Tuesday, April 2, 2013

Compass Arrow and the Dawn of Stealth

This article was a bit of an eye-opener for me. It was my first attempt at a heritage Ryan subject and it was also the first piece I wrote for the new in-house, on-line-only Engineering Department magazine Airspace.

Prior to Airspace I was writing for VelocitE, which had a hard-copy edition plus an on-line companion version. I usually tried to keep the photos and illustrations to a half-dozen or so because not all of them would survive into the print edition if the count went much higher than that. It took me a while to figure out that Airspace had no such restraints. The results were articles like the N-102 Fang in the previous post, replete with footnotes, references and lots and lots of images.

Part of my charter as I saw it was to cover all of the heritage companies during the course of the year, if I could. I was also to do a mix of aero subjects and space subjects reflecting the new Northrop Grumman Aerospace Systems sector

For this particular issue I originally wanted to do an article on the Ryan Model 147S-2, but I couldn't compile enough information to write about it at that time. While I did eventually turn in that piece (the subject of the next post), it was suggested to me that the Compass Arrow would be a very interesting subject in its place.

And it was, as you shall hopefully see when you read the article below. Ironically, a couple of years after I wrote this I began volunteer work at the San Diego Air and Space Museum in their library/photo archives section and have since discovered a tremendous amount of additional data that demands a much more in-depth treatment than what I gave here. 

Fortunately, Craig Kaston, my cohort in the SDASM venture, is becoming the resident expert in all things Ryan UAV, including the Compass Arrow. He is rapidly acquiring the data, knowledge and imagery to do a definitive book on the subject - I just need to convince him to do it when the time is right. 

As to that additional information we've uncovered, it turns out that two of the photos featured in the article are not what they were originally thought to be. Image 2 (and the lead-in image to this post) is actually of a sub-scale antenna test vehicle - however, the saw-tooth features highlighted are indeed part of the full-scale vehicle construction as mentioned.

The other photo in question is of the in-flight shot (number 4). It now appears that it is actually a composited image of the sky with a Compass Arrow taken on the ground at Edwards AFB on 6 October 1971 during a Ryan "Family of Drones" photo shoot. The finished image shows a bit of the pre-PhotoShop magic that all really good p.r. and marketing photo departments did at the time all the time.

And people say photos don't lie...

This article was originally published in the Northrop Grumman Engineering Department's in-house, on-line magazine Airspace, Vol. 1, number 1, October 2010. It is reposted here with permission and has approved for public release case number 12-1535.

Compass Arrow and the Dawn of Stealth

By Tony Chong

While the early days of stealth research became dominated by Lockheed and heritage Northrop, it is easy to forget the pioneering work done by another legacy Northrop Grumman company, Ryan Aeronautical (later Teledyne-Ryan Aeronautical).

By the end of the 1950s there was a growing awareness among some in the Pentagon and industry of the increasing vulnerability of manned reconnaissance aircraft.  The political fallout from incidents involving those vehicles might have severe consequences for the country, the least of which was leaving the United States blind as to what its adversaries were doing.

The logical path in the eyes of those advocates was a remotely piloted vehicle (RPV) configured to do reconnaissance missions.  Despite the advantages of such a system the Air Force was reluctant to pursue a RPV solution.  In the 1950s it was one thing to use a drone for target practice; using it as a long range platform to perform precise, sensitive over-flights of contested airspace was another, more complicated matter entirely.

The downing of Francis Gary Powers’ U-2 in 1960 changed the equation.  In the months that followed Ryan was awarded a study contract, code-named “Red Wagon,” to examine the feasibility of building reconnaissance RPVs.

What eventually emerged after a long and torturous road was a family of modified Model 147 Firebee RPVs, known as “Fireflies” and “Lightning Bugs,” which were used extensively during the Vietnam War.

But Ryan did not stop there.  In 1965 the company pitched the idea of an air-launched vehicle that was designed from the start as a reconnaissance platform; one that could fly very high for over 2,000 miles. 

The CIA passed on the program, but the Air Force expressed interest as a system like that could do over-flights of communist China, which was in the midst of the chaotic Cultural Revolution at the time.  The program was given the green light in June 1966. 

The proposed vehicle was the Model 154 Firefly.  Featuring a low swept-wing of nearly 48 feet and reaching just over 32 feet in length, the Firefly was designed to cruise at 78,000 feet.  Power was provided by a General Electric YJ97-GE-3 jet engine of 4,000 lbs static sea-level thrust. 

But more importantly the Model 154 heralded a new future in the active design and implementation of stealth technology.

Prior to the Lockheed A-12, stealth design was more an accidental happenstance than a premeditated feature.  The A-12 itself deliberately incorporated Low-Observables (LO) features, but only if they did not compromise the aerodynamic design qualities needed for Mach 3 flight.  These included radar absorbent materials (RAM) and radar absorbent edges structures.

Model 154 would use both RAM and edges structures, but also engine location (for infrared or IR signature reduction) and body shaping for the lowest radar cross section (RCS) possible. 

The YJ97 was positioned on the upper body so the RAM-coated inlet could also be shielded by the forward fuselage from below.  The exhaust nozzle was cooled and shielded from below by the aft fuselage as well to lower its IR signature.  Finally, the fuselage and twin-tailed empennage were designed to deflect radar signals away from the receiver.  This gave the vehicle a sloped, slab sided look.

Flight tests of the new Air Force designated AQM-91A Compass Arrow began on 4 June 1968 at Holloman AFB, NM.  Systems development and production ran concurrently as the need was deemed urgent.  During this period Ryan became Teledyne Ryan Aeronautical (January 1969).

A series of problems slowed progress, but all issues were eventually resolved and Compass Arrow was ready to go operational by mid-1971.  A few weeks later, President Richard Nixon announced his surprise trip to China.

Overnight Compass Arrow became politically unusable.  Rapprochement precluded over-flights, so the program was cancelled and all twenty production aircraft were cut up.

Despite its untimely demise, Compass Arrow proved to be a landmark system on two fronts.  It initiated the concept of high-altitude, long-endurance unmanned air vehicles (HALE UAVs), from which Teledyne Ryan would transition to Compass Cope-R and then on to Global Hawk.  And, just as importantly, its designed-in RCS and IR signature reduction efforts showed tangible results which led the industry to more aggressive designs, resulting in the impressive Lockheed F-117 and the phenomenal Northrop B-2.

That is a legacy to be proud of.


Doug Fronius contributed to this article.

For further reading on the special Model 147 RPV platforms, check out: “Lightning Bugs and Other Reconnaissance Drones” by William Wagner, 1982 by Armed Force Journal International and Aero Publishers, Inc.

For a more detailed history on the Model 154 Firefly / AQM-91A Compass Arrow read:  “Fireflies and Other UAVs” by William Wagner and William P. Sloan, 1992, Aerofax

Additional overview information can be found in: “Have Blue and the F-117A – Evolution of the Stealth Fighter” by David C. Aronstein and Albert C. Piccirillo, 1997, AIAA.

Online information on the range of Ryan model 147 Firebee special-use RPVs can be found at: http://www.xs4all.nl/~robdebie/aqm34.htm

Photo Captions

1. – This 3-view general arrangement drawing of the Model 154 shows the matching angles of the canted tails and the fuselage sides to good effect.  Credit: scanned illustration from “Fireflies and Other UAVs” by Wagner and Sloan (artist not credited).

2. This shot of an unpainted Compass Arrow shows the special construction and materials used on the wing and empennage edges structures.  The saw-tooth design, combined with RAM, created bounce traps for radar energy absorption or deflection scattering.  Photo credit: Tony Chong collection.

3.The mothership for Compass Arrow was a Lockheed DC-130E, which could carry two AQM-91As 2,300 miles to the launch point.  The drones were air-dropped between the 15,000-25,000 foot altitude range.  Photo credit: Tony Chong collection.

4. A nice airborne shot of Compass Arrow shows the slight anhedral of the main wing.  A preprogrammed cassette loaded the flight path data points and target information into the drone’s on-board computer.  At any point in the mission, flight control could switch to the direct ground or airborne controller to bring the bird to the recovery site.  A parachute deployed from the vehicle allowing either a ground landing or a Sikorsky CH-3E with a mid-air retrieval system (MARS) to snag the drone as it descended.  Photo credit: Tony Chong collection.

5.All Compass Arrow production and preproduction aircraft (28 in total) were thought destroyed in crashes or cut up after the demise of the program.  Imagine the surprise Northrop Grumman legacy-Ryan engineers had when a military base in Georgia called to say they had one on a pole at their gate.  The parachute recovery test article was retrieved and claimed by the National Museum of the U.S. Air Force.  Photo credit: NMUSAF.

6.Another view of the Compass Arrow after restoration at the National Museum of the U.S. Air Force.  The black paint was likely applied as the probable operational scheme based on those of some of the Ryan Model 147 Lightning Bugs.  Photo credit: NMUSAF.

7.This rather poor photo shows the restored Compass Arrow hanging on display in the Cold War Gallery at the National Museum of the U.S. Air Force.  Note the camera window on the underside a little bit aft of the tip of the nose.  Photo credit: NMUSAF.

1 comment:

  1. A fascinating article, especially the design decisions made to increase the stealth profile. The Army flies drone tests from the airfield next to our building. Their drones are ugly when compared to the Compass Arrow.