Throttle On, Motor Off

[Alan]

I've read often enough about pilot's turning their motors off to land.

I've interpreted that as just being a case of colloquial happenstance and that the pilots were throttling back to land but hadn't developed the correct terminology.

I'm thinking I am the one mistaken now.

Were there any aircraft in the Great War that had a throttle or did the pilot literally have to keep starting and stopping the motor to adjust for speed?

[Lufbery]

Alan,

Do a search of this forum for the keywords: throttle and/or rotary engine. There's been a lot of wonderful information posted on this topic.

The brief answer is that, yes, the engines had throttles and yes, for some motors, the correct procedure was to frequently turn off the motor to land (called "blipping").

The two most common types of engines used during WWI were rotary engines and so-called water-cooled engines -- often called, "in-line" engines. Examples are the straight-six Mercedes engines in the German Albs, and the V-8 Hisso engines in the Spads and S.E. 5s.

These engines worked in what we'd now call a conventional manner. They had a throttle and mixture control. For most of the planes, a power-off approach, with the engine at idle, was the norm. The Spad 13 was an exception. Because of its high wing loading, it had to be landed with the power on.

Rotary engines were a different animal entirely. The propeller was bolted directly to the engine, and the engine and prop would spin together, as a unit, around a stationary crankshaft.

Rotaries also had at least a mixture control, and many also had an air-flow control. Either type (one lever, or two) could adjust the engine RPMs a bit. The two-lever type could adjust the engine over a range of 800 RPM or so.

However, the proper procedure for rotaries was to adjust the engine for take-off, and then readjust it for cruise. In other words, the engine adjustments were more to ensure proper running than to control the aircraft's speed.

So, rotaries also used the blip-switch, which would cut out the ignition while held down, which in turn slowed down the plane. Blipping would cut out the ignition, but not the fuel flow, so pilots had to be careful that they didn't hold down the blip switch too long or too much fuel would collect in the cowl and a fire would result when the switch was released.

A further refinement of the blipping concept was found on at least the Camel (and probably other late war rotary engined fighters): the ignition could be set to fire 3, 5, or all 9 cylinders during one rotation. This also slowed down the plane without completely cutting out power.

I hope this helps,

[Alan]

Wow, fantastic, Drew, thanks. I guess I should've done a search but it isn't the first time I've forgotten to do so...anyway, thanks again! That's precisely what I needed!

[Lufbery]

Alan,

Glad to be of help. Despite the length of my brief answer, there really is a lot more to the subject. Still, as an overview, it should help explain some of the pilot comments you've read.

Just to muddy the waters a bit, I think the French term for the "blip" switch was a "coupez" switch. But I don't speak Frech, and I may be misspelling the term.

One engine that doesn't fit into either category mentioned above is the water-cooled radial engine used in the Salmson S2A observation planes. A radial engine has the cylinders arrayed in a circle around a central crankshaft, but they are stationary and the crankshaft turns. The radial engine became very popular between the wars and into WWII -- especially in America.

However, almost all radial engines are air-cooled. In fact, that's the reason for having the cylinders exposed to the airflow. But the Salmson engine was water-cooled.

I don't know much about the operation of that engine, but I've not read many complaints about it either, so I guess it ran pretty well.

Regards,

[baldeagle]

Drew,
That 3-5-9 cylinder stuff is an incorrect story that has been passed down in print over the years and has misled many people. The 160 Gnome monosoupape has an ignition selector that allows it to run at half speed, 1/4 speed, or 1/8 speed (and of course full speed). It interrupts the firing sequence so that at half speed it takes four revolutions of the engine to fire all cylinders instead of two revolutions, at 1/4 speed it takes eight revolutions, and so on, but all the cylinders are still firing, just in different orders. The Nieuport 28s had this, the Morane A.Is, and a few Camels.
Also, the BE and RE series used RAF engines that were vees, V-12 I think, and were air cooled (and of course normally throttled).

[Lufbery]

Bald Eagle,

Thanks for the clarification. I think I've got it now: the setting is not how many cylinders fire during one revolution, but how many revolutions it takes to fire all the cylinders, right?

In any event, it's an interesting concept: controlling the engine speed with the ignition rather than the fuel/air mixture.

Personally, I find aircraft engines to be utterly fascinating.

Regards,

[baldeagle]

Come to the Golden Age Air Museum at one of the events this year and you should be able to see my 160 Gnome in action, running on a stand anyway, as the Nieuport isn't ready for it yet. The engine is finished except for the accessories, and I built a stand sturdy enough to run it on.

http://www.goldenageair.org

[Lufbery]

Yeah, that'd be great! My wife and I stopped by there last year and got a nice tour of the facilities.

We'll see you there.

Regards,

[Shooter]

Originally posted by baldeagle@Feb 23 2004, 01:17 PM
[b] Drew,
That 3-5-9 cylinder stuff is an incorrect story that has been passed down in print over the years and has misled many people. The 160 Gnome monosoupape has an ignition selector that allows it to run at half speed, 1/4 speed, or 1/8 speed (and of course full speed). It interrupts the firing sequence so that at half speed it takes four revolutions of the engine to fire all cylinders instead of two revolutions, at 1/4 speed it takes eight revolutions, and so on, but all the cylinders are still firing, just in different orders. The Nieuport 28s had this, the Morane A.Is, and a few Camels.
Also, the BE and RE series used RAF engines that were vees, V-12 I think, and were air cooled (and of course normally throttled).

Okay, baldeagle, riddle me this? Was this the same system used to control rotaries in German a/c?

I find this fascinating information, but it opens up more questions. For example, the Dr1 used a la Rhone 9 cyl rotary (when available). Did this rotary engine use the same kind of blip-button retarding ignition system or was another in use,one that simply interrupted spark to the cylinders as long as it was depressed?


Shooter sends

[AAC Cadet Leader]

Is it the Gnome rotary that provides all that wonderful, loud, erratic noise coming out of the Sopwith Camel at ORA? My favorite.