Flight Report - Grumman HU-16A Albatross

Russ Erb

Originally published July 1998

"Albatross! Albatross!" It was with these immortal words of John Cleese1 running through my head that I walked out of the TPS door for my qualitative evaluation (qual eval) ride of the Grumman HU-16A. With me were my intrepid test pilot Jackie Van Ovost, pilot/owner Rich Sugden, M.D., and pilot/crew chief/generally in charge of a lot of things George Northup. Rich Sugden is a Family Practice doctor, which he is quick to point out does not bring in enough money to support an aircraft the size of an Albatross. It seems he also got into some business with computers some years ago. More significant is that he is a Director of EAA Warbirds Of America.

Size

The Grumman HU-16A Albatross is a high-wing flying boat amphibian. It has a wingspan of 85 feet, a length of 62 feet, and a 22,000 pound empty weight. This ain't your neighbor's Piper Cub!

Propulsion

Power is two nine cylinder two-speed supercharged Wright R-1820-76 radial engines of 1450 horsepower each. Versions of the same engine are used on the T-28 and the B-17. Each engine drives a three-bladed constant speed propeller. Unlike most constant speed propellers, these propellers are electrically controlled and hydraulically actuated independent of engine oil. The governor RPM is set by toggle switches, and the governor and prop hydraulic pump are driven by the engine. A prop oil cooler is integrated into the hub dome. The propeller uses a lighter weight oil than the engine. This system allows immediate control of the propellers on engine start without waiting for the engine oil to warm up. On the water at low speeds, the air rudder is not effective, and no water rudder is installed. The primary means of directional control is differential power. At idle power settings, control is best accomplished by moving one prop in and out of reverse. No beta range was available on these propellers. When the engine is running, the propeller is thrusting one way or the other, so immediate control is necessary.

Primary fuel is carried in main wing tanks. Additional fuel can be carried in the tip floats. However, water operations are prohibited with more than 100 gallons of fuel in each tip floats. Otherwise the tip floats wouldn't. Runway landings are also prohibited with more than a 100 gallon difference in fuel load between the tip floats. This aircraft is equipped with wing racks capable of carrying bombs or drop tanks. With main, tip, and drop tanks, this aircraft can carry a total of 10,200 pounds (1700 gallons) of fuel, for a reported range of 3000 miles. This aircraft has flown non-stop from Nome AK to Japan in 16.5 hours.

Landing Gear/Hull

Landing gear was installed for land operations. The main gear retracted into the side of the fuselage, and the main gear strut folded into the side of the fuselage and underside of the wing. During water operations, the main gear well is flooded with approximately 1000 pounds of water. During the takeoff run, the acceleration forces this water through a hole in the rear bulkhead, through a tube which exits near the center of the hull in the low pressure area immediately behind the step. A smaller hole near the bottom of the bulkhead lets out the remaining water.

The nose gear lowers through doors in the center of the forward part of the hull. Damage to these doors can occur if the aircraft if landed on the water in a too nose-low attitude. True to Navy tradition, the nose gear has two wheels. I suspect this was more to save space in the lower fuselage by using smaller wheels than for straddling a catapult track. The nose gear is free castering with no nose wheel steering provided. Directional control during land taxi is provided by differential thrust, augmented by differential brakes (which are generally ineffective for water operations). A less than desirable note about the brake system was that every application of the brakes required pumping the pedals several times. This increased the difficulty of taxiing. The requirement to pump the brakes was verified by the owner as "normal" for this aircraft.

The nose gear compartment is sealed from the hull, and is partially flooded during water operations. A small window in the top of the compartment is visible from the flight deck, giving a quick check if the nose gear is up or down (doors open or closed), at least for daytime operations.

Tip floats are provided for lateral stability in water operations. The underside of the fuselage is assembled with round head rivets, while the remainder of the aircraft is flush riveted. As told to us by the owner, the Albatross was originally designed and built with flush rivets on the underside. After an operational accident, a large hole in the underside of an Albatross was repaired in the field, but the mechanic only had round headed rivets available. Much to their surprise, the water takeoff performance improved, getting off the water 5 to 10 knots sooner. Word was sent back to Grumman, who verified this with testing. Therefore, all subsequent Albatrosses were completed with round headed rivets on the hull bottoms. In an odd twist to the story, because the sheets were already dimpled/countersunk, they used a special rivet which was essentially a flat head rivet, but with a round head added on top of it. Countersunk round head rivets-only on the Grumman flying boats...

Flight Control System

The flight control system is fully reversible (cables, pulleys, pushrods), with hydraulic boost available for the rudder. Hydraulic rudder boost is normally only used during takeoff and landing, and is mostly intended to relieve pedal forces during single engine flight. Rudder boost is not required for normal flight.

Electric trim is provided for all axes, driving trim tabs on the elevators, rudder, and left aileron. A fixed tab is provided on the right aileron. Each elevator has a trim tab, and each elevator trim tab is controlled and driven independently, providing redundancy. Trim is controlled by toggle switches on the panel between the pilots. A coolie hat switch was added to the yoke. Fore and aft movement controls the left elevator tab. Side to side movement controls the rudder trim, not aileron trim. This was judged by the owner as more useful during normal ops, allowing easy trimming for p-factor, torque, and single engine flight.

The flaps are electrically controlled and hydraulically operated. The flaps are also hydraulically balanced, a feature unique to Grumman aircraft. In the absence of air loads, lowering the flap lever lowers the flaps, which may come down asymmetrically. However, as soon as air loads are applied, a cross-feed between the actuators will allow the flaps to re-adjust until the loads, and thus position, are symmetric. I saw this happen during a land takeoff. When the flap lever was set to 15 degrees, the flap appeared to move down about 5 degrees. Shortly after we started moving, the flap moved to the 15 degree position.

Getting In

The aircraft is entered through a hatch (no doors-this is a Navy bird) on the left side of the fuselage. Since the hatch has to be above the water line, it requires climbing a six step ladder to get in.

Stepping inside, the first word to come to mind is "cavernous." We're talking really big! I was reminded of Dean Wilson's Explorer, only with a more substantial looking frame. Immediately behind me at this point was another hatch leading to the lavatory and "head," which can be very important when flying 16.5 hour sorties. This aircraft was equipped with 4 medical stretchers (used as bunks), 4 passenger seats, and enough room left over to set up a nice home office.

Immediately behind the wing is a large hatch in the roof of the fuselage, with a sextant port in the middle of it. I am told that this hatch was big enough to load an entire R-1820-76 engine quick change kit (engine, mount, and accessories) into the aircraft. We never did figure out how you would get the engine out in the middle of the ocean to fix a crippled aircraft without some sort of crane. On the back of the sizeable wing spar carry-through structure (guaranteed to instill confidence in passengers) is a handle which, if pulled, starts inflating a life raft on top of the wing. The life raft would push open a hatch as it inflated, then slide down the top of the aircraft to the left side, coming to rest right in front of the exit hatch. During restoration, this handle was accidentally pulled, and the life raft, which had been stored for 20 years, inflated and slid down the left side, just as designed. Since an inflatable boat is carried in the fuselage of this aircraft, this compartment is used to hold engine oil, a line (Navy for rope) to lift the gas hose up to the top of the wing, and other items.

The top of the aircraft can be reached from the entry hatch using a folding step and two hand holds above the hatch. Alternatively, hatches are located above the pilot and copilot seats. These techniques all work on land or water.

Walking forward through the aircraft (boat? ship?), you step through another Navy style hatch into the flight deck. The walkway is a the same level as the deck (Navy for floor) in the cargo/passenger compartment, but the flight deck on either side is about kneecap height. Pilot and copilot seats are where you'd expect them, with an additional seat behind the pilot and another behind the copilot. A complete set of flight instruments are installed on each side (a good thing considering how far apart they are), with engine instruments in the center. Engine controls (including throttles and mixture levers), propeller RPM switches, flap controls, fuel selectors, radios, and rudder boost control are all located on the overhead center console. A large red lever on the left side of the overhead console controls throttle friction.

A very nice flight director system was installed. A major improvement to the instrument panel was to take all of the warning, caution, and advisory lights from all over the cockpit and consolidate them into one logically grouped panel near the center of the instrument panel.

Enough of that, let's go flying...

Takeoff and Climbout

Our adventure started with a land takeoff from Edwards AFB. Our startup gross weight was about 29,000 pounds, with about 3000 pounds of fuel on board, and a mid-range cg.

Lineup was made with the nose about 10 degrees right of centerline, knowing that torque and p-factor would bring it back around. Flaps were set to 15 degrees down. The propellers were set to full increase, governing at 2700 RPM. The throttles were advanced to maximum power, giving 49" Hg manifold pressure on this day. The limiting manifold pressure was 51" Hg. The left throttle was advanced slightly ahead of the right throttle, again to compensate for torque and p-factor. The rudder was used for fine directional control once it became effective. Rotate speed was 80 KIAS, which was also used as Vmca.

Boy, talk about LOUD! I didn't have a sound pressure level meter with me, but even wearing a noise-canceling headset, it was still louder than I would want to put up with for much longer than a minute or two. I'd hate to think what the boys flying these operationally in the '50s went through. (What?...I can't hear you...) It was so bad during takeoff and climbout that the voice activated feature of the intercom had to be turned off and push-to-talk used.

The landing gear was retracted and the flaps were raised at 100 knots. Due to the immense volume of the hydraulic rams on the landing gear and the limited volumetric capacity of the hydraulic pump, the landing gear do not retract simultaneously. The nose gear (with the smallest volume requirement) comes up first, then one of the main gear, then the other. The yaw due to the unsymmetrical gear retraction can be felt in the cockpit, but can be easily compensated. On one takeoff and landing I had the opportunity to watch the main gear retraction and extension from a bubble window just behind the main gear. (It's an interesting experience to stick your head "through the side" of the fuselage and not feel any wind blast--great view too!) If you enjoy mechanisms and seeing how things work, this one is a real treat! It's amazing how such a complex folding can be done with just two actuators. Even after fully retracting, the main gear wheels continue to rotate for about a minute.

The limit speed on the landing gear was 140 KIAS, which was well above any speeds needed for normal extension and retraction.

The climbout was flown at 120 KIAS, which yielded about 800 to 1000 fpm rate of climb.

So What's It Fly Like?

On our way to and from Lake Isabella, we checked out the flying characteristics. Cruising at 6750 feet, we were making 150 KIAS at 28" Hg manifold pressure and 2000 RPM. That's 165 KTAS to you and me (190 mph if you insist on using those archaic units). At a fuel weight of 2600 pounds, we were burning 97.7 gallons per hour. By rough calculations, for a full load of 1700 gallons of fuel, that would be 17.4 hours of endurance, with a range of 2871 nautical miles, or 3306 statute miles (no reserves). These results match reasonably with the claimed performance.

Power settings were easy to set, assuming you remembered to loosen up the throttle friction.

The L/Dmax airspeed (minimum drag airspeed) for this aircraft was around 135 KIAS as tested, with a very flat thrust required curve. This leads to an interesting technique being used to reach cruise speed. For most aircraft that fly well above the minimum drag speed, the technique is to climb to cruise altitude, push over, accelerate, and then set cruise power. With the Albatross climbing at 120 KIAS, pushing over at cruise altitude and setting cruise power, the aircraft will seem to stabilize at about 120 KIAS. While it may be accelerating very slowly, any pitch bobble up would quickly stop that. However, without moving the throttles and diving to reach 145 KIAS, then leveling off, the aircraft magically stabilizes at 145 KIAS! Almost seems like 25 KIAS for free!

The electric trim was thought to be overly sensitive in pitch and yaw. We were told that no changes had been made to the trim system, other than to remote two switches to the coolie hat switch. Thus, this was the original trimming speed. Roll trim was not tested.

Freeplay in the wheel (yoke) controller was "not too bad," with about 5 to 8 degrees of freeplay in roll. Control forces were qualitatively high, as would be expected in a reversible control system for an aircraft of this size, and appropriate to an aircraft that spends most of its time cruising.

The short period response (pitch damping) was deadbeat (no overshoots). The dutch roll was snakey (more yaw than roll) and damped out after one overshoot.

Stalls were accomplished at 6500 feet, cruise power, clean and with 15 and 30 degrees of flaps. In each case, natural airframe buffet and control yoke shaking were felt 5 to 10 KIAS above the stall. The stall warning was obvious and unmistakable. The stall airspeeds were about 80 KIAS with 15 degrees of flaps, and 70 KIAS with 30 degrees of flaps. In each case, the left wing slowly dropped about 20 degrees and the nose fell through the horizon. Recovery was by letting the nose drop, raising the wing with a bootfull of rudder (boost off), and leveling off. Power was not changed during the maneuver. Recovery took 8 to 10 seconds, even with full rudder, and lost about 500 feet of altitude.

No significant pitch changes were noted when changing power settings. I suspect this is because the c.g. of the aircraft is fairly high. All of the heavy parts of the aircraft (wing structure, fuel, engines, tail) are more or less lined up with the thrust line. Though the fuselage is large below the thrust line, it is mostly a large shell around air space. Pitch change with power might change if the aircraft was heavily loaded.

Now the part you've been waiting for...

Water Landings, Taxi, and Takeoffs

Water operations were conducted on Lake Isabella. Coming in for a water landing is similar to an off-airport landing, with some modifications. Flying a box pattern over the proposed landing area, we looked for any obstructions, such as stumps, floating debris, boats, people, etc. (That's the first time I've ever called boat traffic in an airplane!) To determine the wind direction, you can look at which way the waves are moving. You can also look around peninsulas for "slack water," which is the smoother water on the leeward (Navy for "downwind") side. Even running the checklist is different. The IP was very specific about stating that this would be a WATER landing and that the landing gear was UP. Landing in the water with the gear down is just as bad as landing on land with the gear up. Knowing the wind direction and having cleared the landing area, fly a normal downwind, base, and final. On final, stabilize on the desired airspeed and power setting. If the water is not glassy (tough to judge altitude), then flare as normal.

When you first touch the water is when all similarity to land landings ends. Land landings may start with a bounce but then rapidly smooth out. In water landings, you start out as a high-speed boat, planing and bouncing across the waves just like you were in a fast ski boat. The waves were running about 18" crest to trough when we landed, so the bouncing was definitely noticeable. As the aircraft/ship/boat continued to slow, it would eventually come off the step and dig in, accompanied by a big splash. Now you were floating by displacement instead of planing. About the best simulation I can think of would be riding Splash Mountain at Disneyland or the Log Flume at Six Flags. At the end of the big drop at the end of the ride, your "craft" is set skimming (planing) across the waters surface. After a few bounces, it digs in and gives a big splash. The pilot's biggest job in this maneuver is to maintain the proper pitch attitude, which mostly consisted of pulling back to keep the nose up. We tried one max effort landing, approaching with full flaps and reverse thrust after touchdown. Our estimated water run was about 200 to 300 feet, with water going everywhere! This just goes to show that you can put this airplane down in a much smaller area than you can get it back out of!

Low speed taxiing (ploughing, or plowing if you prefer) is accomplished with the engines near idle thrust. This still gives a good 5 to 10 knots, much like bringing a motorboat into a dock. Speed and directional control is by the engines. A very effective way to control direction at low speeds is simply to put the prop on the side you wish to turn toward into reverse. Pull the throttle to idle, then push up. It takes some practice to smoothly get in and out of reverse, and getting out is harder than getting in. For pilots new to the airplane it is hard to determine if the throttle is in reverse without looking.

Unless you happened to be going directly upwind, steering is a constant effort to maintain direction. That big vertical fin is still out there and is still trying to turn you into the wind.

This is a good time (assuming you're not the one driving) to go forward to the bow. Back down onto that walkway between the pilot and copilot, duck under the instrument panel, turn on the light, and open the bulkhead hatch. This hatch leads to the nose compartment, where you open the overhead hatch, then stand up in front of the cockpit. Turn around and wave at your pilot. Then plug your headset back in so she can hear you. The primary purpose of this hatch is so you can use a boat hook (long pole with a hook) to grab the mooring buoy, which, of course, is out of the view of the pilot. If you look forward, the nose disappears from your field of view. As such, you can spread your arms, tilt your head back, and do your best Kate Winslet impression. Of course, you'll be a lot closer to the water than she was on the Titanic, but hey, think of it as flying low level.

Step taxiing is preferred if you have a long way to go, such as getting back to the takeoff point. This maneuver consists of getting up enough speed to plane across the water ("on the step"), but not enough to take off. Flaps are left in the UP position, which for some reason allows the aircraft to get up on the step easier. Again, the primary job of the pilot is attitude control. Ailerons are used to get the tip floats out of the water (harder than it sounds), and it takes a LOT of aileron! Full aileron takes over 180 degrees of control wheel rotation, with a sizeable force. Add to that pulling all the way back on the yoke to keep the nose up while applying power. Lead with the left throttle to counter p-factor until the rudder becomes effective. As the aircraft comes up on the step, it will probably start to porpoise (oscillate in pitch), which is not a good thing because this is an Albatross, not Flipper! Stop the porpoising by smartly pulling back on the yoke as the nose is going down. Once the porpoising stops and you are on the step, the pitch attitude becomes more stable. Now you've got a big, high-speed motor boat. Directional control is by rudder at this point. Doing this maneuver for the first time will probably leave you feeling short about two arms, between the pitch attitude, keeping the tip floats up, adjusting the throttle, maintaining directional control, and the myriad of other things you have to do. That's when it's nice to have a copilot to run the throttles or something. Step taxiing downwind is even more challenging because with less airspeed, the ailerons are less effective and you may not even be able to get the tip float out of the water. Directional control is also less effective.

Water takeoffs start off just like step taxiing, with a few changes. This time the throttles are advanced to full power, and the aircraft transitions from low speed taxi to step taxi. Once on the step, the flaps are dropped to 15 degrees, and at 80 KIAS, pull back and lift off. Once off the water, its just back to being an airplane.

The takeoff can be rather spectacular to watch from the bubble side window. Applying takeoff power sets up an incredible rooster tail, with water going through the lower part of the prop, up the side of the fuselage, and across the horizontal tail, which doesn't do wonderful things for the fabric covered elevators and rudder. Initially, this water plume fully engulfs the bubble window, but eventually the window clears and gives a spectacular view to the rear.

Albatross Buffoonery

This is an incredibly fun aircraft to fly if you ever get a chance. In warm weather, you can set down on a lake, set the barbecue on a shelf outside one of the side hatches (on the downwind side), crawl up on top of the wing and have quite a picnic. The wing also makes a great diving platform. If you really want to confuse your friends, lower the landing gear in the water (it's okay to do after you've stopped, but pull them up before any more taxiing). Then tell your friends that you're going to swim under the fuselage and see them on the other side. Then swim under, but come up in the nose gear well. There's plenty of trapped air in there. This will leave the rest of the folks wondering where you've gone. You'll have to decide how long to carry on this charade.

I Want To See More!

See a whole mess of pictures on the Albatross Pictorial Tour, courtesy of USAF TPS, accessible from the Project Police Picture Pages Phor Pilots on the Chapter 1000 web site.

1Monty Python's Flying Circus, Show 13


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Contents of The Leading Edge and these web pages are the viewpoints of the authors. No claim is made and no liability is assumed, expressed or implied as to the technical accuracy or safety of the material presented. The viewpoints expressed are not necessarily those of Chapter 1000 or the Experimental Aircraft Association.
Revised -- 19 March 1999