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SureStart throttle/kill switch

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SureStart throttle/kill switch

Old 01-07-2008, 03:10 AM
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propjobbill
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Default SureStart throttle/kill switch

SureStart throttle/kill switch

After learning that I could regulate the engine speed by regulating with my thumb the chock tube on a Cox SureStart I have come up with a neat little throttle, as a throttle it has some what to be desired. I can throttle back to about 5,000 to 6,000 rpm with my sure start. The engine runs rich and must have the throttle opened slowly to regain power. But if you are willing to live with that this may work for you. However as kill switch this little device works great.

I have enclosed some pictures for you to look at. It is made from a sheet of copper, but any sheet metal will do. To go full throttle you simply open it up wide open once you begin to close the flap to less than ½ way it will begin to slow the engine down because of a over rich fuel mixture. When you want to stop the engine you simple close the flap completely and the engine dies. It is held on by installing a #6 flat washer with a partial ball point spring holding pressure on the flap.

It cost all of a few pennies to make and about 10 minutes or less to make. As A throttle it has some what to be desired, but if you are looking for something that will allow you to make an approach and cut the power to come in for a nice slow dead stick landing this will work great.
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Old 01-07-2008, 03:59 AM
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digital_trucker
 
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Default RE: SureStart throttle/kill switch

Great idea! Too bad it's cheating though...yer s'posed to just stuff it nose-first into the weeds when you want to land before the tank is empty.
Old 01-07-2008, 12:49 PM
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KidEpoxy
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Default RE: SureStart throttle/kill switch

Nice gadget.

Would it be posible to have the flap fixed to the needle, rather than freely rotating on it as an axis? That could afford from 1/8turn to almost 1/2turn leaninig as you close rotate the flap over the choke, depending on flap shaping.

When running at low throttle, present configuration has it running very rich, how rich is it? I mean to say, how much needle turn do you need to tune the 'low throttle' you currently have to run propperly mixed at that throttle setting? If it is close to a 1/4turn, then it might be worth looking into clamping the flap to the needlepost to lean as it closes.

Just a thought, if you wanted to develope a 2nd Generation Choke Throttle.

If you do pursue this, remember to keep it correctly rich thru out the rotation, we dont want to run well at 100% and 40% but burn the motor at 80%
Old 01-07-2008, 03:28 PM
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propjobbill
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Default RE: SureStart throttle/kill switch

I have thought about fixing the needle to the plate. If you knew that the needle never needed to change a drop of soilder would work. I am also thinking of how a control arm might be fixed to the needle but so far I have not come up with an idea for that. I am going to play with the idea over the next few days including seeing what kind of results come from closing the needle as I close the throttle if I come up with anything that works I will post about it.
Old 01-07-2008, 04:50 PM
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Default RE: SureStart throttle/kill switch

What about threading the shank of the needle valve. Then use two nuts and a thin nylon washer, one on each side of the "throttle arm" This would give a "firm" but adjustable grip on the needle valve. Just a thought.

Jim H
Old 01-07-2008, 05:34 PM
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Default RE: SureStart throttle/kill switch

Solder a brass choke plate to a wheel collar that fits the needle valve.
Stewart
Old 01-07-2008, 05:47 PM
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Max_Power
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Default RE: SureStart throttle/kill switch

hmm, as annoyed as you guys will prolly be at me for suggesting something more complicated and prolly 1/2 oz heavier, Seems like it might be fairly easy to just use 2 micro servos 1 for throttle , 1 for mixture and use a p-mix in the radio....you would have a totally customizable curve for all throttle settings and you could use a roller or knob to tweak mixture(master) setting in flight too! Todd
Old 01-07-2008, 06:27 PM
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propjobbill
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Default RE: SureStart throttle/kill switch

I just can in from doing my first test on the throttle plate. It is very sensitive as it begins to close. There is little if any difference between 1/8” opening and full throttle. All the variation in speed is from about 1/16” to 3/32" opening down to fully closed. I modifies the shape just a little so as it closed it the movement range from about 3/32 to closed would take longer. At this point I can go from full speed down to about 6, 500 rpm and then throttle right back to full speed. It dies some place between 4,500 and 5,500 rpm. From 5,500 to 6,500 it tends to load up and throttle in very sensitive. I was using a 5.7 x3 APC prop at 6,500 rpm that is about 2oz of thrust, and full speed at about 13900 is about 10 oz of thrust. With 2 oz of thrust that should work out ok for a 12 to 14 oz plane, and bring it in to a pretty nice landing speed.

I will continue to work on it, I won’t be able to test in real flight for maybe a few months. It was warm enough today to fly, but with wind gust at 30 mph I decided to pass. I may be wrong but at this point I feel like I can develop this into a very workable design. From 7,000 to full throttle if worked really great, and I think I can live with that. A 10 cent throttle that will work on a $7.00 dollar engine, and not interfere with the muffler will be ok with me

The above results are without doing anything to the needle. The needle remains set the same as for full throttle. It may be that with work of the needle ajustment as it closes it clould be possible to get a slower good running low speed.

I am also considering drilling a small hole in the tube which would work as a low speed jet and then it would only slow down to a given speed, but if the hole is the right size the engine won't die or go too fast when the throttle is fully closed.
Old 01-07-2008, 07:19 PM
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propjobbill
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Default RE: SureStart throttle/kill switch

My latest Test : I tried drilling a hole in the back plate at 40 thousands of an inch it would slow to about 4900 to 5500 run for a while and then die. I enlarged the hole to 46 thousands of an inch and it runs between 5800 and 6500 rpm. I like that for an idle so I am going to leave it there.

I also noticed that at this point the presure from the spring causes the needle to turn with the plate. The only problem I noticed there was it turned in but not always back out which with a few throttle adjustments it could become to lean, I am sure I can solve that problem.

I just uploaded a picture of it with the .046 hole inthe backof the choke tube
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Old 01-07-2008, 08:53 PM
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Default RE: SureStart throttle/kill switch

Is that an AngleIron (alum) engine test stand?
Old 01-07-2008, 09:54 PM
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propjobbill
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Default RE: SureStart throttle/kill switch

Yes it is 1/8' by 2", I cut out for the tube, and taped 4/40 holes. I use a pipe clamp to attack it to a small step latter. The Sure Start in the picture been modified and has a piece of aluminum plate like you use for flashing a 5”x7” piece cost about 20 cents. With the aluminum the spring digs into the plate and the needle turns with the plate. I just came in from trying it out. With an APC 6X2 prop it works from 6,000 through 19,000 rpm, and works very well.
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Old 01-07-2008, 10:04 PM
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Default RE: SureStart throttle/kill switch

Sweet!
I am glad to hear how well it works,
but like you said earlier, even if it could only knock a 13k engine down to 6k it would be worth it
Old 01-07-2008, 10:47 PM
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Default RE: SureStart throttle/kill switch

19000 out of sure start?
Old 01-07-2008, 11:10 PM
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propjobbill
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Default RE: SureStart throttle/kill switch

The engine has had the venture drilled out. I don’t remember for sure what size, I think it was to 3/16”. I know it is as large as I want to go, at those rpm it only a matter of time for something to happen. It also has an APC prop and they rev much higher than any prop I have tried. With the 2 pitch it has very little resistance. According to ThrustHp that will give me 22.4 oz of thrust but only 35.99 mph prop speed. The larger diameter gives the thrust to pull a light 1/2 a plane strait up, but it doesn’t fly all that fast. The modification gave me at least 3,000 more rpm.
Old 01-07-2008, 11:38 PM
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Default RE: SureStart throttle/kill switch

I wonder if the overbored venuri is affecting the ability to throttle down real low
Old 01-08-2008, 12:40 AM
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Default RE: SureStart throttle/kill switch

Nice work PJB! Sounds like you got those air and fuel molecules working together real good.
Old 01-08-2008, 12:49 AM
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propjobbill
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Default RE: SureStart throttle/kill switch

No, I also thought it would work against the engine at low speed, but if anything it works better than the stock setup. One word of caution for anybody that is thinking about drilling out the venture. It is real easy to break the tube as you remove the spray bar. I used a drill press to do the drilling and drilled starting at the reed side to the air inlet. I also found that if you are not careful when you reach the back of the venture it is very thin and rectangular and if you go very fast with the drill it will break where the spray bar goes through the venture.

But I was amazed that something that simple would get so many more rpm. I did find that after making the modification that it was easier to start if you put 3 or 4 drops of fuel in the choke tube to prime it.
Old 01-08-2008, 12:50 AM
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propjobbill
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Default RE: SureStart throttle/kill switch

No, I also thought it would work against the engine at low speed, but if anything it works better than the stock setup. One word of caution for anybody that is thinking about drilling out the venture. It is real easy to break the tube as you remove the spray bar. I used a drill press to do the drilling and drilled starting at the reed side to the air inlet. I also found that if you are not careful when you reach the back of the venture it is very thin and rectangular and if you go very fast with the drill it will break where the spray bar goes through the venture.

But I was amazed that something that simple would get so many more rpm. I did find that after making the modification that it was easier to start if you put 3 or 4 drops of fuel in the choke tube to prime it.

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