Mounting the Whelen power supply in an RV airplane by Bob Collins
I've had the Whelen Comet Flash strobe system for about 3 years now. I bought it in a wave of buying fever in the Van's catalog, even though I was -- and still am -- nowhere near needing it for the status of my project. I've been cycling it every 6 months or so, while delaying a decision on where to put it.
Like many people, I was going to put it under the baggage floor; I even put nutplates on the floor so I could easily get to it. The problem is, it's difficult to get to the baggage floor without taking seats out, and even the flap mechanism rod. Plus, I've found it remarkably easy to put a dent in that floor, which means it won't take much for the floor to hit the power supply. I also had questions about heat dissipation in that spot and I really didn't want to drill into the fuselage belly for one of the several attach angles.
Putting it in the baggage floor also looked like a lot of work and while I have nothing against work, per se, if someone can do some of it for me, well. all the better. I did receive help on suggestions where to put the power supply. In the photo, you can see how Vern Little installed his; in the floor with the little hatch. It's a nice set-up but it required more, ahem, work.
Don't get me wrong; I have nothing against the concept of putting the power supply underneath the baggage compartment. It's just that as time has gone along, I realize it's not for me.
Poking around a little more, I found a neat set of brackets that Jim Percy made to install his aft of the baggage bulkhead. It's a neat set-up. I think those are then riveted to the side skin..
The other installation idea I found was a nifty one from Don Owens and Roberta Hegy. Both put their power supplies on the side of the flap motor housing. Don was kind enough to send me a couple of pictures, and noted he strengthened the installation with a couple of pieces of angle on the inside of the flap housing. It also made for a short wiring run since it would take, basically, the same path as the wires from the flap motor.
Jim Percy made these brackets to install the power supply aft of the baggage bulkhead.
This idea really appealed to me, mostly because it looked pretty easy. The only negative would come, I figured, if a bunch of sweatshirts or blankets and stuff from the baggage area somehow made its way to the power supply. I have no idea how much heat that thing generates, so I have no idea whether that's an issue. But the feature I liked here was the easy access to it in case of service.
But it was actually a posting on Van's Airforce a few months ago that got me focused on putting it behind the bulkhead. But where. The posting answered the question. " I also called Vans this morning just to see what they might recommend. For the strobe power supply they suggested a plate of .025 or .032" aluminum spanning across, and pop riveted to, the 2 J-stringers, on one side or the other of the fuselage behind the baggage bulkhead. Platenuts can be used to mount the power supply to the plate, obviously before it is pop riveted to the stringers!" according to a poster named Ray.
Don Owens' set-up on the flap motor housing.
And weeks later, Van's was marketing a bracket that fit the specs exactly. It's $15 and it made the decision much easier for me. All I had to do is figure out whether it should go on the left side or the right side and that decision was easy since I figure I'll quite often be flying alone -- right side.
I think this was the proper way to go because, as I said, I've had the system for three years and poking around on where to put it hadn't resulted in any action. When the package arrived last week, I had some time on my hands and the plane was calling. I also have been mindful of reports of oil-canning in the side skin and wonder whether a stiffener -- the bracket -- between the stringers might have any effect. Since this is an experimental airplane, it was worth experimenting.
Installation is relatively easy, although not without a few minor irritants. First, you take the bracket out of the package and fit it on the side stringers. Each flange goes underneath the stringer. Then you just slide it for or aft until you get a good fit, being careful not to twist the plate.
(Note: A Flash slideshow should appear below. If it doesn't, you'll need to install Flash 8)
My immediate concern was the rudder cable that snakes behind the bracket. Would it hit the flange of the strobe mounting bracket? I don't have the pedals and rudder installed, so I just had to eyeball it and it looked like it would miss by about 1/2 inch. So I proceeded.
The bracket comes with four pre-punched holes on the bottom and you use those to backdrill into the stringer. This is where it got a little annoying because you have to use a mirror to first locate the holes, and then a right angle drill to drill into the stringers. Because of the curvature of the fuselage belly, it's impossible not to drill at an angle, so be careful. I used a short stubby drill bit so that I didn't accidentally hit the fuselage side skin.
Once those four holes are drilled and clecoed, you use your handy-dandy rivet guide to mark four evenly-spaced holes along the top and then you drill, using at least a 6" drill bit.
Remove the plate, deburr, dimple the nutplate holes and then attach the nutplates. Van's gives you only four K1000-08 because although you can use this bracket for either the Whelen strobe or an ELT, you wouldn't use it for both and there are four holes for the ELT that are different than for the Whelen strobe.
So what did I do? You've already figured out -- haven't you? -- that I can never make a decision so I put 8 nutplates in (I had extra in a jar), just in case someday I want to change my mind and mount an ELT unit there.
Of course, that was before reading Ray's post on VAF (referenced above) that also included Van's idea of where to put the ELT. "Their suggestion on the ELT was to use the elevator bellcrank rib as one of the main structural components for the mount. It would be strong enough, and access would be through the baggage compartment bulkhead." So while they've marketed a product here that can be used for either the strobe, or the ELT, the location of the product on the airframe only serves one of their recommended locations. Fine with me. On to the installation!
With the nutplates installed -- I really didn't think I'd ever use that old C-frame again -- I again fit the plate in its designated spot (remembering to deburr those stringer holes!) and clecoed it back in place.
Van's supplies the pop rivets and I pulled the four at the top and then the four at the .... oh oh. As you can see in the photograph, I can't get in there with my nice Arrow pop-riveter. My $15 solution just became my $15-plus-whatever-a-stubbier-pop-riveter-costs solution.
No matter, the key benefit of the Van's-supplied plate is it got me to make a decision and actually get the power supply located and it took about an hour to get it done. I screwed on the power supply unit (which fit perfectly with the holes) and then plotted the wiring runs.
I'm taking the SportAir workshop in Oshkosh in January on avionics and wiring (yep, the same one I was at last year when the Meniere's Disease made its first appearance), and hope to have the lighting system runs planned and done by spring.
Putting it in the baggage floor also looked like a lot of work and while I have nothing against work, per se, if someone can do some of it for me, well. all the better. I did receive help on suggestions where to put the power supply. In the photo, you can see how Vern Little installed his; in the floor with the little hatch. It's a nice set-up but it required more, ahem, work. 
