Stealth Black Hawk updated rendering: 1978 document suggests a different shape for the modified UH-60

May 17 2011 - 9 Comments

This is how the Stealth Black Hawk (dubbed also “Silent Hawk”) could look like based on the analysis of all the information available to date. It is sensibly different from the previous sketch; if you read below you’ll understand why.

After publishing the various famous sketches of the possible shape of the modified Black Hawk (dubbed “Stealth Black Hawk” or “Silent Hawk”), together with Ugo Crisponi I’ve continued studying pictures, suggestions, comments and all the information available about the mysterious helicopter that performed a crash landing during the Osama Bin Laden raid. While some hundred thousands readers all around the world, along with major media worlwide, much appreciated our work, others argued that we were giving bad guys some valuable information about a “black project”. Actually, the sketches were based on my initial analysis of the publicly available pictures, that Ugo was able, through a series of attempts, to “translate” into a realistic shape. So, what we did could be done by anybody willing to spend some time studying images and thinking to all the possible modification that could make a Black Hawk, if not stealth, more silent.

Furthermore, a far more in-depth study that could be used to project a Low Observability UH-60 is already in the Public Domain and freely available on an official US military website. It was issued in 1978 by Sikorsky Aircraft Division for the US Army Research and Technology Laboratories and it is titled: “STRUCTURAL CONCEPTS AND AERODYNAMIC ANALYSIS FOR LOW RADAR CROSS SECTION (LRCS) FUSELAGE CONFIGURATIONS”. It shows that first attempts to give the UH-60 some stealth capabilities dates back to 33 years ago. Although I can’t expect the fuselage concepts for low radar cross section aircraft configurations designed at the end of the ’70s still apply today, the basic concept around them could be still useful to imagine a few modifications to the Stealth Black Hawk profile as I initially thought it.

Noteworthy, the shape suggested in 1978 document reminds that of an F-117 rather than that of a more modern stealth, like an F-22. This is consistent with the article published on Army Times titled “Mission helo was secret stealth Black Hawk” according to which the helo has “hard edges, sort of like an … F-117, you know how they have those distinctive edges and angles — that’s what they had on this one”.

Here below, you can read some excerpts of the above mentioned public document that I used with Ugo Crisponi of Aviation Graphic to review the sketch.

Three fuselage configurations for low radar cross sections were developed by the Applied Technology Laboratory. [...] The main rotor pylon fairings and tail surfaces aft of a tail fold hinge for each configuration were the same as those for the baseline UH60A. In the initial portion of this study, the weight and costs (percent of total) were developed for sections of the baseline UH60A fuselage. [...] Structural concepts were developed which could be applied to each configuration using conventional materials. An assessment of safety, fail-safety, and maintainability for each configuration was performed. The change in structural weight and the percentage change in cost for each configuration using the concepts developed were compared to those of the baseline. One concept was selected and applied to the three configurations.
Having selected the structural concept with the lowest weight change and percentage cost change for the three fuselage configurations, the effect on weight and costs using advanced materials was developed and applied to the three configurations. To evaluate the impact of the results of the fuselage study, design attributes of six helicopters were developed using a Helicopter Design Model (HDM) computer program.

Three low radar cross section fuselage configurations for this study were developed by the Applied Technology Laboratory. The first configuration slightly modified the nose section from the baseline configuration; the second configuration changed the fuselage shape along the lines of a truncated triangular prism; the third extended canted flat side shaping throughout the fuselage. The tail surfaces and main rotor pylon fairing were the same as those of the baseline UH60A.

CONFIGURATION 1

This configuration alters the baseline fuselage forward of the mid-cabin section (the cockpit). Although this configuration is different from the baseline, the internal structure must be compatible with the forward cabin to avoid a heavy joining structure. The overall length is slightly increased due to this configuration.

CONFIGURATION 2

This configuration is basically a trapezoidal cross section airframe having sides canted inward 30° and made up of flat exterior structural panels. This configuration is wider at the bottom of the fuselage and narrower at the top of the fuselage than the baseline. This configuration is slightly longer than the baseline UH60A, and its overall height is slightly larger than the baseline. The increased length, width, and height of Configuration 2 does not allow an aircraft of this size to meet the air transportability requirements of the baseline. The narrow upper fuselage causes the pilot and copilot seats to be spaced closer to each other, and shoulder room in the main cabin is decreased. The main cabin floor is approximately 6 inches higher than the baseline from the ground. The increased floor-to-ground height causes difficulties for combat troops to enter or leave the aircraft quickly. Minor modifications of the mold lines for the transition and tail-cone sections were made to properly house the tail rotor shaft of the baseline UH60A.

CONFIGURATION 3

This configuration is basically a flat side cross section airframe having sides canted inward 50 and is tapered in width from a narrow cockpit section to a transition section as wide as the baseline UH60A. The tail-cone is a rectangular section which is narrower than the baseline. The narrow cockpit causes the pilot and copilot seats to be spaced closer to each other; space for four-across seating in the main cabin is decreased. The cockpit and main cabin floors are at the same height from the ground as the baseline. The slope of the windshields may cause problems of visibility for the flight crew. Minor modifications of the mold lines for the transition and tail-cone sections were made to properly house the tail rotor shaft of the baseline UH60A.

ADVANCED MATERIAL APPLICATION

Advanced composite materials can be used in the construction of the three fuselage shapes considered in this study. Studies,  have shown that the use of composite materials can reduce both fuselage weight and cost. The fuselages of this study are relatively lightly loaded compared to fixed-wing aircraft. To efficiently use advanced materials in the fuselages, very light composite skins are used in the post-buckled stress state. [...]

CONCLUSIONS

Structural concepts developed for the three LECS configurations showed that extensive reshaping, as exemplified by Configuration 2, would increase fuselage weight from that of the baseline UH-60A fuselage by 223 pounds and cost by 3.65 percent. When advanced materials were used Configuration 2 decreased
from the baseline fuselage weight and cost by 116 pounds and 3.98 percent respectivdly. Total aircraft performance capability was degraded primarily by drag effects. The aerodynamic analysis indicated that Configuration 2 would have a vertic climb rate at 15 percent of the baseline.  Weight, cost, and performance penalties were less in Configurations 3 and 1 respectively.

Based on the results of this study, the following conclusions are made:

1. The use of advanced materials can result in both weight and cost savings over the baseline fuselage, even with the most severe change in LRCS configurations presented.
2. Without the use of advanced materials, the LRCS Configurations 2 and 3 significantly increase both weight and cost of the total aircraft compared to the baseline UH60A.
3. Minor changes to the nose section of Configuration 1 result in negligible fuselage difference to the weight and cost of the fuselage.
4. Consideration of the total aircraft attributes show that vertical drag penalties appear to be of greater magnitude than the structural weight changes involved with the fuselages of Configurations 2 and 3.
Even with the use of advanced materials, the vertical drag penalty exceeds any weight savings.

The sketch was revised to take the document into consideration (without forgetting it was issued at the end of the ’70s). Even the main rotor was redesigned to make its head slightly larger (with a noise reduction cover sheltering the motion-control technology used to input low-frequency variations of rotor blade pitch-angle, as tested by NASA) .

One last thing worth a mention.

In the aftermath of the crash landing, on May 5, Jon Nowinski, an investigative reporter and founder of the Smoking Gun Research Agency (www.sgra.org) sent me an email to let me know that:

[... ] over the last few days there has been an increased number of late-night helicopter flights to the Sikorsky plant. While that doesn’t entirely stand out as odd, it is interesting to note that normally these flights are related to testing aircraft, as well as consistant with what happens when a Sikorsky helo goes down in military action. After an accident like that, military investigators and officials frequently come out to the Sikorsky plan for a debriefing during which they review the operation

  • http://www.defensieforum.nl Ronald Elzenga

    Interesting!!.. but as you suggest yourself in some way… I think the focus was and is too much on the visual and radar stealth aspects…while I now think the helicopters are more changed with the main focus to make them less noisy. Because, why making them visually or for radar much more stealthy but at the same time using big non-stealthy Chinook “buses” in the same raid? The use of the Chinooks indicate to me there was no need for radar stealth…they used weak points in the Pakistani air defence and maybe also electronic measures to misguide them.

    So I think the correction made at the exhausts are correct. But I think there is no retractable undercarriage (no space for that too) but a slightly modified normal Black Hawk undercarriage. The refuel probe is still in place too I think. Probably they also used the wing construction with the extra external fuel tanks.
    http://www.specialoperations.com/Images_Folder/library11/mh60fuel.jpg
    That could explain both the heavy weight of the helicopters, the fact the helicopters could stay there for such a long time, as also the intensive fire able to destroy the front part of the helicopter in such a strong way. The seals had a lot of explosives with them it seems, but also needed much more then they expected because of the changed plan of attack. A lot of fuel inside the helicopter and these fueltanks made the destruction more easy and intense.

    It would be nice to see some different sketches…But still a great job this one!!

    • http://cencio4.wordpress.com/ David Cenciotti

      Hi Ronald,
      thank you for your comment. Will think about them.
      In the meanwhile, check again this site tomorrow. You’ll read what I think about the Chinooks and their presence on the “crime scene”.

  • Raymond Butler

    Hi David, have a look at the Sikorsky S71.

    I believe the stealth heli-could be a modified S71.

    It would fit the range,payload of the ops that took place.-with inflight refueling option.

    Just an idea…

  • http://www.cover72.net cover72

    Hi. I think you’ve missed few imporant bits of info.
    1) Pakistani radars were oficially turned off (http://www.thenews.com.pk/TodaysPrintDetail.aspx?ID=5806&Cat=13&dt=5/7/2011)
    2) Marcus Weisgerber, Army News quotes “retired special operations aviator” who said “Certain parts of the fuselage, the nose and the tail had these various almost like snap-on parts to them that gave it the very unique appearance”.

    Now, I completely disagree with your sketch as it is. Reason? Look at the advances in the “helo LOD” technology within the past 30 years. Rotors are the biggest source of EM reflections, as well as accoustic noise. Your sketch is assentialy an all-new helo – but all-new stealth helo WOULD have:
    1) either fenestron or NOTAR;
    2) 5 or 6 main rotor blades, not 4 (the more blades, the less noise);
    3) blades would employ NASA and Eurocopter-developed technologies for noise reduction (low-frequency vibrations, “Blue Edge” and “Blue Pulse”)
    4) Commanche-style exhausts
    5) trapezoid tail carrier beam

    But when you look on the wreckage, main rotor has 4 blades – normal S-70 style. Tail rotor is merely a semi-improvized improvement, not major redesign. Tail carrier beam is not trapezoid – it’s circular (part of it is on the wall on the right of the wreckage – see the first image on http://cover72.net/img/StealthHawk_kolaz.png).

    Occam’s razor – if you build an all-new, super-stealth helo, would you ruin it by *keeping the most compromising elements, that being rotors* ? That would make no sense. Your sketch shows “the perfect stealth transport helo” – RUINED by its conventional rotors.

    So I beleive the SF took “standard” Pave hawk and, as the “retired SF operator” said, added cheap “add-on kits” to certain places. Without modifying the superstructure. I thought of tail kit, replacement of tail rotor (easy enough, not as much as the main one) and some superstructure hiding the nose equipment.

    Now, this article pretty much straightens that up. The nose part would apparently be “configuration one”, while the rest of the machine only got addon kits (additional “faceting” panels on the hull, possibly nothing on the tail carrierbeam) and add-on tail stuff.

    • http://cencio4.wordpress.com/ David Cenciotti

      Hi,
      thank you for your comment.
      Dealing the first two points:
      1) Pakistani radars were officially turned off: this is the official statement I’ve already commented both on Twitter and elsewhere. I was confirmed that only some of the radars were off due to maintanence (Alan Warnes, who’s one of the most well informed about Pakistani Air Force). Can you believe that a country like Pakistan switches off all of its radars (that, just to make it clear, don’t see only in one direction but cover – if not obstructed by obstacles – 360°) on the western flank? What if an hijacked plane came from Iran just to let you think to a non-military scenario.
      2) The description given in that article doesn’t seem to me to be as accurate as to be of some help to draw a sketch

      Following remarks: you completely missed the point, as the sketch is not intended to be of an all-new stealth helo. It is just an idea of how a modified stealth Black Hawk could look like.
      1) The sketch hasn’t the fenestron because pictures of the tail of the downed helo clearly show that it has a more or less conventional tail rotor.
      2) Our sketch has 5 blades
      3) As written yesterday, the rotor is thought to embody the NASA noise reduction system
      4) Exhausts: the fist sketches, if you saw them, had more stealth-like exhausts. The new one is based on pictures and has more conventional exhausts.
      5) tail is as per images

      I don’t believe the helicopter was simply made of cheap add-on kits. Obama has unveiled the cost of the stealth: Washington Post May 6, 2011: “We donated a $60 million helicopter to this operation. Could we not afford to buy a tape measure?”
      A normal UH-60 cost around 8- 10M USD….do you really think they used “cheap add-on kit” to modify a helo they’ve started thinking to make stealth some 35 years ago??

      • http://www.cover72.net cover72

        And that’s exactly my point.
        If they really dedicated 60M USD to Pave Hawk modification, they WOULD NOT keep conventional rotor.
        Rotors are The Most De-masking aspects of helos – both as for the sound AND for radar reflections – so it is logical to conceal them (fenestron) or cancel altogether (NOTAR).

        Still, the wreckage has 4-bladed main rotor (see http://cover72.net/img/StealthHawk_trup.jpg) and only minor mod of tail rotor. That does not make sense.
        You spend 60M USD on a “stealth” helo which KEEPS the WORST “anti-stealth” parts? That is logical error. Therefore, I presume there must be another explanation.

        Or, said in another way:
        60M Stealth helo – as the one you’re proposing – WOULD have multipe-blade main rotor, rotor hub cap, radically modified rotor blades (Blue Pulse, or at least Blue Edge), NOTAR or fenestron, shaped tail carrier beam.

        Real wreckage has 4-blade main rotor, rotor head identical to the S-70 one, no metal hub cap, straight rotor blades identical to S-70 ones, NO NOTAR nor fenestron, CIRCULAR tail carrier beam.

        Can you see that? There is a logical discord.
        60M variant is MAJOR redesign – hull gets planform-alignment shaping, front section is removed, main rotor has 5 blades, which would require significant changes to the dynamic system… IF these MAJOR changes were done, WHY on the Earth would they keep such stupid, demasking rotors? Why would they change everything BUT the most non-stealth parts?! That’s my point.
        __________________________________________
        As for the radars – it turns out there was an old agreement between the US and Pakistanis that US forces are allowed to get Ossama without asking. Therefore, “radars turned off” might be just an alibi for the Pakistani government. Anyway, even if only some of radars were offline, there would certainly be a “gap” in coverage deep enough to be exploited. Especially since there are a lot of EW-equipped machines flying near there. Plus, SF choppers extensively use NOE (they got even ground following radars, remember?), so the Pakistani’s probably wouldn’t be able to see them in such a broken terrain altogether without AWACS with good anti-clutter algorhitms.

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