FAQ Discussion List

Question - How Do I tune my model engine? I messed up the factory setting.   How do I setup my low end needle
Answer   Here are some tips to make you an expert at tuning model engines .
FIRST - Don't play with the settings on a new engine, because the manufacturer will have put the optimum settings on already. We can reset the fast settings ok if they are messed up. But we cannot reset the idle settings properly until after the engine runs in and loosens up, allowing it to idle unhindered by the new tightness all new engines have We can only guesstimate fair idle settings to a certain degree on a new engine. then later on after running in, we fine tune the idle until it is at optimum. So if you mess up the idle settings on a new engine, you will probably have it a bit harder to deal with for the first 30 minutes to 2 hours run time. What follows is how you proceed if everything is totally "played with" and "messed up" on any engine, new or old if you are an expert at tuning.
How to setup the needles so you can get your engine started:
1. Idle needle controls the fuel:air mixture below 25% throttle. Use it to adjust the idle and the transition zone from idle to fast aprox 25-35% throttle. Adjust it at 50% throttle, then throttle down to 15% throttle wait 20 seconds to observe the effects of the adjustment.
2. Fast needle controls the fuel:air mixture from 30% throttle to full. Adjust it at full throttle.

Start by screwing the main (fast jet knob) in until it is fully closed. then unscrew the fast needle out until 3 1/2 turns out from fully closed. Now you have a rough and ready setting on the main fast jet so you can adjust setting for the the idle jet .
Set the idle jet at a rough and ready basis point as follows:   Close low end needle valve completely.
Place a 6 inch piece of fuel tubing onto the fuel inlet nipple.   Using throttle servo, throttle up the carburettor to 20% of a circle in the air inlet opening .
Blow into fuel tube and simultaneously slowly unscrew the idle needle . Stop unscrewing idle needle when the air from your mouth begins to enter the carb through the tube or when you hear the hissing sound of air blowing into carb. The flow should be very small. At idle speed (20% throttle) only a trickle of fuel (air in our test ) should enter the carb. This idle setting allows you engine to start but needs to be fine tuned. This is just a ball park setting.
Now close high end needle valve and open carb to full throttle. Blow in fuel tubing and simultaneously open high end needle until you have FREE FLOW of air into carb. You should not experience as much resistance to airpressure as you did on the low end. Your needle valve should be open between 2-5 turns (it all depends on the carb folks).

Starting procedure:
First start engine this way:
Prime engine by opening up throttle to full and block carb air intake hole (or exhaust exit) with finger. With blocked air inlet (or exhaust), rotate propeller anticlockwise until fuel travels up the transparent fuel line and reaches carp fuel inlet nipple. Now turn the prop another 2 and a half full revolutions (2-stroke engine) or 4 and a half revolutions (4-stroke engine) to draw the fuel into the engine and up to the piston.

Reduce throttle from full to 20% throttle (look into the air opening = 1/6th of a full moon open). Apply glow start to heat up glow plug and rotate engine (with finger or 12V starting motor) anticlockwise until engine starts. When engine starts, move throttle to 1/2 throttle, wait 10 seconds and then remove glow start. Do not pass your hand through the prop "disk" to reach towards the glow start. take an exaggerated "safe distance" route with your hand when you remove it.

If engine won't start, vary throttle 5% up and down. If engine will only start above 1/2 throttle, it means your initial low end needle setting was too lean. Richen it by unscrewing about an 1/8th of a turn until the engine starts at start throttle =20% throttle.

Increase throttle again to 1/2 throttle slowly. If engine dies (cuts out like as by a switch) then your low end needle is probably too lean. Richen by (on a clock) 5 minute adjustments screwing out. If engine dies (chokes, grunts, sags, slows down) then your low end needle is probably too rich. Lean by (on a clock) 5 minute adjustments screwing in.

When the engine is warmed up (30 seconds) remove glow start and advance throttle to fast. Chances are your engine will be too rich and may even quit by choking and slow sagging Lean out (screw in) the fast jet a quarter turn. This is a ball park adjustment to get your engine is running at wide open throttle (WOT) so you can then tune it better.

With engine running at full throttle, slowly and carefully lean the high end needle valve until the engine is spinning at its max rpm. This can easily be determined by sound - the pitch rises noticeably. This is where engine is producing most power but the mixture setting will cause the engine to run too hot and overheat. Indeed after 30 seconds you might see the engine slow down by itself as it gets tight due to too much heat. So, to protect your engine form damage, now richen the fast jet a couple of clicks (about 5 minutes on the clock screwed out). Verify this by briefly pinching and releasing the fuel line to the carb. If the pinch test causes the engine to speed up and back down, then you have correctly set your high end needle setting. If engine doesn't speed up much or dies then you are still to lean and need to richen the mixture until it passes the pinch test.

To finish the job nicely - with fast tuning set a little rich and slightly below max power, recheck idle and transition settings. Let engine idle for 30-60 seconds and then snap throttle to WOT. If engine hesitates in the transition, fine tune mixture so that the transition is snappy and idle is reliable. An over rich idle setting allows excess fuel to build up (at idle) in the lower crankcase and when you go to speed up (after say 30 seconds or longer) it sags as the extra fuel gets sucked up all at once, temporarily making it too rich. But it will throttle up if you do it slow enough, this is a sure sign the idle is still a tad rich. Lean the idle out a teeny bit more for perfection.

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(For other engines like OS read the last paragraph first! Then go back here and read down.)

1 GX 5 castor oil based fuel is the ideal fuel to run it in, even for engines which will use synthetic fuel later use 1 litre of castor oil fuel first.
2 on that fuel - if you get it good and hot it will be run in on 1.75 galls, but if you let it idle away cool, the metal is harder and it will be run in on 2.5 galls.
3 the correct idle setting during the entire running in process (MVVS) is a gap of 1.2 mm between cross needle mount and carburettor case.
4 the correct main needle setting during running in begins at 3 turns open from fully closed, and ends at about 1.5 to 1.75 turns open, depending on engine
5 the process is: start, with main needle rich, rev up, lean out to heat it up. Now this reduction of fuel (+ lube oil in the fuel) will cause a slow heat build up (heats faster than air cooling takes heat away) which will cause it to tighten up, and cut out "dead stick" .

The time before dead stick cut out is a function of how much you leaned it out, air temp, and speed of heat build up which depends on how tight it still is, and how far you throttle up.

Rev it up to make it hot, and listen carefully to hear it begin to tighten and slow. You now have about 3 seconds to throttle down to prevent cut out. or you are slow and restart it.

NOW LET IT COOL, by running slow for a minute, and by opening the main needle a 1/4 turn.

Say you didn't lean it out before revving it up again, or didn't wait 30 seconds after leaning, it has built up extra cooling oil in the bottom of the engine. And when you rev up it sucks all that into the engine at once, and cools at the time it should be heating and making more rpm/power.
THATS WHY it revs up in a grumbling sort of way. If you leave it rich, you must have throttled down 1 second before (no time for fuel build up going slow) revving up again immediately. Once the oil builds up (slow over 15 seconds on rich setting) you have to throttle up SLOWLY to give it time to take in the excess juice.

Every time you lean out and then speed up, it "runs in" a little more, and gets "looser" and more friction free. This makes it create less heat when going fast (while lean).
The improvement at full throttle is gradual, and can be seen improving each time. The engine will soon get to the point where at full throttle the air cooling takes away more heat than it can make, and dead sticking will stop happening. On that tank of fuel, the idle will pass a critical threshold for friction, and you will notice that one time you throttle down the idle has become smooth all suddenly.

AFTER THIS STAGE IS REACHED:
Then and only then adjust the idle needle in 5 minute adjustments, in to lean out and speed up idle. Out to slow down idle.
Remember that idle fuel feed passes over to main fuel feed at 20-30% throttle.
So too lean will make idle snappy and nice, but dead stick at 30% due to lack of fuel, just before main fuel feed takes over.
Over rich idle makes idle "grumbling" similar to the way main throttling was grumbling when main needle was rich during running in. And time is required to throttle up from 10% to 30% throttle.
Adjust idle.
NOW REV UP to remove the built up fuel inside, and THEN REV DOWN AGAIN to observe the result of your adjustment on idling. You will achieve a smoothness of idle that only a few other engines can do.
From this point on, the MVVS will flick start every time with no need for starter motor.

The thing to remember about high compression engine like MVVS, West, Webra, Rossi ... idle needle can not be tuned even slightly until after running in is complete.
Until then engine is too tight/hot to idle at all, (or to go at max throttle for more than x seconds = heat = tightens up = dead stick cut out).
After this type of high compression engine loosens up, it is more powerful at low throttle than low compression engines, and that explains why it can develop power from one flick to start every time.
And also explains why it can have enough power at low throttle to be more smooth at that low idle throttle than low compression engines. (which is why the guys with those particular engines have to use extra high nitro to make idle smoother) .

You have full power with 0% nitro or 5%. And if you add expensive 10% or higher nitro fuel no more power will come, it will just make a rattle noise. Waste of expensive fuel. Also burns out glow plugs.

If you bought a low compression “easy to tune” type of engine, then swop the 0% to 5% nitro fuel for more nitro. Say 10% to 16%. Then all the above applies to your OS LA, SC, Thunder Tiger, GMS, Evolution or whatever. You may have to go away from the makers recommended glow plug to achieve 100% reliable flick starting with those engines but once you have the right plug it can be done.
Irvine, Super Tigre and OS FX/SX or AX are half way between the two types in characteristics, and fuel (nitro) needs.
On these "softer" engines, for metallurgical reasons, the running in time is reduced by about half of what it says above.

Question - I am confused by all the fuel types - what should I use in my engine?
Answer That depends on what you want to do. However here is a fuel guide that won't let you down....

For cars: Always Run new engines in on Castor oil based fuel with no more than 5% nitro and at least 18% oil. I suggest Model Technics GX-5. This is 5% nitro and 20% oil. After it is run in, you can either stay on the GX-5 if you are happy with performance (and many car users are), or you can move up to higher nitro eg 10%. as in GX-10 fuel. But if you are using a monster truck, or a rally car on race tracks, you will probably prefer the castor oil based GX-16.
At some point when you are happy you can tune your engine easily, change from castor oil based fuel to synthetic oil based fuel.. Your engine runs nicer, and cleaner on synthetic. To do this you just swop the GX-5 for Go Glo Plus 5, or GX-10 for Go Glo Plus 10, or GX-16 for Go Glo Plus 16 and keep the nitro the same.

For airplanes: Always Run new engines in on Castor oil based fuel with no more than 5% nitro and 18% oil. I suggest Model Technics GX-5. (5% nitro and 20% castor oil) After it is run in, you can either stay on the GX-5 if you are happy with performance (and many plane model fliers are), or you can model to synthetic based Go Glo Plus 5, (5% nitro, 3% castor oil, 15% synthetic oil) which is much cleaner and easier to clean off your model when you finish flying for the day.

How to decide how much nitro is correct for planes?
Well if you have a low compression engine (eg OS, Enya, GMS, Super Custom, MDS, Irvine, Evolution) then you will like a bit more torque and more nitro will give it. So you then should move from Go Glo Plus 5 up to Go Glo Plus 10.

But if you bought a high compression engine (eg MVVS, West, Webra, Rossi) then you will already have all the torque you need to fly well, and there is no need to ever increase the nitro of your fuel over 5%. You may even find that 5% nitro makes your high compression into a bit of a highly strung racehorse. If this should be the case, then try some straight fuel like the castor based GX-0, or the synthetic Go Glo Plus 0 (straight = 0% nitro). Now your fuel cost reduces, and you still have oodles of power.

If your plane has a very big engine of 1.20 size or more, no nitro is required. So just use straight (zero nitro) fuel.
If you have bought the YS 4-stroke you should use high nitro-high cooling fuel. The 20:20 or 25:22 mixes will be nice. The first number refers to nitro and the second refers to cooling oil, so 25:22 fuel would be 25% nitro, 22% synthetic oil (best quality) and the rest methanol. Green Hobby & Model make these blends up as required.

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Q - Model Engine Eating Glow Plugs
I have had this engine for about a year and a half and in the last two months or so it has started going through glow plugs like crazy. It is tuned properly, I'm using new OS no 8 glowplugs, but about every third time we fly, it won't start and sure enough, as soon as we replace the glow plug it starts right up. Any suggestions?
Answer
What kind of fuel? Any fuel additives? Is it running hot or cool?
Also, check the exhaust residue carefully. If you see tiny shiny specks, you have some type of wear going on in the engine, and are shedding aluminum particles. These will kill a glow plug quickly.

CHECKLIST:
The crank can be in contact with the backplate - shedding metal fragments - was there an impact on the front of the prop shaft recently?

The conrod bearing can be wearing (from over-revving) shedding metal fragments, in this case the prop is too small for the lubrication (% oil content) present in your fuel. Use a wider prop diameter at lower rpm.

Too large a prop for the cooling oil present in the fuel causing overheating. Use a smaller prop at a more normal rpm, and normal running temperature.

The nitro % content of your fuel can be too high for the carb settings you have - that is the engine is running too hot, and the oil % content of your fuel is not sufficient to cool your engine - tune richer, and ASAP replace your fuel with a more oil rich, or lower nitro mix.

Are you running the engine hot, before it has completed it's running-in process? A tight engine (not run in yet) at top throttle, on a lean tuning setting, causes abnormally hot temperatures inside the engine and all or some of the symptoms discussed here.

Most common cause: engine is leaned out too much by tuning too lean at main carb needle = general wear, and piston damage.

Second most common cause: a tuned pipe has been put in place of the standard muffler, and the distance from cylinder exhaust port to the narrowing section of the pipe is too short. Result same as too much nitro, or too lean carb = detonation and piston damage.

If you are experiencing detonation, due to pre-ignition (short/small pipe), or over hot tuning/running, this can verified by taking off the cylinder head, and an inspection of the top of the piston.
Detonation causes the plug to blow, and at the same time it causes "pitting" of the piston crown. Little craters, like the surface of the moon, on the flat top of the piston. In this scenario, the third glowplug to blow (prematurely) is usually followed by a hole in the piston top if the cause is not removed and the engine is repeatedly used in this way.

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Q Should I Use After Run Oil?
Answer: Yes. You are wise to use after run oil when the model is finished the days running. There are technical reasons for this. The nitro in the fuel is essentially liquid oxygen, and the methanol is like blotting paper, that is, it soaks up moisture out of the air. The engine is made up of different metals, and stainless steel, aluminium and brass are unaffected, but the other steel parts will suffer rust while the model is unused in storage. After Run Oil helps prevent this rust.
After run oil asists another way too.... Your model has fuel in it while in storage, and the methanol will eventually evaporate, leaving the thickened oil behind. This oil clogs the fuel pipes and makes things difficult next time you take your model out to use it. The dried on castor oil is very hard to remove, like a coat of varnish.
So it is a good idea to buy a bottle of after run oil, and after the last run of the day, and after you empty the tank, drip 4 or 5 drops of after run into the carb air inlet, then turn the engine over 4 or 5 times (by rotating the prop with your finger - no glowstart connected! ) to draw the oil inside where it does its job, and protects your engine when it is not being used.

Q I have a new MVVS engine and the settings off my old engine don't work. What are the correct settings for the MVVS?
Answer: A high compression engine has different settings, and runs in differently to a low compression engine.
Here is where you look for the info on MVVS (it all applies to any other high compression engines also).
First the general info about engines is in the shop website here www.greenhobbymodel.com

The MVVS page is here if you want to go direct. It gives the fuel recommendations & so on. http://www.greenhobbymodel.com/MVVS.html
This link loses the menu bar, so you can't go round the website but it is more suitable for printing out.

For detailed running - in information you should next go to my own personal webpage here ...
http://www.greenhobbymodel.com/norm_flyer/index.htm
If you print out the info in the "running-in" page, you will see a lot of very useful information there.
There is a lot on it, and it's hard to take it all in in one go, so it is worth referring back to from time to time.

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Q Denatured alcohol in Ireland? Do you know where I could get me hands on "Denatured Alcohol"? Apparently it's cheap and works great as a cleaner for monster trucks due to the fact that it's a liquid but evaporates fairly quickly. I've tried quite a few places but no-one seems to have even heard about it.
Answer Pure Methanol works fine for this purpose. Green Hobby in Dublin have it.
They use it for making special model fuel blends for some modellers. Comes in 1 gallon containers for a tenner.
The obvious alternative is unleaded petrol, but the stink it makes !!
White spirit is also a contender as a cleaning agent but it smells strongly too, definitely not for in the house.
What alcohol,has in its favour is the lack of strong odour.
Meths is alcohol with a dye/taste agent added to prevent idiots killing themselves by drinking it.
Methanol is wood alcohol and is a perfect substitute, cheaper, clean, no colouring, low odour, evaporates quickly, leaves no residue - yet it dissolves oil based marks and residues well.

Aircraft modellers : a few drops of methanol thins epoxy glue and slows it down, so it can be used to slow 5 minute epoxy into 10-15 minute epoxy, a very useful set time when building in balsawood.

Car/truck modellers: if you clean the engine with a spirit, be aware that when it evaporates away it leaves the surface it cleaned "dry". So if you clean moving parts with methanol and an old toothbrush, you should put a bit of after run oil, or three in one oil to "wet" the metal, especially important with pistons, liners, and bearings.
Pariffin (or kerosene if you wish) can be used as a good substitute to "wet" the moving parts if needed.

Certain health and safety issues applies to all degreasing spirits. If it removes grease, it can also remove the protective oils we have in our skin. Therefore any toxic chemical which is also present in the degreasing spirit will then penetrate the skin.
Nitromorse, acetone, methanol, unleaded petrol, white spirit all are of a similar haxardous type.
If you are careless .....Methanol can therefore be drunk, breathed in vapour form absorbed through the skin, and you forgot to say it can set you on fire too!
Not only that, but the vapour is heavier than air, and therefore it goes to the ground, where a spark from a shoe stud or static electricity can cause you to blow up in an explosion.

All of the solvents mentioned above are flammable and due care should be exercised.

By the way, the benzine in unleaded petrol is also a very nasty item when allowed to get inside the body

It should be said here what normal practise when using these types of degreasing spirits is ...
1 Use barrier creams (vaseline )
2 Operate in an open well ventilated space.
3 Wear protective gloves
4 Wipe up spillage immediately
5 Don't smoke !
6 Soft soled shoes
7 Replace the top on the container before proceeding to the next stage in your work.
8 Smaller containers are safer than large containers....it is wise to decant a small amount into a smaller bottle for use in jobs, and keep the "master" container in a cool safe place.
9 Wash hands after use, and before proceeding to the next job.
(If I missed any other safe practise points please feel free to add it)

The ultimate safe solvents for cleaning your model : ....
listed in order of safety : Soapy hot water ! ; Vodka ( yes ! ! ) ; Pariffin / kerosene / home heating oil

My personal top choices of the best solvents, listed for effectiveness and cost .....Acetone ; Fire retarded low vapour acetone ; Methanol ; Unleaded
Use with an old toothbrush or a rotary Dremel polishing tool.

Q Why do we empty the fuel tank when we have finished using the model?
Answer It is not the little bit of air above the fuel level in the tank that causes problems.
The fuel tank itself is not air sealed. There is a vent through the exhaust into the air. And also there is an opening through the carburettor needle into the air.
So the nitro evaporates out and leaves the fuel. Even worse the methanol is hygroscopic which means that it sucks airborne humidity and fills with water.
So the fuel degrades quickly while in the tank, like it is in a container with the top left off.
Methanol with atmospheric moisture absorbed into it is the reason for rust inside engines, not nitro. Synthetic oil does not prevent this. But a trace amount of 1% - 2% of castor oil in the fuel stops this. That is one of the reasons why we have a small amount of castor in our synthetic fuel.
A less important reason is that if not emptied, fuel can leak out of the model while in storage and make a mess of your car, garage or wherever the model goes while not being used.
It is a good idea to empty the tank. But it is a better idea to wrap the nose of the model so that both the exhaust and carburettor air openings are covered. A long scarf or piece of cloth is good for this. Just wind it around the front of the model from the prop back to the rear of the exhaust.

Answer If you are on 5% that will be a soft seize. No problem. It happens when the engine stops while hottish.
It stops hot, and no cooling is present after it stops.
the fuel for the next engine firing is sitting on top of the piston and it bakes/fries in a little brown ring of varnish around the piston edge.
You'll see it on the liner in the position of piston top, just below top dead centre.
(On 5%) The metal is not seized at all.

just take off the cylinder head, and use a cloth or dremel type felt polisher and some acetone, nail varnish remover, or white spirit. Don't use abrasives or a slight loss of power occurs, spirit is enough.
When the brown ring is gone, lube slightly with a drop or two of fuel, and put the head back on, then finish running in.

If an engine stops during running-in, and while it is hot, (ie after a fast revving period), assume that it's hot enough to do this again. And just walk to the car, and prime the engine, then pull starter cord once to bring in the extra cooling fuel, and it'll never happen to you again.

BTW , set it a little richer until it's a bit more run in than it is now. You probably just leaned it out a little soon, that's why it cut out in the first place, (assuming it didn't run out on empty tank).

You "might" need a new glowplug to finish running in, it will have got hot too and used a bit of it's life up. They generally don't last the running-in period, so the one in it may perform a bit tired when you get going again.

Question: I am choosing a brushless motor to put into a Spitfire which was recommended to use a Speed 600 brushed motor. I saw an ad for a "cheapo" outrunner which state 90% efficient. I am kind of suspicious of those numbers, they seem too good, 90% efficiency!.....Otherwise any suggestion for other motors

You are right to question the validity of such claims.
All outrunners are less efficient than inrunners. And a figure of 90% efficiency for an outrunner would mean that it is as good as the best outrunners in the world. But it costs 50? Obviously something doesn't make sense.
You could accept 90% efficiency figures if they were from Actro, Kontronik, Hacker or Lehner ..... So I also suspect that the specification you are reading seems to be "very optimistic" at best.

Remember that a 90% efficiency motor makes 10% heat from power used.
A 70% efficient motor makes 30% heat from the same power.
So without burning out, a top quality 90% efficient motor can convert almost 3 times the power of the budget motor and still only produce the same heat.

So if you use 500 watts of power ( eg12 cells at 40 amps = 480W) then a top class 90% efficient motor makes 10% heat or 50watts
But if a cheapie motor is 78% efficient then it loses 22% as heat = 110Watts. Ever try to hold a 100W lightbulb when it's switched on? What will happen in your plane is the cheap motor gets hotter and hotter until the glue holding the magnets in place fails, and then it burns out. Or you must use it on a lower power level to prevent this.

If you choose the cheap outrunner, I recommend you go for the next larger size - even though it is heavier.
Also - If you use a cheap outrunner, accept right now that the plane will fly in a low power way when you get it airborne.

Or get an Actro, Hacker, Kontronik or Lehner in the lighter size you prefer. Mega is almost as good as the best top class motors, but at a medium cost, which makes it excellent value. With these motors your model will weigh less, and also have substantially more power available.

My own suggestion = outrunner Actro C-8, or Mega 600.20.8. These are light and in the 350W area which might be enough).
Also interesting are the still more efficient inrunner Mega 22.20.3E (more powerful still 500W) or a Mega 22.30.4 (even more powerful at up to 800W). They are a bit heavier than an outrunner, but the Spitfire has a short nose, and is prone to be tail heavy, so the inrunner will keep the centre of gravity where it should be, and give you a better power setup.

These replace a brushed Speed 600 which was 190W continuous, and 300 for low motor runtime (10 seconds) and weighed 100g heavier.

Question: What would be a suitable thrust to weight ratio for an EDF jet? What types of ratios are you guys seeing coming out of your jets? Does someone need a 1:1 to have a "nice" flying EDF?
ANSWER Because of the fact that thrust varies a lot depending on whether you are stopped (taxiing) going slow (takeoff) or at full speed (in the air), thrust can be a misleading factor in appraising a EDF model jet.
You will find that most of the guys who are at it for a long time will look at power - to - weight which is measured in either Watts : Kilo .... .

Once you have got the hang of using watts = power , it becomes a simple matter to divide the watts by your battery pack voltage to find what amps will occur with this or that number of cells. It will swiftly become obvious that with a high voltage pack, the amps are lower., and everything works better.

Q I am considering getting a jet to add to my Hangar. I have been on your site but I could do with some direct advice.
1. Is there such a thing as a trainer Jet?
2. Is there something I can train on then use the gear to move on to something faster?
ANSWER Yes there are trainer jets. The secret is to make them smaller and cheaper for the first ones. Also don't cut the wingspan too much as they have a different shape, long fus & shorter wing, so disorientation is a possibility every now and then for a couple of seconds.
"Straight wing jets" make a good first model.
Characteristics are (compared with ic low-wing models) very clean airframe, slips through the air easy, doesn't decellerate much, or descend much on a throttle down, and easy to overshoot landings due to this until you get familiar.
Also when throttle is applied, it puts on a great clip of speed in no time at all, with no apparent effort.
IDEAS:
Are you interested in the jets with props on the nose? (I'm not ! )
There are some ARFs for .40 engine "jets" but the speed is down by 40-50% if you compare with EDF.
Would you try slope soaring a "true" jet with no engine? Speed and orientation is the same, but cost is much reduced.
And jets really slope soar like the clappers due to the clean shape.
If you want EDF, it can be done with a € 10 motor and a profile ARF for under €125 uning the Speed 400 type batteries.
If you want to see pics take a look at the pics of the profile Alphajet on my own website http://uk.geocities.com/norm_flyer/index.htm

The nicer EDF (scale) Aeronaut kits are about €150-250 for the kit and €125 for capable brushless engine, and €40-100 for the fan, depending on what you choose.
There is an Aeronaut Vampire hanging in the shop at the moment, that is mine - to be flown later this year. If you want to look at it.
Their Grumman Panther is to die for. And the Blade 2 - just ask to see it, it's inside the store. You don't need turbines with stuff of that standard.
Then there are turbines - if you have your mortgage organised !

My first jet was an AFF kit profile Alphajet. It had a speed 480 BB and three micro servos, and gave a year and a half service.
Then I did a BAe Hawk, beautiful model but unfortunately I eventually took it off with a reversed aileron.
Then a second profile alphajet, this one is a Klein Aviatik, with a lighter setup so it would fly with all my standard speed 400 model equipment, only the fan was extra, no expensive stuff inside, I've still got it. I fly it PSS - power on slope style. The 2nd Alphajet choice is understandable once you have had one, cheap , cheerful, good on the slope, easy to repair. But a bit fragile for flying from the club field I would think.
The Vampire is coming down out of the shop soon, and taking to the air. These is a video of one on the shop computer.
The A-10 Tankbuster is a twin jet, ready to fly now, but the power is huge, picture a 40 model with a 90 running flat out, and you get my drift. Anyway there is interference glitching on one throttle, so I need time to sort it out, and I'm not getting much time lately. It is waiting to be setup for flight for 3 months now. That is the pic on the shop website title page at the moment.
A hotliner or a pylon racer handles much the same as these models. If you tried a Voodoo, you would get the same very slippery kind of airframe.
I have a twinjet converted from twin prop, to single edf jet. Almost ready to go. . It is an interesting plaything that's not too serious.

Then there is the very nice ones, Rafale, Panther, Blade, L-39 Albatross. All are really nice. The L-39 is a straight wing. The Rafale, Blade and Panther are in the shop. You should look inside the boxes, they are beautifully made. . The L-39 is in the store at my place, so you would have to get me to bring it to the shop to have a close up inspection, some guys are putting Wren turbines into it, but the EDF version has more static thrust, and so gets away safer. Nothing wrong about how it flies with the Wren, it's super, it is just that you can have both a Rafale and a Blade, with all the tasty bits inside for the same amount of cash. So for me, they are all EDF jets, until RC kerosene turbines come down in price, like down to a quarter of what they are now.

Q I don't understand the propeller sizes... What is pitch? What size suits my engine?
ANSWER Two numbers describe propeller size; the diameter times the pitch in inches. For example, a 10 x 6 propeller is a prop of 10" in diameter and having 6" of pitch. The diameter is the length of the prop. The pitch is the distance the propeller will move ahead in a perfect or solid medium at 100% efficiency in one revolution.
Different sizes of motors require different size propellers to keep their operating rpm in an optimum range. Carbon electric props pull a lot harder than ordinary props because of their greater efficiency.

Q What do you think of, measure the velocity of the air exiting the exhaust duct in static then calculate the in flight air speed this may be a good ball park figure?
ANSWER Not really. If you think about it....
When the model is stopped the fan is acting as an air compressor and an air accelerator. A finger inserted into the airstream (a safe distance) in front of the intake can detect the low pressure vacuum zone there (note - this is a very dangerous thing to do! )
But when it is in motion, the air arrives in the intake at no power cost, so the fan then acts as an accelerator only.
The drag of the duct inefficiencies are present in both cases, so may be disregarded for comparisons.

A crude idea is to assume 10% lower power requirements (measured in watts) dynamic versus 10% higher power requirements static.

But did you notice I am still talking about power, not thrust. Thrust can't melt your speed controller or batteries, power demands can. And it is power that keeps your plane off the ground.
In automotive terms thrust might be the gear you have selected, but power is the size of engine under the bonnet.
A lot people think thrust is speed. But thrust diminishes in forward flight. In fact – at full speed - thrust is zero.

Q. Speed Controller Power Cut-off Information. I`ve fitted it to the Plane, but there is a difference between this one and the circular one I had, ....being that the motor dies down like a battery, the servos still work grand in this situation, where as the other one stopped working but I got a good blast from the motor at intervals to get it back, especially when I find the plane downwind and need a good whack to fight against the wind, as apposed to the constant dying out of the motor?? hope i explained it ,sound familiar?
It sounds like your first electronic speed controller may have been a Kontronik. And your new one is a TMM. The Kontronik ESC (either square and yellow in colour with a silvery label - OR -a round circuit board and stuck on the motor backplate) has an undervoltage cutoff.
What this does is cuts off the power to the motor when your battery is nearly empty. This saves power for the servos & receiver to keep them operating, and you can glide under control. But if you throttle down to zero, after 1 second it resets itself. Then you can get a further 1-2 bursts ..."to fly out of trouble" so to speak, before it cuts motor again. However this empties the battery and your receiver is in danger of shutting down after the second or third reset and motor pulse.
The TMM brushless is a similar setup, but the TMM brushed (can motor) controller allows the motor to "wind down" as the battery "gets soft".
As pilots, our senses are more sensitive than the controller electronics so we feel this softening (in flying characteristics) a bit earlier than the cutoff circuit would see it. So we can fly it soft for maybe one more pass, and then prepare to land. Note you would not ignore the cutoff message, so don’t feel tempted to ignore the softening message either. You are maybe 30 – 60 seconds to from where the cutoff would operate with the other setup.
There is a third type of controller that pulses the throttle "vroom-vroom style" to let you know then end is coming.
BTW If it is the TMM you've got, (and we are doing more of these now), then your servos get more power, and can work a bit better. That is one of the reasons we like them.

Question: What happens when you change prop diameter?
As you increase pitch - power required goes up arithmetically
As you increase diameter - power required goes up geometrically.
So a 50% increase in pitch needs 50% mor power, but a 50% increase in diameter needs more than 100% more power.

Diameter gives you "grip" or "traction" onto the air, and benefits acceleration or climbing efficiencies.
So hotliner gliders, 3D funfly and helicopters have wide diameter (usually low pitch) props for climbing.
Indoor planes work better with a wide shallow pitch propeller too because their flight is slow the wings don't carry much load so they are "climbing" or "prop hanging" a lot.

But if you fly horizontal and allow the wings to carry the weight of your model, and are content to zoom around, airplane style, then a smaller diameter prop will consume less power, and allow longer flights, since your fuel (liquid or electric) will last longer - due to the smaller prop.
Then if you want to increase flight efficiency still more, you can (after you have made the prop diameter smaller) increase the pitch, so you get more airmiles per fuel consumed. This is like the very coarse pitch of a commercial (real-size) aircraft. Unfortunately now you can only climb like a commercial airliner !

Most of our props are a compromise between diameter (gets up faster, shorter runway) and pitch (reasonable airspeed once you are up there).

So on the same model setup, in the same model, and with the same motor, you might use a:
10 x 4 (for 3D hovering),
or a 10 x 6 ( (more normal flight),
or a 9 x 7 (more zooming, less climb, longer flight on lower throttle, but at the same airspeed),
or a 8 x 8 (harder to "get away" but very high speed flight)

I have a P-47 with the wide "Pugnose" radial engine cowling. I am worried that my propeller won't work due to the cowling blocking the airflow from the prop. Do I need a bigger engine and propeller?

If you divide the prop blade into 5 equal sections the 4th section out from centre does almost half the total work of the prop. The tip or 5th section does over half of what is left, with the centre three sections picking up the remainder.

eg on a 10" prop ( = a 10" diameter prop with 2 x 5" radius blades each tracing a 10" circle")
We look at each blade separately - so it is two prop blades sweeping the same circle if you see what I mean:

Area per blade and then doubled for the 2nd blade:
centre - 1" out - swept area = 6 sq in (subject to width of hub causing further reductions)
1" - 2" out - swept area = 20 sq in
2" - 3" out - swept area = 30 sq in
3" - 4" out - swept area = 44 sq in
4" - 4" out - swept area = 56 sq in (subject to vortex inefficiencies)

Area for a 10" circle is 78 sq in. Double that for the 2nd blade and we have total swept area for our 10" prop of 156 sq in.
The outer single 1/5th sections is 35% of this total.
The outer pair of 1/5th sections added together are 64% of this total.

The outside ring of swept area is far greater in area than the inside rings. This is the reason why an apparently "too small" prop will fly a radial aircraft no problem. The important parts - the tip and 1/5th in from it are not masked and the parts further in never counted for much anyway. Generally you can use the nomal prop for the aircraft and engine size. If you still have worries, go up maybe 1" in diameter no more. This applies to Razorbacks, Bearcats, Zeros, Sukhois and all similar models with a wide engine nascelle behind the propeller.

Any ideas on how to get rid of the fuel that gets soaked into the balsa and the covering doesn't stick anymore? I have a P-51 Mustang with an MVVS .91 in it with a pitts style muffler, one of the silicone hoses came off inside the cowl and when I re-filled the tank the engine-tank area took a soaking. The balsa is all oily and now the Oracover covering is lifting but new covering will not iron on.

1^st Remove the oil residue
In the past I used baby talc powder to soak up oil. It works like a dry shampoo. Rub it in, leave overnight, brush to loosen and then vacuum it out. Repeat if necessary. If you now wash with a “dry spirit” eg white spirit, methylated spirits or methanol, you will clean the surface more, but you may bring up a little more oil from deep in the wood. That is good because the balse will stay stronger later. But you should repeat the talc treatment to remove this new oil from the surface of the balsa.
If the wood has been seriously weakened
Clean with alcohol, methanol, methylated spirits, or white spirits. Let it dry.
Paint-dampen the wood with diluted wood glue or thinned epoxy glue. Thin cyano glue works a treat, but smells a bit. This sinks in and strengthens the wood from the inside. When it hardens it leaves a clean, hard, dry surface to work on.
Next paint on" a thin coat of fibreglass tissue (eg 25 or 40 grams/ sq metre) using the thinned glue like paste. let it dry. If any lumps are present, sand them off.
Proceed as if the fuel never spilled onto the model.
2^nd Prepare the balsa wood for re-covering
To re-attach film to oily wood, get as much as the oil out as possible using spirit and talc. Then use Balsaloc, it's a liquid form of ultra stickey heat activated glue like what is put on the iron on film at the factory. You paint it onto the previously oil soaked wood, let it dry and re-attaching the film is easy after that because there is heat activated glue on both surfaces, the wood and the covering film.

This is hard to do because of the thin tab foil. Wet towel or tissue work well. Alligator clips are bad. Using a pretty hot, well-tinned soldering iron with flux on the battery tab is the best way. You should work so fast that there is very little heat buildup. A hot iron solders in a second, almost like a spot weld, and the heat is localised. You can get heat sink forceps with flat (no serrations) edge that you clamp onto the tabs and take the heat away from where it is not wanted. Another pair of hands is needed for this but you might also manage with smooth-jawed needle-nose pliers.

Car out of storage - now engine trouble! Have had the car for while now, but haven’t used it for a while. I took it out yesterday and the minute it started it started to rev extremely high. I couldn’t throttle down to idle at all. It was stuck in gear due to engine running fast. Then it drove off top speed down the road. I had it serviced at last time I had it out and it was fine till now. I think its at the right settings but I’m not sure. Any answers?

If you had it put away for a while, and it was ok before it was put in storage. Then later you take it out again a few weeks later, and it revs too high. The settings are ok. Nothing is broken.
But the fuel has dried and gone thick in the fuel lines, partially blocking the outlet at the tank base, and the inlet at the carb.
This fuel blockage reduces fuel flow, which is the same as screwing the needles in to lean out your engine. The engine revs higher, gets hotter, can cut out when going fastish, is harder to start when cold.
Replace the couple of inches of silicone fuel line from tank to carb.
So try opening the main needle 1/4 turn to compensate for a narrowed piping at the "corner joint points".
If absolutely necessary ... open the idle needle 5 minutes approx. Write that down for later when you want to return the settings, if you are unsure how to tune accurately.
You will need to wash out the jelly-like fuel at these particular points, or blow them out with compressed air. Close your eyes, nose, mouth, if you do this because a potentially harmful fuel vapour will be blown away from the area by the compressed air.
When the residue finally dissolves away, more fuel will get to the engine and you will see the car begin to run rich, and you can put the needle setting back where it belongs.

How to test servos using a servo tester when you have no radio You do not need a radio and receiver to test servos.
they can be tested with a servo tester.
This is a little gadget that looks like a receiver with a knob on the side.
Plug the servos in same as for an ordinary receiver.
Rotating the knob operates the servos, or they can be set to move cyclically at a preset speed to test for "glitching".

A good hobby shop will have a servo tester available to test stuff that comes back faulty. If you want to buy one it costs about 2/3rds the cost of a good receiver.

Green Hobby & Model, the R/C source
38 Clareville Road, Harolds Cross, Dublin 6W
Tel (01) 4928776 , Fax (01) 4979946
Sales Norman or Patrick

As a guide (Assuming a decent setup) ....
civilian airliner	150 watts:kg
sport jet	200-250 watts:kg
high performance	250-300 Watts:kg
Display performance	350+ Watts:kg

	Propeller Size Guide Chart
Engine (cu. in.)	E-Motor equivalent	Recommended props inches (diam x pitch)
.05-.10	400 direct drive	6x3, 6x4, 6x6
.10	400 geared	7x3, 7x4, 7x6
.15	400 geared/600 direct	7x6, 8x4, 8x5, 8x6
.19-.25	600 geared	8x6, 9x5, 9x6
.30-.36	hot 600 geared/700 direct	9x8, 10x6
.40	700 geared	10x6, 10x7
.46-.50	hot 700 geared	10x7-8, 11x6
.60	brushless	11x7-8, 12x6
.71-.90	brushless	12x-6, 13-14x6

As a guide (Assuming a decent setup) ....

civilian airliner

150 watts:kg

sport jet

200-250 watts:kg

high performance

250-300 Watts:kg

Display performance

350+ Watts:kg