Sikorsky YUH-60A first flight 40 years ago to this day

[chopper2004]

40 years ago to this day, Sikorsky flew the YUH-60A prototype :)

Cheers

[Lonewolf_50]

Perhaps we should all be raising a glass to our dear PPRuNe colleague, John Dixon. :ok:

[ShyTorque]

John Dixson, I believe... But yes!

[IFMU]

Amen to that! Wished him and my dad a happy 40th.

[Matari]

Interesting differences between the early YUH-60 and the eventual UH-60A.

Just at a quick glance, we can see a shorter M/R mast with beanie cap, a pilot's step, a different tailcone fairing, a different stabilizer airfoil shape, and a ducted roof cowl.

Other than that, the old girl hasn't aged much in 40 years!

http://www.helis.com/h/h60y.jpg

[busdriver02]

I'm curious about the lack of "beanie cap" on the production model, but cheers to John Dixson and crew for probably the most successful military utility helo design in history. It's amazing that 40 years later, so much about that original design is still just right.

[IFMU]

Another big difference between the prototype and today's airplane is the fixed stabilizer.

[JohnDixson]

Thanks Lonewolf, but in my case the toast would be just soda, as in 1989, with the aid of a very good friend, I realized that the good people at Bombay were distilling that product faster than I could dispose of it. It can be historically verified that a month after this epiphany, the popular bar across the street from Sikorsky closed its doors.

Bus Driver, the beanie in the picture is simply a fairing to cover the upper connections for all the rotor instrumentation. I know what you were surmising: that it was a part of the " Tail shake " solution, but that was attained ( on this model anyway ) thru a totally different aft " doghouse " fairing behind the main rotor.

Matari, I will limit my response to your note to the raised rotor, as the story in the book is not complete. First, some history. The original low rotor was due to the air transportability requirements in a C-130. Pilot's office and the safety organization saw a distinct possibility for toe issues: contact of the main rotor into either cockpit roof.engine cowl tops/tail cone, or infantry as they did their thing. Based on the head geometry and the accident history of the USAF S-61 and the USMC S-65, I wrote a longish memo on the subject, which, as you can see in the picture, did not carry the day. What you cannot see in the picture is that there were four electronic blade tracker sensors, one each over the cockpit, both engine cowls and the tail cone. They fed both the onboard instrumentation, and a vertical clearance multi-arrow indicator ( with a memory function button ) mounted on the cockpit glare shield, centered. The first hover flight went absolutely perfectly, but the subsequent two in yard ( Stratford runway is 1500 ft, so forward/sideward/rearward flight speeds are limited ) disclosed that, in simply flaring back to a hover from a takeoff run produced blade clearance over the cockpit of 5 inches ( remember, this is not a rigid rotor ). Remember too, that an Army requirement to flight test to -0.5 G had to be met.

The next envelope expansion flight unearthed no shortage of serious issues, and just one that had a serious spec compliance issue was insufficient forward flight performance, 20+ knots at the top end. While the usual drag reduction schemes were initiated, the senior aerodynamicist assigned produced a theory that was backed up bu massive computer driven airflow diagrams which were posted on the walls of the UTTAS HQ type room. They showed that the airflow up and over the broad, flat cockpit enclosure was increasing the angle of attack of a major section of the rotor disc, and in fact stalling it! By now it is 1975 and we have but 5 months to the Army Preliminary Evaluation. We had a new development chief and April 2nd or 3rd he held a meeting and decided to raise the main rotor 15 inches. May 3rd we flew a raised rotor shaft.The Chief Test Pilot Dick Wright and I made the flight and took the machine out to maximum level flight speed as defined by the 100% Q limit ( design gross weight ). The new development chief met us on the way to the debrief and asked how much faster we had gone. Dick made a circle with his thumb and first finger, and said " that much faster, Bob ". But the news wasn't all bad, as the 3P and 5P excitation was down significantly. At that time, resolving the vibration situation had been going on since October without major success, so this improvement was exceedingly important.

Fits the definition of a serendipitous event. We raised the main rotor in a month ( BTW, it met the C-130 requirement, too! ) in order to get back a major shortfall in airspeed. Absolutely failing at that, we nonetheless totally eliminated the blade clearance issue and markedly improved the vibration signature situation.

I've omitted more than a few details for brevity, but that is the raised rotor story, less the fantastic effort by the rotor/drive train design and test engineering team that allowed a safe test flight one month after decision.

IFMU. I don't type fast enough to cover the story of the stabilator, but like the main rotor that decision was made at a February 11 meeting, and 30 days later, we flew that FBW tail, with the head of that design branch ( a very close relation of yours? )in the jump seat running the electronics.

[Senior Pilot]

John,

We would all like to hear more of your experiences with the YUH-60A, so please get those typing skills up to speed!

I'm intrigued by the loading requirements and the early "transformers" fold up, and the kneeling solution as shown in these two photos:

http://www.sikorskyarchives.com/images/clip_image017.jpg

http://marvellouswings.com/Aircraft/Helicopter/H-60/Pic/YUH-60A%2073-21651%20Rucker.JPG

Can you elaborate on what went on all those years ago?

[SansAnhedral]

Did the YUH-60A frame have accommodations for ESSS from inception? Or were those fittings added later (I cant recall whether or not the upper clevis was integral with the STA frame behind the cockpit)

[JohnDixson]

Sans, the ESSS design was started from scratch.

Senior Pilot, when I retired, I left the UTTAS RFP and about 99% of my files for my successor, thus I cannot tell you the precise load time requirement that existed for the C-130, but it was a few hours. In all of the years that passed after the introduction of the first machines down to the 101st at Ft campbell, I can't recall any actual instance where the Army actually moved UH-60's via C-130. But there are Army units that do things quietly, so one can't be absolutely certain. On the bigger USAF aircraft ( or a Russian Antonov, which we have used to deliver machines to Turkey ), it is pretty much fold the main blades ( as shown in your photo ), take off one of the TR paddles, sometimes the stabilator, and you are in. For the C-130, we made a fairly simple hydraulic kit to deservice the struts ( the details of which I never dived into ).

[GreenKnight121]

This old USMC avionics tech still thinks the initial design blew the "can it use a restricted landing surface" part badly - only to be rescued in the USN's Seahawks with the moving of the tail wheel forward to the aft end of the cabin.

;)

After all, with that tail geometry there was no chance of the tail rotor hitting the ground unless the tail boom had already collapsed.

[Lonewolf_50]

Greenknight, the Seahawk foot print was far preferrable to me. With the Blackhawk, your tail wheel touched the ground while you were a bit more "nose up" than in the Seahawk.

I seem to recall there being a cost associated with that difference in airframe construction, which when the CH-60S (now the MH-60S) was being put together resulted in the non-maritime tailwheel configuration. (Somewhere in the high six figures, low seven figures, depending on whom one was listening to at the time). With CH-60S tied to UH-60L multi year acquisition, this being Bill Clinton era and so little APN-1 money for rotary wing, that had some bearing on the decision to go with the rear tail.

Further comments on that censored, other than to note that the Army finally clued up and put a rotor brake on the Blackhawk ... with the M model. :p

[JohnDixson]

Both important design points, with decent arguments to be seen on both sides:

Rotor Brake. Not a mandatory item in the RFP. SA strategy in responding to the Army Req for Proposal ( RFP ) was to take zero deviations, i.e., propose a machine which met every one of the Army requirements. The Army rotor brake requirement specified that it had to be capable of 1000 full on applications from 100% Nr without the replacement of parts ( that included pucks ). Since the available rotor brake puck technology at the time could not meet this requirement, and because we decided to take zero proposal deviations*, a rotor brake was not included in the Army UTTAS design.

* Due to areas of the proposal that included contradictory requirements, and to my recollection, these were in areas like lighting specs and that sort of thing, certainly none of the major design requirements, we took a total of ten deviations.

Tail Wheel. Decision to equip the SA UTTAS with a tail wheel vs a nose gear was based upon the field usage experience of the USMC and Army S-58 versions, and to some extent with tail rotor strike data on the UH-1 in Vietnam. The intent was simple: protect the tail empennage and the tail rotor during aggressive combat landings in contested unprepared landing zones. No question that it is easier to taxi a nose wheeled machine, but again, that wasn't a main mission. The SH-60B mission was totally different, and involved the necessity of compatibility with a frigate hauldown/hangaring system, which led to moving the tail wheel forward. It is interesting to note that with the tail gear moved forward on the 60B, it was then required to make the tail stinger/strut, along with its backup structure, designed as a landing gear, i.e., good for 12 ft/sec landings.

[busdriver02]

John, I was actually curious about the "beanie" since the S-92 has one. I assumed it is a drag reduction measure.

Only having flown the Huey and Pavehawk (nee Blackhawk) I actually like the "Army" tail wheel location. It makes landing in the dirt very forgiving, I know it's vastly more forgiving than the H-53 gear arrangement. Although I'm sure the rear folding nose wheel on the H-53 made things worse.

Actually one of the coolest things about the H-60 design is the incredibly forgiving CG range. The only times I've seen an actual out of CG W&B sheet had the probe removed (the Pavehawk has a lot of weight in the tail cone). In practice CG location just doesn't matter, as long as it'll fit and you can hover, it's good.

[JohnDixson]

The beanie seen on various SA production models is typically part of the aerodynamic solution to what is termed " tail shake ". Tail shake occurs when relatively high strength vortices are shed from the main rotor head and/or main rotor pylon area, and which then proceed into the tail rotor. They produce enough of an instantaneous change in angle of attack in the tail rotor thrust that the resultant yaw bump is clearly felt, and especially so in the opposite end of the machine where the pilot sits. As you might expect, it surfaces as a random but not infrequent excitation, and depends on the speed of the aircraft, CG and flight condition. Chasing down a solution can be time consuming. On the UH-60 model, we went back to the wind tunnel and used that to make some changes, which we then flew and made even more changes. We were able to eliminate the occurrence throughout most of the envelope without a beanie. That has not been the case with other models.

Test aircraft often sport beanies as a fairing over the connection of all the main blade and rotating component instrumentation wiring, and this was the case for pictures of the original UTTAS machines while they were in flight test status.

Your comment re CG range offers an opportunity to illuminate a comparative truth, that last surfaced ( in my active career ) when the replacement of the USN CH-46 vert rep aircraft with what became the 60S became a subject for discussion and evaluation. People who had not paid attention to the tested and qualified CG range of the UH-60 series machines were surprised. They needn't have been so, as if one goes back and compares the S-65 series against the CH-47 series, ( comparing the CG charts in the flight manuals ) one finds the same thing: i.e., that the huge CG range advantage talked about ( in some circles ) for the tandem rotor machine was just that: talk. Background: I flew the 47 from 1963-65 and liked it.

[Lonewolf_50]

The Army rotor brake requirement specified that it had to be capable of 1000 full on applications from 100% Nr without the replacement of parts ( that included pucks ). Since the available rotor brake puck technology at the time could not meet this requirement, and because we decided to take zero proposal deviations*,
that kind of requirements writing strikes me as curious. (See also some of the sideways flight requirements on Comanche). Since pucks are a consumable item, what is the sense (one wonders) in including them in that requirement? The metal parts like the disc and the other bits and pieces of the rotor brake ... OK, I see the requirements point in how that was crafted.

Thanks for your insights, John. (Also, apologies for incorrect spelling of Dixson in my early tribute post. (blush!)
I flew Seahawks before I ever flew a Blackhawk, (even though the Blackhawks came first).
My perceptions on how the bird should handle in that last few feet down to the ground could be called "backwards" :8.
Tail Stinger: some people, when practicing autorotations, needed that tail stinger to remind them not to land on the:mad:tail. :ugh: There are smart ways to train, and dumb ways to train. The old "I am so good I could auto it onto a FFG's pitching deck" practice auto seems to have been where our squadron had the most tail stinger repaint events. :ugh:

[JohnDixson]

LW, struck us as unusual too. Recall that the Army personnel charged with developing what was called the Material Need Document was composed of a diverse group within the Army Aviation community. There were different constituencies, including the " What's Wrong with the Huey in the First Place " types. The Col. who headed up the group once told me about the landing gear decision, i.e., skids vs wheels and said that it got quite interesting. Not all of the people within the group had enough technical savvy to appreciate the go-withs that attended a basically twice Huey weight-wise machine. A telling sidelight is that in all of the meetings etc that I was involved in over those years, I can't remember any serious discussion from the Army side as to " coulda-shoulda " put in a rotor brake, and I think that might have been the answer: i.e., the group that didn't want one forced an unachievable performance requirement, which took it off the table. Just guessing.

Am curious as to your comment re the last few feet close to the ground on Seahawk? Do you mean after the tail wheel touches down first and you fly the mains on?

[Lonewolf_50]

Am curious as to your comment re the last few feet close to the ground on Seahawk? Do you mean after the tail wheel touches down first and you fly the mains on?
Yes. It's a "feel" thing, or it was for me.
The rhythm of tail/mains in the Seahawk was different than the Blackhawk. I usually felt that my nose was "too high" when the tail touched, having developed my sight picture in the Seahawk. Granted, once one is used to it in the Blackhawk, it's a non-issue, but my initial few low work days felt wrong.

As to the rotor brake: no surprise, the process of requirements development isn't pretty.

[JohnDixson]

If you flew the 60B then, with all the gear aboard plus crew, the CG was more neutral, whereas if you taxi out in a 60A/L with just crew and full tanks, the CG is near the aft limit and it hovers 6-6.5 degrees nose up, which makes the transition from tail wheel touchdown to mains touchdown a good bit longer.

It was good hover practice to ( UH-60 as above ) put the tail on the ground and then do backward figure eights with just the tail on the ground. Then do it on the ground with tail gear unlocked. Not very challenging, but did give one a good feel for where things were.

[busdriver02]

John, it's funny you mention the tail wheel games. I used to play a similar game with my crew, practicing placing the tail wheel on the roof of a building. No practical application, but it was a fun CRM exercise that taught my young co-pilot the true size of the aircraft.

Curious question: what do you think the growth potential of the basic 60 platform with respect to weight. What would be needed to support a max weight of say 26,000lbs? My thought is that lots of modern avionics makes aircraft denser, so while the cabin volume may be good, but the max gross becomes limiting. At least it is on the Pavehawk.

[JohnDixson]

Originally, the design of the S-92 drive train envisaged a transfer onto the S-70, but it now looks like the next iteration will be the JMR.