Rotor downwash

November 6, 2009 by Tim McAdams

Jim Thomas asked, “Are the hazards of a helicopter rotor blast taught to new students?” The answer is sometimes and sometimes not. Being dual rated, I understand the affect the rotor down wash can have on an airplane. As an instructor, it is always something I teach to students.

Wind direction and strength must be considered when hovering near other aircraft. For example, when hovering with a strong right crosswind, leave more room between other objects and left side of the helicopter. The rotor downwash will be very strong on the left side and very weak on the right side. I have had line personnel direct me to park too close to another aircraft that was downwind of the rotor wash. I would just touchdown in a better suited area and explain why once they approach the helicopter.  Some understood, some did not.

However, it’s not just parked airplanes that can get tossed around. I was on a hospital helipad with another helicopter when the other pilot needed to depart. While he was starting up I was busy finishing some paperwork. There were no obstacles and the wind was calm, so the last thing I expected was for him to depart directly over top of my parked helicopter. That’s exactly what he did causing the blades to flex down, and the fuselage to shake. I was sitting in the helicopter with the door open and fortunately was able to get it closed. If I were to guess, he couldn’t have been more than 10 feet above me. I never understood why he did that.

On another occasion, I was hover taxing along the edge of a ramp to parking when I noticed some smaller airplanes rocking a little and in front of me was a pilot with an open door. I moved out toward an empty taxiway and ATC immediately told me I was too close to an active taxiway. I explained why and he said, “Understand, but you can’t say there.”

It’s unfortunate that students are not taught more about this subject. However, many pilots are aware of their prop or rotor blast and act courteously and try to minimize the impact on others. However, some either don’t understand or care. To protect yourself and your aircraft around an airport or heliport, I think the best advice is to always assume you could be subject to a prop blast or rotor downwash.

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12 Responses to “Rotor downwash”

  1. Chris L. Says:

    Good topic… I see this happen frequently with business jet aircraft.

    Recently, I saw a large business class jet (>30,000 lbs) turn around sharply near a small piston-single aircraft. It flung around the control surfaces, and pulled all the tiedowns taught. Luckily it was tied down but it was still not a pretty sight as it was completely preventable.

    I think before starting, powering up, pulling pitch, hover taxiing, and flaring to land. Remembering that any power being used creates air disturbances that can travel out and away from the aircraft in all directions.

    Safe flying and enjoy the ride.
    Chris

  2. Avi Weiss Says:

    Rotor downwash is indeed a big issue on other aircraft to be sure, and like you I learned early on to exercise great care around other aircraft and structures, since a lot of damage can be done quickly given the amount of wind generated. One other related aspect of downwash you didn’t mention that is pretty important to consider is the “sidewards effect” of downwash on the actual helicopter that is generating it, particularly when taxiing down a taxiway with structures (such as hangers, or buildings) on either side of the taxiway.

    Taxiing slowly enough, or needing to stop for a moment, can create an “interesting” airflow pattern around the aircraft, that can cause considerable side-buffet, that can cause unpredictable and dangerous aircraft movement in the narrow confines of a structure-surrounded taxiway, if the pilot isn’t prepared for it. Even if the pilot is prepared, the unpredictability of the airflow can move the aircraft suddenly in ways and directions that seem counter to what is expected.

    When I taxi, I envision my rotor being twice the size it is in terms of what its “reach” can effect. While the rotor may not actually “touch” something else, its rotor wash can certainly be just as dangerous.

  3. Jon S Says:

    Jim, Tim is absolutely right that some pilots are considerate of it, while others are not. And that goes for all pilots, not just on the helicopter side. I have a feeling that the type of pilot who subscribes to this blog, is a member of organizations like AOPA and HAI, actively maintains their proficiency and aeronautical knowledge by participating in programs like WINGS, and who considers themself a professional no matter what level of certificate they hold, probably takes great care to fly neighborly. For helicopter pilots, that definitely includes minimizing the effects of our rotorwash on people and property; and for a r/w CFI, that includes teaching it to students. Every one of my students is taught to “be aware of your downwash, and avoid damaging property or injuring persons; do not hover near parked aircraft, open hangar doors, or people wearing bathrobes.”

  4. chris Says:

    For me, it was always the other way around: I trained at a busy, uncontrolled airport with extensive helicopter operations, but found that the fixed wing drivers were largely oblivious to helicopter…well, helicopter operations in general, but also to the risk of taxiing by or under a helicopter. I can’t tell you how many times I terminated an approach because an RV or Cessna pulled onto the taxiway reserved for helicopter operations, right under our approach path.

    Because of the number of helicopters operating at our airport, there were usually several helicopters being pre-flighted while others were hover taxiing into or out of the apron. No formal training, but you learn to close and latch all doors, secure flight plans, and keep cowlings closed when you’re on the apron.

    Either way, I think it’s a good topic. Since the info in the AIM is spread out over several chapters, I thought it’d be a good idea to create a lesson plan on it. You can find it
    here
    .

  5. Ehud Gavron Says:

    s/affect/effect/

  6. Dennis L Day Says:

    A few years back I had just landed at SJC and was about 30 seconds into my 2 minute cool down when a guy in a Cessna -150 taxied up and shut down next to me. I was in a SK-58T with both engines running (rotor turning) and he put his left wing tip less than 3 feet from the side of the helicopter. He just got out and walked away, oblivious to the four 55+ foot blades turning over his head and aircraft.

  7. Richard Factor Says:

    I could easily embellish this into a “Never Again” column, but the only lesson I really learned is for the other guy to not have done what he did. I had just landed in my Cessna 172 and was slowing down on the runway when a helicopter on the grass next to the runway decided that would be a good time to take off. The rotor blast literally blew me sideways off the runway. I was still going just fast enough (with full flaps) that an immediate application of power prevented me from hitting the ground sideways, and there was (barely) enough space to initiate a go around. This was at an airport where a touch-and-go is prohibited because of limited runway length.

    The helicopter was gone by the time I completed the circuit; to this day I have no idea if the pilot was aware of the potential accident he caused.

  8. Rich Romaine Says:

    Agree that while heavy aircraft wake effects are well publicized, there should be more awareness trained into the fixed wing student/community on the potential dangers of helicopter wake effects. I watched a 172 almost end up inverted at 200′ after he took off from a taxiway (authorized onboard a military base) where an SH-3 had been doing steep touch/go’s. Since the tower wasn’t really that familiar with light aircraft and the 172 driver was probably used to flying something much heavier/faster, neither gave the issue enough heed. Fortunately a good outcome as the 172 pilot righted himself and came back to land…probably with some laundry to do.

  9. Chris Gonsoulin Says:

    I was on final in my Saratoga about 10′ off the runway. A helicpoter had flown over the same runway 50′ above it about 3 minutes before I was to land. I hit his propwash and ballooned up 20′ just before touchdown. fortunately I had plenty of runway and was able to adjust and land safely, but the sudden upblast did surprise me and my copilot/instructor. It could have been the oposite and slammed us down onto the runway instead. I’ll wait longer to land after helicopter traffic in the future.

  10. Ehud Gavron Says:

    Speaking of rotor downwash… this is a good read on the effects of static electricity and dust on helicopters.
    http://www.michaelyon-online.com/the-kopp-etchells-effect.htm

    E

  11. Dane L Says:

    Another thing to consider is that not everyone on the ground knows just how much rotorwash a helicopter can produce. It’s especially important when landing to pick up passengers to ensure that you can do so without moving around cargo, blowing ball caps off, or creating a brown out situation for yourself. Many times in the wildland fire world we will have a bucket dropped on a helispot before before a troop shuttle begins to ensure the pilot maintains good visibility on final.

  12. Chris Anderson Says:

    Most pilots are aware of the ongoing anomosity between fixed wing and rotary wing aircraft. It continues to amaze me that it exists at all, especially in this economy, but I can see why when incidents occur that boil down to simple courtesy as human beings, never mind otherwise talented and intelligent pilots. I’m a fixed wing CFI and am working on my rotorcraft add on rating. My helicopter school is situated near the fuel pumps at the small airport where I teach so I know many of the pilots of both schools. There is also a small cafe near the fuel pumps that provides outdoor seating to customers, most of whom are naturally pilots. One afternoon last summer several fixed wing pilots were having lunch as a helicopter instructor and his student pulled an R44 into place near the fuel station using an electric dolly. As they began refueling another student borrowed the tow dolly and went off to another helicopter. The fixed wing pilots eating lunch immediately began to make side bets on what was going to happen next. The borrowed dolly never returned. The R-44 pilots jumped in and fired it up. Half of the fixedwing pilots were cheering and the other half were cussing as money changed hands. Sure enough the R-44 lifted off and instead of hovering away from the cafe area, turned right into them as they hover taxied out to the runway. The rotor wash not only cleared the table where the fixed wing pilots were sitting, it flipped it and a couple others over. The cafe door slammed shut, chairs and trash cans were blown around and limbs and other debris peppered the cafe’s large windows. Even customers inside ducked. The cheering immediately stopped and a fury of not-so-polite gestures followed. The helicopter instructor smiled and responded with a salute of his own. I was both appalled and embarassed.

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