Building Tip - Fuel Tank Vent Line

[f1rocket]

I do have some more actual flying experience with this set up now that I'm in flight testing mode. When the tanks are full to the brim, the vents will spit some fuel on hot days. The last couple of weeks have seen ambient temps in the mid to high 90's. I've had the tanks topped off because I'm calibrating my fuel flow sensor on the GRT system. Every couple of hours, the vent would flow a couple of ounces of fuel. I don't think it's much of an issue, just a little nusance. With the fuel level below "brim" level, I've never seen it dribble fuel.

Just for a data point, I have the tanks full right up to the bottom of the neck of the fuel cap. Normally, I would not fill the tanks this full but have done so to get an accurate end point for comparing actual versus calculated fuel flows. Once I get the calibration done, I'll back off on the fill point a little to allow for some fuel expansion.

[Captain_John]

Randy,

How is the testing coming along?

I am wondering if another loop or two on the vent coil would mitigate that hot weather fuel belching issue? I see that you have about 2.5 loops there now.

Update please!

CJ

[f1rocket]

My flight testing is progressing well. I have updates posted on my web site. I don't know about adding additional loops. It wouldn't "hurt" anything.

After fixing some problems with toe-in and vertical stab alignment, I have the airplane flying totally hands off with the ball centered. It's perfect. The engine is broke in now and all temps are great. Performance is spot on the Team Rocket numbers. It will cruise at 199 KTAS at 23 squared buring about 15 GPH. If I crank it down to 2100 and 23", the speed drops to 195 KTAS and the fuel flow drops to 10.5 GPH.

I'm getting ready for paint right now. I've got some fiberglass work to do and then I'm going to paint it before the weather gets too cold.

[Captain_John]

Great! Good luck with it, Randy!

Thanks!

CJ

[Dave Cole]

I've considered this vent design for my -7, but the root rib on the tank is set much closer to the edge of the tank skin than shown on the Rocket photo. Unfortunately, there isn't enough room for a vent fitting to be mounted through the bottom surface of the tank skin.

Dave Cole
RV-7 wings

[Captain Avgas]

Originally Posted by Dave Cole

I've considered this vent design for my -7, but the root rib on the tank is set much closer to the edge of the tank skin than shown on the Rocket photo. Unfortunately, there isn't enough room for a vent fitting to be mounted through the bottom surface of the tank skin.

Dave Cole
RV-7 wings

What about this approach....used for an RV7 tip tank. Same principle with coil but venting out through front of wing. It was used by a builder I know...plane not flying yet so not sure how successful it is. But it looks OK although I think I'd go for at least one more loop.

Incidentally, Randy, I don't want to worry you but while your ribs certainly look like they're anodised.....that spar doesn't look anodised to me. Are you 100% certain it's been anodised.

[img=http://img89.imageshack.us/img89/962/tiptank57dz.jpg]

[Captain Avgas]

OK, well that last attempt at sending the photo didn't work so well. Here's another try. Presumably you can enlarge the photo if you want to by clicking on it.

[dav1111]

The RV-10 vent line comes off the very top of the tank 90 degrees down and exits the wing root fairing for a total length of 8 inches. I am not at the part of the build yet but I haven't heard from any RV-10 builders that the vents dripped.

Russ Daves
#40044 RV-10 working on canopy top

[rvpilot]

Unfortunately, there isn't enough room for a vent fitting to be mounted through the bottom surface of the tank skin.

Dave-
Had the same problem on my -8, as it has the same tank. I made the loops, put the vent fitting on to the end of the tubing, and leave it dangling. I then fasten it thru the wing gap fairing when I install it. Sounds like a pain, but it's really not any trouble. I'll try to get some pictures of the installation this weekend if you'd like.
Bill Waters

[Dave Cole]

Thanks. I get the idea. A hole through the wing root faring might just do the trick.

Dave Cole