Back to the beginning: Project Tiger Cub Story part 8

Making and fitting some new bits

Some of the bonding of the foam panels to the longerons is not so good, due mainly I think. to clumsy handling over the years as the bits lay uncared for in the hangar at North Coates. Still that is a simple enough repair with a bit of care.

A trial fit of the rear cockpit section, now bolted together again, to the rear fuselage, is now due. After a lot of careful jiggling about of the clumsy components all the bracket angles are correct and the alignments right she slides together. Probably the first time in more than 20yrs most of the fuselage stands as one unit, really satisfying.
I finish that evening with a big grin on my face.

Then I fall into temptation. What I should be doing is trial fitting the fuel tank and incorporating a fuel drain as the original totally lacked one and I am almost paranoid about clean fuel. I guess I spent too long working in and around working fishing boats also I still need those seat belt measurements.. That was what I should be doing, instead I was unable to resist making up the two replacement tubes for the front cockpit section. My only excuse being that after all the dismantling checking, filling repairing and reassembling I wanted to MAKE something. I had four that were bent, damaged or otherwise unsuitable, no shortage of patterns then. Careful checks showed that, as with all the rest of the tube work they were jig made and identical. I removed the nylon inserts that I would need from damaged tubes and cut the sleeves that fit over the inboard ends of the tubes. I then carefully marked one end of each tube with centre marks top and bottom and the top of the far end of the tube. I then measured along the tube and marked the distance from the inboard end to the bolt hole for the forward bulkhead. Setting up my laser line and level gadget to give a nice clear red line centre to centre and marked the intermediate hole position with it’s centre line. Turning the tube around I marked the bottom of the tube and turning it over I then marked the bottom intermediate and extended inboard end marks beyond the length of the sleeve. Next job was to drive the centre nylon insert into position using a drift marked with the position of the insert as obtained from my patens. The end insert was then tapped into position and the sleeve glued on with epoxy. So far so good

Next thing was set the new tubes into position to ensure that my marking out was accurate. This would mean putting together the front section of the cockpit framing including the engine bulkhead. There was one tube that would not be put in place at this stage. On this tube I had to make up a throttle quadrant as the original double lever unit incorporating a choke lever needed to be changed to conform with a mandatory mod. This had come about because the double unit had  identical levers side by side. no unreasonably the powers that be decided that this was not a good idea. However the mod notification included a drawing of the replacement, so that’s another little job. Making up a spacer so that this tube could go in later I pressed on. Only to encounter another little problem, this time one of my own making. The diagonal tubes that run that run from the cockpit frame to the top of the engine bulkhead could not depress far enough. they being prevented by bolts below the top mounting brackets, some clot had put them in the wrong way around. Damn, to turn them I’d have to remove the top fore and aft tubes of the rear cockpit frame. Oh well, on with the motley, has anyone got a use for secondhand Nyloc nuts? When that is done and the tube work and bulkhead assembled I shine a torch into the bracket holes and the cockpit end and my little cross marks show nicely centered. My mood restored I slip the tubes out and drill them. Replacing them I check the forward holes and my little crosses are again just where I want them. All my pedantic measuring and aligning paid off, good stuff.

Now I ought to start getting my mods sorted with drawings, photos and calculations. As one of my main ideas is to re route the seat harness to save my spine I need to make sure that my proposed route will not foul the fuel tank or control runs. In order to sort this I’ll need to fit the tank. To do that I’ll have to offer everything up to see just how Jim Romain did it.

Back to the beginning: Project Tiger Cub Story part 7

Bent and cracked metalwork

So, on a raw autumnal morning I went back to my workshop for more than a fleeting visit. I was horrified by the clutter that had somehow gathered. I can’t work like that so it had to be sorted and sorted properly. First, the Saxon Micro drip trays just needing painting finished. That done and stowed in the shed I have a bit more room. Next, the replacement wheels for DF now just waiting for the paperwork to be labeled and stored on the right place. Then a general clean. Magic, ready to start, fire up the laptop to check with the workbook and reread the appropriate section of the Kit Build Instructions and study the drawings, it is starting to feel familiar again.

Logical order suggests that first the cockpit frame uprights to have all their plates and brackets fitted, then make up the fore and aft sub frames then join these together to form the cockpit frame. From there connect up to the engine bulkhead and the pile of tube starts to resemble part of an aeroplane again.

With so many types of plates and brackets I check the drawings in the book, read the labels that I attached when I removed them, that seems a long time ago, and lay them out on the bench. When I am happy that I know exactly where everything goes I loose fit it to check alignments, then using my supply of new nuts and bolts  making sure of a good layer of Duralac where needed.

I feel a great satisfaction as a recognizable component arises out of the stacks of labeled bits.

It is also about time that I started replacing the rejected tubes and brackets.

Firstly tube, I have two damaged forward tubes, bent by the nose wheel installation and two of the main uprights to the cockpit section have damage to the sides as if a wire or something similar had been crushed against them. Ok that is the main reason that I acquired kit 208. I am disappointed to find one of the forward tubes is not straight either but the other one and the two uprights look good. This is now a well organized process. Firstly strip off all the plates and brackets and roll it on a flat surface to check it is straight and check that all the anti-crush inserts are in place. Next a good clean down and check any marks with the trusty magnifying glass. This shows a slight deformity beside one of the holes on my last remaining forward tube, Damn. Then the messy rigmarole of the penitrant dye testing to the uprights. Messy but satisfying when as this time the developer shows a pristine white surface

So now I need a length of tube, more tube to make sleeves from and some channel and angle to make brackets from. I remember last year a mention on the BMAA web site of a metals company offering a discount to members. That seems the right place to try first. So I call them  up, friendly sounding guy on the other end has not heard of a BMAA discount but he will ring back in a about half an hour. Two hours later, no call, I ring back. Still sounding friendly he explains that he needs to speak to the States and they are not available for another hour, apologies, will ring back in less than two hours. Three hours later I ring again, he hasn’t found the channel but will ring back shortly. Next morning I ring again, he is still having trouble with the channel but can at least confirm that he is now aware of the discount offer. Leave me your e-mail address, he says, and I’ll send you a quote within threequarters of an hour. Two days later no mail, sod it, if he can’t be arsed why the hell didn’t he say so. Ah well, there are others including my old friends at Light Aero as they are now the agents for Aircraft Spruce also of high repute. So I sit down and dispatch a flurry of e-mails asking for quotes to all those that I’ve got addresses for, maybe that’ll do some good. No response to any of the e-mails, this is getting to be a pain. However after a phone call to Light Aero all is again right with the world. As helpful as ever, they track down what I need and are a bit concerned that they can’t get it to me before Christmas. It’ll have to come from America he says apologetically, but it won’t be long after the holiday. That’ll be fine I say magnanimously, it is, after all 21 December. What a damn good company.

While I await delivery of my new tube and bits I can start a bit of reassembly. First thing is to use the brackets and bits already sorted to put together the rear cockpit section. The uprights come first, then put together the torque tube and pushrod assembly. With this fitted to it’s bearings on the crosstubes I can put together the front and rear sub- assemblies. As the rear cockpit section is where the seat is mounted. When this is in one piece I can temporarily attach it to the rear fuselage giving me all the dimensions I need for the seat harness mod. Before this can happen I need to offer up the rear sub assembly to align the rear fuselage attachment brackets as the lower ones are set 45degrees to the uprights. Getting them close is easy, but things are as they should be and there is no slack in any of the bolt holes the last bit is a bit more tricky. The back of the hole being inaccessible it seems the old torch and mirror trick is the only way.

Another thing I acquired about this time was another set of main wheels, ex Pegasus as fitted to Quantums and AX2000s. Neat units, compared to the original which where the plastic wheelbarrow wheels so beloved of early microlights.

As these where innocent of any bearings I’ve always cringed a bit when looking at them. The Peggy wheels are the same diameter and same weight  but narrower, Ahh, my mantra, less drag, and fitted with bearings. They can even be fitted with brakes, but brakes are for fairies and nosewheel pilots, they are also extra weight.

Wheelbarrow wheels first, another mod for later, although it is very tempting to get side tracked

Early in January my package from Light Aero, or LAS as they now like to refer to themselves, arrives. As I have come to expect from them everything is there and 100% correct. Also the paperwork that accompanies the delivery is the kind of thing that Tec Office goes to bed dreaming about. As good as always, thanks guys. When I’ve opened the package I check that the tube that sleeves two of the others fits, and it does, perfectly. I feel a very strong urge to start making the brackets ect. Discipline prevails  and I regretfully tuck it away until the right time in the build sequence

It’s time to start checking the rear fuselage and it’s not a good start when one of the attachment brackets turns out to have an elongated hole. Sod it! still kit 208 comes to rescue again and that bracket checks out ok. The elevator push rod comes next and that also is fine, then the rear aluminium bulkhead.

This is a bit more complex, with its edges pressed over to just a bit less that 90% to the main plate, attached brackets for the longeron ends and attachment holes for the rudder post. The only way that I can think of for this is carefully, a bit at a time.

After spending most of a day checking bends, corners holes and rivets it all proves to be in good shape Whew.

Back to the beginning: Project Tiger Cub Story part 6

Dreaming up some improvements

Next came a bit of a rethink, I’m looking at so many mods that this job could take forever. Maybe it would be better to take it a bit at a time instead of trying to bury Tec office in paper I’ll do it in stages and sneak up on them. The first thing to consider seems to be which of the mods is best built in when the aircraft is reassembled and which can be readily altered or added later? OK

(1) Engine cooling, as built the Cub had a large hole though the firewall, This allowed access to the recoil starter which filled the hole. An early mandatory required the removal of the recoil starter as the engine mounts were fixed to this and the starter casing proved unequal to the task. After cracking was found the engine mounting was modified which involved the discarding of the starter and it’s housing. This of course moved the engine much closer to the firewall. Engine cooling at this stage was still fine until another mandatory mod to restore the integrity of the firewall insisted the  hole was covered by a plate. Whoops, nowhere for the hot air to go. Right what was needed was another mandatory mod to turn the cylinder heads to an angle to improve the flow. Most Cub owners also fitted a duct from the firewall plate and out though the floor and that mostly does work. I wanted to experiment with fitting a scoop to act as a sort of venturi to improve the airflow from the rear cylinder. That I think can go on the to be done later list.

(2) Seat Belt mod. As the present layout for the shoulder straps makes me shudder when I think about the effect of an accident on my spine. The reason for this is also in the chequered past of Cub mods. The tank was first mounted clear of the fuselage to the rear cockpit sub frame at about pilots head level. Although this had advantages, it was removable for filling and was clear of the blue foam that forms the structure between the longerons (petrol has the nasty habit of dissolving blue foam) it was possible for it to blank the tail surfaces .So It had to be moved. The U section channel that the tank was supported on also act as the anchor point for the shoulder harness so, of course this moved also. The mod involves lowering the tank so that it is within the fuselage taking with it the harness anchor point. This made the harness ideal for compressing the spine in the event of even a minor prang. I was not happy with that as I have no ambition to learn how to drive a wheelchair. The mod that I want in place  involves running a cable from the aft bulkhead though the rear fuselage and adding a raised section to accommodate the strap attachment at the correct level. I hope that I can make that resemble the elegant hump that the SE5 sported. I guess thats one for the initial build list

(3) Tank Mod. As I said before I have two Cubs and only one Cub Tank the other one having ended up fitted to a Rans at North Coates. I do however have a 25ltr Thruster tank and this is a superior item in every way and that is the one I prefer to fit in the first build. This will mean making a mounting system that will withstand 6G when full and as it is aft of the C of G the weight will need to be carefully monitored. Alternatively I can redesign the fuel pipe system to fit a drain valve at the lowest point. That’ll do the job, even if it isn’t such a neat solution. No mod required for that, so my first build will go that way.

(4) Undercarriage. As I mentioned before I intend to revert to a tailwheel undercarriage because it’s lighter, tougher and creates less drag and besides it looks a hell of a lot better.

I also intend to have the main wheels strut braced like the main wheels of the nose wheel undercarriage. As this is effectively a new layout it will require rigorous testing. I do have a set of the standard wire braced main gear from SU.

So I think that I’ll fit this initially thus just reverting to standard Cub undercarriage, no mod needed. I can develop the strut braced version later.

(5)  Streamlining. All those round struts. They are everywhere, wing struts, cockpit struts, undercarriage struts and they are all round factually and figuratively. the drag must be horrendous. Weight of course could be an issue but I’d have to dismantle most of the aircraft to fit them later. So, one more for the initial build list

(6) Clear vision panel…

Whilst the view from a Cub is pretty good for a Bi Plane you just can’t have too good a view so I’d like to make a centre section with a large clear panel though it. That will give me a better chance of spotting those Class A pilots that spend too much time playing with the toys on their instrument  panels and not enough time looking out.

There does appear to be increasing numbers of these. As I have two centre sections I can work on this and add it later. One more for the deferred list.

So, lets see, that’s two mods to be incorporated in the initial build and three to be developed later. That should make life bit easier.

So from these first two a logical order appears. Number one assemble the cockpit sub frame and fit seat. Next make the tank mounting and fit to sub frame. Fit tank and straps check clearance from seat. Offer up to rear fuselage and check clearance from control runs. Load test tank and mountings. Photograph, prepare drawings and write out mod submission.

Number Two, while front and rear fuselage sections are together determine height needed for shoulder strap attachment. Ensure wire from rear bulkhead can reach this without interfering with any of the control runs. When sure that it will work buy the new harness. Then when work to the tank is completed run the wire make the.” hump” from ply and lath ( shades of a Hurricane) or to make something from blue foam which may be lighter. Then as before with photos, drawings and writing.

Number Three, The streamlining. First look into the weights of the materials available, alloy, glassfibre or maybe even carbon fibre. submit mod as before. Fit to tubes on final assembly. Simple innit (OH Yeah)

Just in case there is any problem with runs of the harness rudder cables I’ll fit the tank mount for testing purposes to the cockpit framing from kit 208  from the Cub that was never completed. So taking them out of store I put them together, now with parts to be included in the build and parts that won’t be both in the workshop I must continue to be meticulous in my labelling and stowage. It is both satisfying and exciting to watch the first bits really taking shape .To satisfy my curiosity I try fitting parts from SP, SU and KM to the structure of kit 208 and they all fit. Obviously jig made, but as SP and SU were quite early in the production of the kits and KM and 208 were quite late it does wonders for the confidence.

Then before offering up I need to place the elevator control rod in place in the rear fuselage section . Then I need to run two strings to follow the course of rudder cables to ensure that there no danger of anything chafing or obstructing.

Having got this far life got in the way. The runway at Sheepcoates Farm was now operational so there was grass to cut and roll, huts to build and decking and slabs to lay.
Also the need to fly, preferably DF. Hell that is so close to addiction, almost like being a druggie.

So poor SP once again in her life was neglected. This time it was only for 4 months but on my visits to the workshop once or twice a week to turn over the engines I felt very guilty until the great day I could go back to restart work.

Back to the beginning: Project Tiger Cub Story part 5

Getting under the skin and having some ideas

Having satisfied myself with the filling and glue work to the wings they now hang them back on the wall and await Gary’s verdict. Then  will be another new experience, that of working with Ceconite. this will be possible without further mods as Jim Romain had already done this for SP with one of his mods changing from the original Tigertex.

Stripping the aileron: Now I have to cut the old fabric from the lower ailerons to see what lurks beneath. On SP these are extended to the full span on the lower wings and linked to an aileron fitted to the upper wing.

As the standard Tiger Cub had the shorter lower ones only, I really look forward to flying this little beast with the extended aileron area and the fin and rudder instead of the all flying rudder and no fixed surface. I have a copy of the test flight report and it sounds fun

As I clear away the old fabric I can see a large alloy plate bonded to both sides of the blue foam that forms the infill between the ply ribs and bolted though to hold the bracket for the rod that connects the two ailerons. The bonding of the foam to the ply ribs and the trailing edge strip is in good shape, there is a bit of damage to the edges of the foam but less than I have already sorted on the wings.

Of course this will take time but considering the length of time the poor little thing spent in its dismantled state being moved around the odd corners of the hangars at North Coates with bits being borrowed for other jobs it is really not too bad.

Then a minor success with my control column assembly. My elevator push rod is sorted. After many hours of rolling a emery tipped dowel between my hands and a final lapping in with an abrasive polish she ran sweetly. I temporarily rig the control column just to feel the whole assembly gliding smoothly though its bearings, great.

Satisfied at last with the state of the lower ailerons I hang them on the wall to await Gary’s verdict and turn my attention to the short wide cord upper ones. After removing the Ceconite the underlying foam was in fair nick with only limited damage and most importantly the glue joints were all in good shape. I couldn’t ask for much better than that. As these where parts designed and made only for the Romain modifications I made sketches in my note book to show the construction and dimensions. These could be useful later as when I rebuild KM as I plan to build her as a Romain modified aircraft as well.

As I am just finishing the last of the crack testing it is time to assess what I actually need to replace rejected components. This will be a few lengths of alloy tube and some channel for making brackets. I also better check with Gary that my understanding of the grades required is right

Also it’s time I get ready to submit to mods that I feel will improve this great little aircraft into an even better one. First I want to revert to a tailwheel undercarriage. There are several reasons for this. Firstly it is stronger, both the tubes that carried to nose wheel where no longer straight and I need to replace both of them. I was far from happy with the way that they were mounted on to those tubes. So I was unsure that they would stand up to farm strip usage. Secondly the drag from such a large pertrubance added to the not inconsiderable drag of a biplane, that  I felt that I could do without. Next was the old enemy of all microlighters, weight. A rough estimate the nose wheel gave me about 2kg right up front. This with its counterbalancing lead on the rear bulkhead. I would be happy to lose both of these. Trouble was that I was far from delighted with the main undercarriage of the original tailwheel design. This was a simple tube extending vertically down from the bottom of the front cockpit sub frame each side. This carried the axle with cross bracing wires and was also wire braced fore and aft. While this was certainly light, I did not feel that it was convincingly strong. The Romain mod for the main wheels was tube braced from both front and rear cockpit sub frames looked good but of course was too far aft for my purposes. So I  thought, a combination of the two. I’ll retain the original vertical tube with axle and cross bracing wires. Then along the lines of the Romain mod use tube bracing to the rear sub frame. That would act in both expansion and compression, using a wire brace to the front would provide good triangulation. Strong and light, I’ll draw it up and see what Tec Office thinks.

The second mod that I would like in place early was to the fuel tank and its mounting. As I had two aeroplanes and only one Tiger Cub fuel tank. I wanted to use the 25ltr Thruster tank that I had bought. This was a nicely made alloy tank but one of the best features for me was that it had a sump in the bottom unlike the original. As a guy who owned boats for a long while I get a bit sensitive about water in fuel. To put this together I will need load calculations to prove to tank mounting up to 6G. Not being very clever, my maths will not handle that.  I’ll have to reassemble the rear cockpit sub frame. then the mounting will need to be made and loaded with weight equivalent to a 6G load on a full tank. Then I will need weigh all the bits and calculate the effect on the weight and balance.

All good stuff, but  I’ll be flying it at least the object is to keep me alive, I’ll drink to that.

 The other mods that I have in mind involve the seat harness and streamlining the struts. The first one to avoid compressing the spine in the event of a crack up. The second because I can’t believe the amount of round struts in the design but I can imagine the drag that they cause. I believe that if I can pull it off this will be a fantastic little aeroplane, maybe the kind of thing that Tom Watson hoped for when he did the first design sketches all those years ago.

Everything so far had  been going well, slowly but well. Then I had a clever idea. It was a fiddly job cleaning and going though all the stages of spraying the unpleasant chemicals needed for the crack testing process. This was made worse by the large number of little brackets that hold the tube work together. So I made up a board where that they could all be suspended so that they could cleaned sprayed and developed with minimal handling. Not a bad idea, not put into practice well though. I forgot just how well penitrant  dye spreads. Most of my careful little labels were now illegible, bugger. It was a good job that I’d been methodical. Some time spent checking the workbook and using diagrams and drawings of bracket profiles in the Kit Build Instructions that I’d got from the Newark Museum recovered the situation. I might feel a bit of a clot, but there was no harm done and I’d learned a bit more.

Then I receive a message from Gary telling me the properties of the types of tubing that I had inquired about and saying the type used in her construction should be as in the Kit Build Instructions. So I read those with great care, nope, not there. Next I went though the Maintenance Manual and the Pilot and Operators Handbook, no luck. I then resorted to reading all the mod forms that used tubing, not there. The only thing left was the bulletins and letters from MBA to the builders of the various aircraft that I had acquired parts of, not there either, Damn. It is beginning to look as if I’ll be pestering Guy and the Tec Office. I know that they are always busy so I’ll try Gary with what I have. That is just a description, high tensile thin walled corrosion resistant alloy tube. O yes, says Gary brightly, that is HT30TF and the Plates will be HE30TF. Great, at last, but hang about, I’ve never heard mention of this stuff before. Not in any of the stuff that I’ve read up or, more worryingly, in any of the suppliers catalogues. I tell Gary this and tentatively suggest that it seems most builds seem to use 6061T6. That’ll do the job he says, the old HT30TF was good stuff in it’s day, but things have moved on since then. Talk about going round the houses to arrive back at the obvious. Still never mind it’s now sorted.

We did fly this summer

but not that much. The weather was sometimes flyable at the same time as we were available to fly though often that was just scratching a short local flight under grey cloud. Hedy only managed two landings away from base airfield. One was a flight to the museum at Stowe Maries Great War Aerodrome, where we sampled their marvellous home-made cake. The other was to a fly-in event at Rougham aerodrome.

Hedy takes off