Supermarine Spiteful and Seafang

[Erfolg]

From what I can see in the pictures, I am very confident it was not a fatigue failure, as we know there is no polishing, or beach marks as the crack advances as it cycles. But we knew that.

It has it would appears to be a mottled, puckered surface, as you suggest, a brittle failure.

The shaft being bent could well be a consequence of heat treatment, that left the material brittle and hard, rather than tough and slightly bent. The shafts were probably centre less ground, the bending,just being accommodated due to the process.

In service, the out of balance forces, possibly just due to the spinner not running true, must have been enough to exceed the materials stress level and the rest was history.

[Colin Leighfield]

I think you've summarised it very well.

[Colin Leighfield]

Got the new motor and plucked up the courage to cut it open again and do what I should have done in the first place, make a new rear motor mount and eliminate the original fundamental error.

[Colin Leighfield]

Tonight I finished off setting up the new 1100Kv Professional series motor from 4Max. The previous XYH was 1250Kv. so with this one the plan is to prop up slightly from the previous 9x7. However for the test run I used the existing balanced 9x7. Initially I ran it up without the spinner and it seemed fine. Next I fitted one of the two new carbon fibre spinners purchased on Ebay and shown in one of the 12 August postings. However, as soon as I fired it up it showed signs of out-of-balance and roughness so I throttled back, not quite believing that after two motors and five spinners the problem still seemed to exist. I took the spinner off and ran the motor up again. It was immediately obvious that the motor is damaged, feeling very rough so I'm guessing that a bearing is shot. I can't believe it, I've never had problems like this before, but it goes on and on. I'm starting to wonder if I will ever resolve this. it's getting ridiculous. Has anyone else experienced anything like this?

[Biggles' Elder Brother - Moderator]

Wow - you are certainly having a run of bad luck with this one Colin! But surely it can't go on? Are you saying the out of balance spinner might have damaged the motor? That's unlikely isn't it? After all I guess you tested it fairly gingerly after your recent experience!

But hang on in there - its got to be third, fourth,...er, fifth time lucky surely!

BEB

[Simon Chaddock]

Colin

A rear mounted out runner with a big spinner on as well does put a lot of rotating mass well ahead of the front motor bearing.

Depending on the diameter of the motor shaft and the rigidity of the motor mounting it can be subject to 'whirling' effects even if the whole assembly (including the prop) is in perfect dynamic balance, which of course it never truly is!

From your description it certainly sounds like this sort of problem. The only solutions are to increase the stiffness of the motor mount and/or reduce the rotating mass.

In some respects a front mounted motor is kinder to the bearings as the prop and spinner overhang is much reduced and is matched by the motor bell overhanging behind the rear bearing.

On my Q400 I have gone to some trouble to bring the whole prop (9x5) and spinner assembly as close to the front face of the motor as possible although it still gives me cause for concern particularly as the 1200kV Emax only has a 3mm shaft!

[ROY DAVIES 1]

Nice model Colin, Don't run the motor too hot or the exhausts will shrink !

Re, Shaft breakage it is very difficult to get the hardness just right as the cross section is so small. You will notice this on small sized Allen keys they either work okay or go 'ping' first time you use them or end up like barley sugar. There is a bit of shaft overhang visible and 'a great deal 'up front' In the event of a slight movement of the motor backplate or spinner and prop or a bit of cogging on throttle up the whole lot could start to precess which would be the beginning of the end

[ROY DAVIES 1]

Sorry Simon, I have just noticed your posting with a similar train of thought It looks like it popped up while was typing mine Look at the time, date bar Roy

[Colin Leighfield]

BEB, Simon, Roy, thank you all. Over the years with I/c motors I never used to worry too much about prop balance, it never caused me any serious vibration problems and I never had a motor break. Since increasingly using electric, I'm certainly aware that's it's an issue and I balance all props now, including the i/c ones. I'm not sure how to balance a spinner though and I think the big problem has been getting these long ones to run true. Clearly I struggled with the home-brewed ones, but I expected the commercial ones to be fine, they look identical to those that Irvine sell except that the carbon fibre cone is longer. I've got standard Irvine spinners of the same size and back-plate is identical. They are probably made in the same place.

I originally designed and built this with the motor front mounted. Instinctively I don't like rear mount because of the, to me, excessive overhang, exactly as referred to by Simon and Roy. However after I had the motor in my Seacano tear itself out, I realised that with the small section nose and limited gluing areas there was a problem, so altered it to rear mount and it's been trouble-free since. With the Seafang having a much larger diameter nose area for gluing though I didn't think there would be a strength problem. However, because I was keen to get the very prominent spinner to be reasonably accurate I wanted to use what I co-incidentally had, the ABS plastic spinner from a Pilot Spitfire24/Seafire 47 or one of the 2 identical aluminium versions that I had specially spun for me perhaps 30 years ago and had kept. The Pilot model was 1/10 scale, the same as this project and as the spinner was identical on all of the Griffon engined Spitfires, Seafires, Spitefuls and Seafangs excluding the Spitfire XII and Seafire XV/XVII, I could use one of these. However, because they are of the type that fit in front of the prop rather than having a rear disc like the Irvines do (and I normally prefer), propeller thickness varies the clearance between the spinner and the fuselage nose-ring, so there's a potential problem. When setting all of this up, however I tried I could not get these spinners to run absolutely true. To be fair, I'm no precision engineer and many others could perhaps have done a better job.

Therefore I searched Ebay to see if I could find something of the right diameter which was close to length and profile, which I did successfuly and bought two of the "Irvine type" aluminium/ carbon-fibre spinners referred to above. However, this caused another problem in that there was now an unacceptable gap between spinner back-plate and nose ring, which lead to the decision to open it up and rear mount the motor on a new 3mm thick plywood (not Liteply) plate securely epoxied and reinforced with triangular balsa glued to the fuselage sides behind it. The result is very solid, the nuts on the motor mounting bolts are doubled up with a lock-nut and Loctited.

The result you see here. What staggers me is that after a very brief motor run in which this happened, the new motor is clearly already damaged because it "graunches" when turned by hand and when I attempted another run without the spinner, it obviously had a broken bearing at the very least. So I'm scratching my head. As part of this project I purchased a HobbyKing Spitfire 24, which is also 1/10 scale and is very accurate in most respects. The tailplane is absolutely identical in size and shape to the one on the Seafang, which is as it should be because the Spitfire 22/24 and Seafire 46/47 were fitted with the larger Spiteful/Seafang tailplane. I thought I might be able to use the spinner and 4 blade prop combination from this on the Seafang and have bought them separately as well as as an 850kv motor that is used in this plane. However, the one main compromise that HK have made on this excellent model is that the spinner is not scale diameter, it is slightly smaller, so would require further surgery on the Seafang. Also the prop would be very likely to break regularly with undercarriage-less landings on the grass. I won't be pursuing this idea, but will simply keep these as spares for the HK Spitfire or another project.

For the moment I'm stuck, it's going to be a fiddle getting the motor out but I'll do that. In the meantime I've sent the previous XYH motor with the broken shaft back to George for comment. This plane was finished structurally many months ago and I know that a lot of people have been interested in it. Delays like this over something normally straightforward are very frustrating and I still haven't identified the best solution, but I will.

Edited By Colin Leighfield on 27/08/2014 10:24:04

[Erfolg]

Colin

I had noticed that Ripmax, Spitfire used a spinner of modest size, and what I took to be a non scale nose. Then the penny dropped (after seeing many and a long time) that the curious nose was actually meant to be the spinner. It is just poorly executed and is unconvincing.

I am at present building a 190A Balsacraft kit and a 190D based on the same kit. Balsacraft use the same technique with their kit, of a dummy fixed part of a spinner and a rotating proper spinner.

It is a solution to minimising issues related to large spinners and small, relative to the spinner, shaft.

I will use the technique on the 190A, as a need a heavy motor, which can be hidden in the spinner, so serves a practical purpose. The big issue is, can I, do a better job than Ripmax? Will it be convincing?

Yet the approach may have practical merit for your Spiteful.

It was and perhaps remains my intention to use a large spinner on the 190D. This should be 55mm dia. Now I am having some doubts.

The Ta 152H you have seen uses a 55mm dia spinner without trouble. On the other hand my HK Firenza

also uses a 55mm spinner, that runs out, although after numerous flights has not caused any failure , nor does there appear to be any discernable vibration.

I guess I am as undecided as yourself, and see no perfect solution, without potential downsides.

Another thought, I had a major problem with the Ta 152H, which resulted in the motor tearing out, due to suspected resonance.

I changed the motor, after which there was no longer a vibration issue. Yet the same motor was then used on my trainer for my A test, which continues to now fly weekly without a hint of vibration.

From this, i can supply no definite answers, although I would suggest, that just changing fixing arrangements and items can be enough for issues to become a distant memory.

[Colin Leighfield]

Thanks Erfolg, all fascinating stuff and I will be interested to see how your 190A and D finish up. The Ta152h is a favourite of mine.

However, I think I've found out what is going on. This started with the purchase of the first XYH 35mm 1250Kv motor, 60A ESC and propellers from Giant Shark. These were for the "Seacano". They were very auccessful and are atill working well in that plane. The prop was originally 10x7 but because of the current I cut it down to 9x7 and re-balanced it. As it all worked so well I bought exactly the same for the o/d Seafang, which uses the Tucano design principles and is similar size and weight. I used the same type of prop as in the Seacano and cut it down to 9x7 also and balanced it. This is the prop I have used for all of the testing so far. They were of the type that do not have inserts for different shaft diameters, I drilled them to diameter.

I looked again tonight. The motor shows no play in the shaft and it runs true, but something has happened because it turns over very roughly. I noted that with propeller only it appears to turn over true and although rough and noisy, it will start up and run apparently true also. I then fitted the spinner back-plate with the prop finger tight and it turned over true. I then tightened it up and was surprised that the back-plate was turning assymetrically. I did something then I should have done before, fitted a new 10x7 prop with an insert to match the shaft diameter and tightened it up. It ran true. I fitted the spinner cone and briefly ran the motor. It ran true. Carefully examining the original prop, it looks as if I have drilled it slightly off vertical. When tightened down on the strong prop-driver I think there is enough give in the plastic for it to straighten up. However when tightened down on the comparatively light spinner back-plate, it looks as if it is distorting it and this in turn is causing the spinner cone to turn off-centre.

Therefore my conclusion is that the cause of the difficulty was my inaccurate drilling of the propeller. To be sure that this is right I need to change the motor again, but I'm confident now that I've found the answer and the problem is of my own making. Hopefully I'll have a new motor in by the weekend.

[Simon Chaddock]

Glad you have found the problem but those motors certainly aren't cheap.

I know many will wince but I use the cheapest I can get and If anything fails (how often does it happen?) I can buy another and then another and still be better off.

[Stephen Jones]

Posted by Simon Chaddock on 27/08/2014 23:18:48:

Glad you have found the problem but those motors certainly aren't cheap.

I know many will wince but I use the cheapest I can get and If anything fails (how often does it happen?) I can buy another and then another and still be better off.

+1

I follow the same rule Simon .

Steve.

[Danny Fenton]

Glad you got to the hub of the problem Colin

[john stones 1 - Moderator]

A thorough bit of detective work there Colin, it's an unforgiving hobby at times get one thing slightly wrong and it always bites you, glad you've solved it.

John

[Colin Leighfield]

Simon and Stephen, thank you, I take the point. I've always been prepared to pay a bit more for something better on the basis that it usually saves you money in the long run. However, in the case of these products originating in the Far East and probably many made in the same places but distributed under different brands, I can see that selling price might have more to do with trying to identify a brand superiority which means nothing in practice. In other words, you are probably doing the right thing!

Danny, thank you also. I did get to the hub of the problem, it shows you though that coming at it from an angle instead of going straight to the point isn't always a good idea. It has caused this problem to spin out for far too long. (You started it)!

John, thank you as well. I might be literate but I'm also dim. Most people would have twigged this one on day one. It shows you that the first action should always be to go back to the basics. I keep telling everyone else to do that!

[Bob Cotsford]

Colin, that's exactly why I prefer to use a tapered reamer to open up props. The resulting conical hole locates the prop accurately at the smaller end but the clearance beyond allows the prop to seat itself square on the prop driver.

[Colin Leighfield]

Thanks Bob, I need probably to do exactly that. I've got away with rough and ready for far too long. Do you use a vertical drill stand and what type/size of reamer do you use? Also, who do you normally buy from?

[Erfolg]

I am with Bob, I use a taper reamer, for the same reasons. That I can obtain a good sliding fit on the nose side of the propeller and a loose fit on the back plate side. As Bob has indicated, this ensure that the propeller cannot be unbalanced due to sitting off set and also ensures that the propeller sits at 90 degrees to the back plate.

My taper reamer came from Toolstation for a couple of pounds. excellent value.

[Colin Leighfield]

Thanks for that Erfolg, very helpful.

[Bob Cotsford]

to be honest Colin, I've long forgotten where I got my reamers from, I think it may have been a tool stall at one of the shows. They came as a pair, one sharp tapered and one shallow. They might have been intended for reaming switch holes in panels (:shrug). I use the shallow taper one by hand, it seems to do the trick on gf props. If a lot of material needs to be removed I drill 1/32" or 0.5mm undersize and shove the taper reamer through to finish it to size.

[Erfolg]

For some drilling a hole in a propeller can be outside there comfort zone.

To ex engineering types, it is pretty obvious that the use of a drillpress/pillar type drill will ensure a 90 degree hole.

Ensuring that the drilled hole will be concentric with moulded hole is harder to achieve. A trick I was shown, was to lightly clamp the item to be drilled, so that movement is possible. Run the drill in reverse, (or for small holes by hand) whilst lightly bringing into contact with the hole to be drilled. This will centre the drill and propeller hole. The item is then nipped up, to hold firmly. The drill is then set to normal running and the hole drilled.

I personally use the taper reamer, with a pointy end. I have found to date, that it works really well. I have no of centre holes, plus a really good fit.

Others will have different methods, some work as well, some not (although many will still swear by them).

Edited By Erfolg on 28/08/2014 12:59:15

[Colin Leighfield]

Thanks again Bob and Erfolg, it's all sinking in.

[Colin Leighfield]

I've just ordered a tapered hand reamer on-line from Tool Station.

[Colin Leighfield]

Right, here we go. New outrunner fitted onto 3mm plywood plate. Front end put back together again, ready for sanding and re-painting. Gap problem between spinner and nose-ring resolved. At the moment fitted with a standard Irvine spinner which is too short, but at least it's running true. I'm going to find a way to graft one of my ABS or aluminium scale spinner front ends onto this.