What PSRU Can we Really Trust???

Originally Posted by Dan Thomas

Curiously, we have an old (1966) Massey-Ferguson backhoe here that has, believe it or not, Cessna hydraulics on it. The valves and other bits are all made of cast iron and aluminum and have the old Cessna logo on them. What reason Cessna had for being in that industry is beyond me, unless they had tried the hydrostatic drive on some airplane and had to recoup huge financial losses somehow.

If I recall my history right, Cessna started in the farm equipment business. As a matter of fact, most of the "certified" products we use today are pretty much identical to the originals, which were components from the farm equipment of the day.

Originally Posted by pepsi71ocean

...The most important thing is that V-6's are enharmonic, and are heavily influenced by torque reversals. V-8's and V-12's, (v-10's with odd firing orders) are all inherently balanced......IMO an updated version of this gearbox would do you the best. Along with a Evinrude E-tec 2 stroke EFI outboard engine. They will produce 300HP at 5,000 RPM

???? The big E-tec is a V6, isn't it?
Geez.
Jan

It's beginning to sound like PSRU's are like politicians... they make great claims, but you can't always trust them to keep their word.

Quote: "If a guy wants to fly in his lifetime without spending everything he makes over the next 20 years, he should buy a Lycoming for his project. If he really wants to build his own PSRU for an auto engine, he needs to do that and forget about going flying..."

A pretty strong statement, and I get the gist. I entirely agree that this is not an easy venture, and history seems to verify that. But I don't buy it whole-heartedly. If I did, that would almost be the end of scaled replica fighters, other than maybe jamming a Rotax 912 into the nose.

I fully believe that a knowledgeable person could make a good engine/psru/prop combo without mortgaging his estate. He'd just have to use his noodle, and know more about torsional vibration than I do. I also believe that a successful FWF package could be made without relying on guesswork or unproven assumptions about vibration attenuation, whether one uses belts, chains or gears. Of course, I'm in no position to prove it sitting hear at this box.

Even getting as far as we have in auto engines and psru development has shown real initiative on the part of those who create them. It can't be easy to set about designing/casting/machining/mounting/testing a FWF package, let alone paying for it. However, this type of work needs to go to the next step, at least in some cases, where the inventor/proprietor has backed up his claims of powerplant durability with wishful thinking and sometimes not much else.

I see an opportunity here, for some wanna be makers of FWF packages to pick a popular horsepower category for the homebuilt community, start with what's been done before, yet go forward with the idea of offering a proven,reliable system for builders. I also see, as has been stated all along, enormous challenges technically and financially.

But offer a proven system based on a V6, 150 HP and I think this would sell in numbers. As would a 350 HP unit.

I wish...

Tom.

Originally Posted by Tom Kay

Quote: "If a guy wants to fly in his lifetime without spending everything he makes over the next 20 years, he should buy a Lycoming for his project. If he really wants to build his own PSRU for an auto engine, he needs to do that and forget about going flying..."

A pretty strong statement, and I get the gist. I entirely agree that this is not an easy venture, and history seems to verify that. But I don't buy it whole-heartedly. If I did, that would almost be the end of scaled replica fighters, other than maybe jamming a Rotax 912 into the nose.

I fully believe that a knowledgeable person could make a good engine/psru/prop combo without mortgaging his estate. He'd just have to use his noodle, and know more about torsional vibration than I do. I also believe that a successful FWF package could be made without relying on guesswork or unproven assumptions about vibration attenuation, whether one uses belts, chains or gears. Of course, I'm in no position to prove it sitting hear at this box.

Even getting as far as we have in auto engines and psru development has shown real initiative on the part of those who create them. It can't be easy to set about designing/casting/machining/mounting/testing a FWF package, let alone paying for it. However, this type of work needs to go to the next step, at least in some cases, where the inventor/proprietor has backed up his claims of powerplant durability with wishful thinking and sometimes not much else.

I see an opportunity here, for some wanna be makers of FWF packages to pick a popular horsepower category for the homebuilt community, start with what's been done before, yet go forward with the idea of offering a proven,reliable system for builders. I also see, as has been stated all along, enormous challenges technically and financially.

But offer a proven system based on a V6, 150 HP and I think this would sell in numbers. As would a 350 HP unit.

I wish...

Tom.

The problem with all this development stuff is that the market is so small and won't likely get any bigger. How many people want to build a scale fighter replica, and how many of those will actually tackle it and finish it? Not many. When I was in the scratch-building mode, the EAA told us that the average completion rate was 10% of starts. Kits brought that up some, but I doubt that it's much over 25% now.

So to design, test, correct, test, correct some more, test some more, then finalize all the casting molds and other manufacturing stuff that goes with producing a few dozen pieces, plus the necessary mods to an auto engine (plus the price of the new or little-used engine itself), plus the liability insurance to cover yourself and still put up with nuisance suits from guys who were incapable of flying a snarky airplane and hurt or killed themselves---all of it adds up to a huge investment with little promise of a decent return. Shoot, even Lycoming builds only a few of some of their engine models per year and their overhaul facility, when I call to order a popular engine like the O-320-E2D that thousands of 172s use, might have one or two on the shelf. It's not a big business by any means and an auto conversion isn't going to displace too many certified engines.

Just look at the VW engine. The people selling those for homebuilts these days have to charge some pretty respectable prices, even though they build them from all-new ready-made parts imported from Brazil and Mexico. I could buy a sercviceable C-85 or O-200 for the same money as some of those VWs and it would be capable of producing its rated power for as long as I wanted it to, unlike the VW with its inadequate head cooling. I found that the Soob we had in the Glastar couldn't be run anywhere near redline for any amount of time without causing undue wear and burning a lot of fuel; the valves in those things burn out quick if you try to lean them at higher settings. Compare the Soob's exhaust valve with a Lyc's and see what I mean. The result was a max cruising RPM of 4700, so with a redline of 5600 that's a 20% drop in RPM and gives a much lower cruise speed. The Lyc's 2700 redline and 2500 cruise (2600 if you like) is an 8% drop from redline. So that Glastar cruised at 110 MPH on its 130 hp Soob instead of the 135 MPH on a 125 Lyc that other guys were getting. Hard to market that sort of thing, see?

Dan

+1 on Orion... Several times. Well put.

As to all of that stuff that works on locomotives and tractors, well, they NEED weight to make the drive wheels transmit tractive effort, so they are actually can use heavy systems. But for an airplane, we only need one reduction ratio, not the wide range of ratios used on ground vehicles. And you had better believe that the various series electric and hydraulic hybrid powertrains have potential for vibration too. Each time a winding set passes a magnet or a pump element goes through a cycle of charge and exhaust, you get a pulse...

Tribolic drives have the same issues too.

Here is the deal - We have an internal combustion engine with inertia that is making distinct bumps along the output torque. We have a big inertia in the prop, we have springy things in between, and sometimes we have other inertias and other gadgets that put bumps in the torque too. If someone just builds a system, but does not analyze it or measure the torsional vibrations, we will not know if that system can work long term. Maybe it will work, maybe it won't. Besides torsional resonance, there are lots of design details that all have to be done right...

Short of having a bunch of copies flying for years without broken parts, I am not sure I would want to fly over anything but flat land with one.

Billski

Originally Posted by wsimpso1

+1 on Orion... Several times. Well put....

Am I missing a post?

Originally Posted by wsimpso1

Here is the deal - We have an internal combustion engine with inertia that is making distinct bumps along the output torque.

The Dynacam had a beautiful torque curve. Too bad they couldn't solve their other problems, whatever they were.

Originally Posted by bmcj

The Dynacam had a beautiful torque curve. Too bad they couldn't solve their other problems, whatever they were.

Temporary thread drift warning...

I am willing to bet that the technical (as opposed to business) Dynacam problems boil down to this: You have a thing line of contact between the rollers in the piston and the cam surface. A line, not an area. The bearing area is minuscule and thus the stresses on the cam surface is enormous. No matter how big you make the roller and how hard the surface, it will deflect and indent under the stress and eventually fail, first at a microscopic level, then in chunks. Add to that the constant torque reversals and the pounding this causes on the cam, the cam surface will eventually give up. I know the engine was FAA approved, but I don't think this approval process meant you have to run an engine to TBO and see what happens. I do not know exactly how long a cam actually lasted, but I am willing to bet it would be severely limited.

I have always been intrigued by cam engines like the Fairchild-Caminez and Marchettis, and if this basic problem could be eliminated, they would be a big step forward from the crank and rod mechanism. We don't use the the crank because it is works so well, we use it because we haven't come up with anything better. The Dynacam was a worthy effort.


Back to topic...

Originally Posted by wsimpso1

+1 on Orion... Several times. Well put.

As to all of that stuff that works on locomotives and tractors, well, they NEED weight to make the drive wheels transmit tractive effort, so they are actually can use heavy systems. But for an airplane, we only need one reduction ratio, not the wide range of ratios used on ground vehicles.

I'd love a variable-ratio redrive. It would have a controllable propeller with a wide pitch range (even though this would affect efficiency, changing the outboard pitch as much as the inboard). The engine could run at a constant RPM, optimized for valve and ignition timing, and allowing high prop RPM for takeoff and climb and a lower prop RPM, with very high pitch, for cruise. That would enable us to use a large prop but still keep the prop's tips well within efficient speeds while still allowing the engine to produce power at a higher RPM, reducing internal pressure and other stresses.

It's not a new idea, of couse. Turboprops do it. The engine on the Dash 8, IIRC, turn their props at 1300 for takeoff and 900 for cruise, all at rather high power settings. Free turbines can do that.

Dan

Originally Posted by Dan Thomas

I'd love a variable-ratio redrive.
Dan

The friction drive could provide variable-ratio in a rather simple design.

Originally Posted by BBerson

The friction drive could provide variable-ratio in a rather simple design.

The last I heard of any variable-ratio friction drive highlighted the usual slippage problems that small contact areas suffer. To get traction, high pressures are necessary, or softer materials. Soft stuff wears out quickly and high pressures generate heat and surface fatigue. Such drives are handy for low-power applications in some production equipment, and we used to have an ancient Frasca electromechanical flight simulator that used a bunch of them in the control and instrumentation systems. I bet the old Link trainers used them, too.

The nearest thing to a workable variable-speed drive is the snowmobile setup, where the effective sheave diameters change. It relies on considerable friction, too, as a vee-belt does, and loses energy in the belt's wedging and pullout as the sheaves rotate. And there are slippage losses and a rather short belt life. Jim Bede originally tried this setup on his BD-5 but it increased the fixed-pitch prop RPM as forward speed increased, exactly backward to what an efficient controllable prop system would do.

Dan

I thinkt he best veritable speed prsu would be a combination of a gear and a twin clutch 2 speed transmission, that would engage at a certain engine rpm.

It would be lightweight, and would have a two speed, to allow for different rpm's, higher rpm's for acceleration, and lower ones for cruise.

A number of hybrid cars (notably, I believe, the Toyota Prius) are using "continuously variable" transmissions. There might be some suggestion of technology direction for a "variable speed PSRU" to be had there.

If you want a variable reduction then how about an automatic transmission? I don't know how the weight compares to a PSRU, probably not too badly, and an automatic also automatically eliminates torsional vibration. Well proven too.