Frank Beatty’s D.H.77
by Fred Cronenwett [email protected]
The Royal Air Force needed a high-performance fighter interceptor in the late 1920s. The de Havilland D.H.77, built by the company as a private venture, competed against the Hawker Fury biplane for this role. In the end, the Hawker Fury was selected and only one D.H.77 was built. It was first flown in 1929.
Frank Beatty scratch-built his model of the de Havilland D.H.77 from his own plans. The model is powered by an O.S. 46AX engine. The D.H.77’s distinctive cowl made it easier to hide the engine cylinder on the model.
The full-scale D.H.77 had a full-flying elevator that replaced the more traditional fixed stabilizer and moving elevator. Frank duplicated this feature on his model. The elevator’s pivot point is at the 25% chord location and it worked without complications. Frank reported no problems flying the model with the full-flying elevator.
Frank’s model has a 48-inch wingspan and is covered with Polyspan and painted with Brodak dope. Surface details such as rivets were made from glue drops.
Frank installed a three-line bellcrank to control the throttle. The wide-track landing gear with its distinctive struts provides excellent ground-handling characteristics during taxi.
CL Scale Options
The options you choose for your next CL Scale model should be based on what the full-scale aircraft is capable of doing. Look at the mechanical and flight options for the full-scale aircraft and decide what you want to reproduce on your model.
If you are flying an Extra 300 aerobatic airplane, inverted flight can be used as an option. If you were flying a B-17 bomber, inverted flight should not be called out as an option, regardless of whether the model is capable.
Throttle control and multiple engines can be called out as options in competition and are used throughout the entire flight. To get full points for throttle control, you need to be able to have the model come to a complete stop with the engine at idle. Also, make sure you can shut down the engine from the handle on command.
Mechanical options such as flaps are relatively easy to hook up, but require practice to operate in a scalelike manner during flight. Research the full-scale aircraft to determine how much the flaps are deployed for landing and takeoff.
Full-Scale Example for Options
When you start a new CL Scale model, it helps to understand what the full-scale aircraft was capable of doing. Visit airshows, read books, or watch videos to get a good sense of what flight options can be used. Look for mechanical options that can be used such as flaps, doors, a bomb drop, or an opening canopy.
The P-51 Mustang was capable of limited aerobatics, so a wingover or a loop could be used as an option, although the weight of CL Scale models sometimes makes this risky. The P-51 has two doors aft of the main air scoop that would be easy to set up with a servo or pushrod. One larger door controls how much air comes through the radiator to cool the engine; the smaller door controls airflow through the radiator to cool the oil. Because the pilot controls these two doors during flight, they can be used as flight options. A bomb drop is another option if the full-scale aircraft was capable of dropping bombs.
Retractable landing gear is one of the most difficult items to set up and maintain. The P-51 adds another level of complexity because the inner main gear doors remain closed while the gear is down. To get full points, you would need a gear door sequencer so that the inner main gear doors open, allow the main gear to retract, and then close the main gear doors. The tailwheel also retracts and has doors. If you search YouTube for "P-51C gear swing" you will find a video of the sequence of the P-51’s gear doors and main gear.
How Much Should Your Model Weigh?
All of these options add weight to the model, so it has to be big enough to carry all of the hardware. In the case of the P-51, servos and electronics for the flaps, air-scoop doors, retracts, inner gear doors, and throttle all add weight. Make sure your model has enough physical space and wing area to carry all of the hardware.
Figure out how much wing area you have and determine the maximum weight the model can be and still fly the way you want. Models in the 45-inch range or smaller can typically carry 16–20 ounces per square foot of wing area. Models in the 65-inch range can carry upward of 28 ounces per square foot of wing area.
You might find that all of the parts can fit in the model, but you don’t have enough wing area to lift the hardware. Weigh the hardware and calculate the model’s final weight before installing all of the features.
Large models with wingspans exceeding 80 inches can carry up to 36 ounces per square foot of wing area. These models require more time and effort to transport to the flying field and have more line tension because of their size, but bigger models penetrate the wind better and can tolerate higher wing loading.
There is no magic number for how much weight the wing area can support, but generally the lighter the model, the better it will fly; however, if the model is too light the wind may toss it around. I flew an 80-inch Piper Cub and added 16 ounces of lead at the CG because the wind made it difficult to fly. With the increased wing loading, the model penetrated the wind better while still maintaining a decent stall speed for landing.
2014 CL Scale Contests
I welcome contest reports, upcoming contest flyers, pictures, and any projects you are building and flying. The National Association of Scale Aeromodelers (NASA) Scale Classic (NSC) will be held October 3–5 at the AMA flying site in Muncie, Indiana. There are two more contests you can attend to try to earn an invitation and be part of this contest.
- Ohio Scale — Dayton, OH — August 9–10
- Fellowship of Christian Modelers (FCM) — Muncie — August 23–24 (NSC qualifier)
- Broken Arrow — St. Louis — September 20–21 (NSC qualifier)
- NASA Scale Classic — Muncie — October 3–5
Land softly!
SOURCES
- NASA
- www.nasascale.org
Transcribed from original scans by AI. Minor OCR errors may remain.
