If air taxi services ever take off, you might want to hold onto your hat very firmly. A new FAA report looking at various eVTOL prototypes shows that when they take off and land they have a downwash from rotors equivalent to hurricane-force wind.
Film buffs may remember the opening of the 1965 musical The Sound of Music where the camera swoops over the Austrian alps and zeros in on a distant Julie Andrews dancing in a mountain meadow. What was edited out was Miss Andrews getting knocked on her backside, thanks to the downwash from the camera helicopter.
These DownWash and OutWash (DWOW) effects are notorious for helicopters and are one of a number of reasons why helicopter air taxi services have never been very successful. Since eVTOLs are governed by the same laws of physics as helicopters, the US FAA is very interested in learning as much as possible about the DWOW effects of the new aircraft being developed for what is hoped will be the first truly successful air taxis.
For the new report, the agency tested three unnamed prototypes with a maximum take off weight of below 6,500 lb (2,950 kg) in various rotor configurations and blade numbers. Around these were placed sensors at different distances and heights to measure air pressure to help digital simulators reconstruct airflow patterns.
What they found was that the eVTOLs generated downwashes at speeds of up to 99.3 mph (159.8 km/h). That's a Beaufort wind force scale of 12 or equivalent to a hurricane. The pedestrian safety wind limit is 34.5 mph (55.5 km/h). According to the FAA, these effects exceed agency recommendations for safety areas at vertiports or heliports. Such winds could result in the lifting of unsecured objects off the ground, knocking people about in the vicinity like tenpins, and kicking up enough dust to cause brownout visibility.
None of this means air taxis are off the menu, but it will mean tweaking the regulations and making various recommendations about how and where large eVTOLs can operate. These include extended safety zones, setting up Downwash Caution Areas (DCA) with restricted access, and developing high-capacity computer analysis to better understand the safety issues.
How to deal with air taxis working in the vicinity of Austrian governesses frolicking in the Edelweiss has yet to be determined.
Source: FAA
Fly these craft Especially in high wind ! Multicopters is superior in terms of handling wind the Electric motors react Instantly compared to a helicopter's massive disc where centrifugial forces are so high and the surface area so big where wind greatly affect its agility.coupled with an inefficient drive train and slow moving control surfaces.
Grow up grow wise google is your friend.
Because multicopter motors react instantly, it instantly reactx to the diverse kind if wind forces a craft can experience in flight.
@Dan I am much more concerned with a helicopter having to autorotate during an emergency.
A multicopter have 1st of all indisputably a more reliable power train.
Electric Motors simply does not fail. +1 for Towerman on that.
In the very extreme rare event that a motor does fail, you have multiple redundant motors taking over in an instant where as for a manned helicopter you have to rely on a human to bring the heli down with no power and only get 1 shot at landing perfectly right. Only 1 shot. With 2 motors out a multicopter can choose its landing spot with multiple tries even a 10 year old can do it.
Meantime auto rotation on a helicopter A manouvre as proved again and again over the years is extremely risky lt has lead to 1000s upon 1000s of fatalaties. We have full NTSB records stipulating it in the most vivid detail.
No thanks as soon as EVTOLS take commercial flight i'll never jump in a heli again. EHANG is making Waves in China already !
Electrics is King wuth regards to safety, reliability and low maintance compared to any her power rrain in existance hands down !