Racing and Slope Planes

Mini Acacia (Solero)

Updates

Type: Slope glider
Wingspan: 56.5"
Wing Area: ~288 sq in.
Airfoil:modified RG15
Weight:17 oz.
Construction: Fiberglass fuselage with carbon fiber tail boom, hollow molded wings and v-tail (glass over balsa skin)
Controls:Aileron, elevator, rudder.
Opus-V

Okay, I have to admit that I've never been a huge fan of pod-and-boom designs...I just don't like how they look. But F3X.com had this plane on sale a little while ago, and I knew it to be a good flying airplane, so I couldn't pass it up.

The Mini Acacia (also known as the 'Solero') is the little brother of the large Acacia F3F and F3J planes. The Mini's wing and tail shares the elliptical leading edge, straight trailing edge planform of the bigger planes, but that's about where the similarities end.

Fuselage: As noted above, the Mini Acacia sports a pod and boom type fuselage. The pod is nicely molded and pre-painted. It includes a painted canopy which has all the mounting hardware installed, and fits perfectly. The fuselage, like those of many other small molded planes, is fairly thin, and possibly fragile (I'd gladly trade a bit of lightness for some extra durability). The rear of the fuse is made a of sturdy carbon fiber boom, with a nice molding at the rear for the v-tail to sit on. The boom is unpainted and left in it's natural glossy carbon fiber finish, which looks pretty nice.

Yep, it's a pod and boom.

Wing: The wing is hollow molded, with balsa/fiberglass skins. The grain of the balsa is quite apparent through the white paint on the upper surface of the wing, but otherwise, the finish is good. A feature somewhat unusual on such a small plane is the flat center section with a fair amount of dihedral on the outer panels. The wing is also VERY thin. In fact, it is thin enough that the servo covers have bulges on them to accommodate the aileron servos (more on that later). The outer panels contain the ailerons, which are live-hinged, but have no wipers. The wing attaches to the fuselage with a pair of metal allen head bolts, one in the middle of the root, and the other at the trailing edge.

Lots of tip dihedral.

V-tail: The v-tail is similar in construction to the wing. It's mounted to the fuselage with a single metal bolt. The elevators are live hinged, and like the ailerons, have no wipers.

Assembly: As with most molded planes, there really isn't any major construction. The mounting hardware for the wing, v-tail and hatch are already installed. If you buy the plane through Composite Specialties, you get a three page assembly manual, which gives you pretty much all the information you need to get the plane flying1. This is a nice feature when you consider that many molded planes come with absolutely no documentation. About all there is for the builder to do is to install the push rods, servos, and surface control horns. (I have since learned that some of the Mini Acacias come with the control horns and push rods already installed. Perhaps this was why mine was so cheap!).

I found installing the control horns in the v-tail to be the most annoying part of this model. It seems that most molded planes I've come across have the torque rods and ball-links pre-installed in the v-tail's surfaces. This sorta makes sense in the case where the elevators are already hinged onto the tail from the factory. On the Mini Acacia, this is left to the builder, though. What's odd is that elevators have what appears to be a molded mounting area for some sort of linkage, possibly that's intended to be screwed in. This nice little piece of molding has to be chopped out to install torque rods, though. It's not really a difficult task, and the instructions are very straight forward in how this is to be done. A torque rod is created from a piece of music wire that gets bent to the proper angle show in the instructions. This then gets capped with a piece of copper tubing that gets flattened on the end and has a hole drilled through it to act as the horn.

V-tail linkage
(yes, that's the antenna
coming out of the carbon tail boom).

Like I said, it's not to hard to do this, but I found it aggravating to have to mount both torque rods into their respective elevators while they were still attached to the v-tail. Getting all this set up right without introducing any asymmetry into the horns was a bit nerve-wracking. One of the reasons for buying a molded plane is because everything is essentially perfectly straight and true right out of the box. It would be nice if this was the case with the v-tail hardware.

To my surprise, I managed to mount the v-tail control horns in what looked to be a symmetrical fashion, so I proceeded to the push rod and v-tail servo installation.

The instructions show a single push rod and servo for the v-tail. I wanted to have rudder control, plus, I was a bit worried about the ability to adjust the elevators independently, so I opted to go with 2 servos (Cirrus CS21BB's). For the push rod housings, I used some generic plastic tubing found at the hobby shop, with .047" steel music wire used for the push rods themselves. This wire is a bit smaller then what I could have used with the push rod housings. Any larger then that and the wire tends to bind as it takes the upward curve from the low mounted tail boom to the upper part of the forward fuselage. Once I had figured out where the housings were to go, I used the GOOP method to secure them (see my review on the Opus V for details).

The forward fuselage, while not super roomy, is not overly tight. I got a 600mAh battery pack, Hitec 555 receiver, switch and 2 CS-21 micro servos to fit in with room to spare. If I had mounted the servos a bit further back, I could have probably fit a 7 or 8 channel receiver. For v-tail servo installation, I mounted both servos semi permanently onto a ply platform, and then glued the platform to the bottom of the fuselage. The platform was mounted at an angle to take account for the v-tail push rods rising up from the floor of the fuselage at an angle. For the receiver switch, I made a small mounting platform, and then mounted it and the switch to the forward servo mounts. I then drilled a small hole in the side of the fuse, through which a wire passes into the switch. This allows me to turn the receiver on and off without removing the canopy (which is held on with a screw) , while avoiding having the large switch itself mounted externally.

Flap modification
Inside the forward fuselage.
The thing behind the
servos is the plug for the ballast tube.
A tow hook for bungie launching
comes installed. The little wire on the side is the switch.

Wing construction isn't too involved. There are no control horns on the ailerons, and although some plastic horns are included, they don't look too suitable for a molded plane. I opted to take some large G10 fiberglass horns and cut them down to fit the Acacia. I routed out a slot in each aileron, and epoxied the horns into them.

The next step is mount the servos and set up the servo wiring. I carved out a hole in the wing root for the servo wires, and proceeded to create my wiring harness. For simplicity, I decided to use a single, 4-pin Deans connector to hook up both servos.

As suggested in the instructions, I reinforced the insides of the servo bays with carbon fiber, to prevent the upper wing skins from buckling, either during operation, or in the event that a servo had to be removed.

Also as suggested, I used JR241 micro servos for the ailerons. Herein lies a bit of a problem with the Mini Acacia's wing...it is thin...VERY THIN. There's no way that a suitably torquey servo will fit flush in the wing. To that end, the manufacturer has provided servo covers with bulges in them to handle the greater thickness of the servos. Unfortunately, I found that the bulges still weren't large enough to accommodate the combination of 241's and the underlying mat of CF reinforcement. I ended up having to cut a hole in the covers to allow the servo to poke through. It doesn't look too bad, but I wish someone had put a little more thought into this part. You might be able to fit a tiny servo, like a Cirrus CS10 or Hitec HS50 under the covers, but those servos would be seriously lacking for a fast slope airplane.

View of the fiberglass aileron horn and the servo cover.
Note the servo sticking out through the cover.

To secure the servos, I wrapped them tightly in masking tape, and then glued the servos directly to the reinforced upper wing skins with a dab of epoxy and micro balloons (believe it or not, this actually works really well, even on a high performance plane).

The final step was to route the antenna. Routing the antenna the conventional way, through the tail boom, seemed out of the question, due to the tail's carbon fiber construction. However, the instructions from F3X suggested to do just this. I contacted Tom at F3X about this, who said that sometimes this works, and sometimes not. So, I went ahead and tried it, and lo and behold, the radio range checked great! I have yet to experience a problem with this, even when the plane is quite far away. Of course, you should range check whatever receiver you are going to be using before trying it yourself.

With construction complete, it was time to setup and balance the plane. To my great surprise, I found that the plane needed less then one ounce of weight for balance. This is the first slope plane I've owned that needed barely any nose weight. The 600mAh battery and the forward position of the 2 v-tail servos probably account for this. Final flying weight is only 17oz...half the weight of my other 60" sloper, the Renegade. Had I known it was going to come out this light, I probably would have added some fiberglass or carbon reinforcement to the inside of the forward fuselage and ballast area.

Flap modification
Ready to go!.

Flying: The first flight took place in somewhat more blustery conditions then I would have preferred for a plane of the Mini's weight. Despite a bit of bumpiness, the Mini did just fine. No trim changes were needed on the first launch, and the recommended CG seemed to work out just fine. Some more ballast would have helped, but I hadn't yet made provisions for that. Still, the plane zipped along quite well and was very easy to fly.

The controls were responsive, especially the rudder and elevator. This plane can really crank through the turns. The elevator authority was really quite surprising. If I didn't know any better, I'd say the plane was tail-heavy because of the high pitch response, yet the plane is actually quite stable in pitch, which is very cool. The rudder authority is also very good...much better then on my other v-tailed sloper, the Opus V.

The Mini Acacia's ailerons were a different story. I found the roll response to be somewhat sluggish, and the roll rate disappointingly low. Perhaps this is due to the large amount of wing panel dihedral, or maybe the ailerons are a bit on the small side...I'm not sure. I tried increasing the aileron throw as much as possible, but it didn't help much. What to do...well, for the heck of it, I tried using a bunch of rudder when I did a roll...WOW! What a difference. It actually did a respectable roll that was fairly axial, despite all that rudder. I landed and set my radio up to mix in 50% rudder when aileron was applied. The result was dramatic. Basic aileron response got much better and the roll rate got pretty good. In fact, I was happy enough with the mix that I have left it on permanently. For this reason, I highly advise that if you buy this plane, build it with two v-tail servos so you can have rudder. It's well worth it.

Light lift: With an approximate unballasted wing loading of 8.5 oz/sq ft, the Mini obviously has very good light lift performance. This has become my number one plane for light lift, as it stays fast and responsive in those conditions. As you might imagine, it thermals very well too. Not too surprising...this plane barely weighs more then my Climmax HLG.

Aerobatics: The aileron response is good, but not incredible, so don't expect super quick rolls unless you have lots of airspeed. The rudder, on the other hand, is very responsive, and make maneuvers like hammerheads a breeze. Turning performance is very good, and the plane doesn't seem to lose too much energy in hard pylon turns. In addition, the plane has been very well behaved even in violent maneuvers. I have yet to get the Mini to tip stall.

Speed: While the Mini Acacia is pretty fast unballasted, it's light wing loading means that it can benefit from a little extra weight in anything but the lightest conditions. To that end, I decided to make a ballast tube for it. It actually ended up being a bit over complicated: I wanted a tube that could except the brass ballast slugs that came with my Opus, and I wanted to be able to load the tube from under the canopy, rather then having to remove the wing.

What I ended up with is a fiberglass container that looks a bit like a battery pack for an e-powered plane. The tube sits on it's side, and holds 4 brass slugs (which yields a bit over 4 ounces), in a "double barrel" configuration, with 2 slugs on top, and 2 on the bottom. The slugs actually sit in the rear half of the tube, since that is the part located over the CG. To load the tube, I open the canopy, remove a plug from the front of the tube, and load the slugs one by one. The first two slugs automatically drop in place in the bottom of the tube, and the next to slide in on top of those. To remove them, I just hold the plane upside down, tilt the nose down, and they all slide out.

4 brass slugs are used for ballast
You can just see the open ballast tube under the wing.

Admittedly, 4 or 5 ounces isn't a whole lot of ballast. The instructions recommend 9 ounces, so I sacrificed the ability to add more weight for convenience. Also, fitting in a large chunk of lead or two would mean opening a fairly large hole in the top of the wing saddle, and I wasn't sure I could comfortably do this with out weakening the center of the fuselage. Still, the ballast I do have does make a noticeable difference. Add some weight, and this plane will definitely go fast.

Dynamic Soaring: The Mini Acacia is thus far the easiest to DS plane that I have flown. The combination of light weight and a very thin wing makes for a plane that will accelerate extremely quickly in the DS groove. It almost always immediately gets "on step," and up to high speed. The first time this happened almost scared me. I was flying in light DS conditions, when suddenly things got better. The Mini went from a lazy cruise to screaming fast in half a circle! Compared to my other 60" plane, the Renegade, the Mini just seems so much more eager to get on step and moving. While my other main DS plane, the Opus V is ultimately faster, I don't think it can match this acceleration. I should note that the Mini it is a bit squirrely at times in comparison to my other planes, especially in less than smooth DS conditions. As far as 60" DS planes go, I think the Nemesis is still the fastest/ smoothest I've seen, but the Mini is a close second.

The Mini's responsive, but not overly sensitive elevator makes it great for all sorts of DS conditions. It allows you to pull super hard turns, and fly a large variety of DS grooves. The ailerons too, are quite nice when the plane is in DS mode. Combined with the tight turning radius, they allow you to do all kinds of maneuvers, such as tight backside figure 8's. This responsiveness really contributes to the plane's ability to DS in light or shifty conditions, or at sites that have a very tight DS line.

This plane would probably make a good first "crunchie" DS plane for someone moving up from foamie DS'ers. As always, be warned that this plane will likely not tolerate any sort of DS crash without getting totaled.

Landing: The plane is very easy to land. I set up my radio to give me "spoileron" (both ailerons up) control for landing, as I do with most of my flapperon ships. I wasn't quite sure what to expect, as I've never had a flaperoned plane that didn't have full span ailerons. As it turns out, they work great! Full spoileron slows down the plane very quickly, and aileron response remains good. What's more, even with the spoilerons fully deployed, no elevator compensation is required. I've never had a plane that didn't need at least some up elevator compensation when the spoilerons were deployed, so this is pretty cool.

Spoilerons work great for landing.

Conclusions: This is really a great little plane. It's fast, fun, and maneuverable in a variety of conditions, and it's a good contrast to my other moldie, the fast, smooth, but heavy Opus V. The Mini Acacia would probably make a good first molded plane, as it offers great performance in a relatively inexpensive package.

One thing I should mention is the durability issue. Like many other small molded planes, the Mini's light weight comes at the cost of reduced durability. As mentioned previously, the fuselage isn't very thick, and probably wouldn't tolerate a hard nose-in too well. The wings too have thin skins, and are easily dented/dinged.

As I write this, I have been flying my Mini for about three weeks, and have had nothing but good landings, yet I still have collected numerous small dings on the bottom of the wings from landing on twigs and stuff. For this reason, I think the Mini makes for a good first molded plane, but NOT a good first composite plane. It's a very easy plane to fly, but unless you are absolutely confident in your abilities to land consistently well, you are going to damage it. A non-molded composite plane with either vacuum bagged or wood sheeted wings (such as the NSP Filip Slope, NSP Filip Slope 2 meter or Multiplex Lucky), would be a better choice in my opinion. Still, if you decide to ignore my advice and buy this plane anyway, you won't be disappointed...fun plane!

1. Northeast Sailplanes sells a plane called the Mini Acacia as well. Despite the pictures the website, the plane they are selling is not actually a Mini Acacia, but rather a similar plane called the "Risk." (they may have at one time sold the "true" Mini, but I'm not sure).

(Another version of this review can be found on LiftZone).

Updates:

I was finally able to try out a bungie launch with this plane. We didn't have a true "slope on a rope" bungie with us, but rather some highstart tubing with only a short length of monofilament attached. We used this in conjunction with a pedal launcher my friend made, and it worked beautifully. The plane was rock solid stable on tow, needing no pilot input at all. On release, I would pull up into a vertical climb, sometimes going for all out altitude, and sometimes doing stuff like vertical rolls. It's the next best thing to a DS punch-out. It's lots of fun!

A friend of mine, who also has a Mini, pointed out to me that the v-tail on my plane was getting a bit loose. His had done the same thing after a few months too. Turns out that the balsa spar in the v-tail cracks and gets delaminated from the skin, making the tail flexible at the root. I can only assume this is from DS'ing, since the plane has never been landed hard. Anyway, the fix is easy: just shoot some thin CA into the hold in the v-tail between the elevators. This goes directly to the spar, and seems to fix it up very well.



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