My experience with the FEMA onboard- starter:

by Noël Rumers

Many times I have been asked, how the FEMA starter works, and if it were relevant to build one in a model airplane, or, how one must operate this starter.

Looking back on my experience with the on-board starter, I can say that, it is worth while to build one in the model.

There are a few arguments in favour:

  1. We are flying scale models of motor gliders. When we have sailed around for some time, like normal sailplanes or gliders do, without the use of the engine, it is fantastic to restart during this flight without the need to land the plane first.
  2. Most scaled motor gliders will need a lot of lead built in the nose. This is because of the rather long tail section to the short nose part. Why should I fly with lots of lead in the plane with no special use instead of building in a technical tour de force, with only a lot of advantages?
  3. Active security!!! The engine will start by manipulating a single switch on the transmitter. I, the pilot, will stand behind the model. Never again I have the need to be with my hands in the danger zone of the propeller. Many of us have touched the propeller before, this is all over with this starter.
  4. Last but not least: Why should the scaled motor glider be the last to have a technical achievement?

I can assure you: lead is cheaper!!! The onboard starter will cost about €160.00 ($). But when we look upon the high value that it brings to our scaled model motor glider or any other model airplane, with all its safety to the relative small price, I do not have to consider any further.
I just want to give you the possibility to learn from my experience with onboard starters like I do use in my model, the SF 33 with the FEMA starter in combination with the ZG 38.

Operating the starter:

…We have two types of petrol engines, one that is operated on the ground like the chainsaw engine, and an engine like we build in our models. Both engines are alike, but to start them is slightly different.

To start a chainsaw engine, you first have to close the choke valve, then you try to start the engine. Does the engine give the intention to start running you open the choke valve and start again and the engine will run.

In this way, while still on the ground, you can handle our model engine too.
I will stand behind the model and start the engine. Both hands are free to manipulate the switch for starter and choke valve. I will be able to open the choke valve, stop the electric starter motor, without flooding the engine and not being able to start at all before the sparking plug is dry again.

Has the model been sailing or gliding around for some time, and you want to restart the engine, then it is a different story…

I first have to concentrate on flying the model, I do not have my hands free to manipulate the switch, maybe still other planes are flying with running engines and before I know what was happening, I will have flooded my engine, not being able to restart it.

I have the need for another starting sequence…

At first the electric starter engine must be running, before the choke valve will be closed. When the engine is running, we first have to open the choke valve (the starter motor is still running) and only then we stop the starting process. ( This will not harm the electrical motor because the gears have a built-in one way bearing, when it is overrun it acts like a normal needle bearing.)

All will be possible by the use of only one 3-way switch, built to the top-left hand side of the transmitter. With this switch I will activate only one servo. This will operate both the starter motor and the choke valve, to start the engine.

On the next pages I will show you how the built-up for the starter servo is accomplished, how the starting will be done in detail, as described above, how the carburettor can be rebuilt and the possibility to interrupt the ignition. ( This to stop the engine to hit back on the starter gear).

The FEMA onboard starter is a stable construction that needs little attention or maintenance. But still the gears like a drop of oil now and then. (SAE 80) When operating with the shaft coupling, this coupling should be well greased.
A dry shaft coupling might rattle and it could make radio interference possible. You can hang the shaft in a small plastic like material, suited for the carrying the shaft while turning, in combination with a small pulling spring to hang it to the firewall of the plane.

When you have questions about this matter we are always willing to help you.


Starter servo :

  1. Screw to a standard servo a big servo wheel.
  2. Make from a plastic part a 2mm thick and 5mm wide ring over 180°. At both sides the sharp edge will be ground away under 30°, so that the switch arm can easily glide over it. This part shall be glued underneath the servo wheel. See drawing 1 and 2
  3. Glue a 10Ah micro switch with a 20mm switch-arm to the side of the servo. If you do not have a switch with an arm, you can make one yourself by a small brass or metal plate, a piece of brass tube that will fit into the small holes in the switch.
    The holes are 1.2mm dia so a small shaft made of spring steel can be put in to hinge the soldered plate and tube.

  4. The construction of the cable connection for the servo and the carburettor, shall be made as per drawing 3.
  5. To guide the cable from the servo to the carburettor, you have to bend a brass tube dia 4mm with inside a 3mm Bowden tube. Through this inner plastic tube you are able to run a small steel cable (think fishing line 60lbs). This line is also plastified. See drawing 4. The cable can be mounted on the cable connection of the servo. See drawing 1 + 2.
  6. Install a 3-way switch on the transmitter, before the final cable installation in the model. This is necessary to be able to connect the cable in the right way to both the servo and the choke valve.

Functioning:

  1. Switch in out-position: The cable connection is at this point completely at the front of the servo wheel. The switch is in out position and the cable is under no tension at all.
  2. Switch in middle position: The servo disk did turn for about 1/3. The switch is put in middle position. The electric starter motor is running. The prop is turning too. The cable is under tension but the choke valve is still open.

  3. Switch is in the 2nd position: The servo disk turns another 2/3. The choke valve is closed. The switch is in the 2nd position, the starter motor is still running and the engine will start.

  4. Stop the starter sequence putting the switch back in out-position: The servo wheel will turn back in neutral position. The electric starter motor will stop, the micro switch is no longer pressed. The choke valve is open.

In this way you can control by only one 3-way switch and one servo, the starter and the choke valve.

You are able to run the electric starter motor while closing and opening the choke valve ( this is important in flight ).

In the air I will always start the engine flying against the wind. This will help to turn the propeller while starting the engine. I can also see on the propeller RPM if the engine has been restarted and running again.

Carburettor modifications:

We all know the ZG38 is an easy starter, but with the onboard starter it is even easier.

The experience tells us however that the original layout does not function as planned.
The choke valve shaft is too heavy to operate because of the locking ball built in on the shaft. The force and speed to open and close the valve are big. The engine is getting too much fuel then and will not start at all.

I rebuild the choke valve in the following way:

  1. Unscrew the carburettor from the engine.

  2. Take carefully the bolt out of the choke plate and its shaft.

  3. Take the valve plate out. Mark the position how the plate was built in.

  4. Take the shaft carefully out of the carburettor housing. A small ball and spring will fall out of the shaft hole. ( We will not need them any more ).

  5. Drill a 1.2 mm hole in the centre of the shaft, 2-3 mm deep. This will be at the side of the lever.

  6. See to it that you have a small soft spring ready. This will be mounted between the lever on the shaft and the housing. ( Hereby choke valve shaft rattle in the housing will be stopped ).

  7. Install the spring over the choke valve shaft, put the shaft in its housing hole, and screw the choke plate as marked in place. Secure the screw with a drop of thread glue. See to it that the assembly will be gentle so no damage will be done to the shaft, like e.g. bending, the shaft has to operate very smoothly.

  8. Make a 6 mm wide and 30 mm long plate to enlarge the lever of the choke valve as per drawing.

  9. Build-on a pulling spring connected to a retainer plate that is bolted on the rear side of the carburettor. This spring will always pull the choke valve open.

Modifying the carburettor in this way will guarantee the smooth functioning by pulling a metal cable for closing and opening the choke valve. The ZG 38 cannot be flooded any more.

Legend:

  1. Light spring
  2. Hole dia1.2 mm
  3. Brass nail 1.2 mm soldered on arm
  4. Brass nail soldered onto the arm 2 mm long
  5. M 2 bolt and nut
  6. Pulling spring made from an old oil seal
  7. Retainer plate

The modification of the throttle valve is made the same way as the choke valve.
I also use a 0.7 mm flexible steel cable ( fishing cable, plasticized ). The connection between throttle servo and the throttle runs over a small cable wheel. The original spring always closes the throttle valve.

A cable instead of a fixed metal rod, has the advantage to be of very little weight, so that the shafts will not run out in their housing.

Switching off the engine:

For years now, I will interrupt the ignition to switch off the engine.
I will also adjust the engine in such a way that it is running safe and steady at low RPM. This means that I cannot switch off the engine by closing the throttle valve.
Sometimes a small turn on the throttle screw can make the difference in starting the engine or not, or during the landing circuit when the engine suddenly stops.

The advantages are:

  1. I can always adjust the throttle screw to my interest.

  2. There is no need to adjust the throttle trim on the transmitter.

  3. Due to ignition interruption the engine will suck still some petrol mixture in the engine and the carburettor. The restart of the engine will be in our advantage by the easier starting.

We do need an extra servo and a 2-way switch to make this happen.

Operation:

  1. A small servo, just like the starter servo, will also have a larger servo wheel and a micro switch.
  2. On the ignition spool, see drawing, a wire will be soldered on. A black petrol tube can protect the cable. This can be glued on to the ignition spool and guided through the cooling ribs of the cylinder over the engine mount to the firewall of the fuselage. Here this cable will be connected to the switch. The 2nd wire will be fixed by a bolt to a free hole in the base plate of the FEMA onboard starter and its other end to the switch.
  3. The interrupting servo will be operated by a 2-way switch on our transmitter.

Both the interrupting and throttle servo will be built under the cowling against the firewall.

I have been operating, for years now, my model airplanes and motor glider, without interference for the radio signals.

I want to point out that all these changes that I described above must be made in a professional manner and that they will be made at ones own risk. The warranty of new engines can be expired!