# Electric Hybrid

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##### Well-Known Member
What's often missed is that rigid rotors with an electric engine cannot grow much beyond 2 meters/6 ft or so. Above that, you need exponentially more power to lift a given weight which runs into the power density of both electric motors and batteries.

Worse, once rotors grow beyond 1 meter/3.5 ft in span, you need ridiculously high strength and low weight (because of inertia). That quickly becomes pricey, pricier than a complete ICE.

About 10 rotors per occupant is about the lower limit for man lifting flight. Want less rotors; plan for a cyclic, collective and a gear box.

#### emotodude

##### Active Member
What's often missed is that rigid rotors with an electric engine cannot grow much beyond 2 meters/6 ft or so. Above that, you need exponentially more power to lift a given weight which runs into the power density of both electric motors and batteries.

Worse, once rotors grow beyond 1 meter/3.5 ft in span, you need ridiculously high strength and low weight (because of inertia). That quickly becomes pricey, pricier than a complete ICE.

About 10 rotors per occupant is about the lower limit for man lifting flight. Want less rotors; plan for a cyclic, collective and a gear box.
Sorry you are quite mistaken. Larger rotors are MORE efficient. Here you have a helicopter flying on ~1HP.

#### henryk

##### Well-Known Member
Larger rotors are MORE efficient. Here you have a helicopter flying on ~1HP.
-iff more exactly=generate greater Specific Thrust (kG/kW)...

f.e.= ATLAS >100 kG/kW,
"normal" heli <10 kG/kW

#### leviterande

##### Well-Known Member
Indeed I also fully understood that, using anything electric with any hybrid system involving gas+brushless generator+ regulators is a messy, heavy, inefficient complex way to solve a simple problem: just bolt a prop to a gas engine.

My thought pattern however changed about having electric power:
-Unmatched redundant safety is highly increased.
-Pulse momentary thrust power that can be not only very very handy at take off and landing, it can improve the handling greatly. Not to talk about the added safety in stall/close call moments. I have a motor that weighs complete with propeller, ESC , mount and cables 500grams. It pulls 13,6kg. that is a thrust/weight ratio of more than 27x

A gas central main engine driving a prop and a few other smaller electric motors to assist sounds to me like a good idea. An idea that needs more refining ofcourse as I have another method

#### jedi

##### Well-Known Member
Indeed I also fully understood that, using anything electric with any hybrid system involving gas+brushless generator+ regulators is a messy, heavy, inefficient complex way to solve a simple problem: just bolt a prop to a gas engine.

My thought pattern however changed about having electric power:
-Unmatched redundant safety is highly increased.
-Pulse momentary thrust power that can be not only very very handy at take off and landing, it can improve the handling greatly. Not to talk about the added safety in stall/close call moments. I have a motor that weighs complete with propeller, ESC , mount and cables 500grams. It pulls 13,6kg. that is a thrust/weight ratio of more than 27x

A gas central main engine driving a prop and a few other smaller electric motors to assist sounds to me like a good idea. An idea that needs more refining ofcourse as I have another method
If you want to quote power versus weight for electric without including battery weight you should compare to a hydraulic motor without the accumulator. That can be ten times as impressive. I have seen a 500 hp motor that you can hide in the palm of your hand. And you do not need to cool it.

#### BJC

##### Well-Known Member
HBA Supporter
I have seen a 500 hp motor that you can hide in the palm of your hand.
jedi, I’ve told you at least 1,000,000 times to stop exaggerating.

BJC

#### leviterande

##### Well-Known Member
If you want to quote power versus weight for electric without including battery weight you should compare to a hydraulic motor without the accumulator. That can be ten times as impressive. I have seen a 500 hp motor that you can hide in the palm of your hand. And you do not need to cool it.
I know how awfuly heavy Lipos and Lions are.
Sure, your post would truly be justified if I was talking about using a "pure" electric system in a vehicle. That is not what I am talking about here. As you hopefully read my words, and as I stated in my post I was clearly talking about using electric power as an assisting momentary thrust power system in a vehicle for very short uses during for example take off or emergency... the gas engine is the one still used as the main unit per my last post. Battery weight argument here is not relevant

#### John.Roo

##### Well-Known Member
I know how awfuly heavy Lipos and Lions are.
Sure, your post would truly be justified if I was talking about using a "pure" electric system in a vehicle. That is not what I am talking about here. As you hopefully read my words, and as I stated in my post I was clearly talking about using electric power as an assisting momentary thrust power system in a vehicle for very short uses during for example take off or emergency... the gas engine is the one still used as the main unit per my last post. Battery weight argument here is not relevant
Hello!
Boys from AXTER AEROSPACE had similar idea to use electric motor to give additional power to ICE engine. It was combination of Rotax 912 + 40 hp electric motor. Idea was to have assistance for takeoff and in case of emmergency (Rotax 912 failure).

"Axter Aerospace has developed a hybrid conversion kit for light airplanes. A kit composed by an electric motor, an electric motor controller inverter, a battery, a cockpit control panel and the mechanical parts to integrate the electric motor with the fuel engine. This kit provides additional 40hp to the airplane. This kit integrates the own technology, the electric motor controller inverter, the batery, the cockpit control panel and the mechanical parts."

Just... sorry but I cannot agree with this:
"Battery weight argument here is not relevant."
Battery weight is always relevant.
Forget marketing informations that you can use super high discharge current from small capacity battery. I know - RC model guys are using 25C Li-Po cells. But to stay on safe side (as we always want in aviation) you have to be much more conservative. 3C discharge rate is safe. 5C is real border.
Now I will simplify it:
Power of extra 20 hp = +-15 kW.
To get 15 kW you need min. 3 kWh battery (I would personally prefere 5 kWh but lets use 5C discharge rate).
1 kWh capacity = 5 kg weight
It means:
3 kWh battery = weight of 15 kg.
5 kWh battery = weight of 25 kg.
This is just battery for extra 20 hp power, you need also controller, motor, wiring etc.

All above was about available power, however second important issue is to make decission how long time do you need that extra power. And this will affect battery weight again....

Please do not take this as criticism. Is just "expensive personal experience"
Best regards!
Martin

#### henryk

##### Well-Known Member
Boys from
=FLIGHT DESIGN=

=CT +30 kW E-booster (2009,AERO SHOW)

#### leviterande

##### Well-Known Member
Hello!
Boys from AXTER AEROSPACE had similar idea to use electric motor to give additional power to ICE engine. It was combination of Rotax 912 + 40 hp electric motor. Idea was to have assistance for takeoff and in case of emmergency (Rotax 912 failure).

"Axter Aerospace has developed a hybrid conversion kit for light airplanes. A kit composed by an electric motor, an electric motor controller inverter, a battery, a cockpit control panel and the mechanical parts to integrate the electric motor with the fuel engine. This kit provides additional 40hp to the airplane. This kit integrates the own technology, the electric motor controller inverter, the batery, the cockpit control panel and the mechanical parts."

Just... sorry but I cannot agree with this:
"Battery weight argument here is not relevant."
Battery weight is always relevant.
Forget marketing informations that you can use super high discharge current from small capacity battery. I know - RC model guys are using 25C Li-Po cells. But to stay on safe side (as we always want in aviation) you have to be much more conservative. 3C discharge rate is safe. 5C is real border.
Now I will simplify it:
Power of extra 20 hp = +-15 kW.
To get 15 kW you need min. 3 kWh battery (I would personally prefere 5 kWh but lets use 5C discharge rate).
1 kWh capacity = 5 kg weight
It means:
3 kWh battery = weight of 15 kg.
5 kWh battery = weight of 25 kg.
This is just battery for extra 20 hp power, you need also controller, motor, wiring etc.

All above was about available power, however second important issue is to make decision how long time do you need that extra power. And this will affect battery weight again....

Please do not take this as criticism. Is just "expensive personal experience"
Best regards!
Martin
Absolutely. Battery weight is always relevant. I was just replying to someone who obviously misread/misintrepreted my first post -he assumed I was talking about a full electric system- but I emphasized I was not talking about a full electric system but only a an assisting system. I should have written instead: battery weight is not nearly as relevant then. SuperSTOl applications is my main interest here. How long time we need this extra power is a indeed factor here. My point is that the main engine is gasoline doin all the work even in events like during landing/takeoff. My thinking here is that we ultilise the E powers´s advantages:
very high safety.
very high power to weight ratio.
two very important factors I cant solve any other way

Using the E power only for maybe 10-20 seconds during these few instances and having a safety where each motor is parallel.
Generators for much lower needed power seem not impossible.

/Levi

#### Vigilant1

##### Well-Known Member
Battery weight is always relevant.
Forget marketing informations that you can use super high discharge current from small capacity battery. I know - RC model guys are using 25C Li-Po cells. But to stay on safe side (as we always want in aviation) you have to be much more conservative. 3C discharge rate is safe. 5C is real border.
+1. There are a lot of things worse than an engine failure. At the top of my list: A raging inflight fire.

#### Vigilant1

##### Well-Known Member
If the electric boost is needed for climb, then on every takeoff there will be a period when you can't execute a return to land and also have the ability to do a go-around/missed approach (because you've used up your battery capacity and it hasn't recharged). That's on every takeoff. So, going this route will give you more options if the IC engine fails (a rare event), but will increase your risk somewhat on every climbout.
It isn't a major consideration, but it does complicate flight planning. Two ”fuel tanks". Managing one fuel tank is apparently already the cause of a lot of loss of power incidents

#### jedi

##### Well-Known Member
Absolutely. Battery weight is always relevant. I was just replying to someone who obviously misread/misintrepreted my first post -he assumed I was talking about a full electric system- but I emphasized I was not talking about a full electric system but only a an assisting system. I should have written instead: battery weight is not nearly as relevant then. SuperSTOl applications is my main interest here. How long time we need this extra power is a indeed factor here. My point is that the main engine is gasoline doin all the work even in events like during landing/takeoff. My thinking here is that we ultilise the E powers´s advantages:
very high safety.
very high power to weight ratio.
two very important factors I cant solve any other way

Using the E power only for maybe 10-20 seconds during these few instances and having a safety where each motor is parallel.
Generators for much lower needed power seem not impossible.

/Levi
Levi,
Your concept of power assist for an IC engine in Light Sport aircraft has merit and I am on your side. It has advantages that have not been addressed in this thread and I would like to see progress in this area. As others have pointed out there are also engineering issues that need to be addressed.

My post #165 was not intended as an exaggeration as BJC pointed out, hopefully in jest (He is a friend and qualified engineer also). I wanted to say that once the concept is accepted there are many ways to accomplish the goals and alternatives that should be considered. Hydraulic accumulators are commonly used in aerospace applications for energy storage and use and are well suited for long term reliable service and short term high energy release. Lipo batteries not so much.

Batteries have limits on discharge rate as was well documented post # 168.

I would like an education on capacitor storage cell current and future technology. These may be more suited for your short duration electrical energy boost.

My intent here is to keep focused on engineering concepts and evaluations in spite of the internet limitations.

#### BJC

##### Well-Known Member
HBA Supporter
My post #165 was not intended as an exaggeration as BJC pointed out, hopefully in jest (He is a friend and qualified engineer also).

BJC

#### jedi

##### Well-Known Member
That was quick.

For reference the hydraulic motor I referenced from my limited memory bank was used in the Atlas rocket development program during the space race to the moon in the early 1960s. It was manufactured by Eaton. I think it may have been used as a fuel/oxidizer pump during the engine start sequence.

My job at the time was working for Detroit Diesel. We used hydraulic starters for applications where electric starters did not meet the reliability requirements.

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#### leviterande

##### Well-Known Member
If the electric boost is needed for climb, then on every takeoff there will be a period when you can't execute a return to land and also have the ability to do a go-around/missed approach (because you've used up your battery capacity and it hasn't recharged). That's on every takeoff. So, going this route will give you more options if the IC engine fails (a rare event), but will increase your risk somewhat on every climbout.
It isn't a major consideration, but it does complicate flight planning. Two ”fuel tanks". Managing one fuel tank is apparently already the cause of a lot of loss of power incidents
You got a valid point! gaining something almost always equals reducing something else in aviation as an aircraft is a flying city of compromises. I thought along the lines that the power of the electric assistanse alone can keep you flying safely incase of gasoline engine failure. That is that the electric output maximum thrust power when needed is as high or slightly higher than the gas engine maximum output thrust alone. Ofcourse flight time in this case very short but its better then no power at all.

I got you Jedi ! its a cat mouse game in this flying machines' business.

#### jedi

##### Well-Known Member
We have not done a good job of defining the electric power assist goal up to this point. The OP was a full time IC powered electric drive. The thread was hijacked and diverted to a STOL power assist application.

Those are separate specifications. I apologize for assisting in the divergence but now that that is done I will add one more comment on the STOL application.

My STOL interest is in takeoff and climb to at most 200 feet. I am talking about max power for about ten seconds, maybe a half minute max. That is electric starter motor specifications, not electric flight applications. Therefore the hydraulic motor reference.

Think of a 500 hp five second boost to a kitfox STOL takeoff or a JATO takeoff without the fire and smoke.

Sorry for your waised time. I am done.

#### henryk

##### Well-Known Member
500 hp five second boost to a kitfox STOL takeoff or a JATO takeoff without the fire and smoke.
-superFLYWHEEL have the best Energy/ Weight proportion,
better as LiPo ...efficiency too !

PS=russian T34 have hand drived flywheel starter !

#### EzyBuildWing

##### Well-Known Member
Electric-aircraft....how to design your own.....absolutely essential viewing.....latest vid.....

#### Aesquire

##### Well-Known Member
For short time "lots-o-power" check out the Koenigsegg "hybrid" cars. Really small,fast discharge battery. Home - Koenigsegg

The Regera uses a fluid coupling/torque converter to move from a start, and it's a single speed. Red line on the engine is over 200mph, so...

I think both the range extender hybrid & the STOL Electric replacement for JATO, are both possible, and maybe practical, but in different ways, are limited in scale and expectations.

Range Extender Serial Hybrid with electric motors on the props and an ICE spinning a generator may not be justifiable compared to ICE alone, today, unless there's another reason to go electric like distributed motors.

STOL E-JATO, ( I'm officially Coining the term E-JATO & all variant spelling )think
I think has promise. I'd strongly recommend a primary engine capable of acceptable T/O and climb, and treat the E-Jato as a welcome helped you don't rely on. ( I'm aware having the extra power may cause a poor decision like, "hmm, really close trees in the way out, but I can clear them..." , but if stock power is good enough when you don't... )

It all gets down to power required and weight curves?