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Thread: 503 & tiny tach help needed

  1. #1
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    Default 503 & tiny tach help needed

    My Tiny Tach arrived today, so now I need to set it up & check my RPM on the engine etc.

    My 503 has a single coil with single plug to each cylinder.

    I have set the Tiny Tach to 180* 2 sparks per revolution. I am only guessing at this thinking its a 2 stroke .

    Started the engine and I have to tweak the throttle a wee bit to get a tick over which is around 1800 /2000 rpm. I need to tune the carb slightly to get a better tick over

    I let it warm up for a minute or two and gave it full throttle (my ears are still ringing). The tacho went upto 12,300 RPM

    Before I start altering the fan pitch I want to make sure I have set the Tiny Tach up properly by setting it to 180*

    Or should it be set to 90* as its a twin cylinder 2 stroke?

  2. #2
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    Default Re: 503 & tiny tach help needed

    I think I have answered this question for myself as I have just set the tiny tach to 90* = 2 sparks per 360* revolution divided by 2 cylinders.

    At this setting the max static RPM I am getting is 6230 RPM.

    I know from here I need to lessen the pitch angle of the blades to increase the engine RPM.

    At the moment I am running 9 blades in a 9 hub. The old fan was a 12 blade in 12 hub (black blades)

    Fan duct is 825mm & fan is 800mm

    Gearing 22/54 = 2.45:1

    Craft weight is 165kg approx (170 kg minus the 4"X2" used between the two sets of scales which weighed 5KG)

    The splitter plate is fairly low at only around 19/20cm from the bottom. This is where it was originally as I have used the original mounting holes for it & original duct. I thought normally the splitter was about a third of the duct or is that for cruising craft?

    I now need to decide best way forward from here.

    Do I keep nine blades or reduce to six?

    Do I try to increase the splitter height or leave as is?

    Leave as is & repitch blades to increase RPM 6800 then see how the craft reacts & hovers?

    I know the craft has good thrust from the way it pulled up the hill outside my house from a standing start.

  3. #3
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    Default Re: 503 & tiny tach help needed

    Quote Originally Posted by Al View Post
    I think I have answered this question for myself as I have just set the tiny tach to 90* = 2 sparks per 360* revolution divided by 2 cylinders.

    At this setting the max static RPM I am getting is 6230 RPM.

    I know from here I need to lessen the pitch angle of the blades to increase the engine RPM.

    At the moment I am running 9 blades in a 9 hub. The old fan was a 12 blade in 12 hub (black blades)

    Fan duct is 825mm & fan is 800mm

    Gearing 22/54 = 2.45:1

    Craft weight is 165kg approx (170 kg minus the 4"X2" used between the two sets of scales which weighed 5KG)

    The splitter plate is fairly low at only around 19/20cm from the bottom. This is where it was originally as I have used the original mounting holes for it & original duct. I thought normally the splitter was about a third of the duct or is that for cruising craft?

    I now need to decide best way forward from here.

    Do I keep nine blades or reduce to six?

    Do I try to increase the splitter height or leave as is?

    Leave as is & repitch blades to increase RPM 6800 then see how the craft reacts & hovers?

    I know the craft has good thrust from the way it pulled up the hill outside my house from a standing start.
    I'm no 503 expert but i think it's best with 6 blades in the hub, with the following blade having more pitch than the leading one (only a few degrees)

    thats the way i've seen other engined craft set up anyway
    James Eddy
    (Formula Camera)

  4. #4
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    Default Re: 503 & tiny tach help needed

    Al,
    Don't do anything in a hurry. Take her out in a proper environment against other craft and see what you have got.
    Then one thing only at a time. From your earlier video you look short on lift so I would stay with the 9 blades initially.

    See you soon in your part of the world.

    Kip

  5. #5
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    Default Re: 503 & tiny tach help needed

    So really the first thing to try will be repitch fan to bring the revs up to about 6800RPM (static) then go & have a play & see what I have. I wont be able to try it out until next Wednesday /Thursday if the tide is right. I know beach buzzing is frowned upon, but where I intend to try it out is a mile from any houses and very few people venture (Usually only me with my dogs) to that part of the beach when the tide is out. If the tide is right out then I can have a 1 mile straight X approx 1 mile wide circuit to play on. I'm sure I will find a fence post or telegraph pole to hit

    When we take it out I shall video it so it will be easier to see what changes I need to make if any.

    Counting down the days to Loch Fyne

  6. #6
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    Default Re: 503 & tiny tach help needed

    Hi Al,

    Basically, more blades gives you better lift, but with a reduction in top speed. This is very simple terms.

    So as Kip says, see how it goes with 9 blades. I'd be surprised if it didn't work OK with 6 blades, but without seeing it properly its hard to tell.

    Unfortunately the only real way of finding out is trial and error, which is a pretty laborious process!

    On the tach, I think you have got it sorted. If your 503 rev'ed to 12000rpm then it would be in a thousand pieces around your workshop

    Nick

  7. #7
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    Default Re: 503 & tiny tach help needed

    Tiny Tach fitted properly and I have adjusted the fan blades so the engine is revving to 6740 static.

    I shall hopefully take it down to the beach on Wednesday evening when the tide is out and give it a proper testing.

  8. #8
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    Default Re: 503 & tiny tach help needed

    Had a short play on the beach today, I was surprised just how many rocks were about 7 or 8 inches high. I was never sure how big the rock was under the seaweed untill I went over it. I had only done about a 100 metres before knocking off one of the P clips releasing two segments, not long after I hit another P clip off almost the same place as the first one so 4 seggies flapping. The bit I was most annoyed about was not being able to open the throttle to the max to see how the craft went.

    I had first play, then Brandon had a play.

    The video below may help to determine whether the craft needs more lift, but I think with the 4 segments out in the same area, it maybe hard to tell.

    Anyway here is a video of me beach buzzing on a wet day in the north west of Scotland. Approx 1/2 mile out from the shore and at least a mile away from the nearest house. We were only down on the beach for about 1/2 an hour or so and didn't see anyone else.

    http://www.youtube.com/watch?v=Q1ti8nYtWcE

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