"Circular Logic" Designing an optimum rotary.

MikeW · 12 September 2002, 11:48 AM

Richard,

does the fuel have to be "injected" *just behind the back of the inlet valve, or would it be OK to inject into the "base" of each of 9 inlet manifolds - after all, the aim is to provide a measured and consistent "cone" of fuel particles into the inlet air flow.

To all

are we talking caster oil lubrication here, or a modern synthetic? It would be a tradegy to do away with the smell.

Mike

RLWP · 13 September 2002, 01:17 PM

(Professor Powell mounts the rostrum. An awed hush falls)

Ahem. Consider the modern fuel injection system as used in an automobile. It has several components. An injector that squirts the fuel into the inlet manifold. A fuel feed to the injector. An electrical harness to trigger the injector. A throttle to control the airflow to the engine (and vary the compression ratio(see previous lecture notes)). A mass flow meter to measure the air delivered to the engine. An electronic control box.

The air entering the engine is controlled by the throttle and measured by the mass flow meter (usually by a volume flow meter and a temperature sensor). The throttle position and the mass flow rate is fed to the control box together with an indication of the crankshaft position. The control box uses an electronic "map" to decide how long each injector should stay open to deliver the correct quantity of fuel for the air being used. It the fires each injector in turn at the correct time relative to the crank position. When the injector opens it allows fuel from the feed line to pass into the inlet manifold. The fuel is maintained at pressure by a fuel pump and a regulating valve that spills fuel back to the tank. In addition more modern control boxes will control the ignition system as well.

Let us consider which of these components we would like to fit to the moving part of our rotary and which to the stationary.
The injector. This could easily be fitted to the moving part.
The fuel feed. Apart from making the two connections between the moving and stationary parts this could be fitted to the moving part.
The trigger harness. We need at least one wire to fire each injector. This means several wires. If the control box is on the moving part, we have no problem. If the control box is on the stationary we have to make a multi way connection between the stationary and fixed parts of the engine. Difficult!
The throttle. Ideally we would like only one of these. If this is on the stationary part it could be controlled by a simple cable. However air leaks in the air circuit between the throttle and the inlet valves must be minimised. If it is on the moving part we need a means of varying its opening to control the engine.
The mass flow meter and control box. If mounted on the stationary part we must pass a multi wire harness across to the moving part. If mounted on the moving part we must pass a multi wire harness across to power them.

The simplest conceivable method of using fuel injection is to have a single injector on the staionary part of the engine. This would be on a manifold that feeds across to the inlet manifold on the moving part. Any other configuration means multiple moving connections of wires and fuel pipes. And if we only have a single injector you might just as well use a carburettor mounted on the crankshaft feeding into the crankcase. Now where have I seen that before?

( Professor Powell turns an leaves the stage, to the accompaniment of a bemused silence...)

Richard

Don't forget that one of the main drawbacks of a rotary is that most of the engine is spinning round. Go and open the bonnet (hood) of your car and see how many wires pass from the bodywork onto the engine!

Lufbery · 18 September 2002, 04:54 AM

Why reinvent the wheel?

(Pun intended)

Why not simply make a replica LeRhone, Gnome, Bently, or Clerget rotary? There's a group out there making parts for LeRhones and they hope to eventually start making whole engines. I'm sure there are some folks who would like to make some full-sized reproductions of WWI planes without having to risk an original engine.

Regards,

William · 18 September 2002, 10:49 AM

Dear Lufbery,
It's just meant to be a fun way to learn more about the rotary. It's still cheaper to restore an original than remake one (I recently bought a 110 Le Rhone for less than the folks in Indiana want for an oil pump). When that changes more people will make them from scratch. There are some logistical problems in remaking one also. The crankcase, cylinders, conrods, nosepiece, etc... are turned from hot forged blanks. Forging startup is a very expensive process. To bypass this step requires non-original alloys for strength and may alter cooling properties etc... this requires altering dimensions to maintain strength. Basically will need to redesign the engine, if so why not try to improve it? The bottom line is, I prefer original but thought this might be fun and educational.

fltmech · 18 September 2002, 12:50 PM

I agree with Lubery, why reinvent the wheel. but as an exercise I will submit the following:
2/3 scale Bently
9 cylinder , diameter 33 inches,bore 3.46 in (vw pistons ?)
stroke 4.724 , 400.81 CID, WT approx. 200- 250 lbs.
Cylinders of Aluminum with 4140 Steel liners, cast iron piston rings, Spark ignition 2 plugs per cylinder, compression ratio 5.63
Front and rear case Aluminum, Thrust box and prop hub Steel,
Split crankshaft , master rod with link rods.
Ignition by magnetos, thru slip ring to plugs. Plunger type oil pump. HP approx 65 - 70 at 1300 rpm swinging a 84 inch prop.
Might be usable for a 7/8 scale Nieuport 12 :

Lufbery · 19 September 2002, 04:14 AM

Quote:

Dear Lufbery,
It's just meant to be a fun way to learn more about the rotary.

Well, yeah. I wasn't critisizing the idea.

Quote:

It's still cheaper to restore an original than remake one (I recently bought a 110 Le Rhone for less than the folks in Indiana want for an oil pump). When that changes more people will make them from scratch.

Cool! What are your plans for the engine?

Quote:

There are some logistical problems in remaking one also. The crankcase, cylinders, conrods, nosepiece, etc... are turned from hot forged blanks. Forging startup is a very expensive process. To bypass this step requires non-original alloys for strength and may alter cooling properties etc... this requires altering dimensions to maintain strength. Basically will need to redesign the engine, if so why not try to improve it? The bottom line is, I prefer original but thought this might be fun and educational.

So, one couldn't just machine the pieces? I hadn't thought about that. Are you saying that if you change the manufacturing methods from what was done originally, you'd end up with unforseen differences from the original engine?

Hmm...

Regards,

William · 19 September 2002, 06:23 AM

Dear Lufbery,
Sorry if I seemed touchy its just that it really is meant to be fun and I sense that less experienced folks are hesitant to post on forums in general.
The 110 will probably be used (after overhaul) in a Camel project we are starting. Considered putting it in our Pup as one of the 4 "experimental" Pups that used the 110 but decided to keep searching for an 80 hp Le Rhone or Gnome instead.
Changing materials or manufacturing techniques will change dimensional requirements to suit cooling and mass requirements. Machining the parts is not the hardest part of reproducing the engine. Metallurgy is not my area but my partner is a metallurgist and manufacturing engineer and waxes eloquently about crystallline structures and strengths, it sort of gives me a headache as I'm not very clever. Cost is always the crippler. Besides I love opening crates with gummed up engines in them. I've really enjoyed everyones posts on this topic and it has been helpful to reframe ideas as fantasy vs. practical.
Best regards,
William

Lufbery · 19 September 2002, 08:29 AM

Quote:

Dear Lufbery,
Sorry if I seemed touchy its just that it really is meant to be fun and I sense that less experienced folks are hesitant to post on forums in general.

No sweat.

Quote:

The 110 will probably be used (after overhaul) in a Camel project we are starting. Considered putting it in our Pup as one of the 4 "experimental" Pups that used the 110 but decided to keep searching for an 80 hp Le Rhone or Gnome instead.

Did Camels have 110 LeRhones? If not, how do you feel about using an anhistorical powerplant for a plane?

BTW, is this a private venture, or are you associated with a museum or something like that?

Quote:

Changing materials or manufacturing techniques will change dimensional requirements to suit cooling and mass requirements. Machining the parts is not the hardest part of reproducing the engine. Metallurgy is not my area but my partner is a metallurgist and manufacturing engineer and waxes eloquently about crystallline structures and strengths, it sort of gives me a headache as I'm not very clever. Cost is always the crippler. Besides I love opening crates with gummed up engines in them. I've really enjoyed everyones posts on this topic and it has been helpful to reframe ideas as fantasy vs. practical.
Best regards,
William

Well, is there a practical need for a rotary engine in this day and age? Is there something that a rotary engine would do that can't be done by other types of (less expensive) engines?

I think the answer is yes: no other type of engine can rotate around the crankshaft with the prop! I could see a definite market for replica or reproduction rotaries for people building replica or reproduction WWI planes. I like the idea of a simpler powerplant than the originals for something like a Graham Lee N-17 -- especially if it were affordable.

Have we reached any consensus on what a modern rotary would be like?

Regards,

fltmech · 20 September 2002, 01:20 PM

Lufbery:
There were a number of Camels fitted with the 110 hp Le Rhone, I believe after the change from the prototype's 100 hp Clerget to the 150 Clerget, and before the 150 hp BR1 Bently.
In my earlier post I tried to define a rotary that would fit a Grham Lee Nieuport, I know the N-12 can take a engine weight of 230 lbs. ( I asked Graham, about the weight) I am not sure of the gyroscopic forces that would be produced. :-/

William · 20 September 2002, 07:21 PM

Dear Lufbery and FltMech,
It is my understanding that it was not uncommon to re-engine the Camel with the 110 as it was felt to be more reliable than the Clerget. It is a bit of a paradox. We try very hard to remain committed to original equipment and/or original specs. In fact, the Camel will be a specific airframe(F1535) that would have been engined with a Gnome 160 or possibly a BR1. If and when we find one that can be rebuilt we will replace it with that to be more correct and use this engine in another more correct project or pass it on to someone who can. Currently we are private and relative novices compared to the likes of Roger Freeman and Fred Murrin but are working on establishing 501-c status. Very focused on Sopwiths at present. We've never really thought about a need for a rotary for "non-original" type replicas due to our narrow focus, the idea is intriguing though. I know someone (Munson perhaps) in the mid-west had made a working 5 cylinder I think a few years ago. Thanks again for your contributions to the thread.
Best regards,
William