MA Stratus 90
Simon Lockington

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The metal fan hub uses rubber isolators. Pins from the clutch assembly are pressed into the rubber isolators to transmit drive. Helps reduce drive train vibration.

Here you can see the vertical engine mounts as well as the bottom carbon frame that bolts up into the crankcase of the engine.

The large vertical A-Frames that connect the top frame assembly to the bottom as well as the forward fan shroud mounts.

The large carbon bottom frame showing the engine mounts and the double sided tape to attach the fuel tank.

Preparing the area ready for the fuel tank. Note this is before I realised that the mounting method had changed from velcro to zip ties!

The skids attached to the bottom frame.

Fuel tank assembled and installed.

Carbon top sideframe.

Assembled tail bevel gear and main gear with autohub.

Left frame with mainshaft, bearing blocks and main gear.

Pinion and top bearing block.

Clutch assembly.

Main gear and clutch showing gear ratio plates.

Top and bottom frames assembled. Note that I did not have the engine at this stage.

Assembled swashplate.

Plastic washout assembly.

Tempest head showing new flybar carrier.

Spindle showing one side assembled ready to install in the head block.

Finished head mounted on main shaft.

Assembled pitch slider. Plastic arms with metal links.

Assembled tail hub.

The open tail box came pre-assembled, just had to add the bell crank, pitch slider and tail hub.

A plastic clamp attaches to the carbon boom and the tail box screws into the clamp.

Part of the changes to the upper frames included moving the tail servo up to this location.

The Miniature Aircraft Stratus 90 has been out a fair few years now. It's already has a proven reputation itself as a top quality machine capable of hard 3D flight after flight. I've had a chance to fly a couple at various stages over the last couple of years and have always been impressed with how they flew.

Last year a mate of mine bought one and gave it to me to build and test. The machine would have a YS 91, Hatori 3D pipe, Futaba 9351 servos, JR 770 gyro with servo and a Fromeco regulator so it was going to be fully kitted out.

Unfortunately the build got delayed quite a bit due me moving house and being away for work a bit, but eventually it got built!

I'm relatively familiar with MA machines having owned a Tempest FAI for a while, so I was keen to see how much things had changed with MA machines.

INSTRUCTION MANUAL
The instruction manual I used was one downloaded from the MA website and printed. I didn't bother opening the CD that came in the box.

The instruction manual format has changed, for the better I might add. When I was building the Tempest, there were two seperate installation manuals, one with text, the other with diagrams. This was ok, but I much preferred the layout of JR manuals that incorporated everything onto one page. MA are now doing this which I reckon is a nice improvement.

The manual also has colour images which is a nice touch.

At the start of each assembly section, the first few pages are devoted to a parts listing so you can compare what the instruction manual requires in terms of parts with what you actually have. This is a valuable exercise as missing parts from MA kits is a relatively common occurance compared to kits from Thunder Tiger and JR.

The text in the manual is nice and comprehensive and you're not often left to wonder what the hell they were trying to say. The part that caught me out was the use of imperial measurements mixed with metric. Now I'm from the metric generation, telling me to do something 3/8's of an inch along a shaft is going to send me on a trip to Google to find out how many millimeters 3/8's of an inch equals. I know these are American kits, but I'm pretty confident when I say that the helicopter market is a metric market.

ENGINE/HUB/BASE PLATE ASSEMBLY
MA haven't changed their approach to their drive train and that's a good thing. While they have a unique method of transferring drive from the fan hub to the clutch via two pins slotted into rubber isolators centered by a rubber ball, I quite like the idea. It provides an element of isolating engine vibrations to the airframe which is good. However past experience with the Tempest has taught me that you need to keep an eye on the rubber isolators as they do flog out and need replacing.

The base collet in this particular example was very tight to get down the engine's crankshaft, however I pressed it on by using the fan hub and pushing down evenly, no big deal.

The Stratus uses a rather unique method of mounting the engine to the frames. You replace the four bolts used to hold the back of the engine crankcase together with four longer bolts that bolt through a carbon mounting plate. That mounting plate then has some engine mounts bolted to it which bolt to the engine's mounts. The finished assembly is then installed in the helicopter. Interesting design. When I first saw this design I was worried that this may transmit a lot more engine vibrations into the frames than a 'classic' engine mount design, however that doesn't appear to have been a problem for existing owners.

The finished engine mounting plate is then mounted on the large bottom carbon frame through slotted holes so that the engine can be aligned correctly.

Also bolted into the base plate is the forward fan shroud mounts as well as two large front and rear frame supports that will eventually connect the top and bottom frames together. The quality of both the aluminium and carbon parts really is very nice. Very nice indeed. You can thread in the bolts and do them up nice and tight without fear of them stripping.

FUEL TANK/LANDING GEAR
One thing that hasn't changed since the days of the Tempest is the way MA do their fuel tank clunk arrangement, it's still from the side and you're expected to some how secure the nut within the tank while you tighten it up from the outside. I remember I struggled with this with the Tempest and once again, I struggled with it with the Stratus also. I really do prefer the JR method of tightening up the nuts from the outside of the tank, it makes it so much easier!

The tank is secured to the bottom frames by two large pieces of double sided tape as well as two large cable ties which really secure the tank nice and good. However this is where I ran into the first of many deviations from the manual. The manual said to use velcro straps instead of cable ties, however a seperate bit of paper contained in the fuel tank said otherwise. You really do need to make sure you download the latest manual from the MA website before you assemble your machine because there's likely to be new revisions. Note that the actual fuel tank design is quite different to what is shown in the manual also.

From the looks of how things used to be with the old tank, it sure does look like the improvements yielded from the new tank are a LOT better!

Next the landing gear is assembled, that's pretty straight forward, although you do have to drill your own set screw holes in the landing gear struts, not a big deal though.

FAN SHROUD
Next the fan shroud is assembled. The dremel comes out here to cut an opening to allow the carbuettor to fit without fouling. Also, if you're using a Hatori pipe, you'll need to cut a small section from the side of the shroud so that the header plate doesn't foul. It's all pretty straight forward.

With this, the bottom frame section is complete.

FRAME ASSEMBLY
Here's another area where things deviate from what's described in the manual, the frames. I stared at the frames in my hand for a good while trying to work out why one matched the manual but the other didn't. It turns out that MA have decided to move the tail servo around which resulted in a changed frame design. Once I'd realised that, then we were off again.

I like that the standoffs are nicely thought out rectangular gusset rails rather than just 'posts'. I like the rail idea as I reckon it should had a little more rigidity. I also like the fact they're rails not 'blocks' so there's no unnecessary weight being added.

The radio tray, small as it is, but still adequate is then bolted to these rails.

The main shaft bearing blocks are really nice. They're double bearinged affairs which I really like, that way the main shaft has a lot of bearing contact area.

Once area that I've always really liked about MA machines is the way they setup their tail drive bevel gear systems. On an MA machine, the drive shaft that holds the bevel gear and the dog bone coupling goes right through to a bearing block mounted on the middle mainshaft bearing block. This way the bevel gear can't 'jump' the tail drive's gear during high loads. It really is good. The other benefit is once you've set the mesh, that's it, no more dealing with it again even when taking the tail off. Having dealt with the pain of putting a tail back on a Vigor and realigning the mesh each time, I really appreciate this.

AUTOHUB/MAIN SHAFT
The auto hub and bevel gear system look the same as it was back in the days of the Tempest which is great because it really is faultless. Care has to be taken here, just as with other auto hubs to not damage the sprag bearing when inserting the center shaft.

The mainshaft is then slotted through all the bearing blocks and auto hub. The hub is then fastened to the mainshaft using a dowel pin and set screw arrangement that I like.

You then set the mesh of the tail bevel gear by sliding the bevel along the shaft slightly until the mesh is exactly right.

TRANSMISSION
This particular machine came with an 8.18:1 gear ratio. Like the Tempest, the gear ratios can be easily changed by changing the plates provided with the kit and the pinions. The plate gaurantees that mesh between the pinion and the main gear is correct for the given gear ratio. Each plate is imprinted with the gear ratio it is designed for which is nice.

Carrying on from my earlier discussion about the way in which drive is transmitted from the fan to the clutch via the rubber isolators, the clutch stack consists of the adapter with the pins at the bottom below the bearing block. Above that is the actual clutch which 'seems' to be bigger than it was on my Tempest which if true, is a good improvement. Above this is the actual clutch bell with the appropriate pinion, the top of which is located in the top bearing block. It's a very solid system. It's great because it's supported at the bottom just below the clutch, and at the top by the top bearing block. I like systems that are supported top and bottom like this, it reduces sideways loads on the top of the pinion which stops it from fretting.

There are a few plastic pieces around where plastic is appropriate, for instance the CCPM bell cranks and the anti-rotation guide are plastic which I think is fine. What I really like is that the ball links provided with the kit have a hex driver slot built into them like the Synergy. It's a lot better than the ball and screw affair that JR use.

At first, I thought I was missing some pieces, the tail bell crank that goes between the tail servo and the long pushrod that goes down the boom. However after another check I realised the new frame change relocating the tail servo, meant the bell crank was now no longer needed.

ATTACHING THE TOP AND BOTTOM FRAMES
The completed top and bottom frames are then bolted together. A bit of paitence is required whilst working the clutch pins into the rubber isolators on the fan hub as you don't want to damage them. Once the frames are together, you can then align the engine correctly using the four bolts in the slotted holes in the bottom carbon frame.

It's actually quite nice to be able to split the frames like that by undoing eight bolts! Infact I'm not sure, but I think to get the engine out you'll have to take the top frames off, but that's not a big deal.

SWASHPLATE/WASHOUT
The swashplate is the traditional MA one same as it was on the Tempest FAI. Once again the ball links have the hex slotted holes in them which is great. I did find that sliding the swashplate over the mainshaft yielded a lot of friction. A few dabs of Tri-Flow on the mainshaft and some vigorous sliding of the swashplate up and down the shaft saw it come good.

The plastic washout arms are pretty straight forward, pins with circlips are used to attach the washout links to the arms. This then bolts onto a plastic washout base. I'm all for using plastic where it's appropriate, but I'm not convinced that washout bases are an appropriate place for it, especially for a machine priced in this range. I would have liked to have seen an aluminium base on this machine.

Watch for the washout arms fouling on the anti-rotation guide too. It's not hard to fix, a little loosening of the guide screws while moving it before tightening again fixes this.

TAIL ASSEMBLY
Tail assembly begins with the tail pitch slider. This is a pretty simple exercise, it's mainly plastic and is held together by two retainer clips. Two nicely machined pitch links completed with assembled bearings are then bolted onto the arms of the pitch slider.

The tail blade grips bought back memories for me. I remember how much of a pain in the ass it was to tighten up the locknuts once the assembled blade grip is on the tail hub if you don't have an appropriately sized 'gripping tool'.

One thing that I thought was great was the fact that MA mentions in their manual to balance the tail assembly, a procedure that's often forgotten when assembling these things, but can really save you from having to diagnose annoying tail vibrations.

I was a bit surprised to see the tail gear box was already assembled, it looks like a very simple assembly anyway! The gearbox is open so you can easily work on it which makes a very pleasant change from the nasty enclosed gear box that was on my old Tempest FAI! On that thing you had to often assemble by feel and it wasn't great.

The plastic bell crank is attached to the gear box followed by the earlier assembled pitch slider and the tail hub. The tail hub is secured on the output shaft by a couple of unique looking grub screws which have 'dog points' on them which engage in dimples in the output shaft.

Assemling the torque tube is real easy. The tube comes with the bearing and dogbone already installed which is great and it slides easily into the carbon boom.

The plastic boom clamp is attached to the boom. Some may be sad to see plastic used here instead of metal, but not me. I'm a fan of using plastic here, especially on carbon booms as they grip well and are less stressful on the boom.

The gear box attaches to the boom by plastic tail rotor mounts which grip the boom and which the gear box is screwed into.

The single tail pushrod guide is then attached to the boom, the carbon push rod goes through the guide sheathed in plastic to prevent wearing (which does happen a lot with carbon pushrods).

Attaching the boom to the frames is via a plastic boom mount which slides into the bevel gear dog bone. No alignment needed!

Assembling the boom supports is straight forward, I use the usual method of epoxying the ends into the carbon tubes and attaching them to the helicopter straight away so that one support is not longer or shorter than the other. In this way they fit without stress.

SERVO INSTALLATION
MA machines don't use push-pull arrangements on their servos, instead they use servo supports which are a good alternative. This reduces the side loading on the servo output posts and allows the servo to produce a more direct output to the control surface without moving in the frames.

Installing the servos is straight forward. The built-in threads into the frame make it very easy. The servos either bolt directly against the frame, or to the frame on top of stand-offs to set them out from the frames a little.

You need to get the dremel out again to prepare the servo horns, in this case the large circular Futaba ones. You need to cut a section off the edge of about 5mm. This is so the wheel does not foul on the servo support posts.

Once complete, the servo wheels bolt to the servo output posts using servo bearing studs which thread into the servo posts. The servo supports then attach on top of the output posts. Bearing studs for both JR and Futaba are supplied.

Carbon servo supports are supplied with bearings that attach on posts on the frame at each end of the servo.

The ball links are nice and free out of the box and requires no extra ball link reaming to achieve a smooth action.

HEAD ASSEMBLY
This machine had a Tempest 3D head to go on it instead of the standard Tempest head. However it does have the head block that comes with the Tempest that has the new flybar carrier. This flybar carrier is quite a piece of engineering! The see-saw allows you to adjust the flybar ratio to three different settings.

The flybar is supported in a heavy duty cage style arrangement which I favour over the JR Vigor/Vibe's arrangement of having a single arm for each side of the flybar. The Stratus carrier also uses two tubes that extend the see-saw, this is good because it supports the flybar more and prevents the flybar from flexing.

The rest of the head assembles in the traditional Tempest manner. The head center block is quite wide, similar to the Raptor and uses O-Rings for dampening which has become the standard dampening system for a few years now.

The Tempest heads are still unique in that the blade grip bearings, thrust bearings and spacers are assembled on the spindle shaft and bolted up and then the blade grips are pressed over the top of the assembly and bolted in. I remember this working very well on my Tempest FAI and certainly one of the blade grips on this machine went on very easily, however the other one took quite a bit of persuasion!

The blade grips following the 'leading' style in that the pitch arms are mounted on the front of the blade grip rather than the back like the Vibe. Following the trend of adjustability on the head, you can adjust the delta value by moving the Bell-Hiller mixers along the pitch arms. I just left it in the middle as I've really never noticed the difference whenever I've played with the black arts of delta.

Once again, the quality of the parts used in this kit really are top notch. The machining of the blade grips is very nice indeed, the parts are nice and smooth, not overly heavy and best of all, you don't feel you're going to strip the thread when screwing in bolts.

ELECTRONICS INSTALL
In recent times, RC helicopters are carrying more and more electronic equipment than they ever used to, such as regulators, governors and gyro head units among other things. Unfortunately the amount of space provided in helicopters seems to have reduced! My old Vigor has a huge radio tray with vast expanses of space to load everything onto. The new Vibe however has a lot less room. This trend holds true for many new machines on the market.

Surprisingly, the Stratus actually has a lot of room available for electronics installation. The reciever is mounted vertically on the side frames which allows the tray to be free to carry any gyro and governor head units as well as regulators and batteries. Because this machine didn't have a governor and the gyro is a JR 770 which doesn't have a head unit, the radio tray had more than enough space! It would be interesting to see how a machine with a 'full compliment' of electronics would fare space wise.

What is annoying though is the fact that there is no antenna tubing supplied, nor is there any moulded brackets in the landing gear to support tubing, so where is your antenna supposed to go? I know with the rise of 2.4ghz equipment this is becoming less of an issue, but still.

FIRST FLIGHTS
After suddenly realising that MA still persist with their unique start shaft adapter system (instead of the Hex starter adapter that is the de-facto standard) and also realising that I don't have an MA start system, I had to take an emergency drive out to the Stratus owner's place to get his starter. While some might argue that the MA system is superior - it may well be, I don't really have an opinion - it would be nice for a hex adaptor to be supplied as standard instead of a seperately purchased option.

The YS fired up instantly and settled into a nice idle. The heli spooled up cleanly but was running slightly lean so I richened it up a few clicks on both the top, mid-range and also the bottom. However as I was doing so I noticed the fuel tank was leaking around the output and pressure fixtures which would also be causing part of the leanness so I shut the machine down to fix that.

Fixing the tank problems just meant tightening the fixtures up more which thanks to the Stratus' split frame design is pretty easy. You just undo the eight bolts holding the top and bottom frames together, lift the top frames off and you have complete access to the tank.

With the tank fixed I started the heli and got it into a hover. I was immediately impressed with how stable the machine was, no vibrations and the tracking was perfect. Collective response was crisp as were the cyclics. The heli sat very neutrally in the winds, it didn't get blown around much at all.

In forward flight the gyro wagged a little which was fixed by reducing the gain of the JR 770.

Forward flight stability was impressive, the heli didn't want to pitch in any direction and it did large, accurate loops without pitching at the bottom.

The rudder felt a little strange simply because the standard gyro settings have a huge piroette rate which makes the helicopter tail feel non-linear.

Autorotations seemed to go on forever, the Stratus' light weight certainly helping here.

Just as I decided to start getting into some 3D with the machine it suffered a tail failure during piroetting flips and pounded in. Pounded in good. It turns out that the boom had slipped back which had caused the loss of tail drive. A number of people I talked to later said "Yeah that's what Stratus' do, that's why you have to put a bolt directly into the carbon boom". Well I went back and checked my instructions (created 11/01/05) and there was no mention of that. However the new frames did have a bolt thread to do this. If you're building an MA machine, always check their website for the latest instructions, cause these guys change things on the fly.

The crash was made worse by the fact that when I flicked out of throttle hold after the machine hit, I'd forgotten to take it out of Idle Up so it did a funky chicken for a bit until I could work out what had happened.

The damage wasn't too bad, the tail section had escaped relatively unscathed, however the head area had taken a good hit, the JR tail servo had stripped as had one of the cyclic servos. The huge flybar rocker assembly made removing the bent flybar, a royal pain in the ass, plus, the potential to bend something expensive in that assembly is too great for my liking.

The machine is now fixed, however it's now being transformed into an E-Stratus (with potentially a flybar-less head) so I didn't get much time to form an opinion on how this particular one flew.

WOULD I RECOMMEND IT?
Overall, the machine seems to be very good, it flew (and hovered!) very nicely and it seems very strong. You definately can't mistake it's heritage for anything other than Miniature Aircraft in that it's not as simple as it could be (ie lots of little carbon bits, standoffs here and there etc), a lot of these little appendages look very vulnerable to a crash. The machine is very tough though, anyone who has seen Bobby Watts fly his will know that.

The thing you do get when buying MA is that the machines are based on the same old tried and true designs of the old days. The swashplate and washout assembly can be traced back to the old mechanical mixing machines which is a testament to the design.

MA, like Align, seem to be very dynamic in that when the need to implement a change is identified, they do something about it straight away and incorporate that change in kits as they ship, hence the dynamically changing instruction manuals. Manufacturer's like JR could take note of this.

If you're after a 3D style machine engineered for quality then you'd have to seriously consider the Stratus, along with the Vibe and Synergy. So if you're in the market for a machine like this, then give the Stratus some serious consideration, you won't be disappointed.