Dead Mans Curve (again..)

[Steve76]

Lads,
Just quickly can anyone tell me why the DMC (Height Velocity Curve) does not apply to landing and only to takeoff.
Cheers
:cool:

[redandwhite]

As far as I am aware the 'DMC' DOES apply for landing as well as take-off. Flying to Class 1 for JAR Ops certainly requires a profile to be flown which avoids the area during both manoeuvres. Who has told you that it doesn't?:eek:

[212man]

Steve,
I think you are over simplifying things with your assertion: the HV curve applies at any pertinent stage of flight be it take off, cruise (power line inspection?) or landing. What changes is the size of the curve and its effect.

You must remember that the curve is based on level flight at maximum weight. If the a/c is descending then the power demand for any given speed will be lower and the effect of power loss reduced, hence conversion to an OEI descent and landing easier. If the a/c is climbing at the same TAS then the power will be higher and there will be a period during the entry to descent where the Nr will tend to decay more rapidly, hence making the phase more critical. level flight will be somewhere in the middle. The higher the speed the less variation. The greater the rate of descent the smaller the curve will be.

There will be some weight and ambient conditions where the HV curve is non existent: how else would you be able to certify a Cat A helipad profile and hence the often prohibitively low RTOWs associated with them.

How do you think the LDP is choosen on landing? One consideration is the balked landing case and the obstacle separation requirements associated with that, but the other is the OEI landing case.

I hope that gives the general idea; the HV curve is not a fixed entity and represents the worst case scenario. It may or may not be present depending on the weight, ambient conditions and whether the a/c is climbing, level or descending.

[PPRUNE FAN#1]

I love people who come up with these "rules." Where do they get them- do they pull them out of their arse?

It's jolly well good for supposedly learned instructors to spout off and say things like "the H-V curve only applies on take off." Really? Please show me the wording in the AFM or on the specific chart itself where the manufacturer has come out and stated so.

[Shawn Coyle]

HV curve is a very interesting and little understood piece of work. One of the interesting things about it is that it is done at maximum weight and probably 7,000' DA. Having validated it when I worked at Transport Canada, I can say that it is pretty good for the conditions tested, but not much else.
Takeoff profiles have to be developed to stay clear of the HV curve - and that is one of the things that goes into the published takeoff distance in the FM.
The HV curve in the area below the 'knee' is done at takeoff power, but no pilot intervention time.
But is it valid for landing? Probably not. Low power setting, in descent already, whole bunch of other variables. Shouldn't have to stay clear of the HV profile on landing - I don't think the certification methods require the FM charts to be developed for that - that alone should tell you something.
Also shows one of the benefits of the FAA method of doing things - the industry gets to respond to all proposed changes in the rules and the FAA has to listen.

[Moneyshot]

Once saw an interesting film of the avoid curve being demonstrated on the scout at ETPS. This involved several runs with varying degrees of 'pucker' factor. The curve has two distinct components.

1. The 'knee' and above. From the hover to minimum total drag speed 'say65kt' going up to about 800ft. At heights and speeds above this you're safe!!!

2. The low level/ high speed bit (say 50ft and below and 60kt-vmax).

Not something you should try every day but if your operation fits into the curve whether you're taking off or landing you need to be aware of it. (applies to twins as well as singles, you might lose both).

[212man]

Moneyshot, the HV curve for twins is in the event of a single failure not double. I think you'd be hard pushed to find info on the engineless HV curve for any twin.

What I find interesting is the different philosophies shown by manufacturers in developing the landing profiles. Some like Bell and Eurocopter go for the keep the speed up until approaching ground effect, then slow down; fast /shallow. Sikorsky on the other hand hvae gone for the fast steep approach with high rate of descent followed by split a**e flare to recover at the bottom: practically an engine assisted recovery from autorotation. (that's the UK Group A landing anyway, LDP is 50 kts at 100 ft with 750 ft/min max, keep the 50 kts to 50 ft then flare with up to 20 degrees nose up and apply power to come to a hover). Both work and both keep you away from any HV curve.

The following notes from AC-29C (advisory circular that amplifies FAR-29: large rotorcraft certification) should dispel any rumours about HV curves not being applicable:

Page B - 71
(B) Landing distance. Approach and landing path requirements are stated in general terms in paragraphs (b)(2) and (4) of § 29.75.

The approach path must allow smooth transition for one engine inoperative landing and for balked landing maneuvers and must allow adequate clearance from potentially hazardous HV combinations.

Paragraph (b)(4)(ii) implies that a less restrictive HV envelope may exist for the Category A approach condition in comparison to that determined under high power conditions in § 29.79.

The manufacturer may elect to use this added capability. The added capability arises from the fact that lower power levels, a lower collective setting, and an established rate of descent accompany typical approach conditions as opposed to the more critical high power conditions of § 29.79.

Landing distance is measured from a point 50 feet (25 feet for VTOL) above the landing surface to a stop. For flight manual purposes, the distance is from the point at which the lowest part of the rotorcraft first reaches 50 feet (25 for VTOL) to the foremost point of the rotorcraft (including rotor tip path) after coming to a stop.

[Steve76]

I was really only considering single engine HV curves.
I just wanted a refresher as to the reasoning for the creation of the chart. I think Shawn is right on the money there and 212man's thoughts are quite correct. I know many instructors promote it not only for straight and level but also T/O.
In the last thread about this subject it was Nick L who first enlightened me to the consideration that it was not applicable for landing.
Thanks for your replies.
Steve

[Shawn Coyle]

Regarding the ETPS film with the Scout (I was there at the time and watched the whole sequence).
what was not shown was the engine overtemp afterwards. The engine failure was simulated by closing the HP cock (actually shutting off the engine -very ballsy). Good engine off landing by the student, and the whole thing came to a stop just at the edge of the grass area.
Start up was attempted, but the crew forgot to close the throttle (Scout has throttle that has no 'off' position, just idle). HP cock opened at the appropriate moment in the N1 windup, and we standing behind the aircraft got to see a turbine wheel turn red, then yellow, then white while large flames issued from the back. The TOT gage in the cockpit was so heavily damped that it showed yesterdays temperature, so the end result was one very badly overcooked engine, and some very red faces. Engine had only 5 hours of life left anyway, so no-one was too upset...
But it was neat film.
Merry Xmas.

[SASless]

Shawn,

You should post this input of yours onto "emergency drills " thread......a classic example of what I have been preaching about strict adherence to checklists and either "thinking" or " not thinking" ! Abnormal situation compounded by incorrectly applying well established procedure....all with very good intent... but winds up with a visit to the yellow foot pads one pace in front of the "O-C's" desk.

[donut king]

Two words..........." collective position"

As stated on a previous response, landing parameters differ from t/o as we all know.

I.E. disc unloaded, in descent, ......etc...

D.K

[offshoreigor]

Steve,

Merry Xmas Buddy.

I assume you are concerned with the S76 OEI HVC?

If you can assure OEI Stay Up Weight, then you should be guaranteed the published HVC speed/Height. I know where you are coming from, the AA sometimes has to work outside the curve, Eh?

PS Pooch is on his way to Burma next month, he will be sadly missed here.

Cheers :eek: OffshoreIgor :eek:

[Moneyshot]

It would appear that we've allowed this to get more complicated than it really is. For practical aviation purposes it's nice to know that if you are in a HOGE at say 800' and you lose your (single)engine, you can fully lower your collective from a high position in order to make a safe autorotative landing.
If you are in a descent (lower collective position) then the lever has less distance to go to achieve autorotation. this would be represented by a smaller HV diagram. But who would want to look at an infinite number of HV diagrams during flight (one for each possible lever position or phase of flight)! You have to keep it practical and useable.

[offshoreigor]

MoneyShot.

Respectfully, what Steve76 was asking, pertained to OEI (read multi-engine).

Steve, as I said, it is always a difficult decision on AA to trade off between fly-away and RFM published data.

The thing to remember is go by the numbers. If you stick to the CHC vertical profile, you won't have a problem. It took alot of time to produce them.

If you want more Data, PM me. I can give you a great program develolped by a genius within our ranks.

Cheers, :eek: OffshoreIgor :eek: