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Jun 12, 2012, 03:12 PM
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Build Log

HobbyKing BD-5B

12 June 2012

This will be my first attempt at a build blog. I recently purchased the HobbyKing version of the BD-5B. Here's a link to the product page...

From what I am finding out, this kit is a knock off copy of the Aero-Works BD-5, and it is the evolution (I think) of a kit once available from Cermark. There are several reviews and build logs of those kits elsewhere in the forums as follows:

I received my kit last week and it is beautiful right out of the box. So far, I have assembled the wings, and I have installed the wing servo. One thing I discovered assembling the wings was that the dihedral block was a tad too long. I test fit it in both wings; however, I forgot to make sure the wings would butt together with it installed before I mixed the epoxy. Good thing I used 15-minute epoxy as I was able to quickly unmate the wings, trim about a 1/16" off of the dihedral block, and quickly reassemble the wing. The wing servo took a little bit of Dremel work to get the servo to fit properly, too.

As others have found the rudder control system looks a tad complicated. Also, the rudder and elevator pushrod housing are epoxied to the wrong holes where they enter the cockpit arrow, and do not properly align with the servos. I have some ideas for that issue and will update you all as I go along.

My plans right now are to outfit it with the following:

I picked up one of HK's aluminum spinners hoping it will work:; however [(update 6/30/2012) it does not fit. It is too big for the propellers I chose.]

I am going to try and incorporate advice from all the other logs on this and similar models including nose-wheel reinforcement, motor cooling ducts, rudder linkage, and C-of-G issues, etc. That's all I have time to write for now. More to come as soon as I get home from a few days on the road.

17 June 2012

I have received the E-Flite SixSeries 2700KV motor. It is a little too long for the stock fuselage opening; however, after lengthening the opening by approx. 1/4", it slides right in. I encountered the same problem as rafe_b with the stringers interfering with the motor fitting flush against the motor mount, and I applied his solution - I dremeled them off as necessary for a flush fit. I plan to apply epoxy to the circumference of the motor mount to (hopefully) replace any strength lost from removing the stringer flares. I will hold the fuselage vertical with the nose up so that the epoxy will flow nicely into the corners of the motor mount to fuselage joint.

HobbyKing's pre-installed rudder pushrod exited the fuselage in a near vertical path - how was that supposed to work? I decided to remove the existing pushrod tube (they are very brittle), and I installed a Dubro pushrod housing with a Dubro #951 hooded pushrod exit to avoid leaving a nasty gash in the side of the fuselage where it exits aft. I had to use a #30 bit in my dremel tool to cut a new hole in the bulkhead just forward of the exit to get the proper angle on the tube. After I cut the hole for the hooded pushrod exit, I used a long #30 bit in my dremel, held it at the angle I wanted through the forward edge of the pushrod exit opening, and drilled a hole right through the bulkhead. It was scary but it worked like a champ. I stole another one of rafe_b's ideas and will use a Dubro 2-56 ball link connector on the rudder control horn to compensate for the vertical displacement the rudder horn experiences as it travels because of the slanted rudder hinge line. I think it will work just great. Thanks for the idea, rafe_b!

I mounted the vertical stabilizer today and will finish up the rudder and its linkage once the epoxy is set real well. I used epoxy on the small tab that inserts into the fuselage slot. I used medium CA on the fore and aft ends of the vertical stab. Before I installed it, I removed the covering from the tab for the epoxied part. Before install, I also marked the area out on the fuselage for the fore and aft edges and poked little t-pin holes through the covering in that area so the CA would soak in.

I am loathing the task of trimming all molded plastic. The motor covering with its little louvers looks like a real pest and I do not know how I am going to do it and have it come out looking good. I'll give it the 'ol college try nonetheless.

Everyone talks about adding fuselage scoops to this model. I keep looking at the two beautiful (and apparently non-functional) scoops on the front of the lower wing fairing. I am thinking that if I just put a two holes in the lower surface of the wing, the air from those fairing inlets will flow right on up through the center aileron servo opening and out the back through the motor vents. I am going to try it and see. I should probably add a thin sheet of balsa to the area in the wing where I cut the vent holes for added strength.

That's all for now, because I am back on the road tomorrow flying full scale for a few days. I hope to get this little beauty flying in time for our club's pusher and EDF event next month.

22 JUNE 2012

I think I have everything need to finish the BD-5B; now if I can just get a little more time to do it, I'll be all set. So far I would say this, having read the reviews and Aero-Works' instructions, if you are pressed for time or lack building skills/resources, do not buy the Hobby King BD-5B as their version of this model takes time, a degree of ingenuity, and special tools to complete. From what I have read, the hard work is done for you in the Aero-Works version and you'll be in the air a lot sooner.

The plastic wing-root and belly fairings went a lot easier than I thought they would. I found that my Dremel on low speed with its router bit made quick work of smoothing out the inlets on the belly fairing scoops. I used a combination of scissors, left and right cut tin snips, my belt sander, the router bit, and a file or two to trim the wing root fairings. The belt sander was the key to making quick work of the wing-root fairings. It's hard to tell how the fairings are supposed to be trimmed but if you look close, you will see faint mold lines that suggest where to trim to. Once you get it close, it's just a little here and there to finish up. The opening for the wing is smaller than the wing, so you just have to take a litle off the trailing edge of the fairing so it will lay flush on the wing. Once they were fitted, I glued them to the fuselage with UHU POR glue. I have a little clean up to do, as I have yet to master gluing without that extra step.

I powered up my receiver and brought life to all the servos last night, zeroed them and finished the wing rigging. I went for the holes about 80% outboard on my servo arms on the ailerons, and I think I have adequate hi-rate travel there. I will adjust the low rate travel with my DX-7 transmitter. I zeroed the elevator and rudder servos too and had fun watching the pushrods move fore an aft, as I have not mounted the elevator and rudder yet.

To my dismay, none of my 1300, 1500, or 2100 lipos would fit in the battery tray -- the canopy would not close with any of the batts installed because they interfered with the canopy's forward cross brace! Looking at the Aero-Works pictures again, it appears that its canopy does not have that cross brace, so I sawed it off and now it fits great with a 2200 mAh lipo in there! Thankfully, loosing that forward cross brace did not seem to weaken or distort the canopy either.

I must be dyslexic, because after I looked at the pictures a million times, and the way the pushrod tubes were routed, I could have swore the rudder servo was on the right and the elevator servo was on the left -- wrong! When I went to start hooking up the nose gear, I realized that the most efficient way for the nosewheel steering pushrod to work was the opposite. I went back to the pictures and sure enough, that's the ticket, the correct configuration is the rudder servo is on the left with the servo arm forward and the elevator servo is on the right with it's shaft positioned aft. Live and learn -- having to reposition the pushrod tubes and build a new nosewheel pushrod set me back a few hours.

I have mounted the gear on the wing and installed the wheels. I decided to go with Du-Bro #186MS 1.86" Micro Sport Wheels because they look cool, I think they will help me operating off of our grass field, and they will have lower drag. Their thin profile reminds me of some legacy jet airplane wheels, i.e. they look fast.

I went ahead with my plan, and I cut two each 1/2" holes in the bottom of the wing right below the servo mounting hole on either side of the center ribs to utilize those two scoops on the front of the belly fairing for motor cooling. The air will flow into the scoops up through the bottom wing holes, through the aileron servo opening and out the aft end motor cooling louvers above the motor. Brilliant, I hope.

Next is to install the H-Stab, elevator, rudder, and rig them. Then I have to build extensions for the motor, ESC, and figure out how to fit all up front. I taped everything in place and preliminary checks of the CG looks like it will come out pretty darn close to spec.

25 JUNE 2012

Finally, I installed the rudder and elevator today. Pretty straight forward. As others have found with this kit, there were only two CA hinges for the elevator furnished in the kit but the elevator is slotted for four hinges. I went ahead and used some hinges I had in my stock. I had to lengthen the factory hinge slots slightly to get everything to fit.

I also put a little white enamel on my rudder pushrod exit to blend it in with the white covering. It looks "ok".

Last but not least, I spread some 30-minute epoxy around the internal motor mount circumference to reinforce it where I earlier had to remove the stringer flares so the motor would fit. I hung the airplane vertical with a hook in the nosewheel steering opening for an hour or two so the epoxy would flow into the corners nicely while it cured. Came out nice.

I discovered the other day during some light reading that the E-Flite Sixseries 2700KV motor I bought requires a sensorless ESC. I could not find a suitable ESC anywhere that I trusted, so I caved and bought E-Flites recommended ESC at:
As soon as the ESC arrives I can finally finish up wiring up the power system. Woot!

Considering this aircraft's potential speed and performance I am also going to save the Orange RX receiver for another airplane and go with a full-range Spektrum AR 6200 to be on the safe side.

26 JUNE 2012

Rudder completed! Huge relief for me that the rudder is done. Here's some pix of the rudder.

30 JUNE 2012

Ready for a Maiden! It has been a busy couple three nights putting all the finishing touches on this airplane; however, I think she is ready for first flight. Here's a brief rundown on the final stretch.

Nosewheel steering - I cutoff one half of the steering arm to save weight and to make more room for my ESC that I have secured with velcro under the battery tray in the nose area. The nosewheel steering arm fabrication and adjustment were relatively easy.

Wing vent holes - I went ahead with my plan to cut two 1/2 inch holes in the lower wing surface for cooling. They line up with the belly fairing vents. I made a foam baffle that goes between the belly fairing and the wing steer the air into the holes and up through the servo opening and into the fuselage more efficiently. By the way, based on an RC Universe article, i have also omitted the motor cowling for improved cooling. The instructions tell you to CA the belly fairing to the wing -- I used tape -- Elmers double sided to initially stick the fairing wing and Scotch multi-purpose clear tape on the external edges as a backup. Note: I had drill to large holes at the aft end of the belly fairing for the wing bolts and washers. I also had to install the wing mount hole reinforcing blocks with CA after removing a small amount of wing covering material for them. As one other BD-5 builder noted, taping the belling fairing in place instead of gluing it will aid with future maintenance.

An extra scoop, please. I went ahead with the advice of other BD-5 builders (Aeroworks and Cermarks models) and crafted a small scoop from a white plastic spoon. I installed the scoop forward of the nosewheel with CA after making a small opening in the fuselage for the airflow over the ESC and around the battery.

Motor, ESC, and battery. I used 16 gauge silicone wire to lengthen the ESC motor wires. The E-Flite ESC lends itself perfeclty for this application, because it has bullet connectors on the PCB for the motor wires. The total length of the motor wires came out to 20" so I twisted them hoping to reduce EMF. I used good old waxed aircraft electrical tie cord every couple of inches to maintain the twist. Routing them through the fueslage was easy, and I used a couple of tie-wraps to secure them tot he elevator pushrod housing in the wing area to keep them out of the aileron linkages.

As I have been working on this plane, I noticed a lot of the trim covering (especially the red) is coming loose already. I used a combo of my heat gun and my trim iron to stick everything back in place.

Once everything was in place, I checked the CG against the specifications contained in the Aero Works, Inc. instructions (remember Hobby King provides no manual) of 1.625" from the leading edge at the root. To my delight, the CG is perfect with my setup with no ballast anywhere in the airframe.

I installed the Spektrum AR6200 RCVR with velcro to the left side of the cockpit behind the rudder servo. The satellite RCVR is mounted behind the cockpit aft bulkhead on the left side of the fuselage with velcro. The bulk of the servo wires coiled nicely behind the forward servo trays for improved neatness. Wow, there's a lot of stuff crammed in that little area.

I ran the motor with my Watts Up wattmeter in place and here's what I go with a 6x4 APC e-prop installed using a 99% charged Turnigy 2200 mAh 20/30C 3-Cell lipo at WOT:

Watts: 398.8
Amps: 36

I weighed the airplane as configured above. AUW is 30.4 oz or 1.9 lbs. At 210W/lb, this cute little bird should have performance-o-plenty. I will go with the 6x4 prop for the maiden just to be sure she gets off the grass. I will be running tests on a 5x5.5 prop as soon as I can get my hands on one.

Here are some pix I took to show the completed aircraft ready for maiden flight. I hope to get to the field today or tomorrow. We have an EDF and pusher-prop jet event at our club next week that I hope I can participate in with my new BD-5.

03 JULY 2012

The good news is that it flys! Bad news is, this airplane sucks on grass, made worse by the crap main landing gear that came with from HobbyKing. I did not realize that the gear is practically soft aluminum! The airplane snagged on a bit of reasonably short grass on takeoff, ground looped and folded the left side of the gear completely under the belly. When I went to try and straighten it, I was amazed to discover how soft it was! Come on, HobbyKing! How much would it have cost to put hardened gear in with this beauty! The other nasty characteristic as mentioned in other threads is the pitch problem - it was difficult to trim. It really wants to pitch over with power and it really wants to climb when you pull it off. It was impossible to find a happy medium. Looking again at the motor install, it has a noticeable down thrust angle. I will try to come up with a way to shim the motor or change the thrust angle. My cooling mods seemed to work well as after a 6 or so minute flight, everything was cool enough to touch. Another note: those Dubro wheels have got to go. They came off the rims on landing - lol. I ordered the AeroWorks landing gear to see if I can make it fit. Until the new gear arrives, this baby is grounded.

08 JULY 2012

After the first flight, it was apparent I had main landing gear issues, a flimsy nosewheel and a thrust line issue. Contrary to what I thought following the first flight about no over-heating issues, further inspection of the ESC indicated I did have a cooling problem with the ESC. Here's what I have done to solve them:

1: While waiting for the Aero Works gear to arrive I had a "light bulb" moment and modified a set of gear from an old .25 size trainer I had laying around. I installed hard balsa blocks inside the wing on either side of the center ribs through the servo opening hole. I used the original gear mounting holes for one side of the hold down clamps and a 2mm servo screw for the other. I modified the forward end of the new gear wires so they fit into close tolerance holes drilled through the bottom of the wing into the blocks I installed. This produced a very stiff gear with a 2" wider wheel base and moved the wheels closer to the CG for better takeoff rotation.

2. I modified the nosewheel installation by mounting one of the original centering disks to the bottom of the battery tray to secure the top of the nosewheel shaft and I added a 5/8 dia x 3/16" thick center drilled wood disk to the bottom of the new nosewheel cover I made to replace the original busted on the first landing. This resulted in a remarkably stronger nosewheel. I think it will work great.

3. Upon further inspection from the first flight, I noticed my E-Flite 40A ESC had melted the heat shrink. I am going to put a heatsink on it but until I can get one, I will sue my Castle 54A Thunderbird ESC instead.

4. I removed the Micro-Sport wheels and installed some wider 1.75" lite foam wheels I had laying around. I used the small kit-supplied nosewheel because I did not have anything narrow enough to fit the axle. I am looking for a wider 1.75" nose wheel that will still fit the short axle. Any ideas?

4. I enlarged the forward "spoon scoop" for better airflow.

5. I reshaped the inside surface of the firewall using a Dremel cutoff wheel worn down to 30mm diameter with a piece of 180 grit sand paper spray-adhesived to the backside of it. I inserted the mandrel through the prop shaft hole from inside to out, connected my Dremel to it and "back-sanded" the firewall to a 1.5 to 2.0 degree "prop shaft up" thrust angle (it started out with a 2.0-3.0 prop shaft down orientation and we think this contributed to the significant tuck at WOT).

With all that done it was time for another flight. This time, the BD-5 handled much better on the grass and, although it still hopped a bit, it lifted right off with no problem. Landing was also much sweeter -- it only hopped once but did none of the nosewheel bashing gyrations it did on the first flight. It still pitches down, though not as bad, with WOT, so maybe another tweak to the firewall is in order. The 54A Thunderbird showed no sign of overheating with the bigger "spoon scoop" hole so maybe I am onto something there. We noticed a concerning radio loss at one point so some range checks with different locations of the receiver and sat receiver are in order before next flight. It could be EMI from those long motor wires so we will look at the issue too. I think I can shorten them up a bit and move them around to reduce any EMI they may be causing.

Some pix are included of the new gear and firewall mods along with a couple of pix of the model outdoors. I hope to have a pix of my nifty firewall sander I made soon.

For now, blue skies and happy landings, Tom

August 20, 2012

Since the last flight, a few things:

1) I relocated the satellite receiver to the top of the fuselage just aft of the canopy
2) I Repositioned the main receiver so the antennas are vertical
3) I cut and fit the plastic cowling
4) I added some triangle balsa strips to the sides of the bottom fin - that silly fin broke off twice prior!

Yesterday, I got two good flights of about 7-minutes each on 2200 mAh 20C Turnigy lipos. Ground steering was a problem; however an experienced club member suggested I reduce the low rate rudder travel to about 40 percent with 40 percent expo so I did. Next take-off was easy peasy and it tracked right down the runway.

Although there are many arguments about them, I installed a Spektrum capacitor on my receiver before flight yesterday and I had no other brown-out or reboot issues - could have been the antenna repositioning, but the capacitor doesn't weigh anything and takes up little room so I am leaving it in ;-)

I am getting excellent climb performance with this airplane - I really like the way it flys. My new landing gear works really great on the grass. Speaking of landings, I was flying in zero wind yesterday and found that this airplane slows down quite nicely for landings - none of the hot issues for me that I have read in other threads.

And yes, the bottom fin stayed put!

So that's it - it's finished, it flys great, it's a blast, and I am ending this build log.
Last edited by aviatortom; Aug 20, 2012 at 12:57 PM. Reason: update
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Jul 03, 2012, 07:25 AM
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I had the Aeroworks version, and loved it. If possible, take off on some kind of hard surface, and watch for a PIO on takeoff!
Jul 03, 2012, 11:12 AM
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Thanks for your comments. I wish I had spent the extra $30 for the AeroWorks version. There's no hard surface available in my area so I am stuck on grass. I am wondering a catapult would work for this airplane. I can see where one could easily get into a PIO situation on takeoff. I'll keep that in mind.Happy 4th! ~aviatortom
Jul 03, 2012, 11:21 AM
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Tom, at one point I installed an outrunner and managed to use a 9/6 thin e prop, and it worked much better for takeoffs!

I flew from short grass with this setup, so keep it in mind.

You don't need a catapult, just lots of groundspeed before rotation if you use the smaller prop.

Happy Fourth to you, too!
Jul 08, 2012, 09:22 AM
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Hi Tom,

I had one whileback similar to aeroworks model, I cant remember the brand now..
one thing I notice your main gear location, I think if you move it forward closer just behind the cg you will find she will rotate easier on grass and will do shorter take off
I did that with mine
its a great model to fly. i fitted mine with styriker stock brushless motor n esc back then..
she crash due to the motor end bell come loose and tangled all 3 motor wires and short he esc..
I would buy another soon
Jul 09, 2012, 03:10 AM
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Trexpilot, thanks, that is an excellent suggestion about the gear location relative to CG. In fact, that is what happened serendipitously with with my gear mod, and it flew off grass the 2nd flight much easier (see my update). That motor mount is a problem -- I better be careful with my mods to it too! If I was to buy another -- I would buy the Aero Works version. Best ~ aviatortom
Last edited by aviatortom; Dec 09, 2012 at 08:15 AM. Reason: typo
Jul 10, 2012, 11:05 AM
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trexpilot's Avatar
Glad all worked out well now Tom
Happy flying mate


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