Mc Donnell Douglas YC-15 (part 4)

Parts 1,2 and 3.

In January 1978, the same day the AMST program ended, the C-X (cargo experimental) program began. The CX program was needed because formulation of the Pentagon’s RDF (Rapid Deployment Force) in the late 1970s. CX would serve as RDF’s airborne transport. In short CX combined the roles of strategic and tactical airlifters. Specifically, CX requirements, among others were a max takeoff weight of 580,000 lbs, max speed of Mach0.825, a range of 2400nm, a landing run requirement of 2,700ft, and all of this with a 3 person crew (2 pilots and a loadmaster)

Boeing C-17 Globemaster 3

Out of the CX program came the McDonnell Douglas (Boeing after the 1996 merger) C-17 Globemaster 3. The C-17 first flight was on 15 September 1991. The C-17 was able to combine the tactical and strategic airlift roles because of its STOL characteristics. On the outside, the YC-15 and C-17 have a very similar appearance because both use EBF to achieve STOL.

3 view drawing of the C-17

3 view drawing of the YC-15

The YC-15 made quite a few contributions to the C-17 program. Many of the Mc Donnell Douglas personnel that worked on the YC-15 worked on the C-17 program. During it’s development the C-17 ran into many of the same problems that the YC-15 had. There were excessive thermal, air and acoustic loads on the portions of the flaps that were directly in the jet exhaust.

This table highlights further differences between the 2 aircraft.

Incorrect predictions of airframe drag again resulted in slightly reduced range at given takeoff weights. Range\payload went from 2,400 nm at 172,000lb to 167,000lb. A few years after the C-17 entered service it gained a reputation as a somewhat “short legged” aircraft when transiting the Pacific. However by the year 2000 this was resolved by adding a fuel tank in the overhead wing\fuselage body joint.

Center wing box fuel tank on the C-17

There were also quite a few “lessons learned” that were incorporated into the C-17. Windows for a downward view were moved slightly forward in the cockpit. The YC-15’s GWS was replaced, in the C-17 by an indexed switch attached to a mission computer that calculated optimal takeoff flap settings at a given gross weight. Loading ramp “toes” were added to the C-17.  The thrust reversers were limited to idle when deployed in-flight. Flaps were not moved during the takeoff roll and improvements were made in the DLC. The VAM in the YC-15 became a HUD (Heads-Up Display) displaying far more information on approach to the pilot.

C-17 Heads Up Display

In 1998 the YC-15 was at AMARC and that year Mc Donnell Douglas contracted with AMARC to make the YC-15 again flyable. The YC-15 was to be used as a test-bed for testing defensive countermeasures and techniques for lowering the infared signature of the C-17. The process to make 875 again flyable began in April 1996. 875 was remarkably well preserved aside from many birds’ nests in the nooks and crannies of the aircraft. The JT9D engines had to be reinstalled  and 875 was given the FAA registration “N15YC.”

On 11 April 1997 YC-15 875 again took the air from Davis-Monthan AFB for a shakedown flight. The jet flew for 2 hours 1 minute and taken to 250kt at 25,000ft.  875 was flown three more times before a planned flight to Long Beach for further modification and test work, including the addition of a new paint job.

The YC-15 in its new paint scheme seen at takeoff.

Again 875 was flown again on 11 July 1998 to the Edwards AFB test ranges and some approach work at Palmdale. It was during this work that the number one engine third stage LP turbine came apart. While able to land at Palmdale without incident the YC-15 languished on the ramp until money could be made to make repairs. This was to never be.

After the Boeing/McDonnell Douglas merger, the cost of repairing 875 couldn’t be justified. As of 2002, the aircraft remained at Palmdale.

There was talk of using the YC-15 as an airborne avionics test platform to support the x-32 but Boeing opted for a 737 instead. There was thought of bringing 875 back to test some concepts for the NOTAIL ATT and to test a STOL “tilt wing” concept but none of these came to fruition.

At the time of writing YC-15 72-0876 is on display of sorts at AMARC in a semi scrapped state with the engines removed. YC-15 72-0875 was moved from Palmdale to Edwards in 2008 and is on display at the west gate of Edwards AFB, just off the Century Circle.

You can learn more about the YC-15 and C-17 here and here.

Random Aviation Photo links

I’ve been too lazy to get to part 4 of the YC-15 series this week. I’m having motivational issues.

First up Russian Live Leak has an interesting perspective on the Aviation Museum at Monino.

Here’s a sample of what you’ll see:

There’s a Tupelov TU-4 “Bull”, a Tupelov TU-16 “Badger and a Mil Mi-12 “Homer.”

It’s interesting to see the size difference between the different aircraft.

Next up, a link of World War 2 Russian aircraft. They appear to be taken during the time period.

I’m pretty sure that’s an Ilyushin DB-3.

There has been a lot of interesting books to come out about the Red Air Force after the Soviet World War 2 archives were opened up. Don’t tell anyone that I’m supposed to finish a book review for that…

[*ADDED] Continuing my fetish for twin-boom airplanes. The Warbird Information Exchange has some really cool photos of the Northrop P-61 Black Widow.

Also, today in 1972 was a red letter day in the dangerous skies over North Vietnam. Never forget.

Showtime 100. GIT SUM!

Cutaway Thursday: Northrop F-20 Tigershark

Mc Donnell Douglas YC-15 (part 3)

Parts 1 and 2.

Aerial delivery tests, as part of further operational demonstrations were conducted at China Lake, CA  using dummies for static-line drop tests. Cargo drops with 5000lb to 20,000lb were also conducted from an altitude of about 4750ft. The heaviest drop was a 28,243lb load of CDS containers. The primary result of the drop tests found the troop door was too narrow.

The YC-15 also tested mid air refueling as both a tanker and receiver in May-June 1976. 102 hookups were made with a KC-135. Fuel transfer to the receiver was found to be slow (partly because the UARRSI was not designed for the aircraft). Trails of the YC-15 potential tanker aircraft used Navy and Marine Corps aircraft fly a position slightly below and behind the aircraft to simulate the probe-and-drogue method of aerial refueling.

One of the YC-15 aircraft receives fuel from a USAF KC-135.

A YC-15 acts as a tanker with a Navy F-14 Phantom flying in the “tanker-box.”

On 15 to 17 December 1975 YC-15 876 tested ground loading of Army vehicles.

An AH-1 Cobra being loading aboard a YC-15.

A McDonnell Douglas advertisement for the YC-15 showing an M-109 at the rear cargo door.

Overall the YC-15 was found to be a good airplane but had marginal maintainability. 2 of the biggest issues were was engine maintenance and the flight control system.  Naturally the YC-15 was going to have maintenance issues because it, like all research aircraft, was intended to test technology and not necessarily representative of an optimized “production-type” aircraft (I remind the reader to a look at the differences between the YF-22 and F-22).  Phase 1 tests ended in 18 August 1976. By then both aircraft accumulated 226 flights over 472.8 hours. The YC-15 demonstrated an ability to fly as slow as 62kt to a fast as Mach .78. The initial phases of flight test validates EBF as a valid solution to the STOL problem.

Phase II of the AMST program for the YC-15 began on 7 September 1976. Both aircraft underwent a number of modifications including having a CFM-56 turbofan engine installed on the #4 engine pylon. The wingspan was extended by 22.3ft as a result the wing area went from 367ft2 to 2107ft2! A fighter-type stick was also installed.

Previously shown picture of the YC-15 showing the installed CFM-56 engine on the #4 engine pylon.

On the software side, aircraft 876 had a number of modifications installed including a thrust management system (required because of the increased thrust of the CFM-56) (TMS), an Engine Failure Detection System (EFDS), a digital SCAS and the VAM was improved with a flight director indicator.

Phase 2 testing resumed 12 February 1977 and resulted in 49 sorties for 125.6 flight hours. 876 also went on a tour to NATO member nations in Europe.

In Phase III testing aircraft 875 was returned to original configuration but had a Gross Weight Selector (GWS). The GWS would calculate the optimum flap angle for a given gross weight at various flight conditions. The DLC was improved to operated with and engine out on final approach. All these modifications (including the increased aspect ratio of the wing) resulted in a 10kt reduction in approach speed. The final tally for Phase III testing included 416 flights over 796.3 hours total for both aircraft.

By February 1978 both YC-15s were placed into storage at Edwards AFB.

Part IV will detail the technological contributions the YC-15 made to the C-17 program and the return to flight of the YC-15 in support of that program.

Cross-posted at Bring The Heat, Bring The Stupid.

McDonnell Douglas YC-15 (part 2)

Part one is a general description of the YC-15 aircraft. You can view that here. This post will detail the flight test program of the YC-15.

There were 2 YC-15 aircraft,serials 72-01875 and 72-01876. 875 was rolled on 5 August 1975. The first flight was 26 August 1975. 875 flew from the Douglas plant in Long Beach, CA to Edwards AFB. The only problem during this 2.5 hour flight was a landing gear door found to be ajar. The flight itself was therefore speed limited to 200kts at 20,000ft.

875 flew 3 times over the next 3 days, conducting general flight envelope verification and expansion tests. A further 2 weeks were conducting 7 air-worthiness flights. On 12 September, 875 moved to a Douglas Aircraft Company (DAC) test facility at Yuma, AZ.

876 flew for the first time on 5 December 1975. This flight took the aircraft from Long Beach, CA to join 875 at Yuma AZ.

The YC-15 Joint Test Force (JTF) personnel from the Air Force Flight Test Center (AFFTC), Air Force Test and Evaluation Center (AFTEC), McDonnell Douglas, Boeing (for the YC-14). The (Air Force Logistics Command (AFLC), Tactical Air Command (TAC), Army and the USMC played minor logistical roles in the flight test program. NASA also sent (short take-off and landing (STOL) engineers to analyse data gleaned in the AMST program. The core pilot cadre for the YC-15 was made up of 3 contractors, 3 AFFTC and 3 AFTEC pilots. The competing aircraft were housed in separate hangars with the JTF office between the 2 contactors. This became the model for both the ATF and JSF programs.

The consensus amongst the test pilots and crews was that the YC-15 had generally good handling qualities. The aircraft was easy to fly with the SCAS off and on. There was concern that the pilot could overload the aircraft with the SCAS off but control forces were considered light in both modes.

There was some discussion on whether or not the YC-15 should have a stick or yoke for control input.  The intention was to have a “fighter-type” stick installed but there was some skepticism over it’s suitability from higher up the chain-of-command so the stick was removed. To counter, it was argued that the yoke obscured the view of the instrument panel.

The YC-15 had no natural warning upon entering the stall (i.e. vibration) so warning for the stall relied on an artificial “stick-shaker” to provide some warning within the critical angle of attack. This was judged as an inadequate solution because the shaker could activate in conditions of high thrust and flap settings when the aircraft clearly wasn’t in a stalling condition and because a high stink rate (such as during a STOL landing) could mask stalling conditions. As such, a Supplemental Stall Recognition System (SSRS) was developed and tested during the program. The SSRS provided an aural warning when the aircraft approached critical alpha during a given flight condition.

At gross weights of 149,300 the YC-15 flew STOL approaches at 87kts at a 6 degree glideslope giving a sink rate of 15.4 degrees per second. Conventional Takeoff and Landing (CTOL) approaches were normally made a 127 kts with a typical 8-12 feet per second sink rate with no flare at touch down. In STOL mode the aim-point for touch down was about 300 feet from the runway threshold . The YC-15 tested both flare and no-flare landing techniques in STOL mode. Testing at Edwards AFB showed the YC-15 was unable to land consistently in “hot-and-high” conditions in the required 2000 feet because of the slow actuation of the thrust reversers.

The thrust reversers could be used in-flight with some minor airframe buffet.

Testing the VAM, used approaches very similar to Navy carrier approaches were airspeed on approach is governed by angle of attack. The major issue was that the VAM didn’t display enough information to enable a completely “eyes-out-of-cockpit” approach.

33 STOL and CTOL off field demo landings, at Edwards, were conducted on 5000ft x 200ft runways with markers placed at 2000ft x 60ft. 5 pilots flew these tests and the YC-15s landing gear tire pressure was reduced. It was also found that the YC-15 could taxi over a 4-inch dump at 75-80kts. A unique procedures for the YC-15 during a STOL takeoff was extending the flaps from 14 to 23 degrees during the takeoff roll. Below is some archive video of STOL testing in 1975 (please pardon the music, Creed’s “Higher” just doesn’t work IMO):

During testing cracks were found in the blown flap material and fasteners had to replaced on a cracked rob. This was due to repeated exposure of hot jet exhaust. Direct Lift Control (DLC) (*see update below) was found to be effective for corrected high approach errors in the glide-slope but wasn’t effective for getting too low during approach. Flight path correction was done with a slightly high arrival at glideslope,correct with DLC, and then add thrust.  Maximum DLC deflection angle was 20 degrees from flush on the upper surface of the wing. Orientation of the DLC actuation in the cockpit was a major “human factors” issue of debate among the pilots.

The YC-15 displayed docile engine out characteristics with mild crew indication 4-6 seconds after an engine out occurred. The YC-15 also was unable to meet the range requirement of 2600nm. The aircraft had more drag than predicted giving it a range of 1760nm.

I’ll be standing fast on this post for now. I’m splitting part 2 into this and an additional part detailing some of the operational and international demonstrations as well as technical improvements and further flight test results.

Cross posted at Bring the Heat, Bring the Stupid.

*[UPDATE]: For reader that may not know, direct lift control (DLC) is a system of spoilers, located on the upper surface of the wing. that either differentially control roll and in unison control pitch by dumping lift from the wings. They are common to most airliners.

McDonnell Douglas YC-15 (part 1)

The McDonnell Douglas YC-15 was a prototype developed of the USAF ‘s AMST program in 1972. The competition was the Boeing YC-14.

McDonnell Douglas developed the YC-15 from the Breguet 941s, using extensive wind tunnel testing (for optimum configuration testing) and using Cornell Aeronautical Labs B-26B In-Flight Simulator (for flight control testing).

The aircraft itself is 124.25 feet long, wingspan is 110.36ft, height is 43.30. Max gross weight is 216,680lbs. The interior cargo-box is 47 x 11.8 x 11.4.

Thrust for the YC-15 was provided by the JT8D turbofan (also the DC-9 powerplant) and produced a total thrust of 16,000lbs. The engines were mounted on shallow pylons mounted ahead of the wings leading edge. Thrust reversal was accomplished using so-called “daisy nozzles.” During final approach, with flaps fully extended and facing the engine, the engines provided 54% of the YC-15 lift.

The straight wings consisted of ailerons, double-slotted flaps, leading edge high lift devices (Kruger flaps, etc), and spoilers. The trailing edge devices, flaps and ailerons spanned 75% of the wings trailing edge. The flaps could extend as much as 46 degrees into the downstream. The YC-15 was the first jet powered aircraft to use externally blown flaps (EBF).

YC-15′s EBF

Flight controls consisted of the conventional hydraulic system and a stability and control augmentation system (SCAS). The SCAS was dual channel and 3 axis enabling hands off flight for high angle approaches (tactical approaches) and modes for attitude, altitude and heading.

The YC-15 saw the first use of a heads up display (HUD) system, specifically called the VAM (Visual Approach Monitor). Developed by Sundstrand, the VAM displayed the horizon, flight path scale, airspeed indexer and touchdown point.

Sundstrand’s VAM display

Being essentially a research airplane, the YC-15 did not need to fully conform to MILSPECS. As such it borrowed components from various aircraft, the DC-10 cockpit enclosure, the F-15 fuel pumps, the C-141 stabilizing struts, the A-10 UARRSI, the C-5 cargo handling equipment and other parts from 9 other types of airplanes. Cockpit instrumentation used components from 10 different airplanes.

Here’s a cutaway of the YC-14 and YC-15 for comparison:

Part 2 will detail the YC-15s flight test program.

Part 3 will detail the YC-15 technological contributions to the C-17.

Cross-posted at Bring The Heat, Bring The Stupid.

The Beginning of the End

From the Usual USAF Source…

Final F-4 Regenerated for Use as Aerial Target
The final F-4 regenerated from storage in the Air Force’s aircraft boneyard at Davis-Monthan AFB, Ariz., earlier this month departed the base for Mojave, Calif., for conversion to a QF-4 target drone, announced base officials. This RF-4C airframe, dubbed “Last One,” left Davis-Monthan on April 17, states the base’s April 19 release. “It’s a great feeling to see such a magnificent aircraft fly again to serve the warfighter,” said Eddie Caro, the crew chief assigned to the aircraft since December 2012. BAE Systems will convert the platform into the QF-4 configuration in California and then deliver it to Tyndall AFB, Fla. This airframe arrived at Davis-Monthan for retirement in January 1989 and had been dormant until technicians with the base’s 309th Aerospace Maintenance and Regeneration Group last year began restoring it to flying status, according to the release. The Air Force is transitioning from the QF-4 to using QF-16s as its full-scale aerial targets. (Davis-Monthan report by Teresa Pittman) (See also Three-Hundredth QF-4 Delivered.)

I suppose goin’ down in flames is preferable to rusting away in The Boneyard… or, as Neil put it: “It’s better to burn out than to fade away…“

Cross-posted at EIP.

F-102 and F-106 Flight Testing

Convair’s delta-winged interceptors, the F-102 Delta Dagger and F-106 Delta Dart are icons of the Cold War. Both aircraft had generally the same configuration but the Delta Dart was a more refined design.

The video below shows some of the flight testing that took place with the F-102 up to the year 1957. Footage includes climate testing in Alaska, radome testing through simulated rain, TF-102 flight tests, F-102 structural modifications, the F-102 sidestick testing program, external fuel tank testing, TF and F-102 weapons testing for the MB-1 Genie and AIM-4 Falcon air to air missiles.

Right about this time period, the F-106 made it’s first flight and gradually envelope expansion testing.

It’s important to note that although the technology has changed, the method by which modern combat aircraft are tested hasn’t. Yes, computer processing power has grown in leaps and bounds but there’s no substitute for actual flight test.

Zipper

Lockheed’s F-104 Starfighter, really properly called the “zipper,” was one of the first combat aircraft capable of sustained Mach 2 flight. It had a relatively short career with the USAF’s Air Defense Command (ADC) going from 1958 to 1969.

The Zipper was far more popular among NATO nations, seeing use not only as a fighter but also a stikefighter/fighter-bomber.

German F-104Gs were used heavily in the fighter bomber role. At its peak in the mid-1970s, the Luftwaffe operated five F-104 -equipped fighter bomber wings, two interceptor wings and two tactical reconnaissance wings.

The Marineflieger operated a further two wings of F-104s in the maritime strike and reconnaissance roles. The service history with the Luftwaffe was relatively chequered. Even famous fighter ace Erich Hartmann (the Commanding Officer of the Luftwaffe’s first jet fighter squadron) judged the Zipper as unsafe for use as a combat aircraft. Most losses were due to operating the aircraft at low-level, high speed resulting in controlled flight into terrain (CFIT). 110 pilots were lost in Luftwaffe service.

The video below is from the little-known Marineflieger F-104 display team called “The Vikings.” The video also shows Marinefliegergeschwader 2 (West German Naval Air Wing 2)’s conversion to the Tornado IDS to continue service in the maritime strike role.

A few things I noticed:

Bending the Zipper around especially at low-level took some stones. You can keep your 170kt approach speed and your  150 kt minimum touchdown speed, thank you very much. Then again you only live once right?

The Zipper didn’t take kindly to ham-fisted drivers. You can learn more about flying the Zipper here.

They called NAS Moffett Field and AFB. The variety of aircraft at the different airshow was kinda interesting.

On another note, The Starfighters carry on the great tradition of the Zipper and continue to fly a few examples of her at airshows.

A Runnin’ Mate For Fifi

From the Usual USAF Source…

Group Aims to Return Vintage B-29 to Flying Status: A recently formed non-profit group aims to support the refurbishment of a World War II B-29 bomber named Doc and its return to flying condition, according to a release from the organization. “This airplane is a national treasure,” said Jeff Turner, chairman of the board of Doc’s Friends, formed by aviation enthusiasts and business leaders in Wichita, Kan. “We will not rest until we raise enough funds to restore Doc, find a permanent home, and operate Doc as a flying museum for the world to see,” he added. Group members believe that Doc is the last-known B-29 that is restorable to flying condition, states the March 11 release. Boeing built Doc in Wichita in 1944. Decommissioned in 1956, the bomber spent more than four decades in the California desert until aviation enthusiasts rescued it and brought it to Wichita in 2000. Doc’s Friends now has ownership of the bomber, which currently resides in hangar space donated by Boeing for the restoration work, states the release.

And there’s this, from the Doc’s Friends web site:

Good on ‘em.  Fifi needs a running partner.