Rotor wash and helo ground ops questions

Pi1otguy

Pi1otguy

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While walking through the airport, a large helo (a Huey II? from the county) landed near the fuel pumps between me and the tied down C182. Because the helo didn't shutdown I decided to have me and my pax wait for it to fuel and depart before walking back to the plane. I figured there less paperwork that way.

So now I have a few questions that maybe the rotor guys here can chime in on

1) I was tied down downwind of the helo. If it was an R44 it such it might be no factor, but what does rotor wash look like for heavier birds?

2) Is it standard to refuel helicopters with the blades spinning?

3) What's a reasonable distance to keep from a helicopter when you're on foot?

Pic for context
image4.jpg
 
I was just discussing that with my helo-pilot nephew earlier today. I remembered this video:

 
1) depends on how high the aircraft was. If OGE (1.25 rotor disk height) and moving above ETL (16-24 kts) the effects in the ground aren’t that strong. That’s why if able, air taxi to a parking pad can be safer for parked aircraft than hover taxi. If hover taxing, generally in IGE, less than ETL, the downwash hits and not only flows outward but can have a strong vortice effect. In that case, it’s safest to give a wide margin for parked aircraft. Of course if you fly a real man’s helicopter and can ground taxi, you negate the majority of the rotor wash issue. ;)

2) yes, Rapid refueling or “hot refuel” is common for helicopters. Generally done for ops that require time constraints such as fire fighting, police, EMS, military, etc.

3) Again dependent on how high the aircraft is and how large. A Bell 205 “Huey” hover taxing below ETL and IGE, I think you’re probably looking at 30-35 kts below it. Shouldn’t really knock you off your feet. In fact, in the Black Hawk I wanna say it produces roughly 45 kt wind up to a rotor disk below and I’ve hooked up several sling loads without losing my footing.

Edit: it appears you’re asking about rotor wash while on the ground? Yeah negligible even at “fly detent.” Still gonna have downwash since even with collective full down or “flat pitch” the majority of the span of the blade still has an angle of incidence to it. Not anything to cause damage though.
 
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If it was on the ground and not generating lift, there would be no vortices of consequence. At the prior airport where I was located, there were many rotorcraft flights ranging from B 407’s to S 76ks and the occasional 92. I’ve experienced mild rotor wash once while landing closely after a S 92 made the usual taxiway approach to its pad. When they are on the ground, rotor spinning around 80-100’ from the taxiway, I have felt no rotor wash while taxiing by.
 
Pi1otguy said:
1) I was tied down downwind of the helo. If it was an R44 it such it might be no factor, but what does rotor wash look like for heavier birds?

2) Is it standard to refuel helicopters with the blades spinning?

3) What's a reasonable distance to keep from a helicopter when you're on foot?
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1) As mentioned there are some defining requirements. But generally, as the lifting capability of the helicopter increases, so does the rotorwash they put out.
2) Yes, for various reasons.
3) The general rule of thumb is outside of 3x the rotor disk diameter you should not feel any affects. But for reference, most medium helicopters are capable of 40 mph rotorwash wind speeds which for context tropical storm force winds start at 40 mph. In general, due to the dynamics of rotorwash it has the capability to make things fly that normally would not fly in a dramatic fashion. Unfortunately, in some situations, rotorwash alone has led to a loss of life, so it always best to respect its affects regardless of helicopter type.
 
Velocity173 said:
3) Again dependent on how high the aircraft is and how large. A Bell 205 “Huey” hover taxing below ETL and IGE, I think you’re probably looking at 30-35 kts below it. Shouldn’t really knock you off your feet. In fact, in the Black Hawk I wanna say it produces roughly 45 kt wind up to a rotor disk below and I’ve hooked up several sling loads without losing my footing.
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Sure felt like more than 45kt when one hovered directly over us and scattered our gear all over the runway in Syria :mad:
 
Sierra_Hotel said:
Sure felt like more than 45kt when one hovered directly over us and scattered our gear all over the runway in Syria :mad:
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Yeah I think 45 is good average but I believe I’ve got a chart laying around somewhere that shows between 30-60 kts. Obviously the heavier it is such as combat configured or in this case, external tanks, will push that number to the peak.

 
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Pi1otguy said:
3) What's a reasonable distance to keep from a helicopter when you're on foot?
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A pretty good rule of thumb is two or three times the blade radius, and maintain eye contact with the pilot.

Unlike an airplane, a helo can move sideways or rotate in place. The tail rotor is what you gotta watch out for.
 
OK, you rotor heads. For the test of us, what do OGE and ETL mean? I think I understand IGE means (I thinks it stands for In Ground Effect, but I could be wrong), but I have no idea what OGE and ETL mean. If you are going to use TLAs (I used to work for Intel, that's Three Letter Acronyms) please define them.
 
OGE - Outside Ground Effect (self-explanatory)

ETL - Effective Translational Lift
As speed builds up, the air flowing through the rotor increases (due to the forward speed) and becomes cleaner, as less of the rotor's own turbulent air gets recirculated. Happens around 20 knots, and at that point you will start to generate more lift for the same power than in a hover.
 
Velocity173 said:
2) yes, Rapid refueling or “hot refuel” is common for helicopters.
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But if I try that with a humble 172, all of a sudden the club would probably name a new rule after me.

Bell206 said:
But for reference, most medium helicopters are capable of 40 mph rotorwash wind speeds which for context tropical storm force winds start at 40 mph.
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Somehow telling my pax to clutch their purses as we walk through the tropical storm Bell seems like bad form.:p
 
Pi1otguy said:
Somehow telling my pax to clutch their purses as we walk through the tropical storm Bell seems like bad form.:p
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Ha. But the simple fact they have to clutch anything means you're too close to begin with.:eek:
 
Rotor wash, can I just use the stuff from NAPA or do I need to buy the expen$ive wash from Spruce?
 
It’s gotta be the STC’d and PMA’d stuff or it’s not legal :heli:
 
Bill said:
Rotor wash, can I just use the stuff from NAPA or do I need to buy the expen$ive wash from Spruce?
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Don't confuse it with the gallon of prop wash your instructor made you order from Spruce. While you're there, don't forget to grab 500 feet of flight line, that way you get free shipping. :rofl:
 
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