Nitro RC Helicopter Starting Method Using External Starter with Hex ShaftNitro Heli Hex Shaft Starting

As we discussed in the nitro RC helicopter engine basics section, like every other internal combustion engine, you need to spin the engine in order to start. For most RC aircraft this means using an external electric starting motor to save on flying weight.

There are basically three ways this is accomplished on Nitro powered RC helis.

Starting Shafts

As pictured above, the most popular way is by the use of a starting shaft that runs down to the engine and out through the top of the helicopter. There will be a small cone or hex head on the end of this shaft that provides a mechanical connection with the electric starter motor. The starter motor will spin the starter shaft by means of friction with the cone or mechanical engagement with the hex head.

This starting system is the most convenient method of starting but it has a couple of draw backs.

The biggest issue is with the starter shaft extension is the extension itself. When you are removing it from the cone or the hex head after the engine has started, it can spin out & hit your swashplate or rotor head pushrods and bend them or break a ball pivot.

I have found a very good cure and this problem almost never happens to me anymore. Make sure your starter extension is rotating perfectly true - no wobble whatsoever. I simply put a small amount of epoxy on the electric starter output shaft when installing the extension shaft. I ensure it is running true with a dial indicator before the epoxy sets up. Once the epoxy sets up, the extension will always run strait and true.

The next thing to do is make sure you always lift your starter extension straight up off the cone or the hex head. This goes without saying, but when you are pumped to go flying, sometimes we all forget the most basic steps.

If you follow these two simple steps, starter extension damage will seldom be an issue for you.

This next problem has pretty much been solved with all newer heli kits, but you should know about it. Like the cooling fan , the starting shaft is spinning at the same speed as the engine. If there is any misalignment of the shaft to the engine, it will cause high frequency vibrations.

Just as with fan vibrations, starter shaft vibrations can be identified by fuel tank foaming. If not corrected, the aluminum side frames will usually start to show stress cracking around the starting shaft bearing block.

RC helicopter manufactures have gone to great lengths to minimize this problem by isolating the engine from the clutch and starting shaft. Generally some sort of isolation bushing/s between the engine and the clutch are used so critical alignment is not as important as it once used to be.

Belt Starting

The second method of starting a nitro RC helicopter is by using a small belt that you loop around a machined groove on the top of the fan assembly or bottom of the clutch assembly that is attached to the output shaft of the RC nitro engine. You then loop the other end of the belt around a matching groove on your electric starter hub to spin the belt and the engine.

This system eliminates the starting shaft and any vibrations that might be associated with it. It also reduces the number of parts and cost of the helicopter kit. Of course if you ever want to put a scale fuselage on your nitro RC helicopter, this system won’t work because you won’t be able to access it.

I did have an RC nitro helicopter that used this system once, and I found it very awkward and difficult. You have to put quite a bit of side pressure on the starter and belt so it doesn’t slip. With the other hand you have to keep the helicopter secure.

Because the belt is looped around the clutch and fan, it has to stay in the helicopter and be neatly secured in that configuration after you get the engine started. There is always the possibility it can vibrate loose and jam the fan/clutch – better know how to perform an auto rotation if that happens – I didn’t at the time – oops!

Rear Engine Cone Starting

The third method is by using a special nitro RC helicopter engine that has a starting cone on the back end of the engine. You simply start the engine by engaging the cone with your electric starter from underneath the helicopter.

As with the belt start system – you don’t have to worry about starter shaft vibrations. However it is awkward in that you have to turn the helicopter over on its side to engage the cone.

There are very few engines manufacturers that build these types of engines and very few helicopter kits that support them. You will most likely never run into this starting system, but I thought you should at least understand a bit about it.

Starting Safety

One very important point I didn’t mention but it holds true for all these nitro RC helicopter starting systems... The engine has to be set at idle when starting. If it isn’t, you will find yourself in the way of quickly accelerating rotor blades.

I can’t tell you how scared I was the first time I started a nitro RC helicopter. Even though I must have checked to see if the throttle was in the idle position a hundred times – I had this fear in the back of my head that something would cause it to start at full throttle. No worries – it didn’t even start because in all my fretting over the throttle position, guess what I forgot to do... yup, dumb-dumb forgot to put fuel in the tank. A couple times a year I do accidentally start the helicopter with the throttle set at a high speed or have my throttle hold switch turned on. As long as you are holding onto the rotor head and immediately throttle down or kill the engine you will not get hurt or damage any parts on your heli such as the clutch or rotor head.

The quickest way to stop the engine is by plugging the exhaust outlet on your muffler with your finger. This is much easier than fumbling around trying to pinch off the fuel line; in most cases that will actually make the engine speed up initially for about 4-6 seconds.

Yeah, I know what some of you are saying – “John, if you plug the exhaust, you will flood the engine – you really are a dumb-dumb”. This is true, but I would rather have a flooded engine than a burnt clutch or worse a damaged nitro helicopter.

My Own Disaster Story

I will tell you one last story and an important tip on starting a nitro RC helicopter or any kind of RC helicopter for that mater. Always – always, make sure your RC radio is lying on its back or is secured from tipping over. You could also engage the idle hold switch – something I do all the time now.

I had a very dangerous crash once and almost hit several spectators because the RC radio tipped over. I had started the helicopter and carried it out to the take off area, while I was walking back to get the radio a gust of wind tipped the radio over. This pushed the throttle to almost full and also pushed the cyclic stick forwards to give a forward cyclic command.

Before I could get to the radio, the helicopter shot up and forwards towards a young family who were watching the goings on. Thankfully the heli kept pitching forwards and crashed nose first into the ground before it hit any of them – I was very lucky that day. It was also a good thing I was wearing brown pants.

All kidding aside, this could have been the end of my RC helicopter fun for good if I had hit any of them. I do remember the kids laughing and thinking it was so cool to see the helicopter crash. The parents didn’t seem to realize the danger I exposed them too – I get a rock in my stomach every time I think of this event.

Not the note I wanted to end this page on – but so important to remember.

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