Tiger Moths that Suck

[Centaurus]

Reading old RAF Tiger Moth Pilot's Notes. The starting instructions tell you to "tickle" the carburettor (meaning deliberately flood it). Then the engine fitter (who is also the bloke that hand swings the propeller) turns the propeller backwards to "suck in" then turns the prop forward several times to "blow out" -then after calling "contact" puts impulse magneto switch (front knob of front switches) on the contact position and then flicks over the aircrew with one hand until engine fires.

If engine fails to start due rich mixture the fitter calls "Switches off throttle wide open- blow out".

Technical question: What does sucking in mean? And why is it necessary to suck in? Why 8 turns of the prop (sorry - airscrew!) to suck in but only 4 turns to blow out? If the carby is deliberately flooded then why not do what we do on any flooded engine - and that is throttle open and churn the prop over with the starter motor to clear excess fuel?

And why deliberately flood the carburettor - isn't that a fire risk?
Believe it or not these are serious questions as I have the opportunity to have a fly of the beast next week.

[Lost_luggage34]

Might be an idea to get in touch with Peter Wyld. Top chap that I used to work with at BA. He runs Tigerfly who fly the Moth.

I am certain he will be able to assist. Doesn't suffer fools gladly but after you break the ice a genuinely nice chap who is extremely knowledgeable.

Good Luck

[pulse1]

Anyone who rode a 50's motorbike would know what "tickle" means. It means you press the carb float down to fill the float chamber. Only way you know it's full is when it overflows.

Are you sure you have the "suck in" and "blow out" the right way round. I seem to remember it was four blades with the throttle closed to suck in. Then "throttle set" (1/4") and "contact".

If it didn't start after about four goes, it was "switches off", "throttle fully open" and then back the prop to blow out.

P1

[Speedbird48]

It goes something like this:-

Chock in.
Lift left hand cowling.
Depress small button on top of carburetor float chamber until fuel runs out of the drain. This fills the float chamber.
Close cowling.
Check that the pilot has the switches OFF. They can be seen as they are on the outside of the fuselage.
Tell pilot that you are "Throttle Shut,Sucking In".
Pull prop through four compressions.

It goes something like this:-

Chocks in.
Fuel on.
Lift RH cowling and press small button on top of carburetor float chamber until fuel runs out of drain. This fills the float chamber. Close and latch cowling.
Yell at pilot, "Throttle shut, Switches Off. Sucking In."
Check that the switches really are OFF by looking at them. They are on the outside of the left fuselage. Normaly a set for the front and another for the rear. The one set may be ON but the others must be OFF.
Pull prop through four compressions to draw fuel mixture into cylinders.
Yell at pilot,"Throttle set, Contact. He should advance the throttle about 1/2 to 1inch and put the switches Up for ON.
Pull prop through and it should start.

If it does not start in a reasonable number of pulls you now need to Blow it Out. This is to clear the cylinders of a too rich mixture.

Yell at pilot. Switches OFF, Throttle OPEN.
Rotate the prop backwards for anything up to a dozen compressions.
Yell at pilot, "Throttle shut, switches OFF, and confirm as before.
I always pull it through one compression at this point.
Yell at pilot,"Throttle Set, Contact.
Pull the prop through in the correct direction and it will burst into life, with a bit of luck.

Why do you yell at pilot. 1) He is a pilot!!
2) He is wearing a Biggles helmet and cannot hear too well and your arm or neck is in line for trouble if he gets it wrong.

[Dale Harris]

Think you'll have a long wait to clear the flooding by opening throttle and using the starter motor..................

[BlueEagle]

On a car engine, (normally aspirated etc), the only way to start it after it had been flooded was to push foot fully to the floor and turn over on the starter until it fired, it would usually pick up slowly, 2,3 then 4 cylinders.

This logic may, or may not, apply in the Tiger Moth case.

[Centaurus]

Speedbird 48. Er..Yes...thanks.
These RAF Notes I have say only the front knob of front switches is selected on (contact position). It also states that if engine is cold you suck in. How does one define cold in this case? For example does it mean first start of the day? Or after the engine has been shut down for an hour?

Pulse one. According to my RAF Tiger Notes, one turns the airscrew backwards until the cylinders are clear of rich mixture. And that's what had me tossed because in most lighties that I have flown you turn the prop over in normal direction of travel With throttle wide, in order to clear excess fuel. Why backwards in a Tiger to do the same thing?

Lost Luggage_34. If your man doesn't suffer fools gladly I might be in real trouble. Thanks for the tip, anyway.

[pulse1]

Centaurus,

I'm guessing but, as the Gypsy Major engine is upside down, it makes sense to open the exhaust valve first to drain excess fuel into the exhaust. You will avoid further suck in because the piston will be coming up when the inlet valve is open. Presumably this will also help to blow XS fuel out of the system through the open throttle.

The only other "lighties" I fly have mixture control so you normally do not need to resort to these measures.

P1

[BlueEagle]

This is going back a lot of years now but I do remember, on the Chipmunk, we had to call, "fuel On, brakes On, throttle Closed, switches Off" and show our hands outside the cockpit, at which point the ground engineer would move in and rotate the prop a few times, our instructors told us this was to avoid, "Hydraulicing"
in the inverted engine when it started.
Knew the full technical story at the time but that was back in 1964:(

[Lost_luggage34]

Centaurus - was in no way suggesting that you are a fool. Just wanted to clarify in case any offence was taken !!

[bonzaman]

Centaurus, I am lucky enough to own and fly a Tiger Moth. Unfortunatly I cannot give you the technical explanation for the starting routine. However this is what I was taught, and it works every time. Check fuel on, then tickle carby until full. Fuel will run from drain pipe, wait until the flow stops. Check switches off and turn the prop eight blades back and four blades forward. Turn rear cockpit switches on and front switch front cockpit. Then start by pulling the prop downwards in the forward direction. Strongly suggest you get someone who has done it before to show you how to position yourself and how to hold the prop during this operation. This is the cold start method. When the engine is warm, it will start without the priming action. It is generally warm enough when you can feel it with the hand close to a cylinder.
One final point, when pulling the prop forward for four turns you should hear the impulse coupling on the right magneto make a distinct clicking noise. If you dont it will not start, a gentle tap on the maggy will often do the trick.
Remember this is hi tech stuff!!! Enjoy the flight there is nothing better. As my instructor told me, the Tiger is an easy aircraft to fly but a difficult aircraft to fly well

[Prince of Dzun]

Bonzaman:

Your description on how to start the Tiger Moth is excellent, technically correct in every detail except you have me scratching my head as to the setting of the throttle during the procedure. As I understand it the throttle setting should be correct from the time you move the propeller, and this applies to suck in , blow out or immediate starting of a hot engine. Many an accident has resulted from the throttle being wrongly set or in some cases mistaken for the mixture control which is attached to the same quadrant. It should be done correctly and in the proper sequence everytime.

Prince of Dzun

[bonzaman]

Prince, your point is well made, the throttle settings are most important. So let me complete the picture. During the eight back process the throttle is set wide open. During the four forward the throttle is set closed. Before starting the throttle is "cracked" open. About an eighth of an inch.

[pterodactyl]

bonzaman,

Yes, your procedure is as I remember it. Glad you mention that only a gentle tap is required to resurrect a stuck impulse mechanism. Many Tiger Moths bear scars in the area of the right magneto coupling as a result of being assaulted vigorously by the front cockpit joystick or similar object.

In fact a gentle tap with a 20 cent coin on the magneto coupling collar is all that is required to release the mechanism and is rewarded by an audible "click". Like cracking a safe!

Own a Tiger Moth!!Lucky ******!! Happy flying.:D :D :D

[Chimbu chuckles]

Centaurus,

I would have thought you learned in one being ex RAAF 1950s?

I last flew a Tiger a few months ago.

The method I've always used was as described above. The flooding is because that's the only way you know there is any fuel in there at all.

I swing the prop from behind. The system is not 'live' with just the rear mag switches up (on) but is so with the forward switches up as well. You can reach the front throttle and mag switches comfortably standing in front of the wing and ensure they are correct before pulling the prop through compression.

You do not need to fling it very hard at all...not much more than a flick of the wrist really is all that's needed.

The advantages of starting this way is you control all the various aspects of the start, spark, fuel and 'armstrong' starter. If the aircraft jumps the chocks (I virtually never use chocks in this method) you simply sit on the wing, and flick off the switches/close the throttle...which should only be barely cracked anyway.

And for everyone wondering why the throttle goes wide open when cranking for a flooded engine think about what the throttle actually controls...only the butterfly valve upstream of the venturi.

When you select full throttle you are merely maximising the air which can be sucked (see why it's called suck & Blow?) into the engine by the pistons....that's all...with the butterfly valve wide open (parallel with airflow) the only restriction to the amount of air that can be sucked in by the pistons is the air filter.

A flooded engine does not run because the mixure is to rich to burn...as you crank with throttle wide open (and hopefully mixture idle cutoff) you are effectively leaning the mixture, cylinder by cylinder, until you 'stumble across' the correct fuel air ratio and the engine starts....that's why it starts a few cylinders at a time as well:D

Chuck.

[Centaurus]

Thanks for all the detailed replies. Re the prop swinging - the RAAF taught us to face the aircraft from the front when swinging the prop. The theory I suppose was that you swung down and away from the plane of rotation while leaving yourself an out by diving away if the chocks did not hold. Swinging from the back was a method I have witnessed with unease, because if the Tiger started to move under its own power you could be knocked over by the leading edge of the wing into the prop arc. But as always it is horses for courses.

[bonzaman]

I was taught, and always followed the practice of swinging the prop from the front, if the cockpit was occupied by a qualified person. If starting solo, I swing from the back this enables me to switch off the magnetos if there is any problem. Further when swinging from the back, I hold the centre section strut with the free hand. This prevents me from moving into the arc of the prop.

[Checkboard]

Dear readers of TechLog, according to the search engine, this was the last post in this forum by Pterodactyl.

I have just been informed that Ptero passed away some months ago. On a personal note, over my last four and a half years on this board, I have enjoyed my discussions with him immensely, and will miss his contributions.

It was Ptero's wish that no fuss be made of his passing.

Vale Pterodactyl

[Miserlou]

Forgive me but there are a couple of matters which have not been cleared up.

Throttle closed whilst sucking in.
Throttle set = 1/2-1 inch.
Blowing out I always did 12 blades, backwards with the throttle fully open.

Phraseology. If the switches are to be off, the words are "Switches Off". If they are to be on, the word "Contact" is to be used. It's a safety matter.

Most importantly, the man who is swinging the propeller is in charge. Do as he says.

If you find yourself in the cockpit as the most experienced man then you can tell him what he needs to do but you must still do as he says.

On being the swinger. The pressure of a flat hand against the front surface is sufficient; perhaps the skin of the finger tips around the trailing edge. There is no need, on gypsies, to have any joints around the blade in case of a blowback.

Stand beneath the blade and fall/step diagonally across the propeller arc bringing your hand to your side. Then the only way you can fall is out of the way!

Get good instruction!

Have Fun!

[redsnail]

Yeah I was saddened by the news of ptero's passing. I enjoyed his posts and he helped me out numerous times regarding rides. :(

[Dan Winterland]

The Chippy with it's Mark 8 Gypsy was slightly different in RAF service. As stated before, the pilot calls "Fuel on, brakes on, throttle closed, switches off" and put his hands outside the cockpit where the groundcrew could see them. The groundcrew then repeats this and primes the engine by opening the left cowling to pull a ring which depressed the float on the carb allowing it to flood and then 'wobbling' one of the two fuel pumps to allow fuel flow into the inlet manifold. (holes in the cowling allow the operation of these without opening the cowling providing you have fingers the diameter of matchsticks). Fuel trickleing out of the manifold drain indicated that the flooding was complete.

He then primed the engine by turing the prop through 4 blades. this ensured that there was no oil in the cylindrs which would cause a hydraullic lock and also ensured that at least 2 of the cylinders were primed with fuel. He then opened the right cowling to load the starter cartridge breech. He rereated "Engine primed, cowlings secure, breech loaded, clear to start".

At this point the pilot opens the throttle 1/2 to 1 inch, pulls the starter to fire the cartridge and the engine fires after about half a turn of the prop. Start failures were usually down to duff cartridges. Flooding was very rare, I never saw it once in over a thousand starts this way. One drawback was that this procedure left a small puddle of fuel on the ground - right under the exhaust! This fuel catching light was not unknown, so it was advisable not to start on very dry grass.

With a hand start, the procedure was very similar, the only diference being that only the right mag was used initially, as it's the one with the impulse starter.

On Chippys with starter motors, some pilots start without hand priming. This means they run the risk of a hydraullic lock and will hammer the very puny starter motor.

[wandrinabout]

I did my starting from behind also, worked well for me as 99% of it was done in a solo situation, although had the pax (fare paying) strapped in the front.

Had a glider tow hook on the back, an anchor in the ground with rope and tow ring on. Once start was complete, I could wander around the wing, kit up, jump in, and when ready for taxi just release the tow hook.

Starting from behind is admittedly non conventional but was a matter of neccesity in my case. As pointed out;
-right hand can grasp the centre strut so you can't fall forward
-right hand is close to mag switches
- leave the front door down , easy to reach in and adjust the throttle
-can also put your right foot/leg in front of the wheel if you have no chocks (or tow hook!)
- in the solo situation, make sure the stick is tied back, least the tail rise and smite thee!( had a small string in the rear seat for this, tied to right length with a loop to slip over said stick)

All good fun. Savour the moment when you get your go, some of my most enjoyable flying!!