Thursday, 21 May 2015

Glass Slipper - Fuselage Jig

I have made quite a lot of design progress over the past few weeks. A set of parts has been produced on CAD and sent to Dylan at Lasercraft to make a mini kit for me. This comprises of balsa wing ribs, ply ribs and liteply formers.

So while Dylan does his bit, I have started work on the fuselage jig. I am using DevFus for the fuselage design, the fuselage will be built around a laminated horizontal crutch with the formers slotted into place. The program produce a file for the jig and this is what the jig parts look like.

The output from the application is a file - DXF format - and can be exported for cutting or importing into another CAD system or PDF for viewing. This has been edited to increase the crutch slot size to 3/8" x 1/8" and also enlarge the jig frame slots to fit the 10.5mm square pine that I bought from B&Q.

I have chosen to use jig verticals 1,2,4,6,8 and 10. If I need to add others, I can cut and fit them later.

 An hour or so after marking onto 4mm hard ply and cutting out with a bandsaw.  The T section that the program produces is not required, nor the little triangular notches which simply indicate the former number.

 The lower 'longeron' was nailed - ensuring it was straight - to an old pine shelf (flat). and then marked out for the positions for the verticals. The spacing between the verticals (assuming all 10 are used) is nominally 133mm - there are 9 gaps and the fuselage length is 1200mm long (plus nose block and rudder).

Add the verticals - ensuring that they are vertical and perpendicular to the central longeron and then add the side longerons

I have also added a large ply gusset to make sure the verticals stay vertical and provide extra strength. An excess of glue - this builders ply that I have used doesn't absorb the PVA particularly well

Now waiting for the cut parts to turn up..

Monday, 18 May 2015

Dennis Bryant DHC-1 Chipmunk - Back end

This is my contribution to the RCM&E Mass Build for the Dennis Bryant Chipmunk. Built from the Traplet plan and part kit from about 40 years ago, the plan isn't quite as true to scale as I would have liked.

My build blog is here, but I thought I would put an occasional posting here as well..

This past weekend, I have been working on the tailplane and Rudder. Danny Fenton - a true scale master - has been guiding us through some of the steps needed to produce a realistic looking aeroplane. This is my first attempt at producing anything scale like.

Because all the linkages are hidden, assembly is really quite complex, so a couple of shots to show where I am.

The two linkages - upper rudder, lower elevator are buried in the fuselage under the tailplane and fin
The clevis connects to the tiller arm for the tailwheel, I need to attach the rudder tiller to the same rod.

Broadly, I have used a brass terminal screw block to clamp the rudder tiller. This has a short brass plate with a hole drilled in it The tube supports the axle and arm that drops into a hidden slot in the rudder. The pin protrudes down through the plate and has a soldered washer to retain it.

The tube is now supported by a small strip of lite ply. One problem is that the arms rocks very slightly as the tiller moves in an arc as it is turned from left to right. It moves about 0.5 mm. This is because the tiller lengths for the tailwheel and the rudder are slightly different. However, as you can see, the axle is a sloppy fit in the tube. I am really hoping that I can get away with it...

Now, following Danny's instructions, its time to add some rivets. I have added a couple of strips of vinyl tape to simulate a joint in the metal sub structure and then using small drops of PVA applied with a syringe, I have added a few 'rivets'.

The riveter is a cheap syringe with a little glue and lots of air. Danny uses a little dispending bottle, but my thought was that once I get the pressure right to get a slow but constant flow rate, it should be simple to quickly move from dot to dot adding the rivets. It seemed to work OK.

You can see from this shot they just stand proud..

 When done and allowed to harden ( for a good coupe of hours). the rudder was covered in White Solartex carefully avoiding the rivets as they would flatten under the heat. (in fact I lost 2 in the process)

The next task is to weigh up what order to assemble the rear components, this is far more complex that it looks. I also have to add a carved tailpiece to finish off the rear fuselage. This will totally embed the elevator linkage. However, I cant do any of that until the tailplane and fin detail has been added, so rib tapes and stitching next

This is going to be a long slow build..

Thursday, 14 May 2015

NW Strut - Kenyon Hall Farm

This event is organised by our SCRCS club chairman, Martyn Coles for modellers to attend a nice BBQ and put on an informal evening flying show for members of the Lancashire Aero Club. We are always made very welcome and last night - mainly because the weather was superb, there was a good turn out of models and full size pilots.

 I took along the Gangster, STOL, Flea Fli and Curare. Very nice relaxed evenings flying here. I had a few flights with the Gangster trying out different prop combinations, for some reason its vertical performance isn't as sparkling as it used to be although the engine is certainly still pulling like a train. (12,300rpm on a 11x6 prop - that isn't bad for SC46 on a pipe).

This scale Bell 47 Helicopter was a work of art and flown very realistically

Martyn Coles took some photos and  they have been shared here..

Martyn Coles trying to get his buddy system to work

I used the STOL as a trainer and explained how the system worked to Tim - who was my pupil for the evening. His experience was marred because the ailerons on the Buddy transmitter were reversed - made for an entertaining and at times heart stopping experience.

Starting the OS26FS. The engine is mounted inverted - if it doesn't start straight away it floods quite easily necessitating attempting to start the engine with the model on the side to allow the surplus fuel to drain through the exhaust.

Walking out for the first flight. Tim is attached using the buddy lead umbilical

A better shot of the Bell

Monday, 11 May 2015

UKCAA Retford Fly-in - 10 May 2015

Another great day flying courtesy of Retford MFC.

The best turnout we have had so far with about 25 members present and probably 40 models on show - and mainly flown. There are not many Model Flying Groups that can claim that 50% of the NATIONAL membership were prepared to meet up at a little field on the Nottinghamshire/Lincolnshire border, especially early May, with a decidedly iffy weather forecast. to contend with.

A couple of shots of the event:

The wind strength picked up slightly as the day progressed, probably peaking at about 18-20 knot gusts but the airflow over the field is very smooth with only a little turbulence at ground level due to the upwind boundary hedge, the smaller models struggled a bit, but the larger heavier classics seemed to be almost totally unaffected by it all.

My best days flying this year.

Friday, 8 May 2015

How to build a Contest winning BMFA Dart *

* Note - I haven't actually won a contest with this yet but someone will, one day.

My Model Flying Club - South Cheshire Radio Control Society -  as a challenge for its Fun Fly day has decided to hold a BMFA Dart Challenge. Turn up on the day and (weather permitting), 2 flights and the flyer with the best cumulative score (flight time) will win.

I decided that I would document how to build a Dart with a short photo essay and perhaps a few tweaks here and there to help would be builders.

The kits are available from the BMFA  

Its quickest just to phone them and pay using a debit/credit card

British Model Flying Association
Chacksfield House
31 St Andrews Road
Tel: (+44) 116 2440028
Fax: (+44) 116 2440645

Due to the amount of packing required, its worthwhile rounding up a few friends and placing a bulk order to keep the shipping costs at a sensible price.

So what do you get for £2.00

 A nice sticker, a badge and a kit in a plastic bag. You will also need a building board - mine is pine, but the model could be built on heavy duty cardboard - as long as its flat, a scalpel with a sharp blade or a safety (single sided) razor blade, some glue - PVA is perfect - and - if you carry out my propellor mods, some 20swg piano wire, a 10ba brass nut and washer, small pliers and a pair of wire cutters.

Unpack the kit being careful not to break anything. The kit comprises of a plan, instructions, propeller assembly, a motor stick - pre cut, some lengths of 1/8" x 1/16" balsa and a length of rubber to make up a motor..

Have a look at your balsa, try and identify the pieces that feel the stiffest or are a little heavier - put these aside, we will use them for the wing.

 Pin the plan down, printed side downwards so that you can just read 'PIN DOWN PLAN THIS WAY UP' through the paper. . Use drawing pins in the corners - you don't want it to move..

The first thing to do is slit the plan on the A-A line as shown. The balsa airframe is glued to the plan - this provides the flying surface covering and this bit is under the fuselage while you are assembling the fin.
Mark the motor stick where it crosses line A-A and apply a little PVA glue to the back, making sure it is well smeared - you only need a tiny amount of glue, more will come off on your fingers than is left behind which should only feel slightly tacky.


Pin the motor stick down (the right way up), you need to keep all the parts secure while the glue dries.

The next task is to cut the wood for the fin, simply lay the part over the plan and where it crosses, mark with a scalpel. Don't try and cut through, just mark it by running the blade over where the join will be.

Like this... take the part to a spare part of the board and SLICE the wood in a single cut, don't force the blade through or you will crush the wood

Glue the piece into place, put a blob of glue at the end plus a couple of very small blobs along the underside and smear it down the length. Very little glue is required. Put the part down on the plan and pin into place making sure the joint with the motor stick is sound. Repeat for the next piece

You will need to cut and add a little balsa gusset into the joint at the top of the fin. These are very small and tricky to get right, but persevere, it should be a snug fit requiring very little glue.

Although not shown on the plan, its worthwhile adding an additional gusset at the base of the fin, front and rear, they add a lot of strength for minimal additional weight.

When the glue has dried, use the scalpel to cut all around the fin and lower fuselage up to line A-A. Don't cut off the little triangle of paper at the top of the fin, this gets folded over and reinforces the joint

Cutting along the base of the motor tick to A-A

Fold the little triangle of paper over and glue to the top of the fin

You can now remove the fin and motor stick from the board admire your handiwork..

The wing is built next. From the harder/stiffer wood you put aside above, try and match them in pairs and use the hardest/heaviest wood for the leading (front) edge of the wing. Follow exactly the same procedure that you used to build the fin EXCEPT

Don't glue the joint in the middle of the wing. The spars and cross members are glued to the paper though, just don't glue the central joints yet.

There is one additional cross member on each half of the wing, this does need to be glued into place.

The tailplane is built in the same way. This is a simple triangle shape , don't forget to add the gussets to help support the joints. Definitely the most fiddly task.

The joint at the tailplane tip

When the glue is dry, cut around the wing and tailplane as you did for the fin, its coming along nicely now.

Here is where I differed from the supplied instructions. Dihedral - the wing tips need to be tilted upwards - provides stability to the model. My method of doing this follows fairly normal practice. Cut two strips of wood 2.5" long. These will be used to support the wingtips.

Put glue (fairly liberally) around the two joints at the front and rear of the centre of the wing

Lay out some cling film and pin the centre cross member absolutely flat down, through the film onto the board.

Prop up each wing tip with one of the spacers that you cut, one at each side. Let the glue dry thoroughly - this may take a couple of hours. I also ran a little cyano acrylate (superglue) on top of the paper at each joint and let it soak through. This really needs to set solid before you disturb it.

While the glue is drying and if you feel so inclined, we can start work on improving the propeller assembly. This is a fairly simple shaft drive with the metal arm locating in a spiral notch at the front of the propeller. The problem with this is that it makes a very poor freewheel, when the motor drive stops (runs out of turns), you need a decent free wheel to make the best of the glide. This is my solution to the problem.

First, carefully remove the old shaft, either cut it away or bend the  clutch straight and slide the shaft out. Throw it away.

Using a piece of 20swg piano wire, solder a 10BA nut and washer about 30mm from one end. Make sure that the shaft is cleansed with a bit of sandpaper beforehand - to remove any oil that will prevent the solder from flowing. Use as little solder as possible, we are only trying to locate the nut and stop it from moving

Push the new shaft through the propeller and bend the end over at 90 degrees making sure that there is at least at 3-4mm gap in font of and between the propeller and the nut/washer that you have just soldered into place. The propeller should spin freely

You now need to modify the lock assembly on the propeller to retain the arm. This involves cutting and filing a notch or small slot into the propeller for the drive arm to sit into when its on load. Click on the photo for a large image

Push the shaft through the front bearing. It would be better if you also add a small plastic bead, that sits between the nut and the bearing/shaft. Something I forgot to do.

A loop is then bent into the end of the shaft. This has to be quite tight, but leave the open end like the photo. This will help prevent the motor from creeping off the shaft when its fully wound. You can see why the loop has to be tight - any larger and it would foul the housing assembly.

Glue the tailplane into position making sure that it is at 90 degrees to the fin - i.e. horizontal. Allow the glue to dry

Mark on the front of the motor stick the position of the leading edge of the wing. This should be 1.25" back from the prop shaft bearing,

By now, the wing should be dry. Remove the supports and check that the wing is indeed stiff and will support its own weight. Glue the central cross member to the fuselage, pin it into place and check by eye that the dihedral is equal on both sides.

Nearly finished, just need to add the rear motor peg.

The instructions suggest that a pin is used as the rear peg. I chose to bend this from 20swg piano wire. It gives a larger contact area for the glue and also is slightly larger diameter and that will halp prevent the rubber from being cut by the metal.

Use a pin to make a hole and simply glue the rear peg into place.

That's about it.  Enjoy