The Aerodrome Home Page
Aces of WWI
Aircraft of WWI
Books and Film
The Aerodrome Forum
Help
Links to Other Sites
Medals and Decorations
Search The Aerodrome
Today in History


The Aerodrome Forum


Go Back   The Aerodrome Forum > WWI Aviation > Aircraft

Aircraft Topics related to WWI aircraft, aircraft engines and armament

Closed Thread
 
Thread Tools Display Modes
Old 18 March 2002, 06:23 AM   #1
vickers1
Guest
 
Posts: n/a

:-[ Warning :-[ *The following question contains a great deal of ignorance to the topic of engines. *

Viewer discretion is advised.

Hello All,

I am currently reading Knights of the Air: Canadian Airmen in the First World War and I am a little confused about something.
What I have read is that the rotary engines lacked a throttle control to control the speed of the engine. *However later, when the book talks about the developement of the Sopwith Pup, it mentions that one of its vagaries was that the RoF(of the machine gun mated to an interupter gear) was greatly reduced when the engine was throttled down.

Heres the question:

How do you throttle down an engine when it does not have one?

Have I missed some important developement? Or have I mis-interpreted something?

Please help me clarify this.

Thanks,

Vickers1
 
Old 18 March 2002, 06:39 AM   #2
Michael Skeet
Guest
 
Posts: n/a

I agree with you that references to "throttling" a rotary are extremely confusing. Given that different engines offered different means of control, and that none of these (with the exception, I believe, of the Siemens-Halske rotaries) involved a proper throttle-carburettor link, things are unlikely ever to become as clear as I, at least, would like.

My understanding is that, while rotaries could not be throttled in a conventional sense, some control over revs was still possible. For example:

In the 160hp Gnome the pilot could adjust the rate at which cylinders fired by having alternating groups of cylinders miss one or more ignition cycles (this is often described, incorrectly, as cutting the ignition to some cylinders).

Engines such as the Le Rhone and Clerget allowed the pilot to control the fuel-air mix (using what was called a fine-adjustment lever) and thus increase or decrease revs across a relatively narrow range. This worked in the manner in which manual chokes used to work on automobile engines. I haven't read anything (that I can recall, at any rate) that specifically refers to using this technique at any time other than takeoff.

And there was always the blip switch, which cut the ignition to all cyclinders and thus slowed the rotation of engine and prop.

One of the things that's so frustrating about this subject is that there are lots of first-person accounts of flying rotaries that refer (casually) to "throttle" adjustment. But everything technical I've read on the subject agrees that rotaries couldn't be throttled, because they had no carburettors. More info on this question will be gratefully received.
 
Old 18 March 2002, 06:41 AM   #3
Lufbery
Forum Ace
 
Lufbery's Avatar
 
Join Date: Jul 1999
Location: Harrisburg, PA
Posts: 2,680

 
Some rotaries did, in fact have carbs. I just can't remember which ones right now.

Anyway, check out this post I made a while back on rotary engine control:

...broken YABB link...

Regards,
__________________
Drew Ames

"Drew can talk -- by Jove, how the man can talk!" -- James Norman Hall in "High Adventure"
Lufbery is offline  
Old 18 March 2002, 07:07 AM   #4
Rbailey
Forum Ace of Aces
 
Join Date: Aug 2001
Location: Troy, NY (USA)
Posts: 7,429

 
The last couple of issues of the Old Rhinebeck Aerodrome newsletter had descriptions of the air and fuel controls for some rotaries. Using those, it was possible to control the revs from a few hundred rpm on up, but I gather they were pretty touchy. I don't know if they put copies of the newsletter on-line on their web page.
Rbailey is online now  
Old 18 March 2002, 08:58 AM   #5
vickers1
Guest
 
Posts: n/a

Today at 12:39 pm Michael Skeet wrote:
Quote:
In the 160hp Gnome the pilot could adjust the rate at which cylinders fired by having alternating groups of cylinders miss one or more ignition cycles (this is often described, incorrectly, as cutting the ignition to some cylinders).
Michael,

Could you elaborate on this? I am interested to know how this was done from the cockpit.
Thanks,

Vickers
 
Old 18 March 2002, 09:46 AM   #6
MikeW
Forum Ace
 
MikeW's Avatar
 
Join Date: Aug 2000
Posts: 2,021

 
Very simply....

In a modern car engine, oh all right, in a car engine of 10 years ago or so, the throttle pedal was connected to a butterfly valve in the carburettor. As you opened the throttle, the valve opened allowing more air/fuel mixture to pass into the engine's inlet manifold.

The inlet manifold would be at a lower pressure than the outside air, and the carburettor would sense this and by various means, adjust the mixture of fuel and air to an optimum for the load imposed on the engine - opening the throttle to allow more mixture through will probably require a change in the mixture. This optimum is arrived at by design to give the best power for the load imposed on the engine - you have heard of the mixture being too lean or too rich.


Right then, in a Clerget, and Le Rhone, a simple carburrettor was fitted with a butterfly valve and a means of varying the fuel/air mixture (usually an adjustable needle valve spraybar type thingy) - quite a bit like a car really - with one major difference - They were not connected or inter-dependent.

Instead of the carburettor sensing the correct fuel/air setting for the butterfly valve opening, the pilot had to do it by ear (usually 2 small quadrant levers tucked down by his left elbow).

When taxing, or landing, it was much too fiddly to mess about trying to slow the engine down with the "throttle" and then correct the mixture with the "fuel" control - it was much easier to blip the engine by shorting out the magneto(s).

The real problem was taking off - after take off, aircraft like the Pup and the Camel and the triplane had to have the mixture adjusted during the climb out (because the load had drastically changed), which meant fiddling with the mixture lever - if it wasn't right the engine "choked" and cut out - if in a camel often with loss of life!!

Once airborne, the pilots were able to fiddle about with throttle and fuel so that they could formate on the Flight Leader and maintain position.

Mike
MikeW is offline  
Old 18 March 2002, 10:13 AM   #7
Lufbery
Forum Ace
 
Lufbery's Avatar
 
Join Date: Jul 1999
Location: Harrisburg, PA
Posts: 2,680

 
Mike,

That's a great post, but I think he wanted to know how the ignition could be used to fire only some of the cylinders for any given rotation -- something that I'd like to know too.

Regards,
__________________
Drew Ames

"Drew can talk -- by Jove, how the man can talk!" -- James Norman Hall in "High Adventure"
Lufbery is offline  
Old 18 March 2002, 08:43 PM   #8
MikeW
Forum Ace
 
MikeW's Avatar
 
Join Date: Aug 2000
Posts: 2,021

 
I'm sorry. I still read the thread as basically saying that Rotary engines didn't have a throttle, when they mostly did.

If you had enough time to do it, a Clerget or Le Rhone could be throttled from full power to tick-over and back again, it just wasn't user friendly or convenient.

Using the magneto cut out was a "quick n' dirty" fix to control power. The engine kept rotating by slipstream effect, you just had to hope it would start when you opened the blip switch.

If you look at the control column of a pup or a triplane, the button at the top of the handle is not the trigger for the guns, it's the blip switch - pressing it shorts the low tension winding on the magneto to earth. Once that happens, the magneto can't spark any more and you are left with a windmill.

Mike
MikeW is offline  
Old 19 March 2002, 03:04 AM   #9
Lufbery
Forum Ace
 
Lufbery's Avatar
 
Join Date: Jul 1999
Location: Harrisburg, PA
Posts: 2,680

 
Quote:
I'm sorry. I still read the thread as basically saying that Rotary engines didn't have a throttle, when they mostly did.

If you had enough time to do it, a Clerget or Le Rhone could be throttled from full power to tick-over and back again, it just wasn't user friendly or convenient.
Right. The link I posted above is to another thread where I posted excerpts from a recent article in "Pilot" magazine on flying the Shuttleworth Collection's Pup. That article was a real eye-opener for me. I never realized just how much the pilot had to do to make sure the engine stayed running.

Quote:
Using the magneto cut out was a "quick n' dirty" fix to control power. The engine kept rotating by slipstream effect, you just had to hope it would start when you opened the blip switch.

If you look at the control column of a pup or a triplane, the button at the top of the handle is not the trigger for the guns, it's the blip switch - pressing it shorts the low tension winding on the magneto to earth. Once that happens, the magneto can't spark any more and you are left with a windmill.
Not only that, but some planes, like the Camel and N-28, had a selector switch that would fire only three, five, or all nine of the cylinders on each rotation. I've wondered for a few years now how that worked.

Regards,
__________________
Drew Ames

"Drew can talk -- by Jove, how the man can talk!" -- James Norman Hall in "High Adventure"
Lufbery is offline  
Old 19 March 2002, 06:48 AM   #10
Michael Skeet
Guest
 
Posts: n/a

Some more on this:

Some pilots would mark on the fuel and air lever quadrants the approximate settings required for startup and airborne operation. These markings might aid in rapidly adjusting fuel and air supply to prevent choking or starvation immediately after takeoff. I suspect, though, that as they gained more experience most pilots of rotaries learned to make very rapid adjustments by ear.

I continue to believe that in combat most pilots wouldn't use anything but ignition control to adjust revs, for the simple reason that without a traditional carburettor-throttle linkage it was just too difficult to adjust fuel and air flow into these engines.

Now, as for the selector on the 160hp Gnome:

What follows is based on my somewhat vague recollections of a conversation I had with one of the pilots at Old Rhinebeck several years ago. I had asked him to explain to me how this selector switch worked that cut the ignition to selected cylinders.

He told me that this is not what the selector did. Its true function, as I recall it, was to place a mica disc between the magneto and the brush that transferred electricity to the sparking plugs. This disc was perforated in such a way that, depending on the speed with which it turned, it would prevent a spark from reaching the plugs for a number of engine revolutions. A cylinder thus affected would go through the normal four strokes, but there would be no explosion stage; instead, the piston would (I'm assuming here) be pulled through the rest of its motion by the crankshaft. All of the fuel and oil drawn in to that cylinder would be ejected during the exhaust stroke. Depending on the mica plate's speed, the cylinder might fire again on its next cycle, or it might not. Likewise, some cylinders might fire during a given revolution, so long as contact was made between the brush and the magneto.

So, as I understand it, the selector didn't cut the ignition to a specified number of cylinders. Instead, it specified a number of engine rotations during which none of the cylinders would fire.

The selector, by the way, was (at least on the example I saw) a multi-position switch with a knob control, mounted on the instrument panel--in this case, of a Fokker D-VIII replica. I wish I could remember what the settings were labelled, but I can't.

The corrollary of this function, of course, is that the cowling of an aircraft so equipped might fill up with unburned fuel. When the ignition was restored, the explosion could be quite spectacular (though not actually damaging to the a/c).

That's my recollection. Any mistakes in the above description are mine. Not that there's a lot that can be done about them.
 
Closed Thread

Bookmarks

Tags
throttle, down


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Throttle On, Motor Off Alan Aircraft 26 23 November 2004 11:36 AM
Rotary Engine throttle? antiquegunsmith Aircraft 55 4 November 2004 08:48 AM
Throttle control in the Sopwith Strutter???? Ross_Moorhouse Aircraft 3 6 October 2003 10:53 PM
Fokker D.VII throttle question. AchimEngels Aircraft 12 1 July 2003 09:43 PM
LeRhone Throttle question ot811 Aircraft 85 3 September 2002 11:43 AM


As an Amazon Associate we earn from qualifying purchases.

All times are GMT -7. The time now is 12:42 PM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Feedback Buttons provided by Advanced Post Thanks / Like (Lite) - vBulletin Mods & Addons Copyright © 2024 DragonByte Technologies Ltd.
Copyright 1997 - 2023 The Aerodrome