Urban Air Mobility Rotor Icing Performance Degradation
Open Access
- Author:
- Scroger, Shawn
- Graduate Program:
- Aerospace Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 13, 2020
- Committee Members:
- Jose Palacios, Thesis Advisor/Co-Advisor
Yiqiang Han, Committee Member
Amy Ruth Pritchett, Committee Member
Amy Ruth Pritchett, Program Head/Chair - Keywords:
- Urban Air Mobility
Advanced Aerial Mobility
Icing
Rotorcraft Icing
Performance Degradation
UAV
UAM
AAM
Performance Prediction - Abstract:
- Urban air mobility vehicles for uses such as package delivery or personal transport are being rapidly developed by many companies. Urban air mobility has the potential to be a $500 billion market in the long term. The widespread use of this technology will bring about many safety concerns, one of which will be flight in adverse weather conditions, particularly icing conditions. Minimal excess power available, combined with the high collection efficiency rotors used for urban air mobility vehicles will result in rapid performance degradation in icing conditions. The vehicle will lose the thrust, and torque required for safe flight almost immediately upon encountering an icing cloud. This is particularly dangerous for the vehicles which rely on differential thrust and torque of co-planar rotors to control the pitch, roll and yaw of the vehicle. The aforementioned low excess power available, due to the relatively low energy density of today's battery technology, will likely prevent these vehicles from equipping any electrothermal anti or de-icing technology. Additionally, ice protective coatings have been shown to have low effectiveness, especially if there is any erosion to the coating. This will likely mean these vehicles will be grounded in icing conditions. However, there is still the possibility that a vehicle could unexpectedly encounter an icing condition and it must be able to quickly detect degrading performance and land safely. A 0.812m (32in) diameter rotor representative of those used for urban air mobility vehicles, in both single and co-axial rotor configurations, was tested under varying icing conditions in the Adverse Environment Research Test Systems (AERTS) icing facility at Penn State University. The rotor blades used were not twisted or tapered, although the collective pitch and RPM were varied to change thrust conditions. The maximum tip Reynolds number was 300,000 and the minimum was 200,000. A novel testing technique to acquire iced airfoil lift and drag coefficients for rotating blades was implemented. This method involved degrading performance of the rotor by removing ice from the rotor except for a span-wise ice segment 0.0254m (1in) on each of the blades, centered around the 75% radius mark. This measured thrust and torque degradation, in comparison to clean rotor values, was coupled with the RotCFD performance prediction software to calculate the thrust and torque of the iced section only. With these values the iced lift coefficients were calculated. Thirty-three (33) iced airfoil lift coefficients were calculated and used to develop an empirical equation to predict lift coefficient degradation under icing conditions. With those same 33 observations, the equation predicted iced lift coefficient values with a coefficient of determination (R^2) of 0.933. This equation was implemented in unison with the Han-Palacios correlation to predict iced airfoil drag coefficients. With these values, in combination with a blade element approach to predict thrust and torque, the performance of a fully iced rotor was predicted for a co-axial rotor configuration. The upper rotor thrust predictions were within 6% of experimental measurements at the highest rotation rate, 3000RPM, at both 4 degree and 8 degree collective. However, at 2000RPM the discrepancy increased, under-predicting thrust loss by 12% at 8 degree collective pitch and over 300% at 4 degree collective. Note that this 300% over prediction is only a 2N difference. As the rotor is unloaded, the capability of the proposed empirical equation to predict thrust degradation decreases. Lower rotor thrust predictions were inaccurate, with an average discrepancy of 1148%. This number is heavily skewed by an over prediction by 4600% at 2000RPM, 4 degree collective case which also saw larger discrepancy on the upper rotor. The torque predictions on the upper rotor were within 0.5Nm for three out of the four cases analyzed, resulting in an average discrepancy of 0.54Nm or 25.2%. The lower rotor saw slightly smaller discrepancies for torque. The average discrepancy for the lower rotor was 0.34 Nm or 19.8%. The lower rotor torque accuracy was not seen on lower rotor thrust measurements thrust measurements. This was consistent with clean rotor torque measurements, and suggests higher fidelity modeling or modified assumptions are required to capture the lower rotor inflow accurately.