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View Full Version : Aircraft with tip tanks question.


astroglider
11-09-2017, 05:10 PM
I'm doing some research on fuel balancing procedures for various aircraft. I have no experience with aircraft equipped with tip-tanks and was wondering what the fuel burn procedure is for them? Say a Learjet. I know you have to add fuel to the tanks in a certain order...but what about when you burn the fuel?

Anyone?


123456
11-09-2017, 05:57 PM
probably not the right forum for that question... but maybe some previous corporate drivers can chime in..

ERflyer
11-09-2017, 08:16 PM
I'm doing some research on fuel balancing procedures for various aircraft. I have no experience with aircraft equipped with tip-tanks and was wondering what the fuel burn procedure is for them? Say a Learjet. I know you have to add fuel to the tanks in a certain order...but what about when you burn the fuel?

Anyone?

Tip tanks burn first.


Adlerdriver
11-10-2017, 06:42 AM
I'm doing some research on fuel balancing procedures for various aircraft. I have no experience with aircraft equipped with tip-tanks and was wondering what the fuel burn procedure is for them? Say a Learjet. I know you have to add fuel to the tanks in a certain order...but what about when you burn the fuel?
Tip tanks, external tanks on wings and center line of fighters......generally speaking the gas inside them usually gets transferred out first, so they are empty first. Notice I didn't say "burned first". The fuel in the tank or tanks supplying the engines is always burned first. Those primary tanks get constantly replenished from the tanks that need to be empty first (tip tanks, etc.) It's unlikely that there is plumbing directly from the tip tanks to the engine itself.

rickair7777
11-10-2017, 07:50 AM
Generally...

Fuselage tanks get emptied first, to reduce wing loading. If you burned the wings first, you have a heavy fuselage supported by light wings. The wings would be subject to more severe bending forces in turbulence due to low inertia, especially with a heavier, higher intertia, fuselage resisting movement... ie the wings would move, the fuselage not so much resulting in more severe forces at the wing/fuselage interface.

By emptying fuselage tanks first, you leave the wings heavier with more inertia to resist bending forces. When the wings do move, the lighter fuselage has less tendency to stay put.

Tip/outer wing tanks are usually emptied first to avoid creating a high rotational inertia. If all the wing/fuselage fuel was burned, but you still had fuel in the tips it would be harder to both start yaw/roll motions, as well as stop them. The former is of concern for adequate control authority, the latter is of particular concern for spin entry.

Some airbuses empty outer wing tanks late in flight, but that's because the inner wing tanks are often full at T/O. Once the inners burn down, the outers empty to the inners, with a typical fuel load this happens prior to descent and arrival.

Mink
11-10-2017, 09:06 AM
Only tip tank aircraft I have experience with was the T-2 Buckeye. Tips transferred and were emptied first.

UAL T38 Phlyer
11-10-2017, 10:38 AM
Lear 35: similar in principle to what Adler said. No center-point refueling; it was over-the-wing hoses in the tip tanks. As you fueled, it drained by gravity to fill the wings first, then the tips would fill.

The wing joined it mid-tank, so all the fuel above the wing transferred by gravity. It just kept the wing tank full.

Inflight, once the tip level got below the wingline, there were jet pumps to transfer the fuel to the wing.

As I recall, the jet-pumps relied on fuel-flow from a running engine. If you were engine out, you might get trapped fuel in the tip, which would make roll control dangerous for landing.

As such, there is a big jettison pipe at the back of the tip tank for gross imbalances.

(It could also be used for chemtrails). :D

trip
11-10-2017, 11:29 AM
On my 310, burn off the tips for an hour then burn the aux (tips were the mains). After the auxiliary's empty go back to mains, if you forgot it got quieter.

astroglider
11-14-2017, 04:24 AM
Thanks everyone...good stuff.

jonnyjetprop
11-22-2017, 05:16 PM
While I believe that the OP is referring to tip tanks like a Lear 35, some aircraft that have fuel tanks within the wing structure, but outboard toward the tip. Douglas aircraft often would use the tip fuel last because the fuel filled structure was stiffer and less prone to twisting.

Hetman
11-24-2017, 02:37 AM
Mitsubishi Mu-2:

Both engines feed from a common center tank to which all other fuel is transferred. There are 2 tip tanks and 2 very small wing tanks. Transfer first from tips, then wing.

dera
12-01-2017, 04:42 PM
Mitsubishi Mu-2:

Both engines feed from a common center tank to which all other fuel is transferred. There are 2 tip tanks and 2 very small wing tanks. Transfer first from tips, then wing.

And give a good tip to the poor lineguy who has to refuel that plane... :D

esa17
12-01-2017, 06:01 PM
Fueling a LRJET is easy but there is a process. As mentioned there is only one filler point on each side, on the tip.

If fueling using a single point you have to be cautious of an imbalance because it can cause the aircraft to tip. First side fill to a 125gal imbalance. Proceed to the other side and fill to 250gal and then back to the other side for a top off. During the event you’re likely filling the trunk (1200# in a 35) and being mindful of a bubble. If your aircraft is prone to developing a bubble then you can open the cross flow and try to force it out by sending fuel from the full wing into the the with with the bubble. Leave the cap off the bubble side for best results.

You can also taxi or tug the plane in a few circles and it will clear the bubble.

In flight the tips burn down first. After the tips burn down passed 5-600# remaining you can start bringing fuel forward out of the truck. The purpose of this is to verify the function of the jetpumps which use motive flow to move fuel.

Baffles, flapper valves and a yaw damper are used to combat Dutch roll.

CrimsonEclipse
12-04-2017, 10:02 AM
I'm doing some research on fuel balancing procedures for various aircraft. I have no experience with aircraft equipped with tip-tanks and was wondering what the fuel burn procedure is for them? Say a Learjet. I know you have to add fuel to the tanks in a certain order...but what about when you burn the fuel?

Anyone?

Airplanes with tip tanks vary greatly.

The Lear 25 and 35/36 fuel directly into the tip tanks and use pumps to transfer to the center tank. If you're fueling the "tips only: you can fuel full blast with no kick back. If they need to transfer to the center tank, you have to wait longer to re top the tip tanks. The 36 has a bigger center tank so you may have to wait around longer.

The Westwind I has tip tanks but fuels through fuel inlets on top of the fuselage and flows into the wings and tip tanks. There are also manual valves (little sticks under the wing you pull to manually open) to allow fuel to flow to the tips.
The Westwind II had singlepoint.

MU-2 are just monsters. Tip tanks and inner wing tanks. No fuel imbalance over 50 gallons and getting to the 15 gallon inner tanks was always a PITA due to the limited space between the fuselage and the engine. The even had weird fuel caps. :confused:
It was always fun to watch the wing drip as you fueled one side or the other. Especially if you were alone. Also, NEVER place a ladder under the wind or tip tank.

Twin Cessnas were interesting, the tips were the main tanks and the wing tanks were the aux tanks (except the later models with out tip tanks like the 414A and 421C).
The return fuel line from the engine flowed ONLY into the main tank (tips) this means you had to burn from the tips for at LEAST an hour before using aux tanks. If you use the aux first, the return fuel will overflow the main tanks the dump the excess overboard.
Also, some of them had nacelle tanks to add to the complications.

I'm pretty sure that bonanza tip tanks were directly piped to the wing tanks, (not 100% sure on this one)

G-2's also had tip tanks but I'm not sure about the fueling requirements and burn on that one.

Crusoe
12-11-2017, 12:13 PM
>>Also, NEVER place a ladder under the wind or tip tank.<<

I was looking for this comment. Not disappointed.

NEDude
12-12-2017, 06:48 AM
And give a good tip to the poor lineguy who has to refuel that plane... :D

Holy cow yes! Back in my rampie days we had a corporate outfit with a fleet of 4 MU2's. When they called to ask for fuel, the poor line guy who had to make the trip to their hangar would be gone half the day to fill up those four airplanes. Partially fill one tip tank, then partially fill the other, and back and forth a few times to keep them within balance. Then back and forth between the two wing tanks, and then finally wrap yourself around a couple of the prop blades to reach me main center tank. I HATE(!!!!!) that airplane.

A Squared
04-24-2018, 02:34 AM
Airplanes with tip tanks vary greatly.



Twin Cessnas were interesting, the tips were the main tanks and the wing tanks were the aux tanks (except the later models with out tip tanks like the 414A and 421C).
The return fuel line from the engine flowed ONLY into the main tank (tips) this means you had to burn from the tips for at LEAST an hour before using aux tanks. If you use the aux first, the return fuel will overflow the main tanks the dump the excess overboard.
Also, some of them had nacelle tanks to add to the complications.

I'm pretty sure that bonanza tip tanks were directly piped to the wing tanks, (not 100% sure on this one)



I think that for the Bonanza, it depends on the specific type of tip tanks. I flew a Bonanza with tip tanks. I believe they were Osborne tanks, but it's been a while and I'm not 100% sure. Anyway they fed directly to the engine. The thing is, on this Bonanza, the fuel return was always to the Left main tank , so you had to burn out of the left main for a while before burning from the tip tanks, or you'd lose fuel overboard. Kind of like the Twin Cessnas in reverse. (Same outfit had 310/320's) I discovered this quirk on my first long flight in this airplane. I was repositioning the airplane from Florida to Alaska, fueled everything up for my first leg, started burning out of the tips once I leveled off in cruise. Every so often, I'd catch a flash of movement out of the corner of my left eye. Could not figure out what I was seeing and was wondering if I was imagining things. Then I started noticing that I had significantly less fuel than I calculated I should have. After I landed (early) for fuel, I notice that there were blue fuel stains on the top of the wing coming from the left main fuel filler. Apparently the overflow fuel would build up pressure and force a periodic spray of fuel past the filler gasket and that was the flash of movement that was catching my eye. Although, looking back I wonder how the main tank was pressurizing ... maybe the vent was plugged with a mud-daubers nest. At any rate, once I modified my fuel management technique to allow room in the left main for the fuel return, I found I could fly a lot further on full tanks of fuel.

There are different manufacturers of Bonanza Tip tanks. You may be right that others transfer to the main tanks. That's the way the locker and nacelle tanks worked in our twin Cessnas.

A Squared
04-24-2018, 02:35 AM
Holy cow yes! Back in my rampie days we had a corporate outfit with a fleet of 4 MU2's. When they called to ask for fuel, the poor line guy who had to make the trip to their hangar would be gone half the day to fill up those four airplanes. Partially fill one tip tank, then partially fill the other, and back and forth a few times to keep them within balance. Then back and forth between the two wing tanks, and then finally wrap yourself around a couple of the prop blades to reach me main center tank. I HATE(!!!!!) that airplane.


If you'd sent 2 trucks and 2 rampers over, and fueled both sides at once, you could have fueled the fleet in a quarter of the time. Sometimes the whole is greater than the sum of it's parts.

FlyJSH
04-25-2018, 03:18 PM
414A and 421C).

Also, some of them had nacelle tanks to add to the complications.



Throw in wing locker tanks and get close to seven hours endurance... which was good because reading and comprehending the fuel management checklist took almost that long. Seven hours without a relief tube was miserable.

mherrig97
08-11-2018, 07:08 PM
Not sure how it works in a Learjet but the 172 I fly has tip tanks. They do not feed the engine, instead, they just dump into the mains when I turn the pump on. The main must be at least half empty before I can pump, then I have to switch to the other tank because the tank being filled cannot be feeding the engine. I just flip the switch and it fills, takes about 10 minutes to empty the tip tank, 11gal usable each side.



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