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Monday
Jun212010

Aviation Ancestry - June 2010

March Base: History in the Sky Via Air Fest

By Scott Schwartz

The weekend of May 1-2 saw March Air Reserve Base (formerly March Air Force Base) hosting its annual Air Fest. A crowd of thousands came to view historic and current military aircraft, some of which were flown, and others of which were on static display. Ironically, the base was more than 20 years old when the prototypes of some of the warbirds on display here made their first flights. Known as March Field at the time, the base opened in 1918.

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Thursday
Mar112010

Aviation Ancestry - March 2010

In The Thunderbolt’s Shadow

By Scott Schwartz
 
Northrop YA-9 rests at the March Air Reserve Base air museum. Note the weapons pylons and the placement of the engines. (Scott Schwartz)By the end of the war in Viet Nam, it was clear that slower, piston-engine aircraft were very successful as ground-attack aircraft – more so than their supersonic jet counterparts.  This was due to piston engine airplanes ability to loiter over the target area, carry very heavy loads, operate from rough airfields, absorb a lot of punishment, and fly slow enough to deliver their ordinance with accuracy.    

If the reader thinks that the foregoing describes the Douglas Skyraider, he or she is right.  Although other propeller-driven types served well during theViet Nam conflict, the Skyraider was virtually unmatched in the ground-support role.

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Sunday
Feb212010

Aviation Ancestry - February 2010

Still Earning Its Keep:  The Bell UH-1

By Scott Schwartz

Painted as an Army Medevac helicopter, a privately owned Huey is still going strong at the Nellis AFB Air Show in 2007. Not the exhaust ripple from the Lycoming T-53 engine. (Scott Schwartz)Popular culture generally associates the Bell UH-1 Huey with the war in Viet Nam.  The thumping of its rotor blades is familiar to a generation whose experience with that war was gleaned through movies such as Apocalypse Now.  But, the origins of this aircraft date back to the early 1950’s, when the U.S. Army was looking for a new helicopter to meet its requirement for a battlefield “Medevac,” instrument training, and general utility aircraft.  The reader should remember that jet-engine technology was in its adolescence at this point.  Most “utility” aircraft – both fixed and rotary wing – were powered by piston engines.  Given the power versus weight limitations that are inherent to piston engines, the helicopters that were in the Army’s inventory at the time tended to be underpowered and slow.

The year was 1953. During that year, numerous companies presented designs to the Army, in the hope of landing the contract.  Among them were Bell, with its turbo-shaft model 204, and Kaman with a turbo-shaft version of its twin-rotor HH-43 (the earlier version having been powered by a nine cylinder radial piston engine).

By February of 1955, the Army had decided to purchase the Bell design. Perhaps this was because the Bell 204 was specifically designed to meets the Army’s requirements, and because it was not merely a gas-turbine version of a piston engine aircraft.  Initially, the Army ordered three aircraft for test purposes, under the designation XH-40.

Apparently, the Army had great confidence in the XH-40, because the service wound up ordering six YH-40 service/test aircraft before the first XH-40 ever flew!

Given the power versus weight advantages of gas-turbine engines over piston engines, it is easy to understand why the Army was impressed with the YH-40’s performance.  In that vein, a little perspective is in order.

Weighing more than 800 pounds, the Pratt &Whitney R-1340 nine-cylinder piston engine generates between 500 and 600 horsepower (depending upon the version of the engine in question).  On the other hand, the Lycoming T-53-L-1A turbo-shaft engine that powered the YH-40, weighed in at 540 lbs., yet produced 770 shaft-horsepower.  The YH-40’s first flight took place in 1956, and the other two helicopters that were part of the original order were delivered in 1957. 

Three years later, the Army ordered the aircraft into production as the HU-1A Iroquois.  The production contract called for 100 aircraft, and the official name, Iroquois, was hardly used in practice.  Instead, the aircraft was usually referred to as the “Huey”, based on its HU-1 designation.  

Despite the superior performance of the turbo-shaft helicopter over its piston-engine counterparts, the Army believed that the YH-40 was under-powered. In fact, concurrently with the delivery of the first HU-1’s (which were re-designated as “UH-1’s in 1962 – the “Huey” nick name stuck, though.), the Army was already requesting a more powerful version of the helicopter.

Bell’s response was the UH-1B, which had a 960 shaft-horsepower version of the Lycoming T-53 engine.  The UH-1B’s fuselage was longer, enabling the aircraft to carry seven passengers (plus the pilots), or four stretchers and a medical attendant.  Deliveries of the UH-1B began in 1961.

Combat experience indicated that there was a need for yet more improvements.  One problem was the tendency of the rotor blade that was retreating in relation to the air stream, to stall – particularly during diving maneuvers.  Another issue was the drag created by the variety of weapons that were being mounted on the helicopter.  As a result, the new UH-1C was equipped with a new rotor blade system, a longer tail boom, and an 1100 shaft-horsepower version of the T-53 engine.  This engine would eventually be installed in existing UH-1B helicopters, as well.

Other changes included an auxiliary hydraulic system and a better engine air-filtering system, which was a response to the dusty conditions in Viet Nam.  Production of the UH-1C began in 1966.

As with many aircraft of both the fixed- and rotary-wing type, the design of the UH-1 evolved as more was demanded of it in combat.

In the case of the UH-1, the Army found that the ability to carry additional crewmen (in the form of door gunners) more troops, and/or more stretchers was necessary.  Rising to the occasion, Bell introduced the Model 205, the fuselage of which was 41-inches longer than that of the UH-1B.  This enabled the aircraft to carry 15 people, including the flight crew.  The Model 205 was purchased by the Army as the UH-1D and this version featured the larger sliding doors with two windows each, as well as smaller hinged door near the flight deck.  All of the doors were removable.   Able to carry six stretchers, the UH-1D was a much more versatile medevac helicopter than its predecessors.  Operational use of the UH-1D began in 1963.

A proper discussion of the “Huey’s” combat missions in Viet Nam would probably occupy several volumes.  The reader should know that the UH-1 served in almost every role imaginable, during that conflict.  Besides troop transport and medical evacuation, “Hueys” transported cargo, flew search and rescue missions, flew electronic warfare missions, were utilized as general transportation aircraft, and were flown on ground attack missions, and flew as armed escorts for troop-carrying helicopters.

For ground attack and escort missions, Hueys were fitted with grenade launchers, rocket launchers, and machine guns – in various combinations.

Other branches of the U.S. military operated the UH-1, and Bell practically tailored variants of the aircraft for each service.

The U.S. Marine Corps wound up buying the basic UH-1B; however more aluminum parts were used in its construction (to combat corrosion), Marine Corps compatible radio equipment was installed, and the aircraft was equipped with a rotor brake for quick wind-down during ship-board operations.  These changes resulted in the aircraft being re-designated as the UH-1E.  Navy training and utility versions of this aircraft were known as UH-1L’s and TH-1L’s, respectively.

Though not needing an assault helicopter, the USAF was in need of a helicopter for use in support operations at its missile bases.  The Air Force also required the aircraft to make use of the General Electric T-58 turbo-shaft engine, which it had stock piled in connection with the HH-3 “Jolly Green Giant” fleet.  This resulted in the UH-1F, and 27 of these aircraft were delivered to the Air Force in 1967.

More than 27 UH-1 variants have been built – and this number does not even include the civil 204/205/212 variants, and the same basic aircraft is in production to this day (if Bell’s web-site is any indication). The UH-1H version, however, was built in greater numbers than any other, with more than 5,700 of them coming off the production line. Powered by a 1400 shaft-horsepower version of the T-53 engine, the UH-1H is the “ultimate” of the two-bladed Huey design, and it retained the stabilizer bar mounted on the rotor head, which was originally found on the Bell 47.  Deliveries of the UH-1H to the U.S. Army began in the early 1970’s, and the Air Force also purchased the type.  Some of the Air Force variants were designated as HH-1H’s, and these were intended specifically for use as local base rescue helicopters.

Despite its versatility, the UH-1 is an old design, and the newer Sikorsky Blackhawk has replaced the UH-1 in U.S. military service in all but training and utility roles.

But, there is no need to become wistful about the sun setting on the Huey’s military service.  Sixty years after it was designed, the distinctive “thump” of surplus two-bladed UH-1’s can still be heard in the skies, as these machines continue to earn their keep in the hands of fire departments and other civilian operators. 

Specifications – UH-1C:
Maximum speed: 128 kts.
Service ceiling: 11,500 ft.
Maximum range:  331 nautical miles.


Tuesday
Jan122010

Aviation Ancestry - January 2010

The Plane That Saved The Mustang: The North American A-36

By Scott Schwartz

Surviving A-36 and the USAF museum - at first glance, this airplane looks like a P-51, but notice the extended dive-brakes. The A-36 air frame was basically the same as that of the P-51. (Scott Schwartz)Powered by an Allison V-12 engine equipped with a single-stage supercharger, the A-36 was essentially an early model P-51 Mustang fitted with two dive brakes on each wing.  Other modifications to the airframe included strengthening of the wings, movement of the bomb racks closer to the main landing gear for less wing “flexing” while the plane was taxiing, and the installation of small vent windows in the windscreen side panels.  In addition, two .50 caliber machine guns were mounted in each wing, and two .50 cal. guns were mounted in the lower nose to fire through the propeller.  Naturally, the A-36 inherited the Mustang’s clean aerodynamics; but why did North American turn the P-51 into a dive-bomber?  To answer this question, we must look at the Mustang’s origins. 

In early 1940, the British asked the company to build P-40’s under license from Curtiss.  Rather than building another company’s design (especially one that was already considered obsolete), North American proposed building a fighter of its own. After some hesitation (the company had no fighter experience), the British agreed, and the first Mustang prototype (the NA-73X) flew on Oct. 26, 1940. Flight tests were successful, and the British ordered 320 of the new planes, calling them Mustang I’s. 

Interestingly, the U.S. government kept two Mustangs for itself, calling them XP-51’s. Ultimately, the British received 650 Mustang I, Ia, and II’s through outright purchase and Lend/Lease distribution.  By the time the Lend/Lease order was placed, U.S. pilots had flown the two XP-51’s and were raving about their performance.  As a result, the U.S. retained 55 England-bound Mustangs for itself. The majority of these 55 airplanes were converted into to armed, high-speed reconnaissance aircraft, known as F-6’s. The rest were used as high-speed ground attack airplanes and as low-altitude escort fighters.  The British used their Mustang primarily in the close air support role as well. 

Despite the Mustang’s effectiveness as a ground-support airplane, enthusiasm by the military leaders on both sides of the Atlantic was lukewarm at best.  The British, although satisfied with their Mustangs, were apprehensive about relying on a foreign aircraft.  They were concerned about the availability of parts and maintenance.  Hence, they focused their efforts on developing their own fighters.  At the same time, the U.S. Army was already buying P-38’s, P-39’s, and P-40’s.  By 1942, there was no money in the defense budget for new fighters.  It appeared that production of the Mustang was coming to an end.  

Fortunately, a few people recognized the Mustang’s potential. One of these Mustang “visionaries” was Major General Oliver P. Echols, who was instrumental in the Army’s successful retention of the 55 Lend/Lease Mustangs.  General Echols noticed that there was money available in the budget for attack airplanes, and he brought this to the attention of North American’s “Dutch” Kindelberger.  Kindelberger, in turn, approached   Army Lt. General Henry H. “Hap” Arnold with the idea of turning the P-51 into a dive-bomber, knowing that Arnold had been an early proponent of dive-bombing tactics.

Although Army doctrine held that dive-bombing was ineffective and dangerous, (because of the high dive and pull-out speeds), Arnold had managed to persuade the Army to procure a few dive bombers – the Douglas A-24, and the Vultee A-31 among them. If Arnold would go along with the idea of producing a Mustang dive-bomber, North American’s production lines would be kept open. 

Kindelberger managed to convince Arnold that, by replacing the British armament (two 20mm cannon in each wing) with .50 cal. machine guns, and adding dive flaps, the Mustang would fill the bill as a dive-bomber.  Arnold was convinced, and the first A-36 flew on Sept. 21, 1942.  Only 500 A-36’s were built. The results of flight tests conducted at Florida’s Eglin Army Air Field seemed to reinforce the Army’s doubts about dive-bombing, and the A-36. 

The A-36 dove at speeds approaching 500 mph; the brakes only reduced the speed to about 350 mph.  Unfortunately, one of the test airplanes crashed because it lost its wings during a vertical dive.  Not surprisingly, Army officials decided that the airplane had great diving capabilities for a fighter, but dove too fast for a dive-bomber. As a result of all this, the Army restricted the plane’s dive-angles to 70 degrees.  In addition, the evaluators at Eglin recommended that the A-36 be used mainly as a low-altitude attack airplane, and that the dive brakes be eliminated.  This last recommendation may have given rise to the oft-repeated myth that all A-36’s had their dive brakes wired shut.  Apparently, this recommendation was never adopted as official policy.

“I would like to refute the assertion made by many people that we wired our dive  brakes shut. That is just not true; that would have been like flying into battle with one arm tied behind our backs!” So says retired Army Captain Charles Dills, who flew 39 missions in the A-36 between November 1943 and February 1944.  “I don’t know of anyone who wired the brakes shut; there may have been a few isolated cases of individual pilots having trouble with the brakes, but it was not policy.”  

Dills flew the A-36 on strafing and dive-bombing missions from several bases in Italy.  Despite the Army test results, most pilots liked the A-36.  “I really resent it when people say that the A-36 didn’t perform at altitude – as though the plane was defective!” says Dills  “The airplane was designed to be a low-altitude attack plane, and it did its job very well!

“When strafing, we’d go in to enemy territory at 200 or 300 feet. At this altitude, we had the element of surprise.  We would be there, give the targets a burst from the machine guns, and be gone before they could even pick up their guns.  The slots in the dive brakes gave out an unnerving whine that helped us.  The Germans had a name for us: ‘The Screaming Devils.’ 

“When dive bombing, we would go in much higher; probably around 14,000 feet.  German gunners had a problem in that the computers on their 88 mm guns had to try to predict where the airplane was going to be in 15 or 20 seconds, and when we dove straight down the target, the 88 mm guns could not be elevated to 90 degrees.  So, they couldn’t aim at us until we pulled out; at that point, we were traveling at over 400 mph, and they could not keep up and accurately lead us.” says Dills.  “All we had to do was change our course or elevation very slightly, every 15 seconds or so, and their computers (which were used to set the shell’s fuses for detonation at the intended target’s altitude) could not give them accurate readings.”      

Typical strafing missions involved attacking anything that moved on the ground.  This usually meant trucks and infantry.  Says Dills: “We looked for targets of opportunity – anything that looked like enemy war stuff,” he says. Dills adds: “We did not bomb civilian farm houses, unless there was reason to believe that the enemy was using them as observation posts; in those cases, we were given specific targets to attack.”  Dills describes one such mission, which involved the risk of hitting friendly ground troops.  “One time, we were sent up near the Anzio beach head to attack an “implement factory,” which was being used as an observation post; there was friendly infantry within 500 yards of the place on three sides, he says.”  Dills explains that not bombing this factory would cause even more losses to friendly troops.  “This place was causing losses!” he says.

Typically, attack formations would consist of eight or 12 airplanes – most missions were eight – divided into groups of four airplanes.  Each group would fly in a wide-spread “V” formation, while en route to the target:

“We were not real close to each other… not like the stuff you see in air shows; we had to stay far apart so that we could keep an eye out for enemy planes. We had specific areas to watch, because the lead plane was doing all the navigating.  He wasn’t looking for enemy aircraft.  If his wingman was on his left, that wingman would look to the right, 100 percent of the time. He never looked the other way because he was watching for an attack from the right side.  The element leader would be to the flight leader’s right, looking around and trying to keep track of where we were, in case something happened to the flight leader.  His wingman would be on the right, looking only to the left.”  

The A-36’s would begin their dives from approximately 14,000 feet.  Captain Dills describes a typical dive-bombing run:

“As the group neared the target, the leader would waggle his wings. This was the signal to get in trail (single file behind the lead plane).  As we got closer to the target, the leader would open his dive brakes and roll upside down.  We would follow suit and fly upside down until we were directly over the target.  We would then go straight down, until we had a good aim at the target.  I’ve seen some reports that say we released our bombs at 3,000 feet.  That’s getting a little low. I’d say we dropped the bombs at around 5,000 feet or so.  As you were pulling out, you’d shut the dive brakes and it was like getting a kick in the butt. Your speed would jump from 350 mph to about 450, and you’d get the hell out of there.  If there was no flak, we’d climb and re-group for whatever we were supposed to do next.  If there was a lot of flak, we’d just get out of there as fast as we could and re-group elsewhere.” 

Sometimes, danger came from one’s own squadron mates.  Says Dills: “We were attacking some docks, and I had dropped my bombs; I was flying straight down there were two bombs, right in front of me!  They were no more than 30 or 40 feet from me, and I could not pull out of the dive without hitting them!  They must’ve been dropped by the guy behind me, and I had to fly formation with them until they passed me!  They were so close that I could read right on the bomb 536 pounds, GP (General Purpose)!” 

As mentioned earlier, A-36 sorties consisted of strafing attacks, or dive-bombing attacks that were sometimes followed by strafing attacks.  “We never strafed with our bombs on,” says Capt. Dills.  Once bombs were released, there was no point in climbing up to 10,000 feet for the trip home.  Says Dills: “We were already near the deck, so we’d go home on the deck; along the way, we’d look for targets of opportunity.” 

Even though the A-36 was a formidable fighter in its own right, Captain Dills points out that he and his pilots avoided enemy planes as much as possible, especially when carrying bombs.  The reason for this is that engaging in air to air combat would force the A-36’s to jettison their bombs prematurely.  Forcing the A-36 pilots to drop their bombs before reaching their targets meant a tactical victory for the enemy. 

Some A-36’s did fight enemy aircraft, but Dills says that he encountered an enemy airplane on only one of the missions he flew.  This occurred during a low-level strafing mission with seven other A-36’s over Italy.  Dills recalled the details: 

“We really shouldn’t have been out that day; the ceiling was only 700 feet, and the area was full of hills and mountains.  But, there we were… I was flying on Major Kelly’s left wing, and I fell in behind him, hoping that we could make it through this valley.  As I caught up to him, he turned left into me.  I was still on his left, but now I was ahead of him. I reduced throttle so that he could catch up.  I was looking back and noticed that he was catching up very fast. But, he passed me. I gave it more throttle in order to catch up to him, but he kept going faster.” 

Dills finally saw the object of his leader’s attention:  “There was a Heinkel HE-111 cruising through the valley at 500 feet… of course, Kelly was going a lot faster than I was, and he got the first shot at it and set it on fire.  I took a shot at it as I went by, but I’m not sure if I did any damage.  I wanted to get the hell out of there, because… here came the other six airplanes and they wanted to take shots at this thing too.  So, here we were, fooling around under a 700-foot ceiling, trying to take shots at this damned thing!  I’m surprised we didn’t shoot each other down!  So, I just went off to one side and watched.  I mean, obviously, he (the Heinkel) was going to crash because he was already on fire.  His left wing dipped and he hit the ground at a 45-degree bank.  The wing broke off at the root, where it had been set afire, and the whole wing flew up in the air. I can still see it in my mind, with the black and white cross.  The fuselage slid across the ground, leaving a sheet of flame behind it that was 500 feet long and 50 feet high.  When they investigated after we had captured the territory, the local people said that they had buried 15 German pilots who were on board.  I felt like Major Kelly should have gotten credit for 15 victories.  I mean, what’s more important?  Shooting down the plane or the pilot?  Obviously, the pilot.  If you let the pilot go back and get another airplane, you haven’t really done anything by shooting him down.  But, if you kill the pilot, that’s a true victory.  I hate to put it that way during peacetime, but it’s the truth.”

One of the challenges faced by A-36 pilots was a lack of specialized training in dive-bombing techniques.  A few Navy and Marine instructors were “loaned” to the Army, but most Army aviators learned their trade through improvisation.  Dills recalls: “We had no dive-bombing training in flying school, but when I got to my RTU (Replacement Training Unit) in Sarasota, Florida, they had P-40’s.  We had little 25- or 50-pound things with little explosive charges, and we’d drop them on the bombing range.  We glide bombed at a 60-degree angle, but we didn’t go vertical.  People just didn’t do that – in any airplane. It would have scared the hell out of them, I guess.  But once we got over ‘there,’ people starting shooting at you and you did things that you never would’ve thought of before.  Vertical dives worked so well in the A-36, that we didn’t think twice about doing it in P-40’s (later on) – with no dive brakes!” 

Another challenge was the limited availability of the A-36 itself. Because of the A-36’s limited production run, the number of A-36’s available for combat had dwindled substantially by 1944. Dills never even saw an A-36 until he arrived in Italy.  Once there, he was given some ground instruction, and then turned loose in the airplane.   

“That’s the way we did it; if you were a fighter pilot, you were supposed to be able to fly anything that had wings and an engine.”  The expectation of such flexibility proved valuable, when, due to lack of replacements, the A-36 all but vanished from combat zones by 1945.

Captain Dills finished his tour flying “war weary” P-40’s and 15 missions in a P-47D Thunderbolt.

As many know, the “experiments” involving the Merlin-powered Mustang were successful, and resulted in the P-51B/C.  Except for some structural accommodations for the Merlin engine, the P-51B/C was basically the same airplane as the A-36. 

Short-lived though it was, production of the A-36 allowed the Mustang line to continue long enough for the airplane to evolve into the great fighter that it ultimately became. 


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