Prophet 941 (oz4098)

 

Prophet 941 (oz4098) by Ted Davey 1984 - plan thumbnail

About this Plan

Prophet 941. Glider. Radio control sailplane.

Quote: "Here is a plan of a sailplane I have had for a while. Got it scanned and I think I have it ready to go. Prophet 941 by Davey Systems Corp. 99.5 inch wingspan. Designed by Ted Davey, 1984. Standard class high performance sailplane."

Direct submission to Outerzone.

Update 30/04/2018: Added kit review from Flying Models, February 1986, thanks to RFJ.

Quote: "An FM Product Review: Prophet 941 from Davey Systems. By Bob Cook. Take your choice: potent contest threat or excellent sport flyer, this sturdy design excels in both roles. It's a good one!

The Prophet 941 is a standard class, competition sailplane from Davey Systems Corporation (DSC) of Malvern, Pennsylvania. The number 941, as you might have guessed, is the wing area of the glider. The 941 is basically a scaled-up version of its little brother, the well-known Prophet 2m (oz11909).

The Prophet design is the result of much research and testing with the use of computers to optimize its performance. There are many features of the Prophet that glider flyers will find desirable, especially for competition use. The fuselage is rugged enough to withstand those rough spot landings without sustaining any damage, and the wing is built to withstand the loading applied by a twelve volt winch. A special airfoil gives the airplane the speed to get out of areas of sink, yet allows it to thermal in the lightest of lift. The Prophet can handle winds of 22 MPH without any ballast and winds of 35 MPH fully ballasted. Several options are available including an electric pdwered version.

The Prophet carries with it a good reputation and an impressive list of specifications. I had great expectations of the sailplane and was anxious to get on with the building of the kit and the flight testing of the finished product.

The kit: The kit came nicely packed with all of the parts either bundled, stacked, or bagged. Both die-cut and machined parts of superior quality are included. The hardware packages are very complete, containing everything required. The plans, which are on two large blue-line print sheets, are nicely drawn with a good level of detail. Although the kit is not one for the complete beginner, the all-wood construction is quite straightforward and should pose no problems to the modeler who has mastered basic building skills. With a list price of nearly $100, this is by no means a low-priced kit, but considering the quality of the kit and the advancd design features, it is well worth the money.

Construction: The construction of the Prophet begins with the full-flying stabilizer. The rib and spar structure is light and strong with a thin symmetrical airfoil section.

The next step is the construction of the rudder and the fin. The rudder, which is framed up from balsa strips, is tapered nicely from front to rear. The solid balsa fin is installed in a novel way in that it extends all the way through the fuse and out the bottom to form the tail skid. The control rod for the elevator may be routed through the fin for an all-internal installation, or the cable may be routed through the side of the fuse to an external horn. I chose the latter system since I feel it offers smoother, trouble-free operation, although it is not as clean looking.

The fuselage is quite sturdy with its 3/8 inch thick botom and top slabs. These machine-cut planks not only aid in building a straight fuse, but allow it to be sanded to a nice rounded cross-section. A built-in, adjustable tow hook is installed in the fuse bottom.

The wing is constructed in the standard manner for sailplanes with a shear-webbed spruce spar, cap-stripped ribs, and sheeting from the leading edge on back to the spar. The wing built up quickly with only a couple of ribs needing some trimming for a better fit.

I did not care for the way the shear webs were to be installed and made some changes. The plans call for the webs to be glued to the sides of the spruce spars, forming a box-beam in the center of the wing and a C-beam out near the tips. Take it from a guy who has broken a few glider wings, the shear webbing must be installed between the spars to form an I-beam shape. Although this method is a bit harder to do, and the fit must be perfect, it is a lot better to take a little extra time now, instead of rebuilding the wreck resulting from a broken spar in flight.

When it came time to join the wing tip panels to the center panels, 1 again had my doubts about the method recommended. I replaced the 1/8 inch ply joiner with 1/16 inch ply installed between the spars in keeping with the I-beam structure. I also added a 1/32 inch ply brace to the leading edge joint for added security.

The wing halves are joined by means of a 1/4 inch steel rod which goes into fiberglass tubes embedded in the wing roots. I added considerable reinforcement to the mounting of these tubes since there is tremendous stress concentrated in this area during launching..."

Update 27/11/2023: Added kit instructions, thanks to Cesar Mazzolenis.

Quote: "DSC Prophet 941. Building Instructions.

The Prophet design has evolved over a long period by use of practical design and computer optimization. What was needed? The best L/D to speed envelope compromise - absolute minimum drag to achieve this meant a new concept to optimize each and every component of the sailplane.

The wing was first, since it is the heart of the sailplane. An optimum wing planform with a selected camber line to hold a speed range for up to 22 mph winds wihout ballast - the ability to carry enough ballast for up to 34 mph wind speeds without flying off the design point, and still slow down to a decent speed for landings, resulted in the wing you see on the plans. For you math types out there, it is a highly modified NACA 4410 with a 5% surface drop from 40% of the chord to the trailing edge. The wing has a maximum coefficient of lift of .83 with a designed coefficient of lift of .51.

The fuselage had to be able to withstand repeated hard landings without damage and with no chance of shedding parts to keep those important landing points. Look at the plans again and note the wing retaining method; the wing chn't comc off but it car move. Check the construction on the fuselage - it won't break! Light construction for reduced mass about the axis for ultra-quick response to control inputs meant a short tail moment with large size empennage to keep rudder and elevator movements at a minimum and still maintain quick reactions to inputs. The design is:

· Strong enough to launch on a 12-volt winch.
· Fast enough to leave those sink areas far behind.
· Slow enough to land easily without spoilers.
· Light enough to work even the lightest lift.
· Capable of handling ballast enough to fly in 35 mph winds.
· Clean enough that the drag factor on the aircraft is at an absolute minimum.

You will note as you look over the plans and kit contents that this is a very unique kit in that a number of options are presented for your consideration. In the event you choose to build an electric version or the different wing presented, you will have to make your decision now. Please note that the kit contains all of the wood you need to build the competition sailplane as presented on the plans. You will have to supply any additional material for the option you chose.

The optional plan sheet shows the size and construction of the fuselage for electric equipment but not the installation of any specific motor. As shown, there is ample room for up to 16 cells in the fuselage under the wing. The nose area is large enough for servos, as well as a variety of motors, either direct or reduced drive. In general, the smaller motors, such as a strong 05 to 15, will work best with reducer gears and a folding propellor. The 25 to 40 size will work with either direct drive on a fixed blade or with a reducer gear box and a folding propellor.

This kit can easily be built with any of the new super glues now available. Both the gap filling and quick set types can be used. Epoxy will be needed in the area of the wing joiner tube boxes.

1. Begin stabilizer construction. Build the framework from 1/8 x 1/2 in balsa. Protect the plans with plastic or wax paper and assemble the framework using your favorite super glue.

2. Cut center ribs from 1/8 x 1/4 balsa and notch out for tubes and wires. Glue 3/32 wires in left stab panel and 1/8 tubing in right panel. Set wires and tubes in as an assembly for proper alignment. Don't forget to cut the elevator horn notch in the right stab center rib!

3. Cut 1/8 x 1/8 balsa ribs to length and install. Don't forget the rib in the outer bays that is parallel to the leading edge... "

Supplementary file notes

Review.
Instructions.

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Prophet 941 (oz4098) by Ted Davey 1984 - model pic

Datafile:
  • (oz4098)
    Prophet 941
    by Ted Davey
    from Davey Systems
    1984 
    100in span
    Glider R/C Kit
    clean :)
    all formers complete :)
  • Submitted: 07/03/2013
    Filesize: 1191KB
    Format: • PDFbitmap
    Credit*: eliworm
    Downloads: 3933

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  • Plan File Filesize: 1191KB Filename: Prophet_941_oz4098.pdf
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  • Supplement Filesize: 1433KB Filename: Prophet_941_oz4098_review.pdf
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Notes

* Credit field

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Scaling

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