This document summarizes a study characterizing a hybrid electric-glow engine power system for multi-rotor helicopters. The system uses a glow engine to drive two propellers and generators to produce electricity and offset the power needs of the remaining four electric rotors. Testing characterized the generators' power output and the glow engine's thrust, power, and fuel consumption with different propellers. Analysis showed only two propeller types were viable. Using one type, the glow engine could run for 22 minutes generating 8.66 Joules; using the other, it could run for 40 minutes generating 4.49 Joules. While this hybrid system cannot provide full lift, it can negate added weight and generate power to extend total

1. Characterization of a Hybrid Electric-Glow
Engine Power System for Multi-Rotors
Introduction
Multi-rotor helicopters are traditionally driven by multiple electric
motors. The purpose of this project is to study the benefits of integrating a
glow engine to drive two of the propellers on a hex rotor, while at the same
time generating electricity by using two of the brushless motors as
generators. Using this setup, the glow engine will be providing lift as well
as producing electrical energy to offset the power consumption of the
remaining four rotors.
Figure 1: Hybrid hex rotor concept
The data gathered in this project was used to determine the optimal
drivetrain configuration in terms of glow engine, generators/brushless
motors, and propeller combinations as well as behavior of operation that
will outperform a comparable electric-only hex rotor.
Approach
To determine the optimal drivetrain combination, we separately
characterized the generator and glow engine.
In our characterization of the generator, we measured voltage
produced, current sustained, power input/output, and mechanical torque all
while varying RPM and electrical load.
Figure 2: Generator test stand, generator driven by brushless motor
For the characterization of the glow engine, we measured various
metrics in separate procedures:
• Propeller Thrust Data
Thrust was measured with respect to RPM for multiple sizes of
propellers all from the same manufacturer. The data was collected
by measuring the reactionary force at the motor mounts using a
digital scale.
• Glow Engine Power and Fuel Consumption
Power was measured throughout the RPM range of the engine. The
test was repeated with each propeller to vary the load on the engine.
Fuel consumption was measured by keeping the engine at a given
load and RPM for an extended amount of time and then measuring
the change in weight of fuel tank.
Analysis and Results
After collecting the data from the generator and glow engine, we
determined the optimal propellers and operating parameters to maximize
flight time. We started by determining the added weight of the hybrid
system without fuel as compared to the weight of the all-electric hex rotor.
From there, the minimum RPM necessary to provide adequate lift to
cancel out the added weight was calculated as well as the power necessary
to achieve such RPMs.
Figure 3: Engine power with respect to RPM for various propellers
Then, propellers for which the power requirements were unobtainable
from the glow engine were disregarded. This left two propellers. We
found the maximum electrical power that could be generated with the
engine power not consumed by the propellers.
Figure 4: Electrical power produced per generator with respect to
RPM and electrical load
To determine the maximum flight time of the two viable propellers, we
first developed an equation for fuel consumption vs. RPM based off of the
data from our experimentation. Then, using the power consumption
characteristics of the two propellers of interest, we created a model for the
flight time of each propeller given an initial amount of fuel. We looked at
the maximum thrust we were able to produce with the glow engine for
each propeller. Then we used that information to calculate the greatest
initial fuel load so that the glow engine still provided enough lift to negate
the added weight. From there, we plugged in the initial fuel load to the
flight time models and were able to find the maximum time for which the
glow engine could perform. Using electrical generation data, we
determined the electrical energy generated during the course of flight.
Conclusion
From our study, only two propellers are viable for use in this set up with this glow engine (O.S. 15 LA) and with the generators we used: the 6x4-3 blade propeller and
the 7x4-3 blade propeller. Based on our experimental models, using the 6x4 3-blade propeller, the glow engine can run for 22 minutes and 23 seconds and will generate
8.66 Joules of electrical energy. With the 7x4 3-blade propeller the glow engine runtime would be 40 minutes and 19 seconds and generate 4.49 Joules. Therefore, while
the system with 7x4 3-blade propellers will run longer than the system with 6x4 3-blade propellers, it will generate significantly less energy during its entire flight.
Based on our analysis, the glow engine is unable to provide the majority of lift for the entire hex rotor. It is, however, capable of negating the added weight of the
hybrid system plus fuel and generating power for the electrical system of the hex rotor during the duration of flight which will allow for an overall extension in flight time.
Therefore, a hybrid electric-glow engine powered hex rotor will have a longer flight time than an equivalent all-electric hex rotor. In the future, to determine how much
longer this flight time will be, a full characterization of the power consumption of the electric hex rotor is required.
This work was sponsored in part by the National Science Foundation (NSF) under award number EEC-1263133.
C. Kazokas, S. McNeil, and T. Wiegand
Interdisciplinary Research Experience in Electrical and Computer Engineering
IREECE 2015
School of Engineering and Computer Science, Oakland University
Faculty Mentors: O. Rawashdeh and H. Alzubi
Glow Engine
Brushless Motor
Providing Power
and Lift
6x4 3 Blade Propeller
7x4 3 Blade Propeller