CHRISTCHURCH AND DISTRICT MODEL FLYING CLUB

BMFA affiliation no. 2581

THE BLUEBIRD GROUP - INFORMATION EXCHANGE

Initial Review (edited) by Terry Antell

J Perkins distributes the BLUEBIRD. It’s a R/E electric assist thermal glider. It comes with all parts completely finished, this includes elevator hinging done and fixed, along with the clevises and the motor, prop and prop adaptor are supplied and already fitted. You will need a battery pack, 2 servos, an RX and an SC.

Just fit 2 standard size servos, hook up to the already installed push rods and she’s ready. Oh yes, glue the two halves of the V tail together then fix with the 2 bolts supplied.  You may need to relieve the channels in the V Tail blocks - see Martin’s piece below.

The dihedral didn’t look enough to me. I was proved right. The turn rate was too sluggish for my liking, making the landing a little uncomfortable. The wing had 4” under one wing tip with the other one laying flat on the ground. I made up another wing joiner, this time with 6” under one wing. An improvement, but still not wonderful. I again bent the joiner, this time having 8” under one wing. Marvellous, much more control and she makes lovely thermal type turns.

With a one minute climb, using the motor at max throttle, she’ll glide for around 6 minutes in still air. Now use your skill to increase this.

I have used my Watt Meter, the results are as follows using the 7 cell 1700mah pack.

Fully charged pack = 9.3 volts (8.4 nominal). The results, with the motor at full bore were. 28 amps and using 184 watts. All this with the standard 8”x 4” folding prop supplied. So, buy a 40amp ESC (for brushed type motor remember.)

Comments by Martin Burr

   I have competed my Bluebird, as yet unflown, and here are a few things I noticed; The prop holding nut was loose on mine. The push rods fouled the tail mounting block a bit too easily on full up travel, so I removed a bit of wood from the area. The plastic wing holding bolts were a bit long and were too close to the push rods, so I shortened them a bit to stop them touching, and when I put the battery in using the velcro strap it came off! So I re-attached it using the servo holding screws. Other than that the "build" was a doddle, the C of G coming out about right with no lead needed. The only puzzling things are the Aluminium tiplets, not mentioned anywhere, and as originally there is no wing dihedral I suppose they are to aid turning. I am going to try mine with and without to see what difference they make. Thats all for now .. TTFN Martin

First Flight by Martin Burr

Thought you might like to know I have finally given my Bluebird its maiden flight after what seems like ages of crap weather! It pulled up radically with power on, in its initial climb with the Ruddervator surfaces set flat, the CoG was set at 33% of the wing chord as suggested. After I put in lots of down trim it behaved OK. Also I had too much control surface movement, but I have now reduced it to 12mm up and down which may still be a bit much, we will see. My dihedral is approx 6inches under one wing tip, Derrick tells me his is more like 9 inches ( or is he just bragging). Mine seems to steer OK, but a slalom will not be in its reportoire! Anyway I have attached a pic (on the header page - Ed), taken at Barton by my wife, of the plane on landing approach, what a nice sunset too. All the best for Xmas and the New Year, Martin.

“But” by Dave Enticott

But the rest of us still have to get thr best out of this beast - 3 hits and the problems are not yet finished! Today (24/12) after a good landing, I found BOTH ele/rud horns sheared!! This was exactly in the same place - obviously a result of the low (1C) ambient temperature. Be warned! or, better still change the unit - BUT is this still within the ONE DESIGN rules? - (Yes - Ed) Dave. 

By Martyn Pressnell

May I offer a small contribution on this topic with some observations on the model so far. I took it from its box over the New Year and commenced fitting out. My first impression was that this is quite a well constructed ARTF model, with one or two surprises. The angle section hardwood main-spar can be seen at the root rib. I have not previously had a model with an all-plastic moulded fuselage, preferring the more expensive GRP type. There is no local reinforcing in vulnerable places but this could be added. At £70 this model is a real bargain providing it flies well, and I see no reason why it should not perform.

It is absolutely essential to shorten the wing attachment screws, thanks to Martin for pointing this out with other helpful hints. I added a reinforcing plate on top, joining the wings and secured by these screws, it can be aluminium alloy or plywood. In my kit I found that the ends of the push rods had been bent up in the same plane, this simply does not fit. However it was possible to twist the elevator end by about 45 degrees to put this right.

The motor installation incorporates a plywood disk fitted directly in front of the motor. This carries a packer intended to impart right/down thrust. The mounting screws passing through holes in the plastic nose are vulnerable to a frontal impact on the spinner which would push back the nose. The best solution is probably to make a larger plywood disc fitted to the front of the fuselage. I settled for simply aralditing the disk provided to the inside. It is essential to orientate the packer correctly, this could require alteration after flight tests are carried out.

The metal wing tips are not mentioned in the instructions and it is difficult to see that they can give any improvement, they seem potentially very dangerous to me. Are we contravening the rules by leaving them off, or can we agree to omit them? The way in which wing tip devices are intended to work is by taking energy out of the tip vortices and feeding this back as thrust. In other words they are anti-drag devices. Unfortunately on the Bluebird this will not happen, because the tip fins are fitted to highly raked wing tips. This will strengthen the tip vortex, the opposite to the effect required.

The control system used depends upon the transmitter and equipment available. It is necessary to mix the rudder and elevator controls for this V-tailed aircraft. This can easily be achieved with a mechanical or an electronic mixer installed in the aircraft, enabling a simple non-computer transmitter to work. A minor disadvantage of the electronic mixer is that it may give 50% authority to each control, resulting in too much elevator travel or not enough rudder travel.

If you happen to use Mode I, mixing can be achieved with the V-tail mixer provided within computer transmitters. If you are using Mode II, this mix will not work because your rudder effect is achieved by plugging into the aileron channel. However the elevon mixer, normally intended for flying wings, will solve the problem. This has the advantage of leaving the free mixers available for other purposes, such as introducing corrective elevator under power. In my model the mixing is achieved by using two free mixers but this might change in the light of flying experience with the model.

Comments on the question of dihedral and aspect ratio I will leave for the moment, again flying will reveal all. Winds are gusting to more than 80 mph along the South Coast today, so it could be some time before I venture out of doors.

I've been doing a charge /discharge series of runs on my 4/5 Overlander Nicad battery and the max capacity (discharged down to 7v) that I can get is 1430mah which is quite a bit below its rated capacity of 1700mah.I was wondering if anyone else using these batteries has done a similar check and if so, what results they got. Maybe I have a duff one.

Cheers Ken Spokes

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