Pentathlon Kit Build
 

After a long delay, I have finally started building a Pentathlon production kit. This kit has been staring at me since April, but too many other things just got in the way....including the Nats.

There are a couple of guys who have started building their kits, so this should generate some helpful discussion.

The kit comes with all laser cut wood parts and cnc cut foam parts. Included are a set of build notes and photos on CD.

Here is a pic of a finished model and some shots of the kit contents.

RE: Pentathlon Kit Build
 

I normally start by sheeting the foam parts. Although this is a bit of a long task, once completed, the rest of build can move quickly (relatively) ;).

Those that purchase the kit with all of the 1/16" sheeting will need to inpsect the sheeting and begin truing the edges of these sheets. I normally use a long straight edge and a sharp razor. You can also setup a straight edge sanding jig to do the job.

RE: Pentathlon Kit Build
 

The vertical fin (upper half) is one of the easier pieces to start sheeting. I tape together several sheets of 1/16" balsa. I lay the shuck on top and trace around. Cut this out and you have a skin. Cut out an opposite one for the other side of the core. I use polyurethane glue for all of my skins. I apply the glue to each skin and spread it quite thin using a bondo spreader or similar tool. Carefully place the skins and foam parts together and cure them under pressure. I normally use a vacuum bag, but weight can be used also. If using weights, be sure your work surface is flat and strong. I recommend placing a thick piece MDF board on top of the assembly and then pile on the weight.

The same procedure can be used to sheet the bottom vertical fin/rudder piece.

Sand any overhanging balsa flush to the cores and then prepare to join the two halves. The top and bottom halves should (:eek:) lay flat to one another in their shucks. I had to shim one of my halves just slightly. Apply polyurethane glue (sparingly) to one of the roots and carefully assemble back into the bottom shucks. Again, make sure the halves are aligned properly before lettting it cure...you have time with the polyurethane glue, so check. You can see in the photo that I actually taped the halves together to get my alignment just right before placing them back into the shucks to cure.

RE: Pentathlon Kit Build
 

The rudder and vertical fin can now be marked to cut the hinge lines and fusebox cutout. There is a dimensioned drawing in the build CD that shows the locations for these lines. I tape the marked fin back into the shuck and then run it through my hobby band saw. These surfaces can be lightly block sanded and capped with the 3/8" balsa pieces.

A note about the trailing edge of the vertical fin: This piece extends down well below the vertical fin and will mate with the end of the fusebox. Take a moment to make sure the alignment of this piece is correct so that it will mate up with the fusebox properly at a later time.

RE: Pentathlon Kit Build
 

There are two foam cores for Flow Straightening Devices in the kit. It is the builder's option to use these. I highly recommend using them. 1/16" sheeting will be used with polyurethane glue to sheet these foam cores. Once sheeted, sand the balsa flush to the cores and then glue on the leading edges and trailing edges. When dry, they can be sanded smooth with the skin. I use masking tape on the skin near the LE & TE while sanding to protect the soft 1/16" sheeting. I prefer to wait until later to final sand the LE & TE pieces.

Later, the FSD that rides atop the canopy will be cut and fitted using 1/16" ply templates included in the kit. For now, it can be left as seen in the pic.

I must apologize as I only have the single finish pic of this step.

RE: Pentathlon Kit Build
 

do you sell this kit

RE: Pentathlon Kit Build
 

Check out the web link on the signature of Mark's post. www.insightrc.com It is a great flying airplane and looks like a great kit!

G

RE: Pentathlon Kit Build
 

Thanks George.

On to the stab cores:

Layout the skins using the foam core and shucks to trace the perimeter. The stab skins will require some carbon fiber reinforcement near the stab tubes. These c.f. strips are included in the kit (0.007" x 1" x length"). The locations for the c.f. are shown on a drawing (on the CD). I have used the laser cut stab root rib as a double check to mark these locations on the skins. Line up the root rib to the drilled stab tube holes on the cores, then make a mark on the top of the foam shuck at these hole locations. Transfer the marks to the skin. I then use CA to glue the c.f. to each skin (the inside of each skin:). Alternatively, one could use the polyurethane glue on the c.f.

The skins are now ready for polyurethane glue.

RE: Pentathlon Kit Build
 

Hey Mark,
I like the carbon fiber strip on the stab, never seen that done but I bet it adds lots of strenth.

Keep on building - I'm watching !! :D

maustin

RE: Pentathlon Kit Build
 

I have a question. When sheeting the stab,rudder and wing would it not be easier to pre hinge everything before sheeting? wouldn't this mean perfect alignment of the control surfaces? My old mentor Darrell Kampschror showed me how to do this years ago. He actually ran the wing hinge wood from root to tip to help strengthen the wing without much weight gain. Granted doing this requires the foam cores to be cut for the wood and the wood to be beveled a bit. This ties the wood for the hinges to a fair amount of the sheeting rather than just the edge and foam. Then a template is laid over the wing once sheeted and the control surface is cut out.

Seemed to work well for us.

RE: Pentathlon Kit Build
 

I have thought many a time about trying that method. I guess I'm too much of a creature of habit. I really do need to try it at least once. Perhaps this Winter on the next one.

Here is a link to that very method, nicely documented by Mr. Terry Brox. http://www.mackrc.net/patternwings2/index.htm

RE: Pentathlon Kit Build
 

The stab skins are ready and can be glued on. In this case, I prepared the stab sleeves (fiberglass) to be glued in, and cured at the same time as the skins. I CA'd balsa to the end of each stab sleeve to as an end cap. I pre-fitted the stab sleeves and stab tubes to both cores. Notice that one stab and shuck required a slight shim to make sure they aligned just right. I found this slight error in the foam cutting program and have since fixed the program.

Polyurethane glue can be dripped into the stab tube holes, run the sleeves in with a twisting motion, and then apply glue to the inside of the skins. Assemble everything on a strong, flat surface and apply weights. If using the vacuum setup, each stab will have to be skinned first, then the tube sleeeves will be put in afterwards. However, the same alignment setup on a flat table will be required to make sure the sleeves will line up properly while curing.

Please excuse the picture without weights. I answered a phone call after placing them on the MDF and forgot to get the pic. I used approximately 50+ lbs. per stab panel.

RE: Pentathlon Kit Build
 

With the stab skins cured, the skin edges can be sanded flush to the cores.

The included drawing shows the location for the hinge cut lines for the 3/8" balsa caps. This location can also be obtained using the stab root rib as a guide. The end of the root rib can be marked and used as the cut line for the stab trailing edge. Please note: in picture #4 there are extra marks that are aligned with the spar tube holes. These marks are not relevant to the marks for the location of the TE cap.

Extend this line out to the tip. Be sure to stay square to the root edge. Measure the location of your line at the tip and make sure it turns out the same on the other stab. Another line marked 3/4" further back (toward elevator TE) and the stabs are ready to cut.

RE: Pentathlon Kit Build
 

After cutting along the hinge lines, these new edges can be lightly block sanded.

The balsa caps can then be glued on, including the leading edge material. I use a small amount of polyurethane glue and tape the balsa in place.

Tomorrow, we sand[:@].

RE: Pentathlon Kit Build
 

The leading edges and hinge caps can be sanded flush to the skins (use masking tape to protect the skin!). I usually wait until later to final sand the hinge line bevels and leading edge radii.

There will be another cut required on the stabs before the root ribs can be added. The root must be cut at an angle to match the fuse sides near the rudder post.

Re-assemble the stabs, carefully aligned back into their shucks.

The detail drawing of the stab layout will show an offset at the leading edge that can be transferred to the top of the shuck. Another way to layout the cut line at the root is to use one of the rear fusebox top or bottom pieces. This can be carefully placed on top of the cores so that it's centerline (fusebox top will have this line) is parallel to the stab root edge. Notice that I drilled a small hole near the front of this piece to see through to my parallel line on top of the stab shuck. Move the wood piece so that it begins the cut right at the trailing edge of the stab root. Now mark this line.

Cut along this line on each stab and shuck assembly. Be careful to keep this cut perpendicular to the top surface of your stab and shuck assembly.

Afterwards, the stab tubes can be inserted and we can visually check how well the cuts match the taper angle of the fusebox top piece.

RE: Pentathlon Kit Build
 

The stab root ribs will not be glued on until later. When the fuse is nearly complete, the stabs can be final fitted, which may require very slight adjustments to the root surfaces of the stabs.

Trimming the outboard tips of the stabs is purely a builder's option. To start, I measure along the LE and TE of the stabs to make sure we are starting with stabs that are identical length. I pick a measurement from the root and make a mark at both the LE and TE near the tip. The elevators can be taped back in place using the shucks for alignment, then draw a cut line along the marks that extends over the elevators. Double check the measurment from the root to the cut line and then cut.

After cutting, I measure one more time and block sand if necessary to get the measurements as equal as possible. The tips can then be capped.

RE: Pentathlon Kit Build
 

The tip caps for the stabs/elevators can be sanded flush.

The inboard edges of the elevators can now be cut and capped to clear the rudder travel. I have measured out from the root along the TE of the elevator to yield approximately 35° of clearance for the rudder.

Notice that one end of this cut should be at the TE of the stab root rib. This ends up at the front edge of the stab TE cap (see close up of the marked cut line). Later, when the root rib is applied, the cap we are about to put on will join up nicely to the TE of this root rib.

Once these inboard caps are sanded flush, the stabs & elevators can be put aside for a while.

RE: Pentathlon Kit Build
 

The inboard edges of the elevators can be capped using 1/8" light balsa. Once cured, sand flush to the skins. The stabs and elevators will be put aside now.

RE: Pentathlon Kit Build
 

The bottom rear turtle deck will be sheeted with 1/16" balsa.

The skins can be laid out and rough cut to shape by trial fitting (dry). I simply use masking tape to hold the sheets together. These sheets can be glued together (ambroid is a favorite) to create the skin as well. This core is about 41" long and if you do not have any 48" long sheets, you will have to add another section of balsa to reach the full length. I have not found this to be any problem and in fact, by picking a very plyable scrap piece for the tail end of the core, I can get the sheeting to wrap rather well around the tight radius at this end.

RE: Pentathlon Kit Build
 

Just for illustration, I glued this bottom deck sheeting using weight (I normally use a vacuum bag system). Once the glue is applied to the skin, slide the assembly together from the front, creating a bit of wedge action. With the edges of the skin sticking up on the sides, you will have to block up the weights. I also added some tape in a few places to help apply a bit of pressure from the sides.

In the end the result is satisfactory and the edges of the skin can be sanded flush to the core.

In one of the pics, you will see that the skin cracked and overlapped slightly at the tail end of the core. This is not a big deal, as we will be sanding the bottom radius area away later to install the lower part of the vertical fin.

RE: Pentathlon Kit Build
 

Here a couple pics of what the process looks like with the vacuum bag system.

RE: Pentathlon Kit Build
 

The top rear deck core is a bit different than some. There is a flat area atop the deck that will later be capped with a 3/8" balsa sheet. This cap will provide lots of rigidity and allow us to sand a sharp radius to achieve the designed intent for this section of the fuse.

The sheeting can be laid out and tape hinged along the top edge of the flat. Apply polyurethane glue to each skin. This assembly can then be inserted (wedged) back into the shuck and allowed to dry with weight or vacuum.

Once again, sand all over-hanging edges flush to the core.

RE: Pentathlon Kit Build
 

Work on the wing panels starts with the layout for the sub-ribs. I prefer to use a trailing edge sub-rib to add strength that spot where everyone likes to pick up the plane for you. The traditional sub-rib is located near the end of the wing socket. The slots for the two sub-ribs can be cut using several methods (band saw, hot wire, hand saw).

Test fit the sub-ribs (they should not fit too tight) and the wing tube socket. Be sure to cap the end of the socket before gluing in place. Epoxy or polyurethane glue can be used to glue everything in place. Be sure to get full coverage on all surfaces of both the tube socket and the sub-ribs. I used wax paper around the areas of the two sub-ribs to prevent gluing to the shucks.

RE: Pentathlon Kit Build
 

After sanding the sub-ribs flush to the core, work can begin on the wing skins. My method starts with taping multiple sheets together (edges trimmed straight) to form a large sheet. Make sure you try to match up the individual sheets by grain and thickness (they can vary a lot). I like to align the grain parallel to the leading edge of the wing. There are multiple methods and arguments in respect to grain direction and skinning a wing in general. I trace around the shuck leaving approx. 1/8" extra on all sides and then cut the skin perimeter.

The location for a strip of carbon fiber (0.007" ) needs to be marked. This will be glued in place on each skin for added stiffness.

With the core and shucks for one wing panel placed and ready, glue can be spread onto each skin. Once I have the polyurethane glue spread on the first skin, I add the C.F. strip and then place the skin in the bottom shuck. Align it carefully, and place the wing core on top. The same process for the top skin. The skins can be cured using weight or vacuum.

RE: Pentathlon Kit Build
 

Sorry, it's been a while since my last post on this project.[:@]

The wing panels are now sheeted. The leading edges can be cut from 3/8" balsa (some prefer a medium density for a more ding resistant leading edge) and glued on. One of the sketches included shows the layout for the aileron and hinge line caps.