Re-starting an engine in flight

[Rockdoc]

I suppose the image most of us have of WW1 aircraft being started is someone swinging on the propeller but was it possible to re-start an engine while in the air? On 21st January, 1918, at 16.25 hours the French HQ in Salonika signalled 61 AAS (French) report unknown plane flying very high above the BAY with silent motor. There's no subsequent record of a plane coming down so I have to assume that the plane either had its motor on tick-over, which was quiet enough not to be heard on the ground, or the pilot had turned off his engine for stealth and successfully re-started it after he'd done his over-flight.

Which is more likely?

Keith

[centurion]

Might be able to do it with a rotary (although would have to dive to do it) but it couldn't be guaranteed to start. With an online probably not. Italian bombers in the SCW attacking Spanish cities from the sea would switch of the engines on approach, glide until they released their bombs and then restart, this was possible because they could feather the prop in the glide and then switch it to coarse pitch so that the airflow would turn the engine over. WW1 aircraft did not have variable pitch airscrews.

[Rockdoc]

Thanks. So would you say the chances are it was on a very low throttle?

Keith

[centurion]

Thanks. So would you say the chances are it was on a very low throttle?

Keith

That would be my best guess - you could do that with a Mercedes inline - just have it ticking over

[Rockdoc]

Thanks!

Keith

[27thBN]

Well with the low idle of the German engines yes but to switch off i doubt it IMHO

MC

[Rockdoc]

I had no idea that any plane's engine could be made to tick over, hence the question. I get the impression that the expression "flying high" means over 15,000 feet in the Diaries so, logically, "very high" is higher again. 73rd records the weather as being misty at noon but clear, with a slight SE wind at 18.00 hours so if the plane is not readily identifiable you'd have to think it was a good way up, all of which helps make the tick-over scenario plausible.

Thanks.

Keith

[centurion]

Could just have been a high flying Rumpler so high up that the engine was inaudible from the ground any way. They were fairly immune to either interception or AA fire so there would be no need to approach "silent running". Indeed safer to keep the engine on full power and maintain that altitude.

[Rockdoc]

Fair points. Against that I'd argue that the plane being described as having a silent engine would suggest that they expected to hear something but it's obviously impossible to be sure on such slim information. The signal is not mentioned by either 95th or 99th Sections, both of which could be expected to have had it relayed to them, so it may well be that 73rd, which acted as the direct link to the French HQ, did not regard it as particularly important or, at least, not something they could do anything about.

Keith

[apwright]

In Doppeldecker C666 Heydemarck describes a bombing raid on the railway station at "Yvocourt" (?Avocourt).

A few kilometres from the target and at 2900m (9500') the pilot pulls back the throttle and they glide in. Heydemarck can almost hear the water on the weir below over the whistling of the wind in the bracing wires - he doesn't mention any engine noise! It's probably only the wind that's keeping the prop turning.

They drop their bombs (2x 20kg) from less than 1000m (~3000') and the pilot opens the throttle again and starts to climb. Now at last the AA guns see them and open fire, but their shells burst 1000m too high! The pilot cuts the engine again to stop them climbing further and starts to jink from side to side to make the gunners believe they're on target. And so they make good their escape!

Adrian

[centurion]

In Doppeldecker C666 Heydemarck describes a bombing raid on the railway station at "Yvocourt" (?Avocourt).

A few kilometres from the target and at 2900m (9500') the pilot pulls back the throttle and they glide in. Heydemarck can almost hear the water on the weir below over the whistling of the wind in the bracing wires - he doesn't mention any engine noise! It's probably only the wind that's keeping the prop turning.

They drop their bombs (2x 20kg) from less than 1000m (~3000') and the pilot opens the throttle again and starts to climb. Now at last the AA guns see them and open fire, but their shells burst 1000m too high! The pilot cuts the engine again to stop them climbing further and starts to jink from side to side to make the gunners believe they're on target. And so they make good their escape!

Adrian

Except that the prop wouldn't turn in the wind - not with the compression of the engine against it. If the prop is turning its because the engine is still running - ticking over. One can understand these tactics on a lowish altitude bombing rub but they don't make sense on a very high altitude recce flight. There is much in this account that doesn't make sense - you wouldn't cut the engine to stop climbing (you'd never get it started again) you'd just level off and how does jinking make the gunners think they're on target?

[SiegeGunner]

"Approaching the front, the aircraft came under heavy, well-aimed fire from motorised flak batteries while it was still over our own second line positions. The mist was so thick that the ground could only be glimpsed fleetingly through occasional clear patches. To be able to observe, the aircraft was obliged to glide down towards the enemy lines, losing altitude from 1000m to 500m." (Report of German Artillery Flight 201, 19 July 1916).

[David B]

Why would not the prop turn with wind pressure? I seem to remember that in ww2 when aircraft engines were bigger and more powerful,

windmilling props caused all sorts of problems if the pilot could not feather the prop - one of the reasons that props have this capability.

Also ww1 engines had a low compression ratio - usually in the order of 4.5-5 to 1.

Mercedes also had a compression release lever to aid starting, although in all fairness this lever was not accessable by the pilot.

David

[centurion]

Because WW1 props and WW2 props are completely different. The wind milling prop in WWII is not turning the pistons and crank shaft over, it's problem is the drag it causes and in a multi engined aircraft it made a weak member of the aerial herd abundantly obvious to the circling fighters. The compression ratio in WW1 engines is only low in comparison to later engines.

[David B]

`May I quote my pre war aeronautical bible. 'When the engine stops in flight, the airscrew continues to rotate, oplerating as a windmill, and turning the engine. This is undesireable

because if the engine is structurally damaged, this further rotation may break it up completely. Furthermore, the windmilling airscrew produces a large drag, which may

make all the difference b etween the possibility, or otherwise, of continuing the flight on the remaining engines in a multi-engines aircraft. It therefore becomes worth while on multi

engined machines to fit what are known as feathering airscrews.

Back to the original query it would appear to be undesirable to stop the motor(s) in flight but it is possible. I would prefer to think that the reason for silence was that

the height ;of the a/c made engine noise unhearable or that the engines were being idled, quite possible on an inline or v8 engine.

David

[Chris_Baker]

I'm surprised by the discussion so far, simply because I have in my head that stop-starting in flight was common practice. I am sure I have read of this in some of the classics - Sagittarius Rising, or Winged Victory, or similar. If I get a moment I will see if I can find the quotes.

[centurion]

I'm surprised by the discussion so far, simply because I have in my head that stop-starting in flight was common practice. I am sure I have read of this in some of the classics - Sagittarius Rising, or Winged Victory, or similar. If I get a moment I will see if I can find the quotes.

Yes with rotaries

[Rockdoc]

Going off at a bit of a tangent here but I don't suppose there were any attempts to use silencers on reconnaissance aircraft, were there?

Keith

[David B]

I was told in my younger days (a long time ago) that the major noise produced by an aircraft was not the engine but the propellor which is probably why

- if correct - that engines are not silenced.

David

[4thGordons]

Interesting discussion:

Coincidentally I read this in a letter yesterday: The pilot was flying a French built Sopwith 1 1/2 Strutter:

"During the scrap we had lost several hundred meters altitude, so that when pulled the bus out of the dive, I had to look around for a landing place in a hurry. But there was no place to land. Everywhere the barb wire entanglements were thick and landing would have meant a bad smash. So when about 50 meters from the ground I put on the motor, thinking that I might as well smash up trying to get home as smash up there. Finding I could fly along straight, I climbed back up to a thousand meters and managed to get back home. "

Chris

[stevedrew]

I was asking myself the same question...can an aircraft engine be re-started in flight. I became intrigued by this photograph of a Felixstowe flying boat "Porte Baby" composite aircraft, and how the engine of the parasite aircraft would be started mid-flight.

I posted the question at "The Aerodrome" Forum

http://www.theaerodrome.com/forum/aircraft...e-aircraft.html

Here is an excerpt of one of the replies...

"The history of Felixstowe flying boats written by the great J.M. Bruce in the magazine Flight gives the following about this composite

From the historical point of view, the most interesting experiment in which a Porte Baby participated was the remarkable "composite" flight which was made in May 1916. This was a bold attempt to combine the speed and manoeuvrability of a single-seat experiment to provide an effective anti-Zeppelin weapon.

A Bristol Scout C (No. 3028 - one of those belonging to the seaplane carrier H.M.S. Vindex) was placed on the upper wing of a Porte Baby with its undercarriage just in front of the leading edge. The Scout's wheels rested in crutches which were braced to the engine bearers of the flying-boat's central power unit, and its tail skid was held by a quick-release catch which was operated by the pilot of the Scout.

On May 17, 1916 the Baby took off from Felixstowe with the Scout in place. The flying-boat was flown by Sqn. Cdr. Porte, the Bristol by F/L. M. J. Day. When the combination had reached 1,000ft Day switched on his engine and climbed away. Despite this success, however, the experiment was never repeated.

So the pilot could switch on the engine when seated in the pilot chair Of course there was no other way to do it.

I leave it at the engine experts to give the state of technology of starting rotary engines in 1916."

Of course, the Bristol Scout employed a Gnome rotary engine (80hp if I recall correctly). But an inline engine?

An inline engine could be started in mid-air...inside the airborne hangers of airships such as the Akron (though they generally employed F9C Sparrowhawks).

[LowNslow]

Yes. It is possible in practice to restart some normally hand swung, engines in the air by diving then ruddering the aeroplane to change the airflow across the propeller blades. I have been aboard when it has been demonstrated.

In more recent (relatively!) aircraft such as the Tiger Moth this was taught to students as part of their aerobatic training as it is not impossible to stop the engine with a badly executed negative g manoeuvre.

However it is often pointed out today that a well executed forced landing, planned from say 3000 feet is a lot more likely to be successful than a panic at 1000 feet when the blooming thing hasn't restarted!

I guess the Felixstowe composite departed with the Scout engine already running, as I can't imagine its rate of climb would otherwise be too hot with the added weight and drag of the Scout on the top wing!

[SiegeGunner]

The flying-boat was flown by Sqn. Cdr. Porte, the Bristol by F/L. M. J. Day.

Jeff (Miles Jeffrey Game) Day was lost in action off the Belgian coast on 27 February 1918 while flying Sopwith Camel N6363. He engaged several German aircraft single-handedly and was shot down in the resulting melee. His burning aircraft landed on the sea and he was seen to scramble onto the rear of the fuselage and wave to other members of his flight, who dropped a lifebelt to him. Another aircraft was despatched with a life-raft as soon as the flight landed, and a motor launch from Dunkerque reached his reported position within 90 minutes, but no trace could be found of him or his aircraft.

[Rockdoc]

I was told in my younger days (a long time ago) that the major noise produced by an aircraft was not the engine but the propellor which is probably why

- if correct - that engines are not silenced.

David

That could easily be true, David, thinking about it. The speed of sound is 340 m/s so if we say that a typical prop is 2 m from tip to tip then the circumference the tips subscribe per rev is 2 x pi or 6.28m. The tips would break the sound barrier at about 3,200 rpm, which isn't all that fast.

[Edited to add this section]

Getting back to the topic (sorry! ) can anyone tell me why a rotary engine would be easier to start in the air than an in-line one? Would it be because there were more, small cylinders in a rotary, which would make the force required to take each piston over compression easier? On the same lines, did each cylinder of a rotary fire in turn or did thy fire in multiples?

Keith

[David B]

Keith, have a quick look at the Wiki article. It would appear that a rotary employs a standard 4 cycle engine with every second cylinder firing in order

as the main body turns. Reason why they are odd numbered cylinders

Cheers David

http://en.wikipedia.org/wiki/Rotary_engine