Jump to content

HV diagram and predator control


ADRidge
 Share

Recommended Posts

I've been sitting here thinking about the HV diagram in the R-22, because that's just how exciting my life is on a nice sunday afternoon, and I got to wondering about the shaded area.... the one at sea level and 1370lbs. How exactly would the shaded portion change under MGW? It seems to me that it would become slightly more forgiving as you get lighter. Granted, I don't think there would be MUCH appreciable change, but there's got to be SOME.

 

What made me think about this was watching those great youtube videos of guys in Texas doing predator control in R-22's. I know a feral hog can run around 20mph, and those guys seem to be flying around 50' agl. This combination, at sea level, would put them just to the left of that dangerous elbow in the HV profile assuming they're at max gross weight. But let's say they're at 1270-1300? How much more survivable would an engine failure be?

 

Personally I think either way, you're going to bend something fairly badly if your engine goes at 25kias and 50 feet regardless of pilot skill or external conditions with the exception of gale-force winds. Anyway, I just thought I'd weigh in and see what you folks thought.

Link to comment
Share on other sites

The bottom of the HV curve is for takeoff only. So, it assumed takeoff MP at gross weight. The top of the curve is for cruise flight. Also, the HV curve does NOT guarantee survival, but a total and complete successful touchdown without damage to the helicopter. You are likely to survive an engine failure from any point in the HV curve if you lower the collective when it quits. Even more likely if you pull pitch before impact.

 

If you are flying at 20 MPH and 50 feet, you are much safer than 70 MPH and 50 feet. This is because you are much much much more likely to run into power lines than have an engine failure.

 

I would have to be in an R22 at 20 MPH and 50 feet to tell you if a successful autorotation is possible. I can tell better by feel than by a graph. However, I would guess without the speed needed for a flare, you wouldn't likely save the helicopter. If you said a Bell 47, I would say no problem.

Link to comment
Share on other sites

The bottom of the HV curve is for takeoff only. So, it assumed takeoff MP at gross weight. The top of the curve is for cruise flight. Also, the HV curve does NOT guarantee survival, but a total and complete successful touchdown without damage to the helicopter.

 

Very good point. It's definitely been drummed into my head that the HV is for Takeoff, but I figure if you're cruising at what is essentially just above the threshold for ETL, the HV diagram might be a fairly good indicator of your success rate should the unthinkable happen. The more I think about it, the more I can just envision what is basically an ugly hover auto. Doesn't seem like a person would be able to flare much at 20-25KIAS.

 

Thanks for the insightful reply!

Link to comment
Share on other sites

Also keep in mind, the h/v diagram is for a pilot of "average" skill. According to Bob at the RHC SC, that means a pilot who is signed off to solo. To simulate this, during the cruise sections of the curve, the test pilot had to wait (1 or 1.5 seconds I think) before beginning to lower the collective.

 

And ya, at 25 ft, I doubt you would have much momentum for a flare of any appreciable size, or be able to lower the collective very much before having to pull it all the way to the roof to try and cushion the landing.

Link to comment
Share on other sites

I know a feral hog can run around 20mph, and those guys seem to be flying around 50' agl. This combination, at sea level, would put them just to the left of that dangerous elbow in the HV profile assuming they're at max gross weight. But let's say they're at 1270-1300? How much more survivable would an engine failure be?

 

Lets see, whats the descent rate in an auto? Maybe 1200fpm? so, how much time do you have at 50 feet? Its about 2.5 seconds. Basically you are just impacting the ground as you have just figured out you lost an engine. Whats the chance that you even have a flat spot within 2 seconds of you? I dont care who you are, or what load you have, your ship is about to become an Ebay special. You know the ones....slight rollover damage, needs paint!

 

If youre lucky you might survive long enough to go get back surgery. At least if you were doing 50 knots you could just flare all the way down and keep some rotor RPM.

 

There's a reason they teach 500AGL and 65 knots. The guys playing cattle rustlers are just one engine failure away from death. They might fly for 10 years and never have an issue. Then again, they might not.

 

Goldy

Link to comment
Share on other sites

An auto ROD in an R22 is closer to 2,000 FPM, but you aren't instantly at that ROD. You probably wouldn't even get up to 1,000 FPM if you were at 50 feet. You would have plenty of time to react if you lost an engine, however, you won't get much out of a flare even if it is near vertical.

 

And again, you aren't likely to die, you just won't save the helicopter. If you lower the collective when the engine quits and do nothing else, you will likely survive if you don't run into anything.

Link to comment
Share on other sites

I've thought about this a lot because this fall I flew over 200 hours with the majority doing confined areas and mountain approaches. These type of approaches usually demand slowish airspeeds with power set early which means lots of pitch.

 

Here are a few ideas. No matter your airspeed if the engine quits put the collective full down. If you don't you will loose RRPM and probably free fall the remainder which will hurt. So you are left with cyclic flair to try to manage a bad situation. Don't panic and automatically flair because you are probably too high and now have no airspeed and still a lot of air under you to fall through with limited RRPM to cushion the impact.

 

If the engine quits at 25 kts and 50 ft immediately put collective full down, and wait for the helicopter to descend almost 20 feet then flair progressively to arrive at the magic 8 ft agl with low airspeed and cushion with full collective pull. Even in the R22 with the low inertia rotor system you should walk out of this.

 

My pet peeve with the R22 is that teaching autos is done to avoid overspeeds which usually means starting the flair really really high and very gently. On the other hand a real engine failure you want to wait and flair at 35 ft and do it hard enough to arrive at the ground with little run on. This needs to be talked about because what the student is taught is not usually how it should be done in the real situation.

 

I think 25 kts and 50 ft should be OK with pre-thought of what to do. On the other hand 25 kts and 150 ft would be much harder to pull off with out damage. Just add enough back cyclic to prevent forward pitch with full down collective and then play chicken with the ground. Flair hard at 35 ft and pull all the collective you've got to cushion. This might mean going into the trees, swamp, sidehill, traffic, houses, whatever was on your approach.

 

Try to flair to match the angle of the terrain you will contact. Trees are better to fall through backwards I've been told.

 

Open to other's ideas.

Link to comment
Share on other sites

The HV curve shouldn't be your main concern when the terrain you're over isn't suitable for a landing anyhow. If you lose power there, the machine is a writeoff - period. I would focus on flaring off ALL forward speed before impact, and trying to touch down as level as possible.

 

I also find that a lot of students stick to the POH takeoff profile no matter what terrain are flying over, meaning they always accelerate beyond 40kts before climbing.

When you are taking off over rough ground, fences, trees, bushes and stuff like that, you might actually be a lot better off at 10kts and 40ft than at 40kts and 10ft in case something goes wrong.

Link to comment
Share on other sites

The HV curve shouldn't be your main concern when the terrain you're over isn't suitable for a landing anyhow. If you lose power there, the machine is a writeoff - period. I would focus on flaring off ALL forward speed before impact, and trying to touch down as level as possible.

 

I also find that a lot of students stick to the POH takeoff profile no matter what terrain are flying over, meaning they always accelerate beyond 40kts before climbing.

When you are taking off over rough ground, fences, trees, bushes and stuff like that, you might actually be a lot better off at 10kts and 40ft than at 40kts and 10ft in case something goes wrong.

 

This is an excellent post showing the need for not focusing on one element of flying but correlating many factors into a good Aeronautical Decision(ADM as it should be applied) during helo ops.

Link to comment
Share on other sites

The HV curve shouldn't be your main concern when the terrain you're over isn't suitable for a landing anyhow. If you lose power there, the machine is a writeoff - period. I would focus on flaring off ALL forward speed before impact, and trying to touch down as level as possible.

 

I also find that a lot of students stick to the POH takeoff profile no matter what terrain are flying over, meaning they always accelerate beyond 40kts before climbing.

When you are taking off over rough ground, fences, trees, bushes and stuff like that, you might actually be a lot better off at 10kts and 40ft than at 40kts and 10ft in case something goes wrong.

 

Yes! Statistically speaking, you are better off flying a vertical departure through the HV curve and get above obstacles than flying low and fast to stay out of it. Powerlines still kill the most and engine failures the least.

Link to comment
Share on other sites

This is an excellent post showing the need for not focusing on one element of flying but correlating many factors into a good Aeronautical Decision(ADM as it should be applied) during helo ops.

 

 

Good point... however, we are all being contradictory as helicopter pilots. We espouse, teach, implore the value and safety of the HV curve, yet, almost everything a helicopter does is within the HV curve. ADM is very important but I feel that it all boils down to "Risk Management". This is what a helicopter does, otherwise, we are just rotorheads flying like an airplane! Where is the fun in that?

 

Cheers

 

Rotorrodent

Link to comment
Share on other sites

I have seen effective flares at low forward speed and very little descent rate and I was quite surprised. A former boss of mine who is one of the highest time-in-Robinson pilots around showed me (for my benefit and not my reproduction with students) that a well-timed and assertive flare even with out the "minimal 60 knots" will help and makes a difference on a takeoff engine failure. I don't recommend toying with this concept unless you are very comfortable with the machine and have been spending a lot of time in it recently. But, regardless, it did give me some extra piece of mind. Now I know that if I have a "sudden silence" I will be putting my all into that flare and leveling in the timeliest possible fashion.

Link to comment
Share on other sites

Good point... however, we are all being contradictory as helicopter pilots. We espouse, teach, implore the value and safety of the HV curve, yet, almost everything a helicopter does is within the HV curve. ADM is very important but I feel that it all boils down to "Risk Management". This is what a helicopter does, otherwise, we are just rotorheads flying like an airplane! Where is the fun in that?

 

Cheers

 

Rotorrodent

 

Dear Rotorrodent, can you please explain/justify your statement that almost everything a helo does is "IN" the HV curve? Many of my entire flights have never been in the HV curve, thousands of hours outside the curve! I teach an understanding of the HV curve, when it is relavent and how to minimize time spent in it for helo ops. Also, I teach the transitions a helo rotor system goes thru when transitioning from powered flight to autorotative flight! (Attend a Seminar)

 

Using sound ADM techniques does reduce risks!

 

Fly Safe, MikeMV

Link to comment
Share on other sites

Dear Rotorrodent, can you please explain/justify your statement that almost everything a helo does is "IN" the HV curve? Many of my entire flights have never been in the HV curve, thousands of hours outside the curve! I teach an understanding of the HV curve, when it is relavent and how to minimize time spent in it for helo ops. Also, I teach the transitions a helo rotor system goes thru when transitioning from powered flight to autorotative flight! (Attend a Seminar)

 

Using sound ADM techniques does reduce risks!

 

Fly Safe, MikeMV

 

Correct me if I am wrong, but I think what Rotorrodent meant is that the real value of a helicopter is its ability to operate at airspeed/altitudes that put it in the HV curve such as EMS, Firefighting, Longline, and LE. Sure you can fly all the time and stay outside the curve, but then you might as well use an airplane.

Link to comment
Share on other sites

These are great replies all around, folks. It's interesting to hear what other people think of these things. I just got back into the air today for the first time in almost 8 months, and this topic was on my mind a bit. I'll see if I can get my new instructor to weigh in sometime.

 

Thanks again, folks.

Link to comment
Share on other sites

Correct me if I am wrong, but I think what Rotorrodent meant is that the real value of a helicopter is its ability to operate at airspeed/altitudes that put it in the HV curve such as EMS, Firefighting, Longline, and LE. Sure you can fly all the time and stay outside the curve, but then you might as well use an airplane.

 

Dear RMP, I did not mean that we should always stay outside the curve. Any operation can take place inside the curve as required. It read to me like all our ops are in the curve all of the time(everything we do).

 

Like you stated, wires are more dangerous than an in HV takeoff profile and I agree.

Edited by Mikemv
Link to comment
Share on other sites

Speaking of the dangers staying low to the ground.....this ship apparently was flying so low it had a tailstrike during forward flight!

 

http://www.abc.net.au/news/stories/2010/01/18/2794547.htm

 

Leave it to the Aussies!

 

Fly safe,

 

Goldy

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...