After cleaning and checking the undercarriage legs I notice a difference between the later ones that came with Kit SU208 and the ones supplied with GMJSU (Kit SO175).
While both are fitted with the nylon anti crush insert at the top the earlier legs are single tube at the lower end the later ones are doubled by having another tube inside for the area though which the plates that form the attachment to the axle. Sure enough there is a small damaged area to the lower ends of the earlier legs. I am a bit puzzled by this until I notice that the end of the doubled units are not cut straight as are the older ones but are eased to prevent contact with the axle itself. While they don’t actually touch in either case they are very close on the straight cut tubes. So it would seem that under landing loads it is possible for them to come in contact in the older model. As the legs are angled up to the attachment point this would place them in bending rather than as designed having the load though the two bolts that are in shear and from them straight up the tubes to the main front fuselage framing. It’s bit like a detective story piecing together the development although sometimes it feels almost a form of witchcraft. Well it seem like it at times as I shuffle my Tarot cards (the accumulation of service bulletins and circulars) and cast the Runes of assorted bits a pieces in the workshop the whole thing woven though with the myths and legends from the elder days of microlighting. It is satisfying though as the bits fall into place, SP starts to take the shape of an aeroplane again and end of the rainbow gets a little closer.
Removing the side plates and cleaning up the bits involves removing a peculiar gunk from the undercarriage legs for SU. Strange stuff that has left a golden translucent film over the alloy that while it is not unattractive has to come off so that I can crack test all the bits.
After cleaning I check all the bolt holes and discover that one of the undercarriage legs and one side plate from kit 208 have the holes elongated. Red labels for those and red penitrant dye for the others. As ever it is very satisfying when the developer shows a pristine white surface.
Moving on the main undercarriage axle I clean to the accumulated grime of years to find the wheel bearing surfaces in surprisingly good nick. My luck seemed in as all the holes were still round and the right size then I struck trouble, the darn thing wasn’t straight. Blast it, I laid it on a flat surface and measured, it was certainly not straight, but then I remembered reading somewhere that there was an allowable amount of deflection, trouble was I couldn’t remember where I’d read it or how much was considered acceptable. So, I read again the Kit Build Instructions, nothing there then though the Service bulletins and news circulars, zilch before finding it in the Maintenance Manual. Maximum allowed deflection 1”, that’s right, 25mm; deflexion on my axle? 1.5mm, phew! I sat down and poured myself a glass of wine, it felt as if I deserved it.
So I order up the rivets, job done, we e ell not quite. Ben is now concerned about riveting in general and asks me to let him know in what other positions I have to replace them. Books and drawings spread all over the table I set to finding out wherever else they may lurk Luckily out of the ones that I turn up only one other place that worries Ben. This is the mounting plates for the interplane struts, he tells me that the stress on these is very complex. After a think I see what he means, not only the flying and landing loads transmitted though the rigging wires there are the torsional loads from the changing lift distribution in manoeuvring and at differing speeds and also the loads caused by control deflections. Complicated stuff and way beyond my aging brain cells so it is good for my moral that Ben has to consult Billy Brooks who is just about the most experienced microlight engineer in the country. Between them they come up with an answer. That is that neither are happy to use monal rivets in that position and the recommendation is that I use Avdel Monobolts, a sort of super pop rivet. I trace a source and order some up, how did we manage before the Internet?
Ordering up both rivet types I find that they have more that Bens approval in common, minimum orders for both of a 100 rivets. Oh well I’ll not run out for a while, it also makes me appreciate the brilliant service that I have become used to from LAS.
I write these recommendations into my repair scheme as modifications and send off the latest version. Result! At last the draft MAAN comes back, which will allow me to go ahead. As far as approvals go I feel that I am on the downhill run with just some answers to find about the last missing service bulletins. I put out an appeal on the BMAA forums and the Tiger Cub Yahoo group for these but without much hope. I get two replies but neither is able to help. So I’m back on my own resources again and I start to wade though all the associated paperwork that I have accumulated. This is fascinating stuff, it’s like taking a trip back to the early exciting days of microlighting. I find that I have a very nicely produced sale brochure complete with picture of a Cub flying, undergoing load tests and loads of enthusiastic blurb.
All these pictures are of the first Cub that is now proudly displayed in Newark Air Museum, where the curator was so helpful to me when I started this project so many years ago.
Quote from Test Pilots Report
“Take off, however was a different story. No gentle transition from ground to air with this ship. Full throttle gives a very rapid acceleration with a swing to the left needing firm pressure on the rudder to keep straight. The tail comes up almost before the aircraft has moved and in approximate 20 to 25yds we were airborne and I had to quickly raise the nose to hold the speed back to 40 knots IAS. A glance at the ASI confirmed an initial climb rate of 1000 feet per minute which settles down to 800 feet per minute once clear of ground effect.” Sounds good to me
There are price lists from your local friendly microlight dealer including ballistic parachute systems, I didn’t know that they went back that far. Local flying club newsletters that talk of long past meetings and flyins, many of these seeming just to be held in a farmers field. Also in the collection are newsletters from MBA and Tiger Cub Developments giving warnings that you need to be a taildragger pilot to handle a Cub and introducing a coaching scheme to train pilots. These newsletters also track the introduction of airworthiness requirements for microlights and MBAs struggle to gain approval as the flow of new customers dried up awaiting the outcome. Then as Type Acceptance was gained the company was broke and the banner passed to Tiger Cub Developments.
For me though, the important thing was that I believe from the contents of the newsletters I can prove the content of the missing service bulletins.
Once again out with the spanners! I have a front floor to fit with my nice shiny stainless steel rivets and despite my concerns about using a hand puller on 4.8mm stainless fixings they went in well with a generous dollop of Zinc Chromate. Then an afternoon spent with my collection of bracing wires got to the top of my list. These were just tied into bundles according to the aircraft that they came from and had to be sorted into their various functions. I had wires from GMJSP, GMJSU, GMNKM and Kit 208 but none of them singly forming a complete set. I laid them all out on the lawns at the back of the house and started checking them by length and the fittings still attached to them. After hours of patient detective work I was confidant that I knew where they all belonged and labelled them all with their function and origin. Phew I was glad that was over with. Although I have no intention of using the old wires I need them for patterns when the new ones are made up.
Then out of the blue I get an e-mail from South Africa, a chap called Christian has just purchased a Tiger Cub but is short of information, can I help? His Cub is an interesting little beast with sprung undercarriage and a centre section fuel tank. It has suffered a landing accident but looks in fairly good shape. By UK standards he has had an epic trip to collect it and he has a history of kit building so it seems that little aircraft is in good hands.
Thanks to my assiduous gathering of Tiger Cub paperwork I can supply the handbooks, kit build instructions and most of the Service Bulletins. Loaded on a disc. It is a pleasant feeling to know that all those miles away another little Cub is on its way back where it belongs, in the air.
Just after that disc is launched I hear from Paul who has just obtained one Tiger Cub G-MMIH and almost enough of another one to restore it so we exchange information.
Paul can supply me with some of my missing service bulletins and I have some stuff that is useful to him, result!
After having read some of the (until now) mysterious missing bulletins I find that one that had caused me some concern MS SB 020. Mandatory. In the Type Acceptance Data Sheets in simply states “Rear Fuselage Bulkhead” with no further detail. A bit worrying that as that bulkhead is the anchor point for the rear ends of the longerons the rear tube of the fin from which the rudder is hinged and the tailwheel. Although I have a bulkhead that has done much flying attached to GMNKM it looked exactly to same to me as the ones from GMJSU and GMMKT. Had they all been modified? A bit difficult to be certain, was I missing something? I checked and measured everything, plate thickness, hole sizes the lot, identical! Not really reassured but unable to think of anything else I re-read all the circulars to see if there was a clue, nothing. Then Paul e-mailed me a copy and all was revealed, due to heavy tailfirst touchdowns some lower longeron brackets had been found cracked. The requirement was to check condition before flight, literally lift the tail and look, I’d never have guessed that. So no modification needed just a check, thanks Paul. Copies added to the information disc and sent on to Christian and a new disc to be made for Ben and one niggling worry out of the way.
Back to the workshop first to dismantle the main undercarriage from SU and to check the same bits from Kit 208, as usual taking photos and labelling all the bits.
Then with this done and ready for cleaning I can treat myself to some thing that I have been looking forward to, re-uniting the front and rear sections of fuselage. After much tweaking, fiddling and a bit of cursing the fuselage stood as a single unit for the first time since. 1986.
Following Ben’s visit I set to finishing the front section of the fuselage. The front end I’d left pinned together with old bolts and I had done no riveting until Ben had seen my newly fabricated front tubes. So I completed riveting up the new throttle quadrant so that the throttle support tube could be fitted. I offered it up to strike a problem, it didn’t fit. Humm, it had fitted before when back in the mists of time I had dismantled it. Then I got it, despite the trouble that I’d taken with labelling everything up I’d fitted the starboard upright to the port side and visa versa, Idiot. Ohh well, stupid but curable with care. By cunning use of the triangulation of the structure I was able to remove both main uprights replacing such bolts as held other tubes in place in the right order so that I could swap the offending tubes over while maintaining the structure. Those in place, the right place this time, the throttle support tube slid neatly into place. Then working my way methodically though the assembly I replaced the old bolts with new ones painted with Zinc Chromate and wound on the new nylocs.
I really could now feel that I was starting on the fun bits and get started at installing the controls. First off, the rudder pedals, I fitted them to the brackets that I re-installed on the cockpit floor after crack testing. They moved smoothly on their pivot and the end float was exactly as specified in the build instructions,
I was starting to get a good feeling about this. Next, install the front cockpit floor, no room for error here, as this is structural giving triangulation to the front of the cockpit. I slid it into position and clamped it up only to find that I had pinched the monel rivets that I had bought hold it into place for another job. A bit of a pain, but not a disaster nothing that a call to LAS wouldn’t sort out. So clamping it into place I moved on to the rudder pulley in the rear of the cockpit section. No sign of wear to the pulley bearings so after a bit of a clean up the pulleys spun as merrily as new. Fitted with nice new bolts I slotted them into place and another little job was sorted. The next thing to re-fit was part of one of Jim Romains mods. It was just as well that I had taken pictures of the bits before dismantling. For this one Jim had changed the non-differential cable driven aileron circuit for a rod controlled system that provided some differential to the control.
For this one Jim had changed the non-differential cable driven aileron circuit for a rod controlled system that provided some differential to the control. To achieve this he had fitted a sleeve with two offset arms around the outer tube control column. Attached to these control rods ran to bell cranks that were mounted on an additional tube fitted athwartships.
These provided the differential and another rod each side ran to the bell cranks which are detachable to allow wing folding, these fit to the ends of the aileron control tubes. As I am missing one of the control rods I’ll have to get one made to the original spec. As I have been cleared by Ben to get this done at an aviation workshop to only real problem will be the cost. As the second tubes will be easy to fit later as long as the cockpit sides are left open I can still press on.
The hiccup with the rivets for the floor proves to be to my advantage as Ben is unhappy with the use of monel rivets in that position. He had gone away a worked out the rivet loading, because it was right behind the front bulkhead it was subject to considerable side force from propeller torque and a good deal of vibration. According to the “Big White Book” the FAA standards for inspection and repair, pop rivets should not be used in places where they are subject to vibration unless the rivet walls, without the central mandrill, are up to taking the load. It seems that monel rivets are not, all was not lost though as Ben found some stainless rivets that met all the requirements of the “Big White Book” and the bit in the CAAs own ‘Section S’ that covers side loads on engines.
Then out of the blue a phone call from Ben in the BMAA tech office, he would like to come to see me and discuss the project so we agree a date. I hang up, well press the red button on my mobile but the term “hang up” conjures the wonderful vision of the old Victorian phones. Anyway I digress, but the idea of carting one of those around in my pocket amuses me. Then I begin to wonder what I’ve done wrong, am I going to be manacled and hauled to Gatwick to explain myself? I can think of nothing, so with a feeling of unaccustomed virtue I begin to look forward to the visit.
On the appointed morning I answer the summons of the bell and open the door to find Ben complete with briefcase and camera bag. Over coffee we go though the mod status in fair detail, Ben has written them up in a little table to simplify the mass of Service Bulletins, some from MBA (Micro Biplane Aviation), some from TCD (Tiger Cub Developments) and of course the Romain modifications themselves. As I’d already noticed some later SBs supersede earlier ones and some Romain ones replace or supersede others. It is a bit of a tangled web, but with all the documentation spread over the dining table we unravel it until it makes sense and we agree the final mod status for GMJSP.
Then it is time to view the beast in its lair (the workshop). As it is the first Cub that Ben has seen he is surprised at how small it is, just as I was when I first saw one back in the early eighties. After a good look over to see just how it is put together he focuses in on the replacement parts that I have made and the parts that I propose to have made.
Firstly the made components, the replacement throttle quadrant that I have made to the drawings in the SB that requires the change from original and then the new “A” tubes. These are the ones described in episode 7 and my new ones are made from 6061 T6 alloy. Ben does a quick “back of fag packet” sketch and calculation and seems happy with what I’ve done but he will do a full stress analysis back at the office. I describe my workshop procedures, separation and labelling of parts as well as the checks carried out.
We then retire back to the dining room table and some more coffee to discuss the parts that I intend to have made, the missing control rod and a new set of rigging wires. He seems happy that I intend to have both of these professionally made within the aviation industry and we go though the Aircraft Spruce Catalogue to make sure that the rod end bearings that I need are still available. Firing up the computer we sort though my workbook to locate the sources of components to be used in the final build. After making some notes we head back to the lair, or should that be den I really don’t know what is appropriate for Tigers, for Ben to take some photos.
Finally Ben tells me that he is generally happy with my repair scheme and will sort out an appropriate inspection regime and send it though to me, Result!
After another coffee we head to the farm to view the Cub that is in one piece KT.
Another coffee later Ben struggles into the cockpit and like everybody else is amazed just how much room there is in there, when you are in, a veritable Tardis of an aeroplane. As he remarked it is all very eighties.
So all in all an extremely successful day and I await the documentation plopping though my letter box. I enjoyed meeting Ben and it certainly gave the lie to all the rubbish that has been spouted about the denizens of the tech office. Ben is an enthusiastic microlighter who flies both flexies and three axis aircraft. He has both a Quik and is rebuilding an MW5 and his enthusiasm for microlighting glows around him like an aura.
Of course after such a good day I could be a little biased.
Right. In order to get started I’ll simply put links up to the current URLs of the story episodes on the old Saxon Microlights web site. As explained in the first post, the internal links are hard-wired to the old domain so you’ll need to come back here to jump to another episode. NB. Titles below with a * have been added as posts in this blog and the link amended to suit. NB2. Since we’ve let the old web domain go, those without a * will not be visible. We’ll move them when we get time.
Introduction: It all started with back in 2003 with an ad in AFORS, “own a bit of microlighting history” it said …