Which Engine???

[skippydiesel]

Isn't a high bypass fan jet engine just a ducted fan with the power core, a jet engine ??

 

 

[turboplanner]

Perhaps the future of the Wankel is ceramic (in whole or part) or some other high tech material(s).

In the 1980s ceramic were talked about like autonomous cars are talked about, and we were very excited about never ending engines, no more overheating issues etc. and it all fell apart at the installation stage where ceramics were cracked during the installation process once some serious numbers became involved, and it became clear replacement in the dealer networks was not going to be financially feasible.

 

Back in the late 60's my best friends father had an NSU RO80 - as you infer it did need an engine replacement at rather short intervals but I now realise that this was because 1. the rotor tip seals had a short life and 2. there were very few technicians around to replace them. The solution was to replace/exchange the whole engine with a reconditioned unit (any 1/2 descent mechanic could do that).

What a pity NSU went out of business; their small cars (under 1 litre) were world leaders in performance,

 

My (agree limited) understanding is that the latest generation of Mazda rotaries can expect a similar service life to conventional piston engines.

I haven't been following the progress, but that would be good; my RX2 was a very exciting car for highway driving, and perhaps they have tailored the engine with bigger capacity, less top end power, and the power band coming in lower than 4000 rpm. Also, we don't travel at the trip speeds we were allowed to get away with in 1970, and I suspect even the RX2 would have had a much longer seal life at todays legal speeds.

 

One other teleology that didn't go far (in small aircraft) was the ducted fan - Question if you mated a non/minimal geared rotary with a ducted fan would you have a viable propulsion unit?? (might get over the tip speed limitations of a conventional prop and make use of all that high rpm)

I didn’t have any tip failures in the 80,000 miles I did; Ducted fans are very noisy, but if you got around that and the need for a full size water cooling system incl radiator and fan, you would just have to deal with the o ring seal failures. These allow water into the combustion chamber but in my case I learnt to pick it up early and limp home, or in one case blow sr

 

 

[mnewbery]

In the 1980s Kyocera Ceramics rocked up at a trade show with a 50cc all ceramic engine. They claimed the only parts that were metal were in the ignition ... Ironically one metal part was the spark plug thread which they also made.

 

They claimed the engine never needed lubrication and would happily run on regular unleaded petrol. A similar story with a model based on the Yamaha XJ600 engine in 1992 but this one only used ceramic main bearings and soot from the engine as a lubricant.

 

The issue I documented in my university assignment was that the tiny voids created in the ceramic during the large scale manufacturing process couldn't be economically got rid off. These voids are a result of using a pug mill originally designed for making plastic parts. The voids were causes by gas bubbles in the mix. Placing the ceramic mix under vacuum for a few weeks might have helped. One microscopic void in the wrong place stuffed the whole part. Another issue was that the ceramic parts weren't elastic like metal until at operating temperature so they were easy to damage if mishandled.

 

Looking back, if Kyocera had been successful it would have been an environmental disaster because the parts could not be recycled.

 

Ceramic coated piston crowns and 3D printed parts (blisks and blings for example) have mostly obviated the advantage of large individual ceramic components.

 

 

[turboplanner]

My point exactly. Apparently its ok for you to bring it up. When I do it some tosser starts calling me names

Wide Open Throttle in itself isn't an issue other than something vibrating loose or flying apart, but that can usually be redesigned.

I built one race engine for a maximum 10,000 rpm and another at 12,000 and nothing ever came apart due to rpm.

 

Power demand is the issue; if you think about it, compressing air produces heat, and high temperatures cause most major issue.

 

High temperatures can be mitigated by Intermittent Power Demand applications.

 

Examples include:

 

• Small engine cars in Urban applications
   
   
  
• Trucks doing local deliveries
   
   
  
• Chainsaws
   
   
  
• Motor cycles being ridden with speed limits
   
   
  
• Cars being driven within speed limits
   
   
  

 

 

As soon as the power is demanded combustion chamber heat rapidly builds up, but as soon as the throttle is lifted the temperature quickly drops, so these applications today rarely figure in engine failure discussions.

 

When you take one of these engines and put them into Constant Power Demand applications, this cooling relief isn't available and there can be upper cylinder problems

 

Examples include:

 

Long Distance Highway trucks - example California - Arizona - Texas, where semis cruise in overdrive at 100 - 120 km/hr with only a few situations giving relief down through the gears

 

Race cars

 

Boats

 

Aircraft - operates in a plug of air pushing wind out of the way all the time

 

Stationary Engines

 

Engines purpose-built for constant power demand have SOME components which are different. The target is to get reliability at Constant power Demand

 

An Intermittent Power Demand engine, when put into a constant power demand application will keep getting hotter and hotter until upper cylinder components rapidly wear or fail. The example on the left shows the temperature increase curve. Sometimes the curve rises more slowly, sometimes the temperature may stabilise in the fail area, too late. Sometime the temperature rises so fast (within a second or two), that you don't have time to get your foot off the throttle before the bang.

 

A Constant Power Demand engine has something like the pattern to the right, where the temperature rises when the load comes on, but the cooling design kicks in safely under the fail point, and from there maintains a constant combustion chamber temperature hour after hour.

 

Combustion chamber temperatures can rise to 1500 degrees C, so you can't measure or predict them with exhaust gas or cylinder head temperature probes.

 

Constant power demand engines can be tested to live out the expected constant load on a dyno, but usually in applications like light commercial vehicles or trucks they tow a dyno trailer.

 

 

In my own race history, I have a museum starting from pistons melting every second race, seizures, etc going down through the years, and finally using fuel which took me to an engine life of two seasons. However RA aircraft are fuel limited, where I was not.

 

 

[bushcaddy105]

Does anyone know how to take the weight off the ea-81? I recently had someone say that one guy had it down to 165lbs with the 40 lb re-drive on it. That would be in the rotax range.

If this amount of weight reduction was possible, I would have done it long ago. Even without an alternator and using exhaust stubs and with an aluminium flywheel (not recommended IMHO) I can't see that 165lbs is possible.

 

 

[Jethro Belle]

The classic statement.Anyone here aware of how an engine is "designed" to accomplish certain parameters, or are you all just parroting previously parroted information over and over?

To challenge accepted wisdom is healthy, to ridicule those who believe it is more than expressing humble opinion. I qualified most of my comments and stand by them. I have thermodynamic mechanical lecturer engineering background, plus over 40 years of working on auto-engines, so feel able to post. Your post reminds me of students I taught who "knew everything".

 

Like you I am hoping that those who have done conversions or have greater expertise/experience are good enough to post corrections.

 

If you take a car racing (unless it is exceptional) you upgrade a heap of things including cooling. The conventional wisdom ensures cowboys (if they listen) don't bolt a motor straight out of a car into an aeroplane and expect it the be reliable and have a long life. It does not say you can't start with one and modify it up to work in an aircraft (The questions are: 1) Is is worth it? 2) Is it safe?).

 

Everyone who has followed various aero-conversions with interest knows only a precious few live up to what is claimed in the original press coverage, and even less continue in production today and those move away from their automotive origins each 'upgrade'.

 

You are correct that many car engines have been converted for use in experimental aircraft where safety is not highly process regulated and those doing it take the risk. Those transplants targeted are exceptional engines (most older car engines were not suitable) I am not sure what your point is.

 

This one makes me chuckle, I can just see the Rotax Engineers, designers of some of the highest specific hp modern production engines in the World, assembled at the meeting after the decision was made to build an aero-engine (4 stroke), looking over the design parameters, and one of them puts a hand up: "Excuse me, what exactly is a 'pushrod'?...."

Of course the sad side of that is the engines that Aero don't get from them as they are smart enough to build for the Luddites and not what they can actually build.

My understanding is the Rotax Brand originated from snow-mobiles, which I place in the high performance motorbike class. Where is the humour The fact that Rotax (who have proven themselves to know what they are doing) have chosen push rods shows that decisions must be based upon sound engineering, not pulp-fiction SciFi. What is your conspiracy theory about what Rotax is holding back? Something Bill Gates said? I notice Bill Gates made a big loss on the EcoMotors deisel.

 

I am inspired by those who have successfully used auto-derivatives in aircraft, but do not underestimate how hard it is to make it safe, reliable and long lived. I suspect if the time and modification costs is fully accounted for, those who have done it from scratch will say a Rotax/Lycomtinental would have been cheaper. If you are building to an existing proven conversion, you will be financially in front on capital cost and probably fuel cost or you wouldn't do it, but IMHO you are part of the test pilot elite.

 

I am considering VW conversion aeroplanes, so I am in no way ridiculing anyone who flies behind an 'interesting' engine. If I do go that way I want to have the risks correctly identified so appropriate mitigation back to better than Rotax/Lycomtinental level (my target: not imposing on others who like riskier lives) can be implemented.

 

 

[Jethro Belle]

I built one race engine for a maximum 10,000 rpm and another at 12,000 and nothing ever came apart due to rpm.

Impressive Did you do the calculation about how many tonnes force the piston-rod combination was placing on your cranks at that speed?

 

 

[turboplanner]

Impressive Did you do the calculation about how many tonnes force the piston-rod combination was placing on your cranks at that speed?

LOL, I geared the engines to that, and reverse engineered them until they lived long enough.

 

 

[Jethro Belle]

I didn’t have any tip failures in the 80,000 miles I did; Ducted fans are very noisy,

 

I think @skippydiesel was referring to tips going supersonic noise, rather than them failing mechanically. I too thought ducted fans could be made quieter than a prop, but according NASA JPL Tech-Report 32-7462" A Review of Aerodynamic Noise From Propellers,Rotors, and Lift Fans" by Jack E. Marte 1970 so you are correct!

 

source: JPL TechReport 32-7462

 

The difference is not great, and I suspect the 'higher frequencies' from ducted fans may be easier to exclude from a cockpit. I suspect reduction in tip noise is less than jet turbulence noise increase, so maybe a wavy exit nozzle as appears on some modern Turbo jets may help.

 

Does anyone have first hand knowledge? I only know my RC electric 'jet' whines, unlike my RC electric prop aircraft.

[Old Koreelah]

Bugger. The dream aeroplane I always wanted to build has a ducted fan behind the cockpit. As well as efficency, I expected it to be less noisy than conventional props.

 

 

[Marty_d]

I am considering VW conversion aeroplanes, so I am in no way ridiculing anyone who flies behind an 'interesting' engine. If I do go that way I want to have the risks correctly identified so appropriate mitigation back to better than Rotax/Lycomtinental level (my target: not imposing on others who like riskier lives) can be implemented.

One thing I often hear about VW conversions is "overheating".

 

 

[skippydiesel]

I think @skippydiesel was referring to tips going supersonic noise, rather than them failing mechanically. I too thought ducted fans could be made quieter than a prop, but according NASA JPL Tech-Report 32-7462" A Review of Aerodynamic Noise From Propellers,Rotors, and Lift Fans" by Jack E. Marte 1970 so you are correct!

[ATTACH=full]61425[/ATTACH]

source: JPL TechReport 32-7462

 

The difference is not great, and I suspect the 'higher frequencies' from ducted fans may be easier to exclude from a cockpit. I suspect reduction in tip noise is less than jet turbulence noise increase, so maybe a wavy exit nozzle as appears on some modern Turbo jets may help.

 

Does anyone have first hand knowledge? I only know my RC electric 'jet' whines, unlike my RC electric prop aircraft.

 

To be honest I hadn't even considered the noise factor - my suggestion was based around the earlier comments regarding a Wankel requiring a heavy/complex reduction drive to bring prop speed down - why bring the prop speed down if it can be operated like a fan jet (ducted fan)?? For greater utility it may also be possible to locate engine oi/coolant cooling systems in the duct. As a non engineer I understood that the ducting around a high by-pass fan jet increases efficiency ??

[Jethro Belle]

One thing I often hear about VW conversions is "overheating".

 

Yes, and other things. To mitigate risk on such an aircraft you would need to seriously avoid Tiger country or do serious/regular engine checks/upgrades or run something like the hybrid Axter or the Pipstrel system. A BRS would be on my list to consider, plus some AAI MOOC CREEP crash survivability upgrades. That is why I am not rushing into anything, as figuring it all out will take me a while.

 

Cooling seems to be hot topic of discussion on relevant forums I have read, however I am not sure it is particularly worse than other air cooled engines, is it? A matter of getting your cooling air-flow set up correctly, and that is not really the engine.

 

Of course if the VW output has been significantly increased over stock (it has to be), it would be running into the heat dissipation limits as has been well explained by @turboplanner.

 

What is your take Marty?

[Jethro Belle]

Bugger. The dream aeroplane I always wanted to build has a ducted fan behind the cockpit. As well as efficiency, I expected it to be less noisy than conventional props.

You mean like an RA version the Edgely Optica or the Ligeti Stratos? The Optica was claimed to quiet (see the linked article and Utube videos). I am with you, because small RPT turbo props seem to make more noise than larger Turbo-Jets, but the paper I found suggests otherwise, so cannot be ignored without sound reasons.

 

In the case of the Optica the duct is 'propeller' sized, so I think it controls tip noise without generating much jet turbulence. You are however pulling a lot more drag and weight with a duct that size.

 

A rear mounted engine puts the noise behind you and a duct will avoid stone chips so it has merits (unlike the Long-Ez) . Crash survivability with the engine behind you needs considering. A ducted propeller is safer on the ground.

 

 

[Jethro Belle]

To be honest I hadn't even considered the noise factor - my suggestion was based around the earlier comments regarding a Wankel requiring a heavy/complex reduction drive to bring prop speed down - why bring the prop speed down if it can be operated like a fan jet (ducted fan)?? For greater utility it may also be possible to locate engine oi/coolant cooling systems in the duct. As a non engineer I understood that the ducting around a high by-pass fan jet increases efficiency ??

Yes, good thinking, but efficiency drops at RA air-speeds as the 'propulsion disk' reduces in diameter. The duct weight offsets some/all of a gearbox weight and a G/B allows a larger (more efficient) prop diameter.

 

Placing equipment in the duct may look neat, but it will be in the highest velocity region = high drag. Ducts around the fuselage doubles the area exposed to high velocity so more drag.

 

Turbo-fans work as a unit with the high pressure jet in high velocity aircraft. They generate significant pressure differential, and to my understanding that is when the duct becomes effective by avoiding tip re-circulation, especially at low speeds such as on take-off.

 

Original turbo-fans were direct drive from the power turbine. Striving for increased efficiency has seen gearboxes added to drive larger bypass fans in the high-bypass designs filling the gap up to turboprops. My understanding is the turbo-props don't do near sub-transonic speeds (probably because the tip speed must be kept subsonic).

 

I have done almost nothing with jet engines (undergrad thermo-labs and theory) so hopefully someone who is can post. They are an engineering field in their own right.

 

 

[Old Koreelah]

I also like the channel wing concept; it could be designed to protect the prop from stones, and should reduce noise footprint on the ground, keeping the neighbours happy.

 

 

[Jethro Belle]

I also like the channel wing concept; it could be designed to protect the prop from stones, and should reduce noise footprint on the ground, keeping the neighbors happy.

 

Yes it always interested me since I first saw a picture of the Custer as a boy Hellish wing construction. With power on you will get more lift! Never could work out if it was a good or silly idea (ignoring stone chip protection).

 

 

Less complaints abut flying activities was probably not on the inventors mind back in them good ole days.

 

You may like to build yourself the Stealth SSDR Archon SF-1 kit It is @Litespeed mount in his avitar image It is effectively a channel wing even though they call it a flying fueselage aircraft.

 

Or just build a Custer patent number D176839 :spot on:

[Jethro Belle]

Just browsing diesel and electric ( A great idea) progress and notice that development has generated is first statistics.

 

More details can be found here. Basically it is a Smart Car engine in series with a 50 kW electric motor done by Magnus and Siemens!

 

Rather sums up all that my posts have said. Magnus and Siemens should know what they are doing.

 

A Tesla model S in flames on the ground is bad! I hope this doesn't kill it.

 

The Ecodiesel itself may be an interesting option for some. I have good reports from smart car owners They also have a petrol offering 22 hp more for 10kg less!

 

 

[Marty_d]

Yes, and other things. To mitigate risk on such an aircraft you would need to seriously avoid Tiger country or do serious/regular engine checks/upgrades or run something like the hybrid Axter or the Pipstrel system. A BRS would be on my list to consider, plus some AAI MOOC CREEP crash survivability upgrades. That is why I am not rushing into anything, as figuring it all out will take me a while.

 

Cooling seems to be hot topic of discussion on relevant forums I have read, however I am not sure it is particularly worse than other air cooled engines, is it? A matter of getting your cooling air-flow set up correctly, and that is not really the engine.

 

Of course if the VW output has been significantly increased over stock (it has to be), it would be running into the heat dissipation limits as has been well explained by @turboplanner.

 

What is your take Marty?

I'm not sure whether the VW's suffered from incorrect cooling setup or increased output, or a combination. Just seen a number of stories about them, including articles in flying magazines, and most of them seem to end with the owner finally giving up and replacing it with something else. Enough for me to cross them off the list of possibles anyway.

Agree with the BRS in any case. Any engine can fail over tiger country.

[Old Koreelah]

... A ducted propeller is safer on the ground.

That was a major attraction, Jethro. Twin booms also help to prevent people wandering into the spinning prop.

The prospect of having a heavy engine follow me into a crash takes the shine off those advantages, but maybe it could be mounted low with a long belt to the prop shaft...or just go lightweight electric.

 

 

[Old Koreelah]

...The Ecodiesel itself may be an interesting option for some. I have good reports from smart car owners They also have a petrol offering 22 hp more for 10kg less!

A Smart-engined aircraft was on display at Temora a few years back. Neat but expensive.

 

 

[Jethro Belle]

The prospect of having a heavy engine follow me into a crash takes the shine off those advantages, but maybe it could be mounted low with a long belt to the prop shaft...or just go lightweight electric.

Per the Small aircraft crashworthiness thread the consensus was 'pole vaulting' it above your head through clever collapse of the support. Easy for a high or pylon mount, but not an engine embedded at the rear of the cockpit. This is were a @Dafydd infinitely rigid crash cocoon is needed :pizza:Shame he isn't online anymore.

 

My solution is a close mounted twin arrangement, arranged so the engines flick out and around to the side. I like safety through redundancy, as cost/difficulty skyrockets (say exponentially) as you pursue extreme safety of a single failure route. The question is: can duplication be done cheaper than reducing risk with a single fail route design? If duplication doubles cost, then a risk level is reached when it is the best option, but that is a different thread.

 

Two small auto-derivatives made 'safe enough' may well be cheeper than a single aeroengine. To avoid asymmetric thrust I have considered 'clever' duct design etc etc, but it all adds weight and reduces efficiency and I am no genius to think I can do it when so many others have failed.

 

I wouldn't go with long drive shafts. Bugatti proved that wasn't real good. Several aircraft have been designed such that a drive shaft (passing near the pilot) failure would chew up the pilot I have imagined long drive belts. They would have their own slapping vibration issues and require a stiff heavy rigid structure. Of course both could do it and have done it. It is how reliable and safe they are.

 

 

[Yenn]

There are a lot of VW based engines flying. The Corby Starlet was designed for that engine. They are still making them in USA and I believe they are going well. 80hp is achievable. Above that the EA81 Subaru does well.

 

 

[facthunter]

I don't think they are talking about the VW we have seen in planes like your Corby, Yenn. Subaru are heavy & complex (the later ones) and the redrive is always a need to be done well.. If you want to go flying and not fiddling get a RED superior Lycoming . Just a little bit big for our current weights.. Nev

 

 

[Jethro Belle]

I don't think they are talking about the VW we have seen in planes like your Corby, Yenn.

Yes we are, I think (not to fly across Bass straight: Just local fun and practice for low $). That is what powers stock Sonerai. I know there are many installed and it has a long track record (Without it I doubt I would look at the 'Beetle' motor), so I will check proven-builds and statistics if I go that way. I think that motor is a legacy item now, rather than what you (I) would install in a new build.

 

The Corby Starlet is a nice little aircraft and performance specs seem good. Some Starlets have been outfitted with 2180's (75-80 hp) and these cruise at VNE (185) and climb at 1900 fpm. That is upgraded Sonerai territory! I like having the second seat of the Sonerai II, but its fuel tank location worries me.

 

I see Aaron25 "Sonerai IIL For Sale" had cooked the orignal VW motor, so @Marty_d is on the money

 

If you want to go flying and not fiddling get a RED superior Lycoming

I found the LycomingThunderbolt Engine which is red, and red Lycoming from If You’re Looking for Horsepower and Reliability You’ve Come to the Right Place! - Aero Sport Power and Superior Air Parts :: Features and Benefits of unknown colour. What is the RED superior Lycoming you keep mentioning?