Ive been getting a constant 9-10 minuets over 50+ flights on the Viper runninga Wren 100 with the Std 3lt tanks.
I often do a touch and go or two at the end of a flight and after all that I'm still coming back with over 1/3 of one tank left!
I had noticed that with one tank empty and the other low she takes off very quickly (and then can go vertical, nice)
last week I thought about putting some smaller tanks in but first I rechecked the CG both full and then empty.
Completely empty the CG is 43mm back from the centre of the wing tube but full its 23mm forward of the tube, that's a shift of 66mm!
It flys safely when completelyempty at 43mm (Ive ran it dry to prove it) and is OK with full tanks but I thought I would try to improve things.
I was hoping to bothreduce thetotal weight by reducing the fuel load and maintain a more constant CG throughout the flight.
I had some 800ml tanks identical to the JL ones and found they fitted a treat under the front of the engine bearers so I gave it a go.
I plumed these in parallel then as a front tank I found a 1350ml Dubro type replacing the twin 1500ml tanks giving a total of 2.95lt.
The CG now when full is now 20mm back from the wing tube and creeps forward as the rear tanks empty to 15mm behind.
Now from when the rear tanks are empty its going to be about the same as before with one of the std twin tanks full "success"
I have now had a few flights with this setup and it definitely gets off the ground much more quickly so helpful if you fly from grass.
Wile flying and held inverted it now needs less down stick in the early minuets but being semi symmetrical still need a fair bit.
Flight times and overall wieght are the same as before as its only lost 50ml, tanks empty evenly at the rear andare completely dry after a flight.
I think this is a well worth improvement, cant see any real downside unless your using the space at the rear for smoke tanks
If you wanted you could increase the fuel load by 100ml by useing one of the std 1500ml tanks up frontand still get a more constant CG?
Since the weekend I have fitted an evan smaller 1lt tank at the front so itsnow got 2.6lt andis 3/4lb lighter, look how much room there is now
To be safe Iwill reduce my first flight times to 8 mins, I will let you know how it goes after next weekend weather permiting!