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Hybrid or electric theory?

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Sockmonkey

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Apr 24, 2014
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Flint, Mi, USA
I've said this before but it bears repeating.
It's much easier to make hybriding work in ground vehicles than planes because the electric drivetrain is replacing the transmission, clutch/torque converter, and driveshaft. Those things are all heavy, complex, and cause efficiency losses themselves. A series hybrid car can actually have a lower parts count than a standard one.
The bigger the vehicle, the bigger the advantages of hybriding because the mass of your gearbox goes up fast due to having to handle the forces needed to move that big vehicle.
With most planes the prop is right on the crank, and a prop with adjustable pitch does the job that the gearbox does in cars.
For a plane you have to design the airframe from scratch to exploit the advantages of using a hybrid system for it to be worth it.
 

ElectricFlyer

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Dec 16, 2015
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Richmond Hill, Ontario, Canada
I know many of you have been waiting for me to sound in on this 🤣
For me - Hybridising aircraft is adding Complexity(ICE) to Simplicity(E). C+E=2C
Ok - I am not a math person😜.
But I wholly believe one is better off without the other when it comes to UL aircraft for most cases. Go ICE if range is your thing. You just wanna go out a few mornings/evenings a week for an 45min then E is the ticket.
Exception to every rule!
The example in the vid was interesting - "use E to take off and ICE to cruise". To me, why put in the Epower for takeoff to complicate things with extra weight from the batteries for "take off power"? Epower for emergency back up cruise maybe if the ICE fails - thus if you dont have the height if the ICE fails to do a turn around back to airstrip or to get to that field you just did not have enough glide to make! Which makes me wonder on the stats for UL crashes -- more due to a control failure or power failure?
Lots if interesting stuff happening non the less in the aviation world.
Anyway - like Kuiil would say - "I have spoken" 😁
Cheers
 

henryk

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Joined
Mar 8, 2010
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5,718
Location
krakow,poland
Hybridising aircraft is adding Complexity(ICE) to Simplicity(E). C+E=2C
the main UL phactor=Power/ Weight...

circa 20 kW (circa 30 HP) ICE =10 kg,
+ 20 kW STARTER/GENERATOR (5 kg),
+20 (40 max) kW high RPM E-motor (5 kg) + CR Diff.Gear (5 kg with 2 CR Propellers)

+10 kg ( 2 kWh ACCUs)=

=circa 35 kg...+ PETROL !
 

blane.c

Well-Known Member
HBA Supporter
Joined
Jun 27, 2015
Messages
4,492
Location
capital district NY
I know many of you have been waiting for me to sound in on this 🤣
For me - Hybridising aircraft is adding Complexity(ICE) to Simplicity(E). C+E=2C
Ok - I am not a math person😜.
But I wholly believe one is better off without the other when it comes to UL aircraft for most cases. Go ICE if range is your thing. You just wanna go out a few mornings/evenings a week for an 45min then E is the ticket.
Exception to every rule!
The example in the vid was interesting - "use E to take off and ICE to cruise". To me, why put in the Epower for takeoff to complicate things with extra weight from the batteries for "take off power"? Epower for emergency back up cruise maybe if the ICE fails - thus if you dont have the height if the ICE fails to do a turn around back to airstrip or to get to that field you just did not have enough glide to make! Which makes me wonder on the stats for UL crashes -- more due to a control failure or power failure?
Lots if interesting stuff happening non the less in the aviation world.
Anyway - like Kuiil would say - "I have spoken" 😁
Cheers
Looking at it differently. If you want electric (because the heart wants what the heart wants) and battery energy density sucks, then hybrid.
 

tspear

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Joined
Feb 12, 2014
Messages
798
Location
Oneida
I started a thread a long time ago on series hybrid. Back then, the answer was pretty much the same. For aviation purposes, you will lose efficiency with current aerodynamic choices made. Potentially a change in thrust layout, such as many small props, may change the calculation.

Flip the problem on its head. With the reliability of electric motors, and the life of electric motors, the ability to delivery max power at pretty much any RPM. They are ideal for converting energy to thrust. You can likely eliminate constant speed props, you can place the engine/prop where needed for optimal aerodynamics, structural reasons, or other efficiency requirements. You may also eliminate the running flammable fluid all of the plane. With our planes lasting decades, we have an interest in starting to make these changes and gain as many of the advantages as we can.

With our planes lasting decades, the earlier we we can make the jump the better off we likely will be.

However, the using just batteries does not hold sufficient power to make the plane truly useful. Since the plane will last for decades, eventually the battery tech will get there where it can be the sole source. Therefore, from a design standpoint, we would want to make what is effectively the power source as a replaceable component. Next, we would want to look to other higher volume industries when possible, but we then run into a reliability problem (perception might be the bigger issue than the reality). So from my perspective, using a cheap commercial genset with enough battery power for roughly thirty minutes is likely the optimal solution. By using mass produced genset, you lower costs, by having 30 or more minutes of battery as a backup to the genset, you can make the argument to the FAA genset does not need to meet current PMA or design requirements.

Tim
 

rv7charlie

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Joined
Nov 17, 2014
Messages
1,256
Location
Jackson
While the idea is attractive, 'cheap genset' means 'really heavy' genset. My 12KW not-cheap home backup power genset uses a Generac 992cc Vtwin that's typically rated at around 32 HP continuous, but the genset is only yielding about 16 HP worth of electricity (they derate the engines a lot, for reliability). It weighs 470 lbs; roughly the same as a 260 HP a/c engine.

The next issue is that aircraft are *always* designed around the powerplant (if they're successful). If you design an airframe with 'distributed propulsion' using electric motors, and design into it a 'generator/fuel bay' with current tech, then the idea could work, for particular missions. As storage tech improves, the mission list could likely expand a bit.
 

Dan Thomas

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Sep 17, 2008
Messages
5,660
Flip the problem on its head. With the reliability of electric motors, and the life of electric motors, the ability to delivery max power at pretty much any RPM. They are ideal for converting energy to thrust. You can likely eliminate constant speed props...
I've mentioned before that eliminating constant-speed props isn't an option for any airplane where a wide speed range is desired. Propellers, whether they're driven by an ICE or an electric motor, have a narrow useful range of RPMs. For example, run your 172's engine at idle (650 RPM) and it probably won't even taxi. Double that to 1300 and it will taxi really fast. Add only 1000 RPM to get 2300 and it takes off and climbs. But try to increase that RPM to, say, 3300, by repitching that 76" prop, and you don't gain anything since the tips are now supersonic and the engine's power is consumed mostly by drag. If we use a smaller prop to get the tip speeds down, we lose propeller efficiency and takeoff and climb suffer.

The angle of attack (AoA) of a propeller's blades decrease as forward speed increases. As the AoA gets down to around 2°, the lift falls of so that forward speed stops increasing. If our propeller is near it's max useful RPM, as it will be, the only way to get more speed is to take that fixed-pitch prop off and repitch it to a higher pitch, but now we lose takeoff and climb performance since the engine can't rev up to its max output HP. Or we can install the variable-pitch prop, normally seen as a governor-controlled constant-speed prop, and vary the blade angle to whatever AoA works best in any flight regime.

A fixed-pitch prop is a bit like a car that has only one gear, with the ratio midway between low gear and high gear in the normal transmission. Cheaper to build, but poor acceleration and poor cruise speed. A lousy compromise. Air's low viscosity allows the prop to get away with it, but performance is still severely limited.

As far as the electric motor delivering max power at any RPM? Nope. Power (horsepower) is a function of torque times RPM. Low RPM cannot deliver max power, just max torque, and HP will be low. Physics and math are really destructive to wishful thinking.
 
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