HV Diagram Test Question

Sparker · August 5, 2008

3335. The principle reason the shaded area of a Height vs. Velocity Chart should be avoided is

A- turbulence near the surface can dephase the blade dampers.

B- rotor RPM may decay before ground contact is made if an engine failure should occur.

C- insufficient airspeed would be available to ensure a safe landing in case of an engine failure.

OK, so most of you might not be bothered by the "correct" answer as much as me, but please no cheating!! Answer what you think is right without Googling it.

I was going to explain my answer and annoyance with this question, but I thought a poll might be more fun. I will post my question about this question, and the correct answer later on, feel free to share opinions but please don't go grab the book and spoil it!

Have some fun and lets hear some arguments, and if anybody wants to take a stab at what dephasing blade dampers means I'd like to hear it.

P.S. Who knew at 67 kts a 204B became a rocket ship?

rotormandan · August 5, 2008

3335. The principle reason the shaded area of a Height vs. Velocity Chart should be avoided is

A- turbulence near the surface can dephase the blade dampers.

B- rotor RPM may decay before ground contact is made if an engine failure should occur.

C- insufficient airspeed would be available to ensure a safe landing in case of an engine failure.

OK, so most of you might not be bothered by the "correct" answer as much as me, but please no cheating!! Answer what you think is right without Googling it.

I was going to explain my answer and annoyance with this question, but I thought a poll might be more fun. I will post my question about this question, and the correct answer later on, feel free to share opinions but please don't go grab the book and spoil it!

Have some fun and lets hear some arguments, and if anybody wants to take a stab at what dephasing blade dampers means I'd like to hear it.

P.S. Who knew at 67 kts a 204B became a rocket ship?

The answer should be C: insufficient airspeed would be available to ensure a safe landing in case of an engine failure. The reason not the others. A: It is ridiculous. B: (I'm guessing this is the one you're questioning about) your rpm won't decay all the way if you lower your collective in time. It may get low but you will still have RPM. The problem is you won't get your full rpm during your flare due to the lack of A/S. You need that A/S to transfer into your RPM so you don't have a hard landing. Obviously the lower shaded part at high A/S, lack of A/S and RPM is not the problem. The FAA should specify but at least they're consistent. Just like the FARs.

Edited August 5, 2008 by rotormandan

Wally · August 5, 2008

A. The 204B has no blade dampers to be "dephased by turbulence", an obvious wrong answer

B. "Rotor RPM decay" is only part of the issue. The graph's prepared with lots of assumptions and subjective evaluation in that regard

C. "Lack of airspeed", one of the two variables in the graph, thus a potentially 'correct' answer. Airspeed is energy that can be used to regain NR -answer 'B'- and slow a descent, the presumed issue being addressed by the problem scenario.

There is no simple, rational, scientific answer to questions like this, you have to pick the answer that's least wrong. In the example presented, that's going to be "C".

Edited August 5, 2008 by Wally

Gomer Pylot · August 5, 2008

It doesn't become a rocket ship, it's just at that airspeed you can do a successful auto from any height. C is obviously the only answer that is completely correct. A is just a distractor (almost all multiple choice questions have at least one), and B is incorrect because rotor RPM can decay before ground contact at any speed or altitude if the pitch isn't lowered. If you're inside the avoid area, you will have insufficient airspeed and altitude to do a successful auto unless you're either very, very good or very, very lucky, or both. That's why it's called a height/velocity diagram - it shows where you have insufficient height and velocity for a successful auto, and where you do.

kodoz · August 5, 2008

3335. The principle reason the shaded area of a Height vs. Velocity Chart should be avoided is

A- turbulence near the surface can dephase the blade dampers.

B- rotor RPM may decay before ground contact is made if an engine failure should occur.

C- insufficient airspeed would be available to ensure a safe landing in case of an engine failure.

B is correct because the FAA is always correct. I hate questions like this since they force you to either learn the test instead of learning the info, or you try to rationalize marginal answers and consequently internalize information in a confusing or misleading way. In that spirit, B is better than C because all the airspeed in the world won't help unless you trade it for RPMs, and C doesn't mention making use of that airspeed. I think an interesting poll would be to look at how well pilots do on the knowledge exams if they just studied vs if they just did a bunch of practice tests. I set aside separate study periods for prepp'ing for the knowledge exam and then start all over to study for checkrides.

From the FOI:

When items [on selection-type questions] are to measure achievement at a higher level of learning, some or all of the alternatives should be acceptable responses - but one should be clearly better than the others.

Sparker · August 5, 2008

It doesn't become a rocket ship, it's just at that airspeed you can do a successful auto from any height.

Isn't it the suggested airspeed for best rate of climb?

kodoz · August 5, 2008

Isn't it the suggested airspeed for best rate of climb?

Not necessarily. Best ROC just has to do with drag and power available; I think the climbout profile is determined empirically. Vy in the R22 (53 knots) will take you through the HV shaded areas depending on the conditions.

Sparker · August 6, 2008

OK, I guess majority rules...

Their answer:

C) The chart can be used to determine those altitude-airspeed combinations from which it would be impossible to successfully complete and autorotative landing. The altitude-airspeed combinations that should be avoided are represented by the shaded area of the chart. (H747) - FAA-H-8083-21, Chapter 11

OK, so I agree with answer C for the larger shaded area on the left (the low airspeed area)... What I don't agree with is saying that it is "insufficient airspeed" at 100 kts and 10 feet AGL... I think the most correct wording would be "insufficient time or airspeed would be available...."

I know it says the "principle reason" but if I had not ran across this in studying (I guess that's why we study), I would have been thrown off. Also, why is (B.) incorrect? Isn't that a reason for having an H/V diagram as well?

Reason for edit: forum keeps turning letters with parenthesis into various out of place emoticons.

Edited August 6, 2008 by Sparker

Wally · August 6, 2008

OK, I guess majority rules...

Their answer:
C) The chart can be used to determine those altitude-airspeed combinations from which it would be impossible to successfully complete and autorotative landing. The altitude-airspeed combinations that should be avoided are represented by the shaded area of the chart. (H747) - FAA-H-8083-21, Chapter 11

OK, so I agree with answer C for the larger shaded area on the left (the low airspeed area)... What I don't agree with is saying that it is "insufficient airspeed" at 100 kts and 10 feet AGL... I think the most correct wording would be "insufficient time or airspeed would be available...."

I know it says the "principle reason" but if I had not ran across this in studying (I guess that's why we study), I would have been thrown off. Also, why is (B.) incorrect? Isn't that a reason for having an H/V diagram as well?

Reason for edit: forum keeps turning letters with parenthesis into various out of place emoticons.

One of the assumptions used to make the chart is that there will be some delay in pilot response. The test pilots allow 2 seconds of 'fat dumb and happy' before responding to build a chart useful by the assumed average level of skill of the non-test pilot. But, one doesn't have 2 seconds of unplanned, unpowered flight at low level and high speeds to waste swapping hands on the controls. Remember- you're nose down and honkin' along, when the thrust (NR) that was keeping you UP and going disappears- and it (NR) will diminish, very quickly at hover and or takeoff pitch. And, you'll need some time (vertical space) for the flare to recover, accelerate your NR, or at least get your nose up for a slide on... Thus the 5-10 foot high speed shaded area on the right.

"B" is incorrect because it's not what the chart is about, that is- airspeed and altitude. In the shaded areas the 'average pilot' doesn't have enough of either to trade for energy (NR) to arrest the descent and make a survivable landing. So, yes- NR will decay, but it will in any engine failure with significant power being used, even in a Huey. If you're outside the shaded area, you'll either land before NR slows disastrously (this is why we hover at 3-5 feet) or trade airspeed present at engine failure or gained by trading altitude for energy, rotor speed.

I say again- you will lose NR in a power failure. This is all about being able to do something about that and survive it- airspeed and/or altitude, if you're too high to do a hovering auto.

Edited August 6, 2008 by Wally

Sparker · August 6, 2008

One of the assumptions used to make the chart is that there will be some delay in pilot response. The test pilots allow 2 seconds of fat dumb and happy before responding to build a chart useful by the assumed average level of skill non-test pilot. You don't have 2 seconds of unplanned, unpowered flight at low level and high speeds to waste swapping hands on the controls. Remember- you're nose down and honkin' along, when the thrust that was keeping you UP and going disappears- and it will, very quickly at hover and or takeoff pitch- you'll need some vertical for the flare to recover and accelerate your NR, or at least get your nose up for a slide on... Thus the 5-10 foot high speed shaded area on the right.

I understand the reason for the high speed shaded area, the diagram is easy to understand, my problem is that they failed to incorporate this area into the test question and that makes the question confusing. They say "the shaded area" when, technically it is shaded areas.

me shakes fist · August 6, 2008

I understand the reason for the high speed shaded area, the diagram is easy to understand, my problem is that they failed to incorporate this area into the test question and that makes the question confusing. They say "the shaded area" when, technically it is shaded areas.

I have seen this in many, many tests in various subjects, not just the knowledge test for a pilot certificate. Multiple choice doesn't necessarily mean the correct answer but the best answer. The question asks for the "principal reason" and since the low altitude/high airspeed area counts for maybe 5-10% of the chart, it's not taken into account. "C" doesn't account for every situation, but it's a better answer than "B."

rotormandan · August 7, 2008

OK, I guess majority rules...

Their answer:
C) The chart can be used to determine those altitude-airspeed combinations from which it would be impossible to successfully complete and autorotative landing. The altitude-airspeed combinations that should be avoided are represented by the shaded area of the chart. (H747) - FAA-H-8083-21, Chapter 11

OK, so I agree with answer C for the larger shaded area on the left (the low airspeed area)... What I don't agree with is saying that it is "insufficient airspeed" at 100 kts and 10 feet AGL... I think the most correct wording would be "insufficient time or airspeed would be available...."

I know it says the "principle reason" but if I had not ran across this in studying (I guess that's why we study), I would have been thrown off. Also, why is (B.) incorrect? Isn't that a reason for having an H/V diagram as well?

Reason for edit: forum keeps turning letters with parenthesis into various out of place emoticons.

B is incorrect because R RPM isn't so much the problem. At any engine failure there will be some R RPM loss. You do the down right aft thing and you recover or at least keep it going to deadly R RPM. Now what? You keep it (R RPM) in the green so you can have room to slow your decent with a flare and not overspeed. In the shaded area (upper left) you could probably get you R RPM full but then you couldn't flare with out over speeding or with no A/S = no flare possible and that full R RPM isn't enough to cushion a 1500+ fpm drop. Same with the very high hover auto. If you don't let you R RPM get full then you won't have enough A/S to trade to get it full in the end. Like some one said though, this is for the average joe pilot. If your really good or lucky you might be able to pull it off. Also remember the FAA describes a "successful emergency landing" as no damage to the aircraft at all. That includes bent skids and over sped rotors. Personally for me if no one on board or on the ground gets hurt I'm happy. If I have to spread the skids or overspeed then "F" the ship though I will try to keep it in one piece too.

rotormandan · August 7, 2008

One more to add, the high speed at low altitude isn't a R RPM problem either. It's just altitude. At 100kts and 10ft slight aft cyclic will maintain R RPM but the ground comes fast @ 10ft.