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Kolb Firestar II Project Log (and Discussion)

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Victor Bravo

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KWHP, Los Angeles CA, USA
(Forum administrators, this thread was started in the Tube and Rag area, because I wanted to invite discussion and comments from any and all HBA participants, and this would not have been possible in the regular "builder's log" section. The Firestar is indeed a tube and rag design (even the spars are tubes!).

Let me know if there is some reason this should be moved to another area)

Some of this has been posted in a previous thread, but I'm repeating it here because this is the "official" kick-off and build thread. Forgive any repetition please.

Recently I purchased a mostly complete Kolb Firestar II kit which had been started.

The stabilizers and fin had been completed. One of the wings had been partly completed, then disassembled because the builder had accidentally used the tailboom tube as one of the wing spars.

The primary purpose of this aircraft is to go out and do "off-road", informal running about with no destination, and general knock-around flying. There are hundreds of potential tiny landing areas, dirt roads, small meadows and clearings, and bare hilltops that just beg me to go land there. But having a 60 year old Cessna 172 as my "main ride", most of these places are less than appropriate (or downright disrespectful) to go in the 172.

My search was for a near-ultralight, knock-around, STOL capable airplane that could fold up and live in the hangar under the 172. I had bought an Avid Flyer salvage, and this would have been great, but I could not afford an engine I wanted for it (4 stroke 80+HP). So I gave that to Pete as a test bed for his O-100, which has been discussed on another thread.

My interest and research on the Big Bad Twin V-twin led me to look again at the Kolb series. Not having been able to afford a flying airplane with a 4 stroke engine, I resigned myself to build one on the cheap. So I bought this kit at a good price.

Then an interesting opportunity dropped in my lap (at which point Marlon Brando came up out of the grave with a pinstripe suit and said it was "an offer I couldn't refuse"). So within a few weeks I had purchased this Firestar kit, and had bought a low time HKS 60HP used engine.

The "back story" above is important, because my desire for a flying airplane in a short time completely and entirely drove the decisions for how I wanted to build the airplane. I accepted from the very start that this was not intended to be a show plane, a trophy winner, or a "wow that's beautiful" airplane. As such, I made a decision that the "fine points" of attention to detail, the symmetry and linearity of the rivet spacing, the stuff that separates "workman-like" from "high craftsmanship" were not important and would be sacrificed to save time. I decided my workmanship was to be safe, and within the designer's intended range of quality

When I got the kit, the shipping company had been kind enough to squash and mangle the three tail surfaces. I chose to build new ones, although in retrospect I could easily have repaired the original ones. I just was not familiar with the right technique of removing the stainless pop rivets, and my first attempts to just drill them out resulted in Marlon Brando coming back out of the grave (with his face painted camouflage) whispering "The Horror... The Horror!".

Construction started in mid-April. Thus far, I have been building new tail surfaces (stabilizers, fin/tail fitting ass'y, rudder, elevators). Although at odds with my initial decisions about quick completion, there were a few areas on the original Kolb design (rib tube attachments on rudder/elevator/aileron) that really seemed "a little too lightweight" to me. There was no intent to operate this Firestar as a two seat airplane, it was never going to be a Part 103 ultralight, and I wanted a little more robust attachments in some of the tail parts than what was shown on the plans. I take full responsibility for these modifications and decisions. The extra weight was marginal, and stiffer control surfaces also yield greater resistance to flutter.

For the rudder and elevators, I chose to use a modified version of the Graham Lee / Robert Baslee aluminum tube, sheet metal gusset, and blind rivet design. The original plans showed the upper and lower rib caps (5/16" x .035 aluminum tubes... similar to the "battens" in the hang glider world) simply sitting on top of the leading and trailing edge tubes, through-drilled and attached with one rivet. This has been shown to be adequate on hundreds of Kolbs, but it did not sit well with me for operating in a "rough and tumble" environment.

So as it stands now, I cut roughly triangular gussets out of the .032" sheet metal to use as attachment plate/patches for the tubes on the control surfaces. This matches the gusset construction that Kolb already uses on the Stabilizers and fin. Using gussets instead of overlapping tubes allowed me to use at least four rivets at each attachment location (two on the spanwise tube, two on the chordwise tube) instead of one rivet. The gussets of course add stiffness, carry more shear, and provide an overall more robust attachment at the cost of a small weight increase of perhaps an ounce or so at each location.

So with all that as the introduction, I will try to post some photos in this thread later tonight that show the details of my progress. Again, this thread was specifically intended to foster two-way conversation, so feel free to join the discussion, offer opinions, make recommendations, put me on the spot to answer for my insolence in the face of Homer's genius, etc.
 
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