On the BVM web site, under the KingCat addendums, is outlined a problem with the booms delaminating and cracking, be it under flight ot landing stress/load, or during bumpy transport. My King Cat is nearing completion and I would like to reinforce this area prior to flight as a precaution, instead of waiting for the problem to develop to address it .. My question is, what can be done to reinforce the boom ? Some of the ribs and wood structure deep inside are balsa, some are plywood .. there is not mush access to get in and double up or reinforce any of the wood work, and i can not see how to get any rods or skin doublers in there either .. I have heard some people discuss possibly cutting the booms open to reinforce them, but I definitely do not want to go that far ... any suggestions ?? The only thought I had was to use low pressure polyurethane expansion foam, mixed with shreds of carbon fiber cloth ??? (would be very light and strong... (would run a tube through the boom for servo wires .. ) .


any and all ideas welcome !!!


Wojtek

Try to PM Buck Garza (yeahbaby). I don't know what he did, but I saw his Kingcat at waco a couple weeks ago, and I saw fiberglass all over the midpart of the boom. I didn't ask whether it was a repair or a reinforcement, it looked more like a repair, but I didn't get close enough to really tell. I just saw what looked like a fiberglass tape wrap approximately 18 inches wide.

Good Luck,

Sean

Woj

The answer to your question in on BVM site that you referenced in your post.

See below for a copy:

There are at least 200 KingCats actively flying now and enduring the stresses of high speed flight, High-G maneuvering and less than perfect landings.
There have been problems recently with the booms on two aircraft. As explained in the previous A.D. (July '04), these semi-monocoque structures rely on the integrity of the glass/foam/glass laminate for strength. If the lamination is damaged, i.e. delaminated for any reason (even excessive squeezing during model assembly), there can be a soft spot in the boom structure.
This .020" carbon fiber boom reinforcement kit is offered to all KingCat customers at no charge for the parts and instructions. There will be no shipping charge for USA customers. Shipping outside the USA will be whatever is most economical.
If you have been flying your KingCat a lot and have confidence in the integrity of its boom structure, you may be satisfied with it the way it is.
If you have any concerns about them (booms), we highly recommend installing this reinforcement kit. It takes less than an hour and some SLO-ZAP to accomplish.
The thin machined reinforcement strips have a shiny carbon fiber weave surface similar to that used to decorate custom automotive interior panels. The aerodynamic shape of the side panels is also attractive and should not need any touch-up painting.
Boom reinforcement kits and very detailed installation instructions will become available to be shipped the week of September 20th, 2004.
Due to the numbers involved, it will take us about 4 weeks to supply all KingCat owners. New kits are being shipped with the reinforcement kit factory installed as of September 20, 2004.

Contact BVM at 407-327-6333 (tel) or 407-327-5020 (fax).

Woj,

I just installed the reinforcement kit to my new Kingcat, it is an easy 30minute installation. Call Patty and she will send you all the goodies you need.

Ghost_rider, David,

thanx very much for the quick replies. I was about to start coming up with my own mods, and am very glad that BVM has a fix for this ... I do realize that the boom problem has been limited to only a small # of king cats , and in view of all the KCs out there, and how hard some of them are being flown, im sure for the most part the booms are of sufficient strength and integrity ... I'm one of those people who is paranoid of having stuff as strong and well built as possible. so this reinforcement kit will be perfect .. I have a AT400 going on the business end of the KC, so that also adds to me wanting things as strong as possible …

where is this referenced on the website at BVM ? I have not been able to find it ..


thanks guys !


Wojtek

Kingcat addenedums

If structural problems which affect the airworthiness of these aircraft have been discovered, albeit so far on only two airframes, surely the best course of action would be to reinforce the booms on ALL Kingcats at the very earliest opportunity and preferrably before further flight.
Regards,
David Gladwin.

I agree with David G's assesement - this should be a mandatory AD.

FWIW, I am the guy that reinforced Buck Garza's KC booms the day before GSW. We found a small delamination and crack in one of the booms but he was keeping an eye out and fortunately caught it before it became a flight risk. Buck does not fly high-G or transport his KC on the gear. He did have a gear-up not long before and that may have contributed/caused the crack (per BV).

The repair procedure and materials now listed on BV's Web site looks adequate. On Buck's we used four pieces (one per side) of 2 oz. carbon cloth, about 10" long and 2" wide (tapered) that covered the areas between the diagonal formers in the booms and extending past the formers by 1/2" or so. We used two pieces of 1.5 oz. crowsfoot weave E-glass, extending about 1" past the carbon, that completely wrapped around the booms, providing reinforcement of the top/bottom joint seams. This is way overkill but is completely bulletproof and we can now pick up the KC by the booms, transport it assembled, etc. without worries. I used West Systems resin. Total weight gain was about 4 oz. and could have been lighter if we had more time.

I have a second KC in the works now and will be doing the same to mine before first flight.

Barry

Hi I called BVM and they sent me the kit for free!!! thats customer service at its best I like a company that treats you like this!

In answer to David Gladwin's post I have been told that BVM has already dealt with fixing this problem during the molding process. That said, I suspect (and this is pure speculation on my part) that there is still a need to treat the boom with care since it is still possible with rough handling/transportation/landing to damage one of the holes and cause delamination. The solution employed on Buck's KingCat sounds like way overkill, but nevertheless a bullet proof fix. The solution described on BVM's web site appears to adequately disperse the loads over a wider area if delamination has compromised the strength of a boom in the area of a hole.

FWIW I got my boom reinforcement kit within 4 days of calling BVM. It didn't cost me anything. Thanks BVM.

Antony

No question that the booms on the original run of kits was the Achilles Heel.....the rest of the bird is very stout, IMO.....the vacuum sandwich, semi-monocoque boom construction seems quite solid vertically, but prone to damage with any side load.....

The photos show what happened to my bird after I got a Kangaroo Hop going after touching down a bit too fast......the actual boom contact was not all that violent....no other damage to the boom or rest of the bird....all flex plates remained intact, but the side load snapped the boom clean.....I didn't even notice it until I taxied back and went to pick it up......there were no prior incidents that would have led to an unrecognized stress crack......the model was always transported on foam in my trailers, with the booms well supported.....it happend on flight #25...

While the Barry/Buck fix may be overkill, it really addresses the issue of side load on a long boom moment arm, with the fulcrum at or near the aft end of the center section-boom intersection, where mine snapped....

Tom

Tom,

FWIW, and you probably already know this... that break is almost exactly where the booms broke in flight on the King Cat at the Maine Jet Rally. The structure in that area looks exactly the same on that one as well. I looked it over carefully since I had planned on ordering another one this fall. Everything looked like it was manufactured correctly with no obvious or visible building errors or defects. Seeing how there are failures without hard ground contact, your bounce was most likely just the catalyst, and not the sole cause.

I ordered a King Cat at last years Maine Jet Rally, but it wasn't delivered to me until late winter/early march the next year - 6-7 months . I had planned on building it over the winter, but since it came so late, I sold it off rather than sitting on it all season long. I had decided that I'd order a another one in a different color and build it this winter. I wish I still had the contact information for the buyer so I could make sure he is notified of the problem with the booms, and get an fix kit from BVM. There is no way for BVM to get him a kit unless the buyer runs across the info somewhere and contacts BVM. Hence the need to get the info out to those people that bought the kits second hand, or otherwise not easily identified or traceable.

Hi Steve:

I think that the Turbine ARF's from BVM and Composite-ARF coming out of Thailand are the greatest for those of us who can build but cannot or will not paint....

I think the vacuum sandwich construction in the booms on the KingCat and wings on the Eurosport can be problematic....I fly off grass 98% of the time.....while it is forgiving in many respects, it also can make ground contact in an unusual attitude more damaging as any sharp point like the upper and lower fin or wing tips more prone to dig in, rather than skid like on asphalt....

I don't think the KC boom problem is in the basic design, which is a clone of the BobCat.....I have seen quite a few BC's cartwheeled with no boom fracture, so the problem seems to be one of beef in that area of the aft center section....

Tom

The location of the boom breaks on Tom's KC coincides with the breaks in mine (I hit the ground hard on an underpowered approach, not the KC's fault [&o]) and the cracks on Buck's booms. Having said that, in my opinion it is a weak area that needs to be reinforced on all flying KC's as soon as possible.

No doubt that BVM's fix will work and they have been very proactive in fixing the problem and making reinforement parts available ASAP. Kudos to BVM for responding quickly during such a difficult period (i.e. all the hurricanes and flooding in Florida!). [sm=thumbup.gif]

Having said that, I think it's important to get the word out...thus my post.

BVM's carbon doublers will no doubt work fine. As my second KC is an all-white version, I don't have any issue doing the overkill reinforcement, because it'll be invisible after painting.

Using Tom's boom pic, here's what Buck and I did...



Barry

Hmmm-
Seems to be aproblem there.
Sorry to see Terry Nitch's KingCat go in hard at the US Scalemasters at Gardner Ks. on a demo.
Worst wreck ever, straight in.
Does anyone know if his had the BVM fix kit on the booms.

Marty O

OH! FOR PETE'S SAKE NO!!!!!!

I have no doubt that BVM has fixed the problem at production stage BUT unless the exact history of the booms is known the mod.should be incorporated at the earliest opportunity as I am sure would be done in full size aviation. Posts subsequent to mine have proven my point and clearly the Kingcat boom problem is rather more extensive than is suggested on BVM's web site.

If the nature of the boom construction has been problematic why not revert to the fiberglass moulding as on the Bobcat, the booms on my two examples are absolutely sound.

Perhaps there should be a simple assesment, : what are the possible consequences of a boom failure and what is the downside of incorporating the mod. which should prevent that failure. No contest.

Regards,

David Gladwin

From what I have been told the latest kits already have carbon fiber sandwiched in the layup. My latest kit wsa shipped in early August and did not have the extra CF in it. I added the plates per the addendum, I had already added a strip of 1" wide CF tape top and bottom from in front of the front spar and to the vertical fin. The plates have made it rock solid. My original kingcat survived several not so stellar landings and was trailered over considerable distance this summer, with no signs of stress cracks. I believe that BVM is recommending the reinforcement to all kingcats if my original had not crashed I would have added them to it.

David G. I think the problem is just surfacing so it is being addressed, what more could you ask?

My incident occured on July 25th.....I was in contact with BV shortly thereafter, and several calls since that time.....he has been addressing the issue since then, but with the hurricanes and shipping delays, delivery of the new booms has been held up a bit.....

While inspecting the broken boom sections, I did notice that the actual sandwich did not appear to be quite as solid as I would like.....several spots where the fiberglass inner lining is not stuck to the foam layer, well away from the damaged area.....There are some glue voids between the rather soft balsa bulkheads and around the ply doublers of the anti-rotation pin receivers.....

All of these point to the need to tighten up some of the quality control on the Thailand production line, which I am sure Bob is taking care of as well as using some C/F in the sandwich.......as I noted, this was one of the very early production kits, maybe one of the first 2 or 3 Navy Training Pattern birds delivered last October.....

Depending on how the new booms look, I still might add a little more beef similar to what Barry or David have done.....these booms are like landing gear plates....so much easier to beef up before they crack than repair after the fact...

Tom

I see the reference to the boom reinf. on the website but I can't find the details inthe Kingkat section.
Can someone tell me where to look?

THanks David Pippin

I noticed the opposite Tom, my original was solid but it was one of the first ones out of the molds too. The new one seemed a little less rigid. I am sure the reinforcement I did on my own was overkill but I'm pretty roguh on my airframes.

DR

David R. The BVM website is leaving embodiement of ths mod to the discretion of the user. (if you have been flying your Kingcat etc etc) That is where I think he is fundamentally wrong. This mod, should be mandatory as failures, with potentially catastrophic results, may be totally unpredictable, this unpredictability is one of the major unknowns in the increasing use of composites in fullsize aircraft production, no one really knows the ultimate life of these materials. I think about that everytime I inspect, then fly, a 20 yearold glass fiber Astir sailplane. Just two weeks or so ago a Ka7 glider in the UK ( fullsize) lost both wings with presumably fatal results, a totally unpredictable occurrence (although that machine is wood and steel tube) as was the inflight breakup of a (model) F18 recently. The Ka7 fleet is, of course, now grounded.

The bottom line is this: there clearly is a boom problem on (some) KingCats and a fix is available. It should be incorporated on all Kingcats, except those known FOR CERTAIN, to have been corrected, strengthened during manufacture, absolutely as soon as possible, no exceptions, no discretion. Just sound aviation practice.

Regards,

David Gladwin.

I'm not going to get into a pissing match over this it just is not worth it. The way the directive reads to me (and the fact that I have spoken with BVM about the issue) the reinforcements are being added at the factory to every new kit. They are going to send them out for everyone that requests one. They are recommending the addition of them. Does that not say it all? I have to believe that anyone that owns a kingcat will want to do the mod in order to protect their investment.

David,

you had mentioned in a prior post that you had added reinforcements of your own to the king cat when you first had it. Could you share what you had done on the booms as well as any other parts of the plane ? I intend to fly my KC rather hard (i like to bank and yank em ) and like to reinforce whjatever i can even if its overkill ...

regards,

Wojtek

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