WOTSIT - 4 scratch build

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WOTSIT - 4 scratch build

Post by Graham » Thu Feb 13, 2014 10:40 pm

It goes back almost 6 years, just before I retired and moved to Chesterfield. On my last flight at our High Wycombe site my Black Horse Tornado came in to land and the front wheel hit the only cow hoof hole on the landing strip. The result was a somersault and a broken back. The wing got pierced and the rest was scrap value.

Moving on 6 years, while up in the attic, I came across the Tornado wing in a carrying bag. I decided to make some use of it and try and build something around it. I knew that as it was being built I was going to get the question, 'What is it?' Hence the name, 'It's a WOTSIT - 4'. Now I can base it on whatever design may work. I am no expert flyer or model maker however, I know what I want and, with a lot of help from experienced members I hope to build something that will fly.

One of the main criteria is that it must be very strong so that when it hits the ground hard, and it will, it will not break into little bits. It must also be around the weight of the original Black Horse Tornado, which was 2,700 grams. The cost of the total build must not exceed £80, not counting the bits and bobs I already have. The bits I have are:
1 x ASP 61 4 Stroke engine and silencer
I x carbon undercarriage with 75mm wheels
1 x Spektrum AR500 Receiver
2 x 2.4m lengths of 95mm x 6mm plastic fascia with foam interior bonded

As luck would have it I have just finished putting up a false UPVC ceiling in the dining room and had 2 lengths of 2.4m x 95mm x 6mm plastic fascia left over. It is quite lightweight and strong so I thought it would make a good solid body. With the weather being so bad and with no where to go and nothing much to do it seemed the ideal time to start the project.

1. Firstly I trawled the internet to find and download the Instruction Manual for the Black Horse Tornado. I did this so I had some sort of guideline to go on. Then I downloaded several pictures of models of a similar size and shape, one of them being the Excel 2000. I studied them all and decided to base the size on the Black Horse Tornado and the design on the Excel 2000. I also decided it will be a tail dragger and not a tricycle wheel assembly. As the fascia was 95mm wide I would be making the fuselage 95mm deep instead of the 113mm of the Excel 2000. This is all theoretical until the day it is sent into the air but hey, it is only time and £80.

I cut the basic shape of the body. I make a jig of the wing shape and copied it to the side of the body, cutting it out with a jigsaw and sanding smooth...

2. I glued the three parts together with 2 part epoxy. When this was dry I ran a bead of Dow Corning Aquarium Sealant down all the joints. This should stop any joints breaking apart. It's normal use is to hold glass together up the 10mm thick and it holds tons of water with a small bead so it should easily hold a plane together.

3. The Black Horse Tornado wing got damaged during the crash 6 years ago, I shall do a quick repair job shortly just to keep it all together. Wonderful stuff that Duck Tape you know.

4. The body was left in the house overnight to harden off. In the morning the wing was mounted on the body to see if it looked OK. A few minor filings here and there and it fitted a treat.

5. The engine that is going to be fitted in WOTSIT is an ASP 61 4 Stroke. More than enough power for the estimated 2700 grams anticipated.

6. You may have noticed, as I did that the nose section looked awfully long and too far in front of the wing leading edge...so I shortened it. I also lowered it, making a slight slope from the leading edge. This is now the same basic shape as the Excel 2000.

Yesterday I searched the internet for all of the bits I was likely to need in the near future. I ordered a 10oz fuel tank (just to give me plenty of time to have the bottle to land it, lol), fuel pipe, fuel pipe clips, hinges, wing bolts, plastic bolts for the undercarriage, tail wheel assembly, propeller, control horns, 2 x control snakes, push rod connectors and spinner. No doubt I will have forgotten some items but I will get them when needed. Incredibly they arrived less than 24 hours after I ordered them from Riverside Models in Norfolk.

7. The next job I did was to put in body strengtheners inside, cut the top body section behind the wing to the tail, build the tail fin and cut out the top body section to take the tail fin.

8. Cutting the slots for the hinges was going to be difficult, so I thought because of the fact it was solid plastic on the edges and dense foam in between. I got around this by using a small angle bracket held in a pair of pliers. I heated the bracket up with a blow-lamp until it was almost red hot and then rested it on the edge of the material. It literally sank itself into the material effortlessly and I had melted them all out in under an hour. Crude but it worked.

9. The alignment of the tail fin was checked, though not set in at this point.

10. Next, the tail wing and elevators were made and the hinges glued in with epoxy to both the tail fin and the elevators. I have run out of the UPVC fascia board so was unable to make the rudder fin. I am sure I will come across something one day soon

11. The control horns and control snakes were fitted to the elevators. I drilled out 3mm holes down the centre of the fusleage to thread it through to the front.

12. Fitting the engine mount should have been a straight forward affair....if the body had not parted from the mounting plate. The 2 part epoxy had failed to hold the two parts together and had parted company with the plastic sides. I contacted the company in Barnsley where I bought it from and asked what they use to stick one to another. They said they were not designed to be joined in that way and they used NoNails purely to grip to a wall. They are not designed to withstand any flexing or vibration under stress, so it was back to the drawing board. I got around it by making a 12mm multiply face, glued and screwed to 9mm square hardwood. It was then epoxy'd and screwed in the original place where the plastic had broken away from. It looks a good solid fit. I mounted the engine mount so that the carburettor will be in line with the top of the internal fuel tank.

13. I had a carbon undercarriage, complete with wheels so fitted this next. A 6mm ply plate was made for the inside and 6mm plastic bolts fitted with spiked bolts. The rear tail dragger wheel assembly was fitted however, it not yet complete as I need to get a colett to fit to the shaft to stop it dropping out.

14. The all illusive tail fin came to light. In the back of the shed I found a piece of plastic fibre board, something I bought from the Cooperative Store in Chesterfield when they were closing down. I was an old advertising board which I knew would come in handy one day. I tried to fit the hinges by slicing the board however, as it was only 3mm thick ir did not work very well. So I decided to cut them in, put a 2ba bolt through each of the htree of them and glue them in with epoxy. They are going nowhere.

15. Time to take stock of where we are and lay it out to see what it will look like when finished. I was a bit disappointed when I weighed it in as the finished product is going to be 2900 grams, 200 grams more than I had anticipated. Hope it flies OK and not like a brick. Still a lot to do yet:
Fitting servo tray, servos and radio gear, fixing tail, body top and fin, make mounting blocks for front and rear of main wing. fit engine and fuel lines, make Cof G 110mm behind wing leading edge. All for another day.


Last edited by Graham on Sat Mar 01, 2014 5:44 pm, edited 1 time in total.

David Cowley

Re: WOTSIT scratch build

Post by David Cowley » Tue Feb 18, 2014 7:21 pm

Hi Graham

This I have to see fly, name the day and I will be there, looks good to me.

David C


Re: WOTSIT scratch build

Post by Graham » Tue Feb 25, 2014 8:56 pm

16. Rear tail wheel fitted. Although the bracket is fitted it cannot be completed until I get a retaining collet from the model during the first week of March.

17. Hole drilled for engine throttle cable and engine mounting bracket made.

18. Made the lug retainer for the wings, though I am not keen on this idea. I may make a solid block type that is attached to the wing later down the line.

19. Rudder snake fitted and attached.

20. Snakes for elevators fitted and jointing block made so they operate together from one servo. Still waiting for them to come from China.


Re: WOTSIT scratch build

Post by Graham » Wed Feb 26, 2014 5:44 pm

21. Never did like the two lugs holding the wing on the front so changed it for something more solid. Yes true, if it hits the deck there is more than 2 lugs to break away but....what the heck.

22. Fuel tank fitted, wedged in with foam and a holding block. Fuel pipes connected to tank and holes drilled in front fuselage to take them to where they need to go.

23. Fuel pipes fitted to carburetor and exhaust. Filler pipe bedded into side of fuselage just above the inlet level.


Re: WOTSIT scratch build

Post by Graham » Fri Feb 28, 2014 2:58 pm

Just waiting around now for the Futaba S3003 servos to turn up from China. At £9.52 for 4 including postage it is worth waiting for.
In the meantime I have put in the weight where it is likely to be and used the Club's CofG calculator. Brilliant programme, taking all the guessing out of the game. When the original plane that the wings belonged to was in one piece the CofG was 110 mm behind the LE with a tricycle undercarriage. The new model, being a tail dragger, the calculation states it is now 227 mm behind the LE.

Final weights and measurements
Length = 136 cm
Wingspan = 148 cm

Engine = ASP61 4 stroke
Fuel Tank = 12oz
Receiver = Spektrum AR500
Servos = 3 x Futaba S3003
2 x Tower 9g in wings

Tail weight = 900 gms
Port wheel weight = 1300 grms
S'Bd wheel weight = 1300 grms
Total weigh = 3500 grams (oops)
Calculated CofG = 22.74 cm behind LE
Actual CofG = 22.74 cm behind LE

Still a few bits to buy yet such as snake for throttle, 2 x Y leads, Switch harness, battery holder for 4 x AA 2900ma for receiver.
Still within the £80 budget first set....just!!

In theory it should fly, subject to all the other things I will not yet have thought of or adjusted, such as Motor location and angle, angle of attack, etc, etc.


Re: WOTSIT - 4 scratch build

Post by Graham » Sat Mar 01, 2014 6:22 pm

Still kicking my heels waiting for the servos, etc. I decided to cover it...in Fablon and some of my wife's card making stick-ons. Well, even it does not fly it will certainly look the part on the field. :lol:
I have also ordered a new receiver from HobbyKing which includes a 3-Axis stabiliser, which will give it a more of a sporting chance of staying in the air while it is trimmed. Also give a little extra peace of mind when I am flying....just in case!
How it will look at the flying field
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Re: WOTSIT - 4 scratch build

Post by Colin » Sun Mar 02, 2014 5:15 pm

well it certainly looks like a ... wotsit? :D


Re: WOTSIT - 4 scratch build

Post by Bowdd » Mon Mar 03, 2014 9:59 am


This is absolutely brilliant, it does not seem 5 mins since you showed us the facia material and now it's a plane!

Well done

David Bowdler


Re: WOTSIT - 4 scratch build

Post by Graham » Tue Mar 11, 2014 10:14 pm

Well, it was almost complete. All good things must come to an end and we are now back a few spaces. In fact we are back by about 50%.

I was concerned that the online calculations of CofG were too good to be true. My concerns were confirmed by our resident builder David Jnr, who said the figures were wrong and gave me the proper way of measuring CofG. This new way seemed to indicate the CofG was over 4 inches too far back, saying that it should roughly be one third of the way back from the leading edge. Even half a house brick on the engine did nothing to alleviate the problem so, I took it to our indoor meeting to ask for help from the professional builders, including David Jnr.

The situation was indeed drastic. The material was too heavy for the distance between the wing and the tail. After much discussion it was suggested that initially the way forward was to:
* Take 8 inches off the length from the tail end and move the tail and fin forward
* Drill circular holes in the fuselage between the tail end and the rear of the wing on all four sides
* Drill circular holes in the tail and fin
* Cover the holes with Fablon strip, sealing with a heat gun
* If possible, move the wing back approx. 4 inches
* Move the undercarriage forward to just behind the engine.

The CofG certainly seems to have moved forward substantially just by shortening and cutting out the holes. I have yet to cut the wing in further back, set the tail and fin in at the right angle, etc, etc.

So it was off home and 'let the proceedings begin' here we are 24 hours later.
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Re: WOTSIT - 4 scratch build

Post by Graham » Wed Mar 12, 2014 7:24 pm

After cutting the holes out I put the wing on, loaded all the bits on and balanced it. The Cof G was still too far back so, today I moved the wing back three inches. Bingo, the Cof G is now around a quarter of the way back from the leading edge so I will continue building it back up.
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