let us talk about fuel tank clunks....

[Ohio AV8TOR]

orthobird;11339 wrote: do you believe, in any way, that the felt may or could act as an impediment to fuel flow? reason i ask, i have a 91" yak with a 70 cc twin motor.

tank full, cranks right up.

after about 6 minutes of flight, the tank is 1/2 full or so.



i noticed that if i do a humpty bump, then when i am in level flight and begin to pitch the nose down, then the engine sounds like it is starving, for about 2 seconds. i level her out, then sounds fine again. kind of weird. does not happen when tank is full, and the engine is not overheating.



when i landed it



i looked, and surely enough, if i tip nose down by 30 degrees, i can see in the tank that the clunk felt, about 1/4th is not submerged.

seems to me that the fuel would enter the fuel line via the whacking process.



can air get into the fuel line when it is in this position?

anyone else have any thoughts on this?



and in fact, this was the purpose for my post....

I flew my DA60 powerd Extra SHP and the only problem I had was some flame outs on pop tops which I solved with using idle up. I did change the clunk every year. As for the 30 degrees I watched a DA video on fuel tanks see here and they add a brass tube in the pickup line. I am pretty sure that 30 degrees nose down that clunk is also out of the fuel. Are you sure that you do not have any air leaks?

 

[BalsaDust]

orthobird;11339 wrote: do you believe, in any way, that the felt may or could act as an impediment to fuel flow? reason i ask, i have a 91" yak with a 70 cc twin motor.

tank full, cranks right up.

after about 6 minutes of flight, the tank is 1/2 full or so.



i noticed that if i do a humpty bump, then when i am in level flight and begin to pitch the nose down, then the engine sounds like it is starving, for about 2 seconds. i level her out, then sounds fine again. kind of weird. does not happen when tank is full, and the engine is not overheating.



when i landed it



i looked, and surely enough, if i tip nose down by 30 degrees, i can see in the tank that the clunk felt, about 1/4th is not submerged.

seems to me that the fuel would enter the fuel line via the whacking process.



can air get into the fuel line when it is in this position?

anyone else have any thoughts on this?



and in fact, this was the purpose for my post....

[SIZE= 14px]1/4th [/SIZE]HAHA thats a new one I havent heard before.

 

[Alky6]

Thought that was odd at first too. But makes sense after thinking about it, easier than writing out one-fourth. LOL.

-Paul

 

[orthobird]

Ohio AV8TOR;11394 wrote: I flew my DA60 powerd Extra SHP and the only problem I had was some flame outs on pop tops which I solved with using idle up. I did change the clunk every year. As for the 30 degrees I watched a DA video on fuel tanks see here and they add a brass tube in the pickup line. I am pretty sure that 30 degrees nose down that clunk is also out of the fuel. Are you sure that you do not have any air leaks?

i do not know, what i did was completely re do all the fuel lines and replaced the clunk with a solid brass PSP clunk. the inside tubing is VITON and the outside tube, from the cap to the carb is Tygon, and there is no filter anywhere. there is a filter on the fill line to the tank, and there is also a filter on the gas tank filling station line to the airplane. maybe on wednesday, i will take it out and see what happens.

 

[orthobird]

Alky6;11413 wrote: Thought that was odd at first too. But makes sense after thinking about it, easier than writing out one-fourth. LOL.

-Paul

i am so sorry. i have a bad habit of making up so many abbreviations. part of my job.

 

[Pistolera]

One thing I have found through experience is if you use a piece of brass tube, or plastic, to keep the clunk near the rear of the tank.....it WILL do just that and when you are pointed downward, with lower gas levels the clunk will NOT be in the gas at all.



I have had several dead-sticks (friends as well) before realizing what was happening. Pulled brass/plastic tube out and never had a problem again.



YMMV

 

[Terryscustom]

SleepyC;11311 wrote: I use Danhakl Tanks and just put them in.. no worries.





If you build your own, DO NOT leave 1 - 2 inchs of space between your clunk and the back of the tank. In a hover this can be bad... SERIOUSLY.

I agree with this. In any planes with foam core belly pans I do prefer to make my own with Fiji bottle and PSP caps since I have had a couple of Danhakl tank caps leak. They replaced them, no problems, but with a foam belly you can't just clean it up.....it's already gone.



To the original question though I use THESE filtered clunks. They suck every bit of fuel out of the tank and filter at the same time. I also use two filters on my actual gas can, one is another filtered clunk inside, the other is just before the pump....I use one of THESE from ace hardware because they self clean if you remove fuel and will last basically forever. I have engines that are three years old and if you pull the pump side cover off the carb the little screen in there is completely clean.

 

[Ohio AV8TOR]

SleepyC;11311 wrote: I use Danhakl Tanks and just put them in.. no worries.





If you build your own, DO NOT leave 1 - 2 inchs of space between your clunk and the back of the tank. In a hover this can be bad... SERIOUSLY.

Looks to me that these could stand to me a little longer.

11624=4799-Region capture 4.jpg

 

[Patroller]

I really like the clunk that comes with the PSP kit. The tubing hitting the side of the tank instead of the clunk is brilliant especially with the thinner Fuji tanks. Instead of a filter at the clunk, I use an inline filter just between the tank and the carb.

 

[RJ 706]

+1 on filtered clunks and aluminum caps.

Almost every fuel tank issue I had was with a plastic cap leaking and ruining my day. Gas tanks only leak on perfect blue sky days !!!!!!