Clear Prop! | #4
Surviving the Bear Market, Drones for Intra-hospital Transport, Airframe Optimization for Medical Use Cases, Co-axial Rotor Performance & more
The world is battling with a recession. The US economy has shown negative GDP growth for the last two quarters, central bank rates are continuously rising and unemployment is increasing. While there are a few local peaks in the stock market, S&P 500 is down by 20% compared to late 2021 when it reached its max ever in its 65-year history.
Although we do not know precisely when the stock market will hit rock-bottom - if history is any guide - we are likely getting close to it, ignoring the potential of geopolitical escalation of course. A nuclear event which has a low probability but an extremely high fatality (even if it is a “small” tactical nuke) can send the markets into a frenzy, similar to the shockwaves caused by the advent of COVID-19.
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Nonetheless, startups need to hedge their strategies against such possibilities to survive, and perhaps even thrive. Ryan Breslow’s tweet (founder of checkout tech firm Bolt) on this summarizes some of the mental states that startups (and maybe larger firms) need to attain to keep the blaze going through the blizzard.
As Ryan points out vehemently as well in his tweet, cash is king - more than ever. In the last couple years during the bull market, cash & profits were secondary while aggressive growth was prioritized. This was primarily due to the large sums of capital that investors had access to plus low interest rates for the last decade. Thus, raising money was relatively easier as supply of investment outran the demand from startups.
However today, this trend has reversed. It is much harder to raise money for startups - both in early- and later-stages - across many sectors as it is less risky for capital holders to invest their money into other, less risky assets. Therefore, to be attractive for investment today, startups need to pay attention to the following:
Cut unnecessary / non-critical costs to extend runway to 24 months, ideally 36.
Achieve product-market fit before raising. If no pmf exists, have a clear-cut no-nonsense roadmap to achieving pmf before pitching to investors.
Diversify products/services. If you are in the pre-revenue stage, be agile and look for ways to bring value to customers without significantly changing your core capabilities and team. Pay attention to shifting demand as the world changes.
In addition to the challenge of raising funds, many startups are facing headwinds to bring their products to market and scale their offerings. The AAM industry is no exception and certainly takes this to the extreme: most of the startups are in the R&D stage, much like biotech. AAM startups typically need long runways before commercialization (7-10+ years) due to the capital- and hardware-intensive nature, needing larger amounts of total investment. On top of this, the need for other pieces of the puzzle across the AAM ecosystem to fall into place is extremely important for product commercialization (e.g. regulations & policy, batteries, airspace management, ground infrastructure, etc). This higher risk, compared to let’s say consumer tech or B2B SaaS startups, is amplified due to an eVTOL manufacturer’s dependance on other companies which may also be venture-funded with little or no recurring revenue.
For eVTOL to successfully go through this downturn, I believe AAM companies may do the following:
Diversify into other areas of AAM. One of the greatest examples of this in the industry is Skyports expanding into providing drone delivery services (shorter-term revenue) while keeping its vertiport play separate (long-term vision).
Be on the look-out for consulting opportunities. Cities, regulators, large enterprises and so on are searching for expertise to implement AAM.
Chase strategic investors. They usually have longer time horizons for expected return with more product-driven incentives than VCs.
Outsource talent to contractors. With high uncertainty of how the economy will evolve in the mid-term, focusing on short-term value while hiring developers, marketers and strategists on a project-basis will cut costs down in the long-term and bring agility to the talent force.
Lastly, I believe that AAM companies that are currently private are in a more advantageous position than those who went public, either through a SPAC or conventional IPO. As you can see below, almost all AAM firms that are public today are trading significantly below their initial stock price (except Vertical Aerospace EVTL 0.00 which is trading above $10.00 and EVE Air Mobility EVEX 0.00 about 20% below $10.00).
It is important to point out that all of these firms - except Blade BLDE 0.00, which already flies helicopters & seaplanes on-demand - don't have recurring revenue, if at all. They also have at least a few years before commercialization. Thus, if this economic climate persists for more than a year, these firms will be forced to go for additional funding or be acquired by an entity with large pockets. Both of these routes are challenging when your market cap is down, some by more than 75%.
On the other hand, eVTOL firms that are currently venture-backed, such as BETA Technologies, are better positioned to raise additional funding with none of the additional challenges brought forward by being a public company.
Nonetheless, it will be a bumpy road for AAM startups during this bear market. For many of us who haven’t professionally lived through the dot-com bubble burst let alone the Global Financial Crisis, being cautious, cash-flow driven, and meticulous on all fronts is more important than ever.
Let’s dive into this edition’s papers.
#1: Design of a Service for Hospital Internal Transport of Urgent Pharmaceuticals via Drones
Researchers from San Raffaele Hospital, EuroUSC Italia, and Giustino Fortunato University propose a service design for transporting urgent pharmaceutical goods from the pharmacy to the operating room, all within San Raffaele Hospital in Milan, Italy. Based on interviews with the prospective users of such a service comprising the pharmacy manager and the nursing staff of the operative unit, the current and future requirements, stakeholder roles & responsibilities, and the necessary digital infrastructure are determined. Finally, several KPIs are compared between the current and drone-based service, quantifying the gains and potential deficiencies between them.
Urgent delivery is done through one of three methods today, in order of high to low efficiency: 1) pneumatic tube, 2) delivery by dedicated logistics teams, 3) personal pick-up by operative unit staff. Drone delivery would provide an additional layer of robustness to ops, decreasing the need for the operative unit staff to do deliveries.
Drone-based delivery significantly improves Time KPIs (e.g. response time). Quality KPIs (e.g. delivery accuracy) does not change. Productivity KPIs (e.g. delivery frequency) improve, however they depend on how many drones are available.
The incorporation of a service-oriented digital ecosystem accounts partially for the KPI improvements. A “Drone Delivery App” that provides a common operating picture to all stakeholders plus a connection to UTM is key.
The BFD: It has been long anticipated that emergency & medical users will be the early adopters of drone technology. This has so far been proved in the commercial operations already being done in this space by firms such as Swoop Aero, Zipline, Matternet, Skyports & more. Thus, a hospital-specific analysis is highly beneficial to potentially scale such services to many mid- to large-size hospitals around the world, eventually saving lives. This paper does an especially great job in tying the workflow to existing regulations and associated initiatives at the EU level.
#2: Hover-Propeller Full Design Cycle - Performance and Acoustic
In this paper from the Israel Aerospace Industries and Mejzlik Propellers, researchers propose a design methodology for propellers that primarily operate in hover mode (think multicopters such as the VoloCity). Designing props with good system and acoustic performance is key for UAM. However, these usually have contradicting requirements and thus, a multidisciplinary design optimization (MDO) framework is used. Once the various different types of props were designed, they were manufactured and the design process was subsequently validated by testing them in an anechoic chamber i.e. isolated sound room.
As the number of blades increase from 2 to 4, the total & tonal overall sound pressure levels decrease while the required battery power increases.
Below a certain sound pressure level (in this case ~50 dB), distinguishing tonal noise vs other types of noise such as background, motor and broadband is experimentally challenging due to microphone setup.
While the optimization includes acoustic performance, optimizing for psycho-acoustics (i.e. psychological effects on the human ear) is not considered. However, this is an important aspect as human cognition plays a large role in the perceived level of overall sound pressure.
The BFD: Designing an aircraft is essentially a highly complex and sometimes a non-intuitive optimization problem with a multitude of performance requirements that usually oppose each other. Adding noise to the equation - which is a key parameter along with downwash and battery/range requirements - makes this design problem more complex. Therefore, a tried and tested design methodology such as the one proposed above is certain to benefit engineers in the eVTOL space.
#3: Planning Land Use Constrained Networks of UAM Infrastructure in the San Francisco Bay Area
Researchers from the University of California, Berkeley propose a simulation methodology to model potential vertiport locations in the San Francisco Bay Area. Using k-medians clustering (often used in unsupervised machine learning) and data from local government & Uber Movement, transportation demand across the region is aggregated into multiple clusters. Then, each cluster of demand is assigned to the closest compatible parcel using a BallTree nearest neighbor search. Thus, a vertiport network design for the Bay Area can be created, comparing UAM travel times to ground travel modes.
The larger the number of vertiports in the network, the more the total travel times for an eVTOL trip decrease. Thus, it’s better to build more smaller vertiports spread out geographically vs a few large vertihubs, holding the budget to develop such infrastructure constant.
40 vertiports is the bare minimum for the Bay Area to make the average UAM trip faster than the average driving trip. After 70 vertiports, a significant decrease in UAM travel times occur.
For 70 vertiports, the parcels for vertiport development need to have an area of 2 acres or below. Any parcel size above 2 acres makes UAM on average less competitive to driving.
The BFD: This simulation, given the data, can be expanded to other cities to build a vertiport network design optimized for minimal UAM travel times and maximal connectivity. While this study is a great foundation, other constraints such as airspace design, transportation modes other than driving (e.g. public transportation) and rooftop availability will need to be considered. Only then, the true location and number of vertiports can be derived. To dive deeper into the Bay Area from an airspace perspective, see this thoughtful paper from MIT.
#4: Hover Performance Analyses of Coaxial Co-Rotating Rotors for eVTOL Aircraft
In this paper from Chungnam National University in Korea, the researchers study the hover performance of co-axial co-rotating rotors using CAMRAD II simulation software. The team particularly focuses on varying the following parameters: 1) index angle (phase angle between the upper and lower rotor), 2) axial spacing (the vertical distance between the upper and lower rotor), 3) blade taper ratio and 4) built-in twist angle. Various trim conditions are studied across these variables and the resulting power, thrust and Figures of Merit are compared & contrasted.
For both the trimmed and untrimmed conditions, the optimum thrust and power loading are highly sensitive to the index angle and the axial spacing of the blades.
Generally, the index angle needs to be increased as the axial spacing between the rotors are increased for maximum thrust. The same trend applies to minimum rotor power needed, however the optimal thrust and power conditions do not necessarily overlap.
For the trimmed condition, the maximum Figure of Merit is achieved when the axial spacing is concurrently increased with the index angle.
The BFD: Co-axial co-rotating rotors are an interesting area of research in eVTOL primarily for the promising results on noise reduction. Although other research has already been published on this topic, most notably by a team led by the US Army, no previous research had optimized the hover performance of stacked co-rotating rotors under a trimmed condition for a given thrust coefficient. While noise optimization is key for eVTOL, the overall performance of the propulsion system needs to be incorporated into design to make quiet, electric VTOL feasible.
#5: Airframe Design Optimization and Simulation of a Flying Car for Medical Emergencies
Researchers from Keio University, Japan conduct a vehicle design requirement optimization study specifically for aerial medical use cases with eVTOL. The team interviewed flight doctors, a helicopter pilot and an air medical services firm to determine mission requirements. 3 different eVTOL configurations are explored (multirotor, vectored thrust and lift+cruise) with rotor diameter and thrust coefficient as vehicle design variables. Weight optimization was used across 4 objective functions: 1) total energy required for the mission, 2) noise from rotors, 3) downwash speed and 4) landing area size.
The vectored-thrust configuration was found to be the most feasible for the aerial medical mission. This configuration sets the lower boundary for the battery energy density required at at least 293 Wh/kg.
Based on the interviews, the following was prioritized for the analysis, from high to low: 1) total energy required, 2) downwash, 3) landing area size and 4) noise. While most use cases for UAM prioritize noise, here noise does not matter as much as ground observers are generally more accepting of helicopter noise used for life-saving applications.
Eliminating engine warm-up time of helicopters with RPM-controlled eVTOL rotors is one key factor in total transportation time gains.
The BFD: Aerial medical services may well be one of the very first adopters of eVTOL technology. However, most of the focus among eVTOL OEMs today is geared towards commercial passenger applications i.e. urban air taxi. There is no consensus today on which design configuration(s) and parameters work well for this use case. Research such as this may provide eVTOL firms the necessary framework for designing vehicles by optimizing for various constraints that are specific to the aerial medical scenario.
This edition’s sponsor is Vertical Flight Society. VFS is an amazing resource that I use to access leading technical papers and workshop decks for my work. Whether you are an investor, engineer, researcher, or an entrepreneur, becoming a VFS member can give you an asymmetric advantage in the AAM space.
Membership gives discounted access to more than 15,000 technical papers, presentations and articles. Learn more here.
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My comment is to item #2: Hover-Propeller Full Design Cycle - Performance and Acoustic
My full respect to the expertise and efforts described in the report. Just want to hint at a new potential approach to reducing propeller noise. It is through application of variable twist blades. Variable blade twist provides a quasy constant level (high level!) of propeller efficiency for a changing axial speed. High efficiency, theoretically, ensures low level of wasted energy, which may manifest in silent operation.