Hi gents. I do not misunderstand your conclusions. Matter of fact, it is very difficult to disagree with them. The Problem.
The drawing is not the one I had in my other computer, which is presently in maintenance. I'd like to condense the crux of my disagreement around the Shaft/Arm/Wheel system.
I caught flack in the first thread for stating that the Wheel and Arm were made up of three parts. I was unclear. Let me start by saying that in this assembly I see three elements. The rim, and blades, the face, or disc, and the Arm, or Drive.
The first design concept I see is the "wraparound" feature of the Arm. Attached outside the bearing load, it performs a 180 to wrap the Shaft as it extends forward to capture the Disc. Is this common? I am familiar only with engines that include rotors inside the "Load frame" iow, attached directly to the shaft. As it is, the Wheel drives a load that is outside the bearing plane "The Attach" So I see potential problems with balance, and resonance.
As barit1 says, and TurbineD agrees, these rotors are of immense strength. Now that is subjective, and since failure is obvious, here, I refer to my earlier comment that due fire, the designed fail (rpm) was reduced, perhaps "substantially" as Turbine D points out.
My intention is to direct the comments (if you agree) toward the method of attachment of the Arm/Wheel, and if you are familiar with any potential pitfalls?
Because although TurbineD disagrees with my "Bell" shaped comment, I think we can see that the Arm and disc create a shape that is similar to bell, mushroom, umbrella, etc. and that this shape must resist a somewhat more complex strain profile than the Wheel/Axle tradition.
Your participation is optional, of course, but I am serious, and believe in addressing some of these concerns; at least one person will gain some knowledge, here. And tht would be me....
ad. For instance, as I say, the load is outside the bearing loadframe. Standard would be within at least two bearings, rather than attached at the end of a shaft supported only one side of the load. A corollary might be "whirl mode", where a great deal of mass and energy is "extended" past a point of support, such that the bearing is stressed in ways that are common to rapidly spinning systems, but ordinarily are suspended between two mounting points....
Please note that according to the drawing, the wheel contacts the LPT platform/stator with its blades prior to the more core oriented partition. So the false bearing would have to "wait" for the wheel to arrive post stator contact?
Isn't this IPT blades contact a design feature, to prevent OverSpeed? Scrub off the blades to prevent a drive surface for the gas path? If so, what failed, in this case?
Is the bearing mount portion of the joint connected to the race? So, can the outer race support the wheel, post separation from Arm? I would offer yes, but there would be a lot of play between the race and the inner surface/drive arm?
Note for comparison the architecture of the HP Rotor, supported on one face by the HP cap bearing, and on the other face by the shaft proper? Here, the loads are functionally within the two bearing planes, and the one sided torsional affect is snubbed?
Similarly, although the Fan is supported outside the bearing run, it has two bearing planes, which provide a 'moment arm' to capture the oddities this disc encounters with the atmosphere, and FOD? Connected as it is to the IPT terminus, and the radius of the bearing system it suggests a very robust carriage for the bulk of the a/c thrust.....
TD, barit1, what would be your opinion on the Drive Arm subject to these torsional anomalies whilst under the climb load of the gas path? Would undue fatigue weaken, and/or heat the system? Mind, the HP bearing and the IP bearing rotate opposite each other, at times with a differential of 20000 rpm.
Last edited by Lyman; 11th May 2012 at 09:12.