Author Topic: Tank shape - foward slanting outside of rear side (Read 5460 times)

Dennis Toth · « **on:** March 02, 2014, 06:36:49 AM »

Guys,
Has anyone tested hard tanks with the rear side angled forward? I have an installation that has minimal room in the tank area to angle the rear of the tank out. I thought I could achieve the same results by building the tank with the rear side angled forward. Doing this would put the rear side in the same geometric position as angling the whole tank and allow just putting the tank straight in the compartment. Anyone use this approach?

Best, DennisT

Dave_Trible · « **Reply #1 on:** March 02, 2014, 06:42:01 AM »

Dennis I've never tried that but also never found any need to angle a tank in the first place. 'Good to the last drop' is handled by the good forces of nature. It doesn't hurt anything of course but I never heard of this until the last couple years and wondered why. Really not nessessary and would complicate a tight tank fit situation. The tank is always virtually dry when the engine quits. I just hate to see making stuff more complicated than it needs to be.

Dave

Doug Moon · « **Reply #2 on:** March 02, 2014, 08:42:09 AM »

If you could get a pic of your tank area that would be really helpful.

Are you talking about running a uniflow metal or a plastic clunk?

Thanks

Brett Buck · « **Reply #3 on:** March 02, 2014, 10:21:06 AM »

Quote from: Dennis Toth on March 02, 2014, 06:36:49 AM

Guys,
Has anyone tested hard tanks with the rear side angled forward? I have an installation that has minimal room in the tank area to angle the rear of the tank out. I thought I could achieve the same results by building the tank with the rear side angled forward. Doing this would put the rear side in the same geometric position as angling the whole tank and allow just putting the tank straight in the compartment. Anyone use this approach?

Best, DennisT

I am not sure what you are talking about - could you draw a sketch?

Brett

Dennis Toth · « **Reply #4 on:** March 02, 2014, 11:04:44 AM »

To clarify some, the tank is a metal uniflow hard tank. Looking down from the top I am suggesting building the tank with the rear (near the wing side) angled forward from the inside (say it is 4"long) to the outside (which is say 3 3/4" long) . If you take a sq tank and angle it out (like you would on the mounts) 1/4" looking at the rear of the tank, it is angle forward. All I'm suggesting is building in the angle of the rear side of the tank, with the other three sides straight.

Best, DennisT

Roger Vizioli · « **Reply #5 on:** March 02, 2014, 11:33:52 AM »

Quote from: Dennis Toth on March 02, 2014, 06:36:49 AM

Guys,
Has anyone tested hard tanks with the rear side angled forward? I have an installation that has minimal room in the tank area to angle the rear of the tank out. I thought I could achieve the same results by building the tank with the rear side angled forward. Doing this would put the rear side in the same geometric position as angling the whole tank and allow just putting the tank straight in the compartment. Anyone use this approach?

Best, DennisT

If I remember correctly, and it has been over 60 years since I built one like this. Lou Andrews Trixter Barnstormer used a similar configuration.
His tank used a "normal" fuel (engine) feed line running aft along the inside of the outer tank wall ending near the rear of the tank. The outer side of the tank was longer than the inner side.The fill line, looking "aft", ran from the top left to lower right corner at the forward tank wall. It was angled directly into the airstream/flight path. To fill the tank you held the model nose down until the tank filled and fuel ran out the venturi.
As I said, it was years ago, seemed to work but then what did the "kids" know! :-) anyone remember it differently? I welcome/accept corrections.

Roger V.

Bob Whitely · « **Reply #6 on:** March 02, 2014, 12:32:30 PM »

Dennis, Good idea but won't work. The outside of the tank that parallels the fuse
is what you want angled not the rear of the tank. All models fly tangentially to the
circle some more than others. By twisting the tank so that the front is turned in
and the rear turned out makes the fuel want to stay near the end of the pickup
tube in the back. Angling the rear of the tank as you say will do nothing to make the
fuel stay in the back against the tank wall. Now if you angle the outside fore and aft
wall of the tank with the front closer to the inside of the fuse it will make the fuel stay
in the right rear corner of the tank. This is one of those things that always works
without any negative effects. RJ

Bob Reeves · « **Reply #7 on:** March 02, 2014, 01:44:49 PM »

Quote from: Dave_Trible on March 02, 2014, 06:42:01 AM

Dennis I've never tried that but also never found any need to angle a tank in the first place. 'Good to the last drop' is handled by the good forces of nature. It doesn't hurt anything of course but I never heard of this until the last couple years and wondered why. Really not nessessary and would complicate a tight tank fit situation. The tank is always virtually dry when the engine quits. I just hate to see making stuff more complicated than it needs to be.

Dave

It prevents the Burrp...Burrp....Burrp....Burrp shutoff and gives the clean shutoff you see when the tank is set up properly. Sometimes you get lucky but as Bob said above angling the tank always works with no negative effects.

Dave_Trible · « **Reply #8 on:** March 02, 2014, 02:40:42 PM »

This is probably true in some cases. Tank shape, pickup placement and uniflow pressure or lack thereof can make a difference. Also whether one is flying high or something other than smooth level laps at the end of the run or if there is a little extra vibration. A canted tank would help some. Twist away if you have room. No harm done.

Dave

bob whitney · « **Reply #9 on:** March 02, 2014, 05:08:46 PM »

Dennis ,give me a call

FLOYD CARTER · « **Reply #10 on:** March 02, 2014, 07:32:58 PM »

Tanks that feel to the very last drop are dangerous! Tend to quit without warning! My tanks are rectangular (not wedge) and not canted outward. My engine sputters for 2 or 3 laps then quits. Gives me time to get into a safe position for a landing.

Floyd

Brett Buck · « **Reply #11 on:** March 02, 2014, 10:19:07 PM »

Quote from: FLOYD CARTER on March 02, 2014, 07:32:58 PM

Tanks that feel to the very last drop are dangerous! Tend to quit without warning! My tanks are rectangular (not wedge) and not canted outward. My engine sputters for 2 or 3 laps then quits. Gives me time to get into a safe position for a landing.

Floyd

That's OK for AMA, for FAI it is death.

Brett

john e. holliday · « **Reply #12 on:** March 03, 2014, 07:47:52 AM »

Haven't looked lately, but at one time the Tulsa Gluedobbers had a video of a plane flying with the camera aimed at the fuel tank. Showed how the fuel moved around in the plastic tank while flying. Most of the time the fuel stayed in the outside rear corner of the tank.

Bob Reeves · « **Reply #13 on:** March 03, 2014, 08:29:55 AM »

Quote from: john e. holliday on March 03, 2014, 07:47:52 AM

Haven't looked lately, but at one time the Tulsa Gluedobbers had a video of a plane flying with the camera aimed at the fuel tank. Showed how the fuel moved around in the plastic tank while flying. Most of the time the fuel stayed in the outside rear corner of the tank.

It was a clunk tank with the rear offset from the fuselage by 1/8 inch (canted out). The airplane was a Twister powered with a Saito 4 stroke and always had a clean cut off. Wished we had been able to convert the tape to digital before all the VHS tape players died. Don't think we even have a tape.

Doug Moon · « **Reply #14 on:** March 03, 2014, 09:16:52 AM »

Quote from: john e. holliday on March 03, 2014, 07:47:52 AM

Haven't looked lately, but at one time the Tulsa Gluedobbers had a video of a plane flying with the camera aimed at the fuel tank. Showed how the fuel moved around in the plastic tank while flying. Most of the time the fuel stayed in the outside rear corner of the tank.

I remember that. It was cool! Bob Reeves WENT PRO before there was GO PRO!

Tim Wescott · « **Reply #15 on:** March 03, 2014, 09:25:23 AM »

Dennis:

If, in all this discussion, it hasn't been made clear:

The important thing if you do this is to slant the outside (to the circle) wall of the tank out. If you're building a tank, make the back of the tank wider than the front. That lets you keep the tank capacity as high as possible while still making fuel flow positively to the back of the tank.

I've been building canted tanks, or canting my plastic tanks, since I started getting serious about control line stunt in 2008 or so. My engines always run down to the last drop, then they die. While I've crashed planes for just about every other conceivable reason, I can't recall one running out of fuel and bonking.

If you're really concerned about not getting a warning, you can put your uniflow back a good ways from the pickup tube (I have to do this on my plastic clunk tanks to keep the pickup clunk from fouling anyway). The uniflow will uncover a few laps before the fuel runs out, the engine will go lean, and then the engine will quit.

FLOYD CARTER · « **Reply #16 on:** March 04, 2014, 01:45:29 PM »

I've never flown in an FAI contest. I wouldn't mind being on the FAI World's Team. How do I get nominated?

F.C.

Paul Walker · « **Reply #17 on:** March 05, 2014, 04:37:25 PM »

Howard finally figured out the equation!

john e. holliday · « **Reply #18 on:** March 06, 2014, 08:40:45 AM »

Quote from: FLOYD CARTER on March 04, 2014, 01:45:29 PM

I've never flown in an FAI contest. I wouldn't mind being on the FAI World's Team. How do I get nominated?

F.C.

No nominations are allowed. That is why we didn't have a Junior competitor one year. You have to compete and be the best there is for your country.

FLOYD CARTER · « **Reply #19 on:** March 07, 2014, 11:32:10 AM »

Quote from: john e. holliday on March 06, 2014, 08:40:45 AM

No nominations are allowed. That is why we didn't have a Junior competitor one year. You have to compete and be the best there is for your country.

THAT MIGHT BE A PROBLEM!

Dennis Toth · « **Reply #20 on:** March 10, 2014, 10:33:24 AM »

OK, I agree that the outside edge is slant is more important, I think slanting both the outside edge and the rear would be ideal or just build the tank compartment with enough room to kick the back out.

Next question is what overall shape is more consistent - rectangle with outside edge in a "<" (standard Veco shape), rectangle with pinched outside rear corner (GMA), teardrop (Perfect)? Now what I'm asking is which of these gives a clean smooth cut off without the engine going lean for the last 10 or 15 laps.

Best, DennisT

Dave_Trible · « **Reply #21 on:** March 10, 2014, 11:24:09 AM »

Dennis I like the pinched rear corner. It's an easier slope for the fuel ( which may be why I do pretty well without canting the tank) but it allows more fuel capacity for a given space, which is my main reason to go that way. The standard 'V' full length chews up a lot of potential capacity though they run well.

Dave

Steve Helmick · « **Reply #22 on:** March 10, 2014, 10:59:50 PM »

Many are still under the impression that the CL of the tank needs to be in line with the spraybar, so they mistakenly require the tank be 1" high. Make them 1.5" high, and put the uniflow tube's end in the appropriate place, and you're good to go. The > could be pretty easily above or below tank CL, for that matter.

I needed an ounce more fuel in my SV-11 and added this sump to the bottom of the 6 oz tank. It added an ounce or a bit more. I didn't have to adjust the tank height at all.

Steve

john e. holliday · « **Reply #23 on:** March 11, 2014, 07:55:19 AM »

You should have seen the tank in my first Old Timer called the BoJo. A little biplane that tried to do the pattern. I had to make the tank deep in order to have enough fuel with the wedge/pickup in line with the needle assembly. It worked for me.