Which Engine???

[facthunter]

The Mogas is not a 'controlled" quality product. as Avgas and Jet A1 etc are. If you can't have that it's not suitable by definition. Aircraft parts/

 

fuels/ lubricants etc are required to meet a verifiable standard. Mogas and road diesel can be tampered with..

 

Jethro I don't know what features of the Junkers they have revived, other than opposed piston. I spent years with an opposed piston design but it doesn't have coupled crankshafts. This Gemini engine may be similar to the one I was inclined to go with. I haven't any internal details.. Mine had variable compression ratio. (but I'm not making it anytime soon)… .Nev

 

 

[pmccarthy]

Then how does the FAA approve the Petersen STC for mogas in Lycos?

 

 

[facthunter]

They restrict engines they allow to use it and maybe also what airwork it's allowed to be in.. Mogas is many things, not one constant/ consistent product. If it was allowed for RPT they'd get sued when something went wrong.. If you tell an oil company you are using their mogas they will say At YOUR risk. same with LUBRICANTS. (IF they don't produce a certified oil with a release note). Nev

 

 

[skippydiesel]

Where did all the Wankel's go - long time ago??

 

It always seemed to me that the Wankel has all the attributes needed for a small aircraft engine - smooth, high power to weight ratio, almost unstoppable. Mazda seemed to fix the rotor tip seal issues - so why are they not powering every small aircraft ??

 

 

[fly_tornado]

Rotaries never worked with avgas

 

 

[bexrbetter]

Its back Gemini :: Aviation

 

Gemini :: Gemini 125

 

What do you reckon to that Nev.

The latest owners, about the 27th I think, actually might get something done with it.

 

I spoke to the 2nd last owners about producing it and he, an Englishman, was busy touring Oz on a motorcycle at the time, and was going to get back to me ....

 

When do you predict Lithium battery energy density and safety will match JetA1?

They never will. They are at 25% now, can't ever see them getting past 30%, and if, not when, battery storage ever reach 50% efficiency of fossil fuels, then they will be viable.

 

high power to weight ratio, almost unstoppable.

That is an absolute myth Skippy, go check out what a Rotary actually weighs, 13B or Renesis being the most widely used, and then go look at what one weighs with a redrive attached, then you do the power to weight calcs yourself and, after you have fainted, get back to us...

 

But your not alone, this whole thread should be called Mythdusters with the amount of myths and lores that have been dusted off, once again.

 

 

[Jethro Belle]

My Lycoming runs well on mogas. I don't use it because the mogas caused bubbles at the rivet heads on the tank. It seems that mogas can affect the sealant used when building. Back to using avgas and the leaks were sealed with Loctite 290, but it still looks unsightly.

Thank-you Yenn, I will add aluminium corrosion to my list of fuel issues. Rivets contain cold work stresses making them more corrosion prone (sets up a corrosion cell with the large area of adjacent sheet cathode. Being a small anode results in concentrated rapid corrosion . Extra justification for non-rupturing tank bladders, yes?.

 

I should have included the link with my post = Lycoming - Knowledge Base starting at Unleaded Fuels Part 1 and going to part-4

 

I don't think their concerns cover your corrosion issue. It could be the alcohols content. I know pump-gas can be 'tainted' with cheaper substitutes like the toluene scandal a while back. I imagine some suppliers may not control sulphur very well or someone along the supply chain blends cheaper high sulphur stock. Contents also depend on where the base crude comes from (as evident from the different smells some fuels give, which is from the aromatic content). The bottom line is that quality control for aircraft use is not there. The fuel may be identical in 95% of cases, but you have no legislated assurance, so that unknown 5% is the risk. Even the 10% would probably be undetectable from running your engine on the ground.

 

For engines not designed for poor fuels Lycoming is correct. It is not about immediate engine failure or problems running. Vapour locks in the fuel system are an obvious risk. Low engine power on climb and running out of fuel because uncontrolled high alcohol has reduced the specific energy seem to be the most likely immediate risks you take (IMHO).

 

Also running unleaded in an engine designed for leaded will increase valve-seat recession (all vintage car owners know that). For the low compression Lycomtinentals it was never about high octane. Low compression ratios equal low engine stresses at the expense of fuel economy.

 

 

[facthunter]

They Wankels would be ideal for "proper" sport planes. If they seal well enough to start they will not usually fail in flight. They were used in racing outboards. Fuel economy is not a strong point but is slightly better than a 2 stroke. Mufflers have a big job to do. They are not particularly quiet Turbo charging works. Smaller units can use sun and planetary gearset from auto transmission sources

 

Skippy D, gear driving an alternator is not a good idea It's too "hard" a drive. and shortens rotor windings life. It can be done with rubber incorporated couplers but a simple vee belt does it well enough. Nev

 

 

[Marty_d]

Rivets contain cold work stresses making them more corrosion prone (sets up a corrosion cell with the large area of adjacent sheet cathode. Being a small anode results in concentrated rapid corrosion . Extra justification for non-rupturing tank bladders, yes?

Probably only applies if you have wet wings - most fuel tanks I've seen are either welded aluminium or poly, so rivets don't come into it.

 

 

[facthunter]

Mooney has wet wings with sealant and magnesium alloy spars.. Nev

 

 

[Jethro Belle]

Then how does the FAA approve the Petersen STC for mogas in Lycos?

I suspect the Lycoming Unleaded Fuel pages included in the above post explain how. Lycoming are correctly worried about pump-gas because it is not controlled enough.They define Mogas according to the standard petrol standard plus a few additional controls (tests that the mogas meets a defined level such as vapour pressure). The have certified some of their motors to run on their defined Mogas (I suspect these engines have valve seat inserts). They haven't promoted it widely in case owners rush down the petrol station and start filling with pump-gas.

 

There are some risks with using pump-gas, but like all risk I would guess 95% (wildly speculative) of users will never experience any.

 

I note Auto Fuel STC News | Airplane Fuel News confirms what I stated above about lead. I remember 'nice' grey spark-plugs meant good running

 

With the exception of vapour pressure and reduced calorific value of alcohol, I cannot see why engines and fuel systems designed for mogas (not old aircraft designed for 100LL) would have any problems. I understand the use of pump-gas is widespread within the RAA fleet. Maybe dragging some incident reports may reveal if reduced engine power or vapour locks are an issue.

 

Caveat: Anyone using mogas in their aircraft must make their own risk assessment as my comments are poorly informed opinions of a non-expert.

 

 

[Jethro Belle]

Mooney has wet wings with sealant and magnesium alloy spars.. Nev

Isn't it Mooney that have a bad reputation for wing corrosion, that requires regular inspections? Magnesium in contact with Aluminium is a galvanic cell waiting to happen, so the sealing needs to be better, over many years, than any I know of. Any movement tends to break sealant as it embrittles. Certainly extra concern for any Mooney owners using pump-gas.

 

Any Mooney owners have the facts?

 

 

[Jethro Belle]

Probably only applies if you have wet wings - most fuel tanks I've seen are either welded aluminium or poly, so rivets don't come into it.

 

Hi Marty. I am glad if that is now the case (I suspect RA more than GA). I was responding to @Yenn post #73 and it seems the at least some Mooney models (@facthunter post #86) have wet wings also.

Didn't the F111 have wet wings and the sealants allegedly cause all sorts of cancers in the applicators required to crawl into the tanks to reseal them? Also the Concorde was forced to retro-fit bladders after the flight 4590 crash (Yes: I know that is JetA1 before anyone posts. Yes I know RA/GA are not supersonic before anyone post. The point is that sealing wet tanks against corrosion and leaks is a risk IMHO).

[facthunter]

Lots of aircraft have wet wings. It's less likely in U/L's owing to the way they are constructed. Generally you remove panels and get inside and remove and repair the fairly thick sealant. I know Mooney owners who have done this obviously to save money if someone else had to be paid to do it. Obviously not a fun job.. In service a fair amount of leakage is allowed on larger planes eg Douglas DC-4. and probably many other planes of that ilk. Nev

 

 

[skippydiesel]

They Wankels would be ideal for "proper" sport planes. If they seal well enough to start they will not usually fail in flight. They were used in racing outboards. Fuel economy is not a strong point but is slightly better than a 2 stroke. Mufflers have a big job to do. They are not particularly quiet Turbo charging works. Smaller units can use sun and planetary gearset from auto transmission sourcesSkippy D, gear driving an alternator is not a good idea It's too "hard" a drive. and shortens rotor windings life. It can be done with rubber incorporated couplers but a simple vee belt does it well enough. Nev

Hi Nev:

 

I think you will find that the last Mazda rotaries had vastly improved fuel economy, seal life and mufflers.

 

As a diesel freak I am more than happy with turbo charging - "way to go". I understated it is also considered a positive development in 2/ applications (all sorts of positive benefits not just power) and as the Wankel is pretty much a 2/ it would be a natural for "boosting".

 

My comment on the alternator was more to do with ease of servicing the belt.

 

 

[Jethro Belle]

The latest owners, about the 27th I think, actually might get something done with it.I spoke to the 2nd last owners about producing it and he, an Englishman, was busy touring Oz on a motorcycle at the time, and was going to get back to me ....

 

But your not alone, this whole thread should be called Mythdusters with the amount of myths and lores that have been dusted off, once again.

Can you offer more insight into the Gemini. With modern fuel injection is could work if they can get the power from both cranks combined reliably. They are cleverly combining them as part of the redrive (one component doing two functions to save weight and complexity). If it is the 27th owner it looks more like going the way of the Jumo ! Is it Myth or will it be legendary?

 

The reason I mentioned the Gemini is that it is diesel is that is not quite attempting what is already been successfully covered. I am acutely aware of the weight limitation current diesels impose, and that Jumo stopped production (in a low cost fuel environment), and that most aero-engines bankrupt their creators. Most thread readers may know about Charlie Kenny’s Peugeot turbo diesel Jodel . I haven't read about it in detail, except he seems pretty chuffed with it. My response was I hope their engines don't suffer the bugs their cars seem to

 

I would prefer to fly diesel for safety reasons.

 

 

[skippydiesel]

Rotaries never worked with avgas

If this be true - it would be a positive in my book.

 

 

[fly_tornado]

If this be true - it would be a positive in my book.

all of the documented conversions I could find on the net all complained that the lead deposits interfered with the seals eventually. might go ok if you run unleaded

 

 

[Jethro Belle]

Same with LUBRICANTS. (IF they don't produce a certified oil with a release note).

My reading is that ash-forming additives may foul the spark plugs on aeroplane engines "designed to some burn oil" (I think that is quoting Lycoming). Lycomtinentals run with high piston clearance to avoid seizing because air-cooled heads get hot at full power. I can't see how it closes up the clearance myself, unless the pistons run hotter in an air-cooled engine. Can anyone provide insight?

 

Zinc additives seem to be the main problem, but I understand Zn has been almost eliminated (many think the new high spec oils are not so good because of this) in the new spec oils for catalytic convertor life.

 

 

[skippydiesel]

"That is an absolute myth Skippy, go check out what a Rotary actually weighs, 13B or Renesis being the most widely used, and then go look at what one weighs with a redrive attached, then you do the power to weight calcs yourself and, after you have fainted, get back to us...

 

But your not alone, this whole thread should be called Mythdusters with the amount of myths and lores that have been dusted off, once again."

 

Hi Bex; Couple o points (or more);

 

Given that the conventional piston engine has had a squilian years worth of development to arrive at its astonishing level of efficiency/power of today. I believe just a fraction of this development investment effort would have seen the Wankel rotary eclipse the piston engine. Lets face it, it is a far more "elegant" design with inherent strengths that just makes the self destructing UP- Stop- Down- Stop piston look foolish (much though I love them).

 

The Wankel rotary can rev to astonishing levels (processing air/fuel) to deliver more power than any piston engine of a similar weight - true this then needs to be harnessed through a gear box (weight & complexity) but again with sufficient development/investment this need not be an insurmountable problem.

 

I have seen a back pack sprayer fitted with a rotary engine powered pump - very light and effective.

 

 

[facthunter]

Lead wouldn't be much help as it only works at quite elevated temperatures. That's why it isn't good in the Rotax 912's .Aero oils have additives to cope with lead and the LL100 has something in it (bromine) that causes the white exhaust pipe inner surface you often get when using avgas in vehicles. or aircraft. Mazda are about the only rotary engine builders to get good life out of the seals on the rotors. Norton and Suzuki made versions in motorbikes and the Norton one is used in the Pterodactyl U/L as it is aircooled… the racing outboards must be OK also in the seal department. I've run two strokes on avgas without any problems. (not in aircraft though) but a tech college in Qld got over 1,000 hours from a 582 (I think) Rotax anyhow, without overhaul. This is due mainly to the better separation of the premix from the fuel inside the motor. More oil is left to do it's work. Nev

 

 

[facthunter]

The Lycomings /continentals do run large piston clearances but no more than they need. They have been known to burnish the piston skirts during bed in proves this . Of course the pistons run hotter than the heads. They do in all motors. One method of reducing cold running clearances is to have aluminium cylinders which expand with the pistons reducing the clearance required. When pistons slap around, they tilt and barrel face the rings making them more prone to blow by on load. Good operators use" power on" descents to avoid this with cowl gills closed to keep the engines hot. Looser pistons need more oil to the comp rings to keep the rings sealed also. They do use oil but not as much as some of the older ones did in the 30's. The rotarys used so much castor oil they covered the pilot in it. . Nev

 

 

[Old Koreelah]

...Most thread readers may know about Charlie Kenny’s Peugeot turbo diesel Jodel . I haven't read about it in detail, except he seems pretty chuffed with it. My response was I hope their engines don't suffer the bugs their cars seem to...

I'll bite on that, Jethro. We've had a terrific run from our Peugeots. Their Diesel engines are so good they're used in several other brands. When Chas was planning his conversion there was much discussion of diesels on the Jodel forum. One engineer (who must have worked for PSA) placed a TBO of 10,000 hrs on Peugeot Diesel engines, after testing about a dozen of them to destruction. The first one failed at 12,700 hrs with a dropped exhaust valve.

 

 

[Jethro Belle]

Given that the conventional piston engine has had a squilian years worth of development to arrive at its astonishing level of efficiency/power of today. I believe just a fraction of this development investment effort would have seen the Wankel rotary eclipse the piston engine. Lets face it, it is a far more "elegant" design with inherent strengths that just makes the self destructing UP- Stop- Down- Stop piston look foolish (much though I love them).

 

I share your passion/dream for Diesel I put that in the realm of the possible/inevitable, even if it is a turbo.

 

The Wankel is a seductive design, but it killed NSU then Mazda struggled with it. Always the same reliability limits imposed by physics: seals and thermal loading on the combustion side. I hate to imagine the tribology of the seals screaming through the combustion sector with the lubricant film breaking down due to the wall temperatures (I think @facthunter Nev, keeps warning about most auto-engines not being designed for constant full power output). The elongated combustion chamber on top of the sealing makes limits combustion and high thermal efficiency (most prefer a throbbing V8 with low down mumbo in a big car over a screaming rotary if you get the same fuel consumption. Yes I have rotary friends and understand their thrill of beating V8s.

As a Wankel expert you know all this of course. As an Engineer (or was it Scottie) I know 'ya canna break the laws of physics captain'. I never say absolute never to anything, but unless some new technology is developed that changes those fundamentals, development will not change anything much. If you are chasing diesel then the Wankel with its struggle to keep sealing low compression SI seems the wrong choice (I briefly investigated the idea myself long ago).

 

The humble old, inexpensive, easy to fit, circular piston ring is hard to better for sealing. That is the chief reason we are stuck with the problems of pistons and cranks (achieving a good seal for elongated service proved relatively easy) (IMHO). Wishful thinking about avoiding high accelerations stresses and vibrations ... does not change the reality that without a new technology to seal non-circular shapes, it will not be competitive.

 

all of the documented conversions I could find on the net all complained that the lead deposits interfered with the seals eventually. might go ok if you run unleaded

 

I would never have predicted that. It acts as lubricant/wear coating on exhaust valve seats. Perhaps the high rotor/seal temperatures convert it to an abrasive oxide. Exhaust valves are pretty hot!!!

 

 

NSU owners used to salute each other as they passed on the autobahn. The number of fingers they held up indicated how many Wankels they had replaced Not sure if RX owners continued that tradition

[facthunter]

OK. Even at equating each hour with 100 kms ( 60 MPH) which is hardly a serious HP output, that would be equal around a million Kms for your 12,000 hours is a ridiculous life to allocate to any engine that you might want for a plane... Even Container SHIPS engines only get around 10,000 hour s and they have large wear limits.. Courier vehicles run almost 24 hours/7 and get half a million sort of normally, but they are not working like they would in a plane. Plenty of euro diesels are up there in the weight /power envelope and probably the quality.. You would need an all alloy block based turbo charged engine and all reciprocating parts tend to be heavier than petrol engines of the same displacement.. The time you quote is about one and a half years elapsed time in service. I doubt anyone has done that much testing on any engine. A generating set, compressor or water pump are similar load situations, but not all usage patterns have a max power for 2 to 5 minutes at the beginning of each operating period. Standby generator is similar but their usage is hard on the engines. Life can be quite short.

 

You don't need to go that far for a service life.in a sport plane.. If the engine was capable of a 3,000 hour life RELIABLY that would be enough. Setting a TBO appears to be a lot of guesswork. Once it had some real bearing on what the motor will do. based on reliability in service and approved testing. Today It appears to be a guestimate at best. Nev