Petrel (oz14838)

About this Plan

Petrel. Radio control sailplane model. Wingspan 78 in.

Quote: "An excellent 2-meter design for competition or sport flying. Plans also show how to make 100-inch wings. Peterel, by Jim Ealy.

The Petrel, as in 'Storm Petrel', is a member of the group of various small birds that inhabit the shores of most oceans. These small aggressive birds are extremely maneuverable and can penetrate easily in stormy weather, but can relax and soar with the best in calm, light air.

The model, like the bird, appears to have all of the above natural talents in the hands of a beginner, and can keep the expert from becoming overly complacent. If you are on the contest trail, as well as being a Sunday flier, it will bring home hardware and help you look like one of the experts. I wish to thank one of my favorite experts, Don Clirneson, for encouraging me to make detailed drawings and for showing me and others just how well the Petrel could fly. He gave me the enthusiasm to start the long process of making the drawings, as well as getting homemade kits to the interested fliers - an undertaking not recommended for the sound of mind!

The Petrel was designed for my son to compete in the two-meter LSF contests. While it was being built, he was at hockey camp. He returned the day before the contest, test flew it for three short flights at dusk, entered it the following day, and did quite well! Maybe the advantage of youth (ten years old) and the fact that he is working on LSF Level Four makes some difference. The plane has been flown by several others of greater skill than either of us, and it has made an instant, positive impression. However, the reason for this article is that several 'novice' club members have been handed the transmitter, and most of them felt that they could fly it better than their own ship. Those of us who were watching agreed. Also, the ease of construction and the several variations that can be made during the building appeals to both novice and expert alike.

I teach at THE HILL SCHOOL, an all-male college preparatory school, which has the good fortune to have about fifteen acres of open athletic fields (mowed several times a week), several large basketball courts (for indoor flying) and a pond that can be used for power and sailboats. This lends itself to a good, active model club. As if this were not enough, we also have a very complete metal shop and wood shop. Several students in the past have built .40-size glow engines from scratch, and a possible full-size glider is being talked about for the wood shop under the guidance of the EAA School Flight Program. THE HILL SCHOOL enrolls young men in grades eight through twelve; some become club members, with little or no model experience, and a few have placed at the Nationals. The club needed an easy-to-build, strong and stable ship to teach the novice members how to fly, and the Petrel was the answer.

The design parameters have been selected with regard to the published advice of true experts and winners, and from my own experience and conviction. Most of these convictions are the result of my years of building and designing, but mostly result from the frustration with designs that, with a little more thought, could have been so much easier and logical. This would have made it easier for the young person to be successful and to continue with the hobby. Too many designs are for the well-advanced expert (who rolls his own anyway), or so simple that the beginner will know that when he takes it to the field, everyone else will know he is a rank beginner. We were all beginners, but we tried not to be that obvious about it.

The design parameters are listed as follows, and include a reason for that parameter.

Two-meter wing span: a new challenge and a relatively untried class.

A wide nine-inch chord for the inboard panel and a reasonable taper to a seven-inch tip chord: lots of squares (650 sq in).

The airfoil is a compromise: a thin 9.8% at 31% of the chord but with turbulator spars. The turbulator spars are optional, but they will guarantee extra height on launch and guarantee a true airfoil at high speeds, when coverings deform, thus increasing efficiency - the name of the game!

Notched trailing and leading edges: ten-fold increase in structural and torsional strength. This small procedure takes about five minutes, and is well worth the time.

The spars are a bit much and so is the webbing, but 1/8 x 1/4 spars and 3/32 webbing instead of that shown on the plan will only earn a decrease of 7/8 oz. This decrease in wing loading versus strength at a wing loading of 5.0 to 5.2 oz/sq ft is an academic argument and not a practical one. Besides, some of our friends need a ship that will break winch lines without folding the wings to gain a relaunch!

Ballast tubes in the wings are also optional, and can be made from plastic, brass, or aluminum; however, use brass filled with lead, and not aluminum! Depending upon the tubing size you select, you can add about 2 to 2-1/2 pounds to the ship's weight.

We do some slope flying here on the East Coast, but only when we are forced to by heavy rain. Built as per plans and ballasted to the hilt, the Petrel can be dived and pulled out without concern on your part and without much flex in the wings. The flying stab provides ease of trimming and change of in-flight incidence angle, as well as having the positive effect of no hinge line drag. The balanced rudder is very efficient and sturdy..."

Direct submission to Outerzone.

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