Two cylinder gear-less twin aircraft

[Niels]

Some millitary two stroke drone engines are around 15 kg for half a litre.In my scheme there is already a great part of the crankshafting in the generators plus some crankcase and there is no cylinder heads.
Let us say 10kg for the Junkers parts and two times 4 kg for generators to make 30kW electricity.

 

[TFF]

Lead in gas is only there for old legacy engines that are still flying. Although my friends put Leaded aviation gas in their Rotaxes, it is out of being convenient. Rotax prefers unleaded. They use to carry trunk loads of cans but time and mess made them stop. Regular airplane engines can handle unleaded high octane if made in the last 15 years or so. The brands are prepared. They just don’t make that gas’s for economics right now. Governments don’t want duel gas because if one is cheaper, no way to monitor one using the cheaper fuel where not recommended. It’s older engines. If you don’t fly a lot they can last multiple decades in the US where you are not required to overhaul unless a commercial operation. There are probably 50,000 airplanes in the US that still need the leaded gas. It will be a long time before they are used up.

My opinion you are one motor size too small to emulate a Rotax 912. A Rotax taken care of will last quite a long time. Yes it needs maintenance, but like a car they last a long time. 2000 hours recommended, that’s probably 150,000 miles if driven in a car.
The small drone engine life is measured in 100s of hours not thousands. They are disposable.

 

[Niels]

My opinion you are one motor size too small to emulate a Rotax 912.

Sorry for not explaining well enough.
To displace Rotax 912 I propose to use one electric motor that can turn prop with 60kW at 40 rps.
Electricity is supplied by either batteries,fuel cells or two enginerators of ca30 kW abillity each.
Enginerators can have

either

two pistons in one cylinder driving two phase-locked synchroneos generators of 15kW each

or

two cylinder and pistons driving one generator of 30kw

 

[rv7charlie]

While 'serial hybrid' does lose some calculated efficiency in a direct comparison with an 'direct drive' IC engine, I don't think that the calculus is that simple. Realistically, if it were, non-plugin hybrid cars wouldn't work. NASA, and a lot of other public and private developers, are giving it a look, because of distributed propulsion. STOL, maybe even VTOL, with what could ultimately be a simpler system than a helicopter, while keeping the speeds of fixed wing. And with steadily improving battery tech, the engine can always operate at best BSFC, and, by using the batteries as a big 'capacitor', the engine can be a bit smaller, generating more fuel/efficiency improvements.

Or I could be wrong.

Charlie

 

[Heliano]

I came across this thread out of curiosity. Niels knows what he is talking about. There are two positive facts about electric propulsion:
1 - Reliability. A Rotax 912 IFSD (rate of inadvertend inflight shutdowns) is around 7000 hours; an asynchronous electric motor has a IFSD at least ten times that figure, and it is easy to understand: there is only one moving part in an asynchronous motor: the rotor. A IC engine not only has dozens of moving parts but there are thermal, vibration issues.
2 - Operating costs. The cost per hour of an electric aircraft is a fraction if the operating cost of a fuel IC engine. I exchanged a few ideas with people in Australia who run a flight school using the electric Pipistrel. They've setup a clever schema: they have a "battery charging shop" After each training flight they swap the aircraft batteries. The number of students is high because the flight lessons are more affordable, and a propulsion failure is much less likely than a double, simultaneous IC engine failure in a two-engine aircraft.
My humble view is that electric motors are here to stay but 100% electric, battery-based is a temporary solution (like "blue ray" video players were). Perhaps as fuel cells become cheaper and lighter they will become mainstream.

 

[BJC]

I came across this thread out of curiosity. Niels knows what he is talking about. There are two positive facts about electric propulsion:
1 - Reliability. A Rotax 912 IFSD (rate of inadvertend inflight shutdowns) is around 7000 hours; an asynchronous electric motor has a IFSD at least ten times that figure, and it is easy to understand: there is only one moving part in an asynchronous motor: the rotor. A IC engine not only has dozens of moving parts but there are thermal, vibration issues.

You may be 100% correct; however, the total experience of electric motors (and controllers and batteries) operating under flight conditions with a propeller as the load remains minimal compared to the Rotax 912, or other common combustion engines.

2 - Operating costs. The cost per hour of an electric aircraft is a fraction if the operating cost of a fuel IC engine. I exchanged a few ideas with people in Australia who run a flight school using the electric Pipistrel. They've setup a clever schema: they have a "battery charging shop" After each training flight they swap the aircraft batteries. The number of students is high because the flight lessons are more affordable, and a propulsion failure is much less likely than a double, simultaneous IC engine failure in a two-engine aircraft.

Does the EP have adequate range to allow it to be used to meet the USA private pilot certificate cross-country requirements? Not arguing with the success that you report at the flight school, but, electric propulsion has not yet reached the state of displacing traditional propulsion.

My humble view is that electric motors are here to stay but 100% electric, battery-based is a temporary solution (like "blue ray" video players were). Perhaps as fuel cells become cheaper and lighter they will become mainstream.

We agree that electric propulsion is here to stay. It needs to evolve further (and it will) to become widespread in the USA. I am 10 or 15 years behind on fuel cells. Is the total system weight reasonable? Are you referring to LGN as a fuel, hydrogen, or something else?


BJC

 

[Heliano]

As it stands today, 100% electric aircraft are viable in some niches only, such as flight schools, glider towing, motorgliders, etc. There is a long way to go to make electric aircraft viable for widespread use including cross country. It all boils down to one parameter: energy density. However fuel cells are a (faint) light at the end of the tunnel. Fuel cells are still a little heavy and expensive. But judging by the pace of development I have the impression that in about 10-years time we may have fuel cells that can be easily used in light aircraft, and they will most probably be hydrogen-based. We all hear the argument that handling hydrogen is dangerous, etc. (remember the Graf Zeppelin?) However a more rational evaluation shows that - using the proper equipment - it is no more dangerous than handling gasoline or Jet Fuel (the TWA 747 also exploded, near NYC). Germany's DLR (sort of german NASA) has a prototype in Stuttgart that is a modified motorglider powered solely by a hydrogen-based fuel cell, as the attached figure shows.

 

[Niels]

The big promise ,I think ,from electric propulsion is to have centerline thrust with very high reliability from two independent sources of electricity to one electric propmotor.
Many years ago I read somewherer that piston engine twins make almost as many ugly things as singles.
Is that still true?

 

[Heliano]

Having a single motor with two independent sources of electricity is certainly feasible. However to know if it is convenient or not, one has to evaluate the reliability of such setup. If the source of electricity is highly reliable, then there is no need for two of them. Additionally, if the switching device from one source to the other has failure modes, then those failure modes have to be evaluated. One of the nicest things in aeronautical engineering- introduced a long time ago - is safety assessment. Probability of failure vs. severity of failure (if it is catastrophic, hazardous, major, minor or no effect) combinations are evaluated as acceptable or not. One interesting example is oceanic flying: until the early sixties, ocean crossing with passengers could only be done with four-engine aircraft. Today there are virtually only two-engine aircraft. That's because engine reliability went from one failure per 1000-hour (turbo compound radial piston engines) to one per 500000-plus hours (e.g. GE 90 series)

 

[Niels]

Let me try to calculate and hope for comments from people who know what they are talking about.
We have a normal twin engine ship with two rotax 912 that can fly level on one( if handled rigth )as base.
If 7000hours is realistic for a single 912 then it takes 49 million hours before we have a double engine out.
How many one engine out on twins are handled right?

 

[Toobuilder]

While 'serial hybrid' does lose some calculated efficiency in a direct comparison with an 'direct drive' IC engine, I don't think that the calculus is that simple. Realistically, if it were, non-plugin hybrid cars wouldn't work. NASA, and a lot of other public and private developers, are giving it a look, because of distributed propulsion. STOL, maybe even VTOL, with what could ultimately be a simpler system than a helicopter, while keeping the speeds of fixed wing. And with steadily improving battery tech, the engine can always operate at best BSFC, and, by using the batteries as a big 'capacitor', the engine can be a bit smaller, generating more fuel/efficiency improvements.

Or I could be wrong.

Charlie

One of the big advantages that cars have over airplanes is regenerative braking. That and the fairly modest Accel, cruise, decel profile of the car enjoys VS the torture that an airplane endures.

Hook a boat and trailer on the back of a Prius and run it up a steep grade at full throttle for 3 hours and see how well the series hybrid concept fits the mission.

 

[rv7charlie]

I don't disagree with your point, but in the STOL/VTOL area, I'd expect a more significant takeoff to cruise power-required delta than is seen in a typical fixed wing flight profile.
There's also the issue of power to thrust conversion efficiency, which isn't a factor in ground-bound systems. I must not be the only person who thinks it could work; aviation news media is awash with reports of just about every major player from NASA to the major air transport mfgrs to light a/c mfgrs to the developing urban transport industry looking at serial hybrids. Even short haul airliners with turbine driven generators powering fans & props, to achieve shorter/quieter takeoff/landing operations.

And even the ground-bound rail industry around the world seems to believe it can work efficiently.

Charlie

 

[Sockmonkey]

We all hear the argument that handling hydrogen is dangerous, etc. (remember the Graf Zeppelin?) However a more rational evaluation shows that - using the proper equipment - it is no more dangerous than handling gasoline or Jet Fuel (the TWA 747 also exploded, near NYC). Germany's DLR (sort of german NASA) has a prototype in Stuttgart that is a modified motorglider powered solely by a hydrogen-based fuel cell, as the attached figure shows.

The Zeppelin was mostly because they basically painted the thing with rocket fuel.
The main issue with using hydrogen as fuel is the difficulty in storing it rather than the danger.
Now for hybriding, I think the best best is one of these.

Free-piston linear generator - Wikipedia

en.wikipedia.org

 

[David Lewis]

We all hear the argument that handling hydrogen is dangerous, etc. (remember the Graf Zeppelin?)

Trivial point but the Graf Zeppelin made numerous intercontinental passenger flights in perfect safety. The Hindenburg is the one which suffered the hydrogen fire.

There were actually several other Zeppelins (and blimps) before that destroyed by hydrogen fires, but those catastrophes were not captured on motion picture film.

 

[Heliano]

David, you are right. It was the Hindenburg. There was another factor too: at that time not much was known about static discharging and how to do it effectively.
My mixup was in part because the Graf Zeppelin made several trips to South America. There is still a huge (when I say huge I mean it) hangar designed for the Zeppelin, well maintained, in an air base near Rio de Janeiro.

 

[Niels]

Emrax has some motor and generator options with this power-to-weight ratio:
https://emrax.com/wp-content/uploads/2020/03/manual_for_emrax_motors_version_5.4.pdf

These phenomenal slovenian electric machines from Emrax are axial flux and more compact/low mass than radial flux electric machines.
I have found a drawing I made mid nineties of a non turbocharged radial flux enginerator.
Junkerator was my very original name for it.
To day I would have it turboed and with axial magnetic flux generators like Emrax.
Will a 60kW (like from a 912) be of worth scheming?

 

[cheapracer]

The Pipistrel thing is a fact.

The fact is 40 minutes flying time, and you had better be darn close to a runway, for 8 hours of charging. There ain't going to be superchargers at airfields, and then you're going to have to find a power point, if there is one, and if you can use it..

Hybrids are great for cars due to the range of engine speeds a car requires. A generator can run at it's most efficient rpm range, while the electric motor can serve the wildly varied rpm required to drive the car around the city, mountain road, or highway.

In an aircraft, the engine is already running around it's peak efficiency, so there's nothing to be gained other than maybe a small safety factor, possibly offset by the weight increase with current battery tech..

 

[cheapracer]

These phenomenal slovenian electric machines from Emrax are axial flux and more compact/low mass than radial flux electric machines.
I have found a drawing I made mid nineties of a non turbocharged radial flux enginerator.
Junkerator was my very original name for it.
To day I would have it turboed and with axial magnetic flux generators like Emrax.
Will a 60kW (like from a 912) be of worth scheming?

These guys did it in the 1960s Mate ...

 

[cheapracer]

I am 10 or 15 years behind on fuel cells. Is the total system weight reasonable?
hydrogen,

Hope so, I just tipped a bundle of money into hydrogen stocks. They were actually per-release stocks 2 weeks ago, went public last week and I doubled my money already, yay! Yup, I'm showing off.

The main reason that has tipped me towards hydrogen is heavy transport. The weight is comparable to ICE, so truck transport companies will go with hydrogen due to the extra amount of weight they can move, compared to the loss of money due to the weight being taken up by batteries.

60% of all Europe's railways are diesel, they will be replaced by hydrogen. USA is in the same position.

Aircraft is certainly a possibility for hydrogen being weight critical, and they will not in the foreseeable future be electric, other than bespoke usage like flight schools.

 

[stanislavz]

My two cents. I did run some number before on purely electric solution - but short answer you will get motorglider in the end, if you want any kind of range. You need an L/D of 15 at least, better in 20 ++ range to have more than 100 miles range and/or an few h of endurance. It was quite funny to take Rutan boomerang as an example it was possible to put whole tesla battery (100kwh) + two motors in place of petrol motors and fuel. It was getting 300-400 km range with good speed. On paper. But slower than petrol of course. If gone hybrid way, with petrol engine for "survival/altitude preserve" cruise it would double that at least.