The House of Balsa Spacewalker

HOB comes through again with another great-flying and superbly engineered kit with scale looks.

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Specifications:
  • Type: "Schoolyard Scale" Sport model for glow power
  • Wingspan: 47 inches
  • Wing Area: 329 Sq. in.
  • Wing section : 15% Symmetrical
  • Length: 28.25 inches
  • Recommended Power: .074 to .10 glow power. Power system evaluated was a 7.2v Speed 400 and Graupner 2.33: gear drive on 10 500AR cells driving an APC 10x7 electric prop. 
  • Weight:  28.3 ounces (Glow version typical weight is given as 28 ounces)
  • Controls: Throttle, Aileron, Elevator, rudder
  • Construction: Balsa with some lite-ply featuring laser cut parts, a cedar dowel leading edge, and wheel pants made from die cut balsa pieces.
  • Suggested Price: $54.95 
  • Manufacturer: House of Balsa

If you follow the world of  scale models, it seems that one characteristic of this facet of our hobby is the popularity of certain subjects. Two notable examples that come to mind are the P-51 Mustang and the British Spitfire. Some aircraft just seem to have that certain appeal that attracts, if not requires, the scale modeler to build at least one example during their modeling lifetime. The popularity of certain aircraft types is also reflected in the offerings from the kit manufacturers. While not a flashy warbird like the Spitfire and Mustang, the home built Spacewalker seems to be joining the ranks of the most popular scale modeling subjects. You see a number of examples offered ranging from giant scale plans and kits to the smaller end of the size range as represented by the subject of this review/conversion article.

It is not hard to understand the appeal of the Spacewalker. While looking like a bird from the "Golden Age" of aviation, it actually first appeared on the scene in 1986. It was introduced to the home builder community by its designer, Jesse Anglin. Probably the most recognized example of the original Spacewalker design is the one flown by Hazel Sig. I had the opportunity to see Hazel’s full size Spacewalker at the 1997 Experimental Aircraft Association fly-in. It was easy to see why this airplane has become such a favorite with the scale modeler. I fell in love with its lines and vowed to build one for Speed 400 scale. The model I ended up designing and building is a lot closer to the scale outlines than the subject of this review, but you sure don’t have any trouble recognizing the House of Balsa "Schoolyard Scale" example.

The House of Balsa Spacewalker is designed for glow power. We all know, however, lurking inside the same box is an electric powered model just waiting for an electric power flyer to come along and release it from the confines of the glow power building instructions. House of Balsa offers a number of fine glow power kits, and many of them have been converted to electric power with great success. This article will take a look at the schoolyard scale Spacewalker kit and will also cover the conversion of yet another HOB kit to electric power.

Kit Contents

Opening the HOB Spacewalker kit reveals contents that are becoming pretty typical of the kits being introduced these days. You receive a nice stack of sheet wood containing laser cut parts. For this kit you also get some die cut parts. The combination of both laser and die cut parts is somewhat unique. In this case the wheel pant parts are die cut, and the die cutting is very clean. A pretty complete hardware bag is included that lacks only wheels and items that need to be selected by the modeler based on the chosen power system. For example, you need to provide a fuel tank (what ever that is) and a motor mount. No problem with that since our chosen power source would not use some items normally provided for a glow powered kit. The full size CAD drawn plan comes rolled and ready to spread out on your building surface. One thing that does distinguish this kit is the fact that the laser cut parts have their part identifications applied directly to the part by the laser. This is a nice touch since you don’t have to refer to a parts guide to be sure you are working with the correct part.

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Kit Contents. Assembly Manual. Part identification is laser printed right on the piece.

The kit also comes with an assembly manual. The manual is basically a nice color photo essay on the building steps. There are not a lot of written instructions, because the photos are for the most part self explanatory. The limited written instructions seem to suggest the kit is not intended for a first time builder. After building the model, I would say that with even just one or two previous built up kits under your belt, you will have no problem building this model. The parts fit nicely, and the overall structural design allows the model to go together accurately without a lot of effort. Actually, I found the model a lot of fun to build.

Before we get into the building details of this kit, let's take a brief look at the wood included in the box. Since this project is a glow to electric conversion as well as a kit review, it is important to know if the included materials can be used. Weight is the constant enemy of any model airplane builder, but that is especially true for ones that are to be electric powered. The following table shows the density of the wood supplied for the various parts of the model. 

Components Avg. Density (lb./ft3)
Wing ribs 7.9
Wing spar 12.6
Fuselage sides 10.5
Other fuselage parts 8.6
Tail surfaces 9.5
Wheel Pants 6.3

As you can see, some of the wood densities range to the heavy side of our scale. Further examination, though, suggests that we should be able to use everything as supplied. The wing spars, for example, do not represent much volume and do need to be strong. Hence the higher density wood there actually makes good sense. Some of the other parts are probably just right for a glow powered model where you have a source for constant vibration. So on reflection, it would appear that House of Balsa did a pretty good job of selecting the wood in this kit. As we will see in the building review, a few strategically placed lightening holes makes some of the heavier than needed for electric power parts very useable. With that in mind, let's get on with the description of this project.

Construction

Wing

The construction manual begins with the assembly of the wing. The wing is a very straight forward design with a couple of nice construction features. Since this model was designed for glow power, I did look at each major component’s design to see if there would need to be any changes made to get rid of any structure (and it’s weight) that would not be necessary for an electric powered model. I did not see anywhere in the wing that needed any modification.

The trailing edge is made up of two 1/16" x 3/8" balsa caps and a 3/16" square core. Wing construction begins by laying down the bottom trailing edge cap followed by the core. The design of the trailing edge makes it light and rigid. It also serves as the anchor point for the triangular stock ailerons and center section. Following the layout of the bottom trailing edge parts, you get to see another nice design feature of the wing. The main spar is laser cut from some pretty dense 1/8" sheet. The spar is nearly full depth and includes slots for each rib. This arrangement makes positioning and alignment of the ribs a no brainer. Once the ribs are dry fit in the spar, the spar/rib assembly is positioned over the plan and everything is glued in place. If you use CyA for this part of the assembly, you see a lot of progress in very little time. To finish off the rib and spar assembly, a strip of 1/8" square stock is added to the top of the spar. This brings the main spar up the full height of the ribs, and locks everything together. A real nice and simple design.

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Wing assembly begins with the built up trailing edge. The laser cut spars key each rib to the proper location.  Ribs are positioned on the spar before placing the assembly on the plan. A piece of strip wood on top locks everything in place.

 

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Spar and ribs are lined up and glued to the trailing edge. The supplied cedar leading edge dowel is glued in place along with the spar cap and trailing edge cap. The tip and center section sheeting are now added.

At this point we are fairly close to having the basic wing structure finished. The next step involves another interesting feature of this model, the leading edge. This model uses a dowel leading edge. While that is not all that unusual, the material that is typically used for this type of design is a birch dowel. Birch dowels are notorious for not being straight, and you really do want a leading edge that is straight. Our friends at House of Balsa used cedar dowels rather than birch. Each leading edge was perfectly straight. This was very welcome and they fit the laser cut ribs perfectly. I chose to use an aliphatic resin glue for this step to be sure the bond between the balsa ribs and the cedar dowel leading edge was solid.

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The ailerons are made from supplied 1 inch tapered stock. The wing is joined by gluing each half together. Laser cut holes in the root ribs receive short leading edge dowel cut offs to serve as alignment keys.

With the leading edge in place, you can then remove the assembly from the building board to accomplish the final steps. These involve adding a top and bottom 1/8" square intermediate spars, adding the tips, and adding the center section sheeting. The final step in assembling the wing is to final shape some triangular stock that will complete the wing shape and form the ailerons. When each wing half is finished they are joined together. When joining the wing halves, you encounter yet another creative design feature of this kit. The structural design of the wing does not require any traditional dihedral braces or joiners. Instead, the wing is simply butt glued at the center section. That is not all that unusual, but the trick feature is the way HOB designed in some alignment keys. Since you have several short pieces of the cedar leading edge left after trimming, they provide a set of holes in each root rib to accept a piece of the leading edge scrap. The scrap dowels in turn make sure the wing halves go together in perfect alignment. Very simple and very functional.

Fuselage

Like the wing, before starting the fuselage I looked things over a bit to see if there were any opportunities to lighten things up a bit. I should note that even though the model was designed for glow power, I do give House of Balsa credit for a generally light structural design. Their wood selection was aimed at glow power which made it heavier, but there was not much that needed changing from a structural design point of view. I did make a few adjustments, but they were minor. Even the changes to accommodate electric power were very minor.

Because I thought the wood used in the fuselage sides was just a bit heavy, I did decide to cut some lightening holes. This was done in the aft portion of each side to help reduce the weight behind the center of gravity. I also ended up using only a small portion of the supplied fuselage doublers. The wood for these parts was quite heavy, and since I would not have to worry about engine vibration I decided  leaving out a major portion of the doublers would not be an issue. Addition of the lightening holes and reduction of the doublers saved a half an ounce (14 grams). Not a huge amount, but it did come from the rear of the fuselage. I was not sure how tough it would be to balance the model, so I wanted to make sure it would not be tail heavy.

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Parts giving the best lightening opportunities. One side shows added lightening holes. A large portion of the relatively heavy doublers was not used. Basic assembly is done on a laser cut "backbone".

Construction of the fuselage is very straight forward. A laser cut ‘backbone" is provided that sets the stage for all of the alignment. Basically, you add one side and the formers to the keel and then follow with the other side. Again, simple, quick and accurate. My biggest issue when building the fuselage was to decide on where the battery pack would be located. I looked at a number of possibilities and finally decided to locate the battery in a tray under the forward fuselage sheeting. By taking this approach I would be able to move the battery pack fore and aft over a wide range without interfering with the aileron servo or other internal barriers. I discovered that a tray made to the same width as that fuel tank thing would work perfectly. The backbone had a very nice laser cut hole in the forward section to locate the fuel tank. All I did was to extend that hole back to the rear of the cockpit opening. This provided a perfect guide for locating the battery tray. I made up the tray from material left from the balsa sheets that contained the wing spars. This was 12 pound density balsa, so it was plenty strong. The weight of the added tray just happened to be almost equal to the weight saved with the lightening holes and reduced doublers. The tray was 2 grams lighter. To be sure the battery pack would clear the aileron servo, the tray was glued in place so it extended up into the sheeted forward fuselage section. This required cutting an appropriate size relief in one former. No big deal. That is all I did to modify the fuselage for electric power.

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Laser cut formers make installation of the provided pushrod assemblies very easy. The laser cut fuel tank opening in the crutch makes an ideal place to locate a battery tray. A battery tray was built from left over wing spar sheet material. It fit nicely under the forward sheeting.

Another area that needed a little thinking before I could finish the fuselage was how to mount the motor. The basic design of the model calls for a Hayes beam mount that screws to the face of the bulkhead. After some thought, I realized that since I was planning to use a Graupner gear drive on my Speed 400 power plant, I might be able to adapt the very same specified Hayes glow engine mount to mount my power package. This turned out to work perfectly. I did have to modify the Hayes mount, but that was not difficult. I simply cut the mount in half vertically and did a little shaping so it would clear the Speed 400. I used a battery powered Dremel tool to do the shaping, so it did not take long to get everything to fit just right. The supplied liteply firewall was modified as shown in the photos to accept the rear of the Speed 400. I also cut a fairly large hole in the firewall to allow cooling air to flow to the ESC. The firewall mounts in the fuselage with some right and down thrust. By retaining the firewall motor mount, I was also able to retain the built in thrust settings.

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Firewall was modified to accept the end of the Speed 400 motor and to create a cooling air inlet. A glow motor mount was cut in half to mount the gearbox. The modified glow mount attached to the liteply firewall. Motor and gearbox on the mount.

The fuselage is finished off by adding the rear turtle deck stringers, tail blocks, and the forward sheeting. For the tail blocks the HOB folks did something nice. Usually you have to scrounge up some scrap balsa the same thickness as your tail surfaces to use as spacers when sanding tail blocks to shape. Since HOB was laser cutting the tail surfaces from 1/8" stock, they also cut two nice spacers. This made the job just a bit easier and was definitely a nice touch. Another interesting thing the HOB folks did involved the way the forward fuselage sheeting went into place. Normally, when you have to add sheeting to this area of a fuselage, you have to fit the sheet between facing surfaces. Since this is a "Schoolyard Scale" model, we get to take a few liberties. In this case, the forward sheeting simply overlaps each fuselage side. That makes alignment totally trivial. The overlap is in turn carried forward and aft with the addition of a 1/16" x 1/4" strip of balsa. The covering simply forms a slight taper between the edge and the bottom of the fuselage and does not touch the sides. Pretty simple, and it makes it easy to get a nice looking finished product.

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The forward sheeting overlaps each side making alignment a breeze. Strips are added to carry the feature the entire length of the fuselage. The kit includes laser cut spacers that make shaping the rear fuselage fairing blocks an easy task.

Tail Surfaces

The tail surfaces follow the design approach used by many other models in this size range. Basically you get several pieces that are laser cut from 1/8" sheet stock that need to be glued together. The fit of the parts was right on, and grain orientation of the individual pieces was well done to get best strength. When I finished the assembly of the tail surfaces, I was worried about their weight. The stock they were cut from was on the heavy side by my standards. Because they are located so far behind the model’s CG, I decided to add some lightening holes. I wanted to cut their overall weight by 25 percent. As a result I started cutting holes. I did achieve my target 25 percent weight reduction and there was no loss of strength. Now the real questions is was this really necessary? My 25 percent weight reduction in actual numbers was 5 grams. That is just under a quarter of an ounce. When you consider the relative moment arms between the tail surfaces and the nose, you could argue that saving 5 grams in the tail would reduce an offsetting weight in the nose by about 20 grams (0.7 ounces). That would be important if I had to add weight to the nose to balance the model. Since I had set up the fuselage to allow the battery pack to move over a large range, I did not think that I would have to add weight. As it turned out, I had to move the battery pack almost as far forward as it would go to get the model to balance.  So in the end, adding lightening holes to the tail surfaces seems to have been a good idea. Not only that, but there are just some things we have to do when converting a glow model to electric .... right?

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Tail surface components. Wood was a bit on the heavy side. Assembled components. Addition of lightening holes reduced weight 25% with no loss in strength.

Wheel Pants

To wrap up the basic construction part of this review, we need to briefly discuss the wheel pants. They are made up from 1/8" balsa laminations. The individual laminations are die cut rather than laser cut. The wood supplied was very light, and was also very cleanly cut. A feature of this type of wheel pant construction that I had not seen previously was the use of 3/16" square strips to key the laminations in proper alignment. These keys also created nice faces to shape for fitting the wheels. The only problem I ran into with the wheel pants was my choice of wheels. I wanted to keep weight to a minimum, so I selected Dave Brown treaded Lite Flite wheels. They turned out to be just a bit too wide to fit inside the finished pants. I solved the problem by slicing the finished pants vertically and adding one more 1/8" lamination to the middle. This was certainly easy to do with the balsa pants. The wheel pants are held in place with a single wood screw through the aluminum landing gear leg into a plywood plate. Another example of a simple and effective design feature.

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Wheel pants are assembled from die cut balsa layers and a laser cut liteply insert. To fit Dave Brown Lite Flite wheels, I had to add one additional layer to increase the pant width. Finished wheel pants are light and strong.

Covering and Finish

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Ready for covering. 

If you have read some of my other reviews, you probably get the idea that for small models I like Litespan. You are very correct. The more I use this stuff the more I like it. I guess you won’t be too surprised to learn that I chose to use Litespan on the House of Balsa Spacewalker. As I mentioned in my opening remarks, probably the most recognized Spacewalker flying is Hazel Sig’s. Her basic yellow with red trim was immortalize by the first kit offered by Sig Manufacturing. There are certainly other Spacewalkers flying today, but none seem to leap out at you the way Hazel’s does. I sure found this to be true when I saw it in the flesh, so I chose to use her markings on this Spacewalker rendition as well. For that matter, so did the builder of the model shown on the kit box.

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Basic covering is yellow Litespan. Trim is ink jet printed tissue paper applied with thinned clear dope. Final finish is one thinned coat of clear dope followed by a spray coat of Krylon Workable Fixatif.

The basic model was covered with yellow Litespan. When the basic covering was complete, all surfaces were given a coat of clear dope that had been thinned 50 percent. The red trim was developed by printing all of the necessary shapes on white tissue paper with an ink jet printer. This made it easy to incorporate the distinctive black pin strip that appears on all of the edges. The tissue paper used for creating my trim "decals" was plain art tissue. I use this type of tissue because it is more opaque and creates better color when printing. After printing the shapes, they were carefully cut from the tissue sheets using a fresh single edge razor blade. The "decals" were then applied to the model by placing them in the desired location and then applying dope thinner with a brush. The dope thinner softens the coat of clear dope that had been previously applied and sticks down the tissue trim. When dry, I apply another coat of the 50 percent dope and thinner mixture to just the tissue trim areas. When that is dry I lightly sand the surfaces with 600 grit wet or dry paper. This knocks off the fuzz. One additional coat of thinned clear dope is then applied to the entire model. I let that dry for 24 hours and then apply one coat of Krylon Workable Fixatif from a spray can. The Krylon provides some UV protection and also creates a subtle luster to the finish.

Equipment Installation

When first contemplating building this model, I agonized over the decision on what to use for power. There are a number of choices that could be made. All would I’m sure provide successful results. One factor that strongly influenced my ultimate decision was my experience with my own Spacewalker design. That model is actually larger than the HOB kit and was successfully powered with a geared 6v Speed 400. My only reason for not adopting this power option right away was a difference in my perceived objectives of the two models. My model is intended for Speed 400 scale competition. Full size Spacewalkers are not intended to be extreme aerobatic machines. They fly like a low wing Piper J-3. I had this in mind when making my Speed 400 version on the larger side. It has adequate power, but does not have the power to do a lot of aerobatics. The House of Balsa Spacewalker, on the other hand, is laid out to give good aerobatic performance. The wing has a higher aspect ratio than the full size airplane, and the tail surfaces are proportionately larger. Since this model is intended to give good aerobatic performance, I had to do a little thinking. During that process a light went on. The SR X250 gives good aerobatic performance on a geared Speed 400 power package. The HOB Spacewalker is a bit larger in wing area (329 in2 vs. 260 in2), and should weight just a little bit more. Since the typical weight for the model when glow powered is 28 ounces, I reasoned I should be able to hit that same weight if I used a geared Speed 400 power system. At 28 ounces the model would be just a little heavier than an X250 but would have additional wing area to support the higher weight. As a result, I decided to use geared Speed 400 power for this model as well. Just to make things interesting, I decided to try the exact X250 power set up, 7.2v motor on 10 500AR cells. My goal to keep the model at or below 28 ounces flying weight was almost achieved. The final flying weight ended up at 28.3 ounces.

For electronics, I used a Hitec 555 receiver, a Voltz servo on the ailerons, and FMA S-80 servos on the rudder and elevator. I used a Jeti 350 ESC. For a prop I decided to try one of the new APC electric series. In this case I chose the 10x7. There is adequate ground clearance for the prop, and static current on a freshly charged pack was just barely over 10 amps. 

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Plenty of room for the receiver and ESC in the forward compartment. Lightening the rear fuselage and tail feathers proved to be a good idea. The 10 cell battery pack ended up nearly all the way to the front of the battery tray.

Flying

After what seemed like an endless series of rainy, cold, and windy weekends the weather in the greater Houston area finally presented conditions that would allow the first flights to be made. After the proper range checks and inspections to be sure all the control surfaces were moving in the proper direction, the model was placed on the runway for it's maiden flight. I advanced the throttle carefully and started down the runway. Just before lift off could be accomplished, I made a classic mistake and fed in just a bit too much rudder control. I was greeted with a nice high speed ground loop. No damage was done other than to my nerves. The second take off run was successful, and the House of Balsa Spacewalker was airborne. It climbed out with nice authority. The 10" prop was working very nicely. My only trim adjustment was to add one click of up trim. I had apparently been just a hair too conservative on making sure the CG was far enough forward. The model tracked beautifully. I used the recommended control surface throws, and found the control response to be positive, but not twitchy. The HOB Spacewalker seemed to be on rails. Very nice feel.

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Take off roll is about 20-30 feet. Model climbs with good authority. Control response with the recommended throws is very good.

The model was able to cruise at about 60 percent throttle. Loops were no problem from level flight and are very smooth based on the overall arrangement of the moments. Full power seemed to be very adequate for general aerobatic flying. Unfortunately, just when I was going to start some rolls and other maneuvers,  some strange vibration sounds started coming from the model. They sounded like gear noise, so I decided to keep flying to see if it would work itself out. The noise continued, so I felt it would be wise to be conservative. I flew out the battery pack doing circuits and prepared for an uneventful landing. When power is reduced, the Spacewalker settles into a nice glide slope. The approach was very comfortable and she made a nice, no-bounce landing 6 minutes after the throttle was first advanced. I was not able to sort out the gearbox vibration problem at the field, so I ended the day. While I did not get as much flying time as I planned due to the gearbox problem, I certainly got enough to say this is a great flying bird. 

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The model looks great in the air, and handles very nicely.
(All in flight photos are by Ralph Bradley)

The options for electrifying the House of Balsa Schoolyard Scale Spacewalker are many. I chose a relatively light weight and inexpensive approach. The model flies very adequately in that configuration with more than enough power to handle sport aerobatics. With a little more power, she should be satisfying for even the more advanced aerobatic pilot. She can easily handle a higher flying weight (the specifications say 32 ounces) thereby allowing for larger capacity batteries, and/or heavier motors. A combination that I definitely plan to try is the Aveox 1005/4y as reviewed in the Ezone. This will be done with the 3.7:1 planetary gear drive offered by Aveox so I can keep the nice large prop. Since Steven Horney, our ever patient editor, has been waiting for a while on this article I thought it best to send it in rather than wait for additional configuration testing. I've seen enough to know that doing the HOB Spacewalker as an electric conversion will produce very satisfying results for anyone interested in building this fine model.

Recommendation

The House of Balsa Schoolyard Scale Spacewalker is not an overnight project. It is an easy model to build, but probably should not be attempted until you have one or two previous built up models under your belt. That being said, if you do like to build models from pieces of balsa and related materials, and you have a bit of building experience, this is a definite kit to consider. It combines scale looks with very nice sport flying qualities. If you like to experiment with different electric power set-ups, this model is a great candidate for your creative genius. There is plenty of room in the fuselage to carry batteries, and the open cheek design of the nose makes fitting motors pretty easy. There is no question in my mind that if you show up at your local field with your newly finished and  electrified HOB Spacewalker, you will get plenty of oohs and aahs with many coming from you as you put her through her paces.

E-Mail Contact

If you have any questions or comment, feel free to contact me BradleyP(at)ix.netcom.com

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Power for the House of Balsa Spacewalker martin johnson Electric Plane Talk 18 May 13, 2001 08:53 PM