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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: Heater for my shed
21/01/2018 16:18:09

I work in a concrete double garage with a metal up and over door which I've insulated with double aluminium faced bubble sheet with a noticeable improvement. I'm also gradually adding this to walls where I can get to them. Eliminating draughts is very important though and I've invested in a rubber sealing strip for the floor, for the door to close onto and flexible side seals.

I've put insulation in the roof and heat with a combination of an oil filled radiator (largely ineffective for short term heating and rarely used), halogen heater and fan heater, which I concentrate on my work area which allows tolerable working conditions in sub zero outside temperatures.

I also have a dehumidifier set to keep relative humidity below 70% (with a temperature switch to enable it above 5 degrees C) that has virtually eliminated any corrosion of tools and machinery. As I see it, the 100 or so watts consumed while the compressor is running is being added to background heating so running it is free...(amazing how logic can be made to fit a desired conclusion!)

Edited By Martin Harris on 21/01/2018 16:22:34

Thread: Laser Engines - Technical questions
17/01/2018 19:36:46


17/01/2018 18:30:55

I hope Jon doesn't start thinking we're winding him up deliberately!

While I'm here, do you have any approximate fuel burn figures/tank size recommendations for the various engines?

Edited By Martin Harris on 17/01/2018 18:33:55

Thread: How to stop the covering on ARTF lifting
17/01/2018 11:34:27


Thread: February 2018 RCM&E
17/01/2018 11:03:45

I really don't think that it's as easy as simply adopting the convention that an anode is positive - although this is the case for the majority of devices. This extract gives food for thought:

An anode is an electrode through which conventional current flows into a polarized electrical device. A common mnemonic is ACID for "anode current into device". The direction of (positive) electric current is opposite to the direction of electron flow: (negatively charged) electrons flow out the anode to the outside circuit.

The terms anode and cathode do not relate to the voltage polarity of those electrodes but the direction of the current: whether positive charge is flowing into or out of the device. Conventional current quantifies the flow of positive charge. In most cases, positive charge flows into the device via the anode, and positive charge leaves the device via the cathode.

Conventional current depends not only on the direction the charge carriers move, but also the carriers' charge. The currents outside the device are usually carried by electrons in a metal conductor. The flow of electrons is opposite to conventional current because electrons have a negative charge. Consequently, electrons leave the device via the anode, and electrons enter the device through the cathode.

The anode and cathode have slightly different definitions for electrical devices such as diodes and vacuum tubes where the electrode naming is fixed and does not depend on the actual charge flow (current).

In a recharging battery, or an electrolytic cell, the anode is the positive terminal, which receives current from an external generator. The current through a recharging battery is opposite to the direction of current during discharge; in other words, the electrode which was the cathode during battery discharge becomes the anode while the battery is recharging.

Note that this doesn't imply a change of polarity - and for the record, I always thought that the definition of an anode was that it was the positive terminal until I started looking into this!

I suspect that the conclusion to be drawn is that although Mike was correct (I haven't read the article) the terms anode and cathode should only be used when discussing cell chemistry and for all practical purposes, positive and negative terminals should be quoted.

P.S. I was taught my basic electronics when earth was often regarded as positive and my "Principles A" lecturer taught us to remember that earth falls through a funnel - hence the origin of the diode symbol! (He was a rather eccentric Czech who'd stayed on after coming over during WW2 to work on electronics research...but as my motorbikes were old enough to have positive earths it made sense to me.)

Edited By Martin Harris on 17/01/2018 11:31:09

16/01/2018 22:37:05


Right or wrong? Who knows when you Google but the Battery University is a well known authority.

16/01/2018 19:56:41

I'm no expert but I understand that it depends on which is giving off the electrons i.e. this is the definition of the anode. In a lithium based battery, the lithium ions move from the negative electrode to the positive electrode during discharge so it seems reasonable that the anode is negative in this case.

Edited By Martin Harris on 16/01/2018 19:57:57

Thread: Laser Engines - Technical questions
16/01/2018 19:19:23

It was certainly advocated by the legendary Mick Wilshere for those carburettors on their originally intended locations.

15/01/2018 18:25:41

I fully agree that the debate has been aired fully - I appreciate Jon's position and arguments and we have agreed to differ on this subject.

15/01/2018 15:30:56

Vertical position does seem to be slightly more critical with an unpressurised tank. I know that Jon disagrees with it fundamentally, but a nose up test will sometimes reveal if this is the problem - although your installation looks pretty much ideal.

Edited By Martin Harris on 15/01/2018 15:35:42

14/01/2018 23:22:52

Always worth checking that the clunk hasn't folded forwards - especially if one of the previous landings was less than perfect. The vertical climb would allow air to be sucked into the fuel line in this case.

Colder air is more dense than warmer air, hence the occasional need to richen the mixture if temperatures drop significantly.

14/01/2018 22:00:00
Posted by Chris Walby on 14/01/2018 17:38:59:

Now with half a tank of fuel run through the Speed Air (Laser 70) I have really started to explore the flight envelope and had a couple of problems this morning (one self induced so does not count!).

First up after a number of successful stall turns, the next at full throttle and then as I eased it to 1/4 throttle it seemed to momentarily "cough" and as I turned to vertical down it slopped. Dead stick back on the runway although the hedge did look a bit taller than normal.

That's either a big tank or perhaps you mean half a gallon?

ARTF fuel tanks are often mounted directly to the formers which can encourage fuel foaming, especially as the tank starts to get emptied and bubbles can be sucked through the fuel lines - have you packed foam around the tank? This can reduce the effects.

Thread: Thumbs up for electricwingman
13/01/2018 23:29:36

Time to drop in a quick reminder about Paul's great customer service - which I'm glad to say hasn't changed since I last bought something from him a year or two ago.

I placed an order on Thursday evening which was dispatched (postage free and item slightly cheaper than any other supplier) on Friday morning and arrived via 24 hour recorded delivery around lunchtime today just in time to install it in the model for an air test this afternoon.

It makes a refreshing change from the "service" offered by a competitor who charged £5 for second class post and stated that he aimed to post items within a couple of days of receiving an order...

Thread: Spitfire women
12/01/2018 00:27:29
Posted by Tom Sharp 2 on 11/01/2018 20:15:18:

Diana Barnato was the daughter of multi millionaire Wolf Barnato who saved Bentley from bankruptcy in the 1920's and again in the 1930's.

His engineers developed the Blower Bentley turbo charger, the principle of which, was later adapted for use on the Merlin.

Edited By Tom Sharp 2 on 11/01/2018 20:25:15

I'm no expert but I thought the Merlin used superchargers (mostly 2 stage) not turbochargers - and the Merlin used gear driven axial impellers in its various superchargers. I'm sure the Bentley used a Rootes type supercharger, a very different principle and definitely not a turbocharger...

Thread: Laser Engines - Technical questions
09/01/2018 23:45:35
Posted by Chris Walby on 09/01/2018 22:15:07:

With luck another club member might bring a seat and some tea out while you wait!

We've certainly played pass the transmitter on a couple of occasions over the years...

09/01/2018 21:19:45

Just be very sure that the ball joint retaining nut is securely locked - a detached linkage, partial throttle on an economical engine and a large tank can make time drag a little...

Thread: What rx battery??
09/01/2018 18:57:56

Just top up your LiFe batteries before a session - they can be charged at high rates and don't take as many mAh as a 4S Nixx battery for the same amount of flying time - plus there's negligible self discharge...

08/01/2018 18:35:40

2S LiFe for me (unless I can find any more NOS NiCds for sensitive servos).

Thread: Winters Here Who's Been Flying ?
07/01/2018 23:28:22
Posted by Colin Carpenter on 07/01/2018 19:30:33:

Blimey ! Ron ! I just put a coat on over a shirt , and fingerless gloves if there's a wind ! If it's below freezing might get out a scarf from the top shelf of the wardrobe !!😉 I put it all down to standing by freezing lakes in 1969 when boating ! And of course , ice on the inside of the windows in the 50's !😁 Colin

I go flying at least twice a week in the winter but I dislike the feeling of restriction while wearing a coat to fly so I slip on an extra tee shirt under my club sweatshirt when the temperature slips below a few degrees C - mind you, we do have a heated clubhouse to retreat to between flights. I have started using a transmitter muff (won a couple of years ago in the Xmas giveaway on this forum) when there's a strong cold wind, in preference to thin ex-RAF flying gloves - but then I am a softy Southerner...

Edited By Martin Harris on 07/01/2018 23:31:42

Thread: Fighter Boys . Patrick Bishop
02/01/2018 16:17:32

Try to get hold of "Spitfire on my tail - a view from the other side" by Ulrich Steinhilper - it's fascinating how similar the attitudes and experiences were.

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