jayseas

I'm relatively new to c/l, my question is on the "profile" type stunt planes .I have noticed the tank is always mounted behind the engine forward of the wing. Why not put the tank in the wing and move the engine closer to the leading edge?

icerinkdad

Mounting the tank in the wing has been done. There are a couple of issues... a tank leak is not good news for the balsa and can quickly ruin a model. Also many folks find themselves moving tanks up or down a bit to give the same engine run upright or inverted. That said some designs (like the flying wings used in combat) do always put the tank in the wing.
Bob

BtnFlyGuy

There is also the issue of "balance". The plane should balance right about the thickest part of the wing and the engine is located closer to or farther away to maintain that balance. there is really nothing to the advantage of having the engine close to the leading edge. Most stunt planes have the engine mounted further from the leading edge even than sport planes. Some flyers contend this makes the plane smoother in it's overall response and not as erratic as, say, a flying wing or fast combat. If you ever saw me fly, though you could say it makes no bloody difference where i put the tank, the wing, the tail or the engine.. it's all going into the ground sooner or later. I'm a much better designer/builder than flyer.
The most important point in (an un-pressurized) tank placement is to have the fuel pickup even with the jet in the engine venturi. Give yourself a means to adjust the tank since even a paper's thickness up or down can make a difference in the engine run.

icerinkdad

Chuckling... if you watch a combat match carefully you will find that the best combat wings are not erratic. The pilots can fly them without watching their own planes (the better to keep an eye on the other guy). It is mostly a matter of balance. I have watched combat guys practice by themselves without looking at the plane for quite awhile including flying figure eights and loops... that helps the best of them stay out of the way when a sport flyer like me gets in a match... they wait for me to make a mistake and pounce!
If you have a very short nose on the plane the tail has to be kept very light to keep the balance forward of the 25% point of the airfoil. I know this digresses from the original question but other things come into play with long nose airplanes... like momentum when you start moving the plane in a loop. Take a 5 pound weight and hold it close to your body and start spinning... stopping is relatively easy. Now hold it at arms length and spin at the same speed. When you come to a sudden stop your arm wants to keep moving. Same for a long nose on an airplane. It puts additional stress on an airframe and requires better construction and the pilot has to stop turning (level out) sooner to compensate.
All in all keeping the length of the nose reasonable helps performance. A lot of model airplane engineering is of the TLAR (that looks about right) kind. A longish nose requires an equally long tale to help with both balance and the leverage needed to swing that weight. So for sport models keeping it short works. Its all a matter of what you want.... now if you design your own plane with a very short nose and a long tail good luck on controling it... as getting the balance right will be difficult without some extra weight in the nose....

BtnFlyGuy

Ice, I have an advanced degree in both TLAR and "re-kitting". Iagree with you about the combat guys; they simply amaze me. I'm in the "build and fly for fun" catagory, but as a retired engineer and boat builder Ireally enjoy the technical aspects of this sport. Ijust don't take it to extreme. My pet peeve someone who builds a plane and slaps a less than attractive finish on it just to get it up in the air.
Back to tanks, has anyone ever made a plastic wedge tank? Idon't mind making my own metal tanks or scrounging on EBay, but I'd sure like to have something Ican count on. I'd like to see a plastic wedge with a "clunk" style pickup. Isuppose Icould mount a rectangular on edge and take the humorous heat from the guys at the club. (Unless it works, in which case they would claim to have thought of it first.)

Jim Thomerson

People use regular RC clunk tanks on stunt airplanes with good results. A friend makes metal clunk tanks which work fine. All should be uniflowed, of course. Some use a separate clunk on the uniflow line, some attach the uniflow line to the pickup clunk, some use a hard tube uniflow at the front of the tank. I use metal tanks with everything soldered in place.

JohnBuckner

My Feedback: (1)

I get constant attitude from controlline traditionalist whenever I suggest a modern Tetra or Jett bubbless tank for controlline but you cannot find a better more uniform and reliable fuel delivery system and with no fine tuning required. Think about that 'no fine tuning of the tank'.

Try it once and you will never go back to conventional controlline suction systems.

Fytch

hey john!

may i know how does that work? it is like a bladder to supply pressured feed to the engine??

thanks
Reeve

JohnBuckner

My Feedback: (1)

It is not an expanded bladder providing high pressure such as used with some combat types but it does provide muffler pressure if muffler pressure is avalible in a far more effective way than the common RC muffler pressure/suction systems and far better that the common controlline suction systems.

It uses a hard outter shell that look a lot like a common RC tank with an inner bladder. There is no clunk only a single fuel line to the inside of the bladder in the middle. Muffler pressure is routed to a nipple that applies pressure between the hard shell and the inner bladder. Therefore no combustion gasses can ever reach the fuel and no air can be introduced even from just fueling when done right. This makes bubbles impossible from a full tank to the very last drop. You will not get a more uniform delivery for the duration of the run with any other unregulated system.

Additional hugh advantages are they will perform easily aft as far as the CG and tank position or orientation is not critical at all.

John

BtnFlyGuy

That's pretty nifty! Ihad never seen such a rig, but Ican understand the great effect it must have removing the "bubbleator" effect of direct exhaust pressure.

JohnBuckner

My Feedback: (1)

He, he "Bubbleator Effect" Oh man I gotta remember that one with your permission

John

BtnFlyGuy

John, I'd be honored anytime you chose to quote me.

Fytch

oh, that sounds interesting! i shall try to get a kit and try that soon =)

btw guys, anyone has a OS LA .15 stunt wing plan i could have?? i was thinking of building a faster plane which is able to do stunts.. but not as fast as combat though..

thanks guys

Reeve

icerinkdad

Cool... seems what goes around comes around.... re the Tetra tanks Jim Walker used unpressurized baloon tanks set up like the bladder in those except since he had no muffler he got by with only atmospheric pressure... I remember it working quite well with a 1/2A engine. The key was to find a balloon big enough so that you didnt have to actually inflate it.
Bob

cutaway

I've got some old slow combat planes where the LE is notched out and the tank inset into it. That scheme works fine. These are foamies though. Some structural mods would be needed to to the same with a wood wing.

As a general statement, keeping your "necessary" mass (engine, tank, etc) as close to the CG as possible, and the extremities as light as possible is goodness. The lighter a nose is, the less force control surfaces need to exert to initiate, and STOP, a turn. Extremity heavy pigs, feel like they're skidding around the sky. Extremity light airplanes feel like they're dancing on air and "flit" around like dragonflies.

[link=http://www.rcuniverse.com/forum/m_6837644/anchors_6837644/mpage_1/key_/anchor/tm.htm#6837644]This flapless stunt plane of mine[/link] has light extremities and out turns almost every serious competition stunt plane I've ever seen and does it with only about 20 degrees of elevator throw in each direction. The minimal control throw and lightness help keep it from slowing down in turns...which means a less powerful motor than might be expected will fly the thing successfully.

Jim Thomerson

I haven't used a Tettra tank, but they should work fine. Someone posted on putting the fuel ouside the bladder and running muffler pressure into the bladder. Suppose that would work OK also. [X(]

JohnBuckner

My Feedback: (1)

Here is a link to Tetra bubbless tanks at Central Hobbies, avaliable from three to fourteen ounce.

Not cheap but I will use nothing else in any controlliner with muffler or pipe pressure avaliable or any of my pylon ships and on occassion some problamatical sport RC applications.

Be carefull and assure you are buying bubbless types if you do because they also sell numerous conventional clunk type tetra tanks also.

Jim reversing the plumbing on genuine Tetra bubbless and placing the fuel between the bladder and hardshell certainly may work however makes no sense at all. At best it will be slightly less efficient with the poorly placed pressure port in the hardshell now becoming the feed line.

That silly idea is best filed away with ideas folks just cannot resist in attempts to fix imaginary faults or problems that just don,t exist.

http://www.centralhobbies.com/Fuel/fueltnk2.html

John

build light

Getting back to the original question, and by the way a very good one, what plane you have been considering to shorten the nose of?

Robert

Hossfly

Don't forget that Jett engineering has a fine supply of bubbless tanks. http://www.jettengineering.com/

I have not tried one for CL Stunt but very well may real soon. I do like the 2-4 break for CL Stunt. Can't get away from it!

OTOH, the bubbless tanks are something else for RC. You need to fill with a syringe. You need to pull the air out of the tank first. Gets a bit tedious for the everyday flier but you can't believe the engine performance until you use one and get use to it.

One advantage that I have noticed with my .40 size RC machines is the additional flying time on the fuel. The engine run is so stable that it seems that I get a good 30% or better time using the Jett Bladder tanks. One of these has a tetra. I forget which one.

jayseas

I had no specific plane in mind, i was wondering if it would allow for better performance.

Jim Thomerson

Two general considerations. Most important is having the CG in the right place; too far back and you have a very unstable to unflyable airplane. On the other hand, there is the 'barbell effect'. Torque is force times distance. So one might move the engine forward to move the CG forward. On the other hand, moment of inertia, the resistance to turning, or the resistance to stopping turning, is weight times distance squared. So one might be better off adding a heavy hub or some weight to the nose rather than lengthening the nose, should one want to move the Cg forward.

Fytch

guys, how do i set up an uniflow tank??

Jim Thomerson

Here is what can be done with a hard tank. The usual is to solder the uniflow tube to the fuel pick up tube, about 1/2 inch in front of the end of the pick up. I have built uniflow tanks with the uniflow anywhere from that position forward to soldered to the front of the tank. All worked fine. The Palmer tank, probably the first uniflow used in stunt, has the uniflow at the front outside corner as said above. The tank I am flying now has a longitudinal baffle. Too much trouble to run the uniflow through the baffle, so it is on the inside of the baffle. The tank comes off the uniflow, and the engine richens up, maybe four or five laps before out of fuel.

On my Humongous (pictured on the RSM kit box) I used a K&B 4011 which had a venturi with the NVA about an inch above the bearers. I used an inch thick tank and put the uniflow outlet against the top rear of the tank, right where the wedge started. It ran perfect, except that in a high wind, the engine would wind up on the fourth and fifth outside loops.

If not running muffler pressure, I put a one way valve on the uniflow to stop any possible siphoning, and mitigate any changes in outside air pressure.

DaveSR71

I think Brodack supplies tanks based on the old Veco/Clary/ Fox tanks and uniflows as well.

I have not had to buy any tanks yet, am still using left over stuff from 70s.

jayseas

Should i be useing a one way valve on all my uniflow tanks. if not running a muffler?