quote Originally posted by maryjane: Perhaps Blackrams has had it happen too, as I have in a helicopter. Cruising along in clear calm air at about 1500' and suddenly the aircraft just 'drops' straight vertically (not nose down) about 10-15 ft then continues on as normal. The 1st time it happened while I was on board the most experienced pilot in the CH53 program was at the controls abput 1/2way between Danang and Chulai. "There's that old transient T(?) problem" the pilot remarked. Here's the same pilot a few years earlier https://www.youtube.com/watch?v=VC2E8RJE3Jo (The T problem he remarked on is in referenceto some adjustment on a sensor with the nomenclature of 'T' and a number which I have forgotten. (T-6 maybe) Located on a panel between left gunner window and bulkhead betwwen cargi bay and flight deck and was one of several little screws you adjusted for different 'stuff'.)

Love the video Don. Reminds me of some of the things I tried at one point or another in my time as a mission pilot. As a Test Pilot, it was all business and not nearly as much fun although, I've had a few experiences that could have ended differently had I not practiced auto rotation often and developed a pretty good technique for putting the aircraft back on the ground without the assistance of a power plant. Over my entire test flying career, eight engine failures give one a reason to get and stay good at auto rotations. Rule of thumb, always take the crew chief who worked on the aircraft with you on the test flight (he/she may not have your best interests at heart) and always keep the flight over a clear landing site with a good place to set her down.

I have experienced that drop in altitude while flying a UH-1 while flying IFR a few times, it always gets your attention. As to the specific cause, I always attributed it to micro bursts of downward flowing channels of air. The kind you can't see. The absolute worst situation that got my attention the most was while flying to a destination that required us to fly through an occluded front with several concentrated thunder storms. ATC was giving us guidance and directed us between some major atmospheric down pours through what he described as one or the lesser disturbances/cells. While attempting to maintain the desired and assigned altitude, we entered the cell, initially we began to climb at a rate of about 3000 feet per minute so I obviously lowered the collective to maintain altitude. When we hit the center of the cell, we dropped like a rock and the Vertical Indicator actually maxed out. Scared the crap out of me. Reminded me of my skydiving days in freefall.
Not sure what altitude we ended up at but we maintained a 90 +/- knot forward airspeed the entire time while heading what felt like straight to our demise. Thankfully eventually came out the other side of that downward column of air and back into the clean air upward moving outside and ended up at the previous assigned altitude. Scared the hell out of me and the folks in the back. I apologized but, from the looks of the rear, my apology went un-noticed, they were still throwing up their dinner. The whole event may have lasted 30 to 40 seconds but, seemed like a life time.

Have experienced similar but much shorter or faster/quicker drops like that on commercial airliners since but, nothing like that.
Edited: At this point with what is apparently known, I don't believe this was in anyway related to weather.

Rams

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quote Originally posted by williegoat: I'm curious. Does the pilot change the collective pitch throughout the maneuver? Is there such a thing as negative collective?

On that S 52. I have no idea, that was before my time. I suspect it was similar to what I flew but can't say with any real authority.

But, the birds I flew had a negative pitch (so to speak) on the outboard ends of the rotor blades. That pitch is what allows the helicopter to maintain rotor speed during auto rotation.
So no, the collective didn't have a negative pitch capability in the aircraft I flew.

Once showboating I.................. No, never mind, that one still scares me to this day.

Rams

[This message has been edited by blackrams (edited 03-24-2022).]