S

szicree

Well Known Member
Any updates, positive or negative, regarding the coiled fuel vents in the wing roots used on Rockets. I'd love to avoid that crazy vent line running all over my cockpit.
 
Rocket style Fuel vents

Got them on my -8, got about 60 hours on it now, no problems. Only regret I have is that I didn't find out about this idea before I fought to put the vent line tubing in the gear towers.
Great idea as far as I'm concerned!
Bill Waters
 
Not familiar with the coiled technique. Can you elaborate or provide a link?

Thanks,
 
I think I got the idea

Larry what you do is coil the vent line and secure it in the wing root, the area between the inboard wind rib and fuselage. The long tube length handles the overflow and prevents siphoning. I am a little fuzzy after that, but believe you just run the vent out wing root fairing.

To me the fuel vent must:
  • Will not easily siphon fuel out the tank
  • Provide positive pressure in the tank
  • Not allow fuel vapors in the cockpit
  • Not get blocked (bugs or ice)

If it does all the above, than Yea Verily!

I don't find the per planes vent line too onerous to install, but to each his own. I get real conservative and less brave with any mod that affects a major system, like the fuel system.

One thing I would say is a must, is you vent to the outside. I am not sure as I said but think the Rocket method (coil in wing root) may not vent out and just terminate in the wing root. Not sure how they do it, but that's a bad idea and could potentially lead into fuel in the cockpit in my opinion. G
 
Last edited:
the wing root vents work great, as good as the standard vents, and they are a lot less work. Also it gets more fuel lines out of the cockpit. I have installed them on two aircraft, another one shortly. Credit for this idea goes to Mark Fredrick from Team Rocket. http://www.teamrocketaircraft.com/

Tom Martin EVO wing
 
gmcjetpilot said:
One thing I would say is a must is you vent to the outside. I am not sure as I said but think the Rocket method (coil in wing root) may not vent out and just terminate in the wing root. Not sure how they do it, but that's a bad idea and could potentially lead into fuel in the cockpit in my opinion. G
Click to expand...
George, George, George....We're not as dumb as we look! The vent line is terminated just like Van's design. I used an AN fitting in the bottom of the wing skin that overlaps the end rib.
 
f1rocket said:
George, George, George....We're not as dumb as we look! The vent line is terminated just like Van's design. I used an AN fitting in the bottom of the wing skin that overlaps the end rib.
Click to expand...
Randy, Randy, Randy, no one said you are dumb. You seem to be very sensitive to my post? I am so sorry if I offended you, the Rocket community or who ever else you referred to as "We're". You're smarter, so forgive my ignorance. You seem to be very proud (defensive) of anything "Rocket". For the record if you read what I wrote I did not say this vent would not work acceptably.

In trying to help I clearly stated TWICE, I didn't know all the details past the coil in the wing root. BTW I have seen "internal vents" before (not associated with the so called Rocket vent), and they seemed to work well on those aircraft. I did not call anyone dumb than either. Chances are they're smarter and no doubt the fuel vents meet criteria. Its just my opinion that you can't go wrong by going per-plans (Vans Aircraft). Call me crazy.

I stated, IF its terminated in the wing-root (of a RV) it could get into the cockpit area. I find your response intentionally condescending. I'd like to hear your opinion about facts of the topic, an intelligent debate instead of your animosity toward me. My late mother gave me advice long ago; "If you don't have something nice to say about someone, don't say it". Try it. Peace

George
 
Last edited:
Yikes George, I wasn't offended by your post at all. I was more making a joke of it. I guess I should have put a million smiley faces on my post so you wouldn't go over the edge.
 
Last edited:
I've gotta side with F1 on this, G. From your first post, it appears you weren't looking at F1's picture showing the outside-the-wing vent.
Stand by with cold water buckets, men.
Steve
 
I'm afraid I'm still not sold on this modification. It seems like a pretty obvious method and certainly easier to build, so why didn't (doesn't) Van use it? There must be a downside that I'm not seeing.
 
There's no real magic here. The only difference is that when your tanks are full and the sun heats up your tank, the vent will spit some fuel. Van's design won't do that because the expansion can't push the fuel up as high as the vent line is run inside the cabin.

I've had both styles. One is easier to install and keeps potential fuel fumes out of the cockpit. The other won't spit fuel. Like most things, there are pros and cons to each. I don't really push one style over the other, but rather present an option for folks to choose. In the end, it's your airplane.
 
Beg to Differ

F1,
You commented that Van's design will not let fuel spill out when the tanks are full.....I have a 6A using Van's design and it does it quite often. I actually got soaked in the shoulder once while removing the lower engine cowling....guess the ol' girl didn't want me messing with her that day.
Rags
 
Really? That's surprising. I never had my RV-6 blow fuel out the vent and I don't recall any of my other flying buddies doing it either. Have you been spending too much time in "unusual attitudes"? :D
 
I think this has been asked before, and I don't think I've seen the answer, does the RV-10 use a Rocket type or similar fuel vent? I'm a 9A builder and I'm seriously considering this type of vent. Maybe a RV-10 builder can comment.

Mike
RVB-9A QB
 
Hmmmm???

I was planning on doing this type of vent the first time Randy showed it on the forum.
I am now at the stage of doing just that and it suddenly occurred to me (minutes ago) that you could simply put all the coils in the outer bay and exit the bottom of the tank at that location rather than running the vent all the way inboard and then coiling outside the tank.
If length of vent line is an issue, just make a few more coils. If vertical height is an issue, just make sure all the vertical up portions of the coils add up to the vertical height of VAN's stock vent.

What say you experts?

-mike
 
Outboard fuel vent

If the vent is open within the tank on the outboard side, and is vented outside the wing also on the outboard side, I'd think you'd lose a lot of fuel when that wing is low.

I haven't started building yet, though.
 
Mike,

I think there might be a problem with that. I think you would drain fuel pretty fast from the low tank when at even a slight angle.
You need the coils and the drain at the opposite ends of the tank from the inside end of the vent tube. By putting the coils at the root end, either the drain is higher than the fuel if the wing is low, or the end of the vent tubing is higher than the fuel in the tnk if the wing is high.

I think the main reason for the coils is to prevent fuel loss due to air expansion in the tank when the tank is full enough that the inside end of the vent tube is below the fuel line.
 
ptrotter said:
Mike,

I think there might be a problem with that. I think you would drain fuel pretty fast from the low tank when at even a slight angle.
You need the coils and the drain at the opposite ends of the tank from the inside end of the vent tube. By putting the coils at the root end, either the drain is higher than the fuel if the wing is low, or the end of the vent tubing is higher than the fuel in the tnk if the wing is high.

I think the main reason for the coils is to prevent fuel loss due to air expansion in the tank when the tank is full enough that the inside end of the vent tube is below the fuel line.
Click to expand...
yep,
I jumped on that without thinking about parking a wing high or low. If the coil were to completely fill, a siphon would ensue until the vent entrance was uncovered.

Thanks for snapping me back to reality! :eek:
-mike
 
Today I spent the whole afternoon trying to fabricate a vent I like. I tried the Rocket coil setup and don't like a couple of things: First off, that thing needs additional restraint/support to keep it from vibrating like a big ol' slinky. The engine and exhaust are throwing out an infinitude of harmonics and its a fair bet that one of em will get that thing going. I know I'm gonna hear from guys who've got X number of hours on it without trouble, but the arrangement I've seen pictured is just too floppy/springy. Second, I think I have a slightly better chance of avoiding an ice-up by having the vents in the path of the spent cooling air. Having said all that, getting that tubing bent into the proper shape is a gigantic PITA, but I'm convinced that my next trip out to the garage will get it done. Finally, I'm gonna chuck the vent outlet (bulkhead fitting) in my drill press and grind it smooth as per the plans unless someone has found a method that doesn't look quite so half-assed.
 
mlw450802 said:
If vertical height is an issue, just make sure all the vertical up portions of the coils add up to the vertical height of VAN's stock vent.

What say you experts?
Click to expand...

I'm no expert, but this doesn't work out. If the pressure is adequate to get the liquid through one loop, it'll push it through as many as you like (assuming the pressure stays constant). On the other hand it'll take more and more pressure to pump liquid higher and higher. The multiple loop thing relies on the fact that as the fuel moves into the loops, it relieves some pressure behind it so that it would rarely get to the end.
 
szicree said:
I'm no expert, but this doesn't work out. If the pressure is adequate to get the liquid through one loop, it'll push it through as many as you like (assuming the pressure stays constant). On the other hand it'll take more and more pressure to pump liquid higher and higher. The multiple loop thing relies on the fact that as the fuel moves into the loops, it relieves some pressure behind it so that it would rarely get to the end.
Click to expand...
Actually there are two flow modes here with drastically different results. If the flow is fast enough to fill the tube then your statement is correct but if the flow is slight and the fuel spills over the tops of the coils in a trickle, only the up slopes will fill and they will begin to add in height and, since the down slopes will be full of air minus the small trickle going down the wall, the additive heights will be essentially equivalent to lifting the fuel up a single long lift, requiring more and more pressure to traverse more and more coils.

As unlikely as it sounds, it is true.
 
mlw450802 said:
Actually there are two flow modes here with drastically different results. If the flow is fast enough to fill the tube then your statement is correct but if the flow is slight and the fuel spills over the tops of the coils in a trickle, only the up slopes will fill and they will begin to add in height and, since the down slopes will be full of air minus the small trickle going down the wall, the additive heights will be essentially equivalent to lifting the fuel up a single long lift, requiring more and more pressure to traverse more and more coils.

As unlikely as it sounds, it is true.
Click to expand...

Basically, as far as I can tell the only thing that really matters is the relationship of pressure with temperature and volume. Thingy gets hot, either the pressure must go up or the thingy has to expand. In Van's system, the fuel is allowed to expand and the pressure is allowed to increase (because it's always going "uphill" ). Pass a certain point, and fuel will go overboard.

In the Rocket system, the pressure is allowed to increase only to a certain point (the pressure it takes to get the fuel up to the height of the first coil). Beyond that, the pressure remains constant. Any additional rise in temperature will just cause the volume to increase...i.e. fuel to go into the coils. Pass a certain point, and the fuel goes overboard. It seems like all the uphill side of the coils add up, and they do...the downhill sides add up too, though, and they cancel each other out perfectly. The only one that's "unbalanced", so to speak, is the first one. Since the top of that coil is almost even with the vent anyhow, that's probably negligable and coils are more than likely just behaving as an expansion tank.

As far as venting, there's nothing special about a coil other than it takes up very little space and is easy to make. It would work equally well to just make zig zags with the tubing, or whatever other shape you want, as long as you maintain the proper relationships of volume (length of tubing you use) with height. The whole thing about having the height of the coil higher than the vent in the tank is just to prevent it siphoning out - a totally unrelated thing. Not unimportant, but unrelated.

I just got back from a SuperBowl party so maybe I'm not thinking about this right. I think it's pretty close, though :D

edit: by the way, I'm not suggesting anyone do anything funny like making girraffe shaped vents or anything whacky like that. I'm just laying out how I understand it in hopes that someone will confirm it or tell me where I'm wrong so that I can understand it better.
 
Last edited:
I really think the explanation is simpler than this. The only time you can get any overflow from the vent line is if the outboard end of the line is submerged in the fuel, otherwise no fuel will enter the line. If the vent line is installed properly, the outboard end will be at the very outboard top of the tank. The only time this will be submerged is when the wing is lower than level. Even at level, it is unlikely to be below the fuel level due to slight dihedral in the wing, unless the tank is absolutly full. If the wing is low, the the inboard end of the vent line is higher than the fuel level and the only way any fuel can flow out is if the pressure in the tank increases enough to push fuel out the length of tubing. The main purpose of the loops (either the rocket method or Van's method) is to allow more room for expansion before fuel can escape. Knowing the length and diameter of the vent line, it would be fairly easy to calculate the pressure increase necessary to push fuel to the end of the line. Although a temperature increase could cause a pressure increase, this in itself would probably not cause sufficient expansion. I would expect the only way to get a sufficient pressure differential would be due to altitude increase, all of which would have to take place while the vent is continuosly submerged or the pressure would be relieved whenever the vent line became unsubmerged. So unless you are sprialing (or maybe knife edging) upward for a significant altitude change, you are unlikely to get enough pressure change in the tank to push fuel out.

In the case of a full tank, there probably is not enough air left in the tank to leave enough room for sufficient expansion. I think the issue mentioned earlier regarding adequate support for the loops is a bigger problem than fuel escaping.

Actually, the most likely scenario for escaping fuel would be due to quick roll axis change. Any fuel in the vent line in the lower tank could flow out when that tank is now the upper tank, although most would probably be drawn back in except in very abrupt changes. In this case the Van's setup would probably be a little better.

My $.02. Probabaly not worth that much :)
 
mlw450802 said:
Actually there are two flow modes here with drastically different results. If the flow is fast enough to fill the tube then your statement is correct but if the flow is slight and the fuel spills over the tops of the coils in a trickle, only the up slopes will fill and they will begin to add in height and, since the down slopes will be full of air minus the small trickle going down the wall, the additive heights will be essentially equivalent to lifting the fuel up a single long lift, requiring more and more pressure to traverse more and more coils.

As unlikely as it sounds, it is true.
Click to expand...

I ain't buyin' this. Let's suppose there's enough pressure to lift the fuel a distance equal to the diameter of the loop. As soon as the fuel reaches the top of the loop, a little spills over the top and settles in the bottom of the next. This spilling will continue since the pressure is still adequate to keep the first loop full (1 diameter's worth of pressure). The fuel that is settling in the bottom of the loop will continue to fill symmetrically on both the downward and upward sides of this loop until it reaches the top, at which time it will begin spilling into the next one. This will continue until the pressure drops below the 1 diameter level. You suggest that the liquid will fill only the upward sides of each loop. This might sound right on paper, but having just tried it in my kitchen sink with vinyl tubing I can tell you that it just doesn't work. What I can say is that the same amount of pressure that sends water through one loop, sends it through 5. On the other hand this same amount of pressure is completely inadequate to push the water straight up the equivalent sum of even 2 diameters. Try it yourself.

If the loops really do add up then I could take a couple hundred feet of garden hose all coiled up on a hose reel, hook it up to the faucet, turn it on and get nothing. I've never tried it, but my gut says if I wait a few seconds I'd get water. I'm not itching for an argument, but my kitchen sink science experiment tells me that 5 six-inch diameter loops is not the same as a 30 inch climb.
 
szicree said:
I ain't buyin' this. Let's suppose there's enough pressure to lift the fuel a distance equal to the diameter of the loop. As soon as the fuel reaches the top of the loop, a little spills over the top and settles in the bottom of the next. This spilling will continue since the pressure is still adequate to keep the first loop full (1 diameter's worth of pressure). The fuel that is settling in the bottom of the loop will continue to fill symmetrically on both the downward and upward sides of this loop until it reaches the top, at which time it will begin spilling into the next one. This will continue until the pressure drops below the 1 diameter level. You suggest that the liquid will fill only the upward sides of each loop. This might sound right on paper, but having just tried it in my kitchen sink with vinyl tubing I can tell you that it just doesn't work. What I can say is that the same amount of pressure that sends water through one loop, sends it through 5. On the other hand this same amount of pressure is completely inadequate to push the water straight up the equivalent sum of even 2 diameters. Try it yourself. If the loops really do add up then I could take a couple hundred feet of garden hose all coiled up on a hose reel, hook it up to the faucet, turn it on and get nothing. I've never tried it, but my gut says if I wait a few seconds I'd get water. I'm not itching for an argument, but my kitchen sink science experiment tells me that 5 six-inch diameter loops is not the same as a 30 inch climb.
Click to expand...
I said it seems unlikely but it's an easy experiment. Attach a pressure gage to the source and start with a transparent tube large enough in diameter to allow unfilled flow. Start trickling the water into the coiled tube and pressure will increase to 6 inches WC (in your example) it will then spill over the top of the first coil and will fill the bottom of the second, trapping air in the down going section. As the water continues to flow, the upslope will fill on the second coil increasing pressure to ~ 12 inches WC this will continue as you add coils. The amount is not exactly additive because each section of coil with the trapped air will compress slightly proportional to the number of down stream coils that are filled on their upslopes. The caveats are that you have to start with an empty tube and the flow rate has to be slow enough to not create filled flow. Kind of like the flow you might expect due to thermal expansion of the fuel in your tanks.:)
 
Actually, there would be no reason to coil the tubes in the Rocket Vent if there were no pressure gain advantage from the coils. There certainly is not much gain in volume by doing that. A quarter cup of fuel would probably fill the entire vent line.

-mike
 
You must log in or register to reply here.