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Hobby Lobby Imports Uzi XL ARF Review
Albert Wahrhaftig enjoys this smart looking and rugged aerobatic biplane, with a wing loading of just 5 oz/sq ft. On the next Saturday in still windy weather, I flew two more times. Albert indicates, "This is one great little plane - lively, easy to transport, and just perfect for this Sunday flier."
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| Wingspan: | 28 1/4" |
| Wing Area: | 352 sq. in. |
| Weight: | 12 oz. |
| Length: | 28 1/2" |
| Wing Loading: | 5 oz/sq. ft. |
| Servos: | (3) Hitec HS55 |
| Transmitter: | JR XP783 |
| Receiver: | Hitec Electron 6 |
| Battery: | Thunderpower 3 cell 1320ma. |
| Motor: | Potensky 80W external rotor brushless |
| ESC: | Jeti Advance Plus 8 Amp |
| Manufacturer: | Potensky |
| Available From: | Hobby-Lobby |
INTRODUCTION
The UZI XL is a smart looking and rugged aerobatic biplane, that is compact enough to stuff into the smallest car. Assembled from a relatively small number of EPP foam parts, its mere 5 oz. per square foot wing loading allowed it to virtually float off the ground and fly with a gentleness a near-beginner can handle, yet still power into snappy aerobatics. In all, this little Czech made airplane has a lot going for it.
KIT CONTENTS
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These small parts came packed in a plastic bag.
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Hobby Lobby offered this package of additional items to complete the UZI XL
The UZI Xl came in a compact flat box with a useful full color photo on top. Inside, I was surprised to find the various EPP pieces packed with no protective foam, dividers, or plastic bags. In spite of the lack of protective packing, everything arrived with no damage whatsoever. In addition to the EPP parts, the box contained an instruction booklet, a sheet of blue peel and stick decorations, and a plastic bag full of small parts. Everything else needed for completion was supplied for this review by Hobby Lobby and can be purchased from their web site. The quality of the kit materials and of the components supplied by Hobby Lobby was excellent.
ASSEMBLY
The UZI XL kit contained a 15 page instruction booklet supplemented by a full size fuselage profile drawing printed on two 12x16 inch sheets. The instruction booklet contained 80 line drawings illustrating assembly, 5 illustrating control throws, 1 indicating how the carbon fiber rods should be cut, 1 page of airframe and ESC specifications, and a final page of diagrammed controller programming settings.
Note:The entire “Building Guide” (Potensky's term for the instruction booklet) can be downloaded from Potensky’s web site.
This kit was suitable for those who have successfully constructed fairly complicated "foamies", but no written instructions were included. With only the minimally labeled drawings to bo by, assembly would have been a difficult task for anyone without substantial experience.
Manual
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Drawings from the instruction book: Look at the size of the saw and what it was cutting (a toothpick!).
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Drawings from the instruction book: What is indicated in #29 is far from self-evident.
There were several places where I had to sit and give the more cryptic steps some serious thought, for which reason I have created a separate document to go into more lengthy detail of virtually all the assembly steps. If you're getting ready to build this airplane, I hope you'll find the more detailed page helpful! If you're not quite ready to buy it yet, then this article will give you a briefer overview of what you have ahead of you.
The instructions specified use of three kinds of glue: an odorless CA glue, a polyurethane glue (Pro-Bond) and LA tmel, a contact cement. A bottle of the LA tmel was included in the kit. Where its use was shown in the assembly drawings, a wait of 10 minutes was indicated. I found that it took much longer than 10 minutes for this glue to bond. Left to cure overnight, it did create a joint that was stronger than the foam itself, but I simply used foam safe CA throughout with satisfactory results.
Assembly Overview
As an initial illustration of the difficulties with the instructions, the first drawing (shown above) illustrates attachment of the fiberglass firewall to the fuselage front. Above the drawing of the firewall being attached to the fuselage, a razor saw is shown cutting what appear to be two dowels that are pointed at both ends and fully as long as the razor saw. What? After searching through the kit for some sort of dowel as long as a razor saw, I eventually realized that what was being shown cut in half were toothpicks that are included in the kit! The toothpicks were shoved into holes in the corners of the firewall and served as pegs that reinforced the joint. I knew I had a bit of a challenging assembly ahead of me. The kit turned out to use the toothpicks in a variety of key areas and in a variety of ways.
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Toothpicks reinforce the gluing of the firewall to the nose of the fuselage.
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A cavity had to be carved out to house the ESC. A drawing showed how to bend a tool from 1.5 mm. wire (not included) which, attached to a soldering gun, formed a very precise tool for this purpose.
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The cowl was cut from one block of foam. No dimensions were shown.
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The cowl, ready to attach to the fuselage.
There were no hinges to deal with in this kit. The fin-rudder, stabilizer-elevator, and wings-ailerons are all molded as one piece with a deep “V” between the fixed surface and the control surface, the residual material at the bottom of the V serving as a hinge. The control surfaces were rather stiff, and I wasn’t at all sure my little HS55’s would be adequate to push them, but so far the rudder and elevator have worked well, although I did (see below) have reservations about the ailerons.
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The fin/rudder assembly was simple. Fixed and control surfaces were in one piece with a deep “V” serving as a hinge.
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Where NOT to place the “XL”! This location interfered with the pushrod slots.
The illustration in the instruction booklet showed the decals being ironed down with an iron set to 209 degrees. DON'T DO THAT! The decorations will curl up and distort. A small separate page included with the kit showed that you must place a piece of paper between the iron and the trim being applied. This worked, but be sure not to exceed the indicated temperature. Too much will distort the trim.
I wanted to be able to remove the canopy, so I removed the pegs, put a drop of glue on the tip of each peg, and reinserted them. Then I put the canopy away. I didn't need it for a while.
I had to draw a centerline down the edge of the stabilizer where it butted against the fuselage. I pushed two toothpicks into each stab half. These served as little spars when the stabs were joined to the fuselage. I took care to punch the toothpicks in at a right angle to the stab, both as seen from the front and from the top. If the other end of the toothpick was then aligned with the faint line drawn on the fuselage, I ended up with the stabilizer installed at its proper angle of incidence.
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Rudder and elevator servos in the cockpit. The receiver fit into the cramped space in front of them.
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Pushrod sheaths were pushed into a slit and glued.
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I drew a centerline down the butt end of the wings.
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Holes for the toothpick spars should be on the centerline you drew. On the top wing, the toothpicks had to pass from one half into the other.
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A completed wing!
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Carbon fiber rods passed through the wing struts.
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I made a cardboard jig over the full size fuselage drawing to aid in inserting carbon rod cabine struts at a proper angle.
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Using the jig to insert a cabine strut into the fuselage.
It was time to mount the top wing. Was I going to be able to match the zero incidence of the lower wing? Was I going to be able to avoid warps? Now was the time to work slowly and carefully. I did not manage to do an accurate job at this point, and if I had it to do over, I would make a set of jigs to hold everything in perfect alignment. It turned out that there was one thing in the kit that would have helped....a foam jig.
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This otherwise unidentified piece turned out to be a jig for aligning the top wing.
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Top wing mounted, all struts in place, ready to remove the jig.
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String-weight-wheel tool was needed for hauling servo leads through the twisty passages inside the fuselage.
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Heat shrink tube helped keep the servo plug in line with the string for easier passage through the fuselage.
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The top aileron was held in neutral by popsicle sticks so the rod connecting the ailerons could be adjusted and glued.
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The connecting rod was pinned in place on the top aileron.
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The ESC and motor mount were installed in the fuselage.
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The Potensky 80W motor and included folding prop were istalled.
Using the recommended POT80W motor, this was simple. Two screws held the motor mount to the fiberglass firewall I installed in the beginning of time. The motor simply slipped onto the motor mount and was held in place by a set screw on the bottom.
Wrapping Up
I found that no matter what, I had to lengthen the ESC lead to the receiver. I found that I could use an extension or just splice in some extra wire. I needed my string and weight to get the plug up to the receiver cavity.
Next I balanced the plane. The CG was not shown in the instruction booklet but was shown on the full size fuselage drawing. I set all the control surfaces to 35 degree control deflections each way and noticed that there were three exclamation points placed after the instruction to dial in 60 percent exponential on all control surfaces.
Modification Suggestions?
I built everything stock for review purposes, but I was a bit dubious about aileron activation. A single servo in the bottom center of the fuselage activated the ailerons on the bottom wing. A vertical rod connected the top wing ailerons to the bottom ailerons, so a single micro servo was pushing four ailerons around. The integral hinges formed by cutting a deep V in the wings had considerable resistance, enough that the resistance could cause the bottom ailerons to flex when large amounts of control throw were applied.
My instinct was to cut the ailerons free and hinge them with tape or any choice of non-binding hinges. If I built it again, I would follow my instinct. Additionally, it was difficult to rig the vertical rod with enough accuracy that the upper and lower ailerons were parallel, and there was no way to adjust this parameter. My suggestion would be to cut two oversize half rods, overlap them, and use a modified servo quick connector to make an adjustable connector. The weight gain should be minimal.
FLYING
A First Flight In a Heavy Breeze
The poor little UZI had been sitting for weeks, waiting for calm in the midst of continuous wind and rain. Finally, a tiny space appeared, just enough for a trip to the local middle school play field and one flight in a pretty stiff breeze. I didn’t know what to expect from this small, very light plane with large control surfaces and was anticipating the possibility of a real handful. It turned out that there was absolutely no reason to fret.
Although I am sure you could hold this plane vertically in one hand, apply full throttle with the other, and have the UZI rise directly into a vertical climb, I enjoy naturalistic takeoffs. Set on the ground, with moderate throttle, the UZI seemed to loft itself into the air, reminding me of some of the aerobatic bipes I have seen at air shows. With a little more throttle, it was climbing steeply. I reduced throttle at altitude, the UZI cruised along at less than half throttle. Even with the breeze, the plane was stable and responded precisely to controls. Its stall was gentle and for a Sunday flier it was a lot of fun and looked great too. Rolls in either direction were quick and easily controlled. Loops were tight and effortless. On landing, the little plane touched down gently right at my feet.
On the next Saturday in still windy weather, I flew two more times. This is one great little plane - lively, easy to transport, and just perfect for this Sunday flier.
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The UZI flying high in the wind.
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Dodging trees while flying in a tight space (see below).
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Vertical? No problem at all!
Adventures in High Wind and a Tiny Space
Two weeks later and the wind kept on. There was only one thing to do. Take the UZI over to Red's Hangar One in Rohnert Park, Ca., where Red Jensen, who was flying RC before he could talk, awes customers by flying planes out of the small parking space in front of his hobby shop, darting between parked cars and dodging trees, poles, and phone wires. You gotta see it to believe it. In spite of gusty wind, Red put the UZI through its paces - with a variety of manuevers you can see on the video. Red declared the plane "a dynamite sport flier" but found that because my alignment of the wings was less than perfect, the plane showed some coupling that made precision flying difficult, especially in that wind. When I asked him how he thought the UZI would fly had I been able to be precise in my alignment of the wings, he thought it would be 3D capable, especially with increased control throws and replacement of the stock folding prop with a fixed one. All in all he liked the plane a lot, and it certainly showed its capabilities under these difficult conditions.
Video Gallery
Editor's Note: If your pc does not have Apple QuickTime, you will be unable to view this video. QuickTime is a free download available at Apple's website. Be sure to select the free download on the left edge of the page rather than purchase the extensive product over toward the right.
Downloads
Modification Recommendations, Post Flight
Of course, results can vary according to minor builder-induced differences, so my story may not be yours, but my UZI will benefit from a little down thrust. I had to trim in some “down” during powered flight and then hold up stick when gliding. Building in down thrust would have been best accomplished when installing the firewall at the beginning of assembly. Then if I had too much down thrust I could have slipped a bit of shim up from the bottom and beneath the bottom of the motor mount. As it was, I will encounter difficulty finding a way to slip a shim from the top under the top of the motor mount.
CONCLUSION
I really enjoyed this little small-enough-to-toss-in-your-car-and-carry-anywhere model. It was not for the first time builder or the first time flyer, but it was stable enough for pilots with moderate aileron experience and yet was, as Hobby-Lobby said, “wildly aerobatic”. The recommended Potensky motor and prop were an excellent combination and provided generous and absolutely silent power. With this little gem you can enjoy yourself in virtually any park or school yard.
Discussion
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Jun 17, 2005, 04:35 PM
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Harrison, AR
Joined Sep 2004
25 Posts
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proper prop for the Uzi?
The review stated several times that the Uzi could use a different prop, but no recommendations were given. Has anyone logged time with something other than the stock folding Potensky? Mine had one blade decide to depart in mid-air, so I tried several slow flyer - a 9x6, 10x4.7, and 10x7, all of which caused the motor to have a terrible noise like an armature rubbing or bad bearing at mid throttle. All had been balanced, and the hub thickness had to be planed down slightly ~1/16", from 5/16 to 1/4, since the shaft is only 3/8" long and the prop nut barely had any threads to screw on to. This wasn't noticed until I got back to the field weeks after the folding prop had failed, so I thought it was a motor problem. HL sent a replacement motor, and same thing, but fine with the new folding prop included. They recommended not using anything over a 9x3.8, so I'll have to wait until I get my hands on a few sizes lower than what's on hand, but was wondering if anyone has tried a fixed prop on the original Potensky motor....
I went to slightly bigger wheels for grass, 1.5" vs the little bitty 1.25" (wanted 1.75" lectra-lite but LHS out) so the cute little wheel pants no longer fit, but I was having a hard time keeping them in place anyway. During the initial build I also made the landing gear from slightly stiffer music wire - if you're going to do it, that's the only opportunity! Using a 3S-1500 Kokam battery mounted cross ways (original opening cut all the way through the fuse), with a velcro 'safety belt'. I haven't had much time to fly this pretty little jewel, but it is VERY agile, even with the throws backed way off. It seems either the wind is excessive when every thing is working, or perfectly calm when I'm waiting for parts.... Cheers.. Don |
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Jun 17, 2005, 07:07 PM
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Sebastopol, CA, USA
Joined Dec 1996
513 Posts
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UZI prop
Like you, I lost one blade from my folder when it clipped a clump of grass. They are fragile, aren't they! I also found the prop adapter to be way short and had to trim down the hub of a GWS prop to fit. I think it is a 9x5, but I haven't flown the plane since -- bad weather continues. I'll let you know how it works out as soon as I have a chance to fly it. By the way, how did you get the spinner off?
ALW Quote:
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Jun 17, 2005, 07:18 PM
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Sebastopol, CA, USA
Joined Dec 1996
513 Posts
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Static trial
I went to my workshop and checked. At the recommendation of my LHS, I had installed a GWS 9x7 prop. I fired it up and found that it was smooth at all speeds, so no ugly sounds like you describe. In spite of HL's advice, I think I'll try it in the air and then, if need be, switch to something with lower pitch.
ALW |
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Jun 18, 2005, 03:22 PM
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Harrison, AR
Joined Sep 2004
25 Posts
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Update: picked up a couple of APC Slow Flyer 9x3.8, and it was just what the doctor ordered (Dr. being Justin @ Hobby Lobby). Even tried one before balancing, and it was fine! Hard to believe nothing more than the difference in a 9x6 and 9x3.8, especially at low/mid rpm, could drive the motor nuts like that, but it did!! Good thing, because another Pot folding prop became history after nosing over on a grass clump (sound familiar?) this morning.....
Cheers. Don |
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Jun 22, 2005, 10:39 AM
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Kilkenny, Ireland
Joined May 2002
6,424 Posts
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Dangerous flying
Having had a quick read through your review and looked at the video I felt I should join in here to comment on the video.
That car park you're flying in looks like a very restricted space and you are overflying what appears to be a busy road and a public footpath. Notice on the landing approach how close you came to that cyclist. This seems incredibly irresponsible and posting the video in a public review even more so. There have been many criticisms of the lax attitude to safety that seems to be growing among light electric plane flyers and this sort of flying is at the heart of it. The apparent endorsement of this attitude by including such a video in a review is disgraceful in my opinion and I hope E-Zone will consider censoring these videos to see that they don't encourage such careless choice of flying sites or other excessively dangerous practices. Aidan |
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Jun 22, 2005, 11:47 AM
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Sebastopol, CA, USA
Joined Dec 1996
513 Posts
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Safety
I certainly agree with the necessity of safety consciousness and am often among the first to step in when something dangerous is afoot. In this case, I would certainly never attempt to fly in such a confined space. However, the pilot in the video is an extraordinarily skilled flier who is flying in front of his hobby shop, a territory with which he is very familiar. The parking space is closed and the closeness to the bike rider is exaggerated by the telephoto, so in this case the safety issue is more apparent than real. In retrospect, I should have included a caption under the video and pointed out that this was an exceptional pilot in exceptional circumstances and stressed that for the rest of us this airplane, indeed any airplane, must have lots of open space.
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Jun 22, 2005, 11:56 AM
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Kilkenny, Ireland
Joined May 2002
6,424 Posts
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He may well be a great pilot but I doubt he's infallible. I gauged the proximity to the cyclist by the shadow and elevation which gives a very accurate picture of relative positions. The shadow is almost directly below the plane (judged by the closer shots) and passes just in front of the cyclist.
As you say there are pilots who will probably get away with flying in such spaces but I don't think that means they should do so. I'm glad you acknowledge that it's not a suitable site for the plane and thanks for not disregarding my post. Aidan |
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Jun 24, 2005, 12:33 AM
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Joined Jul 2003
162 Posts
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Wrong Uzi...
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Last edited by MartialArtist; Jun 24, 2005 at 12:42 AM.
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Jun 24, 2005, 08:22 AM
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Harrison, AR
Joined Sep 2004
25 Posts
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Quote:
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Jun 24, 2005, 11:26 AM
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Up North
Joined Mar 2001
424 Posts
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Aio,
Where in the video do you see the little UZI coming close to a bike? I saw a bike in the driveway, but not in the lot. IMHO, it was easy to see that there were no problems here. Of course I can see your point of view about safety, but when we're looking through the "blinders" of a low rez video it is impossible to comprehend the perspective of the actual site. And it is all to easy to criticize as a faceless poster. ------------------------------- AW, Cool video Albert. The great thing about little 3D flyers is that (with precaution) you can fly them just about anywhere. If it weren't for a clerk at my LHS hovering a shockflyer in his store's parking lot, I wouldn't have made the wholesale jump to light electrics as early as I did. I have a shocky, an Airwave Sukhoi, and an XXL (recently reviewed with some video over MY street). I like the XXL a LOT more than the other two! |
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Jun 24, 2005, 02:46 PM
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Kilkenny, Ireland
Joined May 2002
6,424 Posts
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Quote:
I'm not going to get into a row about this. I made my point which most people will admit is a valid one. I'm not basing my comments on guesses from a low resolution video , I'm basing them on what is clearly visible and what has already been conceded. I don't know what your "easy to criticise" comment is all about. Are you saying only positive comments will be taken seriously?! That would make these fora meaningless. Aidan |
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Jun 24, 2005, 04:12 PM
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Joined Jul 2003
162 Posts
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I watched the video myself and the guy riding the bike was more than safe in distance.
I agree, no point of starting something out of nothing. He never got hurt, so that's the good part. 
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Sep 20, 2007, 02:48 PM
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NY State
Joined Jan 2007
2,833 Posts
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I just found this thread and watched the vid. I think people are overly concerned with safety sometimes (yes, I said that, but in this case, that's just a bad area to fly a plane, definitely. I don't think he came too close to the cyclist, but it's right next to a busy road. If nothing else, it certainly is distracting to drivers!
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May 06, 2008, 08:48 AM
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FUENGIROLA (MALAGA) Spain
Joined Dec 2006
138 Posts
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hi, I am interested is this plane and I want to know how does it make 3d? is there another video to watch it?
thank you! |
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