Advances Scale Models A-26 Invader

May 25, 2011 No Comments by

This high-performance twin-engine ARF captures the same thrill and excitement of the full-size bomber

The horizontal stabilizer is attached with a scale dihedral angle and the control linkage is easy to install. The rudder uses pull-pull cable control.

SEEING OFFICIAL COMBAT and civilian service for over 40 years, the Douglas A-26 Invader included two monstrous Pratt & Whitney R2800 radial engines, a wingspan of 70 feet and a maximum takeoff weight of 35,000 pounds. What set the Invader apart from its contemporaries was its blistering top speed of 355mph and its ability to carry a tremendous bomb load with a range of 1,400 miles.

Originally designed as a tactical support aircraft for the Army Air Corps in the early 1940s and first seeing service in 1943, the Invader served in WW II, the Korean War and the Vietnam War. Although later renamed the B-26 Invader after it replaced the retiring B-26 Marauder in 1948, it was again re-designated in May of 1966 as the A-26A. The A-26 has also been used as a target drone tug, a counter-insurgence aircraft (B-26K with 2500hp), and as a firefighter for the National Forestry Service.

SPECIFICATIONS

MODEL Advanced Scale Models A-26 Invader

DISTRIBUTOR Global Hobby (globalhobby.com)

TYPE Advanced Semi-Scale twin engine warbird

WINGSPAN 92 in.

WING AREA 990 sq. in.

WEIGHT 17 lb. 1 oz.

WING LOADING 39.34 oz./sq. ft.

LENGTH 66 in.

RADIO 6-channel or more

PRICE $450

HIGHLIGHTS

� Semi-scale warbird appearance

� Three-piece wing for easy transport

� Impressive scale performance

� Numerous power options

ITS LOW-ALTITUDE STRAFING RUNS ARE BLISTERING FAST AND LOOK INCREDIBLE

The outer wing panels plug into place with a strong aluminum support tube. Both the flap and aileron servos are mounted in the wing panel to keep control linkages short and flex free.

Distributed by Global Hobby, the Advanced Scale Models (ASM) A-26 is an impressive high-performance, semi-scale attack bomber with a 92-inch span. Although it is an ARF, this twin-engine airplane is intended for experienced, intermediate to advanced modelers only. The kit includes a three-piece balsa and ply constructed wing with factory-applied covering, an ABS-molded airframe constructed of plywood, balsa wood and carbon fiber, and ABS-molded cowls and nacelles. The factory paint job is also nicely done. In addition to a generous assortment of hardware, the kit also includes a set of stock fixed gear, clear plastic windows and working gear doors if you choose to install the optional pneumatic retracts.

In the Air

THE FACT THAT THE A-26 IS A LARGE, TWIN-ENGINE WARBIRD SHOULD NOT SCARE YOU

Knowing the left turning tendencies of a propeller-driven airplane, I expected the need for right rudder with not one, but two engines turning out front. I chose to use the ever-reliable Nelson Hobbies Intelligent Glow Driver (IGD) system (nelsonhobby.com) for each engine as added security. Each unit features a microprocessor to control power to the glow plug based on heat rather than the traditional throttle position, as is common with many units. I chose to make one aborted takeoff run at – throttle to check controllability on the ground and note the acceleration. I let the airplane get light on the nose then pulled the throttles to idle and taxied back for the real thing. Much to my surprise, the airplane held a nice, straight track and required average right rudder input. The takeoff is very predictable with a steady application of power and light back pressure during rotation and climbout.

General Flight Performance

STABILITY The fact that the A-26 is a large, twin-engine warbird should not scare you. This airplane required very little trim adjustments on the first flight. A bit of up-elevator and just a hint of right rudder was all that was needed. Climbs, turns and descents were easily controlled throughout the entire speed range.

TRACKING Proper engine setup can make or break how a twin-engine airplane tracks. If one engine is not in sync with the other, a yaw is induced and will cause the airplane to skid. Special care was taken to set up the A-26 and I couldn’t be happier with its tracking. It tracks extremely well both on the ground and in the air.

AEROBATICS Although a few rolls and loops were accomplished, this is certainly not a 3D machine. This is a high-performance bomber known for its speed and agility. If you choose to roll the airplane, use the high rates and be sure to use a bit of top side rudder as you roll through knife-edge, and forward stick is a necessity as you roll through inverted. Remember, it’s a bomber, not a fighter.

GLIDE & STALL PERFORMANCE Stalls are fairly predictable with the gear and flaps extended and should stall straight ahead the majority of the time, provided you do not induce any yaw. Clean stalls can be a bit more abrupt and will more than likely drop the left wing first. The A-26 is equipped with flaps and the optional, retractable landing gear. With both extended, the airplane is very predictable and slows quite well for landing. Depending on the descent angle, power-on or power-off approaches can both be accomplished with success. Keep the nose pointed below the horizon on the approach and you will be a hero every time.

Pilot Debriefing

This warbird is a blast to fly. Its low-altitude strafing runs are blistering fast and look and sound incredible. The throaty roar and performance of the two Magnum .70 4-stroke engines gave the A-26 scale realism and performance.

Don’t be afraid to use the majority of the runway for your first takeoff. Let the airplane accelerate a fair amount before deciding to pull back on the stick. Additional airspeed on the first climbout will help you get a feel for the airplane and give the rudder that extra bit of authority should an engine cough or quit. If an engine failure does occur during any phase of your flight, pull the throttle back as much as is practical to reduce the yaw caused by the operating engine. Level the wings using both aileron and rudder. Make shallow turns to return the airplane for landing. Flying a twin-engine airplane is a great experience and is always a favorite at the field. Take your time during setup and you will be rewarded with a true winner.

CONTROL THROWS

AILERON � � in. (low), � 5/8 in. (high), expo: 30%

ELEVATOR � 5/8 in. (low), � 7/8 in. (high)

RUDDER � 1 in. (low), � 1 5/8 in. (high)

FLAPS 2 in. full down, 1 in. half flap

GEAR USED

RADIO Airtronics RDS 8000 2.4GHz radio system, seven Airtronics 94162Z High Torque servos, two 94102Z servos for throttles

ENGINE two Magnum .72 4-strokes with stock mufflers (globalhobby.com)

FUEL Cool Power Supreme 10% Nitro (morganfuel.com)

PROP two APC 13�6 (apcprop.com)

UNIQUE FEATURES

The engine installation is straightforward. Here, the Magnum .72 4-stroke engine has been installed with the stock mufflers. There’s plenty of power on tap for this twin-engine ARF.

Here you can see the optional pneumatic retractable landing gear bolt nicely into place. This is the main gear and you can see the throttle servo to the right.

By looking at the 23-page manual (81 pictures), it is clear that you must be an experienced modeler, builder and pilot for this project. The manual is written with these assumptions in mind and leave some assembly decision options to the discretion of the builder. Each of the control surfaces uses hinge-point type hinges. They are strong, easy to install and look scale�a nice touch from ASM. Each of the hinge holes are drilled and nicely aligned. Be sure to use a drop of 3-in-1 oil or petroleum jelly applied to the hinge knuckles and keep the gap between the control surface and the trailing edge as tight as possible while the glue dries.

I ran a 12-inch extension from the aileron servos and no extension from the flap servos to the receiver located in the fuselage. I then routed a 24-inch extension for each servo through the center wing section on each side. Identifying and keeping the servo extensions separate is a must. I have found that using paint to color code on each of the connections works best. Use a zip-tie or something similar to keep the servo leads from falling back into the wing root ribs.

An aluminum wing tube is used to connect each wing panel to the center section. Although the wing and center section holes were drilled, the wing tube was not drilled or marked as stated in the manual. Accomplishing this was not an issue. Mark the tube’s center and slide it into the outer wing to the halfway mark. Drill the attachment bolt hole in one half and thread it with an 8-32 tap. Secure with an 8-32 socket-head capscrew then repeat the step for the other end of the tube at the center section.

The rudder has a pull-pull control setup. The kit includes stranded wire and crimp collets. I recommend using silver solder rather than the few drops of CA to secure each of the connections once the wire has been crimped. I also needed to enlarge the opening where the rudder tiller arm drops into the fuselage. I used the pneumatic retractable landing gear specifically designed for the A-26 (available from Global Hobby). The gear fits perfectly into the rails with no issues at all. Attach the air lines ahead of time before securing the gear in place. ASM provides a fair amount of black air line but I recommend purchasing a second color from your local hobby store to help identify the up and down air lines and connectors.

To help minimize the need for nose weight, I installed each engine �-inch farther forward from the firewall and added heavy bullet prop hub nuts. This helped move the CG forward and minimize the weight needed in the nose to balance. I installed the battery in the nose and only had to add 5 ounces of ballast weight to make the A-26 balance properly.

Airtronics RDS8000 2.4GHz Control

The RDS8000 2.4GHz radio system (airtronics.net) is a full-range FHSS spread-spectrum radio and it is an excellent choice for both sport and competition pilots. It is also an excellent choice for an advanced, high-performance aircraft such as the ASM A-26 Invader. Having a full-featured 8-channel system gives you a lot of flexibility when setting up your model.

A few of the special features you would want to consider are:

� Flap-to-elevator mixing so you can adjust the amount of pitch correction and compensation you’ll need when you activate the flap channel to lower the flaps for landing

� 3-position flap switch for up position, half-flap and full-down flap positions

� Aileron differential to set up each control surface’s up and down travel for smoother roll response (more up than down travel)

� Mechanical retractable landing gear endpoint adjustment, not just a switched function (not required for pneumatic retracts)

With so much flexibility, you can choose custom setups to meet your own needs and tastes. Having eight channels is just about perfect for high-performance war-birds. With the RDS8000 2.4GHz system you have the highest product quality Airtronics has to offer and the frequency freedom of 2.4GHz modulation.

DOUGLAS’ FAST TWIN

PHOTO BY JOHN WEIDMAN

Although technically a WW II light attack bomber, the Douglas A-26 was part fighter, part bomber and all testosterone. Most so-called �bombers� had the personalities of transports that just happened to carry guns and bombs. They were relatively slow, stodgy, often heavy on the controls, and were not known for their ability to dance. Not so with the A-26 Invader. The A-26 combined all of the traits that we generally attribute to something like a P-47.

For an airplane that was designed to drop bombs, it was extremely nimble, something that endeared it to its pilots and, with its well-armored cockpit and huge amount of armament it, like the Jug, could both dish out punishment and take it as well. Plus, it was extremely fast for a bomber. How does 355mph grab you? This airplane could really boogie!

In its later versions, it was equipped exactly as you would equip a Jug or a Skyraider: the wings were festooned with hard points that mounted all varieties of rockets and bombs. This was, of course, in addition to its bomb bay, which although not large by bomber standards, could still carry 4,000 pounds of ordnance.

The airplane got into WW II late and had too many initial teething problems to make its mark there. Plus, many of the roles for which it was designed were being adequately fulfilled by the fighters and bombers already in-theater. Five years later, however, in Korea, the A-26, re-designated B-26 in 1948, began to make a real difference, especially at night.

The various models of Invaders, not including the glass-nose pure bomber versions, carried at least six .50-caliber Brownings in the nose, which could be augmented with the forward-firing top turret and gun packs on the side to bring the total machine gun count to an amazing 16 .50 calibers all firing in a cone that was barely 8 feet across. Combine that kind of concentrated firepower with rockets and napalm and it became a nocturnal hunter that literally took the night away from North Korean convoys and trains trying to sneak in supplies under the cover of darkness. With so much highly accurate ordnance, the black beauties (the most basic form of stealth) could quickly deliver firepower on a target in the same pinpoint manner as a fighter. Plus, they could throttle those two 2,000hp Pratt & Whitney R-2800s back until they were barely sipping fuel and loiter at high altitude for long periods of time until called in on a target. Then they would drop down to the treetops and rain death and destruction on the bad guys.

B-26 Invaders were the first attack bombers to go to work in Korea and only 24 minutes before the �police action� was officially called to a halt, they dropped the last bombs of the conflict. But, their fighting days weren’t over, as B-26Ks were among the first combat aircraft to arrive in Vietnam and were still doing what they did best, pounding ground targets, when that conflict ground to a halt. Then, they took on yet another role, that of high-speed corporate transport.

As early as the 1960s, several companies, notably On-Mark and Monarch, converted the speedy little demons into plush, very fast private airliners for business executives who had to be someplace else in a hurry. It wasn’t until bizjets took over that they were pushed into finding work as fire bombers, before returning as one of the stars of the current warbird scene.

Although the airplane failed to make its mark in WW II, history will accord it �warrior� status as being one of the stronger, and longest, overall success stories in propeller-driven bomber aircraft.

�Budd Davisson
VISIT BUDD ON THE WEB AT AIRBUM.COM

CONCLUSION

This new A-26 Invader from Advanced Scale Models takes only about 30 hours to assemble (not including the installation of the included scale landing gear doors). I didn’t use them for simplicity. Although the build is not overly difficult, it does require some planning and thought. If you take your time you will be rewarded. This is a great semi-scale, twin-engine warbird that’s sure to impress everyone at the field.

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