I think the big takeaways from this discussion are that testing is useful, but one must understand the limitations and failure modes of the system which can sometimes only be determined though testing. In the large airplane world we have numbers for brake cooling time after an aborted takeoff or landing at various weights or sensors on each brake. This ensures the following takeoff has enough thermal headroom to prevent a hot brake incident like Zach encountered. It appears his incident was primarily related to a mechanical abnormality or failure (dragging brake pad). His reporting on the failure mode of nylon line termination at the caliper can hopefully prevent someone else from having a nylon line melt down and cause a fire, also using non-flammable fluid is a good suggestion. My lines are 1/8 nylon terminated at the caliper. I may consider adding a section of steel or aluminum now. In experimental aviation (especially on the KR where there are so many variations on how each aircraft has been built) we are sometimes operating closer to the fringes of the known data (unlike much of the unmodified RV crowd with a standard build) but even with a tested, common unit like MATCO brakes there can be issues and failures.
Light general aviation aircraft don’t have brake cooling charts, but after a high speed abort or heavy weight landing it is probably advisable to wait 5-10 minutes before another takeoff attempt. Certainly, training and recreational aircraft with similar braking systems are capable of making repeated patterns and full stop, taxi back circuits without incident. However if one senses a brake abnormality (dragging, etc.) it would be wise to stop and assess the situation or tow the aircraft. While good data on a new build or modifications can be gained from a ground run up to where the controls get aerodynamic authority; doing repeated runs with heavy braking is a recipe for hot brakes and is not advisable without about 20 min cooling between runs. Thanks, Zach, for your report on your incident and the valuable information it provided. I’m glad to hear your KR did not sustain major damage and was fairly easily repaired. I hope to see you at the Gathering. Blue skies and smooth landings, Adam Deem KR-2 N8095K On Tue, Jul 30, 2024 at 8:10 AM Mark Jones via KRnet <[email protected]> wrote: > I am at that stage of high speed taxi testing. I thought I had my brakes > corrected from the insufficient performance during my first taxis. I went > as far as buying new Matco cylinders and installing those. Went for taxi > test yesterday and the brakes are still out of whack. I have determined the > cables are too long and need to be shortened an inch or two. Personally I > would not exclude high speed taxis from the testing phase. > > Mark Jones > Oldsmar, Fl > > N771MJ “WunderBird” > www.flykr2s.com > [email protected] > > > > On Jul 30, 2024, at 1:24 AM, MS <[email protected]> wrote: > > > There's nothing wrong with ground evaluations when getting to know a > freshly built airplane . . . although I've gotten familiar with any number > of airplanes in my long life and never felt the need to do HSTT's. I would > have been looked upon as something of an idiot in fact, had I tried such > antics. > > There are ways to find or diagnose engine problems without racing down a > runway without the intention to take off. Is it too obvious to mention > there would have been no brake fluid fire on Larry's plane had the plane > been operated in a more thoughtful way? Aside from low speed initial > evaluations of gear tracking and braking with freshly-built aircraft, most > HSTT's are performed by guys thinking they are familiarizing themselves > with a new airplane they are a bit afraid of and unexpectedly finding > themselves in the air or blown off the runway by a gust. They panic, try > to force the airplane back on the runway then lose control and damage the > plane. Or they find themselves in the weeds (or worse) having run off the > end of the runway. > > Re brakes, any experienced A&P who regularly services aircraft can easily > tell whether the airplane has been operated by pilots or drivers. Many > fine pilots are drivers of course . . . I've just found in my own life that > the less I use brakes the more skillful I've become. > > I shouldn't have commented on the brake fire. I had no idea it would stir > controversy since most of us are all grown up and have seen enough examples > of poor airmanship to know what works and what doesn't. I'll leave the > topic alone. > > Provecho, > > Mike Stirewalt > KSEE > > > -- > KRnet mailing list > [email protected] > https://list.krnet.org/mailman/listinfo/krnet > > -- > KRnet mailing list > [email protected] > https://list.krnet.org/mailman/listinfo/krnet >
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