SAS, the quoted article history wise is pretty much accurate as to the process the Army employed to arrive at design requirements, but it has one absolute error of substance and another, huge error of missing but critical information re flyoff results.
The error of substance relates to the performance shortcoming quoted for the YUH-60A. That shortcoming was actually true early in development, but remedied prior to the fly-off. I can’t recall if the last main blade change we made, to extend the tip cap to meet the hover and climb performance requirement ( which it did ), was on the ship when the Army did their preliminary evaluation in Sept/Oct 1975. In any case, it was on all of the ships for the fly-off, and that blade configuration was unchanged, going to production.*
During the operational evaluation part of the fly-off, two events occurred which indicated that the Sikorsky prototype possessed an approximate 2000 lb hover performance advantage over the Boeing model. One at FT. Rucker, Shell Field and one at FT. Campbell, op eval site.
1. FT. Rucker. Shell Field. Each competitor had to train/qualify 10 Army pilots to perform the op eval test program. Part of that syllabus was of course external sling loads. On the day in question, Sikorsky was up first. The Army had prepared seven 55 gal. drums full of concrete/iron which weighed 1000 lbs and had an attachment built in. They also supplied a collector cable , enabling the carry of one thru seven drums. We started with seven, picked up the seven, climbed away vertically and did the same for all ten trainees with I think 2 refuelings during the morning.
Boeing then started, also with seven drums. But they couldn’t budge the seven, so they unhooked one and tried that. Couldn’t pick up 6000 either. Unhooked another drum. Now at 5000 lbs the YUH-61 finally got that load airborne, to maybe 3-4 ft. Then in order to get going, trundled along not gaining any altitude until they got to 20 kts or so and then started climbing. I watched this from about 40 yards away. Note: the Boeing main rotor diameter was I believe 48 ft whereas the Sikorsky main rotor was 53’8”.
2. Ft. Campbell. The Army has a new infantry vehicle called the Gamma Goat, which weighed 7100 lbs and they were anxious to see that the UH-1 replacement could carry it. The op eval was now under way and all the flying was done by the trained Army pilots. Sikorsky was first and, with full fuel and standard crew and field configuration ( which is to say, all seats etc. ) picked up the Goat climbed out, flew a pattern and landed it where it had been. The Boeing YUH-61 did the same thing except that the ship had only 400 lbs of fuel, no troop seats and minimum radio gear. Following their landing of the Goat, they went to the fuel farm to refuel. This was reported in detail by one of the Army maintenance test pilots assigned to the program ( two were assigned and each had been trained by the respective contractor at FT. Rucker ).
*The article makes no mention of the hover performance difference, NOR, that the Boeing Production Proposal for the YUH-61 included larger rotors.
Maintenance Differences. Can’t comment on the data in the article, but can add this fact: During the op eval period at Ft Rucker, the Army maintenance troops working the Boeing machines worked every weekend, while the troops working on the Sikorsky ships did not have to work one weekend.
Enough re the flyoff.
With re to the question of design features requirements for an aircraft that operates in harms way, there are several requirements that applied to both the UTTAS and AAH programs ( and two interesting ones that were on the Sikorsky UH-60 but not the AH-64 ).
Crashworthiness. The experiences in Vietnam led to the development of a Helicopter Mil Standard for Crash Resistance 1290. There is a Table 1 which defines the survivable crash conditions and it starts with a vertical impact at 42 ft/sec ( fixed landing gear ) and includes longitudinal, lateral and combined axes. In another section, it addresses the Engines transmission and rotor heads, requiring that these need to remain in place, so as not to hazardous to occupants under a crash condition of 20G vertically, 20G longitudinally and 18G laterally. Fuel systems shall be designed to contain fuel under the conditions in Table 1. Doesn’t allow leaks.
Anecdote: In order to prove compliance with 1290, we had to build a copy of the tank enclosure structure containing the main fuel tank and associated valves, fill the tank and drop it from 65 ft-no leaks. I have seen a picture of an AH-64 crash where the tank was ripped out of the aircraft and sitting on the ground apart from the wreckage-no leaks.
Ballistic Tolerance. As I recall and simply stated, the UTTAS was required to be invulnerable to 7.62 caliber weapons, the control system up to 51 caliber weapons and the blades to 23mm HEI. Components, including the blades ( and redone with the composite blades ) were subject to live fire tests.
I mentioned two items which were not required but were installed on each new UH-60A.
- · The AFCS computer incorporated a separate chip which was in effect a flight data recorder. Not crash or fire proof, but better than nothing. This was the brainchild of the Chief of the Electronic Flight controls group. No cost.
- · A tail rotor control quadrant, which was actually a mechanism located at the input to the tail rotor primary servo, with a very strong spring such that if either of the input cables lost tension for whatever reason, the pilot will retain directional control by flying the functioning cable against the spring. Wasn’t required but it went in. Saved one Turkish Hawk that I know of.
So, in the discussion regarding " making do " with off the shelf civil aircraft to handle an admin mission, but " might " in exigent circumstances be drafted into tactical use, there are huge differences. The other aspect is that I've read that this or that model helicopter is a " military version ". Get them to show you the evidence.