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

[David Davis]

I decided to modify the wing retention system from elastic bands to a dowel and bolt system, pictures below. It only took a couple of hours this morning to get to this stage. I plan to use the front dowel to retain the rear of the battery hatch.

 

There are still a few wrinkles to remove from the covering of the port wingtip, hence the excess covering in the first picture.

 

I have found three wheels among my souvenirs, two of which match! They are slightly smaller than the recommended wheel size, 2.25" as opposed to 2.5" but they'll probably be alright. We have a tarmac runway at our club. I had two nice old Graupner wheels of the correct size but their hubs were cracked so I threw them away. I think that Miss Blue Eyes' Sky Rider deserves some nice looking wheels! New wheels from Steve Webb cost between £5 and £9 a pair but you'd need to buy two pairs, call that £14 for the wheels.

 

Jobs still to do:

1. Cover the upper surface of the wing.
2. Make battery hatch and cover in pink film.
3. Fit canopy latch to the front of the canopy hatch.
4. Make the ailerons, cover, hinge and fit pushrods.
5. Hinge the rudder.
6. Install and connect the rudder and elevator servos.
7. Fit wheels to u/c.

Totaal cost of the build to date: £147.04

 

That'll do for now. I'm going flying!

[David Davis]

Some progress has been made. I've completed the first three tasks listed above except that I have mislaid the canopy latch! The battery hatch is temporarily retained by a small screw locating into a snake inner. I have found the Hobby King film more difficult to use than either Profilm/Oracover or Solarfilm but as most people seem to get on with it well I must be doing something wrong! I was unable to get out all of the wrinkles in the purple ection of the port wing tip. I may cut that section away and try again.

[GrumpyGnome]

Looks a gois job!

[David Davis]

I fitted the wheels yesterday, threw a couple of standard size servos and a 3300 3s LiPo into the model and weighed it. I was delighted to find out that the model weighed 10 ozs less than I was expecting.

 

Note for electric flight enthusiasts. Do I have to build a cradle for the LiPo or may I use velcro to attach the LiPo to the bottom of the fuselage?

[Graham Davies 3]

I've done both David. I prefer a cradle, or at least a platform and use a little bit of velcro to prevent it sliding about, and a velcro strap to keep it in contact. I find that to be practical at the field.

 

I have velcro'd to the fus floor if it's sturdy enough, but it can be hard to get your fingers under the battery.

 

Graham

[David Davis]

Thank you Graham, I'll get on with building a tray.

 

Talking of Lipos I have become friends with a Belgian bloke called Frans. Frans was having difficulties with a four channel ARTF trainer so I suggested he build a three channel vintage model: he wanted to learn how to build anyway. He bought an Electric Junior 60 kit, not our first choice but Colin Buckle was recuperating from an operation and had limited stock at the time. Frans is almost at the stage of being able to fly without me on the master transmitter but when he tried to take off with the J60 he lost control of the model and damaged it. Once he'd repaired it he gave it to me to fly. I'd always told whoever would listen that if the day ever dawned when I couldn't fly a J60, I'd give up the hobby! The model was bound to my transmitter, checked over and range tested. It took off. All went well initially but then the model became very unstable and was performing all sorts of gyrations while I was chasing it on the transmitter. I got it down to a hard landing which resulted in further minor damage.

 

It was only when we had it back in my workshop that the reason for the instability became clear. In repairing the model Frans had built a horizontal box to house the LiPo but it was much larger than the LiPo with nothing to retain the battery. In flight, as soon as the nose pointed downwards the LiPo moved forwards causing the model to dive. Naturally, I hauled on the elevator stick and the model went into a steep climb forcing me to put in full down elevator! Ever tried to fly a model with a moveable cg?

 

Fortunately we have now mounted the LiPo vertically and all is well. Frans is currently building a Radio Queen, so is another member of the club. Picture of the three culprits below!

[Richard Acland]

It can be a bit of a shock when it is all added up. There are two ways of looking at it. If you build an ARTF the cost of the model is a lump sum and a large outlay in a lot of cases. An equivalent sized model built from plans can cost just as  much, maybe more but is usually spread over a longer period buying parts as you go along.

Having built several models over many years I have accumulated many items "in stock"  so the main outlay is in wood. If I total the cost of items I have used at the end of the build it is still a lot of money.

[David Davis]

8 hours ago, Richard Acland said:

It can be a bit of a shock when it is all added up. There are two ways of looking at it. If you build an ARTF the cost of the model is a lump sum and a large outlay in a lot of cases. An equivalent sized model built from plans can cost just as  much, maybe more but is usually spread over a longer period buying parts as you go along.

Having built several models over many years I have accumulated many items "in stock"  so the main outlay is in wood. If I total the cost of items I have used at the end of the build it is still a lot of money.

 

It looks like the cost  of building this model will be in the region of £160 which is £100 cheaper than buying a ARTF Speed Air. Of course it hasn't cost me that much all at one go because I had stocks of balsa wood, glues and other materals before I even started the project. It would have been cheaper still if I hadn't had to buy pink and purple covering material to please Miss Blue Eyes!

[David Davis 2]

A quick question to all of you electric flight afficiandos. Is it alright to epoxy the speed controller to the inside of the fuselage? Space is a bit tight in the Sky Rider's tank bay.

[Nigel R]

I've mostly used tie wraps to keep them in place. Slightly less permanent than epoxy. If you glue it in I guarantee it will go wrong!

 

You could epoxy or glue in one or two of these widgets for a proper job

 

https://www.ebay.co.uk/itm/203773678057

 

That said, why not put the ESC in the cowling area with the motor? My favourite method is to put the motor on 1" long standoffs (threaded studding usually) and tuck the ESC in the gap right behind it.

 

Or mount it underneath the fuselage, out in the breeze?

[Ron Gray]

If I can fit them in cowl tie wrapped to stand offs or engine box then I’ll do that but in the fuselage as long as they can’t flop about (strain on wires) and as long as they have air for cooling then I tend not to anchor them in place.

[Nick Cripps]

Velcro!

[David Davis 2]

Here it is gentlemen, resplendent in Miss Blue Eyes' chosen colour scheme. Started on 23rd June and finished on 23rd November! If we allow £30 for the glues, pushrods, clevises, hinges and horns, the total cost of the build is £163.04. This is about £30 less than an ARTF WOT 4 and nearly £100 cheaper than a Speedair. Of course, it's taken me six months to build it so that has to be taken into account. I could have built it more quickly if family obligations had not interrupted the building process. I was also building another model at the same time as this one, something which I will not do again.

 

With a 3000 mAh battery in the nose it weighs 4lbs 9 ozs and balances on the marked cg. I hope to maiden it tomorrow depending upon the weather. I've flown three different types of WOT 4, my favourite is the ARTF, and if this model flies as well as one of those I will not be disappointed.

 

Graphics by Pyramid Models. Pin striping from white Solartrim.

 

 

 

Edited November 23, 2022 by David Davis 2

[Nigel R]

Nice job DD

 

AUW sounds good, should go nicely 👍

 

17 hours ago, David Davis 2 said:

total cost of the build is £163.04.

 

I've very unsurprised 😉

 

[David Davis 2]

1 hour ago, Nigel R said:

😊Nice job DD

 

AUW sounds good, should go nicely 👍

 

 

I've very unsurprised 😉

 

 

You can knock £5 off that price as I've just realised that I've counted the cost of the wheels twice!

 

I won't be flying it today because I haven't been able to programme my Spektrum DX9 transmitter in time. Oh for the good old Futaba Golds! 😊

[David Davis]

I find myself in need of the advice of electric flight enthusiasts again.

 

I have just connected my old analogue ammeter to the motor, a Protronic 2830 600KV turning a 13 x 8 APC propeller and powered by a 25C 3000 3s LiPo. I obtained a reading of 25 amps. According to my Grade 6 O Level Maths if the voltage is 11.1 volts then the system is producing, if that's the correct word, 277.5 Watts. Dividing 277.5 by 4.6 which is the weight of the model in pounds produces a figure of just over 60 watts per lb.

 

This is vintage model standard isn't it? Will the Sky Rider fly at 60 watts per lb or do I need to invest in a larger prop?

 

I have a "Turnigy High Precision Watt Meter and Power Analyser" but I've never soldered the connectors to it being more of an i/c engine man myself. Perhaps I should do this in order to get a more accurate reading.

 

At least I now know that I can replace the existing 90 Amp speed controller with a physically smaller 45 Amp speed controller. This will make the installation of the LiPo easier.

 

I hope to fly her tomorrow. 

 

 The views of the cognoscenti are, as always, keenly sought.                                 

[leccyflyer]

The voltage of your battery when charged for flight, will be closer to 12.6v than to 11.1v at least at the beginning of the flight - you should recalculate the watts per pound using that voltage - so 25amps at 12.6v =315watts, so around 68w/lb. For a vintage model  that ought to allow a pootle round the sky but she won;t be overpowered.

 

Definitely get some connectors on the wattmeter and that will allow you to experiment with props, motors and batteries to achieve an optimal performance.

[David Davis]

Thank you leccyflyer but the Sky Rider is an advanced trainer not a vintage model. I'll fit connectors to the watmeter when time permits later today.

[leccyflyer]

For a trainer you should probably be aiming for better than 75w/lb maybe up to about 100w/lb. That said, my Modelshack Cricket, which is a similar advanced trainer, flies beautifully on 300watts. I don;t recall the exact weight off the top of my head, but she must be around 4lbs or so. The Cricket has an Emax 2820/7, 3s1p3000mah Tipple Lipo and an 11x6" Graupner folding prop for about 300watts. Plenty of power for a trainer.

 

[Nigel R]

2 hours ago, David Davis said:

Perhaps I should do this in order to get a more accurate reading.

 

Well worth doing. Sticking with 3S, I'd guess a 13x9 (or even 13x10) would bump the power closer to what you're after. The wattmeter is the weapon of choice for finding out.

 

[Mike Blandford]

When I was flying with NiMh batteries and brushed motors, 50W/Lb was more than adequate for reasonable flight, and the motor was much less efficient.

I'd agree the battery voltage would have been more than 11.1V, I see at least 11.6V at 25A after 1 minute of flight on my flight logs, so 11.8 off a full charge would be my guess.

This is about 300W, and the Ammeter will be dropping a small voltage as well.

I reckon it should fly OK. It won't be fast, a 600kv (looks to be 660kv from my search for the motor) motor on 3S won't give a large RPM.

The motor appears to be rated at a max. of 55A, so running at 25A is very conservative. Personally, for 660kv, I'd be looking at using 4 cells and a smaller prop (11x6ish).

 

Mike

[David Davis]

My battery reads 12.3  volts fully charged so I should be getting about 67 watts per lb. We'll see how it goes tomorrow.

[leccyflyer]

Do you mean 12.3v under load? Off load a fully charged 3s1p Lipo should read 12.6v = 4.20v per cell.

[David Davis]

1 hour ago, leccyflyer said:

Do you mean 12.3v under load? Off load a fully charged 3s1p Lipo should read 12.6v = 4.20v per cell.

 

The battery was not absolutely fully charged. I had been using it for the measurements and to ensure correct prop rotation when I changed the ESC.

 

What sort of flight times should I expect from my 3000mAh LiPo? 

[leccyflyer]

Something like 6-7 minutes for a fully charged 3s1p 3000mah lipo, if you are most at high throttle setting, with that sort of current draw. You'll be able to gauge it better once you've flown, measured the voltage and recharged, so that you can see how much of the capacity you have used for the flight.