but nothing about these new magic boxes of tricks. I ummed and ahhed for a while about drilling out the rivets. Eventually curiosity go the better of me :D

It was soon in pieces.
View attachment 92278
Having successfully reduced it to parts, I needed a way to hold it all together again. At first I made some replacements for the mounting screws/rivets, but I soon decided I might like to get at the insides again sometime.
View attachment 92281
I turned up some additional threaded 'nuts' the go on the backside of the threaded fittings to lock everything together but also being removable. While I was at it, I changed the threading from 4-40 to M3 metric so that all the screws on the instrument panel are now M3. (The MGL instruments are all M3 mounting screws.)
View attachment 92280
While I had the ASI open I dug out the sticker sheet I had purchased from aircraft spruce at the same time,
View attachment 92282
and with some careful consultation of the flight manual, put the colored arcs in place on the bezel.
View attachment 92283
I would also like to add the blue line (single engine best rate of climb) but I cannot seem to find any documentation as to what speed this is for the CriCri.:confused: If I find out from somewhere I can now easily open up the ASI to put the sticker in place.
Hi there, single engine is approx 75 mph with flaps retracted.
 

MadRocketScientist

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Canterbury, New Zealand, Earth, Milky Way Galaxy.
A question for anyone willing to chime in,

I have been pondering my wiring layout and started working on the diagrams and I am considering having the mag switches for each engine on their respective sides of the panel. Mainly under the assumption that it would be less confusing as to which engines ignitions were being switched during mag checks etc. I was thinking of locating the two switches for each engines ignitions, to each side of the engine temperature gauges in the picture below (where the red switches I added in MSpaint are ;) )

I haven't really seen any panel layouts from twins apart from the pictures of CriCri that I have downloaded. I haven't seen it done this way before and I am wondering if there is any reason not to do it this way?

Comments anyone?

DSC09042 (Medium).JPG
 

blane.c

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Jun 27, 2015
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3,909
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capital district NY
I wouldn't.

I generally fly with one hand and flip switches with the other. Sheesh if the switches are side by side are you really going to mistake the left from the right?
 

TFF

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Apr 28, 2010
Messages
13,476
Location
Memphis, TN
Put switches on the side the throttles are. Unless you put right throttle on right and left on left. Then I want video.
 

Strasnuts

New Member
Joined
Jan 28, 2020
Messages
1
A question for anyone willing to chime in,

I have been pondering my wiring layout and started working on the diagrams and I am considering having the mag switches for each engine on their respective sides of the panel. Mainly under the assumption that it would be less confusing as to which engines ignitions were being switched during mag checks etc. I was thinking of locating the two switches for each engines ignitions, to each side of the engine temperature gauges in the picture below (where the red switches I added in MSpaint are ;) )

I haven't really seen any panel layouts from twins apart from the pictures of CriCri that I have downloaded. I haven't seen it done this way before and I am wondering if there is any reason not to do it this way?

Comments anyone?

View attachment 92948
I like it, I've flown all kinds of twins and they are next to each other but some of these are big cockpits. This panel is so little and you are centerline I think you should put them wherever you want and what makes sense for you. Looks to me like it would be easy to reach them with the same hand.
 

MadRocketScientist

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Thanks for the comments everyone, I will think about this some more. Current thought is to keep the switches on the opposite sides of the panel but at the bottom corners of the panel in line with the starter switches.

The whole panel is easy to reach with either hand, there definitely isn't room to swing a cat in this cockpit. A mouse? maybe?

Thinking out loud, here are a few other CriCri panel pictures found around the internet.

First is the super cricket from the 70's that had the two 30Hp rotax engines installed. The two ignition switches are directly in front of the throttles. This switch location seems to be used on around 50% of the CriCri builds. Interestingly even the ones with dual ignitions seem to only have two switches. When I get the chance I will have a closer look at ZK-LBW at the local airfield, it has the same setup but with dual ignitions on the engines.
Super_Cricket_05 (Medium).jpg
This next image is the first CriCri ever built, the switches are up on the panel besides the ASI (in the shadow of the canopy frame). I have pictures of several different cockpits with this switch location.
28276461_1537475766369771_5052385639975975812_n (Medium).jpg
Here is ZK-CRI, the switches for the four ignitions are down beside his left knee.
image15.jpg
and finally this panel has the ignition switches about half way up the panel on the left (above the RPM guage).
PICT1777.JPG
 

litespeed

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May 21, 2008
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Sydney
I like the way you have it. The distances are not great so easy access, with either hand or same.

Yours makes it dead simple and hard to make a mistake. Very easy to scan and see whats happening and compare. I like it.

Don't over complicate, no need to follow tradition, it is not a complex big twin.
 

MadRocketScientist

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Canterbury, New Zealand, Earth, Milky Way Galaxy.
And here is the starter wiring diagram.
At this stage I am keeping this complete system separate from the others with its own higher voltage 18 volt battery. I haven't sorted out a way to switch the battery in and out of the circuit other than physically unplugging it. the system runs as a total loss battery, I should get possibly hundreds of starts from one charge but it will get charged more often than that. The battery is sized to supply the peak current draw when turning the engine over. The actual capacity needed for each start is very small.

I also intend to run all the electric systems as a total loss to make things simpler. Charging batteries is nothing new to me as I fly electric radio control aircraft almost every day the weather is suitable.
 

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MadRocketScientist

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Canterbury, New Zealand, Earth, Milky Way Galaxy.
I have been doing some testing of the ignition modules and sorting out what DC-DC converters to use to supply the 6 volts to them from the (at this stage of planning) 12 volt aircraft supply.

I bent out ground strap on a pair of sparkplugs to test the ignitions under more realistic conditions to what the plug experience when the engine is running. I learned this trick from over at the FlyingGiants RC forum. The longer spark distance simulates the higher resistance of the fuel air mixture in the combustion chamber. It is also helpful for testing if the ignition will reach full voltage or if the spark leads need replacement due to internal arcing etc, as well as show up issues that might not appear when testing with the standard plug gap.
DSC09055 (Medium).JPG
I have four of the older Rcexl A-01 ignitions and one of the newer A-02 ignition modules. The newer one is rated up to 12 volts, the old ones I have only accept from 4.8 to 6 volts. According to Rcexl, even the newer ignitions work best with around a 6 volt supply voltage. I think it keeps the amount of heat in the module low. Both of these modules are barely warm to the touch after running for an hour, the older one being ever so slightly warmer due to the higher energy consumption.
DSC09049 (Medium).JPG
I tested the older ignition with the bent strap plugs installed. On 6 volts, the ignition draws 130mA at idle (no spark) and with a current draw of 560mA at 8000rpm. I changed the plugs to some with a 0.6mm plug gap to see if the current draw was any different, pretty much the same results. I used the Rcexl ignition tester and the ignition hooked up the tacho to set the rpm.

Interestingly the newer ignition uses a lot less with a idle current of 83mA and 350mA @ 8000rpm.
DSC09048 (Medium).JPG
I have a few cheap DC-DC buck converters from Ebay that I have been using in my radio controlled planes and gliders. These are 5 volt but the voltage can easily be changed to 6 volts by swapping out an SMD resistor.
After downloading the datasheets for the IC, it appears the Chinese like to skimp on the inductor size, presumably to save cost. While this doesn't seem to affect the operation at all, since it works perfectly fine with my radio and receivers, the output ripple might be slightly higher than it could be. The inductors are sized according to the output voltage, the higher the output, the greater inductance needed. I can easily get the correct inductors to go with the voltage I use, whenever the nCOV pandemic situation clears up that is!!
DSC09051 (Medium).JPG
The ignitions also run just fine on these cheap voltage converters just as they are.
 

MadRocketScientist

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Not much progress lately, but I did reconnect the spark plug boots onto the second set of ignition modules. I had taken these off when I thought that I may need to extend the spark leads, but with the new engine mount setup this won't be necessary. Took quite a while to actually find the spark boot parts due to them hiding in the dark recesses of a box.
 

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MadRocketScientist

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After much thought I have a basic idea of the wiring. I intend to use a total loss battery system with two 12v batteries in a parallel setup. Each battery will power one ignition module for each engine giving some redundancy on that department. The rest of the electrics are powered from both batteries through a pair of diodes. If the master switch fails on one side it will show up in one of the voltmeter displays.

I am also considering running each ignition module from both batteries with its own pair of diodes from both batteries rather than the setup pictured below.

Lots to think about but I am aiming for good redundancy. The capacity of each battery would be at least twice the full fuel flight time.
CriCri wiring draft 1.png
 

MadRocketScientist

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Finally sorted out the routing for the brake cables today. Since the Avid brake calipers aren't handed, I needed the right side cable to exit behind the landing gear bow. Rather than route the cable under the bow itself, causing the fairing to stick down further, I drilled a 4mm hole through the middle of the fiberglass bow. I think it should be okay as there is another 4mm hole through the bow for the mechanism that keep the it centered under the fuselage.To add to the drama I also had to swap the mounting side of the centering mechanism so that there was room for the cable to clear it.
I marked out the hole location and clamped the bow to a hefty Vee block. I balanced the whole mess on the drill press to drill the hole (not pictured).
DSC09117 (Medium).JPG
DSC09120 (Medium).JPG
After removing half of the outer plastic from the cable guide I threaded it through the new hole in the bow.
DSC09124 (Medium).JPG
DSC09125 (Medium).JPG
I removed the outer plastic sleeve off in one piece without cutting it by carefully twisting and pulling it but getting it back over the cable guide again was a right act. When it wouldn't go on more than an inch or two, I pressurized the plastic tube with the grease gun to expand it slightly and after removing it from the grease gun, I quickly slipped it back in place on the cable guide before it shrunk again.
DSC09127 (Medium).JPG DSC09128 (Medium).JPG
I re-installed the gear on the fuselage and once I had it on I realized I need to change the size of some of the nutplates! The gear will have to come off again before I do thoseo_O I trimmed the brake cables to close to finished length and installed them temporarily.

I thought I had a picture taken of the main gear from underneath showing the cable layout, but it seems I didn't hit the shutter button on the camera properly. Its a bit dark underneath anyhow and I didn't really want to roll the plane on its side today. Maybe some other time.
And here is a picture of the left gear leg with the cable in position, the right leg is pretty much the same but the nose of the plane is the other side of the picture :cool:
DSC09129 (Medium).JPG
 

MadRocketScientist

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And in other news, I have done more testing on the ignition modules and how much power they use. After reading in some the user manuals, it seemed that the Rcexl ignitions work just as well on 5 volts even though the newer modules are capable of being powered by up to 12 volts.
The newer V-02 module uses 1.4 watts on 5 volts but this rises to 4.8 watts when powered by 12 volts. The older V-01 modules only handle 6 volts but they still use more power at 6 volts compared to 5 volts. I suspect the modules use a linear regulator and the excess energy is being dumped as heat. Using a small switch mode power supply to drop the voltage to 5 volts before it gets to the ignition module should be more efficient. Then If I choose, I could also run the whole electrical system on a higher voltage, as most of the other instruments can handle up to 28 or 30 volts. I am not sure about the radio though.

I tested the real life current draw of the instruments and got the following.

Swift Airspeed indicator 185mA @12V
MGL Blaze ALT-6 ALT/VSI 117mA @12V (max backlight)
MGL Vega TC-4 86mA @12V (max backlight)
LED voltmeter 13mA @12V
Rcexl LED tacho 60mA @5V

Using the V-01 ignition modules the system amp draw so far is around 1.3A @ 12V however I still need to allow for a radio, GPS and maybe a datalogger.
 

TFF

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Those original boxes were designed to run on five cell Nicads; soup du juor of the early 2000s. When Lipos came out people were putting two cell on and sometimes popping the box with a full charged battery. Made sense they move the power up for possible three cell Lipos.
 

MadRocketScientist

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Those original boxes were designed to run on five cell Nicads; soup du juor of the early 2000s. When Lipos came out people were putting two cell on and sometimes popping the box with a full charged battery. Made sense they move the power up for possible three cell Lipos.
The latest version can run on 14.4volts! I think the current draw might still go higher with the voltage though. If I ever get one I will test it to see.
 
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