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Sep 03, 2017, 05:57 AM
What could possibly go wrong?
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RCM Trainer 60 Flight Journal

Hi, nothing to report just yet, this is a placeholder post. I'm test-flying all these control system mod's tomorrow and I'll report how it goes. I'm really hoping the steering system on the ground now works reliably, that was why I started all thise work. It now has a spring-protected connection from the steering control rod to the steering and rudder servo, and hopefully instead of bending the axle or steering arm, any bumps on the ground or from skewed landings will now be absorbed by the springs. It got so bad for a while I couldn't taxi it at all, had to place the model on the runway and manually straighten the wheel, and it'd still swerve on take-off. Touch-and-go's weren't possible like that as the model would slice across the runway, further straining the steering. But this should fix it.

Also now using my best servos, which happen to be micro digitals, on ailerons. They'll be much faster, torquey and with much higher resolution than the Emax rubbish I was using before - they'd wanna be for the price anyway. If these work out well I might start budgeting and planning to get a couple more high-resolution servos, maybe Hitec D-625 ir 645. My Rx. can get up to 2048 steps of resolution with these, I'd need a Hitec Maxima to get the full 4086 but 11-bit would be plenty. The 5085's should give me 1024 steps, and the old analogues were probably equivalent to about 300. They were weak, stripped gears and were starting to act strangely so it was time to upgrade, and as I already had one 5085 I realised another one of those for ailerons would be a significant upgrade, at the cost of one servo. Hope it's true! I do notice they're much faster and I can see the improved resolution on the ground, I look forward to seeing what that means in the air. I've also completely replaced the linkages between these new servos and the ailerons, there' no possible looseness in them now (See the blog entry before this one for details). All new elevator pushrod too, lighter and stronger and with better retention, not that there was anything wrong with the old one but I had the CF shaft and wanted to try it.

The rudder and throttle links were not replaced, but both were fully dismantled, checked and adjusted. The rudder link is a Gold-n-cable in a guide sleeve, I added extra anchor points to stop it moving and to reduce the flexing that affects rudder position especially at neutral stick. Throttle should idle correctly with the stick at zero, just reach WOT at full stick (both of which it now does), and I've set the engine kill switch so it briefly fully closes off the throttle when you want it to. So it's had a complete control system overhaul, and recently the entire mechanical front end went through all that too. Engine mount removed, fully cleaned, serviced and replaced, ditto the whole front end.

Now all I have to do is fly it, and see how much better it is! Looking forward to that. I've averaged more than once a week since the start of June, the entire winter. Now it's officially spring and the weather just now is superb, the forecast is for an almost percet day. Can't wait!
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Sep 04, 2017, 08:17 AM
What could possibly go wrong?
Thread OP

Flight log Monday 4 Sept 2017

I had a good long session at the RC club today, mainly so I could flight-test all the modifications I've made to the model in the last couple of weeks. As I've posted that's a long list of changes, but the quick summary is, a completely new nosewheel steering system, new pushrod and linkages for elevator, new aileron servos, remounted to suit their different dimensions to the last servos, and new linkages from those to the ailerons, inc. pushrods, with new clevises, servo arms and all the locks, circlips etc. to make it reliable. Plenty of other stuff too, but those are the most important sections and they're the ones that needed to be field tested. Short version is that everything worked very well.

The most important change *should* be the aileron servos, but what's really making the most difference to me is the steering. I've posted it elsewhere but basically I completely replaced the old steering linkage. There had been several problems within the steering system, but while I was using a flexible cable instead of a rigid shaft it would never be fully solved. The new linkage uses a carbon fibre shaft with steel rods each end, attached to a ball link at the steering arm and a spring-protected connection at the servo end like a Servo Saver. It's a big success and now the steering works great! Driving it across lumpy uneven grass doesn't bend and throw the wheel or entire linkage out of kilter, and without flex in the shaft it's more accurate. *Finally*, after many weeks of trying, I've got steering that goes straight ahead, and stays that way until you steer..That has been driving me nuts! with the wheel going crooked all the time and I couldn't fix it in the field. But I've posted all that elsewhere. Steering may not seem a big deal, but if you want to practice touch-and-go's (circuits and bumps) in a tricycle-undercarriage model, you need straight, accurate steering. As soon as the wheel touches down it steers the plane, possibly sharply, so you can't just continue in a straight line and take off, and it might even swing about hard and tip over. Finally that's no longer a problem, and I can do all the touch-and-go's I want. The worst problem I had is taken care of.

Some other work was a new elevator pushrod, from the same CF shaft as the steering rod, with all brand new rods, fittings and retainers on it. Not much to say about a pushrod, except that it's the right length, strong, works well, and this time it's lighter and less bulky. But, I did have to add a lot of down-elevator trim to the model. I started out with the elevator visibly flat to the stabiliser, but the model climbs too much like that. If anyone knows why that is and what's the cure, please share it with me. I know planes climb when adding power but this is too much. I've added enough down-elev. trim to balance it, but there has to be a better way. Where's the problem originating? And I'll fix it there.

Then the ailerons. New Hitec HS-5085MG servos and entirely new linkages, inc. servo arms, pushrods and all the fittings thereupon. I used heavy duty 2-56 Du Bro clevises because I *really* don't want to strip the threads on these pushrods again. That caused aileron flutter last time I flew and I nearly lost the model. But I'm not that sold on these HD clevises, I think I'll change them again. They're too hard to adjust for trim. I'll cut the threaded end off and solder on a brass threaded coupler, then use the same Sullivan Gold-n-clevises I have everywhere else. They're the ones I prefer by far and when used properly with jamb nut they won't come loose. I find they mate much better to the threads on a Sullivan brass threaded coupler than those threaded wire rods, much better.

So those are Hitec's "premium" micro digital servos. They're basically just like the rest of their 5-series so they're not *that* premium, though they have metal gears and I think 2 ball bearings on the output shaft. They're certainly way better than the eMax ES3103's I was using. I've had to replace 3 of those without them ever getting a serious collision, they don't like too much of any shock I think. Plus one of the 2 I had installed recently started acting strangely and I don't trust it any more. It moves, chatters, buzzes and carries on for a couple of seconds after every time you move them with the stick. The new 5085's are better in every way - noticeably faster (actually the eMax claims 0.11 seconds for 60 degrees of arc travel, vs. 0.12 for the 5085's, but it's obvious you can *see* the Hitec's moving faster), 50% more torque, much smoother, and with much higher resolution. I'm told you can get 1024 bits of resolution with any 5-series digial, which isn't exceptional, but it's much better than I could expect with those crap eMax's.
Using the new servos, they are plainly much faster and more responsive than the old eMax's, and the resolution does give finer control. It's not automatically easier and better to fly, it's *different!* most of all. It *feels* different. So I need some more practice on them to get used to the difference. I guess I'd trained myself to cope with poor servos, but these, especially offering fine control, need time to develop a feel for them.

Flying today I mostly just did basic rectangular circuits, and touch-and-go's. The weather wasn't terrific so I didn't bother doing "tricks" so much, just a few things I wanted to practice like wingovers. In particular, since the wind was 180 degrees around from the usual direction, I wanted to try the opposite-handed circuit off the main runway. For whatever reason i found it much easier to approach for landing from that end. With the steering fixed up I could do my touch-and-go's without fear of arcing off the runway at speed, and the ailerons were, well, better. The entire model's had a major overhaul over the past 2 or 3 weeks, not just all the work on the control links but the entire engine compartment's been removed, fully cleaned, fixed, serviced and set back up again. Tank and battery compartment's the same, it's all been re-packed and fixed up. I didn't replace the rudder linkage but I did improve it with 2 more anchor points to reduce play and flex. So it's all in very good functional condition. It does feel slightly different, but that's mainly do to de-bugging it, as it were, and it's well worth it.
OK not an actual flight report, but an idea of the results of all the work that's gone into it lately. It's always more time and effort than you expect.
Sep 06, 2017, 03:36 AM
What could possibly go wrong?
Thread OP
What a perfect day today would have been, I went flying on Monday as the forecast was excellent but it turned out to be windy. But the predicted break in the winds seemed to happen today, it was clear and sunny and almost dead still. You know how hard it is to get a day with that little wind, middle of the day, in those nice conditions here? In the world's 3rd windiest capitol, on average? Pretty hard. But, it wasn't to be, I've been begging for work and I got it. So I look at my life this way, I either go flying models or earn money, could be worse eh? Next scheduled day flying should be Saturday, and best to get there early as it looks like it'll be nice and gentle until about lunchtime, then get rough after that. I'm starting to realise what I consider a good flying day here is probably a little borderline to many people elsewhere, but I'll take any day I can get.

I put out a call for help regarding some aerodynamic issues I think the model has, and I got back some very helpful and encouraging replies. I thought maybe I'd built it wrong with incorrect Angle of Incidence at the wing. But the advice I got is that the CG is probably too far forward. I'd believe that, as first of all it has those symptoms - gains altitude too readily on throttle up or with increasing speed (they all do that, I just think it's too much), and sink rate is high for a trainer of this type. I actually like that, I think it's great I don't have to drop the throttle to idle when I'm still 2 turns away from final, but I have always suspected it's because something wasn't the way it should be. The 2 helpful replies I got both predicted the model would act this way before I mentioned it, and both said it would be for the same reason - CG too far forward. That makes sense, because I already thought it probably was. When I was going for my solo wings the instructor checked CG and the first thing he did was shift it quite a way forward from where I had it. I'd checked it the night before on a Vanessa rig, and it indicated that CG was right on the money, exactly at the forward point of the recommended range shown on the plans. The instructor said it should be at the front edge of the spar, where the plans show just behind the rear edge, a difference of about 15mm, so that's significant. First thing to do is to sling it up in the Vanessa rig again, see exactly what I've got after all the work and internal mod's lately, and take it from there. I'd like to get rid of the ballast in the engine bay if possible, 30g of lead added by that instructor. I'm sure his rule-of-thumb is a good one, usually, but I always felt funny about it since this very well-known design shows one thing, and the model ended up with it set to another thing altogether.

That's all fine now that I have something to work with, I'm happy to hear two experienced people come to the same conclusion for the same reasons, and recommend the same cure, shift CG aft. And that even tallies with something I thought wasn't right in the first place. Cool! If this model didn't have this funny tendency to rise and fall so rapidly depending on throttle setting it'd be an improvement. I'll get to test that soon.

Tomorrow I decide if I'm ordering a telemetry set to go with my Hitec gear, I really hope I can do it. It's a good deal and has upgrade paths. I really wish I could find a full-time position somewhere so the income I can spend on things like that was steadier and more predictable, but at least I've ended up with a model to fly and more on the way. If I can get that set I'll have all the gear I originally wanted (and still do), that'd be nice.
Sep 10, 2017, 03:41 AM
What could possibly go wrong?
Thread OP

Flight log Saturday 9 Sept. 2017

Flew the model again yesterday, had a good time of it. The main object was to test the model with its newly altered CG position. If you saw the build log thread then you'll know I've been investigating some problems it has in flight, and I had some good advice that the C of G was probably too far forward. (By the way if you follow this blog, or that thread, you won't miss out on reports, they're echoed in both). I was told that signs of this are that on adding throttle the model climbs sharply, and cutting throttle the model dives readily too. It's definitely been behaving that way, particularly the climbing problem. I knew that the CG position was well forward of the design range shown on the plans, as before I started soloing on this model an instructor set up the CG for me at the front edge of the wing spar, standard practice he assureed me. But I think in this case it would have been better to keep it as it was. The plans CG position is about 3mm or 1/8" behind the *rear* edge of the spar, not the front edge. So that's a good 15mm back from where it was. I was also told that once it moved I might have to add more down elevator trim (stick forward).

I removed the front ballast that had placed the CG so far forward, and also moved the battery pack further aft in its compartment. That place the CG slightly aft of the front of the range on the plans, so it's well within the designed position. Not quite at the front edge of that range, but still towards the front of it.

At first, I was disappointed as the tendency to climb on throttle (or anything else) was actually initially worse than it had been. But I kept at it and added lots of down elevator, and after a flight I also wound the clevis in several turns on the pushrod (elevator) or I'd have run out of trim on the Tx. You can now see a visible angle of several degrees between the tailplane (horiz. stab.) and the elevator, angled down. When I launched again, I found that so long as I had enough of this trim, the model was in fact flying MUCH better than ever. Success!

Previously, it'd tended to climb on just about anything on the controls, so it gained and gained altitude all the time until I dove it back down. But, if I cut the throttle such as for final approach to landing, it'd sink very rapidly. That's another classic sign of too-far-forward CG. But now those tendencies are just about corrected. It should climb, of course, if you add throttle when the model had been trimmed for level flight, but it was just doing it far too much. Now it's much more reasonable. Another benefit is that turns don't balloon so much and if I take on a slow, broad-radius turn it's now much easier to keep it flat (constant altitude) by the time I level out. That was almost impossible for me before.

This is a question of setting positive, neutral or negative stability. With the very forward CG it had too much positive stability. This is usually presented to student pilots as the ideal, and it sounds good, doesn't it - the model will return itself to level flight, hands off. Great! Gets you out of trouble. But I don't think that's actually what you want so much after all. For starters, this climb and dive characteristic sensitivity to throttle, that can't be a good thing. As soon as you're beyond your first basic training and can at least hold a turn and complete a circuit without getting into trouble, you don't want it climbing every time you so much as look at it. You just want to *fly* the thing, not battle to control altitude. So I don't think setting the CG so far forward is really doing the student much of a favour. I heard the way to check it is to dive at about 40 degrees, and watch for how much vertical space the model needs to pull out level. You measure this in wing radii, eg. if the model's a 60" span, a tight pull-out might be 12 to 15 wingspans, or about 60 to 75 feet vertically. (~up to almost 25 metres). The less positive stability, the greater that distance. A fully neutrally stable model will keep on diving, at that particular throttle setting. That's more like what I wanted. So, with the new balance point, mine was barely pulling out of the dive by itself at all. GOOD!! That's much more like what I want. I'm not a raw beginner any more, though of course I'm still learning and have a way to go, and I don't want excessive positive stability any more. I'm not battling just to control it in a turn, I fly quite confidently now in fact, so I don't want it fighting me in the name of stability for its own sake.

I'm very much happier with the way the model now handles. When I apply throttle it doesn't suddenly tilt up and climb for the sky, it *gradually* starts to gain altitude with speed. Same with throttle-off, it doesn't nose over and dive but gentle starts to sink. Another example of the improvement is in landing. Before, when I throttled off to approach, the model started to sink very rapidly. Much more than any other trainer I've seen or tried. I actually did like that, because I can't stand it when you want to land and you have to cut the throttle all the way to idle, halfway through the downwind leg with a long way still to go, and by the time you're over the runway threshold the model might still be much too high to make it to the ground by the time you get there. However, it was probably too far the other way. I didn't cut throttle until I'd made the last turn, and even then if I cut it fully it'd sink so fast it might hit ground *before* the start of the runway, so it was sinking too fast. I had to keep on enough throttle to get it to the threshold, and that increased air and ground speed, so the landing itself was harder. It's tougher to correct as you go, such as for a cross-wind, and when it lands there's still enough ground speed that it would use up the entire runway to roll out.

Now, with the re-set CG, it's much better. I find I cut the throttle, not to idle but maybe 1/8 to 1/4, about 3/4 of the way along the base leg (before the final turn onto the landing approach), and it still comes on down fast enough to be convenient but not so fast as to be difficult. Then with a little throttle on, when I flare for landing the ground speed is nice and slow, looks like about a jogging pace, and it's much easier to do a GOOD landing. Nice and gentle, and with that reduced speed the roll-out is short. This model has good wheels, very low friction, so it still rolls out for a while and I'll usually have to steer it off to slow it down, but I don't believe in having high friction in the wheels as brakes. Anyway, that just makes takeoff harder.

Overall it's a massive improvement, but there's still work to do. It does need a large amount of down-elevator trim, and I think that can't be right. I've got some trimming instructions to follow now, and I think the answer might be wing angle-of-incidence, so I'll look into that. Will report later.
Sep 20, 2017, 03:46 PM
What could possibly go wrong?
Thread OP

Flight log Monday 18 Sept 2017

Summary of improvements and repairs
Another beautiful day, the only good flying conditions all this week and to the limit of available forecasts. This was basically a day's check flights after I crashed it and repaired the damage, all to the rear end. I'll post pictures of the damage and repairs to the maintenance log later. I stripped the rear 40% or so of the fuselage completely so i could access all the damage properly, and got it repaired nice and strong. That's been detailed in the build log. Once again the rebiuld after a crash has given me a better model overall, it's really getting pretty good now! But I had to work for it, I was up very late the night before to get it all ready for flying but I pulled it off just in time. Glad I did, I was sorely tempted to just forget it and skip the day, but if I had I'd have wound up going well over another week until I could fly it. It ended up being another great day and great result.

The CG being shifted was the first really major improvement to flying this model it's had recently. Now, on top of that, the completely rebuilt control system is paying off big time, it's been well worth the effort. It isn't a critical flight control, but you've got to have good steering on a trike model to do those touch-and-goes, and takeoffs are difficult if the steering keeps trying to swerve you off the runway. I had it going well, then the new steering system got minor crash damage, but has come out better than before now. It's reliable, durable and accurate. *FINALLY!!* I can just drive the thing straight and it'll actually GO straight! That's been much harder than it should have been but we got there at last. I'm proud of it, using a CF main steering shaft with ball joints both ends and a servo-saver-type spring linkage at the servo arm. That's all new for me and it's a big success. You can adjust the tension of the springs or move the two collars to fine-tune the steering, and that's just what I've done (remember to switch the Tx and Rx ON so the servo stays centred while doing jobs like this).

I couldn't be much happier with the model right now, all the work paid off. Those controls are now greatly improved on every channel. New elevator pushrod, more compact, lighter, stronger, perfectly trimmed. Rudder cable still the same but I added extra anchor points. More importantly, the rudder control horn wasn't well aligned with the hinge line, so I shifted that. It was asymmetrical before, you could see the greater throw to one side than the other. Now I've shifted the horn I see 40mm throw both left and right, and it centres spot on. Ailerons with the new, much better servos and brand new pushrods, wow, what a difference. If I'd only done these and nothing else I'd be ecstatic with the improvement, but that's just one element.

Elevator is much better now, but all this time I haven't been using elevator differential. I only really worked out I should be using it recently, I asked BTE for a picture of rear-mounted servos for the Venture 60 and he kindly obliged. Then I realised on one picture that the elevator servo horn was offset strongly, so just like ailerons you have "more up than down". I've got to do this, I've set mine up symmetrically up/down and as a result I'd used more throw overall so that it was the same up and down. But of course you don't need much down elevator, you rarely throw it into a dive anyway and never so violently, and for inverted again you won't need much. But up elevator you use all the time in turns and everything else.

Flying the model now is a pleasure and not such an effort. For example, approaching to land or for a TAG, I have such better control now. Easy to correct the line with just a lean on the rudder stick, just a little pressure and not throwing it hard over like a Playstation. The fine control with the ailerons is very helpful making small adjustments as I come in. Now it's re-balanced for a more aft CG it just flies so much better all around, I can tell from those easier, flatter slow turns, better figure 8's, it doesn't suddenly climb all over the place and glide slope is still steep but it's steady. Great throttle response as always, now it's nice and linear with the throttle stick. Elevator new pushrod has taken care of pitch trim, rudder's been sorted out and with the rest of the upgrades it's become a very nice flyer. I haven't yet started working my way through the Futaba model trim manual but I will, I'd like to check stuff like aileron differential and to follow all the checks in there. I find that as the model gets better adjusted and tuned, it's so much easier to fly of course, but that also means that as it improves I can more easily find other details to trim out.

This is no basic trainer, no way. It's much more demanding on the pilot than the club trainers I did lessons on, it takes more input and concentration to fly it cleanly around the circuit. But the pay-off is that it's so agile and aerobatic, it can look pretty good up there when you go for it. I use at least half a dozen Immelmans most flights, that's one of my favourites now! I rarely see others doing them. Anyway this model's got enough power to do the half loop, but the roll-out at the top with these new aileron servos is so nicely controlled, same with Split S's, nice and lazy and the roll-out at the end looks great. I'm working on 4-point rolls now, I know a dihedral high-wing will never do great 4-pointers but I need to practice anyway.

So overall the work has been a big success, and it's flying very well. I've been seeing many improvements as I go and now they add up to one sweet model for a plain old high-wing trainer. That's been a lot of effort, if I go back to when I got aileron flutter and decided to do ALL the links, and then just when that was looking good I crashed it and had to fix them up yet again. But as I said, crashes aren't always a total loss and can be an opportunity to improve, and that's been the case again here. The sections I worked on are definitely improved now.

Wednesday 13th Sept 2017 - CRASH REPORT
Wednesday was another day of ideal conditions, but at one point the engine cut out and I had little air speed as it was, and not much room to recover. I ended up hitting the boundary fence and doing a fair bit of damage to the tail area, the seams of the floor to one fuselage side, almost completely broke the tailplane off, some long cracks/splits, but was able to repair it in time to fly it on Monday. I'll post this again but see the build log for more.
Last edited by BernardW; Sep 20, 2017 at 04:12 PM.
Sep 29, 2017, 01:46 PM
What could possibly go wrong?
Thread OP

Flight log Wed. 27 Sept 2017

Think I missed another day in the log, and this one's late, I'll go back and check. Doubtless I babbled about it somewhere. Anyway this was another superb day, the weather had the decency to stick exactly to the forecast (I really only check the winds, rain and temperature can just about do what they want so long as I can fly in the winds), still in the morning and a breeze picking up steadly after lunch. Never got very high, maybe 15 kmh at most. The model is flying well but I had the wrong prop on it, I was using an 11.5 x 6 which is really too fast for this engine. One the first flight I did an approach for the first touch-and-go of the day and only noticed there was no longer a nosewheel as it was about to touch down. It was too late to go around so I tried to flare it as far back as possible but pretty soon it came down on the bare wire nosewheel leg, and forward-somersaulted without damage. THere was no sign of the wheel and front axle, they're be out in the bush somewhere, so it looked like that might be it for the day but someone there is restoring an ancient 70's trike trainer and just happened to have the front nosewheel leg with wheel on it in his car, and the main (wire) undercarriage. And no other parts! The one spare thing he had was some ancient wheels of a suitable size which he offered to me. And I had a spare axle and even more amazingly, everything fit first time and I flew again for the rest of the day as normal. I've since bought a new lightweight wheel. Beware those old style semi-pneumatic rubber wheels, they are surprisingly heavy, around 40-50g each for the trainer-sized ones, some are even more with metal hubs. The cheap foam ones I'm using appear to be crap but at least they were cheap (gee, fancy cheap stuff being crap) and they're certainly light, about 5g each. Up to 1/10 of the weight of the old style, that was one large instant weight saving I made on this model.

I now have an HY/Bolly 11.5 x 7 prop on it, I wanted to see what a higher pitch does for it. My guess is that the taxi speed will be faster, it's already too fast for me now. The engine won't really idle much slower until I twiddle with the throttle linkage again, and I'd have to jog along to keep up with it. That's not a thing I usually do. Ever. I could trim the idle further down but that closes up the max. RPM a bit. I'll have a play with it tomorrow. The previous 12.5 x 6 I was using has been really good but it's had too many strikes and the tips were starting to look pretty shabby and it really didn't look like it'd be balanced, so I stopped using it after the last strike. I cleaned up the tips tonight and re-balanced it, I'll keep it as a last-ditch spare, though I think it'll be alright. I've also got a pristine APC 12 x 6, the basic standard for this engine and model, so I've actually got a good little selection to compare. But first I'll try the 11.5 x 7. I think a smaller diameter will always be handy on this model, the borrowed wheel was smaller so that cost a little more prop clearance. Now it's got the original sized nosewheel again, same type I balanced it with and the nose sits a little higher again, both those factors will help. The last prop on it would have been a little lighter than the one before, but the nosewheel a little heavier, balance shouldn't have changed real much but it did actually need a little up elevator. There are other things that could be.

I finished my last batch of fuel, now got that heli fuel re-mixed. It was 20% nitro 23% fuel, I had 1.5L methanol added and then a bit more oil again (coolpower same type) so it now should be about 12.5% nitro 17% oil. Next batch I'll just go back to plain old 10% nitro, I tried higher at 15% but didn't see a benefit, it actually used more fuel, needed tuning richer (that was part of the reason for the consumption) and costs more. Forget it. So this started out as 2.7 L, I've added 1.5 plus 100mL oil so I've got 4.3L, over a gallon, for $10. Sweet.
Flying again today.

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