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The Cost Of Building: Recording The Financial Cost of Building a DB Sport & Scale Skyrider. A Surprise for Miss Blue Eyes.


David Davis
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I have decided to put myself in the position of a modeller returning to the hobby after a break of twenty or thirty years who is unsure as to whether to build a Skyrider or to buy a Speed Air for £263. I'm assuming that he's kept his modelling tools but has no wood, glue, hardware or covering. The engine/electric motor, speed controller, propeller, fuel and radio are not supplied with the Speed Air so those items will need to be added to the cost of building and covering the model.

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The fuselage sides have been built, F2 and F3 formers cut out and glued into position. This morning I fitted the fuselage into my SLEC fuselage jig, glued the sternposts together and sheeted the upper rear fuselage. Incidentally I consider the fuselage jig to be one of the best investments I've ever made. I've never had a banana fuselage since I bought it. I reckon that I have spent about 3.5 hours getting to this stage but I will keep a more accurate record of construction time in the future.

 

To reach this stage the Hypothetical Returner would have needed to buy: 3 sheets of 1/8" balsa, I sheet 1/4" balsa, 1 sheet of 3/8" balsa, 1 sheet 3/32" balsa, a piece of 6mm plywood and a bottle of glue. I am using aliphatic glue throughout unless otherwise stated. He will also need to buy a 3/16" balsa sheet for the nose sheeting. For modellers more used to the Metric System 1/8"=3mm, 1/4"=6mm etc.

 

On the question of which of my two electric motors to use I am in a bit of a dilemna. The prototype weighed 5lbs but apparently 6lbs is an acceptable weight. (That's between 2.3 and 2.7 kgs.) The maximum recommended weight of a model for the AXI 2820/10 is 2.5kgs while the Pro-Tronic 2830 is capable of flying a model weighing 6kgs or 13lbs! I'd hate to overpower it!

 

The advice of electric flight enthusiasts is keenly sought. I am not going to buy a new motor for it! ?

 

Fuselage in jig.JPG

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48 minutes ago, David Davis said:

 

On the question of which of my two electric motors to use I am in a bit of a dilemna. The prototype weighed 5lbs but apparently 6lbs is an acceptable weight. (That's between 2.3 and 2.7 kgs.) The maximum recommended weight of a model for the AXI 2820/10 is 2.5kgs while the Pro-Tronic 2830 is capable of flying a model weighing 6kgs or 13lbs! I'd hate to overpower it!

 

Ignoring the apparent ability to power a 6kg model with 700watts at its disposal, I would go for the Pro-Tronic and prop it to suit the 3s packs which (I think) you will be using.

You'll be looking at around 50A to give you 500+watts, assuming that you're in the 5lbs+ weight range. If it were me, I'd use the 4400's, and/or parallel two 2200's, otherwise your flight times will be pretty short.

Some will say that you need 120 - 150W per lb, but in my experience, for normal 'sport' flying, that's massive overkill. Most of mine fly perfectly happily on 100W per lb or a little less. Depends on your style of flying, I guess, but I tend to use the throttle and use the wing to fly on, rather than the prop (waits to be shot down!!) ?

Kim

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Hi DD,

 

What Kim said!

 

However, using ecalc the Axi on an 11x6 will give you slightly more thrust that weight at 6lbs. So it will fly it no problem. Calculated flight time on a 4500 pack (the software doesn't have a 440 one!) is around 8 minutes, so sounds about right.

 

If you use the DM2830 you'll need a 14x8 prop or thereabouts, but will get a slightly better flight time.

 

Basically, either will work. However, from the ecalc results I would choose the Protronik; less marginal and better efficiency.

 

Graham

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3 hours ago, David Davis said:

The fuselage sides have been built, F2 and F3 formers cut out and glued into position. This morning I fitted the fuselage into my SLEC fuselage jig, glued the sternposts together and sheeted the upper rear fuselage. Incidentally I consider the fuselage jig to be one of the best investments I've ever made. I've never had a banana fuselage since I bought it. I reckon that I have spent about 3.5 hours getting to this stage but I will keep a more accurate record of construction time in the future.

 

To reach this stage the Hypothetical Returner would have needed to buy: 3 sheets of 1/8" balsa, I sheet 1/4" balsa, 1 sheet of 3/8" balsa, 1 sheet 3/32" balsa, a piece of 6mm plywood and a bottle of glue. I am using aliphatic glue throughout unless otherwise stated. He will also need to buy a 3/16" balsa sheet for the nose sheeting. For modellers more used to the Metric System 1/8"=3mm, 1/4"=6mm etc.

 

On the question of which of my two electric motors to use I am in a bit of a dilemna. The prototype weighed 5lbs but apparently 6lbs is an acceptable weight. (That's between 2.3 and 2.7 kgs.) The maximum recommended weight of a model for the AXI 2820/10 is 2.5kgs while the Pro-Tronic 2830 is capable of flying a model weighing 6kgs or 13lbs! I'd hate to overpower it!

 

The advice of electric flight enthusiasts is keenly sought. I am not going to buy a new motor for it! ?

 

Fuselage in jig.JPG

 

I assume we're excluding the cost of the jig as that's 'desirable', not 'essential'? This is an interesting exercise.....

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21 minutes ago, GrumpyGnome said:

 

I assume we're excluding the cost of the jig as that's 'desirable', not 'essential'? This is an interesting exercise.....

 

I think if you include the cost of the jig you would also need to include the cost of all the tools used!  I have an identical fuselage jig. It's beginning to look a bit tatty but I've had it for 20+ years and I wouldn't be without it. I even built a boat hull on it!

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My tongue was firmly in my cheek....... although someone buying an ARTF trainer may well not have access to all the necessary tools - I'm thinking balsa knife for control hinges, and soldering iron for removal of film around tailplane/fin.  I'm getting carried away ? 

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The fuselage under sheeting has been fitted. The next stage is to fit the battery holder. The servos will be monted on a ply-balsa-ply sandwich but I will wait until the last minute to position them in case I have problems with the centre of gravity. It has taken me six hours work to reach this stage.

Fuselage underside sheeting fitted.JPG

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The basic construction of the fuselage is now complete. It appears to be a very sold piece of work like many David Boddington designs. However, I have come across the first problem, sorry "challenge" in management-speak! The Skyrider was designed for a 35-61 two-stroke engine. These engines would have used a 10" or 11" propeller. The model features a tricycle undercarriage but with the 14" propeller recommended for the Pro-Tronic DM 2830 the propeller tips would touch the ground. 2.5" wheels are recommended. I suppose I could increase the wheel size to 3" or 3.5" (7.5-9cms) but anything larger would look silly.

 

The short-kit comes with a number of patterns or templates which are printed onto sticky back paper. The idea is that you remove the backing paper from the pattern and stick it on the wood. In the past I have always used carbon paper to transfer the plan image to the wood, either that or in the case of rectangular formers for example I have simply measured the fuselage and dimensions and drawn a rectangle on the wood. With this model I have used the templates with success.

 

Ayway, on to the tail surfaces!

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As I recall, the DB plan for this shows the engine mounted with a large amount of down thrust. Have you replicated this with your electric motor installation, or gone for something more "normal"? It will be interesting to see how well it flies, with or without the down thrust.

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Paul and Jonathan, thank you for your contributions.

 

The motor is a 660KV motor. I found a stash of electric props in my workshop which I had forgotten about. I found that I had a considerable number of 13 x 7 two bladers which will probably fly the model and some 10 x 7 three bladers. I'd originally cleaned and painted another smaller nose leg before I realised that it would be too short to accomodate a 14 x 8 prop as suggested by Graham Davies. I found a longer, apparently unused nose leg amongst my souvenirs which I have fitted. It would be difficult to remove it now that the motor mounting plate is glued into position.

 

As for downthrust, yes the plan shows a considerable amount of both side and downthrust. Guess I'd better incorporate some into the construction although some with better knowledge of aerodynamics than I claim that it is not necessary on radio controlled models.

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  • 4 weeks later...

As of today £36.36. IIRC all of the wood is priced from the SLEC website and the other parts from Steve Webb.

 

3 off 1/8” sheet   £8.46
2 off 1/4” sheet   £7.68
1 off 3/8” sheet   £5.57
1 off 3/32 sheet   £2.65
1 off 3/16” sheet   £3.50
Wheels   £5.00
Nose leg   £3.50
    £36.36

 

 

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  • 4 weeks later...

I've got to the stage of joining the wings. The plywood joiners / dihedral braces shown on the plan extend out 23 cms to the fourth rib where they terminate in a right angle.

 

Would I be better off tapering the braces to infinity between the third and fourth rib, or cutting a bird's mouth in the last 2 or 3 cms of the braces or doesn't it matter?

 

The wing does seem to be very strong already!

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  • 1 month later...

In early September I received a phone call from my brother-in-law. He told me that my sister, Sue, who had been diagnosed with pancreatic cancer in October 2021, was close to death and that I'd better hurry if I wanted to see her still alive. On 10th September I set off for "home" where I arrived the following afternoon. She was conscious and we were able to hold a brief conversation but I don't think that she recognised me. She was on heavy doses of morphine and she died the following Thursday.

 

Death has been making a rich harvest of my friends and relations during the last six weeks. In early September my step-son, my ex-wife's son not Miss Blue Eyes' lad, died suddenly of an eneurism. He was only fifty-nine. Then while I was in England I heard that a friend who had been the treasurer of the model aeroplane club had been killed when his car fell on top of him while he was replacing the exhaust. Then my elderly aunt died in early October but she had been very ill for months.

 

Naturally all of my aeromodelling activity ceased while all this was happening but I returned to my home in France on 3rd October. I have joined the wing of the Sky Rider. The next stage is to cover the underside of the wing then fit the servos and the upper centre section sheeting. I have only used one dihedral brace as the wing appears to be very strong already. I plan to glass the centre section just to be on the safe side. For the strip ailerons I have recycled the survivors from the crash of SLEC Fun Fly. The signal from the transmitter failed and though the controls went to neutral, the model was in a shallow climb at the time, it stalled and hit the ground wrecking the airframe beyond economical repair.  I've had to cut them down as they were a little too wide but they are also too short so I'll have to scarf in some extra wood.

 

 

Wing fitted (1).JPG

Wing fitted (2).JPG

Fun Fly Apres Maiden. (Small).JPG

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I'm afraid I didn't make a good job of the scarf joints so I've set those pieces a side for another project and cut two 1" strips from some 1/4" sheet. The plan shows 1" x 1/4" TE stock as the ailerons. I have decided simply to round off the trailing edges of the ailerons while planing a bevel on thier leading edges for the hinges, however, if I were to follow the plan exactly I would need to add £6.28 to the cost of the project for two pieces of 1" x 1/4" TE strip! This takes the overall cost so far to £133.04.

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