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Laser Engines - Technical questions

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Jon - Laser Engines21/05/2020 08:31:51
5510 forum posts
268 photos

What i suggest DD is you take the plugs out and play with some crocodile leads for a bit. Twiddle the dial, see if you can get a good glow. Try running the plugs in series and in parallel to see what you get.

Some power panels can spit out enough amps, others cannot. On my own engines i use a 2.4v 6600mah nimh pack made up of 4 subc cells (2 series 2 parallel) and i then wire the plugs in series with +ve power going into one plug and -ve coming out of the other with the crankcase completing the circuit.

If you do use the power panel and set the current for the twin, make sure you mark the position and reset it to a lower level before you fry all of your single plugs

Tim Flyer21/05/2020 08:43:36
1289 forum posts
236 photos

I went the “old fashioned route” and have stopped only relying on glow sticks.  I just use a glow stick in addition when starting my twin, as I mostly run single cylinder engines.  

I made a small ply box with an ammeter on the lid and a 2v lead acid 4500mah battery.

it only needs charging occasionally and certainly not every session. I much prefer using glow leads as the clips grip the plug better and are less affected by engine vibration than a stick which wobble like a pendulum. It’s also convenient to unplug the other end from the battery rather than having to remove the clip from the cylinder head when You want to delay starting.


The battery only costs £5.99


Edited By Tim Flyer on 21/05/2020 08:44:20

Edited By Tim Flyer on 21/05/2020 08:48:53

Ron Gray21/05/2020 09:24:01
2173 forum posts
941 photos

I use one of these, expensive, yes, but brilliant and I only charge it about once a year! For my Laser twins I connect them in parallel which works well with this glow driver. Having said that, I believe Neil Tidy starts a twin on one cylinder then puts the driver on the other!

Martin McIntosh21/05/2020 10:55:55
3419 forum posts
1213 photos

A while back I posted the simple circuit I use on my flight box, only four components and maintains a constant voltage. Can put it on here if anyone is interested.

JENJEN21/05/2020 11:22:55
9 forum posts


Certainly would be interested in receiving your circuit information,

Chris Walby21/05/2020 11:35:52
1240 forum posts
303 photos

Like the idea there Tim...Nice and simple so less to go wrong and so off to the shed to find an ammeter!

Scott Edwards 221/05/2020 12:27:17
216 forum posts
97 photos

I tinkered with using a single glow battery for my Vees with mixed success. If you can safely get two glow sticks on the plugs that's great, but on most installations you can't.

I now use two cheap 12v power panels, each running off a 3S 1000ma Lipo. Each glow plug is on a different circuit, via a 3.5mm jack plug. It gives me flexibility to give each plug whatever amps it needs, and control them individually from a safe distance. I can then use either panel on my Laser singles too.

Certainly works for me anyway 👍

Martin Harris21/05/2020 13:14:33
9337 forum posts
249 photos

I'm afraid that I'll be upsetting Jon a little wink as I intend using a South Herts Models twin glow unit with the 200v in my Tempest. I promise to set the engine up to run properly without glow support though! As it is almost inevitable that I will need to add nose weight, choosing between adding dumb lead or a functional battery is a no brainer for me, especially as I was gifted an IGS-2 which is lurking unused, which will give starting convenience at little or no cost.

I've used one of these systems for a decade or so on the ASP160 in my 1/4 scale J3 Cub very successfully.

My no doubt muddled thinking is that the glow unit is primarily there for convenience in starting and with a twin, has the benefit of in the unlikely event of an air bubble or similar dropping a cylinder, it will allow it to restart while the other cylinder maintains the engine revolutions.

Jon - Laser Engines21/05/2020 14:14:50
5510 forum posts
268 photos

Set up correctly the south herts glow driver is the only one i would ever consider using as you can adjust it to not come on when its not needed due to its plug temperature sensing ability.

Essentially, i would tune the engine with the glow disabled via the tx, get the everything setup nicely and then turn on the glow. Adjust the dial so that even at idle the plugs are off, but just on the cusp of switching on. That way it wont actually be running on the glow but will have assistance if the plugs cool below a certain value.

If set this way it will have no impact on engine tuning and will provide power to start the engine or rescue it if the need arises.

Still dont really recommend it though as its just more stuff cluttering up the place cheeky

Also, lead isnt dumb, its super useful as it stops the model crashing due to a heavy backside wink

Edited By Jon - Laser Engines on 21/05/2020 14:15:22

Martin McIntosh21/05/2020 14:38:02
3419 forum posts
1213 photos

power panel 001.jpg

Above is the simple circuit I have used for years. As long as the regulator is bolted to a metal plate to dissipate the heat and you do not use a higher voltage than 3.7 (1C lipo) I am fairly sure that it will light up more than one plug. The voltage, being regulated, will not drop. If you use a higher i/p voltage then the excess will cause it to heat up considerably. Don`t use 12V. You could probably dispense with the capacitors for this application.

With no R`X` fitted it will o/p 1.25V which is the very minimum; this can be a very low value, low wattage resistor if you need a higher voltage which you will not. Cheap versions of theLM338K can be found on line.

Below is my panel. The switch is a multipole with them wired in parallel to handle the current and is biased `off` in one direction to test the plug, the other way being normal `on`. Don`t leave it on forever or the battery will eventually discharge.


power panel 002.jpg

The right hand side is normal 12V for a starter; the top right switch is for the fuel pump. The ammeter was pinched from an old car battery charger.


Below is a diagram for an on board glow which I used on a W/C F3A. Close the throttle and the switch toggles to power the plug. At about 1/3 stick it turns it off. This used to baffle the timekeepers who would start their stopwatch at `clip on`. I simply flicked the prop!

Remember to open the throttle after the motor has been stopped or you will flatten the battery.

on board glow 002.jpg

The E is now back in RCM&E.

Edited By Martin McIntosh on 21/05/2020 14:39:42

Nigel R21/05/2020 15:11:13
3916 forum posts
678 photos

"I am fairly sure that it will light up more than one plug."

It'll do 5A max, given enough heatsink.

The 338K is obsolete now (as in, the big round T03 package).

Try the other variant - LM338T - which is a TO220 type, and cheaper. Stick with a reputable source (not ebay!)

Martin McIntosh21/05/2020 15:32:13
3419 forum posts
1213 photos

The 338t is still only 5A. I use one on a self contained glow start. Being the plastic TO220 type it needs a much thicker/larger heat sink.

You could always have more than one unit on the same power panel for multi cylinders.

tigerman22/05/2020 14:33:14
220 forum posts
1 photos

Qustion .I have a Laser 180 and it is in a Wots Wot XL .I have just broke the prop on a landing and need to replace it .I noticed the broken prop was a APC 16x8 prop but when I look on the Laser web site I am now wondering if this prop was a bit to small .Can anyone recommend what prop would be best on my Laser 180 in my Wots Wot XL please so I can order the correct prop for this model


tigerman22/05/2020 15:12:34
220 forum posts
1 photos

Just look up the recommended prop for a Laser 180 and I do not know how I came to be running a 16x8 .I notice on the Laser web site Jon recommends a prop from 17x6 right up to a 20x6 ,so the 16x8 was to small .Thinking of putting on a 18x8 but what would be the best for the Wots Wot XL ?

Denis Watkins22/05/2020 15:30:39
4448 forum posts
113 photos

I like the ground acceleration of the 16 x 8 Tiger

So expect a longer ground run on the 18 x 8

But wait for Jon, he is the man

tigerman22/05/2020 16:43:49
220 forum posts
1 photos

I was going to ring Jon but I do not want to keep bothering him ,he is a busy man but I am sure he will reply on this forum in good time

Scott Edwards 222/05/2020 17:06:40
216 forum posts
97 photos

A 16*8 is perfect for a 155, so that's a great excuse to buy a new engine as you already have a prop for it 😁👍

For my 180's I use an 18*8 or a 20*6. For scale, I like the wooden Falcon 20*6 from Propguy. For sporty stuff I've tried the Gsonic, Master Airscrew and Menz 18*8. I prefer the Menz, then the Gsonic, the Master Airscrew is a bit heavy.

I've never found an APC 18*8 but would like to try one.

Jon - Laser Engines22/05/2020 17:10:04
5510 forum posts
268 photos

18x8 would be good, 17x8 perhaps? it depends what you are after. 18x8 will give you constant thrust and good downline braking, 17x8 will probably give more speed but you need to thrash the engine harder. Im told by customers 18x8 apc wide props work well but have never tested it myself

Jon - Laser Engines22/05/2020 17:10:40
5510 forum posts
268 photos
Posted by Scott Edwards 2 on 22/05/2020 17:06:40:

A 16*8 is perfect for a 155, so that's a great excuse to buy a new engine as you already have a prop for it 😁👍

8*8 but would like to try one.

Dont give him ideas, im miles behind as it is.

Rocker22/05/2020 21:10:20
351 forum posts

Can you use a wooden prop (18x8 ) on a Laser 180 ,or is it best to stick to a APC 18x8 prop ?

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