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New throttle system for Rotax


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So how frustrated have you been with the crap throttle and cable system on the savannah?....yeah everyone hates it. Always having to rebalance the carbs and the throttle never tracking correctly with either throttle rod. Well never fear a solution is at hand :)

 

A guy in NZ came up with a new throttle coupling bar system for his savannah. He posted some pics on FB and Danny Leach and I have been looking at it. Danny came up with some further improvement ideas for how to easily mount it all and literally just make it plug and play

 

Pics are placed here and I will upload a quick video to youtube to show the operation of it. We fitted it last sunday and ran the engine and balanced the carbs with a Carbmate. A huge difference now. No slop or uneven carb operation also the carb balance is rock solid. The centred LED of the Carbmate literally does not move now from idle to full power.

 

We were only going to make them up for our small group but there seems to be a big interest in them and so far it looks like we will be making at least 10 sets and thats mostly for Savs but they will work on any rotax engine independent of type of aircraft so we may end up making kits for them. No idea yet on cost but probably not that much. Biggest cost is getting the laser cutting done and some smaller parts that will need to be done on a CNC lathe and the bearing blocks can be made on my CNC mill at home. I was going to get all this done anyway as I have 2 engines to be done and Danny has another engine as well as the one he has just done and a couple of other guys in our group so making enough for 6 or 7 It costs not a lot more really to make a batch or 20 or 30 up. Its just laser time and CNC lathe time. The material which is all stainless 3mm plate and some 1/2 inch stainless tube is relatively cheap..the ball links are not that much each and the stainless threaded rod isnt expensive

 

As a side note you may see a funny looking CDI in the pictures. Thats #2 CDI that was built and tested and still running even though its a 3D printed case for the past 3 years on Danny's Sav...

 

Quick video

 

 

 

 

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Suggest you fit OS washers as required to ensure those rod ends are captive. They can separate.

I believe it's standard practice on all rod ends associated with engines.

We fit them also on all the rod ends associated with the flaperon control linkages etc.

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How is the linkage connected to the throttle lever. In the video it looks like a rod linkage.

How did you solve the movement between the engine and the airframe with respect to the throttle linkage. That is, as the engine moves, it would change the throttle setting slightly (and continuously) and with the vibration, it might cause increased wear in the carbie mechanisms.

Secondly, do you have a failsafe setup as with the stock setup so that if the linkage separates in flight from the control the engine will still go to full throttle?

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Oh the hours I've spent trying to sync the carbs......even getting new bowden cables made.

The problem is always getting LINEAR synchronisation.

Tuned to low rpm... no problem.

Tuned to high rpm.... no problem.

Getting both..... now that's hard.

I'm intrested in this kit where I could connect ONE of my throttle cables instead of both.

 

Secondly, do you have a failsafe setup as with the stock setup so that if the linkage separates in flight from the control the engine will still go to full throttle?

It looks like both factory springs are still used.

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The failsafe is of course you can either fit the springs or not fit the springs to the carb levers. Its up to you really.

Yes its a solid rod but because its pretty much a direct straight attachment the motor only rotates through its longditudal axis so that sideways movement directly at the side of the control rod from your throttle mechanism is minimal unless your motor is moving a lot in the mount which it shouldnt. Remember these are done for savannahs but realistically pretty much every aircraft is similar or can easily be made to do the same. I am putting one on the rebuilt Sav I am doing and also one on my Rans S-21. The rans has a centre position throttle so not sure how I will do it yet but in the scheme of things I dont see it as being any major issue at all. The other way is to use those linear rod arrangements..the Rans uses them for the aileron control in the new wing. This systm will mount on any Rotax it just depends how you get your throttle actuating cable or bowden or lever system to that side attachment. The carbs will always remain in tracking no matter what. Danny has test flown his and is pleased as punch with it...and he has slightly softer brand new engine rubber mounts on his engine so his engine does move a little and he found no issue at all with it.

I dont have a picture of the firewall connection but will get one to show but it is a direct rod connection from the cross bar on the savannah setup

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I'm of the opinion that those springs provide a second important function: as well as pulling the carb to full throttle in the event of a cable/linkage failure, they also take any slack out of the linkage, and they take it out in the same direction on both carbs. Or put another way, in the event that wear results in any slop in the system, if you don't have the springs then the carbs can constantly move a little in and out of synchronisation.

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Hi Bob

Its a matter of preference I think. With a solid system like this is then you can either have them or not. I personally think the springs are ok for the bowden system but with the solid system it really makes them not necessary. You would have to have a lot of wear to start getting slop in this system. Its all stainless hardware and good quality ball links. the actuating rods are 5mm stainless and the main pivot is 1/2 inch stainless tube. I suppose it all goes back to how you are attaching to that system. The carbs have no way of going out of sync once setup and with only one control actuating attachment to operate them its pretty hard to see any issues. Like everything though it would need to be inspected at annuals

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Good points, Mark. Time would tell, suppose, and in any case very simple to check for any slop each time the lid was off.

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They are steel balls in cast alu housings. We are looking at some high quality machined ones at the moment but want to get it at a reasonable cost of course. There is still a few finer details to be done yet. This one you see is all hand made so need to draw all the brackets for laser cutting and the bearing blocks and the throttle lever rotating attachment need to be drawn then CNC. The 1/2 inch tubes need to have the ends turned down to a fixed 12.5mm size so they fit and rotate perfectly in the bearing blocks also some washers lasercut to sit inside both blocks to stop the shaft from sideways movement...still a bit to do but this was to make sure the concept and angles all work fine...and they do it works a treat. Looks like at least 10 sets are wanted so far so may make up enough to do 25 sets..keeps the costs of the laser and machining down. will be a few weeks to get it all sorted

 

Oh and I need to keep working on Mabel too :P

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I stand in awe. You would appear to have solved one of the most irritating idiosyncrasies of the 912 carbrettored range - please include me as a possible purchaser of the production model.

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Hold on. Wouldn't that be

A guy in NZ came up with a new throttle coupling bar system for his savannah. He posted some pics on FB

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Yes the queue is starting to get longer than we anticipated

The original concept was done by a guy in NZ...we have refined it a bit more and made it sturdier and better angles.

Danny and I were talking tonight about the connection types depending on your aircraft. Part of our design is a new throttle lever on the carb so we will make the rod style of attachment and also a attachment for bowden cable that should sort out the different throttle attachments. Will need the springs of course if using the cable drive to the rack

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Bob..he chased me today and asked me if he could get some of our parts for them. He is actually a South African living in NZ...he is a motorcycle engineer. Danny has done all the hard work on the design so far. I just cut the stainless and sourced the tube and other stuff. But 2 heads are always better than one :)...We are good at reinventing the wheel at times :)...oh and he flys a Sav :)

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For the tube bearings, could you use a hydraulic pipe clamp around an off the shelf sintered bronze/ brass/ ptfe bush?

May keep the cost down for custom parts and make future maintenance easier.

Examples below.

 

https://www.ebay.com.au/itm/Stauff-Single-Tube-Pipe-Clamps-6-4mm-42mm-Hydraulic-Industrial-/383247471493

 

 

https://www.ebay.com.au/p/2258485189

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Thanks again Mark for making the effort to share the improvements that you make to your aircraft. I would like a set as well if that is possible.

Cheers.

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Hi Mark. You are a busy man. One aspect to consider will be the routing of the carb heating tube. It’s quite a tight fit in the OEM set up, in fact I had to flatten mine a little to fit it down between the air box and engine. I’m sure you will work it out.

 

As an aside, I have just removed the throttle arrangement that I made utilising rods, but the difference was that my rods were actuated from the LH and RH sides of the OEM throttle torque tube mounted on the firewall, then directly onto the carb levers. I found that with any movement of my engine, it would upset my carb synchronisation. As a test, if you push and pull sideways on your prop, you will see quite a lot of movement of the engine. With my (now obsolete) arrangement, when the engine moved, one throttle increased rpm whilst the other decreased, which made for rough running. Your design will address the carb imbalance issue that I had. You may see a little throttle “hunting” with your system when you have your friction lock on, but depending on how smooth your new prop is, I may turn out to be a non-issue. Cheers for sharing. Perry

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Downunder we found that the tube is not perfectly round. So we shave them in the lathe to make sure they are perfectly round so they actually end up at 12.5mm. The bearing blocks I will make on my CNC and the cost of the material is cheap and so is my machine time and then I can make them suit the sizing we use.. WE use those clamps for antennas for building beam style antennas. They are very good

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Hi Perry yes that was always the issue with using the sav crossbar at the firewall for driving the rods. because the crossbar is at the carbs now all that movement is taken away. Dannys test flights with this new arrangement havent shown...so far any issues with hunting and he has softer engine mounts and you can really move his engine in the mount. Time will tell with more use but it certainly looks and works far better than the standard ICP system. We currently use a solid drive rod from the original single point of the ICP crossbar at the firewall and the movement of the engine doesnt seem to make any difference but driving the system from a cable and using the carb springs should stop that issue if it does become one

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Danny Leach. Now that is a name I haven't heard in years. Bright lad, he used to come to Rodds Bay with his father. G'day Danny from Ian Borg

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Yenn yes Danny only lives about 2km from me. We do a lot of stuff together playing with our Savannahs and other stuff. I have known him from the RC plane days going back 20 years or so. If you need anything Danny can find it he is a whizz at getting stuff and finding obscure bits. He builds beautiful stuff and also his workmanship on fibreglass or alu is outstanding. Very smart guy when it comes to anything mechanical

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Downunder I checked with the local Stauff agent here while I was out this morning..the blocks are too wide for what we want and also the mounting hole sizes are too large. If they were narrower and had smaller mounts they would be a good choice for quick and simple

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Great work Mark, grouping up with adjustable hard links is definately the go mate, the multi cyl racing superbikes got on to this as well eh, old mate Kiwi must have noticed it is better as well, Well done sir. Cheers Mick

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