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New throttle system for Rotax


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Work is progressing on the production version of the throttle mod

 

The hand made brackets I have now drawn up and modelled in 3D software. This then allows me to 3D print 100% size versions with reasonable accuracy so we know what we get when everything is laser cut. There has been a few revisions done to get the angles correct and some hole spacings. Had a test fit tonight of the main shaft and brackets..The levers and bearing blocks are all perfect now all looks really good just need to extend both the top bracket mounting holes at the rear about 1.5mm to allow for the bends in the brackets. Then print some more models with all bits attached including the carb throttle lever and finalise it then I can think about the laser cutter guys

 

 

 

 

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I don't know if this picture is any use to you but the only thing I would be worrying about that could upset this system you are proposing is if you start to get some vibration happening especially because you are putting a little bit of extra weight on the backend of the carburettor which could make the intake manifold more vulnerable to cracking.

 

I don't remember what aircraft this photograph was taken from but it shows how they made a simple bracket that stopped any carburettor movement whatsoever.

 

This may be a necessary addition to the whole system you are designing to stop any vibration or harmonics entering the installation you are completing.

 

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I have never seen that bracket before thanks for the picture...The whole system doesnt weigh much at all and it does tie both carbs together so not sure if it would be a problem. Dannys has an hour or two up on the original so far and no issues and will have another few hours up on it after this weekend as he is flying to the savannah muster on saturday. Carb balance is extremely rock solid too. I am making up a onboard carb balance monitor that will sit on the dash and connect to the ports on the carbs themselves rather than disconnecting the balance tube to do it. I have found a pressure sensor that should be perfect for doing that then will just have a LED bargraph that you can look at while flying or turn it around so you can adjust the balance while at the front of the plane.

 

The only thing I hadnt considered was if you had pods and not a airbox. Those pics show there maybe a small issue of clearance, This was designed for a savannah which has a specfic airbox. I have a set of pods here so will fit them to the spare engine and check clearance and see if the one system can be made to do both types of air intakes

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We are going to try the port on each carb..there is a pressure port in the base..it will only be a small pressure hence the need for a different pressure sensor. We have just got a new digital gauge to connect to that port to see what we get and because its a dual port gauge we should be able to measure the difference

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I don't know if this picture is any use to you but the only thing I would be worrying about that could upset this system you are proposing is if you start to get some vibration happening especially because you are putting a little bit of extra weight on the backend of the carburettor which could make the intake manifold more vulnerable to cracking.

Normally theres a tension spring from the balance clamp to the top carby screw to take some weight off the carb as pictured.

I can't see the weight of this device making much of a problem.

 

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I wonder if those with a dual cable operation system could leave ONE cable system connected to ONE carb, over (or under) your linkages?

I this was possible, far more aircraft could use this system and it would be easy to fit by removing the throttle cable from one side and adding your linkages.

Edited by Downunder
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Your rating a lot of weight a long way out from the carburettor mount. The only thing that attaches the carburettor is the rubber boot and the makeshift spring which can and can't work once it has been stretched a few times.

 

It was just a suggestion that as you are adding the additional weight out the back you are going to put more load on the carburettor boots and as you know these have a history of cracking, the more vibration and load out the back the more load you will be putting on the boots. Why not eliminate this area of failure and stabilise the carburettor completely. A lot of the carburettors are now using bigger air filters which in themselves are heavier. The small air filters are robbing horsepower so I was told. I will be really interested to see how it works out over time, you'll probably find Rotax copy it !

 

One of the things I'm just thinking about from memory one carburettor sits further back than the other carburettor so the one that sits further back is going to be subjected to more vibration and harmonics.

 

My memory is slowly coming back as to why the aircraft had these brackets. The clamp which attaches the carburettor to the rubber boot never used to have a spacer that would prevent over tightening so over time people would continue to tighten this clamp until the clamp itself was touching and this would pop the carburettor off, usually on start up but sometimes on shutdown and sometimes midflight. Rotax decided to add the spacer to the clamp so people couldn't over tighten this clamp anymore and this was introduced after a fire and fatality on the ground which was a result of one of the carburettors coming off an aircraft in the Czech Republic and catching fire and then exploding. This is why the manufacturer went to these carburettor brackets. I still can't remember what brand of aircraft it was but this might come back to me the more I think about it

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We currently use a rod as the drive type but have a bracket for cable operation we are working on so it will only ever be one drive source from the firewall. The std savannah uses 2 cables and this is the issue. One is way longer than the other so travels a different distance. This way the carbs have no option except to track exactly parallel. Because the rear bar is offset we have adjusted the hole connection difference distance to compensate for the very minor difference using the rear coupling bar

 

I have used the makini carb couplers they are much stronger and made from steel inners. They dont suffer the corrosion issue that the rotax alu ones do and are also much stronger. I do see the merrit though of that support bracket so will look into it.

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That support bracket is on TL-Ultralight aircraft. It continues down to incorporate a drip tray. Makes very stable carbies.

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