430 vs 407 airspeed limitations question

[407 too]

we are kicking tires (skids) on a bell 430, but have a question for you people (other than bells slant)

the 407 has a vne of 140, the 430 is 150

why the significant cold weather degrade of vne with the 430 ??

eg. 4,000 ' pressure alt. at 0 deg C
430 is 150 kts 407 is 140 kts

minus 25 C
430 is 120 kts 407 is 140 kts

that a whopping 30 kts off vne and 20 kts off the 407 - not good if you are looking to improve vne ??

any thoughts, is it just AI error compensation, are you still at 150 kts ground speed ??

[NickLappos]

That is probably due to rotor tip Mach effects, and is real. The airspeed system could not be that far off and still be certifiable. The regs call for + 5 knots in cruise as the max calibration error.

What is the rpm and radius of the 430 rotor, we can crunch the tip mach from that.

[rjsquirrel]

407 too,

watch that hover chart for the 430, they show a line for "all wind azimuths" and another line at much higher gross weight for "wind plus or minus 45 degrees off nose" and max gross weight.

The "wind all azmuths" line has normal tail rotor, like most helicopters, I am told.
The "wind off the nose" chart has no tail rotor control to spare, and is an LTE waiting to happen. I have heard that you should use the "wind all azmuth" gross weight for your operation to be safe.


PM me for more details if you want.

RJ

[Encyclo]

Bell provides the two types of chart to insure you have enough margin;

Landing on some rigs or other restricted helipads, you might not have the luxury of keeping wind at +/- 45. If you are operating in a non-confined area, proper technique would have you facing into wind.

Although this may appear to be stretching the aircraft performance, it is actually providing more accurate performance numbers for different conditions. Most other OEM publish only one chart...:confused: is that good or bad?

[407 too]

348 RPM and 21 ft radius

[rjsquirrel]

Encyclo,

No, I think you have it backwards. Most manufacturers provide helicopters and charts that provide you with enough tail rotor control to not worry about the wind, their charts are all the "wind any azimuth" line.

The extra weight that you carry if you load to the other line with the wind only off the nose has a lot less tail rotor capability, much closer to LTE.

In other words, the 430 chart lets you load up the main rotor with extra gross weight and weaken the tail rotor until you can't take a cross wind.

[407 too]

would you really get into an LTE situation or just encounter an over-torqe situation,

BIG difference as one would then assume the tail rotor would be undersized to counteract torque

[rjsquirrel]

The tail rotor is not undersized as long as you use the right line on the hover chart (the "wind any azmuth" line). If you mess up and come in too heavy with a crosswind, you will Not overtorque, you would run out of pedal, and start to spin. In effect, the main rotor torque is more powerful than the tail rotor can handle, so they offload the main rotor by reducing weight to keep the tail rotor happy - that's what the "wind any azmuth" line means.

That's why they tell you to keep the wind off the nose. If you use the higher weight on the "wind off the nose" line and get into a crosswind, you will get LTE.

They do not go out of their way to explain it, do they?

[407 Driver]

407 Too,
Not many 407 operators in Central BC that may be looking at a 430. I assume you fly DLA ? ;)

[212man]

407 Too,
not sure how the groundspeed is relevant in this discussion???

("any thoughts, is it just AI error compensation, are you still at 150 kts ground speed ??")

[NickLappos]

407 too,

It probably is Mach effect:

Those numbers show that at -25 degrees at 4,000 ft at 120 kIAS, the blade tips are at Mach 0.94.

At 150 knots at 0 degrees at 4,000 ft, the tip is Mach .95

Usually, we limit ourselves to mach .94 to .96 at the tip. This is shown on the S-76 power off Vne, which drops a bunch in cold temperatures, for this reason.

212man, I think 407 too is just saying "is it really going faster than the airspeed gauge says?" when he uses groundspeed. Wanna bet he knows the difference? ;)

BTW, RJSqurrel, that wind off the nose stuff I posted here on pprune about 2 years ago, and someone (the Sultan?) argued that it wasn't true, but you are right on.

For some reason, the FAA allowed the 412 and 430 to be approved to fly at weights where the tail rotor is inadequate to hover in any cross wind (!!!!!) The higher weights they allow on the chart where you have to be sure the wind is always off the nose are absolutely foolish for people to operate in. It is LTE waiting to happen, and the pilot who hovers there and runs out of pedal will find everybody blaming him, because the flight manual gives everybody else an excuse to be let off the hook. Operate at that higher weight, and you will be alone if something happens.

[407 too]

Nick,

that makes perfect sense, funny i din't think of that (guess thats why you get paid the big bucks)

rj,

thanks, great weight for this will be granted in decision


407driver

have to remain silent - for now :O


212man

what nick said


if this goes through, would be hard to say good-bye to the 407
(performance, fuel/weight management etc etc)

[407 too]

the shaded area with respect to wind azimuth is 45 deg off nose up to 45 kts.

that leaves a lot to play with

operating in the shaded area and having a 5 kt crosswind shift as you are about to touch down is not as drastic as with a 30 kt crosswind shift

how about a shift to the off-load tail rotor side ??

is this more of a Bell-cover-your-butt shading ??

i understand the reason for this, but 1 to 45 is a stretch

maybe over 20 kts would be more reasonable ??

:confused:

[NickLappos]

407 too,

Those are degrees off the nose, not knots!

I think the way to read those charts is:


wind from any azimuth = "Normal tail rotor capability"


wind within 45 degrees of the nose = "Almost no tail rotor capability"

[407 too]

Nick,

with respect to your last reply, re-read the chart, and found that i fell victim to poor understanding of presentation

white area, - all azimuths up to 35 kts, and 45 deg off nose up to 45 kts

shaded area, - relative winds plus/minus 45 deg off nose up to 45 kts

both are descibing activity in area b (shaded)

in effect area b is for winds 36 - 45 kts. (i suggested 20)

i focused on the description of area b only

that makes a lot more sense, wouldn't do a 25 kt downwind approach in my operation anyways !!

[Encyclo]

Nick, I'm a little surprised at your statement: 'wind within 45 degrees of the nose = "Almost no tail rotor capability"' As a former flight test guy you know that what goes into the flight manual does account for some safety margin, and is calibrated to a "min spec pilot".

OEMs don't make perfomance charts by flying test cards until an incident happens and then back off one notch to get the performance data. Again, there are margins put in so these charts are safe.

If we follow the approach that the +/- 45 chart is unsafe and we should go with the 360 chart only, why not do the same with any other performance charts that have variables?:confused:

[NickLappos]

Encyclo,

No, I undersand the words quite well, having discussed them with the FAA guys who helped write them. The limits do allow for positive control power during the maneuver, as written, but that is all. See Shawn's clarification of my original statement about "10%" remaining control authority in the hovering downwind thread. Any pedal input needed, including occasional hitting of the stops, is allowed, as long as when against the stops, the yaw is going in the direction of the pedal input! That is about as close to zero margin as anything I can think of.

The issue is the ability to predict the need for anti-torque. The chart as published is not unsafe, it is merely very marginal. Should you attempt to hover OGE, or in crosswind with the MGW, pretty bad things will happen. If you temporarily pull too much torque on entry to the hover, you will run out of pedal. When that happens, do not expect anyone to say, "Poor Baby!" expect them to say "Pilot error."

It is also true that the 412 and 430 are the only helos on the planet with that little tail rotor margin when operated at that weight, regardless of its approval status. The very least we should expect is that pilots who use that "extra" gross weight, (at the expense of tail rotor capability) should at least KNOW that is what they have done. Don't you agree?

Regarding the "min spec pilot" concept you think exists, I don't know where you got that from! The philosophy of the FAA is nowhere close to that "requirement". Procedures must be so that it takes no "unusual pilot skill" to achieve the result. In other words, procedures require the usual pilot skill. Min spec is a great deal below that. Few procedures are designed for min spec pilots, especially procedures where no pedal margin is built in.

[Shawn Coyle]

To add my two cents worth -
The 45 degrees off the nose segments are there to permit the helicopter to have a higher density altitude to operate in - and works on the assumption that the pilot can determine the wind direction within 45 degrees of the nose. If you can't determine the wind direction (lack of cues, etc) then you shouldn't use that chart.
Interestingly, there is no FAA requirement to have enough tail rotor to maintain a steady heading in a maximum power vertical climb (in some helicopters you can hover at maximum weight and be below takeoff power). Perhaps that would solve the problem.
And just because you are in this 45 degree segment doesn't mean you're on the edge of LTE, by the way.