MW Fly Engines

For general discussion of the Just Aircraft family of aircraft.
Includes: Highlander, Escapade, Summit and SuperSTOL.

Moderator: scubarider2

MW Fly Engines

Postby Jakkals » Sun Apr 27, 2014 1:53 pm

Has anybody on the forum taken a look at the new MW Fly engines?
Opinions?
http://www.mwfly.it/index_file/homemwfy.htm
Pieter
Jakkals
New Member
 
Posts: 10
Joined: Sat Dec 31, 2011 8:07 pm

Re: MW Fly Engines

Postby R Rinker » Sun Apr 27, 2014 6:00 pm

I think we'll be hearing a lot more about this one. If I read it right, the prop rotates backwards from 'normal'...the main bearings are ball bearings & the rod bearings are needle bearings. This relieves a lot of heat from the oil so it doesn't need an oil cooler. They claim the bearings are designed to take full power for 3 thousand hours! Counter balancing takes a lot of stress off the bearings. Big difference seems to be, its not made by a big corporate machine that throws something out there just to make money and forces you to like it the way it's cheapest for them to make. It "appears" they are passionate about it and working long and hard to get it right. I don't think there's a pilot alive that is altogether cynical when it comes to a new powerplant. We all want someone to get it right at a price we can afford. And really, how good does it get...a company making engines in the town that produced the Stradavarius line of stringed instruments over 300 years ago!! Looks like the 130 horse is going into production and the 150 is close. At the end of the production line they wring it out and document it. No current manufacturer does that except for a custom shop somewhere. So???
Rodger Rinker - Rocky Mountain House, Alberta, Canada
Super Stol build/January 2014
NL7AL & VE6RWR
User avatar
R Rinker
Veteran Member
 
Posts: 169
Joined: Thu Jan 24, 2013 1:07 am

Re: MW Fly Engines

Postby rmullins » Tue Apr 29, 2014 6:49 pm

I stopped at their booth at Oshkosh last year. Good looking engines with nice castings/machining. It would be nicer if they had a hundred or so flying with a track record...
Rick Mullins  #144
Cincinnati, Oh
User avatar
rmullins
Veteran Member
 
Posts: 321
Joined: Wed Jul 16, 2008 8:01 pm

Re: MW Fly Engines

Postby R Rinker » Wed Apr 30, 2014 2:01 pm

...and until they do it is totally 'faith being the substance of things hoped for'! When you have a few thousand hours with your life in the hands of a Lyc. or Cont. over the Bearing Sea, Arctic Mtns. & wilderness, etc. and you really know that if you meet their needs they will bring you back..there is definitely a loyalty bond with them. It's taking me several years to break that bond and convince myself to trust a Rotax in their place. Although Rotax is getting a track record in the southern regions, it still has to prove itself in the cold, so I'm still in the uncomfortable position of being a test pilot and developing my own install mods and operating procedures.
One big thing to prove will be the ball & needle bearings instead of the conventional Hydrodynamic journal bearing. http://kingbearings.com/files/Engine_Be ... y_Work.pdf is a good site to explain the basics. One quote from them is:
"Rolling bearings, in which a load is transmitted by rolls (balls) to a relatively small area of the ring surface, can not withstand the loading conditions of internal combustion engines. Only sliding bearings providing a distribution of the applied load over a relatively wide area may work in internal combustion engines."
So Hydrodynamic journal bearings work great at lower rpm such as a Lycoming runs, but at higher rpms the problem becomes a cavitation of the oil fluid boundary pressure layer separating the metal parts. Thus the need for a rolling style bearing in higher rpm engines such as chain saws, etc. run, and the fly definitely runs at a higher rpm. So the conflict in engineering constraints becomes one in which the fly engine runs at high enough rpm that the cavitation issue compromises the reliability required in aircraft engines, so they are dealing with that by going to a rolling style bearing. This begs the question of...can they overcome the aforementioned issue of distribution of loading which heretofore has required journal bearings? Another big question is how does Rotax deal with this?? Does anyone know if they use journal or rolling bearings? If they use journal bearings, then how do they deal with the cavitation issue at the higher rpms they run?? If they use rolling bearings then possibly technology has advanced to the point where they have overcome the issue of the loading pressures. Loading pressures possibly decrease by getting horsepower from higher rpm as opposed to bigger pistons running slow, but this also makes balancing & counterbalancing a critical issue...
Rodger Rinker - Rocky Mountain House, Alberta, Canada
Super Stol build/January 2014
NL7AL & VE6RWR
User avatar
R Rinker
Veteran Member
 
Posts: 169
Joined: Thu Jan 24, 2013 1:07 am

Re: MW Fly Engines

Postby markdille » Thu May 01, 2014 9:59 am

R Rinker,
Actually, journal bearings thrive off of velocity across the bearing surfaces in order to stay hyrodynamic. Without velocity, the oil film will not sustain itself allowing the surfaces to go metal to metal. As with everything, there is a balance between pressure or P and velocity or V for long life. Most journal bearing manufacturers list max PV values for their bearings, and in many cases maxes for each individually. However, in designing journals for reciprocating components, max P is almost always approached far before max V, and V is always changing and reverses as theta changes staying fairly low. Rotating components are the opposite. V is high and fairly constant with a fairly low P that can vary by induced loads depending on application. I'm very surprised by the use of the ball and needle bearings mentioned. They require a much larger and therefore heavier housing design to meet the same load requirements. The only perceived advantages of going to such a design that I could see, would be an oil bath versus pressurized lubrication, not likely or desired in a continuous use reciprocating engine, and installation/assembly due to the design of components. A bearing assembly as they mention can allow the block to be a single solid block with the crankshaft inserted from the side. Again, I can't imagine how this could be an advantage, but it would be a necessity if the block were designed as such. Interesting for sure. Their website didn't offer much, so I couldn't really look at it in detail.
markdille
New Member
 
Posts: 15
Joined: Fri Aug 19, 2011 7:40 pm

Re: MW Fly Engines

Postby R Rinker » Thu May 01, 2014 3:34 pm

I find it interesting also. We didn't go this deep into the engineering in A&P school..I always knew journal bearings worked better at the top end but thought it was mainly because the engines used gear driven oil pumps which dramatically increase the hydrodynamic pressures at higher rpm which serves to keep the parts well cushioned from each other. Evidently the cavitation issue of the oil fluid boundary pressure layer separating the metal parts kicks in at some point limiting the max rpm in a journal bearing. Possibly under well controlled perimeters that point is fairly high, but in the real world of thermal shock, occasional high temps, quality control of the oil, etc. any occasional cause would determine the limit. I'm surprised how all these new companies don't open the door to more information and rational behind their designs, such as telling us the max PV values on the bearings. They did say something about the bearings would handle 3,000 hours at max RPM! That statement is so challenging that it requires some verification for credibility I get a little skittish about the depth of the engineering department when they keep us in the dark on these issues and have to speculate like I'm doing here. I'm not qualified to approve or condemn the design issues we are discussing, but I look for credibility and want to understand the issues before writing a check with a number as large as these engines cost. The Lycoming (& Cont.) engines have no real secrets..they are inefficient gas hogs, but we know they work and why. People get nervous when they mess with changing anything at all on them even as benign as lightening the case..remember the I0-520 problem..so how can a company think they are going to sell us an engine with ball & needle bearings running in an oil bath like a chain saw, for an airplane, without a really compressive information department. So does Rotax run journal bearings?? I'm assuming they do, otherwise they probably wouldn't need an oil cooler.. (I know little about Rotax - but will soon be learning)
Rodger Rinker - Rocky Mountain House, Alberta, Canada
Super Stol build/January 2014
NL7AL & VE6RWR
User avatar
R Rinker
Veteran Member
 
Posts: 169
Joined: Thu Jan 24, 2013 1:07 am

Re: MW Fly Engines

Postby markdille » Thu May 01, 2014 4:52 pm

R Rinker,
Designing components for journal bearings is fun, especially when that assembly formerly used sphericals, and the design parameters lend themselves to journals. Assuming good design practices and assembly procedures, it can make a good engineer look super human. Journals will take one heck of a force load, are fantastic for shock loads, and extremely compact (read small and light) and cheap to make and replace, comparatively speaking. The PV value as previously mentioned is a bit of voodoo within the bearing world. Each manufaturer has their own method, and they hold that pretty close. I can't say how they actually come up with that, nor will they tell you outright.

As I had said before, in a reciprocating engine, especially a lower rpm, high rod load aircraft engine, the challenge is actually keeping the velocity high enough, not slowing it down. In general terms, the best journal bearing surface is a perfectly flat surface (no grooves) that has roughly a square shaped surface, i.e. width roughly same as diameter. When velocities are lower than ideal, or surface pressure is above ideal, or both, a charge groove is sometimes put in the oil path. This takes away bearing surface area, but it significantly increases charge pressure 360 degrees, and is thus the lesser of two evils when this situation exists in maintaining a hydrodynamic sysyem. In extreme cases, small diagonal grooves are cut in, spanning out away from this charge groove. These are common on half knuckle joints where the bearing itself is much smaller and velocities even lower, but the load is the same as seen at the crankshaft.

In reference to the cavitation comment, the only reason I see something like this happen is if the sump isn't large enough, and the oil pump starts sucking air, or the system is low on oil. What I "believe" everyone to mean is in reference to the creation of aerated oil. This can happen when a bearing is sprayed at too high of a pressure. This will never happen on a journal bearing, as all journal bearings are injected, i.e. low flow and high pressure at the point of use. However, other bearings in the system may require spray pipes resulting in atmospheric pressure at high flow rates at point of use, thus making it possible to recycle aerated oil. This is very easy to avoid, and requires due diligence in lube assembly design. A properly sized pump and sump with its piping and orifices will not create this aerated situation for the type of oil used. I've messed with this before, and didn't start seeing aerated oil that recycled into the charge pump until about 225 psi with Omala 220 at 150 degrees F as an example. Aircraft engines probably run somewhere from 45 psi to 130 psi if I were to guess, depending on temperature and rpm at the time of measurement.

One thing that does concern me in a continuous use, fairly high speed design, such as an aircraft engine (compared to say the gearbox of a hoist), is a bath design greatly increases lubrication friction due to high speed sloshing. This will increase lube temperatures just by itself requiring more cooling capacity. Well I guess there's another thing too. Aircraft see a lot of turbulence, so a bath is not very stationary, which will elicit even more sloshing. I can't imagine they're using a bath, but maybe i'm wrong. This really goes against all standard practices. They have to be injecting oil.

Designing and building an aircraft engine from a clean sheet of paper would be tons of fun. There are some fairly low hanging fruit due to modern technology and flight experience over the last several decades that engineers could utilize. Preparing all the paperwork, red tape, and legal issues, would not be fun, however. I take my hat off to any who try, successfully or unsuccessfully.
markdille
New Member
 
Posts: 15
Joined: Fri Aug 19, 2011 7:40 pm

Re: MW Fly Engines

Postby R Rinker » Thu May 01, 2014 9:02 pm

Mark, The cavitation issue I was referring to is not the flow inside the pump or lines but inside the bearing itself. Evidently, so I'm told anyway, the rotation of the crank or rod creates a 'pumping' action inside the journal between the surfaces separated by the hydraulic pressure. Quote.."a loaded journal displaces from the concentric position and forms a converging gap between the bearing and journal surfaces. Two types of cavitation may form in journal bearing: Gaseous cavitation associated with air and other gases dissolved in oil. If the oil pressure falls below the atmospheric pressure the gases tend to come out of the oil forming gaseous cavitation voids. The cavities are carried by the circulating oil to the pressurized converging gap where they redissolve in the oil and disappear without any damaging effect. Vapor cavitation forms when the load applied to the bearing fluctuates at high frequency (e.g. bearings in high RPM internal combustion engines. The oil pressure instantly falls causing formation of cavities due to fast evaporation (boiling). When the pressure rises the vapor cavities (cavitation bubbles) contract at high velocity.Such collapse results in impact pressure, which may erode the bearing material. The oil pressure creates a supporting force separating the journal from the bearing surface. The force of oil pressure and the hydrodynamic friction force counterbalance the external load F. The final position of the journal is determined by the equilibrium between the three forces.In the hydrodynamic regime the journal “climbs” in the rotation direction (left side of the bearing). If the journal works in boundary and mixed lubrication the hydrodynamic pressure force disappears (the other two forces remain). Thus, the “climbing” direction is opposite to the rotation direction and the journal rolls up the right side of the bearing."
Obviously there is a graphic associated with all this which visualizes it. It all gets so convoluted that it amazes me how any engine manages to run dependably under varying, real world conditions...
Rodger Rinker - Rocky Mountain House, Alberta, Canada
Super Stol build/January 2014
NL7AL & VE6RWR
User avatar
R Rinker
Veteran Member
 
Posts: 169
Joined: Thu Jan 24, 2013 1:07 am

Re: MW Fly Engines

Postby markdille » Fri May 02, 2014 7:50 pm

Theoretically, that is all correct, however, the probablility is almost zero in the aircraft engine application. A rotating journal on a crankshaft has a progressive change in load direction, even when shock loaded. This lends itself well to avoiding cavitation issues. Nominal fits leave a very small volume for the lube film layer and flow is very low, so even when volume changes do occur due to load direction changes, the high lube pressure and associated low flow easily tolerate these changes at the bearing surface location with the speeds we're talking about. As far as speed is concerned, I've had many more issues with cylindrical and spherical roller bearings skidding over the lubrication at high rpm and high load. My experience isn't with very high rpm, but an aircraft engine isn't anywhere near high rpm, being roughly the same velocities I deal with. I'd consider an F1 engine from 2013 and before or a GP motorbike high rpm.
markdille
New Member
 
Posts: 15
Joined: Fri Aug 19, 2011 7:40 pm

Re: MW Fly Engines

Postby R Rinker » Fri May 02, 2014 9:11 pm

Since props are loosing efficiency past 3000 rpm or before, when they want to get horsepower out of a lightweight small engine they have to go to higher rpm to up the horsepower and a gear box to slow down the prop. I believe the Rotax and the fly engines run around 5500 as the red line. I believe chain saws and weed eaters run around 9,000 rpm and up. You know much more than I do about this than I do Mark, I'm just making some general statements so I can get some help trying to keep up with it all. I will be buying an engine soon and I'm trying to buy into the faith that the Rotax is OK. I've worked on Lycomings and Continentals for many years and as time goes by my respect for them continues to grow more. When Rotax first came on the scene as an aircraft engine they were a joke to us..the gearbox and drive problems made flying them a version of Russian Roulette. I still don't know what type bearings they use...I was somewhat astounded that the Fly uses ball & needle bearings...if this works then I'd like to gain some knowledge so I can understand and move on as things develop. I'd expect these engines will soon begin to find homes on Superstol's and it will take years to find out if they are reliable. On the bearing issue, I was just wondering...gas turbine engines run a type of ball bearing on the main shaft which runs at 10,000 plus rpms, do they not? I believe those bearings have a high pressure oil injection for lube and cooling...I've never worked on them and have had no special training on them..I just know they work very well...somehow..
Rodger Rinker - Rocky Mountain House, Alberta, Canada
Super Stol build/January 2014
NL7AL & VE6RWR
User avatar
R Rinker
Veteran Member
 
Posts: 169
Joined: Thu Jan 24, 2013 1:07 am

Re: MW Fly Engines

Postby markdille » Fri May 02, 2014 9:39 pm

I don't know much about the specifics of turbine engine design, other than what was learned in school way too many years ago, but ball bearings can typically handle very high rpms, just not much in the way of radial load. They are decent in axial load for their relative size and typically serve as thrust bearings which is probably what it is doing on the turbine design.
markdille
New Member
 
Posts: 15
Joined: Fri Aug 19, 2011 7:40 pm


Return to Just Aircraft