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Jun 19, 2007


Rotorcraft Engr

Ok, plain and simple, let the crews of these aircraft who will be putting themselves out there select the aircraft that they want.

PaveHawk Driver

Ok folks, enough speculation and postulation.

Lets gather some facts then put out some opinion and have a reasonable discussion of the pros and cons of the HH-47 for CSAR:

1. The original ORD (come CDD) was written at ACC and required a "medium lift" aircraft with no definitive maximum size.
a. A "Medium lift" helicopter specification is not defined in FAA or DoD pubs anywhere but was loosely defined by congress years ago.

2. The CDD/SRD was changed at AFSOC around 2005 for purportedly administrative reasons. These changes were not vetted through the Joint Requirements Oversight Council (JROC) because of their "adminstrative nature". The wording changes didn't hurt Sikorsky or Lockheed's entries but did allow the HH-47 into the contest by reducing the airspeed requirement and changing "mission ready" in three hours to "flight ready" in three hours.
a. There is a significant difference between "mission ready" and "flight ready". The former wording would have eliminated the 47 from the contest. Furthermore, Boeing, in-house, demonstrated that they could remove and reinstall the pylon in under three hours. Operational removal and reinstallation of the 47's aft pylon before and after airlift takes a minimum of 4 hours with a crack crew (reported by a high-time maintainer from the 160th SOAR who does this all the time).

b. Boeing for their proposal, also self-described the H-47 as a "medium lift" helicopter despite references on Boeing's own web-pages about the H-47 as a “heavy-lift” helicopter. (remember, medium-lift is not formally defined anywhere except in that obscure congressional reference) This was a convenient description change that allowed entry into the contest.

3. Boeing enters the contest and given its’ advanced integration of glass cockpit, EW self-protection (SIRFC), and IR countermeasures (DIRCM/AAR-54), and TF/TA radar, and incredible specific excess power available from those monstrous T-55s, meets many of the block 10 CSAR-X requirements in block 0 with a currently open production line. This makes acquisition of the 47 a lower risk acquisition proposition for the system program office; especially given the accelerated block 0 delivery schedule imposed by the AFSOC staff in early 2006.

a. It doesn't take a rocket scientist to figure out that TEREX earth moving dump truck can do the work of a one ton pick-up requirement; Albeit at a significantly higher procurement and operational cost. What are those costs?

4. Costs:
a. Maintenance: Older designs require more maintainers and maintenance man hours per flight hours than designs based on proven modern hingeless or elastomeric rotor systems, composite fuselages, leak-isolating hydraulic systems, and LRU designed components…PERIOD. The 47's fuselage is still a 1960's aluminum and rivet design and does not incorporate the structural redundancy, flexion & vibration tolerance that composites afford. Nor does it incorporate active vibration control which will extend life-expectancy for dynamic and load-bearing structural components. 47s are famous for their fuselage cracks much like the 308 beam cracks in the HH-60Gs they're slated to replace.

b. Operation and sustainment: T-55 engines burn alot more fuel per hour than CT-7 series motors (almost twice as much per hour per motor)...period. While the 47 does already incorporate advanced systems to protect it from RF or IR SAMs, other modernization efforts will be required to make the airframe more “survivable” = “less vulnerable” given hits. Sustainment and moderization efforts to bolt-on vulnerability reduction (vice designing it in from the beginning) are expensive and costly in terms of weight which equals payload reduction, and fuel reduction which equals range reduction. Also, will 141 aircraft be enough to keep key component manufacturers producing parts for this 40+ year old design long into the future? Right now the new Army H-47 deliveries are being delayed for gearbox, materials and other sub-contractor delays. How can Boeing claim that their production line for this aircraft would be low risk when they’re already late delivering to the Army at a lower production rate?

c. MILCON: The 47 is huge; actually 1 foot shorter than a C-130. This means that none of our existing CSAR squadron hangars can house the 47 and the USAF will have to POM and fund the hangar and ramp space for these behemoths. Real estate is a rare commodity on most USAF flight lines. This has not been talked about much in public forums. I don’t have specific figures on what it costs to build a hangar and helicopter ramps, but it ain’t cheap.

d. Airlift: The 47 as a larger multi-rotor aircraft will have a larger logistics footprint. One of the biggest CSAR complaints in the 90's was that CSAR assets couldn't move far enough left in the TPFDD timeline to get to the fight for day-one of the war. This drove AFSOC to cover the mission from day one until CSAR forces arrived because AFSOC had higher mobility priority than CSAR assets. AFSOC performing the CSAR mission is what caused much of the command and control SNAFU's in Desert Storm and OAF. Won't the larger footprint of the 47 cost CSAR a backseat again in terms of mobility priority? Won't this again cause the mission to shift (during the early days of the war) to the only USAF vertical lift platform left in AFSOC; the CV-22 (which was ironically deselected in the original CSAR-X AOA)? Won't this create the mission mis-prioritization that drove the CSAF to move CSAR back to ACC in 2006? A move that ensured that the concerns of the Joint/Combined Air Component Commander drive the organize, train, and equip requirements for his CSAR forces.

5. Other significant considerations:
a. Vulnerability: Modern helicopters are designed from the lessons learned from shootdowns in Vietnam. From these lessons, helicopter designs changed to incorporate composites in blades and fuselages that distribute loads equally around damage that would be catastrophic in solid metal parts. Designs changed to put less critical components outboard of more critical ones such that projectiles would have to get through components like generators that won't bring you down before it hits things that will like hydraulic pumps and fuel controls. Designs changed to make fuel system components self sealing, and frangible in the event of crashes. Designs included changes to make interiors “spall” resistant such that aircraft shrapnel from hits is minimized from causing injuries to crews. Fuel tank and structure designs that tolerate the hydraulic ram effects of rounds hitting liquids is another change. Redundant powertrain drive paths and flight control paths are another key vulnerability reduction design. The 47 was designed before these Fundamentals of Combat Aircraft Survivability were codified by Professor Robert Ball. For example, the 47 still has it’s primary and secondary hydraulic lines within 24 inches of each other and adjacent to the single, 9-piece, synchronizing shaft in the tunnel between the aft and forward transmissions. Bolting these post-Vietnam advances onto a 47 is cost and weight prohibitive.

b. Other Key Performance Parameters (KPP) that were glossed over:

1) Blade de-ice: is essential for an all-weather CSAR platform. Boeing was not penalized in the analysis for not having blade de-ice on their aircraft. They claim they can take the de-ice design from the H-46 and easily put it on the 47. Reality says otherwise. The de-ice system is not designed for the 47 blades, has not been qualified or spin-stand tested nor tested in–flight on the 47. This is higher risk than what was assigned in the analysis.
2) Shipboard compatibility: YGBSM. 47’s on ships for CSAR forward alert presense? Certainly not on as many types of ships as the other contenders could.
3) Air Refueling: Does the 47’s extremely long refueling probe, extraordinarily long arm from the pitch axis to the tip of the probe and huge pitch inertia present problems with cyclic control during air refueling? Some probe-equipped MH-47 units don’t let pilots with less than 2500 hours perform air refueling due to this difficulty. Has the USAF addressed this shortcoming in terms of available CSAR pilot experience levels and requisite training that will be associated with maintaining A/R currency? I doubt it. I don’t think the question has even been raised.

6. Other questions to ponder:
a. Is platform acoustic signature a tactical concern for CSAR crews? If so then which platform is quietest? Was this evaluated in the selection?
b. Which aircraft will perform best in brown-out conditions in terms of the ability to maintain ground visibility? This is the # one helicopter killer in the desert right now.
c. Which aircraft has the lowest RCS? Lowest IR signature? Does the selection of the 47 mean it will have to employ more robust, heavy and labor-intensive susceptibility reduction systems to compensate for it’s increased RF RCS and enormous IR signature? Was this data analyzed in the proposal comparisons?
d. Does a tandem rotor present twice the potential Doppler signature to threat Radar SAMs? Is this a weakness that must be overcome by robust on-board ECM?
e. Does an active terrain following/terrain avoidance radar present a vulnerability to detection?
f. Does the sheer size of the 47 mean that there are fewer places on the planet that it will be able to land to recover survivors? Will this force more vulnerable hovering hoist recoveries where a smaller aircraft could have landed? Or can the 47 do the tail wheel landing that we see in pictures all the time in those same confined areas?
7. Ok, but aren’t there some good things that the 47 brings to the fight? Yes!
a. Tested, fielded and operational, sophisticated and integrated cockpit, EW and IR self-protection suite. Good stuff OK there are some hiccups with SIRFC but it's still good stuff. !

b. Lot’s of payload to carry lots of ammo, patient treatment equipment etc. Payload is always good as it brings range and useful load to the fight

c. High altitude performance. Specific excess power by definition is a key element of the 47’s benefits; perhaps the single greatest element in the whole analysis. 8150 combined shaft horsepower (2x T55-L-714A engines) is boat-load of power available.

d. Surprisingly good maneuverability. The 47 has such high roll-rate control authority that pilots have to be cautious. If I remember right, designers even had to “de-tune” roll-rate authority because its potential was too high for the airframe. Specific excess power also helps in the maneuverability department by allowing crews to sustain aggressive turning maneuvers during gunnery or evasive maneuvers.

8. Last question to ponder: Are the above 4 benefits worthy enough to override some very important KPP requirements established in the original PRV/CSAR-X ORD/CDD and the downsides presented above? I’d love to hear some other opinions or fact challenges on this topic.

Steve Colby


I read a couple of the BLOG entries on the 47 downwash issue. The ironic thing is that the only article I've read recently that holds a shred of downwash aerodynamic credibility is that penned by Michael Fabey, Aerospace Daily & Defense Report, http://www.aviationnow.com/ – 6/22
who actually addresses downwash as a function of disk loading which is wholly correct. The other BLOG entries look alot like the protester companies feeding the conspiracy theory by taking a stab at the Chinook. Now there are plenty of reasons that the Chinook is the incorrect choice as a CSAR-X platform, but downwash probably isn't one of them unless you examine closely how hard it is to safely accomplish a litter hoist recovery through the side door of a 47.

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