You may have previously seen my posts about crashing my Minimax and having to rely on a lady with a claw hammer to help me extricate myself from the wreckage. Since then I've bought another Minimax and now given away the airframe of my original UK 88 model (similar to the 1030) aircraft.
My new Minimax is a UK 91 model (similar to the 1100R) and is an interesting one in that it was originally built with a Rotax 508 4 stroke engine powering it. I have managed to get hold of some photos of the aircraft with that engine in it, and I'll post one of them here. However, for reasons unknown, a previous owner has removed the 508 and replaced it with a Rotax 503 2 stroke engine. This is the DCDI variant with twin electronic ignition systems, but it's been fitted with a single carb and not the two carbs the DCDI is normally fitted with.
Since having the engine changed the aircraft has undergone several other changes as well. I don't know why it was done, but the wings have been recovered with silver Oratex and the fuselage is now blue and silver instead of the original red. It also has an extra 10ltr alloy tank mounted on the floor of the cockpit between the pilot's feet. So with a fuel capacity of 30ltrs it's quite a nice aircraft that also benefits from having an M5 electric starter fitted.
Now for the bit about the brakes!
When I bought the plane I took it up for a test flight, and when I landed I noticed that it seemed to curve to the left a bit as I slowed down on the ground roll. I put this down to my own footwork or lack of, and accepted that as I was used to a different 'max it was probably me who caused it to go left on landing.
Come the day when I flew it home to the airfield I'm based at, the weather was foul with low cloud and lots of rain showers for me to dodge around. There was a 25mph tail wind that assisted me on my journey, but I still chose to land halfway to take on extra fuel in order to make the total journey distance of around 130 miles. When I landed at the refuelling stop I hardly had any ground roll at all due to the 25mph headwind I landed into, so I didn't notice any tendency for the plane to turn left. Furthermore, whenever I took off I never noticed any turn to the left either, so I just put it down to my own inexperience with this particular plane.
When I landed at my home strip I wheeled it on instead of doing a 3 pointer and noticed that the plane turned left as I slowed. This became even more noticeable when I applied the brakes. I will say at this point that the brakes on my old 'max were separate, with separate levers, so I could adjust the pull on one wheel or the other if I noticed the plane trying to turn in any particular direction. However, on this aircraft the brakes are both operated by a single lever, so I can't operate just one brake to help keep the plane straight.
Having brought the plane to our strip I was keen to get to know it a bit better, so a few days after ferrying it home I took it up for a half hour flight. The flight itself was good fun, the plane is very comfortable and has excellent performance thanks to the Rotax 503 up front, and it was with some reluctance that I decided to land. When I did I wheeled it on again and found that the tendency to turn left had increased, and as soon as I applied the brakes the turn tightened up very quickly. This meant the plane did a groundloop to the left, and as it did so it shot off the side of the runway and into the soft earth where there's crop growing.
So now my new plane has a crack in the fibreglass fairing under the prop, the spinner has a dent in it, and the front is covered in mud. Not only that, but as the plane spun to the left the right wing dropped and touched the ground just as I came to a halt. Doh!
After getting it back to the hangar I decided to find out what was causing the left turn and found that the left brake band wasn't sitting straight on the drum. It was sitting at a bit of an angle, so that if I applied the brakes, the left brake band caught on the edge of the drum instead of the outer face, with unpredictable but so far bad results.
I've since removed and replaced the wheels and the brake drums and bands, and now have a totally different braking set up at the wheels. All that's left to do now is separate the cables at the lever end so that I can operate each one individually. However, the damage has been done, and now I'm trying to sort out the spinner and the fibreglass fairing.
Since the incident (which happened last September) I've also discovered other damage that I wasn't aware of at the time. Because the right wing touched the ground it pulled backwards, and although there's no damage to the rear strut connection or the rear spar, there was damage to the fuselage. The diagonal stringer that attaches at the top of station 4 on the right hand side popped its glue, and the cockpit coaming on the right hand side snapped! I've taken a couple of photos of the snapped wood and how I T88'ed it back together along with a couple of strengthening bolts, and I've attached them to this post.
So now I'm just giving the glue a week to cure and harden before I refit the right wing and go flying once more.
I understand the tendency to "sister" the longeron with a piece glued on across the break. Unfortunately this doesn't work because it is weaker than the original member. This is because as stresses run along the longeron they concentrate at the break. This stress concentration means that the piece added on is subject to much greater stress than the original continuous piece. It will tend to break again next to the original break.
The best way to repair a break is to cut a number of very thin layers of stock, use a jig behind the broken member to make sure it is taking a fair shape, and dish out the area either side of the break very carefully and smoothly into a very shallow curve each side of has a length which is at least 8 times the thickness of the longeron. An orbital sander with a random orbit disk is the safest way if the access allows. DON'T use a rotating disk sander. Glue in enough layers of wood bent into this very shallow curve, with good structural epoxy like WEST System(tm), so that you can shape the repair area back to the same dimensions as the original longeron Many will recommend longer than 8 times the thickness for each arm of this laid up in place scarph and there is nothing wrong with that. It is just that at 8 times thickness I've never been able to test any reduction in strength over a solid piece of the same dimensions.
I flew down to see 'KJ at John Hamers place in my Chaser 508 (my avatar) abt 15 years ago. Its wings had just been re-covered at that time.
The 508 installation was free-air cooled with a collecting duct and was a VERY tight installation (with its oil tank) inside the cowling. 508s are a bit fussy. Ask me how I know. I didn't buy it but I was tempted. I'm not surprised the engine was changed. John H always championed the 447 over the 503 and there has been debate on this forum as to which is more practical.
There were two versions of the 503 - earlier single carb single contact-breaker ignition with forced air cooling as fitted to my old Flash 2 Alpha G-MTNI and my current Minimax G-CBIN, and later ones with forced air, dual carbs and electronic ignition. Apart from the pain of adjusting the points I prefer the single carb and ignition.
DON'T FIT GOOD BRAKES!
Band-brakes are really simple. Easy to inspect in the PFI and very easy to make them differential. When you really need the brakes the temptation is to over apply them. Ask me how I know. If they are a bit crap they'll save you some spannering and woodworking.
The 503 that's in KJ at the moment is a bit of an oddball in that it's a forced air cooled DCDi, but has a single carb. It's also been fitted with an M5 starter I'm very happy to say. The engine and starter sit in a metal framework that bolts to the firewall, and the engine actually sits in a metal sling or cradle, made up of two large L shaped pieces of metal that then bolt to the metal frame through four Lord mounts.
I found the 503 to be much more powerful than the 447 at getting the plane off the deck, and it's quite smooth as well. The only thing is that it's more thirsty at present, and I may be able to do something about that as the EGT's never go above 500 degrees at the moment, and my old 'max had them sitting at 600-620 nearly all the time in the cruise.
I've attached a couple of photos so that you can see the engine fitment, and as you say, it's a bit tight.
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