propfan
G'Day again!
Please not the propfan again. The fluid dynamics of an unducted fan give it the dimensions it possesses. In the same way that a die manufactured to extrude a cold rectangular section of rubber possesses a weird and woderful shape when working with the molten subject so it often is with research models. You may visit many a hydrodynamic lab where a test model of dictinctly funny shape is rotating at distinctly funny speeds in a distinctly odd fluid flow to model something in scale more easily, cheaply and accurately than is worth doing on the real thing.
Many an engineer has therefore thought along the lines of "Hey, if I build a test model this funny shape to reproduce behaviour at entirely different speeds in a different fluid flow regime might it not do very well in its own right?" No because the necessary flight regime has to be flown at a scale of twelve inches to the foot and 6076.1155 ft/sec to the knot, knock seven bells out of the competition and not out of the airfame and its unfortunate passengers.
The propfan was a devout political endeavour rather than a carefully considered engineering project. It played to a political stage, had some pretty wacky actors as principals, some reluctant names including R Shevell himself and Billy Practice and some who thought "What the heck".
I admire the late Prof Silverman of Edinburgh who as much as any single man gave the project legs maybe as early as 1965-66. But he goofed on the propfan when he was past the peak of his powers and no shame to him. His was the field of marine propellers and steam turbines and brilliant ideas in the field of closed-cycle turbines. Who can doubt the genius of Siverman, GFC Rogers and many, may others?
Players in the propfan saga were NASA, some diligent and good names in the propeller world [one of whom I dined with recently and is in cracking form!], some whacking egos, GE engines and Douglas.
Computational Fluid Dynamics was primitive and the P&W engines then in the ascendancy were gas guzzlers and no mistake. But..
The fuel crisis that brought propfan its 15 minutes of fame had long since puttered out before someone at last put propfan out of its misery. The LRC propfan project had a mesmeric fascination that could glaze the eyes of a rattlesnake but thanks to the generosity of America in placing documents in the public forum read all about it with a thorough NASA web-search. Even without reading between the lines it is one heck of a lulu in the folly stakes.
In urban myth for many the propfan was so super-efficient that General Electric who were project partners secretly did a deal with P & W and R-R to hush the whole thing up. Yeah. And Elvis married Lady Di.
Propfan failed not through conspiracy, lack of funds or anything but it acquired an unstoppability beyond all reason as many an ill-suited love affair shows. It failed to meet its principal objectives unless it flew so slow that it consumed just as much juice anyway and more or less and did for retinal surgery and orthodontists what Attilla the Hun did for the mortuary business.
Surely not that bad?
In terms of Tractor v Pusher argument it is far easier to make propfan in its early development a pusher and leave tractor problems till later. Noise and vibration virtually define it as rear-mounted. Ahhh, we have to have a T-tail and unrelieved bending moment in the wings. No problem as such as long as we get deep stall and shaker solutions right. Bummer that we have to do it but okay, we will. Forget that we really need to understand what constitutes airframe-engine matching. Rear-mounted engines its gonna be despite having more strength in the tail than we'd really like. Now as for survivability of uncontained blade shedding, I wish you hadn't said that. But soemone will think of something.
Now as for contra-rotating blades or not an unducted fan is not contained in a diffuser like an axial compressor or fan stages and has all the drawbacks of a propeller in a free airstream Every single one except that people want to get from A to B at something like M0.72 cruise if they are going to buy into this aircraft.
The more you push turboprop or profan designs into direct competition with what are accepted as conventional aircraft the more rapidly they lose all their virtues and retain all their vices. They funnily enough morph themselves back into B737/A320 sorts of configs.
By all means read the Langley Research Center papers but it was a kooky idea from the '70s when computational fluid dynamics was in its infancy. The late Richard Shevell (Douglas)who had something to do with it said that the best place for a propfan was on a Boeing aircraft. He was not entirely joking.
I had also better come clean on something else. One of the screwballs on propfan was my own late father!
Guys back home! Still on the wagon and still under the cosh. Longing to get back home....
The "E"
PS speeling polees I cant be bothered to correct my mistakes. I just wanna come home!
Last edited by enicalyth; 26th Sep 2005 at 16:19.