As I write this, winter has begun. This is when I like to perform a thorough inspection of my models. My last flight on my reliable Der Jet Vampire ended with a total brake failure. The brake caliper seal blew out from the caliper groove.
I took the brakes apart and found extensive wear on the wheel hub. This model was approaching 400 flights with its original wheels and tires, so this was to be expected. The brake system is a disc brake unit with brake pads pushing out against the wheel and also squeezing a disc in between the wheel and the brake caliper. It’s a strong, effective system.
I reinstalled the seal, reassembled the brakes, and the seal immediately blew out again. This would not be a simple fix.
I took the brakes apart again, assuming there must be something wrong with the amount of travel—allowing the caliper seal to move out of its groove. A couple of measurements comparing the brake that was failing and the other side that was working well showed roughly a 1/2-inch difference. Normal end play would only be approximately .010 inch to .020 inch—a substantial difference. But where should I look next?
I first assumed wear, but a quick check of the brake pads showed they had equal wear, so I ruled that out. Next, I checked the depth of the wheels and inspected them from the hub lip to the brake contact point. Again, there was nothing substantial. I checked the depth of the wheel bearing to the wheel hub, and that was where I found the problem.
The wheel bearing had moved roughly 1/2 inch within the wheel hub, caused by the outward pressure from all of the years of flying. This movement widened the gap between the brake caliper and the wheel hub.
I pressed the bearing back to the proper depth, cheating a little and using some J-B Weld to create a lip to prevent future movement of the bearing within the hub. I then reassembled the brake system, and the problem was solved. The brakes worked like normal except for a small seal leak when the brakes were applied, which was not unexpected. The seal on the guilty brake had signs of damage from when it had blown out during landing.
Fortunately for jet modelers, Eric Clapp, owner of Jet Central USA, not only sells Der Jet airframes, he stocks some parts. After a quick call, a new set of seals was on the way. With the seals installed, the brakes now perform like new with no leaks, and solid, even application. The aircraft is ready for its next flight.
SR-71
How about scratch-building a competition-quality, composite twin-engine jet model—not just any aircraft, but an SR-71? That’s what Lance Campbell did throughout a period of several years, and what a grand model he has created.
Lance approached the SR-71 Blackbird methodically, breaking the engineering and fabrication into logical steps that led to his amazing model. You may have seen pictures of this special and well-recognized aircraft throughout the last few years.
This is a 1/8-scale aircraft with an overall length of 13 feet and a wingspan of slightly less than 7 feet. It is powered by two JetCat P-120s, which are reliable turbines with many years of service.
This model is operated under the Large Turbine Model Airplane (LTMA)-2 Permit to Fly program, allowing it to be flown at AMA fields and events. The LTMA-2 is for turbine-powered models that weigh more than 77.3 pounds ready to fly. It’s a good permit program for these large aircraft.
I am a strong supporter of using the LTMA-2 permit process as our models get larger. A quick check of the aircraft registered to date shows how active this permit process has become, which is another AMA success story.
The SR-71’s fully molded composite airframe was made from Lance’s molds—created from the plug he carved, shaped, and finished. Think about that—a hobbyist who created his own 13-foot plug, molds, and is able to make the airframe. That in itself is an incredible accomplishment for one person. Then add in his attention to detail! As Lance developed this airframe, he learned new composite building techniques.
Like many dedicated Scale modelers, Lance has stories about the special people he met as he researched the SR-71 and searched for the smallest details to get everything right on his model. He had surprising assistance from people who stepped forward and were able to provide documentation beyond what one would normally find in books.
This is part of the joy of creating a unique Scale model. I would imagine few people have ever acquired so much information about the SR-71. It’s all in the drive to build the model as accurately as possible.
To design the SR-71’s landing gear system, Lance started with Tom Cook’s retract units, combined with landing gear struts of his own design and fabrication. It’s a solid system built to be reliable and rugged. Lance collaborated with Glennis Aircraft (now closed) to create the wheels and brakes. The company came through in style—right down to the white rubber compound from which the tires were molded.
Lance wanted a correct landing parachute that would reliably operate. He contacted Details 4 Scale and asked the company to help him create a complex parachute system.
The system has a pocket with scale double doors and a spring-loaded floor system that launches the parachute up and out of the aircraft for proper inflation. This is a neat feature and a grand accomplishment for Lance and for Details 4 Scale. We have some wonderful modelers working as suppliers in this hobby.
I could go on and on about this SR-71. If you want to get a taste for what it takes to create such a wonderful masterpiece, Lance has provided the story of his creation of the SR-71 on a website listed in “Sources.”
The story of designing, building, testing, and flying the SR-71 is worth the time if you’ve ever dreamed of creating a special model, but be aware that Lance provides plenty of information on this website. It will take some time to cover it all, but it’s worth the read.
SOURCES:
Jet Pilots’ Organization (JPO)
www.jetpilots.org
Lance’s Jet Page
www.mmrca.org/lance
Details 4 Scale
(208) 233-4721
www.details4scale.com
