H.E.R.O. hybrid power unit preliminary study

This study intends to identify and evaluate the reductions in fuel, carbon dioxide emissions, and operational costs that a specific hybrid power unit could provide in a typical small passenger aircraft, to be then scaled to bigger aircrafts (above 5 tons).
Researchers, professional pilots, and software experts engaged in the project to collect the following information:
The findings of this study will serve as the basis for further validations in practical applications.

Two engines, a Lycoming O-235 and the H.E.R.O. hybrid power unit, were compared during the analysis.

Interest in hybrid electric-thermal technology is sparked by two primary factors: the reduction of fuel consumption and emissions, and the need for a backup power source in single-engine aircraft for safety reasons.
Hybrid electric-thermal technologies are available and viable for addressing aviation industry obstacles.
Using two engines, the aircraft can use the electric engine during phases of high fuel consumption, such as takeoff and climb, and phases of noise reduction, such as landing near populated areas.
This technology was selected for the HERO power unit in order to provide the best alternative for passengers and freight aircrafts over the next decade and beyond.

All hybrid electric-thermal engines are parallel systems with low costs and simple production processes, but they are significantly larger than the series engine and permit fewer component modifications to optimize hybrid retrofit systems.
The HERO project will create a system of in-series power units with huge advantages for energy optimization and flying performances.

The specifications for the Lycoming O-235, a common engine in small and medium aircrafts, can be found at this link.
While H.E.R.O. is a series hybrid power unit, it is made of a thermal engine, an electric generator, a dedicated power management software, and other key components that are now under NDA protection.
Horizon funds will be used to test and develop the H.E.R.O. power unit.

In this study, the following hypotheses have been made:

  • The flight in exam is split into the following phases: takeoff: 5 minutes; landing: 5 minutes; climb: 5 minutes; cruise: 45 minutes. 
  • Regarding the cost of fuel we have accounted for 2,31 €/Lt, while the cost of electricity is fixed at 0.24 €/Kw h and we considered a cost of 60 €/L . These parameters are informative due to their periodic variations.
  • The Lycoming power settings have been taken from the official engine manual which suggest the following: take-off and climbs power setting 100%, 43.18 L/h, output power 85,7Kw; cruise power setting 65%, 22.30 L/h, output power 55,74 Kw; landing power setting 5%, output power 4,3Kw, 2,4 L/h.
  • The H.E.R.O. power settings are the following: take off and climbs power setting 100%, 20l/h output power 90Kw; cruise power setting 55% & 60%, 11 L/h & 12 L/h, output power 49.5 & 54 Kw; landing and idling power setting 5%, output power 4,5Kw, 0,78 L/h.
  • The propulsion battery considered has capacity of 15Kwh.
  • Electric engine power 85.7 Kwh.
  • The H.E.R.O. thermal engine has a weight of 65Kg while the Lycoming O-235 L weights 112Kg.

Take Off & ClimbKwh
Thermal engine output power4.29
Engine power dedicated to the Alternator to recharge the battery0
Max electric engine output85.7
Max battery drainage85.70
Propulsion battery cruise recharge0
Thermal engine output power55.00
Engine power dedicated to the Alternator to recharge the battery0.00
Max electric engine output55.00
Max battery drainage0
Propulsion battery cruise recharge0.00
Thermal engine output power4.285
Engine power dedicated to the Alternator to recharge the battery0
Max electric engine output4.285
Max battery drainage0
Propulsion battery cruise recharge0

The following data table depicts the power distribution of the H.E.R.O. hybrid power unit in various flight modes and considering the following flight plan:

  • 5 mins  take off
  • 5 mins climb
  • 5 mins landing
  • 45 mins cruise.

It is hypothesized that the H.E.R.O. team will define and develop the flying modes; a specific management program will be built and installed on an aviation-approved CPU.
Using a hardware interface installed in the cockpit, the pilot will be able to control the flight modes.

Fuel Consumption

Lycoming O-235 LHero setting
Fuel hourly rate consumption (l/h)
Fuel consumption for take-off and climbs43.180.78
Fuel consumption for landing2.400.78
Fuel consumption during cruise26.3611.00
Fuel consumption by phase (l/phase)
Fuel consumption for take-off and climbs (5 mins each)7.200.13
Fuel consumption for landing (5 mins)0.200.07
Fuel consumption during cruise (45 mins)19.778.25
Total fuel consumption (1hr flight)27.178.45
Fuel consumption comparison-68.91%

CO2 emissions

CO2 emissions are calculated from the fuel consumption considering that there are 652 grammes of carbon per liter of petrol.

Lycoming O-235 LHero setting
CO2 hourly emissions (Kg/h)
CO2 for take-off and climbs17.210.31
CO2 for landing0.480.16
CO2 during cruise47.2919.73
Average CO2 emissions64.9820.20
CO2 emissions comparison-68.91%


Taking in consideration the noise of a full electric plane like the Pipistrel Taurus which has a noise emission of 65db(A) and a plane using the Lycoming O-235 like the Long EZE by Eigenbau which has a noise emission of 77 db(A). Using electric power for take off, climb, and landing, and only the thermal engine in idling, we can estimate a noise emission of approximately 66 db(A), but additional testing and data collection will be required to evaluate this information.

Yearly Running Cost

To calculate the yearly running cost the following assumptions have been considered:

a) Fuel cost: 2,31 €/lt; Electricity cost 0,24 €/Kwh

b) Solar panel efficency is set to a conservative 20% source

c) Lycoming o-235 L oil fuel consumption source

d) Engine oil cost: 60 Eur/lt

Lycoming O-235 LHero “Long Range” setting
Yearly data
Fuel consumption (L/Year)3260.001013.40
Electricity consumption (Kw/Year) from the grid01714.0
Yearly CO2 emissions (Kg)7797.922424.05
Yearly running cost
Fuel cost€7,530.60€2,340.95
Oil Consumption€1,836.00€240.00
Electricity cost€0.00€411.36
Solar panels recharge (100+290 W)€0.00-€39.69
Maintenance costs (50 hrs)€1,800.00€1,350.00
Maintenance costs (100 hrs)€3,200.00€2,400.00
Maintenance costs (TBO)€750.00€375.00
Total Costs€15,116.60€7,077.63
Average Savings

Flying Range

The range was computed using the fuel consumption of each flight phase (5-minute takeoff, 5-minute climb, 45-minute cruise, and 5-minute landing) and the amount of fuel in the wing tanks.
The central tank was disregarded because it will be replaced by a battery in the H.E.R.O. power unit.

Flying range
Lycoming O-235Hero setting
Flight hours5.8714.71
In Km (at 300 Km/h)1759.524412.86