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Member postings for Martin Harris

Here is a list of all the postings Martin Harris has made in our forums. Click on a thread name to jump to the thread.

Thread: Light Relief
05/04/2020 17:01:01
Posted by Chris Walby on 05/04/2020 14:36:47:

Well a bit of everything and even a twin allowed to join the flight!


23 minutes of something for everyone, superb.

Bit over-generous with the primer on the Mossie's port engine?

Great quality video - and what a collection!

Thread: Laser Engines - Technical questions
05/04/2020 12:39:50

If I might make a suggestion...

It sounds like the camshaft has seized into the outer bearing (the end float being until the cam gear hits the outer follower) so if you can get the cam followers to drop out then you should be able to remove the cover complete with the camshaft. If you haven't already done so, remove the cylinder head and pushrods and hopefully knocking the inverted crankcase on a block of wood will allow the followers to float free of the camshaft. A strong magnet might help to get them moving if they're sticking but it's the outer one that is important to move out of the way.  You will not actually need to completely remove them - if the heads are level with casing there's more than enough clearance.

If it's seized as I suspect then it may well be caused by rusting in the bottom end so a complete stripdown will make things easier and you'll probably need to do it anyway.

Edited By Martin Harris on 05/04/2020 12:56:06

Thread: Making Steel Fittings. Question.
03/04/2020 21:28:35


Thread: Focke Wolf Ta 154 Laser
01/04/2020 15:24:47

It was those "rare spacers" that I was wondering about - what's their function?

01/04/2020 13:01:12
Posted by Chris Walby on 31/03/2020 21:07:26:

20190526_205847.jpgPS Not engine or tank final position!

What's the story with the engine mounting bolts, Chris? Is there some sort of flexible mounting going on?

Thread: Flat Car Battery from non-use of car
01/04/2020 12:47:23

Assuming that like most people on this forum, you have a multiple battery technology charger for model use that runs on 12v, you could charge your car battery on a Lead-Acid program using those LiPos as the power source. Much kinder on the cells, terminations and cabling than using them to jump start although I have heard of people using them in this way for emergencies.

Thread: Does the size of spinner effect prop performance ?
31/03/2020 19:22:54

Little or no sign of performance issues during 1/12th scale combat bouts with this - however odd the prop looked. No the tips are not concealed by the grass!


7"x5" prop to comply with combat rules for the .15 engine and a 2 3/4" spinner to conform to the scale outline of the fairly little known Me309 which I "designed" when looking for something a little more individual than a Spitfire to use for competition...

Thread: Vibration absorbing engine mounting
30/03/2020 13:28:57

Full size propeller driven aircraft often have "avoid continuous operation" rpm ranges due to harmonic vibrations so it can't be an easy fix to eliminate them, although changes in propellers can shift them to different rpm bands - one often overlooked reason why a prop change can have a dramatic effect on noise testing.

Edited By Martin Harris on 30/03/2020 13:35:17

Thread: Low wingers,very twitchy,recommend expo.YES/NO
27/03/2020 14:47:32

An interesting snippet in a video I've just been watching on the design philosophy of the FW190 - there was mechanical expo built in to the control circuits of all three axes. Watch from about 19.30 if you're interested...

Somehow, I missed the last responses to this thread - to make it clear, I was referring to movements and responses within the "normal" range and how I felt that there might be a possibility of less linearity than on full size at our low Reynold's numbers.

Thread: Wanted parts for Enya 90 and 60 FS engines
26/03/2020 23:22:27

The smart answer is because they can...but I think you're lucky the handling charge was only £8 as I've heard of much higher handling charges. The justification is that they have to manually remove the package from the largely automated system for Customs and Revenue to do any necessary checks and administer the duty payments on their behalf but it does add a lot, especially where the value is relatively low.

Edited By Martin Harris on 26/03/2020 23:24:28

Thread: Can I or can I not fly?
24/03/2020 19:11:34

While I get an immense amount of pleasure flying my models, a large part of the experience is in interacting with other members, helping out where possible and exchanging banter. I'll certainly miss my flying but this crisis is so much more than just an inconvenience and I'm just hoping that by abiding by the Government requests, instructions and no doubt soon laws, all of my clubmates will still be around when we finally get on top of this.

Thread: SC 52 2t
24/03/2020 10:34:09

Just after 10.30

24/03/2020 10:29:19
Posted by john stones 1 on 24/03/2020 01:25:40:

My word Cymas, those are noisy, you considered going lecky ? devil yes

Try turning your volume down John! cheeky

Thread: Laser Engines - Technical questions
23/03/2020 19:13:00
Posted by Ron Gray on 23/03/2020 18:37:14:

Hi Tim, I use the HD one from Just Engines with an old 6s (well 5s as one cell is dead) to power it. No problem turning over any of my Lasers or my gassers.

Spooky...I use exactly the same set-up with a 6S that had a cell cooked by an incorrectly specified motor pre-installed in a Hobbyking Hawker Hunter. To their credit, after some initial discussion, HK admitted the error and replaced the burnt out EDF unit and battery. A bit of internal reconfiguration provided me with a 5S battery that was/is perfectly adequate for the task of powering my starter.

The larger starter works with any engine that has come its way - the only shortcoming is that on a pair of Lead Acid batteries - and to a lesser extent on the 20 odd volts supplied by the LiPo - the switch contacts have a tendency to weld together...a flick or five on the switch usually frees them!

Thread: IC Engine Bearings...
21/03/2020 23:13:25

I'm sure Stephen is entitled to express his opinion but I don't think his post is in the same league as those of Barrie's clear explanation and Jon's contributions - and his patience. Thanks to these experts, the apparently illogical statement in question has been clarified, probably not only to me but also to a number of other forum contributors who had come to the same empirical and seemingly logical conclusion.


Edited By Martin Harris on 21/03/2020 23:15:52

Thread: Insanity seems to be setting in
21/03/2020 11:52:56

Seemed to be normal stocks of oranges and other fruits in ASDA yesterday morning. TBH, there seemed to be little sign of hysteria - people keeping a reasonable distance apart and plenty with small packs of toilet paper in their baskets while larger ones were on the shelves. The only normal food that was totally out of stock was eggs although choice of pasta [yuk] hand wash and washing up liquid were limited.

Thread: IC Engine Bearings...
21/03/2020 10:48:19

Barrie's explanation sounds as if he really knows the subject and certainly backs up what you've been saying, Jon. The amount of expansion/vibration seems to be at the crux of the matter, which is why I wondered if you knew what a typical crankcase temperature might be. It's certainly a surprise to me that the front bearing retention is sufficient to control any movement especially when I've seen so many just fall out after heating engines in my wife's oven!

Thanks for sticking with this and helping me to understand something that seems very counter-intuitive. Measuring some crankcase temperatures will be on my list of things to do!

Edited By Martin Harris on 21/03/2020 10:59:36

21/03/2020 02:10:54

I'd appreciate that.

One thing to ponder is my Irvine 40 that had noisy bearings - and was almost impossible to get to cut with the throttle fully shut. When I stripped it, I found the front bearing had been spinning in the housing, obviously causing an air leak. This behaviour had been there from new although it increased in severity after some extended running, leading me to believe that the housing was machined slightly oversize in the first place. I rebuilt it with new bearings and a smear of Loctite 648...which apart from stopping the bearing spinning, cured the minute or two of idling before the engine would eventually stop!

I would suggest that the tiny amount of play between the crank web flange and the bearing is taken up once the engine starts and pulls the crankshaft rear flange snugly up to the inner race, moving the front bearing away from its seat by an equivalent amount - as you've said, the crankshaft length is fixed and bearing housings have precision dimensions between their seats which cannot be oversized or the bearings would be preloaded. What sort of temperatures are encountered at the front bearing of a typically installed engine? It would seem logical that a combination of heat and vibration plus the propeller thrust would move it in the housing unless there's a dramatic difference between that and the temperature we heat the casings to in order to remove old bearings.

I believe that the end float that you're seeing on engines with loose front bearings is as a result of the "nip" on the bearing being lost and this self adjustment not holding any more.

FWIW, I do accept that the slight end play apparent in my good engines is probably due to bearing clearances!

Any idea how they get those ships propellers off? I think we both appreciate how effective tapers are in holding components - the rotating forces on a simple Morse or other form of taper in a machine tool must be enormous!

Edited By Martin Harris on 21/03/2020 02:36:38

21/03/2020 01:30:54
Posted by Dickw on 20/03/2020 15:38:55:

I must admit to being a bit confused by this discussion, but then I am an electrical engineer not a mechanical engineer. I would have thought that which bearing takes the thrust is a design decision not a universal principle.

I have attached a simple drawing and would be pleased if someone could explain why it might be wrong.

From memory of my pre-electric days I had a number of "single ball-race" engines with plain front bearings in which the rear bearing must have handled the thrust. That could be changed by adding a front "ball-race" but it surely doesn't have to does It?


thrust bearing basic options.jpg


Isn't the correct drawing a combination of the right hand end of the top drawing and the left hand end of the bottom one, with a smidgeon of clearance to be added?

Edited By Martin Harris on 21/03/2020 01:37:12

20/03/2020 21:25:19

If it's so simple, perhaps you'd like to explain where I've gone wrong Stephen?

P.S. It's just occurred to me that if you happen to bolt a pusher prop onto the engine, then the thrust WILL be carried by the front bearing!

Edited By Martin Harris on 20/03/2020 21:35:17

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