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-   -   fuel tank position (https://www.rcuniverse.com/forum/rc-airboats-246/1309600-fuel-tank-position.html)

Realdo 11-27-2003 04:27 AM

fuel tank position
hi to all !
I'm new in rc world, and i build one air-boat to start with.
Now, when is all finish, problem is come.
Vertical engine mount with horizontal engine. i have only 200cc tank and i mount on opposite side from engine exhaust and placed vertically. top of the tank is in line with carb, but lower side (bottom) of tank is cca 15cm below carb. fuel line is cca 5cm long and i use pressure from exhaust. tank is placed on this side because the space between engine and air-rudder is to small for horizontal tank mount. will be this tank mount ok or i must make new stand, with engine in normal, vertical position, and put tank horizontally in line with engine.



TERBObob 11-27-2003 08:45 AM

RE: fuel tank position
First , I assume you are talking about a nitro engine , correct ? If yes , then I would suggest , since you have not done the mount yet , it make the fuel tank as even as possible with the motor. If you choose to mount the fuel tank lower than the engine , you should be prepared and ready , to possible use a pump , to pump the fuel up rather than depend on the back-pressure created in the exhaust , which might not be enough to get the fuel up to the engine . If you are talking about a gas engine ( still 2 stroke , but the ones like on a weedeater ) , then no , the height is not going to be a problem.
Hope this helped and welcome to the board .

Realdo 11-27-2003 08:55 AM

RE: fuel tank position
thanks TERBObob for fast reply.
sorry, for my mistake. yes, i use os max 40fp horizontally mounted. now i must to do new engine stand and put engine vertical and fuel tank on back side of engine, or i will make some modification on stand to put tank in same line with engine. if i make modification tank will be abt 2cm higher than carb. is this will be ok ?

thanks again


TERBObob 11-27-2003 09:06 AM

RE: fuel tank position
Yes , slightyly higher will be fine , but lower , and you always take the chance of needing an additional pump to pump the fuel .
When you get her done , please post some pictures when you can . We would also like to see the progress as well if you could ?
Always remember , the two most important things while doing our boat -

1) have FUN building , running and fixing it

2) be SAFE ! for yourself and others around you .

( and don;t forget to get some pictures up , if you can [8D] )

pro27 11-28-2003 02:36 AM

RE: fuel tank position
You are right on the money here TURBObob!
I just responded to another topic here about a removable pod, and the mod needed for the fuel tank position.
Feels good to help out someone new doesn't it?[8D]

Realdo 11-28-2003 03:40 AM

RE: fuel tank position
thanks TERBObob
after this i will made some modification on engine stand. engine will be stay in this (horizontal) position but tank will be moved and placed on top of stand (over engine). this is abt 2 - 3 cm higher than carb.
pictures......come soon. (finished boat, don't have step by step)

boat is made on polyurethane board with polyester. 3 ply - 200g/mtr-sq. total weight 5,3kg. length 850cm, width 490cm, height boat 10cm and engine pod 17cm - total 27-30cm. engine os max 40fp, sanwa 2ch dash V. tank is made from baby shampoo bottle 200cc, radio-box is made from plastic 1kg ice-cream box. this is short but you will see the picture.

thanks again


Realdo 12-09-2003 01:50 AM

RE: fuel tank position
1 Attachment(s)
pictures is here.

Realdo 12-09-2003 01:55 AM

RE: fuel tank position
1 Attachment(s)
and more....
note: first run is canceled due to strong wind and bad weather. wait next saturday. we will see.......
any question about construction ?

TERBObob 12-09-2003 02:11 AM

RE: fuel tank position
Very nice ... love those control horns .... hey ... now the most important part of the whole thing now that you have her done ....
Get out there and have

[center]FUN ! ! !

pro27 12-09-2003 02:18 AM

RE: fuel tank position
I can see that you may have a fuel feed problem in the near future.
It would have been better to mount the tank horizontal, instead of vertical.

O --- ok

O : not ok

The O is the motor, the --- & : are the tank.

With the tank mounted horizontal, with the centerline of the tank centered with the centerline of the engine (carburator), will give you your best overall fuel draw. Using the muffler pressure helps this quite a bit. Also, a little higher than center is also ok.

The way you have it now, vertical, it will run fine for a few minutes, but will have a hard time sucking up the fuel. Even with muffler pressure, it will have a hard time pressurizing the tank enough to be able to use all the fuel in it. It has to overcome too large of an up-hill travel. You will end up depriving the engine of fuel and it will die out.

Without rebuilding your pylon....
I would suggest adding a horizontal platform on the same side you have the tank on, and mount the tank there. You may have to offset it a bit because of the bottom of the motor. This will work better than the way it is now.

For a better idea of what I am tallking about, check out the Verner site's photo pages and look how this is done on some of them that have the side mounted engines.

Realdo 12-09-2003 05:48 AM

RE: fuel tank position
hi TERBObob and pro27. thanks for nice wishes about my first rc toy :)

note for pro27: ill start engine with this tank position and will run nice for me. engine is not full run in and i will see what going on when i try it on the sea. if it stop you see my first aid fishing tool for this emergency situation.
but in this time engine work fine to the end of tank. no problem with "full" power and idle on near empty tank.
on first nice day ill try on sea and send picture with comment.



pro27 12-09-2003 09:47 AM

RE: fuel tank position
If it is working, then don't change it. Sometimes things do work out, even when all signs say it shouldn't. After all , theororists say that a bumble bee should not be able to fly....but it does!

Will be looking forward to more pics[8D]

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