This circuit is a derivitive of the FET switcher (here). It's a stripped-down version, intended specifically for glow engines, and differs in that the front end has been beefed-up with a couple transistors.
Why?
Stay tuned, for all shall be revealed.

The heart of this circuit is the trusty old CD4013 - otherwise known as a 'dual d-type flip flop'.
Mean anything? Fret not. But maybe it is worth knowing that the '4013 and the n-channel FET are both from the MOS family, because that means two things: 1) they hate static electricity, and 2) they need at least 4 volts up their input pins in order to operate. Which is where things start to get interesting...
Before the advent of UHF R/C equipment, most every PPM receiver would present a healthy 4.8-volt PPM signal to the external device - whether it was a servo, a speed controller, or a switcher, etc, etc. But then came along 2.4GHz equipment and suddenly that healthy 4.8V signal was reduced to around 3 volts. This is bad news for some ancillary units - especially MOSFET devices - since 3 volts is too weak to drive their inputs. So this lower signal has to be boosted, and this is where transistors Q1 and Q2 come into being. In short, the unit presented here will now work with just about every PPM transmitter on the market.
Bog-standard off-the-shelf components are used throughout, all shoe-horned on a piece of Veroboard measuring 2.3" x 0.8".

Begin by cutting a piece of Veroboard, 23 holes x 8 tracks (fig.1).
Flip the board track side up and make 21 breaks at the locations shown. You can use a 3mm or 4mm drill to do this.
In order to get the correct orientation, note that location A1 is at the top-right corner.

Next, flip the board component side up and insert the 10 wire links as shown in figure 2.
Because three of them are located under the chip it is important that the links are soldered first.
Use single-strand telephone wire or similar, but notice that the link shown in column 18 is thicker. It carries the negative supply rail to the MOSFET, and because high currents will flow you will need to use stout wire. For example, you could use copper wire used for domestic house lighting ciruits, or 45Amp fuse wire.

Before soldering any components you might want to familiarise yourself with the pictorials below. Compare them with how they look in figure 4 on the right.

• Q1 Emitter is at location C4.
• Q2 Emitter is at location G6
• Q3 Gate is at location C19
• Pin 1 of IC1 is at location B13.
• The positive leg of C2 is at location F10.
• The LED cathode (denoted by a 'flat' on the body) at location A22.
• Location D2 is shared by resistors R1 and R2. Insert both before soldering.

Probably a neater way of doing it would be to paste a parts-placement overlay to the board first. It's just a matter of then stuffing all the components where they are shown.
Although aligning the overlay to the board can be a bit tricky, there are perhaps two advantages:

1. Reduces the chance of soldering a component in wrong location.
2. Gives the board a neat PCB-type appearance.

Be sure to connect the servo lead exactly as shown. The signal wire is usually coloured white or yellow. Solder it at location A1. Solder the red (positive) at B1 and the black (negative) at C1.

The 1.2-volt positive wire shares the centre terminal with the glowplug at location F22, and the 1.2V negative at H22. The blue wire (D22) is connected to one of the engine mounting bolts.

Setting up is dead easy. With the unit connected to your receiver, and the transmitter switched on and the throttle stick at idle, the on-board LED will most likely glow. If not, then try tweaking the trimpot either way.
The aim is to have the glowplug on while the throttle stick is at idle. When the throttle is advanced the plug should then extinguish - usually at some point around 25% of full throtlle. In order to do that you simply hold the stick at the desired position, then tweak the pot until the on-board LED turns off. The exact setting depends on your particular engine set-up, but is easy to do and only takes but a few moments.

Note: Initial testing of the unit can also be carried out with the aid of this servo tester.

(1) You might want to have the LED in a convenient location in order to know when the glowplug is actually on. In my case I opted to mount the circuit board in the fuselage, just forward of the Rx battery. But once the wing is in place it's nigh impossible to tell if the LED is on or not. So by mounting a remote LED near, say, the charging socket, means you get a clear, at-a-glance indication of what's happening.

(2) Regarding resistor R5, the reason I stuck a relatively high value there is to keep the current draw from the Rx battery to a reasonably low level (because the LED robs its power from the receiver battery). I used a super-bright version in order to be able to see it in strong sunlight.

(3) Running the glowplug from 2 x 1.2V series cells would probably destroy it - or at least shorten it's life dramatically, but since I had a couple 2400mA double-A cells doing nothing, AND a 2-cell battery holder, it made sense to use them. If you go this same route, then you will have to drop the voltage a tad by inserting a high-wattage resistor, like so...

The image shown on the right is obviously too large in the real world. It has to be reduced in size first. So once you've copied it to your drive, and in order to have the printout match the actual board dimensions, you need to set your printer reduction to 54%.
When you get your first printout, hold it, and the board, against the light, then align the holes nearest the corners. If you're lucky they should be pretty much spot on. If not, try adjusting your printer setting just one per-cent plus/minus either side. It's a case of trial-and-error for each individual printer. But starting with 54% will put you in the right numbers.
Once you're armed with the correct setting, make a final printout on gloss photo paper. Roughly trim it to size, but leave approx 5mm around the perimeter. Paste the board and the printout with Pritt-Stick, then align / stick them together. Try not to get glue on the printed side, because it sticks like you-know-what and looks pug-ugly.
Trim off the excess overhang.

Pushing them skinny legs of resistors, etc, through plain-paper overlay is easy. Pushing them through gloss paper isn't. Jab a needle through there first.