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Falling through the bottom


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The area I train in is 5,000' MSL, and usually around 6-7000 DA. Sometimes while doing auto's it seems like we are ""falling through the bottom", meaning when I initiate the flare it doesn't slow the descent rate or airspeed. At first I didn't understand what it meant, what it felt like, or what it looked like. Now i have a better idea of the feeling and do a slight flare earlier when it feels like it's happening to see what it feels like. The question I have is what is happening when I'm falling through? Is it the difference from winds/temps at ~800' to ground level, is it a shift in the winds, or is it just that the air closer the ground is significantly hotter/less dense? It just worries me that if I was actually in an emergency situation without the ability to go around, what would the outcome be if I was "falling through"? Just for reference this is in an R-22 with Airspeed about 65 knots, and VSI usually at 1600-1700 in a straight in. When it's "falling through" it's usually indicating 1,800' or higher at the 200' check.

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I typically associate "falling through the bottom" with not flaring hard enough. If you are too gradual with the flare it won't arrest the vertical speed enough and you feel the ground rushing up on you.... especially true at high DA where your vertical speed is even greater. I would not do a slight flare earlier... that would just the make final flare even less effective. You have to get used to seeing the ground rush as you are established with your airspeed in the auto until your initial flare height at 40-50 feet.... then pull her back!... With the high DA it may be necessary to start bringing in pitch earlier in the flare to arrest the descent.

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Sometimes while doing auto's it seems like we are ""falling through the bottom", meaning when I initiate the flare it doesn't slow the descent rate or airspeed.

 

The question I have is what is happening when I'm falling through? Is it the difference from winds/temps at ~800' to ground level, is it a shift in the winds, or is it just that the air closer the ground is significantly hotter/less dense?

 

It just worries me that if I was actually in an emergency situation without the ability to go around, what would the outcome be if I was "falling through"?

 

As Apiaguy called attention to indirectly in the post above, you’re simply not preforming the maneuver correctly. The main purpose of the flare is to stop the rate of descent. Secondary, the flare slows forward speed and increases the RPM.

 

However, the flare is only effective in accomplishing its main and secondary task if the helicopter has forward speed across the ground. Without sufficient forward air speed the flare is ineffective in arresting your rate of descent, thus your so-called “falling through the bottom.”

 

Bottom line, if your rpm, airspeed or timing with respect to flare application is inadequate, the flare effectiveness will be deficient.

 

Apiaguy is correct in stating that you must become accustom to seeing the ground rushing up as you maintain your established airspeed until your initial flare height. Some subconsciously start easing that cyclic back as the ground rushes up thereby bleeding-off needed airspeed prior to the flare. Consequently, ending up starting the flare, as the airspeed falls below 45-40 knots, were the flare is ineffective in arresting the rate of descent. Take note of your airspeed at flare entry next time.

 

It’s not a textbook or by the numbers maneuver. Constantly changing characteristics even from the same helicopter from one day to the next. It’s mostly visual judgment gained by practice and experience. Get with an experience Flight Instructor and he or she should be able to isolate the problem and put you on the correct path.

 

You need to get it done in the helicopter in the air.

Edited by iChris
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I don't think this is an airspeed/attitude issue. It sort of feels like when you are in cruise flight going through an updraft and as you fly out of it you feel the helicopter drop and have to add collective. That's what the slight flare does is stop this increased descent. It seems to happen more often in the summer. This increased descent rate is usually felt around 100' when RPMs are green and AS is at 65. Next time it happens I'll double check everything to see if something is slightly off that I'm not noticing.

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You could be getting into a situation where the asphalt 100' and below is now artificially increasing the DA right before you are in a position to flare. There was an issue that came up a while back at work with a helicopter doing a hoist op. Everything was fine with the machine... as they moved in closer to the rock face the pilot had to continually increase power. They were at the top end of their power settings to begin with. Hovering near the rock face made it an issue. Move away from the hot rocks, power got better. Slide back in.... issue came back. Came back later in the evening when it was cooler and did the hoist. It was something for discussion at the local restaurant. But it made sense. If you are pushing the limits as it is...... maybe the extra few degrees could be all it takes. It wasnt anything we did any studies on.... just pilots sitting around thinking "Hmmmmm.... could have been."

Edited by Flying Pig
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+ 1 to Flying pigs theory. I have seen this happen when it is sunny and in an auto over different color terrain below 100 feet. It can be a very stable condition so that each time we did an auto it was reproducible and predictable.

 

What were the conditions when you experienced this?

 

Try doing it on a cloudy day or near sunset and see what happens.

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I'm going to make a statement that I hope doesn't stir up too much controversy.

 

-That helicopter doesn't belong there.

 

I'm not tying to pick on the flight school (I don't even know who it is) or the helicopter (R22).

I actually really like the R22 and I absolutely love flying in the mountains and high DA's for the challenge of it…..however, I don't want anything to do with an R22 at that DA.

 

I recall a few years ago landing on a mountain ridge at 7,000' on a cool day. The Long Ranger I was flying was at its limits to land safely. We were however, within the charts of performance. After landing and shutting down the crew mentioned to me that an R22 crashed on the same site the year prior. All I could say was "they had absolutely no business here with that machine".

 

You need to know your limits as a pilot and know the limits of your aircraft, period.

 

I hate hearing flight schools promote "high DA training" and "all your training time counts as mountain time"

 

I would try doing an auto with that helicopter where it belongs (low DA's) and see if that helps.

 

No offense ment,

Fly safe!

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Flying Pig,

 

Yeah, I can't say I would recommend making that flight in an R22 lol.

 

The original question posted in this thred just made me think about it; "6-7000' DA" for training. It's honestly just asking for trouble to be training people up there in an R22. Just look up some NTSB reports and you will see what I mean.

 

I'm not claiming to be an expert; however, I have a fair amount of time teaching in the R22 and most of my "commercial" flying experience has been in the mountains in helicopters that are meant to be there.

 

I just don't want to see people get sold on the idea that they need mountain and high DA time during their training…you don't need it, you will get it when you're ready. It's just like many other things in your career that will come with time and experience. You always have something to look forward to and keep working towards.

 

So, like I said to the OP; just for the heck of it, go try a flight if you have the opportunity, at sea level. Flying an R22 is tough enough especially when you have low time…why make it harder than it needs to be?

 

Fly safe everyone!

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The area I train in is 5,000' MSL, and usually around 6-7000 DA.

 

Now i have a better idea of the feeling and do a slight flare earlier when it feels like it's happening to see what it feels like.

 

The question I have is what is happening when I'm falling through? Is it the difference from winds/temps at ~800' to ground level, is it a shift in the winds, or is it just that the air closer the ground is significantly hotter/less dense?

 

 

I don't think this is an airspeed/attitude issue.

 

It sort of feels like when you are in cruise flight going through an updraft and as you fly out of it you feel the helicopter drop and have to add collective.

 

That's what the slight flare does is stop this increased descent. It seems to happen more often in the summer.

 

 

What’s this “slight flare” you’re quoting? There’s no one-flare-fits-all solution. The flare timing and application required for an autorotation done with rotors in the green@65 knots, into a 12-knot headwind on a mild temperature day, will not be the same as required for an autorotation done with rotors in the green@65 knots, no-wind, on a hot day. The latter would require a more aggressive flare to arrest the higher descent rate.

 

Airspeed and attitude are an important issue. Airspeed is the source of energy for the flare. After you’ve establish your airspeed, holding a constant attitude we allow you to hold airspeed all the way to the flare were it is most needed.

 

You’re at the controls and you have to make the correct control inputs. If the rpm is in the green, the airspeed 65 knots, the flare properly timed and applied at the correct rate, will prevent fall-through.

 

The environment we fly in is constantly changing. You must adapt to fluctuating, irregular, and inconsistent conditions. That’s why the autorotation maneuver is mostly visual judgment gained by practice and experience and not a by the numbers maneuver.

 

Don’t make excuses about DA, updrafts/downdrafts, wind, too hot, too cold, etc. After you’ve done your best with your preflight action, becoming familiar with all available information concerning the flight, the rest lies in your inflight skill and experience.

 

Factors that affect the power required, affect your rate of descent. You can approximate the rate of descent in feet per minute by multiplying the required power (@ level flight at the same altitude & airspeed) by 33,000 and then dividing the result by the aircraft gross weight. Not so much the math, but the relationship.

 

Rate-Of-Descent ≈ (HP Power Required) (33,000)

(Gross Weight)

 

This post also relates to your Sept. 2014 post:

Link To: Weight VS Descent Rate-Autorotation; Posted Sept 2014

Edited by iChris
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As usual you can't argue with iChris' assessment. Although he points out not to make excuses for DA and its effects are pointed out to us from the beginning of flight training the perceptual effects of DA are often only gained through actually experiencing it. It's one thing to read that TAS increases with DA, it's another altogether to feel like your screaming along the ground way faster than usual for some reason or that rate of descent seems unexplainably high. I wasn't there and hate to second guess but would bet money that the kinesthetic sensation of "falling through the bottom" is almost guaranteed to be a result of fewer molecules occupying the same volume of air. 65 knots on one day just isn't the same as 65 knots on another day. The amount of flare to initially slow descent doesn't translate the same from day to day or even LZ to LZ because of this.

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"Ummm..... your R22 doesn't belong up there sir."

The mountain course we taught had us up in the Tahoe area in R22’s during the summer and winter seasons. Sometimes we’d stage out of Reno, other times out of Truckee… Fun times…. Challenging and sometimes scary… Subsequently, the company switched to S300CB’s and they performed about the same, if not a little worse…..

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I wasn't there and hate to second guess but would bet money that the kinesthetic sensation of "falling through the bottom" is almost guaranteed to be a result of fewer molecules occupying the same volume of air. 65 knots on one day just isn't the same as 65 knots on another day. The amount of flare to initially slow descent doesn't translate the same from day to day or even LZ to LZ because of this.

 

That’s true; the helicopters power-on level flight performance is congruent with its autorotation performance under the same conditions. More power is needed to hover in high DA conditions; consequently, more power is needed to arrest the descent rate and make a smooth landing at the end of an autorotation as a result of high DA conditions.

 

The rpm decay with collective pull is faster, the collective pull less effective, and the cyclic flare less effective; therefore, flare timing is far more critical. That’s why I recommended the OP get with an experience Flight Instructor to isolate the exact problem he’s having.

 

The R22 has the capability, since under CFR §27.87 it was demonstrated at 7,000’ DA; however, that doesn’t necessarily mean the same performance is easily repeatable by the end user.

 

As a general rule, autorotation training should be performed at no higher than the current IGE hover ceiling and for routine training, no higher than the current OGE hover ceiling. This is not a limitation, since safe autorotation landings can be made above those ceilings. However, there’s usually no need for routine training under the worst-case conditions.

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The mountain course we taught had us up in the Tahoe area in R22’s during the summer and winter seasons. Sometimes we’d stage out of Reno, other times out of Truckee… Fun times…. Challenging and sometimes scary… Subsequently, the company switched to S300CB’s and they performed about the same, if not a little worse…..

What was the point of switching to the 300CB? A 300C, yeah. Definitely. The CB? Heck no. You are MUCH better off in a Beta II.

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What was the point of switching to the 300CB? A 300C, yeah. Definitely. The CB? Heck no. You are MUCH better off in a Beta II.

Without getting into too much detail, Robinson Corp wasn’t willing to cooperate with a longtime request of the flight school owner. With that, a fleet replacement took place and, at the time, the CB was the only realistic option. Financially speaking -that is…. Even so, the school still offered the mountain course with the CB and with some course modifications; it did the job…..

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  • 2 weeks later...

The responses I get on this forum are pretty outstanding, it helps to have 10 different perspectives from pilots with much more experience than I have. I have a better understanding of what's probably happening.

 

I think it's a mix of everything mentioned; high DA, low pilot skill, in the warmer months significant difference between ground and temps aloft. They all work together against me.

 

As much as I want to believe I know what I am doing, I still have plenty to learn. It seems like manipulating the controls is easy, I can make the helicopter do what I want it to do. It's the recognition of when to do it that needs improving, the concept of "staying ahead of the helicopter". All in due time I guess....

 

On a side note, I just got back from the Robinson Safety Course, man what a difference! I want to fly at sea level all the time now. It's crazy how much more performance the 22 has there, you have like 5" of reserve power instead of hovering at MCP. The autos feel like a steep approach!

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