Blackridge & District Model Flying Club
Electric flight projects
GAF NOMAD |
The full size
The Nomad was developed in the late 1960's, and the two original prototypes made their first flight on July 23rd, 1971. The Australian Government Aircraft Factories(GAF) are the major producers of aircraft since WWII. This plane was originally designed for the armed forces, but limited military requirements meant that the plane was used for civilian use. The small turbo-powered STOL aircraft was used in hope of some continuity of useful aircraft production. The Nomad has wings braced by a strut on each side and this strut is attached to a smaller wing to allow the use of a main landing gear unit. The main power source is two Allison turboprop engines, each driving a constant-speed propeller with the ability to reverse. Versions of the Nomad have included the initial production N22 with room for up to twelve passengers and had a fuselage length of three ft, four inches. The N24 had its fuselage lengthened to three ft, nine inches and could seat fifteen people. Current versions of this aircraft include the thirteen passenger N22B, and the seventeen seat N24.A twin float N22f was given to the USA in 1979. There is were short fuel military versions which are Mission Master, Search Master and Search Master L. All of these planes are usable for different roles and there are about one hundred thirty nomads in service. About half of these planes are in the use of the military.
Some of the Nomad’s specifications are: It is a type STOL utility aircraft It’s power source is two 298-kW Allison 250-B17N turboprops It’s performance speed is 311km/h. It usually flies at 21,000 feet and has a maximum range of 840 miles. It’s length is 41 feet, its height is 18 feet and its wing area is 324 square feet. Some of its operators include Aeroco, Douglas Airways, Independent Air Transport and Rhine-Air.
The model
Project - 54" wingspan electric powered model for 2 geared speed 400 motors. All foam construction. Std Rx and servos on elevator, ailerons, 40A ESC, 8 cells 2400mAh flight pack.
Having been introduced to the delights of electric flight on the GWS A-10 park flier, something a bit more ambitious was considered for the next E-project. Having a vague memory of seeing (and liking) photos of the GAF Nomad in the distant past, a search of the Internet came up with loads of information and pictures. I was hooked again!!
A plan was duly drawn up for an all foam model with a wing span of 54". Power would be supplied by 2 MFA Rocket speed 400 motors with Mini Olympus 2.5:1 gearboxes turning 8 x 6 APC E propellers. The basic fuselage structure would be from 1/2" and 5/8" Polystyrene foam sheet reinforced by 1" triangular foam strips. Wing, tail, fin would be airfoil sections foam. Covering to be paper and white glue (this was changed and the model(s) have been covered using 25g lightweight fibreglass cloth and resin).
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Plans
for the Nomad on the drawing board |
October 31st 2004......
As a naturally 'heavy' builder (a builder of heavy models that is!!) it seemed like foam was the way to go to get some lightness built in. Having some foam blocks left over from previous wing cutting projects there seemed to be ample material for a set of parts (or 2 sets since 2 models were to be built). A new hot wire cutting bow was made and as the old power supply unit (PSU) had failed, a new one was required. The new power supply was built from a design published in RC Model World July 2004 with all the parts required from Maplins or Rapid Electronics listed by part No. which was very useful. (should anyone plan to build a PSU from this article feel free to contact me, there are 2 major circuit errors which need to be corrected before the power supply will work properly).
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The
new cutting bow and power supply ready to go |
Having sorted the PSU, a jig was made to cut sheets of foam 1/2" thick for fuselage sides and 5/8" thick for fuselage top and bottom. The cutting jig was simply a base (foam in this case) with 2 lengths of 1/2" (or 5/8") hardwood fixed down with double sided tape. A block of foam is laid between the hardwood lengths and the cutting bow drawn over the wood to produce nice flat sheets. As 2 kits of parts were being made it was easier to cut a block to the shape required first then slice it up into sheets afterwards.
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Jig
for cutting foam block into sheets |
It took only a short while to cut the fuselage sides, tops, bottoms and windshield blocks. These were then assembled, glued up with white glue and reinforced with strips of 1" triangular foam. The wing mounting seat was then cut out using the hot wire cutter and templates. Once the wing seat doublers (1/2" x 2" foam sheet) and crosswise strips of 1/2" x 1 1/2" foam were glued in place front and back of the wing seat opening, the fuselage was found to be very strong and light. So far so good.
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The fuselage assembled and
glued |
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Foam
wing and fin in preparation |
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Veneered foam wing version
'kit of parts' |
January 1st 2005 .....
Parts for two Nomad models have been made, one being built by myself and one by fellow Club Member Johnny Mackie with both models progressing well. Fuselage parts and wings have been cut and assembled and both sets of parts have now almost finished the glassing stage. The resin, lightweight fibreglass cloth and accessories were supplied by FibreTech in the UK (http://www.fibretechgb.co.uk) and have proved to be excellent products. This was my first attempt at glassing a model but after a few handy tips from Johnny the results are quite pleasing and add significant strength to the model for little extra weight.
The wings are cut from white foam, one set veneered, the other set with spars reinforced with carbon tows and a 2mm ply dihedral brace. Both wings are covered in 25g lightweight glass fibre cloth applied with resin as per Fibretech recommendations then given a further coat of resin. Very strong. The motors / gearboxes are mounted on liteply plates/bearers which are then epoxied into cutouts on the underside of the wing.
The full size Nomad has a small winglet supporting two undercarriage 'pods', one on each side of the fuselage. As the models will have no undercarriage, the blue foam pods will be glass clothed and given an extra coat of resin to resist landing damage.
January 19th 2005
Some initial tests have been done with the Astro Super Whatt Meter (An excellent tool for setting up motor/battery/prop combinations, available at the present time from West London Models for £49.99).
Tests were done using the fitted MFA 400 motors with Mini Olympus 2.5:1 gearing. A freshly charged 8 cell (9.6v) 3000 mAh flight pack was used with measurements taken at full power (full throttle?). First model is 90% complete and expected weight will be around the 4lb mark.
These results indicate that the Nomad should have enough power with either prop size. A Watt per lb ratio of 40 or up should provide a 'sports' level of performance which is fine for this type of model.
With a wing area of 366 sq inches and a projected weight of 4lbs, wing loading will be around 25 Oz/sq ft which means it won't be a 'floater'.
That's how it looks on paper, we shall see how it turns out!
January 26th 2005
Nomad #1 more or less completed. Motor nacelles were made using slices of blue foam fixed with white glue and sanded to shape. Radio gear installed is standard Sanwa receiver and servos.
BEC function on the Kontronics 40A speed controller was disabled by removing the power (middle) pin on the ESC receiver plug. This wire was taped back to the main cable so the BEC function can be enabled again if required in the future. A small 250 mAh 4.8v receiver battery was fitted to replace the BEC (this battery failed during pre-test flight checks and was replaced by a std 500mAh receiver battery, contributing to poor first flight). See test flight section below.
Paint finish is simply Dulux satin emulsion painted on. Crude but effective although a sprayed finish would have been more refined and saved some weight. Trim details were made from Solartrim and vinyl graphics sheet. De-icing boots and windscreen painted on with black enamel. Hatch for flight pack can be seen in the pic below.
Final weight came out spot on estimate at 4lbs exactly. Weight without flight pack is 2lbs 12 oz. Kan 8 cell, 3000 mAh flight pack weighs 1lb 4 oz!! Wish li-poly packs were a bit less expensive!
Apart from minor items still to do (like make a cooling slot and exit for the flight pack, very important), this model is ready to go when the weather is suitable.
With the fairly high wing loading, first flights will be on a breezy day and with a hefty chuck to get it off. Johnny keeps going to the pub to 'practice his arm movements' ready for the big day. Not sure I believe that!
Model #2 is well under way and hopefully will be ready to fly in the not too distant future.
May 22nd 2005
Model #2 completed and first test flights of both models flown this week.
Model #2 (Johnny's red and white version) flies great. Powered by a 7 cell 1700mAh NiCad flight pack, 8 x 6 APC E props fitted and weighing 3.5 lbs (1.59 kg) model flies well with C of G at just over 25%. With the small wing area model needs to be built light and at 3.5 lbs flight is very scale like. The 2 geared MFA Rocket 400 motors make a nice sound during low fly pasts.
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Well done Johnny, nice one.
Model #1 (mine) has a few problems to get sorted before flying as well as #2 model. From a hand launch, model struggled to gain height and was landed (landed itself really!).
Model weighs 4lbs (1.8 kg), has the same MFA geared 400 motors fitted but with 9 x 6 E props. This model is a bit too heavy so some weight savings will be made by replacing standard servos and receiver with micro ones and eliminating full size receiver NiCad (will use BEC). 9 x 6 props will be replaced by 8 x 6 APC E ones.
This setup works for Johnny's model so expect flight characteristics to be similar when these changes have been made.
June 8th 2005
Weight of model #1 was reduced by 3oz by fitting micro servos, chucking out 250mAh Rx NiCad (turned out to be faulty anyway) and removing some heavy 4mm silicon cable by shortening leads. Std size Rx left in place. BEC on ESC was reconnected.
9 X 6 props changed to 8 x 6 APC-E ones (this made the biggest difference to flying performance).
Fitted with 7 cell 3300mAh battery pack model flew great with no major trim adjustments. Plenty of power and handled the windy conditions with no problems. Both models are now flying well and will cruise on around 2/3rds power (throttle?).
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Summary..
Motors
Duration of flights so far (7 for model #2 and 2 for model #1) has been around 3 - 4 minutes, always landing well before Low Voltage motor shut-off cuts in and with plenty of power left. Both models sound great in flight with the twin geared motors sounding just like miniature turbo-prop engines.
Project has now been completed successfully with some interesting new construction techniques learned (usually the hard way!).
Happy days!
Feel free to contact as below with any queries or for any additional information required.
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