In keeping with my promise to pass on any cold weather problems encountered with my Foam/Dynel KR-1, I submit the following experiences.
A few weeks ago the plane was rolled into a friend's garage here In Anchorage for some general maintenance and a thorough inspection. It was strictly for my own curiosity - to just see how everything looked. The small cracks that had previously appeared in the wing fillet area (see January 1974 SPORT AVIATION, page 54) were patched and painted. Some other corrections and additions were made, such as rubber shock mounting the engine and installing a gear up warning light. Yes, it almost happened ... and if not for some very observant tower controllers my little KR-1 would have needed a new prop and face lifting.
Well, so much for the near mishap! After this general maintenance, cleaning, and additions were made, it was time to leave the garage. On this particular day the outside temperature was around O° F. My friend, Dave Daly, and I gave thought to possible contractions of the skin due to the abrupt temperature change. The garage was allowed to cool for about an hour and the plane seemed about right for exposure to the direct cold. After raising the garage door for an additional 15 minutes and allowing the plane to cool further, we decided to wrap blankets over the fuselage and wing roots to relieve the sudden shock of the Dynel and epoxy skin coming into contact with the 0° air. The garage had already cooled to 40° when this extra precaution was taken. We rolled the plane out and loaded it onto a snow machine trailer and tied it down. Once loaded and tied down, Dave and I stood there pleased that our precautions had worked when a sharp noise, almost as loud as a small pistol, sounded in the chilled air. Of course, the smiles turned to instant fear as we found a crack about 18" long around the front fillet area of the right wing root.
Well, about 15 "IF'S" later, we pulled it to my driveway for safe keeping until I could repair the crack. Once parked, I left and did not return to look over the damage again until late that evening, at which time I found five additional cracks in the fillet areas and two skin fractures at the end of the main carrythrough spar. All of these cracks have not impaired the plane structurally, but has presented the aggravating work required to patch and paint them.
The whole point to this experience is to let others know that the KR-1, in my opinion, cannot be taken into a warm area and suddenly moved outside without a thorough cooling off period. I feel that no less than 24 hours should be allowed for this slow, cool down transition.
Giving the entire matter much thought, it became very clear that the problem lay in the fact that so much of the wood structure is nestled in and around the fine insulating properties of the foam. With the foam warm and it, in turn, keeping the wood structure warm and the skin being exposed to the cold and contracting such as it does - then something is bound to occur.
My previous experiences with cold temperatures and the KR-1 have shown that no real faults have appeared as long as the plane is left outside to ride along with the normal up and down changes. The temperature has never dropped suddenly enough at any time so far to cause the aforementioned situation. But this problem could well hinder the pilots who have the convenience of an overnight warm-up for the next day's intended flight. Or in my case -- just routine winter time maintenance and inspection.
In summary, the KR-1 will stand up to normal outside up and down temperatures, but possible cracking could occur if brought into a warm area, for whatever reason, and then rolled outside without the estimated 24 hour cooling off period. This precautionary exercise should be taken in situations where the outside temperature is below 40° F.