Helicopter questions

[Matthew]

Might as well put this in the "Training" forum:

The accident at Pearl Harbor got me looking into at least one flight envelope I didn't know about - settling with power.

On the way home from work, I got to watch our local traffic chopper guy doing his job. As I was getting into my car, I could see him hovering over one of the most messed up highway intersections in the KC area. Seeing him hover is never a good sign, because that means he's filming something gone wrong.

He flies a Robinson now. He was hovering about 1000' AGL while he did his report.

My questions: hovering. Is there an operational ceiling? It was pretty windy, so he might have had some forward airspeed even though his groundspeed was zero, does that matter?

 

[Velocity173]

Yep, helos have ceilings. Different types as well.

Not a Robbie guy but for instance, the B407 has an 11,000 ft hover limit for both IGE and OGE. Max operating altitude (limitation) is 20,000 ft.

At 1,000 ft, while obviously OGE and requiring more power than IGE, a Robbie should be able to hover with no problems. Yes, a headwind, just like for airplanes, is beneficial but for different reasons. The headwind for a helicopter decreases induced flow and reduced rotor tip vortices, thereby reducing drag and the amount of power necessary to sustain flight. We call this translational lift. If it's strong enough of a wind, it becomes effective translational lift (15-24 kts ...ish). In forward accelerated flight, as you go thru ETL, the aircraft actually climbs without any increase in collective or pitching back of the cyclic. Wind can make a huge difference in maintaining flight for an aircraft operating at max altitude / gross weight.

If the news guy were to lose an engine at 1,000 ft, he'd have sufficient time to reduce collective (auto), nose it over to get some speed and find an open field / parking lot to set down in. A light little Robbie can auto at darn near ETL in the right hands. In a 407, 55 kts is the min I'm looking for.

 

[denverpilot]

Yes. There's multiple service ceilings so to speak.

In ground effect hover, out of ground effect hover, and forward flight.

It ties back to what you were thinking about. If the wind is calm the rotor system is producing all of the lift via rotation.

In forward flight (ok any direction really) the addition of what we fixed wing folks think of as "airspeed" also adds to the lift produced for the advancing blade.

Just like for us fixed wing schlubs, there's a free book on the whole shebang from FAA...

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/helicopter_flying_handbook/

 

[Matthew]

Is there a point between IGE and OGE where there is a dustinct difference?

I've talked to the local newschopper guy, a really nice guy and a good GA advocate, and heard him mention the white out that happens when landing/hovering in snowy conditions. Is there a condition where air gets dispaced IGE then gets sucked back in from above? I think this is a problem in confined spaces?

 

[RotorDude]

Is there a point between IGE and OGE where there is a dustinct difference?

I've talked to the local newschopper guy, a really nice guy and a good GA advocate, and heard him mention the white out that happens when landing/hovering in snowy conditions. Is there a condition where air gets dispaced IGE then gets sucked back in from above? I think this is a problem in confined spaces?

IGE becomes OGE once you are more than a couple of rotor diameters above the landing zone.
Whiteout/brownout is always a danger when landing, and yes, it will get sucked in and visibility can go to zero before you can say Frank Robinson.

 

[Velocity173]

Is there a point between IGE and OGE where there is a dustinct difference?

I've talked to the local newschopper guy, a really nice guy and a good GA advocate, and heard him mention the white out that happens when landing/hovering in snowy conditions. Is there a condition where air gets dispaced IGE then gets sucked back in from above? I think this is a problem in confined spaces?

You can tell the difference going into / out of IGE more so if you're heavy and operating at a high DA. If you're climbing out in a vertical take off like in EMS style (altitude over airspeed), you can feel the climb rate slow to a crawl, you look down and you're temped out and torqued out. Next thing you know, you get a "check instrument" light because you're pulling 102 %...oops. Slight reduction in collective, nose it over, get thru ETL and you're home free.

The air getting sucked back into the rotor is called "recirculation." Yes, confined area stuff. Once again that goes back to induced flow, which creates in induced drag, which results in increased power requirement. It can make you work your butt off especially landing at a high rise pad and your rotor wash is being recirculated back at you in varying degrees. The collective gets a workout.

White out can suck just as bad as brownout sometimes. Especially at night and under goggles, it's just not restricting your vis it reflects light so all you see is one green mess. At some point, the PIC has to make a decision to land or abort the approach. Many a helicopter has flipped over (dynamic roll over) while trying to pull off a zero vis white out / brown out.