Run DMC

[collective bias]

Went for a jolly (checkride actually) recently with a highly experienced pilot who spent his entire time convincing me that the Dead Mans Curve does not relate to the approach phase of flight. News to me.
Being in anything at 200ft while only just achieving translation is plain scary...let alone in a Robbie.
According to him having at least 12kts with only 100ft ROD will avoid VRS. TRUE but it is sure to give you a sore back if the donk stops.
Your thoughts.......

[212man]

What kind of approach requires you to be at 200' and 12 kts? VRS is generally said to be a consideration when below 30 kts and more than 500 ft/min with power being applied, which more than allows for a normal approach to be made.

It is true, that the HV curve does not directly relate to an approach because the curve assumes level flight. The power required to descend at 100ft/min and 12 kts is a lot less than for level flight, so it is true that the effects of an engine failure would be less severe (though pretty exciting none the less!) If you look at the Cat A approach profiles for twin a/c, they normally stay out of the avoid curve, though sometimes clip it as recognition that you are actually descending.

Maybe your instructor's 'pucker' reflex has not been properly developed, mine would be in spasm in the same situation.

------------------
Another day in paradise

[rotorque]

Your teasing the fixed wing blokes by saying that last bit !!

[RW-1]

>>Being in anything at 200ft while only just achieving translation is plain scary...let alone in a Robbie.<<

Eeeeeeeek !

I'm with 212, while HVD is ideally for level flight, and I don't know of a situation where you would want to be at 22' with 12kts, it still benefits you to know where on the curve you are sitting at any given time ....



------------------
Marc

[Arm out the window]

We used to do touchdown autos in Squirrels at the ADF helo school from 50 ft and 60 kt to give students some idea of what potential there was for a soft landing from a low, slow(ish) situation in that aircraft.

You could get an OK landing out of it, but I wouldn't have wanted to go too much slower than that, probably bend lots of aircraft for not much gain.

For normal ops, the 'standard' approach we taught was a constant angle from 300 ft 60 kias plus wind, reducing speed to maintain an 'apparent walking pace' to arrive over your spot.

This was certainly in the avoid curve, but was a forerunner to approaches to confined areas where you obviously couldn't charge in at high speed.

However, if I was approaching to a big open area and had no reason not to, a power terminated auto profile would be the go - in auto, so no problems with vortex ring, with the power coming in as you levelled to the hover.
Not really practical unless you're landing in a footy field, but an idea anyhow.

Thoughts anyone?

[lmlanphere]

I think that type of approach would be fairly unsettling for passengers....that is, if you are carrying any

[Letsby Avenue]

I suppose hovering at 300ft at night is out of the question then?

[offshoreigor]

CB:

Ask your "Experienced" friend what the hell does vortex ring state have to do with the Dead Man's Curve.

The DMC has absolutlely nothing to do with VRS. It simply states that within the avoid area, a safe landing in the event of an engine failure, cannot be guaranteed.

Basically you have to explain to him that if he is going 100 kts at 5 feet or 12 kts at 200 feet he might not have the required performance available, critical engine out, to land with a warm and fuzzy feeling.

By the way, you can also mention to your friend that I've never heard of a helicopter with a translational speed below 25 kts! Basic aerodynamics.

Cheers, OffshoreIgor http://www.pprune.org/ubb/NonCGI/eek.gif

PS: Collective, I think you should rely more on what your own personal professional knowledge tells you rather than the percieved knowledge of a so called experienced pilot. You know your stuff, so go with it. Know your job and you will rarely have a problem.


[This message has been edited by offshoreigor (edited 02 April 2001).]

[This message has been edited by offshoreigor (edited 02 April 2001).]

[212man]

Offshore is of course correct to say that VRS and HV curves are not related per se, though both are a consideration when looking at approach technique.

I'm not sure about the "no translational below 25 kts". Most ASIs don't indicate at the sort of speed that you normally encounter translational lift. Generally I'd have thought 15 kts was nearer the mark.



------------------
Another day in paradise

[CTD]

Being at 200ft and 12 KIAS or less is not at all uncommon for longlining / external load operations, or when approaching or departing over obstacles such as tall trees.

The Height Velocity Curve is developed for both hover and fwd flight profiles. Your instructor is incorrect in his statement that the curve does not apply to the approach phase. A REASONABLE approach offers negligible relief from the chart over straight and level flight, as the potential energy upon engine failure is very similar. The hover profiles tend to be a little more critical because of the higher power settings used and the rate of Nr decay upon engine failure.

Some helicopters have one blanket HV chart, others have multiple or sectional charts for different gross weights and Hd considerations. In any case, the development is the same, using the highest gross weight (or OGE hover weight) for the applicable chart region. To simulate average pilot reaction time a delay is implemented before pilot action is taken during testing and development. For areas below the 'knee', this delay is typically 0.5 seconds, above the knee it's 1.0 seconds.