Something I've been pondering at work (while driving a bus): Most rotary engine failures are not catastrophic failures. Most piston engine failures are.

A typical failure on a rotary engine leaves the engine still able to operate. Often it's at reduced power, but numerous people have shown (me included) that a one-rotor engine is still able to move the car around. A failed apex seal, side seal, or even an entire blown rotor don't cause the engine to completely fail.

Also, the dual ignition systems come in useful. Even if one half fails completely, the engine still makes enough power to move the car.

In a piston engine, most failures are complete. Ignition failure, timing belt/chain failure, physical engine damage (thrown rod).

Personally, in terms of reliability, I'd rather have an engine that can suffer a significant failure and still be somewhat usable. It's less likely to strand me somewhere.

Is this a reasonable analysis? Reading various posts, a LOT of people have managed to get home after an engine failure that would stop a piston engine completely. Same for the transmission - 4th gear usually works even after the rest fail (silly NA transmissions).

-=Russ=-

 

yep thats about it. the other two rotary fail modes, the water seal and the rotor oil seals, usually leave the engine running fine and the only problem is lots of smoke, and more smoke

 

About everything short of loss of oil (pressure)...
A seized motor is a seized motor.


-Ted

 

from a volumetric standpoint, rotaries are 10 times more reliable than piston engines.
for a 400 hp rotary to last 50k miles is an amazing achievement. that's about 5 horsepower per cubic inch!!!

now, how long would your pappi's 350 last if it were trying to pump out 1500+hp on pump gas?

 

This is why the rotary is getting more popular with the aviation crowd.

 

Exactly. It can overheat and still run (destroyed coolant seals near the spark plugs, crushed rotor housings etc). If you shut it off, it may not restart, but at least landing an aircraft with an overheated rotary won't be a near-death experience (for the pilot, anyway).

 

Absolutely true. And if you run a rotary at over 80% power all day long it will just smile at you and say "that all ya got, wimp?" Typical continuous aircraft use only calls for a 75% power settings or less. The service life of automotive-conversion boingers in this environment is drastically shortened when pushed to these limits, often with catastophic engine failures being the result. Thus far, the only auto conversion engine that can match or exceed the 2000 hour service life of a $30,000 certified aircraft piston engine while returning the same performance is the Mazda rotary. Others have shown promise but have yet to put up the hours.

But if an apex seal gets thrown the engine's power (now running on only one rotor) is reduced to about 35%. This is barely enough power to maintain level flight. The problem is that now engine vibration has increased to the point that you can no longer run at max rpm. This means you now have less than 35% power--- not enough to maintain level flight.

But the limited power will still extend your gliding distance, making it much more likely that you can make it to the nearest airport or open field. This is more than can be said for a piston engine that has thrown a rod or lost it's coolant. A boinger that has swallowed a valve can still limp to an airport if one is close enough, but swallowed valves on boinger aircraft engines is a much more common occurrence than busted apex seals in rotaries.

And those who can afford to own an aircraft in the first place (even a $50,000 homebuilt) don't usually get too fazed by the cost replacing a $3000 engine core.

 

My dream plane is a Long-EZ powered by a rotary... maybe even a 20B, if I win the lottery or something. Or... *drools* a Defiant powered by dual rotaries.

I've been an aviation geek for a while, just can't afford my license. I knew that a lot of people were using 13Bs in planes, but I didn't realize that they were holding up so well. I knew that the auto engine conversion people tended to run into problems with engines breaking when asked to put out 50+% power for long periods of time, but I guess I never connected it with the fact that the rotaries (with proper cooling) can hold that kind of power output pretty much forever.

-=Russ=-

 

Actually a license isn't that expensive, especially in the U.S. You could have your private licence in less than six months if taking lessons at a minimum rate of two flights per week, and total cost shouldn't exceed $5000.

Of greater concern is the cost of building and then owning your own plane. A long-EZ is plans-built and one of the least expensive high-performance planes to build, but it will still set you back $50,000 from start to finish. Even spread out over a five year build period this is $10,000 per year. If the $5000 for a licence is unattainable...

On second thought, scratch that--- NOTHING is unattainable if you're willing to put forth the effort. This includes taking on a second job and/ or finding a more profitable career or business.

As for problems and teething pains of auto conversions, most of the initial challenges have been worked out by previous builders. While piston auto conversions will always have the high-rpm-for-extended-periods-related drawbacks, the rotaries are holding up very well. Just ask Ron Gowan from Arizona. He's had a 13B-powered Long-EZ for about 15 years.

 

Eh, the whole "college" thing was a huge damper on income. I'm graduated now, so I can hopefully get the money within the next year (for a license). Make up for the driver's license that I'm probably losing (I like going fast).

Any chance Ron Gowan will be at Oshkosh next summer? I'm planning to make my way up there this year (went in the past, became a swimmer, couldn't go, now can go again).

-=Russ=-

 

I don't know Ron personally so I couldn't tell you. But Tracy Crook is there every year with his rotary-powered RV4. There will also be a few of his buddies who also fly rotary-powered planes. Tracy's company is called Real World Solutions. He manufactures reduction drives that mate the 13B rpm to the propeller so that the propeller receives best power at it's ideal rpm of 2400 to 2800. Check out his website at www.rotaryaviation.com for info on Oshkosh arrival times and where they'll be parked.

 

My dream plane has been a Lancer IV pressureized w/20b turbo.

 

Hm... you win What kind of cruise speed/altitude could you run at with that? Pretty much into the jet ranges, I'd think.

I'll definitely look up Tracy if I go - my engine is rebuilt with their kit, and running great (and they were wonderful to deal with too!).

-=Russ=-

 

I spent last summer helping build one of these planes. Since the cost for one is on the order of $300,000+ by the time it's finished the only takers are those in the cost-is-no-object category. And these guys don't **** around with auto conversions--- they're using Walter 601D turboprops putting out over 700 SHP on a 35 to 38 gallons per hour fuel burn.

A 20B modded for 350 to 400 hp burns around 20 to 23 gph at 75% cruise, but runs on avgas rather than the less-expensive kerosene-based jet-A used by the turboprop.

This boils down to the Turboprop returning higher cruise speeds and higher altitudes for a higher fuel bill--- but not as much higher as the gph difference would indicate. Besides, these guys can afford it. And if you can afford this plane, it would make sense to go turbine.

The 20B is more suitable for non-pressurized applications (although with a turbo it could certainly be used in pressurized aircraft) and in planes too small to accomodate a turboprop and the necessary fuel load. The velocity XL, Vans RV8 and Harmon Rocket come to mind. This engine is the perfect replacement for certified aircraft engines like the 300HP+ Lycoming IO-540.

 

With a 20B turbo cruise altitude could go upwards of 25,000 ft, and cruise speed at that altitude in a Lancair IV would true out to almost 300 mph. Not too shabby at all.

But performance with the same plane using a Walter 601 turboprop would be around 350 mph at over 30,000 ft. Almost as high as the big jets, but not as fast. Big jets (and biz jets) cruise at 500 to 600 mph, or around Mach .7 or .8.

 

WOW 300,000+ Damn I guess it's been a long time since I've reserched these planes(had aviation mechanic training 9yrs ago). I remembered the engine (turbo charged Continental IO360 or something like that) needed would cost around 50k back then and also a fast build kit was like 80k. Misc items (instruments, extras, ect) were like another 50k-70k. I guess I'm just completely clueless to the overall investment. Either way, a 20b would definately make it cheaper to fly and operate. Also since you have the experiance, how do you think the below 20b hp/rpm specs would perform in this kind of plane?

RPM: 3,769
RWHP: 195

RPM: 4,092
RWHP: 300

RPM: 4,307
RWHP: 400

RPM: 4,576
RWHP: 500

RPM: 4,845
RWHP: 560

RPM: 5,437
RWHP: 600

RPM: 6,175
RWHP: 628.8

To me with about 460hp available in the 4,307 rpm range, this would be ideal for mileage and longevity. These specs are from Red-Rx7's 20b Fd w/T72 dual BB turbo. I would personally use a GT42 in this application because Red has already maxed out the T72 with his engines flow capabilities. IMO the Gt42 would flow more efficiantly and be less stressed under these conditions.

 

This is the first I've read about this particular 20B. I'm assuming the owner uses it primarily for racing because Mazda rotaries used in aircraft are best optimized for reliability. This means a max. of about 150 hp per rotor, ie: 450 hp for a 20B. Above that value the engine's life span is compromised. This max hp value typically comes at 6500 to 7000 rpm. Assuming these values are reached via a turbo (also necessary for pressurization), and also assuming you have an adequate cooling system that will fit under the cowl so as not to increase drag any more than necessary, this setup should yield a continous cruise hp at 80% power setting of around 360 hp.

This is certainly better than the performance that would be provided by a TIO-550 (albiet with a higher fuel burn), and would certainly work in a Lancair IV-P. My point with the turboprop was that for rich guys who can afford to spend 1/2-million bucks on an airplane the turboprop is the way to go.

As for the original advertised prices for these planes yes, back then they were advertised much cheaper for the kits and engines. But the advertised projected completion costs were (and still are) shall we say, "optimistic". And this was before the pressurized version came out. The IV-P (pressurized) tacked tens of thousands of dollars onto the price of the kit and at least an additional 1500 hours to the estimated build time. No matter what anybody tries to tell you, you're looking at over 4000 hours to build this plane.

One more thing: The IV-P has vicious stall characteristics. The winglets used to reduce stall speed cause the plane to flip over onto it's back if you actually do stall, and altitude loss during recovery is on the order of 1500 feet--- but only if you're an experienced test pilot. Most of us mortals can't get this plane out of a stall/ spin from any altitude. There have been several people killed in this exact scenario in this plane.

Still, they're the fastest kit plane available and seat four big fat people very comfortably. If you can find a partially completed kit for cheap, keep the panel simple and inexpensive and do all the work yourself it's not unreasonable to figure on building a 20B-powered Lancair IV-P for around 150K.

 

Eeeewwww.... so basically a Lancair IV is in the "Absolutely do not stall" list. Yuck! I'd read some articles on them a while back in Sport Aviation and somehow managed to miss that point (or it was never discussed). That's no fun. Do most people put a stick shaker/stick pusher in them?

-=Russ=-

 

I'm not surprised that many who read aviation magazines aren't aware of this IV-P tendency. Kitplanes and other magazines tend to downplay these tendencies, especially if the plane in question belongs to one of their primary advertising clients.

I've never seen a stick-shaker used on homebuilts. As I understand, stick shaking is a result of aerodynamic forces acting on control surfaces at impending stall--- turbulent air going over the wings at high angles of attack then passes over the elevator, causing the stick to shake. What most people use now is an angle-of-attack indicating system that has both audible and visual warning cues. The indicator is mounted directly in front of the pilot at eye level.

I believe Lancair still supplies kits for their ES model. It has the same fuselage as the Lancair IV but unpressurized and with fixed gear and a larger wing. It's not prone to the vicious stall characteristics that are associated with the IV, and while not as fast will still cruise at over 250 mph. The Lancair Columbia is the certified version of this plane and sells for around 300K right out of the factory ready to fly. I'm not sure about the current kit price, but I'm guessing a new ES kit + build costs and a 20B could be done for 150K, or even for under 100K if you find a partially-completed one from a builder who either gave up or ran out of money.

 

https://www.rx7club.com/20b-forum-95/dynod-my-car-293958/





Hmmmmm 150hp per rotor for relaible operation? So making this kind of power(even at a low 4300 rpm for a rotary) wouldn't necessarily be reliable for a 20b in the long run? Also he was running a max of 13.6 psi of boost and put down 628rwhp. The hp me makes at such a low boost level is crazy for a rotary. That low boost level goes to show how maxed out the turbo was during the run because the turbo couldn't keep up with the engines flow capabilities. It burned out in a couple thousand miles.

 

I probably should have elaborated a little more when I stated that 150 hp per rotor was about the max for reliability. The biggest benefit of boost besides hp is decent torque at low rpm, something normally aspirated rotaries lack. This is very desireable in cars.

But the requirements change when an auto engine is converted for use in aircraft--- you now have a completely different environment with different requirements. In aircraft use, low-end torque is a non-issue, since the only time the engine is below 2500 rpm is at idle or during taxiing. 150 hp per rotor can be achieved by porting and intake/ exhaust tweaking.

But boost can still come in handy here for shortening take-off rolls and providing pressurization at altitude. The trick is to provide enough boost to accomplish this, but not enough to a) risk detonation and b) exceed the capabilities of the cooling system inside the confines of the cowl. Either excessive hp or excessive boost can create excessive heat, which provokes detonation and all the demons that come with it. But a combination of both make things even more complicated and harder to tame.

A normally-aspirated or lower-boost rotary installed in an aircraft can exceed 2000 hours before overhaul. A highly-boosted engine doesn't last as long. The FD is a prime example---- compared to n/a rx7s the FD doesn't seem to be putting up the 200,000 to 300,000 miles that can be expected from well-maintained n/a engines. Many need to be overhauled after only 100,000 miles or so.

 

You neglected to mention "Providing sea level power at altitude." As I understand it, most turbo aircraft don't use the turbo to provide additional power down low (though it certainly could be used for that if needed), but to maintain sea level power to a significantly higher altitude. The air's darn thin at 20,000+ ft, and a NA engine won't be producing significant amounts of power at that altitude. But with a turbo, it can be running at close to sea level pressures (or closer than it would be otherwise).

-=Russ=-

 

Very good point. That was so obvious I forgot to mention it. This is actually the primary purpose for turbos or superchargers in aircraft. Extra power for take-off and climb and a source of pressurization are secondary benefits.

 

You brought up alot of great points that I never thought about. I didn't think about how much harder it would be to tune the engine because the propeller blades aren't going to put as much load on the engine as compared to if the engine is in a car rotating tires while on the ground. I can see now how it would be harder to tune for a specific max boost level because of variations. Personally I was planning on running a max 8psi on a GT42. That combination on a stock block 20b recently dynoed 408 rwhp in an Fc. A little exhaust porting and some S5 higher 9:7 compression rotors should give that same engine a littel more power in the mid range at a lower boost level. Detonation shouldn't be much of a problem at such a low boost level. Also I don't think 8psi or less would be too stressfull in the long run with a 20b.

 

sounds a bit w/o substance.

based on NA rated volume flow per rev, the boosted 13B otto cycle engine matches with the 2.6L TT skyline otto cycle engine. For each putting out 400 hp, more skylines would be able to go at least 50K miles, from what I've read.

But they will not get there with as much style. The FD is a gem.