Liquid fueling

[metiz]

I want to get into liquid fueling. I've been tugging around propane tanks for to long now, time for a change. I eventually want to get into valveless planes, starting off with a plane that will carry my 40 pound chinese. Looking for a big plane that does not have a high top speed to get into things (having the time to panic AND make course corrections would be fantastic )

I've been getting some advice from people but nothing realy into detail.

Asuming big engines, 40+ pounds:

(1) What kind of fuel is the best choice
(2) What kind of fuel pump do I need, where can I get it
(3) Should I start with an atomizing nozzle or should I use a vapour coil
(4) adding to the above, is a vapour fueling system suitable for flight engines?
(5) what kind of injectors do I need?


Any people that have some experience with this sort of thing can help me out here? I'm willing to spend the money and I'll post all results on the forum.

[Johansson]

40 pounds in a RC plane? Are you going to build a 1:4 Boeing 747 model?

[metiz]

a model resembling the plane on top of the forum should be a good place to start

[Eric]

That wouldn't be the best idea, target drones are made for flying fast in a straight line, if you try to do tight turns like you would need to on a RC plane, it will literally fall out of the sky. V tail planes are also touchy.

To say that putting a 40lb thrust engine on a trainer plane, would be unwise, is an understatement. If you lose radio contact there's the possibility it could fly many many miles, before leveling a house.

[Bruce Simpson]

I want to get into liquid fueling. I've been tugging around propane tanks for to long now, time for a change. I eventually want to get into valveless planes, starting off with a plane that will carry my 40 pound chinese. Looking for a big plane that does not have a high top speed to get into things (having the time to panic AND make course corrections would be fantastic )

I've been getting some advice from people but nothing realy into detail.

Asuming big engines, 40+ pounds:

40lbs is a *lot* of thrust and will cause problems for several reasons.

Firstly, you will need a large model to carry an engine that size and the fuel it will consume.

Secondly, In most countries, models over a certain weight (20Kg here in NZ) require certification by a suitable authority. They're no longer "toy planes" and the potential danger they pose to the public means they have to be carefully scrutinized throughout the build process and prior to flight. To illegally fly such a model risks significant civil and criminal liability.

(1) What kind of fuel is the best choice

Gasoline is the easiest and most weight/volume-efficient fuel for this kind of application.

It vaporizes fairly easily, has a decent stoichiometric ratio (so you don't need so much) and is cheap/readily available compared to most other options.

I have successfully used Jet-A1 in larger engines but it has combustion modifiers in it which reduce the speed of the flame-front (designed to make it less "explosive" in a crash) and that makes it very difficult to use in small engines -- it simply doesn't burn fast enough.

(2) What kind of fuel pump do I need, where can I get it

An automotive fuel pump (rail pump) will be needed for an engine this size. You can get these from automotive wreckers and most will deliver at least 65psi of pressure with good flow rates. These are typically a vane-type positive displacement pump. Don't get duped into buying a low-pressure diphram pump, they won't deliver nearly enough pressure.

(3) Should I start with an atomizing nozzle or should I use a vapour coil

I'd vote for an atomizing nozzle. They don't require starting on a secondary fuel (such as propane) or any warm-up and deliver far more consistent runs than a vapor coil setup, especially if you intend to throttle this engine.

(4) adding to the above, is a vapour fueling system suitable for flight engines?

I wouldn't use one -- mainly because they don't give precise enough throttle control and aren't as reliable as a good pump/nozzle setup.

(5) what kind of injectors do I need?

Get some spray nozzles of the type used in boilers. There are a bewildering array of options (flow, cone-angle, solid/hollow-pattern, etc) so you'll have to do a bit of trial and error to get it right. You should be able to work out the required fuel-flow from your TSFC figure and the projected thrust levels. Don't make the mistake of just getting the highest-flow nozzle you can -- that will compromise performance at lower power levels. One system I've used very successfully is to have an idle nozzle and a main-flow nozzle. The idle nozzle is a low-flow unit so that you get excellent atomization at low flow rates and the main nozzle is for providing the fuel for "above idle" operation. This setup also eases startup, allowing for low-power starts -- which also require little or no forced air, depending on the engine design.

I hope this helps.

[metiz]

Thanks for all the help, very usefull indeed

I think I'll head everybody's warning and not go with the 40 pound plane plan. The reasons for wanting to use a 40 pounder were that the bigger the engine the easier the liquid fueling becomes and that a realy big plane would be a more slow "glider" like plane where you can afford making slight stearing mistakes and still have the time to respond instead of having to do so in half a second lest your planes crashes and burn. That and I have a 40 pound engine ready to go.

So how about a 20 pound engine? Asuming similar RC plane rules in the Netherlands, I should be able to get the weight of such a plane under 20kg easily.

[Eric]

Half of huge is still too big.

I'd say no more than 10, and thats probably pushing it.

A 10 lb engine could still push a big plane at considerable speed, big with a low power to weight ratio doesnt necessarily mean slow, it might not accelerate as fast but could still be capable of going faster than you could control.

I'd go with a 6 lb engine with a big draggy augmenter on it, so that you have low speed power that drops off to about 6 lbs at speed.

[Bruce Simpson]

I'm running 10lbs-thrust valved engines on my model aircraft now and they are *more* than powerful enough for the average ARF model.

As an example, the TameCat ARF weighs in at 6.5lbs (plus another 0.5lbs for fuel) and with a 10lbs-thrust engine it is very fast, despite its huge wing area and very draggy body.

The advantage of an 8-10lbs engine is that there are plenty of cheap ARF models that you can fit these engines to. I've converted a Long-EZ, BobCat52 and TameCat to pulsejet and in every case, once I sorted them out, they were decidedly overpowered compared to the prop-driven versions.

[Mike Everman]

Nice input, Bruce and Eric! Thanks.

[larry cottrill]

Metiz -

I hope you will forgive this blasphemy as it stems from a lifelong prejudice and will be slammed by just about everybody, but here goes: Why radio? If the point is to experiment with liquid fueling while training yourself to fly a model while at the same time avoiding the destruction of life and property, why not U-control? For a 10-pound thrust engine, a model of at least 6 ft wingspan (i.e. 2 metres) with a lot of wing area and a big, thick airfoil would handle it nicely, especially considering the drag of a pair of 80 ft stainless control wires. If you think you can find enough space to fly a jet R/C model, you can surely find a 160-ft diameter clear patch of more-or-less level ground to fly from. Tricycle gear with huge "larger-than-scale" tires would help takeoff and landing and add significant drag.

You would have absolutely dead certain positive control; you can arrange and re-set the control sensitivity as low or wild as you like; if the wing is big and draggy enough, you'd have speeds in the sub-100 MPH range; your fuel system could be extraordinarily simple; your plane and the engine itself (if kept exposed) would be easy to observe at all times during flight, since the distance from you remains fixed; I could go on and on. I can tell you, I learned a LOT by building and flying a jet this way just a few times! And yes, bigger planes than what I've just specified HAVE been flown U/C.

My original jet trainer for the Dynajet weighed in at SIX POUNDS (!), did 90 MPH on 80-ft braided bronze fishing lines and flew like a charm. Its only real drawback was the high line pull (calculated ~ 25 lb), since I only weighed in at about 120 lb myself at the time. I had to really dig in my heels and lean back to hold it. But, I always had perfect control. The wing of that model is rather thin, 4 ft wingspan -- a solid hard balsa plank carved to a lifting airfoil. The construction could have been much lighter ans draggier, of course. The glide and landing were beautiful to see, I was told. Tricycle gear with three 4-inch rubber tires.

Oh, well ... just a thought.

L Cottrill

[metiz]

Hey Larry thanks for the imput

sooo....what's "u-control"?

[Mark]

http://en.wikipedia.org/wiki/Control_line

[PyroJoe]

Hi metiz,
I echo Larry's views on starting with the u-controls. The investment to learning ratio is excellent. The noclass mac site has a Glider Trainer (looks to be a russian trainer) in their DEC 2007 .pdf found here:

http://www.noclassmac.com/NoclassFlyer/ ... index.html

I like the simple construction, and the ability to train without the need for a engine or anything electrical.

[larry cottrill]

Thanks, Mark -- I was actually surprised at how good an article that is. And, it is correct that, generically, we should call it "control line" flying since U-Control is, in fact, a trademark name. However, there are thousands of us who will always think of control line flying as "U-Control", especially those of us who have never used the mono-line method.

The only thing in any way "difficult" about describing control-line flying (and something confusing to beginners) is that UP control does not always make the model go up and DOWN control does not always make it go down. The reality is as follows:
- LEVEL control makes the model fly a great circle (NOT necessarily level !!!) around the imaginary sphere
- UP control makes the model rotate in the direction of an inside loop
- DOWN control makes the model rotate in the direction of an outside loop

Thus, to make the model climb quickly in a brief 45-degree "ramp", I would briefly deliver a sharp UP control, then LEVEL during the brief climb, then a sharp, brief DOWN control to level the model out at the higher altitude position. To ramp back down would be a sharp DOWN, brief LEVEL, and sharp UP to level her out again at shoulder height. The problem with this description is that it makes it all sound intricate and difficult, and it DOES require a good sense of timing and hand/eye coordination -- however, when a fairly slow training model is set up with relatively low control sensitivity, the technique becomes completely natural in almost no time.

As suggested in the article, the chief limitation is that you only have pitch control, i.e. your model is limited to operation on the surface of an imaginary sphere with one side of the model always facing you. One very nice advantage (in my experience) is that you actually have the "feel" of the controls at the handle (in the case of large models). Larger control line models require a lot of room to operate, but have the advantage that they aren't troubled by light winds. Stunt maneuvers should always be done on the side of the sphere where the wind is at your back, since that ensures tightness of the lines and therefore, very sure control.

L Cottrill

[Bruce Simpson]

Larry, when learning to fly U-control you don't "ramp' or jerk the controls at all.

U-control models can actually be *very* easy to fly.

Hold the handle vertically so that the rearmost control line is at the top of the handle. U-control models are set up so that pulling on the rear line makes the elevator go up.

Keep your arm and wrist straight.

If you point your entire arm at the model, the elevator should be level

If you lift your whole arm (to say a 15 degree angle above level) then the elevator on the model will move to the up position but, as the model rises so that it is once again in line with your arm, the elevator will return to the neutral position so the model will stop climbing and a straight line will again exist from your shoulder, through your arm through the wings of the model.

This works because when you raise your arm (with a rigid wrist), you're effectively applying tension to the top/rear line which causes the elevator to go up.

Likewise, when you lower your arm so that it's below the model, tension is applied to the bottom/front line which causes the elevator to go down.

With the straight arm technique, controlling the model is simply a case of raising and lowering your entire arm -- the model will follow. What you have here is a negative-feedback control loop that is self-correcting.

Once you are familiar with the model's flying characteristics, then you can relax your arm and use wrist movements to control the model but the rigid-arm method makes it *very* easy to fly these things if you've never done it before.

Using this technique I've seen 8-year-olds with absolutely no experience fly a full tank of fuel on their first attempt.