Jump to content

Low-G Condition Caught On Video


charlicopter
 Share

Recommended Posts

 

First video I've seen of low-g... Discussion???

 

 

Wow- Great video. He completes a full roll and then chops off the tailboom....I've seen (been in) a 206 in that same climbing manuever several times, usually ends by letting the ship fall off to one side....

 

I had no idea the 1100 was subject to that kind of roll forces in what appears to be a very small low G factor.

 

Surprised it has taken this long to reveal a video that looks 40 years old.

Link to comment
Share on other sites

R.I.P. to the pilot but this video is a great learning/teaching tool about not just low g but 'display' flying. Two things I find striking- the seemingly low forward speed of the helicopter at the onset of grief and also the fact that it appeared to be unrecoverable despite the fact that the rotor did not seperate until the t/b strike on the second full flip. Show your students this video when teaching them about "recovery procedures" for low g.

 

I'd also like to add that everyone thats ever read the rotorcraft flying handbook are going to conclude that this is definitely low g. Could very easily just have been a major control component failure.

 

fly safe

Link to comment
Share on other sites

that doesn't look low G, plus, what maneuver did he do that would even warrant a low G situation? The rotor disk was loaded at that moment, all he was doing was a slow airspeed/cyclic climb. It starts a quick roll left, followed by hard roll right and the resultant situation. I believe the rotorcraft handbook states the helicopter will roll in the direction of tail rotor thrust, which would have made the FH1100 roll right.

Link to comment
Share on other sites

Excellent point. It's definitely easy to write it off as Low-G, but component failure certainly would be another perfectly valid explanation for the severity of the right roll.

 

I think that another one of the more striking characteristics of the roll however is that the pivot is not longitudinal, but on an axis from the tailrotor and through the apparent C.G. More like a half-roll-half-tailspin sort of thing... Classic Low-G.

From my simulator experience, that is EXACTLY what Low-G looks like... Even the full roll. I've entered some pretty severe Low-G conditions intentionally in the sims and consciously avoided a left-lateral cyclic correction to avoid mast bumping. Sometimes when you try to reload with aft, the thing is just too far gone and it goes all the way around, only to come apart at some point the next time around... I think that it gets worse if you put in too much aft because you are tilting the torque of the rotor aft, which HELPS the roll progress. Pretty scary stuff.

 

And you're definitely right... this goes into the CFI toolbox for sure!

Link to comment
Share on other sites

that doesn't look low G, plus, what maneuver did he do that would even warrant a low G situation? The rotor disk was loaded at that moment, all he was doing was a slow airspeed/cyclic climb. It starts a quick roll left, followed by hard roll right and the resultant situation. I believe the rotorcraft handbook states the helicopter will roll in the direction of tail rotor thrust, which would have made the FH1100 roll right.

 

I agree. I'm not sure that it's low-g either. If it is low-g, I don't see what the pilot did to create a low-g situation. He wasn't coming out of a hard climb and he didn't nose it over.

Link to comment
Share on other sites

if its Low G, then i've been taught wrong and been teaching alot of people wrong. because that does not have the symptoms of a Low G situation. The initial roll left knocks Low G out of the situation. If it were, you would see a roll right initially, followed by a pilot input left to TRY and correct, which of would lead to a bad situation. im voting "NO" on Low G here.

Link to comment
Share on other sites

Another vote for low-G.

The initial left roll could have been pilot induced as it was VERY little left roll. He obviously came out of an aggressive climb after a dive and just leveling off anything but SUPER gentle after that is going to produce a low-g situation. Remember how difficult it is to get a good perception of speed from that distance and angle AND it is an OLD clip. He was in a dive and we all know he was MOVING when he got to the bottom of that but looking at the video it looks like he's barely going 20 kts!

Don't judge the maneuver based on the speed you perceive. Judge it on what you have hopefully been taught, what you hopefully know and hopefully what you are teaching your students.

It's Low G.

Link to comment
Share on other sites

He was JUST coming out of the climb, causing the Low G. That roll happens as soon as that disc becomes unloaded. The left input the pilot may have initiated would not have ANY effect on the fuselage BECAUSE the disc is unloaded. The disc MUST be loaded to have an influence on the airframe.

Remember it's difficult to judge things from these viewing angles but you can still easily be ascending in a low g maneuver (giving the impression of a cyclic climb) with a forward cyclic movement that isn't enough to point the nose down. Still creates low G.

Link to comment
Share on other sites

I agree: Think of a parabolic arch in a plane like the one NASA uses to simulate 0-G. You can be going UP and still be in freefall... think of those ammusment park rides where they launch you straight up, then let you fall back down. You're in freefall as soon as they stop pushing you up, and you're still going up, but you feel weightless.

 

Low G is just when your vertical acceleration reaches something close to

-9.8 meters per second^2

 

You can be going up and still meet those acceleration requirements.... you just won't be going up for very long.

 

Also, if you look at the his attitude just before you lose sight of the ground, he pulls in a lot of collective and starts that steep climb, which means a lot of antitorque. Great scenario for Low-G-Roll because the tailrotor thrust is so high.

Then, if you look closely at the rotor disk just before the roll occurs, you can see it pitch forward pretty far.

Link to comment
Share on other sites

taken from rotorcraft flying handbook

 

 

Also, in a counter-clockwise rotor system (a

clockwise system would be the reverse), there is no

main rotor thrust component to the left to counteract

the tail rotor thrust to the right, and since the tail rotor

is above the CG, the tail rotor thrust causes the helicopter

to roll rapidly to the right,

 

There is no doubt that you can get low g in a climb. one think to take into consideration is that the TR has to be above the Center of gravity and a forward cyclic motion needs to happen. In a climb the tail is low so the nose has to go down for a low g pushover scenario. ANY forward intertia with cyclic pushover can cause low g(even 15 kts of forward airspeed can induce roll). In this video i do not see the nose pitch down at all to create the roll. With such little forward intertia(airspeed) the pushover has to be a little more abrupt then if one was going 110 kts. We would see more of a nose low pitch attitude with such low airspeed before one would see a rapid roll. Just my .02 but i think it was control malfunction.

Link to comment
Share on other sites

My 2 cents. Low G can occur any time you feel light in your seat. Remember Low G means Low Gravity.

 

In this video you know the helicopter is being demonstrated so it is being pushed hard. He (she) is making turns, climbing, descending, and doing both at the same time. At the point were it goes out of control it is my opinion that the helicopter is nearing the top of intended climb. Planning a turn to the left the pilot moves the cyclic to the left and to level the climb pushes forward. This is were the Low G comes in. Pushing forward a little to abruptly at this point will cause a Low G situation.

Link to comment
Share on other sites

Any idea where and when this happened?, I searched the NTSB database back to 1962 for FH1100 and the only Low-G was weather related. In what year was the first FH1100 produced?

 

I think we can all agree that the pitch up and push over at the end is not something to be tried with a teetering rotor system. Not that I'm going to go out and test my theory but, if the pitch up had been followed by a banked turn before feeling light in the seat, the outcome may have been different. This is of course assumes mechanical failure was not a factor.

 

Mike

Link to comment
Share on other sites

the nose has to go down for a low g pushover scenario.

 

I'm not completely sure about that. Reason being, the TR is out on the end of the T/B which is acting upon the fuselage as a giant lever. Sure, optimally the TR will be well above the CG to produce the roll but when you think about it, what MAJOR difference does it make where the helicopter is in reference to the CG? The CG is completely distorted due to the low g anyways and the fact is that the disc is unloaded so it isn't having any influence on the AF anyways right?

 

I know you're quoting from the RCFH but there are a few more things that I am not sure I agree with in that book that we could discuss further in another thread at another time if you'd like. It's a great book but it's not the bible.

Link to comment
Share on other sites

I'm not completely sure about that. Reason being, the TR is out on the end of the T/B which is acting upon the fuselage as a giant lever. Sure, optimally the TR will be well above the CG to produce the roll but when you think about it, what MAJOR difference does it make where the helicopter is in reference to the CG? The CG is completely distorted due to the low g anyways and the fact is that the disc is unloaded so it isn't having any influence on the AF anyways right?

 

I know you're quoting from the RCFH but there are a few more things that I am not sure I agree with in that book that we could discuss further in another thread at another time if you'd like. It's a great book but it's not the bible.

 

 

i guess i should have worded it as "nose lowering" not restricted to nose low. I agree with you on the book. I'm giving my opinion based off what i saw at the robinson facotry when they were allowd to demonstrate low g. That nose has to be forced down with forward cyclic and i just didn't see that in the video. Especailly with the lower airspeed, the nose pushover would be more pronounced.

Link to comment
Share on other sites

NTSB Identification: LAX83FA362 .

The docket is stored on NTSB microfiche number 22780.

Accident occurred Thursday, July 28, 1983 in PORTERVILLE, CA

Aircraft: FAIRCHILD HILLER FH-1100, registration: N450FH

Injuries: 2 Fatal.

 

ON 7/27/83, MILD MAST BUMPING OCCURRED DURING A PUSHOVER MANEUVER WHILE A HILLER FH-1180 WAS ON A FLT TO CERTIFY NEW ROTOR BLADES. PRIOR TO THE INCIDENT, THE HELICOPTER WAS ACCELERATED TO 90 MPH. THIS WAS FOLLOWED BY A PULL-UP & DECELERATION TO 80 MPH, THEN THE PUSHOVER WAS INITIATED. THE HELICOPTER REPORTEDLY ROLLED SHARPLY TO THE RIGHT & PITCHEDNOSE DOWN WITH SOME YAW TO THE RIGHT. RECOVERY WAS MADE WITH LEFT CYCLIC; HOWEVER, DIRECTIONAL CONTROL WAS LOST BEFORE RECOVERY & MILD MAST BUMPING. ON 7/28/83, FH-1100, N450FH, A STANDARD PRODUCTION MODEL, WAS FLOWN TO EXPLORE THE PHENOMENON. AFTER 2 PUSHOVERS WITH INCREASING SEVERITY, IN WHICH CONTROL WAS RETAINED, THE PLT ATTEMPTED A REPETITION OF THE PREVIOUS DAY'S MANEUVER. WITNESSES OBSERVERVED THE HELICOPTER ROLL & YAW TO THE RIGHT & PITCH DOWN AS IT BEGAN TO BREAK UP, THEN BURN & CRASH. AN EXAM REVEALED THE MAIN ROTOR BLADES SEPARATED AFTER MAST BUMPING & MAST FAILURE OCCURRED. THERE WAS EVIDENCE THE PLT MIGHT NOT HAVE BEEN CURRENT IN TEETERING ROTOR SYSTEMS & RECOVERY FROM LOW G ROLLS.

 

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

 

CYCLIC..IMPROPER USE OF..PILOT IN COMMAND

AIRCRAFT HANDLING..NOT MAINTAINED..PILOT IN COMMAND

 

 

Contributing Factors

 

LACK OF RECENT EXPERIENCE IN TYPE OF AIRCRAFT..PILOT IN COMMAND

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...