Tuesday, 31 March 2015

Post NPOD Repairs

As I mentioned, I had a pretty bad day at the NPOD. Two flights and two broken models, breaking one model is rare, two is pretty unforgivable.

One thing I never do anymore is rush into a repair. Carefully collect all the parts making sure that you are not aggravating the damage and put it aside for at least overnight. Things (nearly) always look better after a sleep.

Groovy 50

This was actually worse. My initial assessment was that the firewall had simply come unglued down one side of the fuselage, the undercarriage was bent and I had a broken wheel.

 After removing the tank, engine and engine mount, it was clear that the firewall had broken away at both sides, the reinforcement pieces were shattered and the LH Fuselage side had crumpled between the front two formers.

To repair this, the fuselage side had a piece if 1/16" ply inserted to reinforce the side (full depth), and all reinforcement pieces were carefully removed using a scalpel. New triangle pieces were cut and the whole lot glued and clamped and Araldited (Slow Set) into place. At this point it was noted that the Firewall had a crack in it, so the whole lot was ripped out again before the glue hardened and a new Firewall constructed using 6mm ply (the original was 4mm).

All clamped up again and allowed to dry overnight.

A final clean up is required to remove one or two rough edges. That left hand edge now looks somewhat neater but you can se the 1/16" ply doubler that has been fitted.

Because the former was slightly thicker, the engine mount is now 2mm further forward which meant that the cowl needle valve access point needed moving slightly as well

It now became a simple matter of bolting everything back in again ensuring that the thrust line hadn't changed (too much). I suspect some minor changes will be required after the first test flights though
The undercarriage (aluminium) was simply folded back to the correct shape. The cowl had also been damaged when the undercarriage folded - the two additional cracks were simply epoxy patched on the inside. A couple of evenings work and it seems ready to fly again.

Gangster 63

This had a very clear break just behind the cockpit. I remember when I built it that I considered this to be the weak point in the design. However, repairs were really quite easy

First thing is to jig the fuselage so that it is straight and glue the remaining parts together so that  there is sufficient hold while proper repairs are carried out.

Repairs basically comprised of adding large 3/16" balsa gussets at each break - 8 in total were added. As very light wood was used, this will have very little impact on the CG position.

With the covering stripped away, you can see where the fuselage has been butt join repaired

The Gussets were added just behind the wing inside the fuselage sides: There are also two more above this from the upper longerons, the lower point of the far one is just visible above the lower gusset

Two more at the top just behind the cockpit. Note the stepped sheet cross piece. The original design had no cross sheeting, this was a change that I made to add a little extra stiffness. The cross sheeting is fitted all the way back to the tailplane

Two more large gussets added under the fuselage behind the wing mounting bolts. Note the overlap direction. I think this provides a better glue contact and also a better load line.

Finally recovered and it looks almost like new

I am not expecting any significant trim changes as a result of this repair, time will tell though.

Monday, 23 March 2015

Skelbrooke NPOD

Organised by Bob Rowland on behalf of the GBR/CAA this was meant to be a gathering of 12 club fliers (of mixed abilities) as students and 3 top class FAI flyers as mentors. In the end, only 10 club flyers turned up, but it looked like it was going to be a great day.

Weather conditions were very cold and quite windy, approximately 10mph in the lulls and gusting to 20mph at the peak.

The strip is quite exposed so the weather conditions really rammed home.

The format of the day is that each club pilot would be assigned to a tutor. The tutor would then get the student to fly the clubman's schedule and provide guidance on positioning etc.

The schedule is as follows:

  • Rectangular Take Off
  • 2 Inside Loops
  • Immelman turn
  • 1 Outside loop
  • Split S
  • Cuban 8 with no rolls
  • Stall turn
  • Slow Roll
  • 1/2 square loop with roll on exit
  • 2 turn spin
  • Rectangular Approach and Landing

With the exception of the Cuban 8 - no rolls, I had done all these manoeuvres before.

I took the Groovy and as a reserve the Gangster. I didn't really expect to use them both.

A few photos from the day:

Matt Hoyland's exquisite Citrin. This is what a £4000++ airframe looks like..

Gerard's Monolog

My little Groovy - looked very small compared with the other airframes around

Sebart Angel


Axiome 70

Axiome 70
So, as I was flying i.c. powered (noise restriction on site), I was last to go and was mentored by Matt Hoyland - you probably couldn't get a better pilot as a mentor.
It was clear from take off that the little Groovy was struggling, it was struggling to make any headway and was being buffeted about a lot. It definitely felt and looked underpowered.
Matt was quite patient with me but for some reason, the engine died at 8 minutes into the flight while only about 50 feet up and the rush to get back to the strip resulted in a heavy landing which cracked the engine firewall and bent the undercarriage. Investigation showed that I had run out of fuel - I normally get a comfortable 12 minutes per tankful.
So that was my first flight gone. I prepped the Gangster and waited my turn for the second flight.
This was better although I was still struggling with the conditions. I lost count of the number of stall turns I attempted, I kept losing the baseline after the recovery, I think I was following the box line back. The result - again, I ran out of fuel again - about 30 seconds before the alarm triggered. The dead stick approach landed about 15m short of the strip - in the adjacent field and I managed to find the only rock  around. The result - a broken fuselage and then end of my days flying.
During the lunch break, Matt demonstrated just how the Clubman schedule should be flown. Absolutely amazing to watch, a standard to aim for.
The afternoon session was for a contest and the 9 remaining flyers battled it out flying the schedule over 3 rounds. I used my time as a scribe and it was very interesting to see how the flights were scored, in my humble opinion some were a little generous, others a little tough.
However, I learnt a lot, I need to do a lot more practicing in adverse condition and get that Groovy engine sorted out

Thursday, 19 March 2015

Hanno Prettner Magic - Part 3

A bit of progress in the past few days. The Magic is taking precedence now - mainly because I am using my large Building board and there isn't as much space available.

The retracts have been added - and as a bonus, here is a little video coz I know you all like them.. I have added 1/16" soft balsa infill around the retract mount to give the sheeting something to stick to.

Quite pleased with that nerd the retracts and wheels are fully retracted and out of the draught when retracted.
The hinge for the flap. I actually made a small mistake with the hinge line, it should be 3mm higher - I have located it centrally. I may cut them out and redo them, I'll weigh it up.
The angled wing tip was a bit more tricky than I thought it would be. Getting all the spars cut to length and at the right angle was a bit difficult. When I got round to doing the other tip last night it was much easier - lessons learned and all that... There will also be a 1/16" ply facing which will go on after the wing has been sheeted.
Although not shown on the plan, I have added 1/16" balsa webbing down the length of the wing. This adds a lot of strength and my flying is definitely not as good as Hanno's so I think I will need all the strength I can get.
The false LE and TE have been sanded to the correct profile, this wing is now ready to be joined to the other half when completed then sheet covered.
Repeat for the other wing - but with far less textual information. Just remember to make one of each side..

Anyway *some* progress - not much though..

Aileron mounting rails. I wanted to mount the servos from underneath (like I did on the flea fli) - However, the depth of the servo is 3mm too much - never mind. The balsa sheet bracing is in place because there isn't much wood under the bearer.


Working on the wing. The Other wing half has been skeletally completed.
Time to join the two halves
I am adamant that this wing will be straight so that when I set the dihederal, I propped both wing tips up using these little jigs under the last rib. This will ensure that both wings will be identical (warp wise)


Joining up the centre section was fairly easy. As both panels were propped up it was simply a case of sanging the LE, TE and spars so that everything touched where it should. Building on the plan ensured that I had the correct LE sweepback


All clamped up while the glue dries...
Now. the plan shows that the panels are joined using 10mm balsa across the centre bays only. I am decidedly unhappy about that and elected for a tapered 1/4" spruce spar across the 4 centre bays - top and bottom. To compensate for the dihederal, the upper brace is inlaid by an additional 1.5 mm at the centre and the lower has the extremities tapered. This looks much more rugged, but I would welcome advice on whether it will be strong enough..


Another shot.


This shows the amount of tapering required on the lower brace - more than the upper brace because the wing is tapered.


And after it has been planed and sanded to shape.


Adding the lower skins. Cut as per the plan using 3/32" balsa sheet - not especially good quality although it looked OK when I did the cutting. The U/C holes are a bit on the small side. I'll open them up after the upper sheeting has been done.


Note the holes for the Servos. I am putting Tower Pro MG996 servos in for the ailerons.
I have got a bit further than this, the other panel has also been sheeted (lower surface) and the servo mount for the flap servo has been added.


I have followed BEB's lead and brought the five servos to a HD15 pin D socket and plug. I have to admit that I am not really happy with this and may move to a similar solution that Martin McIntosh used on his P51. The only reason I am unhappy is that the wires were too big for the solder buckets so I am not getting maximum strength from the joint. I don't think they will fail though..


The socket is mounted on a liteply plate and is deliberately placed at the fuselage side so that there is space for the plug to fit alongside the fuel tank.


A switch has been fitted for the retract power - a NiMh 4 cell battery which will be located in the wing root. This is sat next to the Flap servo


With the servos fitted and wired (and TESTED!) I have laid up the sheet for the upper skins. I am using slightly harder wood than I used underneath.


Adding the skin. I have used PVA to glue the skin down. The multitude of weights scattered around help ensure good adhesive contact. Just how many objects can you get on a wing before it gets totally crushed.


With the skins in place and trimmed back, the LE is glued in, stripped from 3/8" balsa sheet


Slot cut out for the battery and lots of elastic bands pulling the LE in place.


Upper view of the wing, LE has now been trimmed and sanded and the wing is almost ready for glassing.


Lower view. The wheel bays have now been sheeted, but my circular wheel orifices are definitely not circular. Its amazing how a mm or so of deviation is so obvious when it is meant to be circular. The wheels are a very close fit, less than 1mm in places - other places its a bit more... blush


Finally for now, the upper centre section. I'll use velcro to keep the battery in place and a bit of filler is needed but apart from that I think it looks quite neat. Note - you wont get a close up of the wheel bays... nerd

Next job is apply the ply wing tip caps and the bits of TE that are not flaps and ailerons, then glass it.

Hanno Prettner Magic - Part 2

The cowling. Before I can fit the upper deck, I need to get the cowl fitted.

To get rid of the run marks and the air bubbles, I have sanded down the cowling using 80 grit sand paper. The cowl was measured for height from the prop driver to the Firewall and cut and filed down to size. the holes for the prop driver, cylinder head and needle vale removed and a test spinner (not the final one) fitted to check alignment. Note also the test fit of the first of the two decks that I made.


An underside view. I have to admit that I am really quite pleased with this. nerd There is a very slight gap at the join with the fuselage sides, but nothing a tiny bit of filler wont cure.

Installation of the pipe. I made a clip for the rear end of the pipe to hold it in place - I'll probably replace this with a spring clip at the centre of the pipe later.

I have added 8 hardwood mounting blocks and a hard 1/8" square balsa flange to support the sides of the decking. After a bit of consideration, I have decided to use the second of the tunnels/decks that I made and started trimming and sanding it down to fit.

A bit overexposed in the bright sunshine yesterday afternoon. but you can see the air intake for the cooling air above the cowl - I still need to make the outlets..

The fit at the rear of the fuselage. Again a couple of minor gaps that need help with a bit of filler. I am still sanding down the decking to remove the blimps caused by the problems removing the first of the two decks that I made..

Apart from giving the cowl and the tunnel a couple of coats of primer I have done very little on the Magic. I ordered the wing ribs from Belair and they arrived last Thursday. The Flea-Fli was cleared off the bench and work has now started on the wing.
This very much a 'Metric' model - none of the standard wood sizes have been anglicised so I have to make a couple of compromises. It is amazing though - just how difficult it is to get a 1/4" wide spar into a 6mm slot..
Spars. The spars are listed as 6x8 mm and made from balsa. I originally was going to go for 1/4 x 3/8 spruce (planed down a bit) but then decided to settle for 1/4 square balsa with a 1/4 x 1/16 spruce cap. So the first job was to laminate the spars.


(Look a bit warped but they really are straight - just a distortion of the wide angle lens)
This is just marginally less than 8mm but adding the spruce cap adds a huge amount of strength for very little additional weight.
Pin down the upper spar (wing is being built upside down) and a quick push together to make sure everything fitted.

Next step - mark out the slots for the retract bearers, cut 1/8 ply doublers and get them glued up.


Cut the ribs back where the flaps will be located.


All the slots etc. were marked and cut using a square over the board and drawing verticals from that point. The excess was cut using a razor saw.


False leading edge glued in... The u/c bearers have also been added as well. One problem I have spotted is that the U/C pivot point is about 8mm inbound from the point shown on the plan. Which means the wheel well will also have to be moved in a bit.


Finally, the upper spar and false TE have also been added. I am using Kevlar cloth (again) for the hinges and laminated the false TE/hinge block as described in the Flea Fli build.