Rotary modifications

[Len Evansic]

OK, so I'm new here, and still feeling out the various engine choices that others on the forum have used, before I commit to anything. I understand the reason that many auto-conversions are used and some of the issues encountered. When it comes to the rotary though, I find myself constantly scratching my head.

 

In almost every detailed page I've found so far, it seems as though everyone disables some oil injectors in their engines, and instead use a pre-mixed 2-cycle type fuel. Why?

 

Why disable the lubrication system, and why bother with the hassle of having to mix oil with the gas, as if it were a 1960's Saab?

 

What other changes have to be made to the engines, and why do so many people choose the rotary over other more conventional auto-conversions, like the Subaru or the converted Benz diesels? Is it just to be different? I am genuinely curious to find the answers to these questions.

 

-- Len

[Jon Matcho]

...why do so many people choose the rotary over other more conventional auto-conversions, like the Subaru or the converted Benz diesels?

Some quick reasons for the rotary are:

• Comparable weight & HP to a Lycoming 360
• Fewer moving parts to break
• Inherent low vibration
• Cost effective

A visit to www.rotaryaviation.com will leave you convinced of the merits of flying a rotary engine.

 

The Subaru conversions were rumored to have insufficient HP for a while, but one visit to www.eggenfellneraircraft.com should convince you otherwise.

 

As far as other auto engine conversions go, they just need to hit the magic HP+weight combination so that they're comparable to a Lycoming. In other words, a Chevy V8 is likely too heavy to allow the nose to remain down without 500lbs of ballast in the nose.

 

I think that many builders and flyers choose Lycomings because they want to get in the air more quickly. There's also the established infrastructure of suppliers to recognize.

 

Initially I thought that a rotary would be the only option for me, but with quite a few years of time left for me to decide, I'm keeping all options open. When's that Honda engine coming out?

[Len Evansic]

Initially I thought that a rotary would be the only option for me, but with quite a few years of time left for me to decide, I'm keeping all options open. When's that Honda engine coming out?

I'm hoping for the Honda too, but came to realize that the pent-up market demand will make this engine not too affordable in the near future. When you look out there at the turnkey (converted or new) engines, it appears that the price range is from $20,000 - $75,000. I'd be willing to wager that the Honda will fall into a $35,000 or higher price after a year on the market. Rotary is my next-best bet for the reasons you cited, since I don't want the vibration and noise of a typical Lycoming. engine.

 

I guess my worry about the rotary is with general reliability and hassle. It can't come close to the cooling efficiency of a conventional engine, because it doesn't have the necessary surface area for the coolant to extract heat from. A good external cooling system could cause problems by dropping the coolant temperature too much, inducing thermal shock. I also don't want to be mixing fuel and oil like I would for a chainsaw or weedwacker.

 

-- Len

[Nathan Gifford]

I am curious about the automatic oiler just like Levansic is about the oiler.

 

Thanks

[CBarber]

Dang it!!!! I just typed out a long detail explanation of the oil injector thing and a couple of othe rotary points....then my 'puter farted and I lost the post.

 

Go to my webpage at www.LoneStarVelocity.com nad then go to the "engine" link for some good links to rotary information. As mentioned there is www.rotaryaviation.com . Also, www.flyrotary.com and Paul Lamar's pages at http://home.earthlink.net/~rotaryeng/ACRE.html . Paul has some very strong opinions <g>...but some of his basic papers are VERY informative. Also, John Slade, afaik, still moitors this list as well as the other canard forum. He has flown his turbo rotary.

 

Good luck.

 

All the best,

 

Chris

[mtorzews]

Quick answer to the oil thing.

 

This may not be completely acurate but close enough.

 

All engines need oil on the compressions seals. Piston engines put oil on cylinder walls when the piston is up from the big oil reserve below it. When the piston comes down the oil on the cylinder wall lubricates the ring to wall interface. The ring also wipes most of the oil away so that little is burned.

 

Rotary engines don't have the ability to apply oil to the wall. The backside of one combustion chamber is another combustion chamber. The engine needs oil for the apex seals (equivalent of rings). The only way to get oil there is to have it come in with the gas. Car people don't want to add oil to thier gas so Mazda has an injection system that injects crank case oil into the gas. Rotarys burn more oil than piston engines.

 

Now one the faults of the rotary is poor apex seal life. The reason is crankcase oil doesn't mix well with gas, and there isn't enough oil injected. (too much injected hurts emmisions and oil consumption). 2 stroke oil is designed to mix with gas. You can improve the engine life and reliability by removing the oil injection and adding 2 stroke oil to the gas. Rotary race cars and planes typically do this. There is also a add on oil injection system that will inject 2 stroke oil from a seperate tank. But it doens't make sense to me. Its just as easy to add oil to the gas tank as the oil tank. And adding oil to the gas eliminates a system could fail.

[Len Evansic]

...You can improve the engine life and reliability by removing the oil injection and adding 2 stroke oil to the gas. Rotary race cars and planes typically do this.

Thank you very much for the explanation! This is definitely helping me to wrap my brain around Wankel engines.

 

Now more questions. So how much does this improve the life of the engine? How much oil needs to be added to the gas, and is it available at most airports? Does this mean that there is no oil in the crankcase, or whatever you call where the crank passes through?

 

I've seen quite a few articles talking about oil consumption on Lycoming engines. Does the rotary use more oil than a Lycoming typically does? I know this last one may look like a troll for an apples to oranges comparison, but I am curious about this as gas and oil are necessary consumables.

 

-- Len

[Nathan Gifford]

Does the oil seperate out if it is left in the fuel too long? Also, how hard is it to get 2-stroke oil at an airfield? Do you carry a bunch with you?

[David Staten]

Thank you very much for the explanation! This is definitely helping me to wrap my brain around Wankel engines.

 

Now more questions. So how much does this improve the life of the engine? How much oil needs to be added to the gas, and is it available at most airports? Does this mean that there is no oil in the crankcase, or whatever you call where the crank passes through?

-- Len

The standard "mix" as I am hearing others use is 120:1 ratio.. this is approx 1 oz of oil to a gallon of gas.

 

Remember that the stock rotary injects and burns CRANKCASE oil that it siphons off the pressurized oil system and places in the oil injection system. A diagram of the oil system is depicted in the Hayes Mazda RX 7 manual. The oil that is used in the crankcase is NOT intended to be burned and is NOT clean burning. The resulting soot/carbon deposits from this BURNED injected crankcase oil is one of the leading (as related to me) causes of wear in the Mazda 13B engine. This soot builds up in the apex seal grooves and causes the seals to not be able to spring back and forth properly, causing increased wear, loss of compression and the such. Mazda chose to go with this system instead of adding a 2 stroke oil tank plumbed separately for apparent marketing reasons (what do you MEAN my $40,000 sports car has a "two stroke" engine in it, and that I burned it up by not keeping that oil tank full"???)

 

Two alternatives are presently kicked around... The easiest is to simply remove the oil injection pump, the injector nozzles and their air tubing and simply add 2-stroke oil to the fuel in the prescribed ratio. There is a margin of error here depending on how much fuel you add and how much oil you add, but I should think erring on the "too much" side in oil quantity is not as critical. For a velocity with a 60 gal fuel load, thats 2 quarts or so of oil for a fill up of gas. Carry a gallon with you at all times and you can fly a full tank away and a full tank back and not have to sweat finding it at the FBO. If you need it bad, you can take a crew car to a 24hr Walmart and get SOMETHING to get home on.

 

The more complex but "purist" approach is that taken by the racers. They use the stock oil pump but have a diverter that siphons oil from a separate gravity feed tank filled with clean burning 2 stroke engine oil. The pump controller in stock form is linked to the throttle linkage, so full throttle = full oil injection. I am hearing that people flying with this type of oil injection are disabling linkage (which would be complex, if practical at all - custom intake systems) and wiring the pump in the 3/4 to full open position. This doesnt really cause a problem, since the majority of aviation flying is at a steady, high power setting, so the oil flow is being permanently set to match the average power setting. For the Velocity that Chris Barber is building (and I am rebuilding the engine for) I figured that a 5 quart tank on the firewall would suffice (a full tank of fuel to fly away, a full tank to fly back, and half a gas tank's worth of reserve injection oil)

 

In using either of these alternatives, the passage from the engine's oil system to the oil injection system is plugged, and the engines oil system operates normally otherwise. Keep in mind that the "oil injection pump" is a separate beast from the "engine oil pump". Roughly, oil flows from the pan, to the "engine oil pump" to the oil cooler, to the block and oil filter, THEN is distributed to the rotors, shaft, turbo and bearings, before falling back into the pan. If properly built and not abused, using the separate oil injection system should result in MINIMAL to NO engine oil burning and as a result you shouldnt need to top off the engine oil in the pan regularly, rather only need to change it at regular intervals.

 

Chris Barber, who posted a few posts ago, had some links to follow. Some of these will lead to a WEALTH of information, both practical and theoretical on the wankel/rotary engine in aviation use. Biggest benefits of the rotary appear to be minimal vibration (compared to aviation engines), overlapping torque pulses (again, less vibration), only 3 major moving parts (no cams, valves, lifters, rods) and few catastrophic failure modes. I am aware of a few engine failures with the rotaries (which I attribute to growing pains, such as testing turbochargers) and so far all of them were able to develop partial power until landing.

 

I am rebuilding the engine for the Velocity project after doing lots of research, have access to the Hayes AND mazda shop manual, have the tools to measure out all the tolerances, and am replacing ALL the seals/springs/wearables. By using 2 stroke oil, I am hoping that come time for the next "rebuild" that there will be minimal carbon fouling found when we tear it back down. Not even sure what to plan on.. we will follow compressions and not rebuild until needed.

 

Total cost for the engine so far: $700 for THREE used J-spec mazda 13B turbo engines (without turbos.. jspec means approx 40K miles and REMOVED from service). A factory new renesis RX8 engine would be about $5500. Few hundred $$ for tools that I did not already have (air tools, dremel, engine stand and hoist come in handy). "Master rebuild kit" with seals from Bruce Turretine or Tracy Crook $900 range (yet to be bought). Count on another $2000 for EFI/engine monitor and another $3000 for a lightweight PSRU (gearbox... engine runs 6000 rpm, prop runs 24-2800 rpm). Contrast this to a 200 hp lycoming costing NEW > $25,000.

 

Also, running auto gas at whatever its current cost is (usually a $1/gal less) than avgas. You can add a lead scavenger soln to the fuel tank if you have to fuel with avgas away from home. You can use www.airnav.com to find autogas vendors on airports.

 

Hope I gave you some good information.

Dave Staten

[mtorzews]

David Staten gave a much more thorough (and better) answer than I did, but missed Nathan's question.

 

2 stroke oil is designed to stay in solution with gas. It won't mix out.

[CBarber]

LOL, Dave is good at that......he should run for office. He and I both have a knack for "over answering" questions. But I have an excuse.....I am a lawyer

 

All the best,

 

Chris

[Len Evansic]

Chris, Dave, and Mike,

 

Thank you all. Rotary is definitely starting to look more attractive to me now. I wish there were some sort of long-term reliability registry for auto engines and their reduction units, but I guess that's why these planes are experimental.

 

Now if I can get someone to answer my questions in the Subaru forum...

 

I guess I'll go to check on the crickets.

 

-- Len

[Nathan Gifford]

David,

Thanks for the concise explanation and everyone else on fuel mix. I can now see why people remove the oiler.

 

My other question is what does Jon Slade use? Also, how do you add the oil? A little at a time or just dump it in and fill?

[David Staten]

David,

Thanks for the concise explanation and everyone else on fuel mix. I can now see why people remove the oiler.

 

My other question is what does Jon Slade use? Also, how do you add the oil? A little at a time or just dump it in and fill?

Slade premixes in the fuel tank. And I do not have any idea just yet how he accomplishes the mix. He has a contact link on his webpage at www.canardaviation.com.

 

Dave

[Jon Matcho]

This does bring up one of the not-so-good points about auto engine conversions -- the need to use automotive fuel ("mogas") instead of 100 low lead airplane fuel ("avgas"). I understand 100ll is going away in a year or two, but do not know whether the replacement will be something that my car engine would like.

 

I think it's a major PITA to have to worry about logistics for filling your tanks with "mogas" when it's generally unavailable at the airport. Eggenfellner talks about 100ll in their Subaru engines working fine, but I haven't seen much talking about 100ll in rotary engines.

 

The rotary-oil issue is not as bad, but still has its challenges. How do you really know how much oil to mix? The 2-stroke analogy is also good -- poor 1/2 required oil into tank, fill half tank w/gas, poor remaining 1/2 of oil into tank, fill tank w/remaining gas. Mix thoroughly. (?)

 

Anyone care to shoot down these concerns to keep an automotive conversion appealing for me?

[Nathan Gifford]

In most auto engines lead can do two things: Coat sensor components and alter their performance; render the catalytic converter inoperative.

 

The old lead acted like a lubricant and octane enhancer in bygone years. Over all, if the stuff does not kill the seals or instrumentation I believe the engine will do just fine.

[CBarber]

AVgas CAN be used in the Wankle rotary. It can even be MIXED with MOgas. You are not gonna be stranded. If memory serves the only drawback will be you should clean your plugs a little sooner since some of the ingrediants in Avgas can foul the plugs sooner. As a matter of fact ther is a Hydrogen Wankle (Mazda prototype only) and talk of it running on Deisel.

 

As to adding oil to the fuel, IMHO, this is much about almost nothing. For a MINIMAL effort, you get a cleaner, longer running engine. It is my understanding that the EXACT mix ratio is NOT a big issue (within limits). Those who do it still debate on the subtlties of the exact amount. I THINK I have read that there have been cases of even skipping adding it with no ill effect. Of course, I am sure that would have been an isolated incident. Doing so repeatedly would surly damage the engine.

 

I applaud your efforts to become informed and as you gain insight to move on. Too many folks, I feel, will "major in minor" issues as oppossed to fitting the information into the big picture. Adding the oil seems to be much less a pita than some of the issues that Lycosourus owners must put up with....like cracked cranks, split valves and EXPENSIVE parts (and labor).

 

BTW, when I first started flying in 1977 (first 3 lessons at 16 yrs old...did not get licensed 'tilll 83 and then did not fly for years due to being a professional student), they were warning of the end of LL. Back then they said it would not be available in a "couple" of years. Ok, that was 27 years ago and we still have it. Now I do not mean to imply that it really won't finally go away (esp. since I think there is only one manufacutruing plant producing it today), but your Wankle choice can reduce the impact.

 

YMMV.

 

All the best,

 

Chris

[mtorzews]

John slade poors the oil into the fuel tank. For a 1 gal to 1 oz ration add 20 gallons fuel then add 20 oz of oil (I don't know the ratio he uses though). The oil mixes immediately with the fuel. No need to do anything else.

 

He carries a gallon of oil in his plane for fuel up time.

 

For in depth answers join the rotary mail list.

 

http://lancaironline.net/lists/flyrotary/List.html

[David Staten]

In most auto engines lead can do two things: Coat sensor components and alter their performance; render the catalytic converter inoperative.

 

The old lead acted like a lubricant and octane enhancer in bygone years. Over all, if the stuff does not kill the seals or instrumentation I believe the engine will do just fine.

Aircraft use of automotive engines at this time are exempt from the use of catalytic converters, since they are "off road" and not licensed for use on the public roadways. So, no worries about using 100LL from that standpoint.

 

The other biggie is the coating of the oxygen sensor in certain EFI engines There are some high dollar O2 sensors that are resistant to this effect, and there are some EFI's that do not utilize an oxygen sensor to determine mixture (Tracy Crook's EC2 being the primary example in my mind, but there may be others). Some EFI's use the sensor for "setup" and once set no longer require an O2 sensor. So, that issue is not a biggie either, if you plan for it from the beginning.

 

Lead fouling of plugs can be a problem, but i believe there are scavenging agents available that can help with that problem. Also, simply having a well adjusted mixture can prevent the buildup of lead deposits (just in the same manner that you lean during taxi to prevent fouling with lyc/conts).

 

Fueling logistics present a valid issue: Mogas is not routinely available at airports. At the few airports that it IS available, its not that much cheaper than Avgas (ON FIELD) except in a few isolated locations. Airnav is not a good source of who really has Mogas, since SOME fields show it as available on search, but closer review shows that its not available on the field at the FBO.

 

However, looking at the mission profile for the Velocity I would anticipate that much of our flight will be within the round trip capabilities of the aircraft. That eliminates fueling out. I will gladly pay a ramp or tie down fee for the gracious use of someones facilities, if I am not inclined to buy their fuel. On the cases where we have to fuel "out", Avgas is not incompatible with the engine's innards (we aren't using an oxy sensor) and can mix without issue.

 

Something I am contemplating but have not had a chance to discuss with Chris Barber just yet (remember, I'm doing the engine for his plane) is the possibility of obtaining a Rushce/Fuelman type card account, and a few rubberized bladders (similar to transfer tanks/ferry tanks). This card account is a fleet fueling account system I used to use when I worked in EMS and Fire Depts. Its not limited to one brand, and its pretty universally available. I am already considering the installation of a transfer tank in the bed of my pickup truck for fueling the aircraft and would need to plan on a fuel card system of some kind anyways. In my case, most of the LONG trips I would be taking would be overnighters or longer, usually to see somebody I know, and it would not be a big deal to use a few small (10 gal) collapsible transfer tanks to get fuel from outside the fence and bring it to the aircraft. Once empty, roll em up and stuff em.

 

I admit it sounds like a bunch of work. But.. Super U/L costs $2.00 a gal in Houston. It wont take a lot of fuel purchases for this system to pay for itself with regards to Avgas. On a tight schedule? In a hurry? Racing the Weather? Then screw it, and get the blue stuff.

 

The reason I keep mentioning a fuel account of some type comes back to one key issue: an airplane is an "off road" vehicle. It is not licensed to operate on the roads. Therefore it's fuel does NOT need to pay state and federal fuel tax. When I set my former vol fire dept up on a fuel card account, the sales rep told me that any off-road engines could be fueled tax-exempt: generators, separate pumps (not part of the fire engine..etc). In Texas that amount comes to 38.5 cents per gallon. So, Super unleaded into the plane at a current cost of $1.60/gal.

 

Transfer tanks can be as simple as some plastic marine tanks in the bed of a truck, to a 50 gal metal tank with attached pump, nozzle and cover. Stay under 55 gals unless you want to bust DOT rules (CDL, placards, etc). Tanks over 55 gals must be plumbed into the fuel system of the transporting vehicle as "aux tanks".

 

So.. how much convincing do you need to be able to fuel your plane at your HOME field for $1.60 a gal and still be able to use the existing 100LL infrastructure when you must?

 

Sorry for the long winded diatribe.. its what Im good at.

Dave

[CBarber]

Dave,

 

Nice post.

 

Chris

[David Staten]

Today I tried to put my "money where my mouth is" and it appears that the "Fuelman fuel card" approach is not going to work for me.. not enough projected volume and they actively discouraged my application. I followed up with Chevron/Texaco.. the most likely brand to be used locally.. and their fleet card setup does not allow for what I was envisioning. It appears that what I was describing (with the tax removed on the front end) was something these card services only offered to governmental entities (such as the fire dept I was working for).

 

I did some additional digging and it appears that from a FEDERAL standpoint, for PERSONAL use there is no deducting the 18.4 cent/gal federal excise tax on gasoline. There are specific conditions that DO apply to both autogas and Avgas that apply to certain business and nonprofit situations (flight schools??). The Federal Guidelines can be found at http://www.irs.gov/pub/irs-pdf/p378.pdf

 

The STATE portion of the fuel tax.. 20 cents/gal in Texas, however, appears to be WHOLLY refundable if autogas is used in an aircraft. I will be subject to recordkeeping requirements with regards to an audit trail, but essentially I save my reciepts and fill out a reimbursement form and submit to the state comptroller. This actually works to my benefit since I can get the best fuel deal available (within quality limits) and then get the refund on top of that. Your state may vary.

 

I envision having a credit card used SOLELY for fuel and or airplane use, perhaps a "one card" fleet card system that can give a detailed reciept. I might be charged a few cents/gal for this priveledge but even 20 cents / gal discount is significant.

 

I will mention this to one of the local flight schools who has been running mogas in part of their fleet, and been paying cash at the pump into their transfer tank.. he may be able to claim both state and federal taxes.. and he uses at LEAST 100 gal/day mogas.. thats over $10K in combined tax load he may be able to get back.. I know he could use the help, and maybe his tax man will agree that its kosher.

[karoliina]

Interesting talk about tax deduction since I live in a country with insane gasoline taxation and therefore gas in my country (Finland) is very

expensive.

 

Yesterday the car fuel was cheap, I refueled my car and the fuel

did cost 1.102 euros per liter. 1 gallon = 3.79 liters.

Euro is about 1.26 USD. Therefore we can calculate how much it did cost

with your terms:

3.79 * 1.102 * 1.26 = 5.26 USD per gallon (and I consider it cheap).

AVGAS is becoming more expensive and it's price is expected

to increase by 100%. What if a gallon would cost more than 10 USD?

Your friend used 100 gallons per day gas, how he would liked if

that would have costed for him 1000 USD per day? Yes, that indeed

is going to happen in Finland.

 

Because of the high gas price here, I am especially interested in

alternative engines to Lycosaurus. Lycosaurus produces a very little

power compared to its enormous thirst.

 

Also, because of this, using an aerodiesel engine would be a very good idea

too except that the aerodiesel motors are very expensive (purchase price)

if compared to a auto motor running on gas (such as the RX7/RX8 motor).