Jump to content

Does R22 h-v diagram apply to approach


alexc
 Share

Recommended Posts

I am taking flight training for PPL. I have a question for pros here: Robinson training guide and all instructors do mention to follow h-v diagram for takeoff, but people rarely mention it for approach. R22 training guide didn't explicitly mention to follow h-v for approach either, so I assume h-v diagram doesn't apply to approach?

Link to comment
Share on other sites

Here is a nice article about H/V Diagram. My understanding is that it is for takeoff. I am sure you will get some really good insight from the real pros. But the gist of it (my pov) is you are heading up, reactions, reaction time, etc will be different if you are on approach (already heading down, etc). But, I could be wrong and too simplistic.

 

http://blog.aopa.org/helicopter/?p=653

  • Like 1
Link to comment
Share on other sites

The H/V applies ALL of the time. The trick is to avoid or minimize the risk of every take-off AND landing. Sometimes pilots get lazy and don't put all of the factors in their favor. Short cuts can save lots of time & money. Getting away with poor procedures reinforces repeated risk until one day the pilot may wish that he minimized just one more risk that day.

 

It can be as simple as taking the time to back up and use ALL of the available area for take-off or taking the extra time for a better LZ recon before landing.

 

We've all done it to one degree or another but when you are going for a checkride, its the most important time to be able to explain what the risks are and what you are doing to minimize them.

 

The conditions and factors change all of the time. Its reasonable to spend more time in the Deadman's Curve upon approach if its a tight, unknown LZ with lots of hazards than it is to rush on in just in case the engine might quit. The pilot may be asking himself, "Am I more likely to clip a wire or lose the engine?"

 

Regardless of the decision though, the H/V risks remain.

Link to comment
Share on other sites

I am taking flight training for PPL. I have a question for pros here: Robinson training guide and all instructors do mention to follow h-v diagram for takeoff, but people rarely mention it for approach. R22 training guide didn't explicitly mention to follow h-v for approach either, so I assume h-v diagram doesn't apply to approach?

 

The HV curve is based on higher power settings. The point where the curve turns back toward the airspeed base line is called the knee. Up to the knee, the curve is based on takeoff power settings. After the knee it is based on climb/cruise power settings. Keep in mind that in both situations that the collective will be fairly high compared to approach.

 

Unfortunately, many instructors really don't have a good handle on the HV curve and what it signifies.

Link to comment
Share on other sites

The H/V diagram will tell you based on your airspeed and altitude if you are in a position to make a successful autorotation. You should endeavor to operate outside of the "dead man's curve", and inside the area of safe autorotation in all phases of flight.

Link to comment
Share on other sites

You should endeavor to operate outside of the "dead man's curve", and inside the area of safe autorotation in all phases of flight.

 

And if you do that you might as well fly an airplane...helicopters make money "inside the curve" not outside :P

  • Like 2
Link to comment
Share on other sites

Alexc,

 

Your CFI should be teaching you about the below listed items concerning the HV diagram to give you a clear understanding of it.

 

FAR Part 27, development of the HV diagram at MGW and Std. Atmosphere, the four elements that encapsulate it (airspeed, altitude, the aerodynamic transitions from powered flt. to autorotative flt., loss, recovery and stabilization of Rotor RPM and time to accomplish the transitions or not). Also, the three factors that determine where the Rotor RPM will stabilize and the value of flying a stabilized rotor system in autorotation.

 

Certainly recognition of being within the shaded area and avoidance or techniques minimizing time therein should be emphasized!

 

There is no point of the diagram that is calculated or established during a descent! It does not apply to approaches!

 

CFIs and pilots that have attended my "C&E" Seminar are schooled in the items listed above. Unfortunately, as Rich mentioned, most CFIs and pilots do not understand the diagram or the elements thereof as shown by the responses here.

 

Best wishes,

 

Mike

  • Like 3
Link to comment
Share on other sites

To say it doen't apply to approaches, while true, is a muddy statement.

 

It is true that it is not tested with a decent rate prior to the autorotation, but that doesn't mean there isn't an h/v relationship that is safer in the event of an engine failure on approach. It simply isn't factored into the testing.

 

Other factors to consider is the testing under zero winds, 7000' DA and a smooth hard surface.

 

I would contend that the h/v curve doesn't apply to most of our operations, when looked at from a simplistic view of wether we are on approach or not. We rarely operate at the specific conditions required for the certification testing. It is naive to think that a foot of height or knot of airspeed (or if we are on approach) put us in or out of the "safe" area.

Edited by C of G
Link to comment
Share on other sites

C of G,

 

You are right, there could be a H/V curve tested and developed for approaches.

 

However, the OP is talking about those that are currently published and specifically the R-22. In that case those H/V diagrams do NOT apply to approaches for the reasons Mike pointed out.

  • Like 1
Link to comment
Share on other sites

Alexc,

 

Your CFI should be teaching you about the below listed items concerning the HV diagram to give you a clear understanding of it.

 

FAR Part 27, development of the HV diagram at MGW and Std. Atmosphere, the four elements that encapsulate it (airspeed, altitude, the aerodynamic transitions from powered flt. to autorotative flt., loss, recovery and stabilization of Rotor RPM and time to accomplish the transitions or not). Also, the three factors that determine where the Rotor RPM will stabilize and the value of flying a stabilized rotor system in autorotation.

 

 

That's all correct....

 

 

It defines an envelope of airspeed and height above the ground from which a safe power-off landing may not be possible. The diagram is normally designed around three portions: (a. the level flight (cruise) portion, (b. the takeoff portion, and (c. the high-speed portion. The high-speed portion is omitted when it can be shown that the rotorcraft can suffer an engine failure at low altitude and high speed and make a successful landing.

 

The first two conditions require that a transition be made from powered flight to autorotation, were the helicopter is in descent with the incoming relative wind driving the rotors. The transition requires a time delay factor. The landing approach places the helicopter in a descent profile that is tailor-made for entering autorotation; thereby, decreasing the transition time. Therefore, that diagram would need to draw-in somewhat if we wanted to factor in landing approach. As it stands, the H-V diagram was not designed to represent the approach profile.

 

The H-V diagram is general in context and designed to meet the certification requirements of CFR 27.87 and provide the pilot general information. Too many over complicate this subject.

 

HVFigure.jpg

Edited by iChris
  • Like 1
Link to comment
Share on other sites

C of G,

 

You are right, there could be a H/V curve tested and developed for approaches.

 

However, the OP is talking about those that are currently published and specifically the R-22. In that case those H/V diagrams do NOT apply to approaches for the reasons Mike pointed out.

 

I guess my point was a step beyond the OP's question. I was merely pointing out that unless you are flying under the specific conditions of certification requirements, ie at MGW, at 7000'DA with zero wind and over a smooth hard surface, the H/V curve doesn't apply to you. You can certainly say that it doesn't apply to flying an approach, I was simply saying, in actuality it almost never applies as it is shown in the RFM.

 

That is not to be mistaken as saying you can fly willy nilly and as long as you have a ROD, that you can disregard your h/v relationship in regards to an engine failure. I'm pointing out that several factors effect the size of the h/v diagram and it's not possible to account for all of them and that the diagram is only a performance criteria that must be calculated and demonstrated for certification purposes under very specific criteria. Go outside of the parameters and it is not calculated.

Link to comment
Share on other sites

Many CFIs that I have trained are teaching the expanded understanding of the determining elements of the H/V curve for various pilot certificates. Many of our current turn over CFIs have not been taught the application of the H/V diagram and pass it on to their students as best as possible.

 

At all levels the main PTS points are "Recognition & Avoidance" when possible or minimum time in the upper shaded area.

 

C of G made some good points for consideration about choosing airspeeds and altitudes for actual approaches with considerations for the outcome with an engine failure. These were good to mention but beyond the scope of the initial question about the R22 POH HV diagram.

 

In my evaluations of many pilots & CFIs, I have found that the HV and helicopter performance are the two major areas of insufficient training/understanding and that ADM & RM training are almost non-existant.

 

Hopefully the pilots that come here to learn will get the best out of C of G, iChris, JD and others that bring valid info and sincere help information wise.

 

Best to All,

 

Mike

Link to comment
Share on other sites

The H/V diagram will tell you based on your airspeed and altitude if you are in a position to make a successful autorotation. You should endeavor to operate outside of the "dead man's curve", and inside the area of safe autorotation in all phases of flight.

 

Personally, I take exception to the phrase 'dead man's curve'. It sends the wrong message to students. An auto-rotation from inside the curve does not mean you will have a fatal accident. All it means is that the successful outcome of the auto-rotation is in doubt. The thing is, that when helicopters are operating within the curve, generally, the terrain below them is such, that a successful auto-rotation is in doubt anyway. Overall, what the term successful means in this case, is that the helicopter will be more or less flyable after the event. Considering the ground under most longline guys, an auto rotation is successful, if you can preferably walk away from the helicopter.

 

The longline guys call the HV curve,, the Money Curve. The deeper in you are the more money you should be making.

Edited by rick1128
Link to comment
Share on other sites

I love watching the powerline pilots work while tethered to hot transmission lines, but I wince when I think about an engine failure just then. A ball of junk you can walk away from is about the best outcome you can hope for.

Link to comment
Share on other sites

Thanks for all the replies, very very helpful!! I think I understand much better now. After reading the post here, I happened to find a similar answer in "FAA - Rotorcraft Flying Handbook" (I should have read the book more carefully :( ), the book says "H/V diagram depicts the critical combinations of airspeed and altitude should an engine failure occur.... An engine failure in a climb after takeoff occurring in section A (shaded area) of the diagram is most critical. .... An engine failure while descending through section A of the diagram, is less critical, provided a safe landing area is available..." The explanations in the book are similar to what you guys just discussed.

Link to comment
Share on other sites

I'm just gonna throw this out there. In my most humble opinion, the h/v diagram applies to all phases of flight. Takeoff, cruise, and approaches.

 

It height vs velocity. There is higher risk of balling up a helicopter on a takeoff due to an engine failure, and the reasons are important to understand. But to say it doesn't "apply" to approach to landing i don't think is correct.

Link to comment
Share on other sites

Pohi. Id say its important to realize it does not apply at all to approach. Try and shoot an approach staying out of the curve. Any check airman would fail you for flying like that. I would say what is really important to remember is that more helicopters are balled up cause of hitting things or lack of power then from engine failures these days. Take it slow and stabilized.

  • Like 1
Link to comment
Share on other sites

It's called a height velocity diagram. Not a takeoff altitude airspeed diagram.

 

Just because a takeoff is more critical doesn't mean that other phased of flight do not apply.

 

If it was designed for takeoff, they would have called it that. It's an informative graph representing height vs velocity and areas to avoid if possible. Its kinda in the name.

Link to comment
Share on other sites

Flying helicopters is a dynamic skill. That is, it’s not one-skill-at-a-time or one-decision-at-a-time kinda thing.

 

With that said, an approach can momentarily terminate into the shaded areas of the HV curve. Once the decision is made to continue to the touchdown spot, you are operating within the curve until reaching below the zero speed non-shaded area. Simply put, any approach where you are required to utilize hover power and walk the machine down (descend) to the LZ. This is known as backsliding into the curve. Can this be called an approach? I think so. Albeit very slow and sometimes vertical but “approaching” nonetheless. “Walking it in” can be done for a myriad of reasons and most often associated, with off-airport ops. Again, it’s a dynamic situation which evolves into operating within the curve. It’s a conscious decision and understanding the ramifications is what this is all about. The fact is, as a working helicopter pilot, at one time or another; you must put your full faith in Ms. Rolls Royce, Mr. Turbomeca, Ms. Lycoming or Mr. Pratt & Whitney…….

  • Like 2
Link to comment
Share on other sites

It's called a height velocity diagram. Not a takeoff altitude airspeed diagram.

 

Just because a takeoff is more critical doesn't mean that other phased of flight do not apply.

 

If it was designed for takeoff, they would have called it that. It's an informative graph representing height vs velocity and areas to avoid if possible. Its kinda in the name.

 

One thing to keep in mind is how the HV Curve chart is developed. The manufacturer using certification guidelines from the FAA, test flies the helicopter to develop the numbers necessary to produce the H/V Curve chart. One of the guidelines is power settings. Maximum takeoff power is a requirement for the low end of the chart. And cruise/climb power is required for the upper portion of the chart. Both these power settings require more collective input than approach. So while there may be a speed/altitude combination that could have unsuccessful autorotation results, it will be much lower than what is depicted in the published HV Curve.

Link to comment
Share on other sites

I agree with how it is made.

 

How it is made does not change that it is for all phases of flight. By making it as large as possible, it gives the pilot a larger margin for error if the pilot avoids and/or is aware of the risks of operating in the shaded area.

 

To make a blanket statement that it does not apply to anything other than takeoff is not correct, and can build a false sense of security in new pilots because they may think they have nothing to worry about cruising along at 150 feet and 15 kts because that chart does not apply.

 

I still think that anytime a helicopter has a combination if height and velocity that chart is good to keep in mind. On takeoff, there is high power, high drag on the blades so yes, they will stall faster on an engine failure with no pilot input and the pilot has less time to successfully autorotate. A helicopter on approach has low power, low drag, and will have more time before pilot input is made, but it is still smart to realize that operations are in the h/v diagram. Especially on steep approackes where there is even lower airspeed and more collective applied than normal.

 

As was stated before, it's not a limitation, it's an informative tool designed to help a pilot be aware of how their particular helicopter operates.

Link to comment
Share on other sites

Wow, I can not believe that pilots still do not get the point about how the HV curve is developed.

 

Look at the diagram posted by iChris. No point along the outer line is established in a descent!!!!!!!

 

Bottom portion is during a take off (climb) with high pitch angle and maximum loss of Rotor RPM with no time to regain or stabilize the RPM or rate of Descent should the engine quit.

 

The upper portion is during level flight, again not in a descent.

 

If your helo is in a descent, this chart does not apply, simple as that. Also there is no correlation between what the FAA named the chart and when it applies.

 

Sometimes I like the info on the net, other times I cringe that inexperienced pilots learn

incorrectly here.

 

As a FAASTeam Rep. my goals are accident reduction through training. Safety & Educational Seminars fix some of this but not when pilots blindly make statements after the correct info is presented here or elsewhere.

 

If the engine quits during an approach, be PIC and fly the helo to the ground doing the best you can.

 

Be Safe,

 

Happy Holidays

 

Mike

  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
×
  • Create New...