Foam Kit Bashing 101 Finale — Kfir Setup, Flight Review & Making Repairs

Fly, crash, repair…repeat…

Check out the full series of videos and articles at: thercgeek.com/kitbashing

Welcome to the final episode in our foam kit bashing series!  It was quite the journey getting here and I actually didn’t intend on it taking as long as it has to document the whole series, but life has been crazy with no signs of slowing down it seems (plus, I just started a new position at work!).  If you’ve just found this series, we have gone through and completely transformed a Freewing Mirage 2000 into an Isreali Kfir.  As a part of that, we covered the transformation process talking through the building methods in converting the airplane using balsa wood and foam, we’ve talked about painting and finishing and we’ve also covered how to make panel lines and add realistic weathering.  I hope that you guys have enjoyed the series and are geared up with some new techniques to try on your models!  To finish this series up, I thought it would be best done providing a little discussion on how the airplane flies in it’s new form as well as some of the things that were done in wrapping the airplane up and getting it tuned in the air.  Also, I had a little incident with the airplane at the Warbirds & Classics event which tore out the right main landing gear mount.  So, I thought it would be a good opportunity, now that we have this nice new airplane, to show how to make cosmetic repairs when they are needed as well.

RADIO SETUP

In doing all of the final setup for the airplane, I didn’t want to change too many things all at once since the airplane flew well in the Mirage 2000 configuration.  I knew however that I did want to change out the radio.  Airtronics has been my go-to radio for quite literally, decades (even had a sponsorship with them).  Though a good radio, it’s a system that’s just not supported in the US anymore and frankly, SANWA/Airtronics gave up on the airplane market years ago anyway.

I’ve been flying the Graupner MZ-24Pro for a while now and have found it to be a really nice radio.  The programming capability is awesome and the price is exceptional for what you get and so I knew that I wanted to get it installed into the kfir.  In setting up the rates on the new radio, I set everything up the same as the Mirage 2000.  With the additional trailing edge piece we added to the surfaces, I knew that the effectiveness would be a little more, and so made sure I had 3 different rates to choose from (like always! 😉 ).  Ultimately, once the CG was sorted out, I settled on mid rate elevator with about 20% expo and low rate aileron with 10% expo.  This equates to 9/16″ max elevator throw and 1/4″ max aileron throw.

 

THE EXTRA COOL AFTERBURNER MOD

The other thing added was an afterburner setup that a friend of mine designed.  It’s a “center-burner” concept where the lights emit from a tail cone attached to the motor vs a ring around the outside of the exhaust.  In the air, it is the most convincing afterburner I’ve seen to date and really adds a lot to the looks of the airplane in the air.  My friend and I are in the proto-typing stage on this AB setup, so hopefully sometime in the near future they will be available through my 3d printed products page.  The concept is awesome and it works great!

 

A DISCUSSION ON CG

Finally, the most important part, was the aircraft CG.  This, I actually messed up on  a little bit.  First of all, it’s important to note that the addition of the canards to the airplane moves the CG forward.  When doing the CG calculation, the canards are accounted for in the planform and so they move the desired CG point forward as a result.  This I knew going in, however, when I flew the airplane as the Mirage, I was flying 5800 mah packs and the airplane was a little nose heavy.  So, in the process I had picked up a lighter weight Roaring Top 5000 mah pack and made it such that I could move the battery back a little bit further.  However, I made the mistake of not double checking the CG with this new pack compared to the Mirage 2000 CG placement before the first flight of the Kfir.  So, what I ended up with was an extremely tail heavy airplane that was like riding a wild bull on that first flight.  Thankfully, deltas remain pretty stable when they’re tail heavy and though it was extremely pitch sensitive and required quite a bit of down elevator trim, I was able to get the airplane back safely.  The lesson here is had I double checked where the CG fell out with the 5000 pack before the first flight, I would have realized my error…but I didn’t…

With my oversight (and lesson) learned, moving the CG forward incrementally over a few flights, the CG was dialed in.  Ultimately it needed to be about 1/2″ forward of the Mirage 2000 location.  To achieve this, the battery capacity was upped to the Roaring Top 5800 pack in addition to adding a couple ounces of weight in the nose as well.

I want to point out that I have been using Roaring Top batteries for some time now and they are some fantastic batteries.  For the same capacity and C rating, they lighter weight than the packs I’ve been using and they put out great power.  Needless to say, I really like the packs!

 

MAKING COSMETIC REPAIRS

As mentioned earlier, I brought the airplane with me to the Scale Squadron Warbirds & Classics event which was where I was able to get the CG all dialed in.  This is where I was really able to start to really enjoy the airplane.  Unfortunately, I ended up dropping the airplane in on a landing which tore the right main gear mount out of the wing.  So that resulted in some road rash on each of the wing tips and a couple other areas.

To fix it, it was a matter of filling in all of the affected areas with light weight spackle and then sanding it to shape as necessary.  From there, it’s pretty much a repeat of the process we’ve discussed in this series.  I went through and applied a couple coats of polycrylic to seal up all the filled in areas and then locally airbrushed some primer over it.  I did two primer coats over the affected areas, so after the first coat I sanded it smooth with 180 grit sand paper which helped blend and fill everything and then after the second coat wet sanded it with 600 grit which made it paint ready.  To airbrush the primer, I simply sprayed the rattle can primer into a paper cup and then used what was collected in the airbrush.  This gave good control over where it was sprayed keeping the primer localized and controlled which you can’t do with a spray can very easily.  I should point out that the primer and sand process is what blends everything to even and smooth out the surfaces, so is a very important part in getting the repairs to blend into the existing finish.

With the affected areas wet sanded, it was then a matter of touching up the paint and weathering and then locally reapplying the clear coat in those areas.  The hardest part of any repair is usually matching and blending the paint (and of course not causing more rash in the repair process).  So, when we have areas that just don’t blend perfectly, this is where I’ll use the weathering to try and blend things together when needed.  Also, sometimes when making repairs, it makes sense to mask off specific panels instead, especially when we touchup the paint.  You can play games like this because sometimes having a slightly off color panel looks nice and scale since commonly accessed panels are often touched up on full sized aircraft.

Lastly, in fixing the gear mount it had simply just pulled out of the foam.  So, that was epoxied back in place.  While I was at it, I stress tested the left gear mount to make sure it had solid contact in the wing.  It tested out solid, so I just added an epoxy fillet around the edge for extra assurance.

 

FLYING THE “DESERT LION”

Since we’ve put in all this work and we have this awesome looking and very custom airplane, the real question always is “how does it fly?”  The last thing we want is the worlds largest desktop model!  Well, I’m happy to report that the airplane flies awesome!  I did have to work through a few bugs getting the CG sorted out which is pretty normal for a new airplane, but once that was all done, the airplane really locked in solid.  The whole kit bashing process added about 12 ounces to the airplane which includes the new parts we added, the finish which came out very smooth, and about 1.5 oz worth of nose weight.  Not too bad all things considered and in terms of performance I don’t notice much of a difference.  In the process, we added some wing area through the leading edge saw tooths and trailing pieces and now have the canards helping us as well.  The pitch and roll response is pretty similar to the Mirage, but with the larger surfaces, I found I needed to add a little bit more expo to get the feel where it needed to be for all phases of flight.

FLIGHT VIDEO

In terms of how the airplane looks, it looks amazing in the air.  It comes across quite scale and the afterburner is just the icing on the cake.  The Warbirds & Classics event is out at the OCMA flying field which is in Black Starr canyon next to Irvine lake.  That terrain was just about the perfect desert backdrop for this Israeli airplane and it looked so real flying around out there.  Scott Plummer from AirShowVid was at the event and captured some amazing photos that really make the airplane look like the real thing.

ABOVE PHOTOS CREDIT: Scott Plummer, AirShowVid

One final note I’d like to make is that since the ventral tank covers about 50% of the cheater grate on the underside, I opened up some auxiliary air inlets in the main gear wheel wells.  I originally flew the airplane without this, and the airplane flew well, but not quite to the same performance it was as the Mirage 2000.  Opening up the gear wells helped liven the airplane performance up back to what it was before.

 

FINAL THOUGHTS

At last, this concludes our series on foam kit bashing!  I really hope you’ve enjoyed the series and are equipped with some new techniques to try out.  I really enjoyed creating this Kfir, though I probably spent way too much time on it.  That’s the beauty of something like this though, we can make it as much or as little as we want.  Also, all of the techniques we’ve discussed, especially the finishing techniques, translate onto all sorts of models and mediums, so I hope you’re inspired to give some of them a try and to experiment.  It’s all about practice, so the more we experiment, the better the results on each model and the results are always worth it.

Now, with our kfir done it’s time to think about our next long term project.  I can tell you, my competition Skyray build has been calling me for a while…it may be time to get back to it if I can avoid getting distracted by other projects!  Until next time, I’ll see you at the field!

HOORAY!

2 thoughts on “Foam Kit Bashing 101 Finale — Kfir Setup, Flight Review & Making Repairs

  1. Wow, awesome work Chris!
    How are you liking those Roaring Top? Never heard of them… you think they would hold ok @ 95A+, ok for your 12S A-7 too?

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