Why did the Caminez engine fail?

One problem with these types of engines is that the crankcase is larger than a conventional crankcase of the same stroke.

I would have to do some analysis to be sure, but I think the pistons might have heavy side loads

Main problem would be the complexity/cost.

Jonathan T. Schmidt

RCKid:

The Caminez engine beat itself to death when it ran. There was too much play in the linkage arrangement to keep the roller followers in contact with the cam surface.

Regards,
Terry

Doesn't look to me like there's side-loading on the pistons at all -- the interior of the skirts rides on the outer races of the large roller followers...

I can see several problems:

First is the very large mass of the pistons in this design, due to the heavy bearings that communicate the piston thrust.

Second is the four-bar linkage that controls piston movement for everything other than the power stroke. Wanna bet this doesn't wear at the same rate as the cam/follower -- or, for that matter, deflect at high rpm at a comparable rate?

Third (and probably the killer) is that lubricated roller or ball bearings just don't do well in this kind of application. Hard to lubricate them (and don't even THINK of using grease lubrication in this situation!) and the load on the races, particularly the inner one which doesn't seem to float, is grossly uneven. Even a little incipient brinnelling on races or rollers will rapidly snowball -- NOT a good thing in an aircraft engine (which is about the only thing I'd expect an engine of this configuration to 'package' well for!)

This reminds me of the 'sun-and-planet' drive used on some early steam engines to get around somebody's slightly earlier British patent on the crank. Do I smell an attempt to get around the master/subsidiary rod drive of the radial engine?

RME

Thanks Terry,
I had suspected it was something like what you say. I wonder if the play in the linkage was due to inaccuracies in machining the cam back in those days. Today, with CNC machining, it would a snap.
May I ask from where you got your information.

RCKid:

ref: page 579-580, "The Internal Combustion Engine In Theory and Practice- Vol.2", by CF Taylor 1987.

Regards,
Terry

Better off with this epicycloidal mechanism:


This application is for steam, but you could make a pretty mean 2-stroke out of the concept. This design doen't show the crank balancer that would be required to keep the cetrifugal loads evenly distributed about crank centre.

The design looks more feasible than many I have seen, and would probably be quite compact, as well as vibration free. Don't think you would need a seperate flywheel though!

Mart

I found a story on this engine in a book at the local college library and the reason they gave for failure was: “It passed government tests, but in Navy trials it vibrated excessively due to inherent dynamic imbalance and broke down due to inaccurate machining of some of its internal parts.”

It also said that the engine needed a large 4 bladed propeller – which acts as a flywheel.

From Aircraft Piston Engines by Herschel Smith.

aviat
I don't understand the bit about this engine having "inherent dynamic imbalance". Since all cylinders are in the same plane and opposite pistons have equal and opposite accelerations, this engine should be in perfect dynamic balance.
Jerry

Jerry
Smith does not say what caused the vibration but he said it passed the government test, so maybe it did not show up until flight tests. There are several things that may have been in resonant frequency such as propeller,airframe, or parts of engine itself, that could have caused problems. Today, each engine, propeller, and airframe combination has to be tested and certified seperately for vibrations. For some of the problems involved see

Jerry

Here is another site that shows the problems thar P&W had with one of their engines several years later.


Cheers

aviat
Thanks for pointing out these engine sites. They make very interesting reading. I was aware of these type problems in aircraft applications but these articles point out just how common and severe they can be.
I guess my point is that the statement by Herschel Smith makes it sound as though the "engine" was inherently out of balance and that this lead to failure of the system. The engine is in fact in perfect inertial balance and is so without the use of heavy counterbalance weights.
To be sure, the torque fluctuations, due to the intermitent firing of the cylinders, would have serious dynamic effects on the rest of the system just as in any other piston engine.
My guess is that in the mid twentys, when this engine was built, they really didn't have a hold on what was causing the problem (torsional resonance) or how to solve it so they gave up. If the P&W 2800 had been built in the twentys under the same conditions, i.e. lack of war pressure, it most likely would have been dropped also.