Turbo Rotaries and Temps

[JETninja]

Many years a lurker (and learner!) finally posting a question, hope the experts look down here in the Aviation Forum.

Not my plane, but I plan on building one like it some day. Cozy MkIV (homebuilt composite canard) with a Mazda 13B with a To4 on it. After replacing a bad EGT sensor, the owner is seeing temp's up too 1800F. A few others with experience with this combo (Rotaries are known for higher EGT's)often see temps in the 1850-1870 range, which from what we understand is creeping into the negative zone for the Inconel blades and possibly lessening Turbo life.

Aicraft runs Mobil 1 though I do not yet know the wieght.

My question was if there was any particular brands/weights that could help in any way? (lower temps or known to resist such temps best) I was thinking maybe Mobil Truck & SUV (Delvac Syn) or Shell Rottella T. (which I ran in my 1.8T Passat for years and now in my '95 M3)

Any insight would be much appreciated.

Thank You!

 

[Jimbo]

I remember having a Mazda rotary on the engine dyno at school. The exhaust manifold would glow orange when we put a real load on it for a few hours.

The first question to ask on oil selection is: leaded avgas (100LL) or mogas (91 unleaded). If the answer is mogas, then I would consider Redline, avgas, Aeroshell blend or Exxon Elite.

There is a Cozy at my EAA chapter with a non-turbo Subaru six in it and even that engine is running too warm. It is difficult to get enough cooling air into the cowling with a pusher configruation.

 

[wileyE]

my 02, I'd set it up without the turbo and fly it. Then add the turbo later. Veri-ez's, 1 with a 3cyl sprint turbo, another suburu turbo. Fighting cooling and detonation issues when your trying to maiden voyage and learn the plane proved to be a giant PIA. I feel that without the turbo we wouldn't have had the problems we did.

I'm no rotary expert but my cousin used to race them. At the time guys were shying away from synthetic oils because rotarys normally consume some of it. Rumor was it would glaze and the rotor seals wouldn't seal as well? Another they did was add two cycle oil to the fuel for better seal.

 

[Drew]

Most rotary engines in aviation applications are NA and not turbocharged. I would recommend that you not consider using a turbocharged rotary engine in an airplane. NA rotaries are bulletproof and can spin 7000-8000 rpm all day long without any problems. Turbocharged rotaries are very sensitive and can blow easy if mixture is not optimum or if overboosted.

www.rotaryaviation.com is a good source of information for you.

I hope to one day drop a 13b into a kit plane.

 

[JETninja]

Actually adding a proper low boost Turbo (not the stock ones, they fail rather quickly) fixes two of the major pain in the butt rotary problems in aircraft, Noise and Muffler's failing due to heat. The high heat makes it very tough to find a suitable and lasting muffler that will fit under the cowl. A Turbo eats up most of the noise, and last's a lot longer then the average muffler on one. Gives you the benefit of some nice Altitude capability also. Because of these facts, more and more Rotarys are going boosted.

I'm sure for the most part the aircraft I mention used Autogas 95% of the time. One thing he's looking at that affects the temps a bit is the ignition advance.....

With modern seals they last a good long time and don't eat oil, though most don't trust the auto oil system and add premix since some oil must be added to the mixture for the seals. Thats different then what you run in the case.

Also, these days with Tracy Cooks (your link) controllers mixture and boost are very easy to control. Not looking to make a race motor (400+ HP 13B's are quite common in the street cars) but more around 250-300HP Max....

 

[Cujet]

JETninja,

One thing to keep in mind, EGT is in a direct and locked relationship with inlet air temperature. So, if you can lower the inlet air temp by 25 degrees, you will lower the EGT by a similar amount. Intercoolers are a good first step. As is a large turbo with the compressor running in the best zone. (produces less unwanted heat). Keeping the exhaust backpressure low with a large turbine section is a BIG factor.

Think back to the Porsche 930 air cooled turbo. Big turbo, low boost, very laggy. But the engine lived forever! Those engineers got it right.

There is no way I would consider a turbo rotary as safe in an aircraft. I have had too many friends die in hombuilts. Watched one go down at a fly in due to sudden loss of power.

Kitplane mag had an interesting set of stats on engine factors in crashes. No surprise here, certified engines had the fewest crashes. Then came non certified aircraft engines, such as aftermarket Lycomings. Then auto engine conversions then 2 stroke engines.

Chris

 

[Cujet]

BTW, today's certified piston engine aircraft engines have the best BSFC numbers of ANY piston gasoline engines made today. Better even than the prius engine! On gasoline, you will not be able to get better economy than an aircooled aircraft engine, no matter what your friends or magazines say.

Sorry to go so off topic, but I thought you should know.

Chris

 

[gtx510]

I wouldn't use M1 T&S, M1 EP, or any HDEO (Rotella, Delo, Delvac, etc) in a rotary engine.
Especially if you're using a stock OMP set-up.
All the above oils have high levels of sulfated ash which can form abrasive deposits.
Between the oil injection (= oil burning) and the fragile side and apex seals you can see how this could be bad.
Just look at the carbon build-up in your average rotary....


I think a better rotary synthetic would be the newer "Euro" stuff.
They have 1/2 the sulfated ash of a HDEO or M1 T&S/EP and come as thick xW30's or xW40's.
German Castrol 0W30, Motul, Amsoil, Elf, Liqui-Moly would all be good choices.
Look into BMW LL-98 and LL-01 and Mercedes 229.3 and 229.5 oils. VW 505, stuff like that....


And if you really want to clean some of that carbon out and unstick your seals you might try some www.auto-rx.com
But ask around first and see what people think about it in a rotary.


Turbo rotaries don't just go blowing up for no reason.
Overheating is a common rotary problem.
So's not changing the oil enough, or diluting it with fuel by not letting the engine warm up before you shut it off.
So is breaking seals from detonation of pre-ignition, which can happen more with a turbo.
High EGT's don't help either.
But if you've got enough fuel and aren't overboosting then you should be fine....

 

[K-Man]

Ah, rotary questions. Wankelman to the rescue . . .

1. If the plane's owner is running leaded avgas at all, he must never, never run any synthetic oil. Look in the archives in this forum about Mobil's AV-1 synthetic aviation engine oil for the reason. Synthetic oil and leaded avgas do not mix in any engine, rotary or piston.

2. Mazda has always specified low- or no-lead fuel in its rotaries, even in the early 1970s before unleaded pump mogas became widely available. The owner needs to stick with that advice and use unleaded mogas at all times.

3. To run a turbo successfully in a Mazda rotary that wasn't already set up for it as the later RX-7s were requires reducing the compression ratio. This must be done. You cannot simply slap a turbo on an existing normally aspirated rotary and expect good long-term results, and this applies to most piston engines too. Lowering the compression is to avoid detonation at all costs, which will kill a rotary even faster than a piston engine. Racing Beat sells a reduced-compression rotor kit for turbo applications.

4. Check the fuel supply. If the engine is running lean because the fuel system hasn't been upgraded for more output, then that's asking for trouble too. That will cause elevated temperatures and potential overheating.

The high exhaust gas temperatures might well be a consequence of not following one or more of these. However, racing Mazdas did have EGTs approaching 2000 deg F, so . . . Running advanced ignition timing constantly to get a few extra HP is not a great idea either, any more than with a piston engine. Mazda apex and side seals are no more "fragile" than are piston rings in a conventional engine, but common sense should apply in any application instead of a blind desire to wring out every last HP.

Tracy Crook's website and publications have a great deal of useful info on cooling and other issues with converting Mazda rotaries for aviation use. Look at his solutions before you take the plunge (in either sense), and tell him Mr. Krampitz sent you. I don't want that other guy, or you, to fall out of the sky.

 

[K-Man]

Comment about Auto-RX in a rotary: I don't see any reason it can't be used to eliminate carbon. There are plenty of home-brew solutions to carbonization of rotor faces that involve various chemicals, and Auto RX would probably work as well as any. Most of the solutions seem to involve spraying or pouring it in the spark plug holes and allowing it to soak for some time (hours/days) and then turning the engine over slowly with a breaker bar and repeating the procedure to cover all rotor faces. This is all at your own risk, of course.

 

[gtx510]

quote:

---

Originally posted by ekrampitzjr:
3. To run a turbo successfully in a Mazda rotary that wasn't already set up for it as the later RX-7s were requires reducing the compression ratio. This must be done. You cannot simply slap a turbo on an existing normally aspirated rotary and expect good long-term results, and this applies to most piston engines too. Lowering the compression is to avoid detonation at all costs, which will kill a rotary even faster than a piston engine. Racing Beat sells a reduced-compression rotor kit for turbo applications.

---

No you don't.
It's very common for the FD3S guys to use the high comp rotors out of the S5 FC3S n/a engines and use them in the 13b-REW. Helps the turbo spool quicker and gives you more mid-range.

Reduced comp rotor kit, huh? Sounds like they're selling you used turbo rotors. And if you don't know what you're getting you might end up with the heavier S4 ones.


Talk to Adam at www.rotaryengine.com
He makes GOOD apexseals for a fair price. And he refinishes housings and irons.


Lean conditions can destroy ANY turbo engine.


fwiw, I use to work at Puresports. The rotary shop in San Diego that burnt down last spring...


ATF down the plug holes and crank the engine, old trick....

 

[K-Man]

Racing Beat has offered these special rotors for years, since the early 1980s if I remember correctly, before any factory Mazda rotary turbo was offered here. They are custom fabricated for Racing Beat and are not used.

You're talking apples and oranges on engine components, GTX510. You can probably get away with using FC-3S high-compression rotors in a 13B-REW, which was designed for twin turbos from the outset, and I specifically excluded the later RX-7s that had turbos from the factory. My reference was to older normally aspirated rotaries that someone wants to turbocharge after the fact, and I stand by what I said. You shouldn't do it without the necessary internal modifications. A number of people are using old 12A and pre-late 1980s 13B engines in aircraft, and those engines are what I'm addressing.

In general, in aircraft conversions, the newer the rotary the better. The normally aspirated RX-8 RENESIS engine is actually a far better choice for aircraft than most of the older rotaries, but try getting your hands on one.

There was a fad back in the late 1970s-early 1980s for sticking turbos on small four-cylinder piston engines without modifying the engine to handle the extra boost. Ads from various outfits for turbo kits were common in the car magazines then. One Car and Driver test of a Honda Accord showed impressive gains in power and performance, including a gain in top speed from 90 to 110 mph, until the engine melted several pistons. The same risk is there with an older rotary.

 

[gtx510]

Racing beat offers LIGHTENED rotors.
Ther are NO aftermarket rotors.

no, the n/a S5 rotors really wake up a 13b-REW.
so does some mild portwork.
300bhp, a fair amount of torque, good top-end power.
I don't know much about planes but that sounds like a good engine to me.

It's a PITA to turbo a 6-port, n/a engine. It's silly not to start with the tubro model.

The only hi-comp rotors you're finding for a 12a are the 12:1's out of the RX-3 SP, good luck.
Older 13b's have HEAVIER rotors.
Why are you using the old, clunker motors when you're saying the newer stuff works better?

I don't like the exhaust ports on the Renesis motor.
And they're fairly brittle engines too.
6-port motor has no low-end but the auto/4port motor seems like it'd be decent if turbo'ed.

Have you heard of www.turbotom.com ?
Or an intercooler? programmable fuel injection?

[ August 22, 2006, 11:29 AM: Message edited by: gtx510 ]

 

[unDummy]

High exhaust temp is normal in the rotary.

To reduce the temp, run less turbo boost, less compression ratio, more fuel, less timing, and more oil/water cooling. All that will cost power which shouldn't be too much of an issue. Reliability is more important then the last ounce of HP.

Slap a wide band o2 sensor on it and get some readings.

Coolant and oil temp readings should also be logged.

How much premix is being used?
what type of fueling, carb or injection? size?
fuel pump size and filter?
radiator and oil cooler sizes? location? thermostat? engine RPM usage range?
turbo specifics? boost PSI amount? intercooled?

 

[Max_Wander]

2-stroke oil in the gas makes rotaries impossible to wear out and destroy!!!