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by Anonymous 16 years ago
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This is an excerpt from John Dullighans wonderful "Cinderella Bird"
Most of the time, the H-46 was flown just like any other helicopter, especially if it was in formation with others. But if you were assigned a medevac, especially if the LZ might be ‘hot’, a maneuver called the ‘Buttonhook’ was particularly useful. H-46 pilots claimed that by flying a ‘Buttonhook approach, the ‘Phrog’ could get into a LZ quicker than any single rotor helicopter. The less time the aircraft was exposed to hostile fire the better so it was a good idea to get into the landing zone, land, pick up the casualties and get out as quickly as possible. Doing a long straight in approach from altitude, gradually slowing into a hover would get you shot down very quickly. The Buttonhook was started directly from cruise speed and low level by setting up a high drag turn which resulted in rapidly decreasing speed and decreasing radius of turn which resulted in an increasing rate of turn. The airplane was never going in the direction it was pointing and it was rapidly decelerating.
H-46 pilots used the characteristics of the twin rotors to develop the 'Buttonhook', so called because from above, the maneuver traced a path over the ground that looked like an old fashioned buttonhook. It was most effective when the desired landing direction was 180 degrees from the initial heading, but the heading difference could be as low as 75 degrees. The aircraft appeared to start into a normal turn but as it slowed rapidly it rotated sharply, seeming to hang in space at the end before swiveling into position.
A ‘Buttonhook’ is begun at an airspeed above 120 knots at an altitude no higher than one hundred feet. The start position is close abeam the intended point of landing/hover, one hundred meters but no more than two hundred. First reduce collective pitch to a minimum (trying not to disengage the sprague clutches and dropping the engines off line) then raise the nose of the aircraft from five to twenty degrees, thereby maintaining or reducing altitude slightly. Then roll the aircraft to bank angle not exceeding forty-five degrees while applying sufficient yaw input to maintain balanced flight. At the same time smoothly come back with the stick (full aft cyclic) and increase collective pitch, which will cause the aircraft to "hook" around in the direction desired with no gain in altitude. The desired result is a controlled loss of altitude accompanied by a substantial loss of airspeed; usually dropping from 120 knots to below 40 knots in five seconds. The increase in collective pitch must be substantial to ensure engines are on line and spooling upwards, in preparation for landing power. Then as the aircraft rotates to the desired heading, roll out level and increase collective to full power if necessary. The aircraft is now almost stopped in a position to transition to a hover or a landing whichever is desired. This maneuver required practice to get right. Common mistakes were:
· Not keeping power on during the entire maneuver, so that on roll out on the desired heading, the engines are at idle and cannot spool up quickly enough to prevent a hard landing. A hard landing could result merely loosening the fillings in your teeth to requiring the airplane to be carried back home slung from a Sky Crane.
· Maintaining too low a collective pitch setting. This extends the maneuver by not slowing the aircraft rapidly enough thus overshooting the landing/hover area and having to 'drive' to the zone after aligning the aircraft on the new heading. This left the aircraft low and slow and out of position, extremely dangerous if there was any opposition.
· Not reducing the collective sufficiently, resulting in a climb in the sharp turn. This increase in altitude unnecessarily exposed the aircraft and extended the time it took to achieve landing or hover.
· Allowing the nose to drop during the sharp turn to new heading. This sets up a dangerous, low-powered rate of descent at very low altitude.
It wasn't taught in flight school but any pilot who got shot at, quickly learned it from the experienced pilots. The 'Phrog' had so much excess power most of the time, it was rarely at maximum weight, and would accelerate much quicker than a Huey. You could jink nicely with it since it had a very high crosswind component, thirty knots at least, so you could point somewhere other than the track you were making, at the expense of higher drag.
To learn a ‘Buttonhook’ was not easy and there were many hard landings. But the typical pilot in Vietnam was flying most days, well over one hundred hours in the average month, sometimes more. When you fly that much, you get good. The aircraft seems to do what you want without any conscious thought. Yes, it was dangerous, but it saved lives. My friends from that era, all now retired, conclude that there is nobody left in the Marine Corps who can fly a buttonhook. I described the maneuver recently to a young Marine H-46 pilot, and I could tell that he found it hard to believe that people did such things. He certainly wasn’t prepared to try one. And given the amount of time he flew, he was wise. But if he was being shot at, he might change his mind.
The entire text can be viewed @ http://www.airsceneuk.org.uk/oldstuff/h46/h46.htm
Posted : 2006-11-15 06:28
Neat Stuff Tom
I'm not surprised that todays CH-46 drivers can't do it, since it would require a manual engagment of the "Hover Aft" feature at an airspeed far beyond NATOPS limits! LOL! I don't think they could do it if they wanted to, could they? I mean, it requires a manual Hover Aft, not the later automatic feature, correct?
Wow, were we ever impressive coming into a "HOT" zone! I'm sure more than one lost the airspeed and turns doing this manuever but their good fortune but the close enough to the ground trhat it wasn't as big of an issue as it could have been and they didn't have far to fall! LOL! Great memories of gutsy Pilots and the Crewmembers that trusted them wth their lives every single day! Would love to do some of that stuff again!
Posted : 2006-11-17 12:08
Buttonhook
I agree with all of it Tom....
We all got good at it....and we tried to pass on much of the skill and technique to the new guys at New River while we prepared for another tour (I got two)....as far as the nonsense about hover-aft goes....I flew the crap out of both As and Ds.....and the only difference in the air was usually the amount of side-flare required if the nose attitude was not as flat as one wished on short final.....lots of adjustments in rate of descent and angle around the last 20 degrees of turn (a falling, spinning anvil)....either way, it worked well....and most of us are still here.....(we used to joke that the NVA would ignore an approaching A/C doing that, because they figured we were dead anyway......why waste the ammo....)
S/F,
Mike
Posted : 2006-11-17 18:30
Topic starter
NATOPS Version
I have attached the "By the Book" landing procedures as described in the CH-46D Flight Manual as well as "Hover Aft" procedures.
Just in case anyone forgot..................
Posted : 2006-11-20 12:59
Did it many times, in a Huey, mostly medevac and recon team stuff. All it is, is a modifed/exadurated side flare. Something you plan to use OR use because you are going to overshoot the spot if you don't do it. I used to instruct it's use keeping below 50' agl as a way to stop quickly without putting the tail rotor in the ground or gaining altitude. The tips of the main rotor you can readily see in front and on the sides, tail rotor not so visable. You might wind up flying backwards with the tail up at a 45 degree angle(or more) and full up collective trying to go the other way, but if you were at one with the aircraft, it worked out. Never tried to put this in writing before, I just did it, showed them how to do it and hoped for their best. Did not really press most PUIs to perfect manuver, but exposed all I could to it.
Lanny
Posted : 2006-11-26 02:28
Buttonhook
I saw the Subject 'Buttonhook' and was surprised to see the extract from the article I wrote in 2000 for a "Zine" in England. I had written to the editor, name Gary Parsons, taking him to task for using a pictire of the Phrog to illustrate an article on the H-47, the Chinook. The mistake is quite understandable for a member of the British public, the RAF operates the Chinook, so when a civilian, even an enthusiast sees a twin rotor helicopter, it is understandable that he would assume that it was a Chinook. But I told Gary that as editor of an aviation magazine, I held him to a higher standard and he should know he was looking at an H-46, not an H-47.
He agreed with me but claimed to know next to nothing about the H-46, except that the Marines flew it. After exchanging several long emails, Gary told me that I already had the outline of an article. He encouraged me to write it, saying the H-46 deserved to be better known. I wrote it and he edited it, jazzing up the story somewhat. Something about reading like an engineering report. I told him to put it back the way it was or take my name off it. I knew that members of Popasmoke would read it and it had to be factually correct. We eventually agreed. Actually, I've just read it for the first time in years and it holds up pretty well. My description of the Buttonhook is a bit confusing but Popasmoke readers know what it is anyway. And of course my remarks about the present day pilots, although true at the time, are not any more. They are doing virtually everything we did but at night at 30 feet.
Norm Clark, the senior Boeing Tech Rep and a Popasmoke member tells me I'm wrong about the reasons for the midair breakups. They were not caused by whirl mode flutter but by a variety of different reasons. He is King of the H-46 in my book, he has spent his whole career, more than 40 years, working on the H-46. He worked on the original design team, in 1966 he accompanied HMM-164 'in country' did at least 3 (maybe 4) tours in Vietnam and spent the rest of his career with the H-46. He still works for Boeing. What he doesn't know about the H-46 isn't worth knowing.
I got a number of emails from various people, both in England and the US. The English wanted to know how a Limey ended up in Vietnam. Was I drafted? No I replied, I volunteered. Americans, especially Marines, had the attitude, "Of course he ended up in Vietnam, that was where the War was.
John
Posted : 2006-12-01 01:29
Showed it to many soon to be qualified folks. 'nuff said.
Best I ever did was with a "105" slung underneath...Good thing we had minimum crew and approximating low fuel.
Hooper
Posted : 2007-09-04 23:17
H-34 buttonhooks
I was in country '66-'67 as a Dog [ H-34] driver. Our version of the buttonhook was to head for the LZ low level [ treetop] high speed [ for a '34]. At the edge of the LZ, simultaneously you would yank the nose up to about 45 degrees while dumping the collective to the bottom and splitting the needles [ full auto ] and kicking right rudder. The nose up kept you from losing altitude, the split needles kept you from ballooning up. The rudder spun the nose around 180 degrees going from 45 up to 45 down [ midway the bird would start actually going backwards ]. As the nose passed about 90 degrees of the spin, start pulling power back in to max to stop backward flight. As the nose reached 45 down, backward motion should be stopped so yank the nose up to level. As nose comes level, reduce power and drop into the zone. Happens a lot faster than trying to explain and it got real ugly/exciting if your timing on any part got out of sync. Probably in the red " Not Recommended " section of the Natops. Mostly for Medevacs in a hot zone. Semper Fi Joe
Posted : 2008-12-07 21:19
