Hobby-Lobby F5B Tiger Review

Sunday, June 15, 2008

by Chris "JustPlaneChris" Boultinghouse

Specifications:

Distributor: Hobby-Lobby, International
Type: Sport or F5B Competition
Flying weight: 38 oz. / 1077 g
Length: 36.5 in. / 927 mm
Wing span: 67 in. / 1701 mm
Wing area: 330 sq in / .212 sq m
Wing loading: 16.5 oz/ sq ft / 5.03 kg/ sq m
Radio: JR 9303 transmitter with DSM2 module, Spektrum AR6200 receiver, 2 Hitec 125MG thin wing servos on ailerons, and a Hitec HS65HB for the elevator
Power system: AXI 2217/9D + PG3 outrunner motor w/Gearbox, Jeti Spin 44 ESC, and PolyQuest 3300 3S Lipo. Prop is Aero-Naut 14x12 carbon folder.
Power output (static): 46 amps / 527 watts, 5200 rpm
MSRP (airframe only): $339.90
Price as tested (not including transmitter): $970.20

Introduction

The F5B Tiger, distributed by Hobby-Lobby, International, is a fully-molded electric-launched sailplane. This type of model is often referred to as a "hotliner", and is similar to the models used in F5B competition. For those not familiar with F5B competition, the models are required to fly both distance (speed) and duration tasks, with the caveat that the motor cannot be run while on the course. This means the models must possess incredible rates of climb, since they must streak back to altitude as fast as possible before re-entering the course, as well as the ability to go fast and glide for long distances. Of course since they need to make "pylon racer" turns at both ends of the distance course, the models must also be extremely strong to withstand the g-loading. The Tiger fits the description! Soon after Hobby-Lobby contacted me to do this review, a large box arrived at my door. Having built and flown many models over the years, I have pretty high standards when it comes to fit and finish so I wasn't sure what to expect when I opened the box. I am happy to say I was very impressed with the workmanship and quality. All the details were there - from the wing bolt sockets to the "wipers" on the ailerons and elevator. The airframe is of absolutely stunning quality, with no imperfections in fit and finish to be found no matter how close you look. Let's get on with the build!

Construction

There is really no "building" to be done with the Tiger, since the airframe is completely molded and arrives fully assembled. The wing and tail are bolt-on affairs, so the only tasks left up to you are the installation of the servos and the motor. Hobby-Lobby provided a fiberglass firewall with my Tiger, but unfortunately the bolt pattern of the AXI motor did not match any of the holes. Upon further measuring, even had I slotted the mount for the bolts, there would have been very little material left around the bolt holes. Since the mount is also too large to fit inside the nose without sanding, I simply made a mount from 1/8" aircraft plywood. The mount was then bolted to the motor and slid in from the wing opening. Once I was satisfied with the fit and position, I mixed a batch of 30 minute epoxy and milled glass fiber to a thick consistency and epoxied the firewall in place. A neat trick is to use the prop hub/spinner assembly to assure the mount is parallel with the front of the fuselage. Simply slide it onto the gearbox output shaft until it touches the fuselage, while pushing the motor forward from behind (use a stick to reach it). Tighten the retaining bolt and let everything cure.

Servo installation may be a bit of a surprise to some folks, since they are epoxied into the airframe! The first step is to remove the mounting lugs, since not only can they not be used, but they also simply won't fit if you leave them on. There are no pushrods supplied with the Tiger, so I picked up some 12" standard pushrods and Sullivan clevises from the hobby shop. The aileron pushrods are quite short, with Z-bends on the servo end and a clevis for the aileron horn. Speaking of the horns, these are nice brass units that thread into sockets that are molded right into the ailerons! All I had to do was drill out the hole slightly so the clevis pin would fit, then they were threaded into the ailerons.

Fishing the servo wires down through the wing is made easy with pre-installed pull-strings! Just plug in a 12" extension cable, tape the string to the end, and pull it through to the opening in the center of the wing. Here's a trick: Use a length of waxed dental floss to tie the connector together on the extension so it can never come unplugged.

The servo horns must be trimmed quite short in order to fit everything under the supplied servo covers, but that doesn't present any problems since you don't need much control throw anyway. One item to note: You will need to notch the lower wing skin so the aileron horn can move forward, otherwise you won't be able to get any downward aileron travel. A rotary tool made short work of that task.

Once I was satisfied with the linkage geometry and operation of the servos, I cleaned the servo case with denatured alcohol, then carefully wrapped the servos with good quality clear packing tape. The seam is on the upper side of the servo, and the bottom side was carefully scuffed with a scouring pad to promote adhesion. This is done so that if the servo ever needs to be removed, one can slit the tape and (eventually) peel the servo out. I then mixed up a batch of 30 minute epoxy, thickened it with colloidial silica, and epoxied the servos in place. Be sure to clamp the ailerons level when doing this. Care taken here will assure a first flight that brings no surprises with out-of-trim ailerons. When the epoxy is cured, make sure your ailerons still wiggle the right way, then tape the servo covers in place with bits of clear tape. The wing is now complete!

Installing the elevator servo proved to be trickier than the aileron servos. There is no horn provided for the elevator, so I made one from a bit of carbon fiber plate I had in my scrap bin. You could also use a scrap of printed circuit board, or even 1/16" aircraft plywood (though I'd soak the pushrod hole with thin CA for durability). The pushrod simply has a 90 degree bend on the elevator end, and a Z-bend for the servo. Obviously there is no way to adjust it, nor can you remove the servo arm once it's installed, so be sure you get it right the first time! The elevator servo arm must be trimmed even shorter than the ailerons, so you must be very careful with the Z-bend geometry to allow proper elevator travel without binding. Again, just take your time and make sure it's right before you epoxy it all in place. As with the aileron servos, the elevator servo was wrapped in tape before being epoxied into the fin. A nice cover plate hides it when installed.

The rest of the building is simply installing the receiver, ESC and battery pack. Initially I was concerned that the motor wires might try to rub against the outrunner motor, but their stiffness combined with the location of the ESC keeps them tucked tightly against the inside of the fuselage. Just be sure to check yours, and if they try to rub use a bit of double-stick foam tape to hold them to the inside of the fuselage. The battery pack needs to be just about as far forward is it'll go (without touching the motor) to get the CG in the correct position. Hobby-Lobby recommends the CG be set at 2.5" aft of the leading edge at the root, and I found that to be a nice setting based on how it flies.

Flying

The weather here in Central Texas has been abnormally windy this year, putting a damper on flying anything other than larger helis and planes. Add to that the record-setting heat, and we decided to go for an early morning first flight for the Tiger. We arrived at the Austin Silent Flyers field at 7:30 am on a Saturday morning and set up the Tiger. After the obligatory pictures, range check, and camera-person briefing it was time to put this beauty into the sky. My friend and fellow aviation addict Rob had the honors of tossing it for me while my lovely bride Liz filmed. After one final control check I added about half throttle, Rob tossed it, and away it went. After it left his hand I rolled on full power and pulled it vertical. I think I can summarize the climb in one word: Yeeeeeehaaaaaa! After climbing for only 5 or 6 seconds, I shut down the motor and pushed over at the top. The aileron trim was perfect, but I did need to add a few beeps of down elevator for a hands-off glide. The first turn revealed a bit of adverse yaw, which was easily corrected before the second flight with a bit more aileron differential. Other than that, the flight characteristics are simply amazing. It is smooth, it is fast, and it has no bad habits at low speed. Even though it was early morning, I was able to find and work a couple of small bubbles of lift. I can already see that it is going to be one of those "fly it till your neck hurts" planes, with such good thermalling ability from only a 5 second climb! Of course, the most fun part of a plane like this is to convert altitude into airspeed, and show off with fast passes, large loops, and other smooth aerobatics. The Tiger excels at this, and emits a very pleasing whistle (no doubt from the cooling hole in the spinner) as it screams by in a fast pass.

Conclusion

I can honestly say this is one of the more enjoyable planes I've flown in my 28+ years of RC flying. While certainly not cheap, the Tiger is a stunningly beautiful model that flies as well as it looks. The power system that Hobby-Lobby recommends pulls it vertically without effort, and is a fine choice. However, if you are on a budget, you could certainly use a lower-priced low-kv outrunner direct drive and still have a lot of fun. A search of the electric sailplane section of some of the online forums will reveal several power system options to consider.

While we did get video of the first flight and some flybys, my camera people had a very tough job. This is a very fast model, and it gets small very quickly. Combine that with the white wings and cloudy sky, and they had a nearly impossible job trying to follow it in the viewscreen. So please do keep that in mind while watching the videos, and don't think badly of their camera skills.

If you are an intermediate to advanced pilot looking for something different, or are a dedicated sailplane guy who wants to try a self-launcher, please do give the F5B Tiger from Hobby-Lobby a look. I don't think you'll be disappointed.

Note: If you would like to see all of the 100+ photos that I took during the build process, check out my Flickr album.

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