I want more range. I don't want to fit wing tanks for a dozen reasons. That means increasing the size of the front tank. I already carry a range extender carrying ten litres which takes me to thirty. This fits between the pedals and if a T shaped tank were made that could be fitted into the space where the existing tank sits instead, I could reasonably expect to get thirty. I would like to get it to fit without cutting up the airframe but it doesn't look as though I can. I am going to remove the fuselage tank, mock up a polystyrene block to find out what I can do and still get it to fit back. It may be that I need to cut into the fuselage. If I remove the turtledeck on my 1600R, I could liberate some space, and put in a bigger tank with a curved top and a central filler. That means cutting through the top of the fuselage between stations one and two,fitting the tank and reinstating the turtledeck. This looks like the best way to fit a bigger tank and a relatively easy way to handle the installation by repositioning and widening the lower tank mountings. I might flange the new tank so it would bolt into the top skin of the fuselage and restore the lost strength. I don't know enough about the structural implications to be sure if this is a sensible idea. If any of you people know better, would you kindly consider it, please and let me know your opinions.
Have you considered a tank under the seat and little transfer pump? It wouldn't take a very big battery to pump a tanks worth, or even a little manual pump. I also seem to remember reading about a rear auxiliary tank arrangement behind the seat before.
My existing range extender with pipes and pump offers more than I thought I could get under the seat. I shall have a look but then there is the hassle of filling it up inside the cockpit.Either it fills slowly or you need to take the seat out and that is a chore on my a/c. I think the one tank solution will be best. George has pointed me towards his site where he has done just that on his Himax so I think I need to look at the possibilities.
Putting fuel in the wings increases the limit load factor and maneuvering speed while putting more fuel in the fuselage decreases load factor and maneuvering speed. These changes are small with the weights being considered and diminish as the fuel is burned.
Putting fuel in the wings increases the limit load factor and maneuvering speed while putting more fuel in the fuselage decreases load factor and maneuvering speed.
...but in the case of the Minimax where the wing tanks are at the very inboard of the wings does it make that much difference?
...but in the case of the Minimax where the wing tanks are at the very inboard of the wings does it make that much difference?
It makes a difference because the fuel weight will be a significant part of the wing panel weight, maybe as much as half, regardless of where the weight is distributed span-wise, so the inertial relief offered is great. Remember the inertial relief is the wing weight multiplied by the load factor. Because the maneuvering speed differs with the square root of the load factor, the change in maneuvering speed is much less.
Interesting. The change in manoeuvring speed is due to pitch stability? W&B is obviously a key thing, some place tanks behind the seat which seems foolhardy to me. Filling the volume above the tank under the turtledeck Keeps the CG shift as similar as possible and there is a big hole in the upper surface anyway, big enough to put a pilot in! My initial idea would be to grow the tank to around 35 litres, adding 25 # and moulding a flange around it to hold it onto the reinforced edge of the new hole. A couple of maxes in the UK have baggage doors in the turtledeck but I would prefer to glue it back once the new tank is in.
I think if you are going to drop a tank in between stations 1 & 2 it would be prudent to either refit & reglue the turtledeck afterwards, or to use the top skin of the tank as the new turtledeck, as you suggest. The curved turtledeck will be a useful stressed skin element in the total stiffness of the forward fuse which I doubt could be removed without a strength/stiffness penalty.
You haven't said what material you are considering, but I guess either aluminium or glass. With aluminium, cracking is likely to be a problem in a loadbearing application, and this could result in fuel leaking into the cockpit. With grp, weight is likely to be an issue.
You haven't specified the reasons why you don't want to fit wing tanks, but I reckon a retrofit tank in the forward fuse would be more hassle & work than one in the wing bay.
One other idea you might want to consider is a belly tank (ISTR BobH has a small one he fitted). This could be fitted to the underside of the fuse with no structural mods. If it were triangular in section, it could be long & narrow to minimise drag. Rough calcs give dimensions of 400mm base x 125mm height x 1m long to give 25 litres. It could be shaped to fit the lower fuse such that its c.g. coincided with the aircraft c.g.
A simple way fuel in the wings was explained to me is as follows: Any and all fuel (or other weight, bombs, ammunition etc) in the wing carry their own weight and as such put zero load on the wing-spar in flight.
I am actually considering moving some fuel into the wings, so I want to ask. How do you vent the wing tanks so they don't leak fuel? I tried to look it up, but it is unclear to me. If you roll the plane steeply, wouldn't fuel leak out of any vent lines anywhere near the tank? Especially if you join tanks on each side with a T fitting.
In a coordinated turn the fuel will remain at the bottom of the tank, just like flying level or on the ground. As long as there is positive g, fuel can not spill out. So, unless you fly upside down (negative g) there is no problem
For venting, I use a little brass tube in the fuel cap facing into the airflow. This is to stop the tank forming a vacuum when fuel is consumed; and facing forward it slightly pressurizes the tank in flight.
I am actually considering moving some fuel into the wings, so I want to ask. How do you vent the wing tanks so they don't leak fuel? I tried to look it up, but it is unclear to me. If you roll the plane steeply, wouldn't fuel leak out of any vent lines anywhere near the tank? Especially if you join tanks on each side with a T fitting.
TEAM used to sell plastic tanks that mounted in the wings. I had one in my Airbike. The tank held 5 gals of fuel. The vent was in the filler cap which was mounted on a neck on top of the tank.
I bought two of the wing tanks last summer. These hold 6 gal each and are shaped to fit within the rib profile. I believe my AB may be the prototype AB. The spar mounts are at the top of the spar so the wing sets lower and there is an extra rib bay on each side with no bottom. I had to fabricate mounting structure. They are very nice, fit well but realize that is 78 pounds of weight if they are filled (fuel plus the tank and structure weight, 42 pounds more than the legal 5 gallons. Performance is ………………..interesting.
Conventional wisdom somehow always dictates more fuel.what about a smaller engine like a hirth f33 that burns 1gph. I don't remember what the 277 burned, I think it was slightly higher.
A simple way fuel in the wings was explained to me is as follows: Any and all fuel (or other weight, bombs, ammunition etc) in the wing carry their own weight and as such put zero load on the wing-spar in flight.
Unless the external load (like drop tank ) is shaped to produce some lift, weight of external load ( and any additional internal load ) needs to be borne by the wing spars.
On the ground, the weight of any additional load on the wings, has to transfer to the fuselage and finally to the landing gear, through the wing spars.
In flight, the weight of the additional load does not need to transfer to the fuselage through the spars, but still, the spar at the load attachment point has to bear the load of the newly added weight ( fuel etc ). The added load does not disappear. It is carried by the spar at that location. Just that it does not transfer to the fuselage.
In airliners, the weight of the fuel in wing helps to reduce the bending load on the wings. How would this be possible, if the fuel in the wing carries its own weight ?
Makes sense to me. I think they probably really mean that the weak spot is where the spar attaches to the aircraft, not the spar itself, so load put directly on the spar is much easier on it then load slung in the middle of the airplane.
Or as you said, the drop tank or bomb is shaped to lift its own weight in flight, which I honestly find very clever..
Simply, Va is the speed at which at maximum gross weight if you suddenly move the controls to full deflection the airplane will stall just before it reaches it's maximum rated G load. So, if you plane has a G limit of 4, at some particular speed pulling full up elevator will cause the plane to reach 4 Gs. If you fly faster than Va you will pull more than 4 Gs and may break the plane.
Surprisingly, to some, as a plane gets lighter the maneuvering speed is lower. And, conversely, a heavier plane has a higher maneuvering speed.
Moving cg aft lowers stall speed and thus maneuvering speed slightly. When I proposed moving weight to the wings from the fuselage I was referring to the effect on the load factor and how it affects maneuvering speed.
Why not the wings? Firstly they will need to be recovered. That involves time and money. My aircraft lives 40 miles away and I have few facilities at the hangar. A new structure will need to be made in the wing. More time. The tanks tend to come loose and the wing has to be opened up periodically. It is not possible to put a camera down the wing to inspect it. The wing is not as strong as a fuselage. A hard landing with a full wing tank might be quite damaging. If the aircraft is to be derigged the tank needs to be drained. I think I am going to remodel the floorboard and space the pedals out an inch each side. That will give a nine inch wide space to put in a sub tank and that can be fifteen litres. A pump to send the fuel to the upper tank when required should do the trick.
When I purchased the AB last year it had the original 2 gallon header tank in the fuselage between the pilots legs. It also had a 5 gal Walmart tank on a shelf on the bottom of the fuselage behind the pilot. The engine could draw from either tank but not at the same time. The performance was ok as far as an ultralight goes. As near as I can tell, it originally flew with a 250cc Zenoah and the two gallon tank, then a Rotax 277 and the two gallon tank, then the Rotax 447 it now has with the 7 gallon lash up. Although all fuel in the two 6 gallon tanks is now pretty much on the CG, the extra 21 lbs. of fuel have decreased the rate of climb with a 220 lb. pilot (me) from about 300 fpm to maybe 50 to 100 fpm on an 85 to 90 degree day. Just cause you can carry extra fuel it is not always a good idea. When you add weight beyond the design weight, you become the test pilot on just about every flight. I have arranged the fuel system so that each tank is on an either/or both system so I can fly safely with fuel in just on tank. The tanks almost meet at the centerline of the AB so there is no noticeable adverse roll with an empty tank on one side and a full one on the other. Joe
Wow, that is incredible that just an extra 20lbs can mean the difference from 300fpm to 50fpm!!!
I should go on a diet.. I have an artist friend who is helping me paint my max, and she only weighs around 95lbs. She's so light that if she wore a paramotor engine backpack, she would be able to fly upwards vertically (170lbs of thrust from a blackhawk ..150 something, and the unit itself weighs 42lbs.. plus 95, you do the math!)
I suspect the minimax would fly a lot better with her vs with me.
We don't get 90 degree days. We don't get many places to fill up, either. Options for touring the Max are limited here. Lots of Trumpwalls in the sky as well. I can either hop from field to field or find a bigger tank. My aircraft will have streamlined struts but already has a lowered engine and reflex. Anything I can do to lose drag is being done to increase range but given 65 mph and around 11 lph thirty litres will only take you 140 miles safely in still air - and we don't get much of that either!
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