A Model Reversing Propellor - How does it work?

As stated in a post in one of my threads, ME ontains a wealth of interesting and useful information as I found out last night.

I fly collective pitch rc helis and blade reversing on those is much more obvious with a decent lever on each blade grip actuated by the up/down movement of the swashplate and linking rods. As i read this diagrams the principle is the same here except that each blade has it's slot into which the stub on the sleeve fits. What is likely confusing is that the pic shows the neutral position where both stubs/slots line up. In operation whne the sleeve is pushed forwards you'ld see the leading leading or trailing edges (depending on which methos is chosen) of each blade being actuated - one stub each side of the sleeve but at mirror points on the blade root slot.

Edited By pgk pgk on 04/01/2015 11:22:05

pgk pkg,

Thanks for the quick response.

Didn't make myself clear unfortunately. Headache is my excuse

I do get the operation of the lever and how it moves the props via the 'Sliding Shaft', but not how the 'glut/sliding sleeve' allows the 'Sliding Shaft' to slide inside the revolving outer/drive shaft but not spin as well. That pin seems to put a spanner in the works.

Sometimes the obvious are not so obvious as on this occasion no doubt. On occasion the old grey matter steadfastly refuse to do their designed duty.

An end view drawing would no doubt solve the mystery, but I just cannot be @rsed to make one right now.

Geoff - Need to study the helio mechanism, and something I didn't think off.

Edited By OuBallie on 04/01/2015 11:47:28

So is the sliding sleeve constantly rotating to power the prop?

I can only imagine that the sliding sleeve also rotates at the same speed as the shaft - otherwise it would be impossible for both halves of the outer shaft to be one.

Neil

Neil is right, both parts must move and that operating lever at the front end has a sleeve arrangement to allow it to move the sliding part back and forth while the sliding part is rotating. This is the equivalent of the fork in a gearbox.

If the prop blades are twisted then the twist can only be correct for one rotation, ( and one pitch) which would be forward of course. Aircraft with variable pitch props can often use them for braking, but with the same feature, eg the blades are not as efficient in reverse. For a model we could probably accept the loss of efficiency of flat blades.

John

I remember seeing a reversible prop on a Google site a few yeas back when I was looking for something else in boat design, and I think the whole works revolves, and the internal actuator rod is moved in and out at the inboard end. The one I saw was used on a constant speed motor, and the boat speed adjusted by varying the prop pitch.

Ian S C

It's the same principle as my RC Helis except they use seperate push/pull rods additionally controlled by the swash so you adjust the angle of attack further during each rotation for steerage. Here things could be modified to allow steerage or presumably even closer to the heli if you wanted some vertical control for a submarine?

Thanks guys

So it's the Glut that holds the key.

What about lubrication for the Sliding Shaft?

Surprising and annoying when ones brain cells stall and refuse to do ones bidding, especially when trying to solve a problem.

Geoff - Grey matter can now go into recovery mode

Grease?

All it does is slide back and forth relative to the sleeve and shaft as we now know it rotates at the same speed.

Neil

Err John, the outer tube only connected to the power source, inner shaft not on this occasion.

Geoff - Spare ribs tonight There's no decent drool smiley.

bogstandard2

Is that a Raboesh brand variable prop in the photo.

I have two of them unused. Do not think they manufacture them any longer but I think I could machine my own up now with a bit or reverse engineering.

Hayden

The boat I owned had a similar affair to this but I just used it to feather the prop when I set the sails.

So I assume the design I had was a crib from this fully reversing type or perhaps I wasn't utilising it to the full.

One thing I do know I've seen more than one boat where the prop has pulled it's self free of the coupling and walked out to meet the rudder under reverse drive. Ooops less pace more ace.

Geoff - I believe the sliding sleeve is your problem as there is one one view of it shown. The sliding sleeve I think will be in two halves bolted together and have a bigger outer centre section with a circular slot in the middle to accept the pin that goes through sliding shaft and outer sleeve shaft. The pin through the shafts obviously would then rotate with the shafts, but the shafts would only have one small hole through them to accommodate the pin. Does this make sense, what I have wrote as Little Ern would have said?

Chris - suffering with a cold and counting the minutes to beer 'o clock (7 pm).

I think the problem with understanding how this device works is that the drawings actually omit several quite important parts of the set up.

The tube with the sliding shaft inside IS the propeller shaft - that is stated in the write up, and it does rotate with the propeller as it is screwed into the propeller hub. Where the operating lever intersects the two shaft there is a sleeve that can slide on the outer tubular shaft, and that sleeve carries a pin that is able to cause the inner sliding shaft to move to and fro inside the tubular outer. The item marked "glub" is a block or possibly two semi-circular collars, attached to the handle, that fit into the groove in the sliding sleeve. This block or collars can move the sleeve along the outer tubular shaft until it contacts either of the stop collars. In doing so the inner shaft is moved to and fro, moving the sliding block in the prop hub and altering the pitch of the blades.

What is causing some confusion I think is that the drawings do not show the overall outer stationary stern tube or stuffing gland that would be needed in an actual installation. Also there is no indication of a thrust bearing, which would either be the end of the stern tube or a proper thrust bearing unit somewhere along the length of the tubular shaft. Taking the drawing at face value all the prop thrust would seem to acting on the reversing rod lever through the sliding sleeve assembly. I would expect with this type of arrangement that there would be a thrust bearing assembly capable of keeping the outer tubular shaft located axially in both directions as you're relying on being able to lever the inner sliding shaft against the outer to alter the prop. Without a locating bearing you'd be more likely to be moving the whole tube and prop backwards and forwards, as shown with pretty much contact over the whole of the interface surface between the sliding shaft and the outer tube there wold be quite a bit of friction even with grease lubrication. If I were building this I think I'd be machining some of the inner sliding shaft diameter down to give clearance but having regard to keeping it central by leaving a short section in the centre at full diameter as well as at each end - but that's a detail really. The drawings are not I don't think intended as "working drawings" even though there are some dimensions so much as presenting an idea or design for adaptation to your particular model.