TT 54 propeller thread is anticlockwise to unscrew!

[Lee Smalley]

i do not use a lock nut on my TT130 as it does not fit with a spinner, i don't have problems !!

[Steve Hargreaves - Moderator]

Jim...for what its worth I use a steel washer between my adaptor & the prop retaining nut to give a flat base for the adaptor to tighten against. The main holding force comes from the large retention nut.....tighten this as much as you like.... Try & make sure if you cut the adaptor down that it has a square face (not easy without a lathe)....

 

If you lean on the brass adaptor too much you will strip it. I find a good nip does the job here....

 

And as we all know "a good nip" is exactly half way between "nipped up" & a "gentle heave"....or you could use the metric equivalent of "leaning on it slightly"...

[Steve Hargreaves - Moderator]

Jim...having re-read your post I'm a bit concerned that you might have tightened the adaptor INTO the recess in the retaining nut......this is not good as you are now tightening the flat face of the adaptor against the internally tapered face of the retaining nut......you will probably damage both by doing this......

 

EDIT

 

PS...Sorry ignore my last comment.......I was forgetting that TT do things slightly differently & "reverse" the order of the nuts from the more conventional OS & Clones.....

 

I thnk your idea ia a sound one Jim & would work well but not with brass....it simply isn't hard enough to provide the force you need to pinch the splines together without bits being shaved off it (as you have found by the bits of brass you are encountering)...

 

Perhaps this is a new product opportunity.....spinner adaptor/locknuts for TT engines.......they would need to be made out of hard steel though....

Edited By Steve Hargreaves on 12/09/2011 12:26:26

[Biggles' Elder Brother - Moderator]

I'm afraid your analysis is probably correct Jim. Brass is too soft a material for the tightening going on here - especially if you modes have effectively created a thin walled conical indent.

 

If you have access to a reasonable lathe then turning up an adapter is easy. But it does really have to be steel and as Steve says probably a pretty hard high tensile steel at that. Small "hobby lathes" struggle a bit with sort of material is my experience.

 

If you decide to go down the Just Engines route then I'd strongly suggest that you ring them and talk through your requirement, making it clear that , unusually, the splined "nose" is on the propnut not the lock nut on the TT. They may already be fully aware of that of course - but its worth checking. Alternatively you could go for a solution with them where you swap the prop nut for a more conventional style one with an indent and then use a matching lock nut/spinner adapter.

 

BEB

[Peter Beeney]

Jim,

Whilst I’m generally in agreement with BEB and Steve, I think I might sum this up as follows.

In the first instance, you don’t need the locknut at all unless you consider that the engine is going to detonate, (or whatever we are going to call it), and throw the prop off; and my right-up-to-date thinking on this is that even if the locknut is on and tightened correctly it can still be thrown off, i.e. in some cases the locknut does not retain it at all, so I assume this can happen anyway and I always (hopefully?) take any necessary precautions. The fact that this happens very infrequently also might be a reasonable factor here, you could certainly assume it’s most unlikely it would ever happen. As I said before, if you need the locknut to be able to use the starter correctly then I would consider looking carefully at all this again. That should not be necessary.

Secondly, like Steve, I always make very sure that all the pressure surfaces on the propeller mounting are adequate, perhaps using washers and/or insulating tape etc. For instance, some APC props have a shallow recess cut around the hole in the centre boss, I’d pack that with an appropriate washer; and because I invariably use a plastic spinner I don’t want any suspect areas. Everything has to be rock solid!

Like you, I pay a lot of attention to props, I’ve seen the evidence of long gone encounters between hands and props far too many times, so I’m not going to take any chances. Saying that and then using a plastic spinner might seem like a contradiction in terms but as I’ve said I’ve have no scruples about these at all. If nothing else they are simple and durable, if necessary instantly disposable, and the metal ones on four strokes can sometimes be a pain in the neck, then discrepancies start to creep in… … need I say more?

I'm sure I can remember the first four stokes not having locknuts, I have one of the very early OS 60FS, with the exposed valve gear, and that certainly doesn’t. The first time I saw this happen was on a OS 90FS, that was in the air; and that had no locknut either. However, I think the problem must have fairly rapidly become apparent, because soon part of the advertising blurb became the fact they were supplied with locknuts. I’m sure I long thought it was the definitive answer, and probably it is to a large extent but not quite 100%!

Regarding Steve’s theory about the plastic prop becoming soft with heat, I don’t think I’ve every seen any evidence of this; and again unless the engine detonated I don’t think it would ever be a problem anyway. I suppose you could argue that if you shut the throttle quickly the prop running on would undo the prop but I think that is pretty much a supposition that can be ignored. I’ve not tried this but I suspect if you applied heat in the form of a flame to say an ACP prop it would most likely catch alight before it became appreciably softer.

I can’t quite see from the photos, but does the male nut have a shoulder on the back that locates into the washer that goes against the prop? If it doesn’t then I would simply find a standard hex nut to fit the crankshaft, tighten up, find another nut, I have a well filled squirrel store, tighten that up too, and there should be enough room left to screw the spinner adaptor nut on. If it does have a shoulder on, which means it’s a pair with the nut then I’d just use a suitable plain washer. I’ve done all this in the past, often, with no adverse repercussions. I’m just lazy and I always take the easiest way out!

Incidentally, squeaks and groans are generally the order of the day when it comes to all thing brass. Also, if my memory serves me correct, and I must admit that’s a bit suspect too, you don’t use a lubricant on brass or cast iron. This was from an Engineer that I knew, so long ago we were in another life it seems now. Perviously he had built a Pou-de-Ciel, or Flying Flea, but he wasn’t a pilot; I think someone else had flown it, just before they were banned, around 1937, I think.

Hope you soon fix it ok! Good Luck.

PB

[Jim Burton 1]

Thanks again Guys.

 

I might be over-cautious here but I have this day ordered from RC World what looks like a bargain solution (compared to the the JE tenner plus job).

 

A spinner adapter kit comprising 1/4" UNF Long. Supplied complete with shaped nut and washer and where applicable, an aluminium sleeve is also included.

It's halfway down this page if'n you're interested in taking a deko.

http://www.rcworld.co.uk/acatalog/Spinner_Adaptors.html

 

Looks as though it completely replaces the TT nuts and includes the drilled adapter for the spinner to be attached.

 

So I shall hope to rest easy once this is in situ - not having had your wealth of experience in distinguishing between what might happen or what seems highly unlikely, I'm going to have to go for the 'belt and braces' approach - for four quid I'm going to be a happy man, and not have that horrible 'what if?' feeling gnawing away all the time the engine is running.

[Braddock, VC]

One thing you may want to look at is the rear of the APC prop hub, you will see that there are cast in depressions that make it impossible for the knurled face of the prop driver to have anything other than a minimal "bite" on the prop usually resulting in the crankshaft standing still whereas the spinner and associated nuts continue to revolve when using an electric starter.

If you slightly overfill these depressions with roket powder and drip cyano in then file the excess flush; upon refitting to the engine you should notice an immediate improvement.

[Jim Burton 1]

John, thanks for that - I'm guessing you're not a UK resident, as Googling 'Roket powder' gets me into Guy Fawkes territory and possibly a visit from the heavy squad .

 

That apart - my first reaction is, it's a great idea - I've looked at the back of APC props (a lot, recently ) and have noticed that the more 'eye-bulging' torque I apply to the prop nut, the deeper the footprint on the back of the APC prop when removed for inspection. This would be on a trial install, without the spinner backplate, just directly onto the crankshaft faceplate (serrated all over)and there's a clear impression on all the rear prop surfaces that touch. Nothing on the 50% empty areas though!

Are APC missing a trick here, or is there a reason for the 'missing matter'?

 

As you rightly state, there is a relatively small area of direct metal-to-plastic grip - and when I substitute the spinner backplate, the only serrated area that contacts the APC is the small brass centre 11mm portion.

 

However, APC are not stupid or careless with their designs - there must be a reason why the rear centre section is recessed deeper than the rear outer ring. I'm guessing this is so that the 'power' of the nut torque on the centre part 'pulls in' the centre of the prop until the outer ring is flush, i.e. the 'recess' is drawn level by spanner application on prop nut. A sort of controlled deformation. I'm guessing APC would have given this the once-over in wind tunnel smoke tests. And found it to be good. Indeed, depend on it happening in most circumstances - unless, of course, the 'empty areas' were 'filled in' by a non yielding cyano/roket mix. More grip? For sure.

Worry beads out on the 'controlled deformation' expected by nut pressure vs outer ring surface geometry though.

 

What would happen if you were to 'flatten off' the whole backside with Roket and cyano mix is anybody's guess - would it alter, for example the dynamic properties, indeed the pitch of the prop which was designed to have this extra tensile stress coming from the drawing in of the the centre detent until it matched the outer ring (became parallel viewed from the side).

 

Clearly APC produce this design by the million - there must be a reason why the centre is recessed, and I don't feel inclined to mess with it, despite the undeniable allure of having a flat surface three times the area for back grip.

 

Others, as is so often on this forum, may disagree.

[Martin Harris - Moderator]

Roket powder is generally available in the UK (5 Star Adhesives?). I believe that some people have used baking soda for the same purpose - I haven't tried it myself but I don't think it's necessary for APCs.

 

My guess would be that the idea is to promote just what you've observed by higher contact pressure than with a flat face, getting the serrations to bite effectively. I can't imagine APC going to all that trouble for no reason.

[Biggles' Elder Brother - Moderator]

Your RC world solution looks a good one to me Jim, and has the advantage that it brings the TT into line with the rest of the known universe in terms of the relative shapes of prop nuts and spinner adapters!

 

Let us know how you get on with it. It been a good thread this so far, interesting and lively discussion all carried out in a totally gentlemanly fashion! I would expect no less of course

 

BEB

[Braddock, VC]

Simply because apc have made "millions" of their props doesn't make the design correct, if what is said is the case why don't wood prop manufacturers recess the back of their props or graupner or ram. The reason the recess is there is a function of the molding process, it's less of a problem with the larger sizes of apc but still a problem.

Buy a graupner 12.5x6 prop and fit it to the tt54 and watch your troubles disappear.

FWIW it's the reason I don't buy apc props anymore. Much prefer giant cod's JXF series, 1/3 the price and as quiet as the apc.

There was another problem with apc which concerned the concentricity of the central hole, they forgot to give instuctions that the hole at the back was the concentric one and consequently had to be drilled from the rear, this caught quite a lot of folks out but may have changed as I've not bought apc for yonks..

[Steve Hargreaves - Moderator]

Looks a great solution to me too Jim....let us know how you get on. You might need to watch the threads though as these seem to be American threadforms (for the spinner bolt) rather than metric.....

 

I like APC props but find the price a bit hard to swallow...especially at the larger sizes.....I've just bought a couple of JXF props from GC to try & at £1.94 for a 15 x 6 the value speaks for itself....not flown them yet so can't comment on the performance but initial impressions are very favourable......I wish they did a 15 x 8 & a 10 x 5 though.....

 

Some interesting stuff about/from APC here regarding concentricity & tapered holes.....

[Peter Beeney]

Once again I’m mildly surprised by what seems to be a tiddly little conundrum within these realms of aeromodelling. With the greatest respect to John Gibbs, and his post are very factual, he’s obviously sorted this in a very logical and skilled way, but I’m afraid my difficulty is simply that I’ve never seen any of these problems with ACP props to start with! Or with any other types, that I can remember. I may have personally experienced a slipping prop, but that’s an exceedingly rare animal. So why is so different for some people, is it different ideas and techniques perhaps, or simply just coincidence?

Interesting, trying to think about this, I’m now wondering why this appears to be. I don’t doubt for one moment that what John says about making the surface area of the back of the prop bigger is true, but I’m now also wondering why this is so. If you increase the surface area you reduce the pressure on those surfaces proportionally. My reasoning to think that goes something like this.

Firstly, I think we have to assume that the prop nut can only be tighten up to a certain point, and so transfer the pressure through the prop to the driver. This pressure will be exactly the same if the hub is ‘solid’ or ‘hollow’.
If we now assume two surfaces, each one unit of area bearing together with a force of ten units of pressure, then we could say the pressure is 10 units of pressure per one unit of area. If we then reduced the area of one surface by exactly half the pressure would stay the same but we could then say the pressure on the reduced surface would be 20 units of pressure per unit of area. So as I now see it, the reduced area of the back of an APC prop, i.e. the thin rim, applies a considerably higher concentration of force on the prop driver than a solid hub and I have to say it seems to me this is as it should be, but maybe this is not entirely borne out by John’s post.

Therefore I thought it might now be time to take a quick look at the prop and spinner in a way that I’ve seldom done before. So slipping one off the Irvine 53 it’s obvious the prop driver is serrated to obtain a grip on the prop, as indeed I think they all are. The centre of the driver is slightly recessed, as is the driver on an SC 52FS that I’ve also looked at. So straightaway the only part of the the ACP prop that can touch the driver is the thin rim, or outer edge of the hollow back of the prop. Where the prop has pressed against the serrated driver under the sort of high pressures I’ve tried to describe above it has formed matching ‘teeth’ in the plastic, which lock it to the driver and which I’m sure are prefect for preventing any slip. The back-plate of of the plastic spinner then fits against the front of the prop, unlike the aluminium spinner, the back-plate here going behind the prop, then the washer and then the nut; and, of course the spinner cone is held on by two self tapping screws. This spinner is quite old, but looking at it carefully there are no signs of wear or strain at all, and because the motor invariably starts instantly there is no starter rubber wear on the spinner cone either. Assembling it all back together takes just under a minute and I’m totally convinced this will not be the slightest cause for concern in any way for probably the life of the model. What then could be better for sport flying, at least? So I’m wondering where any of these issues come from?

Oddly enough, I find I very seldom have to drill out the holes in the props, as well. They always seem to be a good and proper fit, too.

I have to admit this seems rather like old hat and pretty basic stuff to me, I really didn’t realise that propellers and spinners could be so complicated…….

PB

[Martin Harris - Moderator]

Well, I asked APC earlier and this was their reply:

 

The void in the hub on many of our sport propellers is mainly for weight savings. The grip is most effective at the outer diameter, so adding material on the inner portion of the hub will not do much for added grip. We do not recommend this type of modification.

 

 

[Tim Mackey]

Complicated...you want complicated... try matching up all the variants of electric motor shafts with collet adaptors, some of which think its fun to use fractions of a mm like 3.2mm instead of simply 3, for the motor shafts, not to mention the actual propshaft section which never simply fit the standard APC type prop hubs. Then add into the mix folding prop assemblies with their odd sizes of spinner backplate holes and various blade root thicknesses etc.

[Martin Harris - Moderator]

Are they truly 3.2mm or are they actually 3.175mm (a good old imperial 1/8")?

[Tim Mackey]

Gawd knows...I was only citing this as an example - I have seen loads of different sizes quoted, and of course, unless you have the exact same one to match the motor shaft, they simply wont fit correctly

[Jim Burton 1]

Thank you Martin for contacting APC. Their response about weight saving seems good 'best practice' for flying machines and sort of explains the 'empty area' though not the purpose of the designed indentation of the centre ring vs the outer ring.

 

However, they and you might like to view the backplate of a typical aluminium spinner. "Exactly the same" as PB uses, for example, and doubtless thousands of other flyers worldwide. What do we see on this photo? (excuse the paint overspray, I've been doing something else!!).

What we see is that, even allowing for lens foreshortening denying us true perspective on this quick hand-held shot, the 'grip that is most effective' that APC speak of, i.e. the outer ring of the prop back, is relatively ineffective, as all the 'grippy' serrations on the ali spinner backplate are confined to an area surrounding the small brass insert. And what we might call the inherently 'slippy' contact area (no serration) is getting all of the important contact portion of the outer ring - that which APC are hoping/trusting will deliver the 'grunt'.

 

Interesting that APC did not comment on the reason for the 'indented' relationship of the inner and outer circles. I reckon I'm right - the inner circle is indented to 'pull' more pressure onto the outer circle, which as APC confirm, is the 'business end' of the contact area.

 

Clearly on this type of ali spinner backplate, the prop design defeats itself. One day, perhaps, prop manufacturers might make their own spinners, although plastics and aluminium in the same factory are unlikely to be friends.

 

 

[Jim Burton 1]

Well, as a footnote to this lengthy thread, I am happy to report that the Great Planes spinner adapter kit arrived this morning and does exactly 'what it says on the tin'.

Directly replacing the TT nut and locknut and with a threaded nose ready to receive the spinner nut, it all fits together like a dream. Job done.

 

With the return of decent sunshine, I might even be able to get some flying in at last

 

Once more, thanks to all of you for your thoughtful, patient, helpful advice.

[Lee Smalley]

I don't think apc make their props to fit whatever spinner you may or may not use, they make them so they grip drive washers I have never, and I have been using apc for nearly 20 years, had one NOT grip, Apc when they came out were quieter gave more performance and were most of the time cheaper than graupner props, that's why most people swoped, in this hobby generally if a design is rubbish they don't last too Long, MDS engines are a case in point

[Martin Harris - Moderator]

Jim,

 

With respect, I don't think you've chosen a typical example for your photo. I've compared a few of my spinners and APC props and even a fairly extreme example such as a this 13 x 7 on a 2" spinner seems to give a perfect match.

 

[Jim Burton 1]

Yeah, you're both right - the 'fault' if we are going to apportion blame, does not lie with the APC design, but in the design of my 45mm spinner backplate: yours, Martin, has just what is missing from mine - a serrated area large enough to match the position of the outer prop ring. And Lee, absolutely - the drive washer on the engine has grip all over its surface so is ideal for total contact area with prop back rings.

 

Could I ask you Martin, the manufacturer of the spinner and where it was bought? I ask because the various suppliers (retailers) sites that I have checked just show a shiny photo of the assembled spinner and do not show the inside backplate view: so if I bought a larger 50mm one for my APC 12x7 I might still end up with the same problem.

[Steve Hargreaves - Moderator]

Jim...I really think you have reached the point of paranoia & are simply worrying too much.....you've already gone much further than the majority of us in sourcing your super prop adaptors...

 

Assemble the prop, spinner & everything else....give the retaining nut a good heave with a well fitting spanner & I think we can practically guarantee success....even if the propellor boss & spinner serations don't quite match up....

 

One thing you need to understand....if you ask 10 aeromodellers what they think you will get at least 11 opinions.....

 

I, myself, have several opinions on most topics.....

 

PS....a 12 x 7 might be a bit much for a 54 4 stroke.....11 x 5, 6 or 7 would probably be a better match.....

[Martin Harris - Moderator]

Jim,

 

The majority of ali spinners I have were boxed in white cardboard with red print and marked JP although 1 or 2 were Ripmax branded in clear plastic blisters. They seem to be generally available at model shops.

[Lee Smalley]

yeah 11x6 will be good when finally ran in 12x6 for scale 11x6 or 7 for sport