fuel tank installation?

How do you guys construct the nose of your planes so there is room to mount the fuel tank above the needle valve center line on an inverted engine installation? I'm building a Ruffy and there doesn't seem to be a way to install the fuel tank center line "above" the needle valve. It looks to me like this would be true for any inverted engine installation. The hardwood engine mounts limit the upward location of the tank. Or, does the inverted engine require the tank c/l to be mounted slightly "below" the needle valve? to get even upright/inverted engine runs?

There are a couple of ways that readily come to mind. (1) mount the engine on aluminum pads. (2) move the uniflow outlet in the tank toward the engine mounts, if needed. I did the latter for my Fox 35's mounted inverted. Just a mater of moving the uniflow above the pickup line, not parallel, in your standard 1 in. thick wedge tank.

Moving the uniflow vent is not as reliable, and certainly not as quick as moving the tank itself.

1) You may notch the engine bearers an eighth of an inch or so to give yourself room.

2) The better way is to mount the engine on pads. These can be aluminum or phenolic (circuit board material). The phenolic works extremely well and usually comes in 1/16 thickness. Glue two together. You can get this material at Radio Shack and other places and it cuts easily on a jig saw, band saw, or your trusty Dremel table saw.

These pads can be made somewhat longer than the engine lugs themselves and very much help to spread the load on the maple mounts. This way you don't have anything digging in, nor do you wear the paint off and allow the maple to become oil soaked.

Just remember, if you choose to mount your engine on these pads to move the mounts higher by the same thickness as the pads so that your thrust line remains in the same location.

>
>Just remember, if you choose to mount your engine on these
>pads to move the mounts higher by the same thickness as the
>pads so that your thrust line remains in the same location.

Ah yes, it should have been obvious

wish I'd ask before I built the fuselage! If I use these pads now the engine thrust line will be lower by 1/8 inch. Is this a problem? I can reshape the top block (it's not attached yet) to account for the repositioned engine but will this upset the alignment of thrust line, wing center line, and horizontal stab centerline?

>wish I'd ask before I built the fuselage! If I use these
>pads now the engine thrust line will be lower by 1/8 inch.
>Is this a problem? I can reshape the top block (it's not
>attached yet) to account for the repositioned engine but
>will this upset the alignment of thrust line, wing center
>line, and horizontal stab centerline?

A lot will depend on the design. If you are building a classic, or especially old time design, this may be important in order ro maintain the characteristics of the design. However, most designs are not so critical (it is mostly a series of compromises) that moving the thrust line 1/8 of an inch won't make a drastic, or maybe even noticeable difference.

Or comporomose. Mount the enginen on 1/16 pads. It will still give you some adjustment up, if needed. Again, depending on the engine and the like, most set ups are pretty close to straight on with the needle.

(Disclaimer: Having made that last statement, Al did some experiments once with an engine where he made it so he could raise and lower the needle valve. He concluded it didn't change things. Some, therefore, have concluded that it has to do with crankcase volume, not needle location. Try to tell that to the 4-stroke enthusiast, however.

And now the real kicker: We have a Fox 35 in which the piston was replaced with a 36 piston and the head changed. Same sleeve, same rod, same case, same needle location, same crankcase volume. The tank needed to be raised 1/8 inch--inverted engine--for the run to stay the same compared to a stock Fox 35.

At this point, I don't konw what all affects the tank location, but still it should be close to where the needle is located.

But do make that tank adjustable in height--both ways. You don't know what you are going to need.)

>
>>wish I'd ask before I built the fuselage! If I use these
>>pads now the engine thrust line will be lower by 1/8 inch.
>>Is this a problem? I can reshape the top block (it's not
>>attached yet) to account for the repositioned engine but
>>will this upset the alignment of thrust line, wing center
>>line, and horizontal stab centerline?
>
>A lot will depend on the design. If you are building a
>classic, or especially old time design, this may be
>important in order ro maintain the characteristics of the
>design. However, most designs are not so critical (it is
>mostly a series of compromises) that moving the thrust line
>1/8 of an inch won't make a drastic, or maybe even
>noticeable difference.
>
>Or comporomose. Mount the enginen on 1/16 pads. It will
>still give you some adjustment up, if needed. Again,
>depending on the engine and the like, most set ups are
>pretty close to straight on with the needle.
>
>(Disclaimer: Having made that last statement, Al did some
>experiments once with an engine where he made it so he could
>raise and lower the needle valve. He concluded it didn't
>change things. Some, therefore, have concluded that it has
>to do with crankcase volume, not needle location. Try to
>tell that to the 4-stroke enthusiast, however.
>
>And now the real kicker: We have a Fox 35 in which the
>piston was replaced with a 36 piston and the head changed.
>Same sleeve, same rod, same case, same needle location, same
>crankcase volume. The tank needed to be raised 1/8
>inch--inverted engine--for the run to stay the same compared
>to a stock Fox 35.
>
>At this point, I don't konw what all affects the tank
>location, but still it should be close to where the needle
>is located.
>
>But do make that tank adjustable in height--both ways. You
>don't know what you are going to need.)

The airplane is a Ruffy... I've already made some changes that would prevent me from flying it in a "classic" event. The engine mount hasn't been drilled yet nor has the fuselage top been installed. I have a Fox .35 and a Thunder Tiger.25 (as modified by you...). At this point either could be installed> I've got to make that choice...

Looks like the easy option is to go with the engine mount "pads" and accept the 1/8" lowered thrust line. It seems highly unlikely that I have the flying skills to notice any difference in performance.

Ron,
I use 1/8th pads and cut the bearers down 1/8th if it for anything other than a fox 35 or Tiger 60. (big shakers except for Larry F.'s 35s).
As for lowering the thrust line 1/8th, I would do that instead of having to rebuild the fuse. Shouldn't be a problem with the Ruffy.
Bill <><

There'll probably be flack for this one, but I've given up on bearers. In all my full fuse stunters I have Dave Brown radial motor mounts. I push the engine as far back as possible in the mount then forward about 1/32" for clearance. Then I cut off the excess. I use a 1/4" firewall and 1/2" triangle stock in the corners behind it reinforced with 3/4 oz. glass and 2 hour epoxy. This gives me the entire unobstructed bay for tank installation. I also have gone to uniflow/clunk tanks and extend the cowl back under the tank bay for easy access. I us guide pins and screws to mount the cowl and interlock it to the nose. I've yet to experience any vibration problems and I've even done this with Foxes and McCoys.

Randy-

What material for the firewall? Is any special upper-block carving necessary to accomodate the radial mount?
Thanks.

Serge

Serge,

1/4" birch ply. Very little additional material to be removed, I've never come close to breaking through. Infact, I haven't actually weighed the components, but I think it ends up a tad lighter then bearers. On all the models I've done this way I can reach in to all 4 radial bolts with the engine in place.

Ron,
I am not sure what kind of tank you are using (or engine), but usually if the engine is on the hardwood bearers, the old metal tanks would put the centerline pretty close to the center of the spraybar. If your engine has a sprinkler type venturi, which usually is located closer to the crankshaft than the spraybar types, it could be pretty hard to get above tank center above the fuel outlet. In these cases, sometimes you need to make an asymmetric tank with the wedge more aligned with the location you want the pickup at. Also moving the uniflow vent (if that is what you are using) works too (as Jim mentions). It may be the only option if you are using a plastic clunk tank.