JP3 running speed

[steamraiser2]

Simple really, the proper variable speed throttle arrangement typically fitted to JPMs has the high and low idle set by stops on the on engine throttle handle. If you only connect to the bell crank and have no stops it is easy to hold the throttle above the intended max rpm.  

[flatplane8]

10 minutes ago, steamraiser2 said:

Simple really, the proper variable speed throttle arrangement typically fitted to JPMs has the high and low idle set by stops on the on engine throttle handle. If you only connect to the bell crank and have no stops it is easy to hold the throttle above the intended max rpm.  

Ah, see what you mean now, thanks for clarifying.  Our JP3 is now controlled via a cable mechanism and we use the stops built into that to achieve the same thing. Yes, too much tension on the speeder spring could cause undue load on the engine.

[BWM]

3 hours ago, flatplane8 said:

I'm not sure I see the logic in this as the spring works in tension only (until coil bound then I guess you could push on it), but I'll be trying out this very thing (morse control onto the speeder spring) on the JK4 later today in the workshop so will report back.

Likewise, I don't understand how any pushing could be achieved, as the spring is unsupported it tends to sag if would too far in (by which time my engine would have already stalled). I only added a ring to mine because the spring held the governor in even when wound fully in, a previous visiting 'engineer' stretched the former spring to achieve the same result which I viewed as a bodge and swiftly replaced it.

[steamraiser2]

6 hours ago, flatplane8 said:

I'm not sure I see the logic in this as the spring works in tension only (until coil bound then I guess you could push on it), but I'll be trying out this very thing (morse control onto the speeder spring) on the JK4 later today in the workshop so will report back.

Who said anything about pushing the spring? The speeder pulls the rack open under tension when the throttle is opened and is over come by the governor rod pushing in the other direction at max speed. Therefore the assembly works in both directions ,pulled open by the spring, and pushed shut by the governor. Both acting on the bell crank.  Properly adjusted the speeder spring is always under some tension. 

[RLWP]

30 minutes ago, steamraiser2 said:

Properly adjusted the speeder spring is always under some tension. 

This is the important bit, just to amplify the point. If the spring is always in tension, there is always an opposing force on the governor and it will be following a linear change

 

If the spring lets go, you get step changes from something to zero, then back to something again. Not helpful. You can get this with the internal spring on the more modern Listers

 

The extra spring in the mechanism is even more likely to give weird results. Putting one spring opposing the other adds the rates together, increasing the force on the governor - not what you'd expect. And if either of those ever goes loose, things will be all over the shop.

 

Thanks for this stuff, Geoff

 

Richard

[flatplane8]

Here is a little video taken last night of a Morse control being used on a Lister JK4.