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Chop tail off in the hover??

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Chop tail off in the hover??

Old 13th Mar 2021, 16:45
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Seriously, is there any helicopter that you know of or have flown that would not have provided sufficient margin under those conditions? And no corner cases like it was a hurricane or something. Just a plain old nice flying day like they had.
No, simply because we operated with a minimum of a 10% thrust margin whenever possible, especially for high power scenarios like confined areas, mountain flying and any OGE hovering.

You can calculate your thrust margin by looking at the max weight on your OGE graph - for them 2500lbs and reducing that by 10% - ie 250lbs which is 120 lbs lighter than he was at the time of the accident.

His DA was around 1200' given the temp and elevation so he was further up the graph than you imply.

The example in the R44 POH of weight and balance shows full fuel isn't available with 3 POB and a small amount of kit - how much baggage would they have for a fishing trip? And the example uses 170 lbs per pax which is light by anyone's estimation, especially in outdoor gear.

Given the layout of the HLS and the wind direction he should actually have had a reasonably clean airflow, certainly above the treetops even though the report cites mechanical turbulence from the low buildings and the trees (with a max estimated of 20 kts, I feel this is unlikely.

Not sure why you think the yaw induced panic could have happened anywhere on the trip - the proximity of the trees was what seemed to panic him.
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Old 13th Mar 2021, 17:46
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Originally Posted by [email protected] View Post
No, simply because we operated with a minimum of a 10% thrust margin whenever possible, especially for high power scenarios like confined areas, mountain flying and any OGE hovering.

You can calculate your thrust margin by looking at the max weight on your OGE graph - for them 2500lbs and reducing that by 10% - ie 250lbs which is 120 lbs lighter than he was at the time of the accident.
That's how YOU operated. Unfortunately, in the world of light helicopters, in order to get any real work done, only loading to 90% of max. gross is usually a dream.

His DA was around 1200' given the temp and elevation so he was further up the graph than you imply.
Not at all. If you enter the chart at the 2370lb line, move upwards to where it intersects the 23.6C line (interpolate as required, of course), then across to the left, you will see he can operate at up to a pressure altitude of over 5000ft at 23.6C, i.e. a density altitude of over 7000ft. There is no problem here. Again, he had tons of margin. Not in your book, or the way you fly for the military, but tons in any light helicopter operator's book.

The example in the R44 POH of weight and balance shows full fuel isn't available with 3 POB and a small amount of kit - how much baggage would they have for a fishing trip? And the example uses 170 lbs per pax which is light by anyone's estimation, especially in outdoor gear.
Where are you getting your numbers? Basic empty weight of a Raven II is 1510lb. Full fuel is 287lb. Max. takeoff is 2500lb. That leaves 703lb for people and stuff. Few R44s are that light. Let's say he's got 20lbs of options on board (which is very conservative, it didn't have a lot of options). Call it 683lbs. That's three 200lb guys and 80lbs of cargo. And that's about right, because the only place to put that much stuff is piled on one of the seats. You can't fit it in the stupid little cargo areas under each seat. Again, I'm not seeing any problems here. In fact, this all but proves he was not over gross at any time during the flight unless his cargo was gold bars or him and his passengers were huge, both an unlikely state of affairs.

Given the layout of the HLS and the wind direction he should actually have had a reasonably clean airflow, certainly above the treetops even though the report cites mechanical turbulence from the low buildings and the trees (with a max estimated of 20 kts, I feel this is unlikely
Agreed!

Not sure why you think the yaw induced panic could have happened anywhere on the trip - the proximity of the trees was what seemed to panic him.
I'm basing my assessment on the following passage from the report: "When the helicopter cleared the tree tops, it began to slowly yaw to the right. The pilot applied left anti-torque pedal input; however, the helicopter continued to yaw and the yaw rate increased. The pilot then deflected the anti-torque pedals to the right and back to the left several times to check for pedal response while the helicopter continued the right yaw. The pedal inputs did not arrest the right yaw.As the pilot was trying to control the yaw rate, alternating nose-up and nose-down pitch excursions began with increasing amplitude. After at least 2 full rotations to the right the main rotor severed the tail boom as the pitch excursions increased beyond a controllable range."
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Old 13th Mar 2021, 18:16
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Any trip is only as good as your planning. Weights, fuel, endurance, weather are the staples of planning and shouldn't reveal any surprises. What seems to have surprised this guy, as a relatively low-time inexperienced pilot, were the planning considerations that are needed to operate safely in and out of a confined area. When you're grizzly and ugly, a confined area is rotor span plus 2 feet. When you are just starting, an open football field can be a confined area. The accompanying aircraft with him got uncomfortable and threw it away, this guy didn't realize he'd run out of ideas until he was over committed to the landing. He was obviously thinking of getting home and maybe what a great fishing trip this had been, instead of thinking what 'gotcha's' were lining up for him. It's a tale as old as time, if you change the plan, change the thinking.
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Old 13th Mar 2021, 20:39
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A78, there is no “your world” vs crab’s military world (at least not this time round).

I admire your patience. You are of course 100% right. And crab didn’t read the book.

The MTOW (of 2500 lb) is not a power limit. The power margin is not the difference between the actual weight and MTOW, but between the actual weight and the weight the engine could lift under the current circumstances (disregarding MTOW restrictions). Or as you correctly pointed out, by the difference between the current PA and the OGE ceiling at the current circumstances (which was massive).

The only limit was the pilot’s lack of skill and recency.
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Old 14th Mar 2021, 10:58
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And crab didn’t read the book.
Mea Culpa, that's what comes of rushing things when the rugby is on - doh. The example in the POH has 4 POB not 3.

What was I thinking - questioning aa777888?, the font of all Robinson related knowledge

Last edited by [email protected]; 14th Mar 2021 at 11:11.
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Old 14th Mar 2021, 20:50
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Originally Posted by [email protected] View Post
Mea Culpa, that's what comes of rushing things when the rugby is on - doh. The example in the POH has 4 POB not 3.

What was I thinking - questioning aa777888?, the font of all Robinson related knowledge
Surely he makes a good point?

Taking procedures from (relatively) powerful twin turbine aircraft and applying them to R44s is not a practical or realistic way to operate.
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Old 14th Mar 2021, 23:19
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Taking procedures from (relatively) powerful twin turbine aircraft and applying them to R44s is not a practical or realistic way to operate.
For those earning a living using the aircraft as a tool - probably not, but they are likely to be more experienced and better trained and therefore far more likely to anticipate problems and be better placed to deal with them if they occur..

Those with PPLs and low time would be better served to give themselves as much safety margin as possible.

Operating into confined areas at close to max gross weight is something to be done very carefully and progressively.
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Old 15th Mar 2021, 00:38
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Originally Posted by [email protected] View Post
Operating into confined areas at close to max gross weight is something to be done very carefully and progressively.
Hmm,...that was basically every day training in the R22.
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Old 15th Mar 2021, 07:16
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Hmm,...that was basically every day training in the R22
Clearly I am talking about proper confined areas like the one in this accident, very limited on space and requiring OGE hover and vertical descent, not just something you have to make a slightly steeper approach into.
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Old 15th Mar 2021, 15:46
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Originally Posted by [email protected] View Post
Clearly I am talking about proper confined areas like the one in this accident, very limited on space and requiring OGE hover and vertical descent, not just something you have to make a slightly steeper approach into.
So am I
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Old 15th Mar 2021, 16:32
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My PPL(H) training was into a site surrounded by trees, requiring OGE hover and about 100ft vertical descent / ascent to leave. Same site was used on my PPL(H) skills test.
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Old 15th Mar 2021, 20:03
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And are you both typical of the PPLH trainees? Do you think all PPLH trainees operate out of such sites?

What is taught regarding performance planning on Robbies regarding confined areas?

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Old 15th Mar 2021, 21:02
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Originally Posted by [email protected] View Post
And are you both typical of the PPLH trainees? Do you think all PPLH trainees operate out of such sites?

What is taught regarding performance planning on Robbies regarding confined areas?
Well, I don't know what the "typical" training is, as I am not a CFI.

However, the way I was taught to handle off-airport landings is to crawl it in, basically just riding that vibration down at around 150fpm. So before committing I'd pull it back to pretty much a hover (while still high enough to abort) then check my MAP to see how much I have between what I'm pulling and what my takeoff limit is. If there's at least an inch and a half, or two (depending on just how steep and how high the takeoff will need to be) go for it.

Now I can't speak for other schools, but I went to one of those "CFI Factories" that pumped out CFIs like Tic-Tacs.
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Old 15th Mar 2021, 22:05
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That's not performance planning, that's a reasonable technique for confirming the performance you have is sufficient for want you have planned to do.
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Old 15th Mar 2021, 22:37
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Originally Posted by [email protected] View Post
That's not performance planning, that's a reasonable technique for confirming the performance you have is sufficient for want you have planned to do.
Hmm,...guess you're right. What can I say, most of my off-airport landings are of the, "hey lets land there" variety.

I'm sure there's some pre-flight performance stuff they taught me, but I'd have to go look for it (think its on my kneeboard), as I haven't actually "planned" to land off-airport since my checkride.
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Old 16th Mar 2021, 08:12
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I'm sure there's some pre-flight performance stuff they taught me,
You don't need much - the OGE hover ceiling vs gross weight chart in the POH is the place to start having worked out your pressure altitude and expected gross weight.

You need at least OGE performance and ideally some extra - unfortunately there are no graphs to tell you how much extra you have got.

Hot and High is correct that the MTOW isn't a power limit but taking 5 or 10% off the weight would guarantee you a thrust margin of probably more than you need if the weight line is the first limit you hit rather than the OAT or Pressure altitude.

If you have the performance on the chart then you just need to confirm it before committing to landing - I'm sure you check your hover MAP against the placard to make sure it is correct before transitioning.

Once in the vicinity of the landing area, pull to your calculated max take off MAP - ie your max continuous plus 2.8 to make sure it is available without Nr decay or exceeding any other limits.

One problem is that the OGE graph is based on 5 min take off power and not the max continuous MAP which may pass people by if they are not paying attention - the problem being that if you need 5 min power to achieve OGE, you have no spare to deal with turbulence or any unexpected rate of descent - hence my advice - especially if you are hot and high, to have a thrust margin.

Now a 5% thrust margin was defined in various military Operating Data Manuals (same as POH) as sufficient to overcome light turbulence or manoeuvre gently in the hover - in a couple it quantified a vertical rate of climb of between 100 and 200 ft/min so it is not a huge amount of excess power.

Clearly such advice doesn't exist in the POH but you could experiment to see what difference 1 inch extra MAP gives you from an OGE hover - it will at least give you an idea of the difference between Sea Level at plus 23 degrees and 5300' at plus 23 degrees since the max continuous MAPS are only about 1.4 ins apart from the placard.
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Old 16th Mar 2021, 11:08
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R44 Raven II POH is available online from Robinson. Section 5.5 (Performance) contain the graph of weight / OGE Hover, Take-Off power, Nil Wind at Density Altitude.

In addition, relevant to the actual Tread topic, Section 4 contains the checks that should be done after every engine start, and the hover checks - which includes "note MAP"

Craab - you make a good point. Don't recall being taught in PPL lessons "performance planning" for the confined area flight we were going to undertake. General planning for a flight (weight & balance, performance, fuel, route and diversions, etc) but not specifically planning ahead for this. Certainly was taught - as Robbie notes - how to assess the site, check available power for OGE and descent / climb-out, and how to approach and get into the site. That is not the same thing, as you say. There is therefore room for a training improvement there.

Training did include "artifically lowered" power so that you had to decide not to go in, or once in artificially lowered margins to show what might happen you now had to get out with less power than you might have wanted. This included towering but also restrictions so tight that you could not get out - as a means to showing you how to take responsibility for stopping and rethinking, rather than pressing on until you hit a tree.

I thought (still do) that the technical training was good and it left me with with this. The site we used in training for confined area was very (by my standards) tight. When first shown it from above, my reaction was "I appreciate the skills and training, but I am never going into a site like that when I have my license". I have stuck to that decision ever since, and take the view that "just because I can" doesn't mean that I should. There is, in reality, no justification for me to act otherwise as I only fly for pleasure. I do use these techniques - icluding OGE hover and descent into a lawn surrounded by Scots Pine trees, but the space is more than 3x larger than my old training area.

I would add; some years after getting my PPL the airfield stopped the use of that confined site and instead provided one surrounded by low bushes & shrubs and actually open on one side. Nothing like as challenging, and though technically "safer" to learn in I don't think it provides as good a training experience. Doing annual LPCs at that field, using that site is pretty much a non-event to me, and I think the risk is that you don't see the value of making all the right checks and asking the right questions as then you land on something that is "less difficult" than some of the Heli Pads provided on the airfield (close buildings giving recirculation issues, for example).
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Old 16th Mar 2021, 15:09
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Originally Posted by [email protected] View Post
You don't need much - the OGE hover ceiling vs gross weight chart in the POH is the place to start having worked out your pressure altitude and expected gross weight.

You need at least OGE performance and ideally some extra - unfortunately there are no graphs to tell you how much extra you have got.
Exactly right.

Hot and High is correct that the MTOW isn't a power limit but taking 5 or 10% off the weight would guarantee you a thrust margin of probably more than you need if the weight line is the first limit you hit rather than the OAT or Pressure altitude.
Those margins simply don't exist in the real world of Robinson helicopter operations. R22 useful load is 490lb. With two 170lb people inside that's less than full tanks, or less than two hours endurance. Raven II useful load is already discussed below and is equally challenging with 4 people and stuff on board and a desire to get real work done. If you are in a Raven I, or a fat pig of an R44 like a Clipper II (aka Raven II with pop-outs) with air conditioning, now you have lost 100lbs of useful load. The bottom line is that these machines are nearly always flying at near max. gross when full.

The only time you have the sort of margin you are talking about is when you are flying an R44 with only two people on board (or an R22 with one). If you want a "rocket ship", two people and half tanks. And the performance difference is dramatic. That makes for safer initial training, but ultimately one must learn to fly the machine the way it will really be used, and that means at max. weight. In the R22 that happens by default. In the R44, at least at the school I attend, that happens by finding two other erstwhile individuals to fill the back seats and endure max. performance takeoffs, confined space landings, and ham handed auto's without puking (screaming is allowed). Normally these are more students and it's actually quite a bit of fun as each student rotates through the pilot's seat. The repartee meter does get pegged!

Robinson marketed the R44 Cadet to address this issue, but it's just such a dumb choice on so many levels. Few small schools will buy one because they need a machine they can use for more than just training. And it actually offers too much performance and does not prepare one for the real world of a regular 44 loaded to the gills.

If you have the performance on the chart then you just need to confirm it before committing to landing - I'm sure you check your hover MAP against the placard to make sure it is correct before transitioning.
If you mean check your hover power vs. the 5-minute max. on the placard, of course. That is (should be) taught and is a no-brainer. It's generally taught that if you've got 2" MP below 5 minute max. you can make a max. performance takeoff. This was well and thoroughly taught to me, with innumerable exercises involving artificial power limits. During my private and commercial training there was a lot of emphasis placed on "making it out safely", including such things as shuttling partial loads to a spot where a max. perf. was not necessary and other techniques.

Once in the vicinity of the landing area, pull to your calculated max take off MAP - ie your max continuous plus 2.8 to make sure it is available without Nr decay or exceeding any other limits.
Actually the landing power check, if you even need one (you did plan it, right?), is generally as follows: assume level flight 500ft above the landing altitude at Vy, then see if you've got 6 or 8" of MP margin (depending on who you talk to) against 5 minute power (don't forget to check OAT, pressure altitude and the placard!) If you do then you are probably OK for OGE hover. This is poorly taught in my experience. At least it was where I learned. We did spend a lot of time exploring the lack of OGE hover using artificial power limits in a run-on landing environment, but never for spot landings, which I felt was an unfortunate hole in the instructional repertoire. I have since developed that experience after the commercial check-ride, but I feel it should have been sooner. In the school's defense it can be difficult to train if you don't live in a hot/high environment, and the potential for a training accident is high.

One problem is that the OGE graph is based on 5 min take off power and not the max continuous MAP which may pass people by if they are not paying attention - the problem being that if you need 5 min power to achieve OGE, you have no spare to deal with turbulence or any unexpected rate of descent - hence my advice - especially if you are hot and high, to have a thrust margin.
Welcome to the wonderful world of very light helicopters where those margins are razor thin if they exist at all.

Now a 5% thrust margin was defined in various military Operating Data Manuals (same as POH) as sufficient to overcome light turbulence or manoeuvre gently in the hover - in a couple it quantified a vertical rate of climb of between 100 and 200 ft/min so it is not a huge amount of excess power.

Clearly such advice doesn't exist in the POH but you could experiment to see what difference 1 inch extra MAP gives you from an OGE hover - it will at least give you an idea of the difference between Sea Level at plus 23 degrees and 5300' at plus 23 degrees since the max continuous MAPS are only about 1.4 ins apart from the placard.
Again we have the rules of thumb for MP margins as discussed above, that are admittedly not in the POH, to go by. They have proven themselves over the many decades that Robinson helicopters have been in service.

Regarding confined space operations: I can't speak to other schools. The school I use is a pretty good school in this regard. Like any school they are obviously focused on getting people to pass the FAA checkride. But they will train you just as hard and thoroughly as you can safely be trained. Not every student learns at the same rate, not every student wants to be an accomplished helicopter pilot (e.g. wealthy guy in a hurry--just make me good enough--one major reason for the Robinson accident rate). But for folks who have the drive to train more comprehensively, this place will take you way, way beyond paved runway to paved runway and Farmer Jone's field. During my commercial training surprise landings were as common as surprise auto's. Instructor says "See that hole? Put me in there. See that pinnacle? Put me on top." One of the more challenging sites is a mountaintop transmitter site that is very popular with the instructors. It's a forest of guy wires and tall pine trees and a 15ft square gravel pad on a jaunty slope. Really great stuff.

One does see quite a bit of this sort of thing on the schools who like to publish on Youtube. Mischa Gelb's stuff, for example. One would like to think that all schools are teaching the same stuff to the same level, but of course that is not true.
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Old 16th Mar 2021, 16:01
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So you'll be able to tell me what extra performance 1.4 inches of MAP gives you in an OGE hover then?
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Old 16th Mar 2021, 16:16
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Originally Posted by [email protected] View Post
So you'll be able to tell me what extra performance 1.4 inches of MAP gives you in an OGE hover then?
Give me a procedure to follow and maybe I can make that measurement.
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