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engine hanging: with or w/o main gear? (-7, not -A)

rv7charlie

Well Known Member
Being somewhat of a deviant in some (not all) areas, I've installed the motor mount, gear legs, wheels, leg fairings, and pants to get all those odds & ends properly aligned without the wings in the way. Pants & fairings have now been removed & stored.

Now I'm contemplating the removal of the gear legs & returning the fuse to its dolly to do the engine/cowl fitting, plumbing, wiring, etc. This is with the idea that work will be easier with the fuse closer to the ground. I'll eventually need to 'unhang' the engine to have it overhauled (waiting until the last moment for that expense), so any rework would likely have to happen anyway.

Also, I haven't yet riveted on any of the top skins, front or rear.

Any major issues there if I hang the engine at this point?

Thanks,

Charlie
 
<SNIP> I have the same question and there was never a response...

Due to my non-standard configuration (dual battery, dual alt, EFI) the plans placement of firewall-mounted items like batteries and contactors may not work out, and there's a lot of stuff downstream of that (fuse block installs, wire runs, etc) which I can't do until those are in place. As there's very little "prior art" for this setup on a -7, at least that I can find, I don't feel comfortable going ahead and doing this until the engine is hung and I can see exactly how much space I have to work with. Thus I'm planning to build the engine up and hang it so I can install these components. Once I have the batteries and contactors placed and some of the routing determined I can pull the engine and proceed without it in the way.

I was hoping to be able to hang the (preserved) engine with the fuselage on the dolly--it's supported under the spar carrythrough, plus another support at F-710. At the least, I figured it would take a hold-down weight at the tail to keep it from tipping forward off the dolly, and maybe a sawhorse under the firewall, but if it's going to take more than that I may just ballast the rear end, put the gear legs on, and put it on the gear for a while.

Right now the upper skins (forward and aft) are attached with clecos only.

Anyone else tried this?


And yes, I know building/hanging an engine this early isn't really a preferred way of doing things, but I don't have the time for marathon building sessions and my luck on guessing placement of items without both ends in place has been poor at best. I really don't want to get the batteries and contactors in place and then find out that they either (a) want to share space with an oil filter, standby alternator, or governor, and/or (b) can't be accessed without pulling the engine off.
 
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When I was building the 7 Turbo Subie, I bet I hung the engine 5 times to get all the unique equipment to fit on the firewall.
When doing my current flying 6A, I had the engine on 2 times to fit the non standard EFI/EI equipment.
Normal RVs, I usually have the engine on once to confirm equipment & control locations, than remove it till all the other airframe stuff is done.
I don't see the point in permanently hanging the engine too early, just gets in the way & you end up with skinned knuckles trying to work around & behind it.

So, hang it, do your planning for firewall components, controls, & wiring. Take it off again & store it till you actually are ready for engine, baffle, & cowling work.
An engine hoist & a buddy make it easy & quick job to R&R the engine for fitting.

Charlie - for your situation & generally, I'd prefer to work on the firewall while the fuselage was on it's gear.
 
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So, hang it, do your planning for firewall components, controls, & wiring. Take it off again & store it till you actually are ready for engine, baffle, & cowling work.
An engine hoist & a buddy make it easy & quick job to R&R the engine for fitting.

That's pretty much exactly the plan; I was just trying to forestall "just do the engine stuff at the end, it goes quick" when I have a non-standard install and a very slow build pace.

My main question, though, is "do I need to put the gear on or can I leave the fuselage on the dolly?"
 
For planning purposes, I'd just position the engine with the hoist with bolts & insulators to get positioning correct, leave it on the hoist. Your main difference will be the aux alternator interfering with stock battery location. Look at moving it from right to left side of firewall pocket. This will impact prop control cable slightly, hole repositioning can be done. Battery contactors don't take much room so easy to mount where ever. If you are remote mounting oil cooler, still room below the battery on the Left side. You may need custom lengths on oil cooler hoses. Confirm cabin heater location and control cable. Plan your sensor/engine wiring harnesses to come out near the top corners of the engine mount to keep maintenance access as open as possible (you will thank yourself later!). I'd locate the second battery somewhere aft in the fuselage (you don't need super heavy cabling to it because you will only be starting from primary battery (I hope!).
Hope these random thoughts help
 
Thanks Ralph! I definitely hadn't thought about moving the second battery aft but that's at least an idea. We'll see if I can make it work up front, though.

Things look easier on a nosewheel airplane (from a battery access standpoint anyway) and there are more pictures out there...
 
I am all for doing everything you can with the plane on a rolling platform because it is much easier to work on the cockpit from above than climbing up on the wing or a stand to work.

I thought I did everything I could before going on the gear but I was wrong. I got anxious to see it on the gear and let that get the best of me, so up it went.

If I were to do it again, I would keep it on the platform longer and then build a 12" - 16" or so box with wheels to raise it up to so it would still be low but I could work on the FAB, baffles, and other engine parts. Then put the gear on.

Either works so have fun however you do it!
 
Generally, after the canoe (or QB fuselage) is together, I'd put it on short wood legs attached at the spar attach points. This would allow easy moving, tilting on it's side, strong enough support if I crawled inside, what ever position required. I would leave it on my wood legs till everything inside is done that can be done, even top skins if the model would allow. At about that point I'd put it on gear legs as I'd rather do the FWF & firewall stuff at waist level rather than bend over or worse, be on my knees to do all that, painful for me.

If I remember correctly, you were thinking lithium batteries, so weight wise (even more so if you were doing dual PC680s or such) you don't have to crowd everything on the firewall, you only need the primary battery closest distant to the starter, the aux battery could be mounted wherever.
 
Generally, after the canoe (or QB fuselage) is together, I'd put it on short wood legs attached at the spar attach points. This would allow easy moving, tilting on it's side, strong enough support if I crawled inside, what ever position required. I would leave it on my wood legs till everything inside is done that can be done, even top skins if the model would allow. At about that point I'd put it on gear legs as I'd rather do the FWF & firewall stuff at waist level rather than bend over or worse, be on my knees to do all that, painful for me.

As things sit now, the top of the firewall is at sternum level. I can stand next to the fuselage and rest my hand on the cockpit rails/longerons. It made rigging the wings really easy (other than having to crawl under them all the time while they were installed--my shop leaves me with inches to spare at the wingtips); working inside is a mixed bag. A low platform works well but I wind up climbing inside a lot, too.

On the other hand, I guess there is one argument to be made for keeping the airplane this high and riveting the skins on now: it almost forces you into installing things in a way you can access later!


If I remember correctly, you were thinking lithium batteries, so weight wise (even more so if you were doing dual PC680s or such) you don't have to crowd everything on the firewall, you only need the primary battery closest distant to the starter, the aux battery could be mounted wherever.
Yep, planning on lithium right now. I'd still like to keep them both up front to simplify wiring and not be running even more wires aft; things are tight in the carrythrough and the cover/"tunnel" over the fuel pump.
 
What I did

Bob,

My Vans instructions say it's handy to keep the top longeron about navel height for as long as possible. That worked out to about 14" ground clearance, so I made a low stand with $10 worth of wood.

I put short pieces of 4x4 into the recessed areas where the gear goes and rested those on the stand. I'm happy. The tail needs ~20 lb of down force.

You asked about under the center section. I thought about it but didn't want to hassle with calculating stress from the weight of engine on that longer lever arm.

Bob
 
I mounted my engine mount to the engine with it on the hook, then mounted to the firewall several times to check clearances positions of controls etc. I still made the final too soon though, and did it when the gear would carry the load and still needed 80# of sandbags in the aft fuse (no emp).

The issue with mounting and leaving is (to me) the weight balance issue, I don't consider the firewall structural and the mounts are made to carry the engine loads. I used the lift to keep the balance until the gear could carry the load, the opportunity for creases in the lower skins was too high a risk for me due to it the high weight on the spar and certainly not the firewall. YMMV.

Last thought, I might jack or block under the oil pan to carry weight of engine but for other reasons this does not seem an advantage in the build.
 
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The issue with mounting and leaving is (to me) the weight balance issue, I don't consider the firewall structural and the mounts are made to carry the engine loads. I used the lift to keep the balance until the gear could carry the load, the opportunity for creases in the lower skins was too high a risk for me due to it the high weight on the spar and certainly not the firewall. YMMV.

I'm having trouble understanding how hanging the engine on the mount, and supporting at the main wing spar, will somehow "crease" the lower skins. In flight the weight of the engine and prop (at up to 6 g's!) is transmitted through the engine mount, into the weldments and attachments on the corners, and into the longerons and skins of the forward fuselage. It's reacted into the center carrythrough, from there as shear into the wings. The whole forward fuselage is trying to bend down under those conditions. So I don't really see how supporting a bare fuselage plus engine under the center carrythrough will create a structural problem. Balance sounds like it might be an issue--the CG of that combination, without empennage, tailwheel, or wings may be forward of the carrythrough and thus necessitate a forward support--but simply from a structural standpoint I don't see it. The forward fuselage handles those loads all day long in flight.
 
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