North American Observation O-47. Free flight scale model.
Quote: "THIS North American model will prove highly interesting. It combines both beauty with excellent flying qualities. The tiny Hornet motor pulls the model through the air at a clip which we are sure will thrill you time and time again. The model is colored in silver with a black patch on top of motor cowl and part way back on fuselage to windshield. Many novel features have been built into this ship such as removable motor mount, removable cabin hood to gain access to batteries, etc. We advise you to spend a great deal of time in building
this model and you will be more than repaid for your efforts.
By enlarging the plans four times that shown in the magazine, a duplicate of the model we built will be had.
Construction of Fuselage. The fuselage is built in two halves with a beam through the center for addi-tional strength. After all the formers have been cut to their proper shape place on a flat surface, edges up. Stringers now are attached from front to rear. Cement these securely. After the two sides are completed, cement them again.
Construction of Wings. Cut all wing ribs from 1/16 sheet stock with the exception of rib A. This must be 1/8 thick. Spars are tapered from 1/8 thick sheet balsa wood. Wing tips are made of 1/8 sheet balsa.
Wings are fastened securely in body as shown in top view of plan. Wings are covered when attached to fuselage as additional strength has been built into them to prevent any warping.
Construction of Tail Surfaces. These are built upon a flat surface from 1/8 square, 1/8 x 1/4 and 1/8 scrap sheet balsa. To add further strength to elevator attach two small struts to under side which in turn are fastened to bottom of fuselage. These are attached after tail surfaces have been covered. Cover tail surfaces before attaching to fuselage. Pin them to some flat surface in order that they will not warp.
Construction of Motor Mount. Select a good grade of hard wood and cut to the required size as specified on plan. As you will note, to remove entire motor together with mount it is only necessary to unscrew two small bolts in the front and pull out W dowel at rear of mounts. All other small details are clearly shown on plan which you should have little or no trouble following.
Covering the Model. Previous mention was made in regard to covering wings and tail surfaces on this model. A good grade of bamboo paper is used for the covering. Attach to the framework surfaces with model airplane cement which has been slightly thinned out. In covering the fuselage it will be necessary to cover in long strips between stringers. This is to assure you of a good covering job. After all the parts have been covered, spray with a light coat of water and let stand until dry. This will cause the paper to be-come taut. Two to three coats of clear model airplane dope are next applied with a light sanding between each coat. Further coats may be added depending upon the finish you desire.
Testing the Model. Assuming the model is now completely finished with gas, batteries, etc, ready for flight, it is necessary to balance it. Place a finger tip under each wing tip approximately one-third of the distance back from leading edge. Model should rest in a very slight downward position, one or two degrees. If this is not had, shift batteries in rack to secure the proper balance.
Next, launch the model from hand gently over some tall grass so as to prevent any injury to model. This will further give you the proper balance. If model when launched from the hands glides gently to the earth in a slight downward angle, it is properly balanced. Aluminum tabs in wing and rudder are for directional and lateral balance.
Bear in mind to be very careful in balancing your model and running it un-der power so that you will not damage it on its first test flight. Check everything carefully before launching the model."
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Update 25/02/2019: Added article, from scans found online at https://books.google.co.uk/books/about/Flying_Magazine.html?id=iRqI-1xucWgC.
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* Credit field
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This model plan (like all plans on Outerzone) is supposedly scaled correctly and supposedly will print out nicely at the right size. But that doesn't always happen. If you are about to start building a model plane using this free plan, you are strongly advised to check the scaling very, very carefully before cutting any balsa wood.
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