What does everyone think about making functional drop tanks? If made of Kevlar and braced properly, they should be durable enough and would hold plenty of fuel for extended flight times.

Don't do it!

It would be kind of like a bomb if it fell off wouldn't it!

You're talking about actually dropping them, right? Probably not a good idea, primarily because you don't know for sure when/if they are empty to drop them. However, making drop tanks that actually hold fuel (and that are not actually dropped in-flight - more like an auxiliary tank - i.e., centerline tanks on an F-16, F-15, F-18, etc.) is done all the time and works well...

Bob

I didn't intend on actually dropping them while there was still fuel in them. Auxilary fuel tank is a better term. I just wanted to see if other people have done it before with success and how to go about it. After Mr. Matt's post it does cause me to think about the saftey issues of an auxilary tank. It could come detached from the model in a high g turn and impact the ground. I'm not sure if it would explode or not, but it sure would be a concern. Maybe if there was a HDPE tank inside the kelvar, that would make it safer.

Yea, lots of guys have made the centerline tanks functional - a buddy of mine put a round duBro tank in his F-15 centerline tank and he could fly it with it on or off. When it was off, the place where the centerline tank plugged in just became his normal tank vent (where he plugged in his overflow tank on the ground) and when it was on, the tank vent was on the side of the centerline tank.

Its not really a safety issue, IMHO, just make sure that the tank mounting is secure. Easy enough to do...

BTW, Global Jet Club used to sell a kit to do that for a 1/8th F-16, but I can't find it on their website right now...

Bob

I've seen on these forums that some people have had issues with the kevlar tanks splitting out at the seam. Does anyone have information on this? I know there are only a few laminating epoxies that are intended for use with kevlar. They have special formulations. Could this be causing this? In my experience, the material always fails before the adhesive.

check this link

http://www.globaljetclub.com/Aircraf...Eagle-ARF1-9-5

I am flying my F-15 with this 35oz drop tank. It's mounted it securely onto the all carbon fiber engine bay area. If the wings will already come apart before you can pull enough G to detach this device. However, just like any full scale aircraft, you don't want to pull high G with heavy external store.

Mike

Do it man....some time ago i met a guy who had been the first to accomplish this.He used a f16 centerline tank,that had a inner bottle installed to hold fuel,had a pitot pressure tube and an internal servo for in flight drop.worked very nicely.i guess ctr tank is most easier as you need not be concerned as would wing tanks about differencial levels.

Not really a problem if the seams are glued correctly. Overlapping seams are the best and need to be roughed up with course sandpaper to get a good bond. The Hysol products (BV's Aeropoxy and Vpoxy) work very well in this application.

Craig

Mike, thanks for the information. I hope my tanks come out as nice as yours. Boy, I bet that F-15 is a blast to fly!! Great looking aircraft!

I'm building an F-100 so it didn't have a centerline external tank, which would be nice as the weight would be near the CG. I think the only thing that was carried on that centerline station was a special store (nuclear weapon).

I may have some weight and balance issues while in use, so I may have to draw from both the left and right tanks at the same time and feed a central header tank in the fuselage, possibly an overflow tank. How does yours operate? I see a fuel pump in the tank which makes sense for a reliable fuel feed, but on mine I think it would be heavy to have one pump in each tank. Can you give me some advise?

Thanks,
Brian

Craig,

Good information to know. I'm getting started with my first turbine project and haven't had the pleasure of working with the Aeropoxy, but others tell me it is very strong. I found a similar product at Dreamworks Model Products that is only $54.95 for the complete kit. It's Loctite 9462. It looks like BVM must just be re-boxing and charging more.

Brian

what type of nuke did the f100 carry? if it were large enough you could replicate it and use it as a tank as such.would be a something different.just a thought.

Sorry my post got cut off.

I assume you meant a wet drop tank that you end up dropping during the flight. Kevin Whitlow did this a long time ago with success. I tried it with less success. In my experience you end up needing a parachute on the tank to avoid damage on the drop, not worth it IMHO.

I've done both auxillary fuel tanks that did not drop, and also dummy tanks that did drop. I haven't had much success dropping a real aux fuel tank after the fuel is gone - mostly because of the separation of the fuel line - really a lot of trouble to accomplish, and not always reliable.

The non-droppable aux tanks are really easy (on the fuse centerline). I take the scale tank, cut it apart around a convenient panel line and then find the biggest plastic bottle that will fit into the scale tank. I always get funny looks at Walmart/Kmart when I'm looking for shampoo bottles that fit - BTW, round shampoo bottles are about the only bottle that will work. Most of the others have funny shapes that don't really lend themselves for this project. Plumb the plastic bottle just like any other tank with a clunk, vent, etc., and then I place it at the last point in the fuel system (outside vent line) so it will empty first. My outside vent line is attached to the tank to vent the whole system. Make up some thin ply tabs to epoxy around the circumference where you cut the tank apart, and then drill and screw the front part of the scale tank back on. Feed your vent and fuel lines through the bottom of the aircraft, and the fasten the tank onto your pylon securely. I've never had a problem losing the tank during flight, but make sure it is mounted securely. Most of the time I end up with around 30 or so additional oz of fuel. My F-15 took a 38 oz shampoo bottle, and has worked just fine. So far, I've had good success doing this, and it can add much needed fuel. I've done a Bobcat, a couple of Rookies, and a Skymaster F-15 so far, and all have fed fuel with no problem.

Dropping dummy wing or fuse tanks is really easy using BVM release mechanism. I put wing tanks on my MiG 15, and they worked fine. So far, dropping them over grass on the side of the runway has protected them from damage. Kevin Whitlow has had good success dropping a couple of Nerf bombs off his Bobcat - I think using the BVM system, too.

I'ts not hard, and is fun, plus by adding an external tank you can extend your flight time, but be aware when you take off with a full fuel load, you can sure tell it. The airplane will be heavy, but will lighten up as the load burns off.

Have fun, and try it - it really is easy.

Regards, Les

Back in the mid-90's, I had a functional centerline drop tank on my Yellow Aircraft F-18. I simply cut their scale fiberglass tank in two, installed a Dubro cylindrical tank and plumbed it to a bulkhead union-style barb fitting on the top of the fiberglass tank and a flush vent fitting on the bottom then spliced the two halves back together. A similar bulkhead barb fitting (with the barb filed away) was installed on the bottom of the fuselage and a short piece of Tygon was placed between the two fittings. After 3 minutes of flight, I'd release the tank while giving a bit of up elevator. The tank would separate (taking with it the short piece of Tygon) cleanly and the tank fell to the ground surprisingly softly. Typically I'd release the tank on a mid-altitude pass just off the far edge of the runway and pick it up after the flight. The only time the tank was ever damaged was when it happened to fall on a rock and that was just a superficial fibrerglass repair.

I used the tank at several major events and nobody even suggested that it was unsafe. Everyone seemed to think it was pretty cool.

These days there is a better selection of fittings for an even cleaner installation.

No problem, go for functional drop tanks.

Regards,

Jim

Dan Gill (www.Details4scale.com) makes a centerline tank for the A4 that can be used on many jets where it is the right size, and close to scale shape.

It has an inner tank that holds about 50 oz, removable nose cone, and a scale outer shape. I have one on a Yellow Aircraft F-15C and the extra fuel is really useful. Works well. I learned a lot about the use of very large tygon and fittings, and pressure drops in fuel systems ... it is amazing how the pressure builds up on multiple series tank connections.

I have mine plumbed, going backwards from the fuel pump: to a BVM UAT, then to the two main tanks in parallel (feed and vent lines are paralleled), main vent to the suction port on the belly, and belly vent then becomes the system vent.

I am using the stock yellow tanks and if you fill too fast you see them start to "inflate" from the pressure of feeding the belly tank .. all of which is plumbed with large bore brass (which comes with Dan's tank) and large-bore /316" tygon.

I did do a little bit of reinforcement of the floor of the fuse where the tank pylon attaches, and tied the mounting plate to the formers in front and behind the mounting area. I could imagine a fair amount of aerodynamic stress as well as gravity (the tank, when full, is pretty heavy, and imagine the plane in a steep bank and a not perfectly coordinated turn) so I felt this reinforcement was important.

Really happy with the results.

Dave

Seems the f100 carried the mk28,mk7 nuke bomb,both of which have a centerline tank appearence.

thereby,you could have the wing tanks feed to the "nuke" centerline.....and should there ever be an inbalance issue..punch the whole lot off to recover stability.just a thought.

That's a great idea and would turn some heads at the field. The Mk7 looks like the biggest bomb in size. Man that thing is huge. I'm not sure how the F-100 got off the ground. The F-100 carried the B61 as well as the Mk28(B28) thermonuclear weapons. I think the Mk28 or B61 looks like the best candidate for a centerline tank as it looks the most streamlined. Here's a few pics I found. I would be pretty nervous being in a room full of those things.

Bet the F100 used alot of runway for sure,wonder if the bunker had a humm from all the radiation those bombs you know had to be emitting,lol.I think that would be different and very sweet to employ as i have not yet seen such configuration done yet,saves internal space as wellplus the safety factor to go clean wing if needed in a pinch.release mechs must be fault free though.would be really cool to fly with just the nuke...exhaust the fuel in it..punch it off in a simulated bomb drop.Nice.

I don't think F-100s ever carried anything on the centerline. Where would you put it, there just isn't room. The rear of the nose door ends at the front of the speed brake. The speed brake goes almost all the way to the main gear doors, and since the main gear doors are hinged at the centerline of the plane there just isn't room for a pylon. The gear doors and speed brake are colored black on this 3 view. It appears that the "special" weapons would have been carried on the inner wing pylons.

I've seen a lot of jets with an overflow tank sitting on top of the wing in a very nonscale mannor taxing out.
A functional centerline tank could double as the overflow tank and carry a little extra when needed emptying first on the vent side.
I also used the dubro round tank under my F-4 for that and run the engine on the test stand with that same tank.
Haven't considered a release for it tho.

It's not necessary!!! don't do it!How many minutes you want to fly?You'll add weight and maybe this wiil cost you.

rcmigpilot :Hello my friend...a little searching the web reveals that it is the F100D that was configured to carry centerline stores.the "D" model has a thickerwing airfoil,flaps,modified notch in the speed brake,enlarged fin and stab.Also has a weapons computor that allows the "dive toss" manuver to send the nuke on a six mile bye bye.So therefore depending on the speed brake the nuke could be used centerline.just a thought.thx.