So I figured I'd update this thread with the continuing saga of the P-40 landing gear. Since the last update there has been multiple attempts at flight with landing gear failure or damage occuring on all of them.
- The second attempt ended, like the maiden attempt, with a hard left departure into an immediate stall. This sheared off the gear and required a repair.
- Third attempt was very much the same. Getting this thing to track straight on takeoff roll is truely a nightmare, but I believe with a few adjustments to technique it will be OK. The extreme light weight and the large 3 blade prop add to the torque roll and left turn tendancies. A MUCH lighter prop has now been installed and this will help a bit with less rotational mass.
One thing that is VERY clear is that the retract units are not up to the task. I am on my third set of these Hobby King units. Even with the modification to the rotation link they have more play in them than I would like. They also have a BAD habit of burning out. Prior to Flite Fest 2017 I spent several hours working with the gear and was happy to have them working well... Only to have one of them fail when I was setting up to fly her on Sunday.
After giving myself time to vent over ANOTHER gear malfunction I put her on the bench a few weeks ago and rebuilt the failed retract using parts from the previous burned out units. A new motor had the retract unit working well and I cycled her through dozens of times on the bench before reinstalling it.
After a few cycles installed this unit stopped functioning again. I gave myself another week or two to vent and built the Sea Duck as a distraction. When I came back to it last night I found that the gear that mates with the drive screw was stripped. I made an attempt to replace it with a gear from another unit but it proved to be too much of a PITA. Add to this that spare units of these retracts have been unavailable from Hobby King for several months.
All this has lead me to the conclusion that I made the wrong choice several years ago when I started this project. At the time I didn't want to spend hundreds of dollars on the expensive Robart units and I thought I could keep the extra full length spar in the wing un-cut (See Post #3 in this thread). The designer demonstrated that the retract housing transfers the load just fine, but I didn't want to cut it if I didn't HAVE to. At this juncture I'm now in for 3 sets of "cheap" retracts at about $150 each, PLUS I had to buy the struts at about $90 that would have been built-in to the fancy Robart units. That's $540 spent on gear that don't work, plus probably a solid 80 hours fighting with them (especially if you count the time I spent fighting with the doors that would have just bolted on to the Robart unit).
I hated to throw in the towel, but I'm done spending time fighting with unreliable and unproven gear. I've ordered the pricey Robart units and will be modifying the airframe to fit them. It should be a straight forward process, but even if there are new problems at least I'm heading down a new path instead of going in circles. Our club will be hosting a Warbird event this fall and it would be WONDERFUL to see this in the air at that event.
Sorry for the novel... just wanted to bring everyone up to speed on the last several months of "progress". Pictured below are the sad, grounded P-40 at FF, my pile of broken retract units, and the shiny new Robart units that are on their way.