I have a evolution .46nt engine. The problem i am haveing is that the engine starts backwards. I know that I am starting the engine the right way. In the past if the engine started backwards I would have to turn it like I was starting it backwards and it would start the correct way. I had the engine put in my closet for about two months to four months. But now the engine starts backwards no matter which way i turn the prop.I an spiningg a 9X6 reverse pitch prop which is smaller that the one that is recominded for the engine

P.S. The engine is on a 24" long airboat (swampbugy if that is what you know it as) but it is a airplane engine. I could not find a pull start conversion for it or an electric start. I also can not use a 12v eletric starter as you can see in the pics below

Keep trying.....

I would use a little more pitch on the prop like a 9-7 or 9-8 but I doubt you will find one in reverse pitch.

well the the smalest prop size recommended is a 10X5

See if you can find a 10-6 pusher prop. It looks like it will clear your hull and the extra diameter will help the engine start in the correct direction

A 9x6 on a 46 is way too small.

Try to less priming.Overpriming causes such reverse starting.But in your case insufficient flywheel effect can be the cause.Then I think a colder plug helps too.

Connor,


You are over-priming it for sure, like Turk1 wrote.

After priming the engine properly, I have seen some Evos that responded great to back-flipping.
You don't turn the prop backward; just 'bump' it against the compression.

It will take you a while to get the feel and it is best if the prop is mounted, so the blades are horizontal, as you start feeling the resistance of compression.

This is good for flipping regularly and also for back-flipping.

When the engine starts with a pusher prop and you are facing the prop, it should blow air in your face...
Cooling is impaired, as long as the model is standing still and will only be sufficient in flight.

Bruce,


On a .46 used for very high RPM, not with the standard muffler, a 9x6 could be good...
But not in this case. I would say a 10x6 pusher will do a much better job.

Like others said, too much fuel in the engine when starting will do that. Pull or pinch off the fuel line next time, then let it run off the fuel in the crankcase. Often, just before the engine dies, it will kick off in the correct direction for a couple of seconds and sound much happier when it does. You can often release the fuel line just at that point and off she goes, a technique I use when I've pulled too much fuel in during choking, but not I guess entirely recommended by the safety committee. A better tactic is to go easy on the priming/choking. You can simply pull off the line (and the muffler pressure line too unless you want to bath the model in fuel, or plug the fuel line) and hit the engine with the starter to let it burn off the excess, don't worry which way it is running at that point, just let it burn up fuel.

Once/if you get the engine idling, try pinching the fuel line to see if and how much the rpm increases before it starves.. you can release it before it dies. A small increase is okay, but if it speeds up notably then your idle mixture is too rich fer shure. Lean it a bit at a time . A clue is the transition from idle to high throttle - with plug heat off. Too rich and the engine will stumble when you advance the throttle. The idle needs to be towards the lean side, so that the rpm only jumps a little with the pinch test. A too rich idle does no good at all. The engine is not producing a lot of heat at idle but remember that by leaning out I don't mean going too far, but just to the point where it runs and transitions cleanly. If the engine dies quickly when you pinch the line then you have gone too far [okay, I see the Evo 46 has an idle mixture limit too - if so you're not going to go too far]. Ideally (ideally to me.. others may differ) if you pinch the line, the rpm should increase just a wee bit, and after about two seconds or so the engine should start starving for fuel. You should do all this after setting the top end correctly, then check the top end once more afterwards.

I found these comments from a reviewer:

"The engine started easily and was running very rich. It took nearly a full turn of the high needle to get it running from a four-stroke note to a rich 2-stroke. On the low end, the engine wouldn’t accelerate well when advancing the throttle. Even when advancing the throttle slowly, the engine would stumble and then stall. Making an adjustment to the low-end screw had a positive and dramatic impact. The engine was running extremely well. Even with the high-speed needle turned all the way in (lean) against the limiter, the engine was still a little rich. Since this was the first flight it was decided to leave the mixture slightly rich. If it remains rich in subsequent flights, the limiter can be readjusted to allow the engine to run leaner."

Don't go too far on a pusher airboat, stay comfortably away from peak rpm when setting the needle. Sounds like the built in limit is a good thing.

A 9-6 is not going to hurt your .46, but it is on the small side for your application and a prop with more disc area and perhaps finer pitch is going to perform better. For an airboat you have a lot of load and the top speed is not high enough to warrant a prop running at a pitch speed of 100 mph+. A 10-6 pusher is as mentioned a better choice. If you could find an 11-5 pusher even better, but I don't think there is one. Master Airscrew has a 10-6 pusher, APC makes 10-6 and 11-6; In truth, since a smaller prop runs cooler the 10-6 may be the better choice from that standpoint, but for the airboat if it fits, the 11-6 may work really well too. Perhaps try that after getting some running time on the 10-6.

In terms of running up your engine static, to tune it, test throttle transition etc., personally I would recommend fitting it with the tractor (normal) prop of the same size as your pusher - that way you get all the time in the world to set it up with no fear of overheating due to lack of forward speed, and you can spend a whole tank full of fuel tinkering if you choose to or need to.

MJD

cpbpilot,

You might consider lowering your cross-brace for the rudders to about half way down, then get a starter with en extension on the shaft. These MAY be available for ducted fans (I'm not a starter guy). I'd try to borrow one, if possible, to see how it works.

I don't believe I've ever seen an X-Acto tool box used as part of the model before...unique!

Looks like a fun boat. The only air-boat I ever built was a free running 1/2A one published in FM in the mid fifties. Lotsa fun.

Good luck with yours.

George

I don't see cooling being an issue there will plenty of air flow regardless what direction it moving

----------------


Pusher engines do overheat more often than tractor set up engines, unless there is a shroud placed around the propeller AND engine. It is a fact of life, believe it or not.

The heli boys used to (may still) have a special prop nut and a special extension for their starter motors available. Ducted Fan folks too, now that I think of it. Using the correct one of these set ups, you could reach in between the rudders and electrically start your engine. Good luck.

Wrong, Ed!


Prove it to yourself!

Just take your normal 'tractor' prop plane and place your hand behind the prop, in line with the cylinder, at full throttle.
There is a VERY strong cooling flow of air in that vicinity.

Now, place your hand at the same distance in front of the same prop... Do you feel anything that could be described as a strong cooling air-flow? Anything that remotely resembles the powerful blowing that your hand felt behind the prop?

This is what an engine 'feels' when it is spinning a pusher prop.
Only in high-speed forward flight will the relative 'air-flow' be able to sufficiently cool the engine - or if the pusher installation is a shrouded engine ByroFan...

An 'open' prop in static conditions, creates a partial vacuum in front of it, which air from all directions comes in to fill; not necessarily from directly in front of the prop, so the forced flow between the cylinder and the head cooling fins, can be described as 'limited' and can even better be described as 'marginal'.

A Cessna 337 Skymaster/Super Skymaster has two identical Teledyne-Continental IO-360 engines... The rear engine of this set requires expensive maintenance twice as often, even though it is used mainly in flight... This only happens due to inferior cooling of the pusher engine. It is also more likely to fail.

thanks for all the advice i will definitely use it in the very near future like this weekend

the box is used so that the recever and battery dont get wet whiile it is in the water and just in case i flip it over in the water i dont want anything falling out and and i used the x-acto tool box b/c it was already builtand everything fit in it nicely

I would suggest that you do not get a colder plug than the OS 8. That plug is really too cold for the .46NT. It will run well with the OS 8, but it will really run great with a hotter plug. The OS 8 makes it difficult to start and run up to wide open throttle. Same for the Evo .455 engine.

i am going to keep the same glow plug that i have in it for now but does anyone know where i can get a 3 bladed pusher prop in 10X6 to 10X8or9 size

An OS #8 is plenty hot for that engine as well as any other sport type engine in that size range. It is the recommended plug for all the OS engines in that size. An A-3 will work as well as will an Enya #3.

An OS8 won't make it hard to start. If the plug was damaged, now that would.

I answered in your other thread. Now I see what you're trying (wrong) to do. I had the 60 size Dumas Swampbuggy and a scratch built 40 size. I made it easier on myself by having the engines facing forward. Guess that's why the plan designers did it that way also. As one poster mentioned, the engine will stay much cooler and you can then use the electric starter. Turn the engine 180 and your life will be in better sync with the universe.

Forgot to mention, you need to put fuel tubing over the rudder rod detent screws. Metal to metal rubbing will cause RF interference.
I'm surprised the engine will run at all -- The tank outlet should not be more than 1/2" below the centerline of the carb unless you have a pumper on the back of crank case.

That worried me too but I was focussing on the mixture issues.

I have built maybe 3-4 airboats like this over the years, in .15-.25 size, and they have always been great fun. However I ran all of them in tractor mode with the tank in the engine pod. CG has never troubled me, they all bank into the turns. I make the pylon flush with the rear of the engine/tank pod, and use that as the vertical fin, with a single large rudder hinged off that and no water rudder. They all had great rudder authority, and could be driven on water, grass or snow. Good cheap fun. Most were made from foam flutterboards covered in either polyurethane or epoxy finish, and a square of 1/8" plywood bonded to the deck where the pylon fit through for support. I inset the pylon into the foam with liberal amounts of epoxy (though now that it is availableI would much sooner use Gorilla Glue or Probond), and glassed or V-stocked the corners to the plywood base. Never ripped a pylon out, though I never drove one into anything at full speed either. Hold the engine pod for starting and launching though.

The smaller all foam flutterboards I used to get at our erstwhile Canadian Tire chain worked great for .049 free running airboats, up to .25 powered 2 channel affairs. A little nose weight was needed with the .25, but the performance was really good, and decent with a .15FP. I haven't looked for those board for a while, I worry about their availability now. Of course, cutting one from 2" foam is hardly a major foam cutting challenge.

I still have the equipmentless hull of the .25 version, I should snap a picture. These are "great fun for the kids" too, simple and worry free RC giggles. Other than starting and launching of course, but that's why Dad is there! Here boys, better let me test drive it some more..

MJD

loughbd- you are dead wrong about the correct plug for a .46NT. It does not matter what OS recommends as this is an Evolution engine. I didn't say that it would make the engine hard to start.

Dar,
Are you sure you don't mean the Cessna "Mixmaster" Well at least that's what the folks I know call'em.
Pete

I'm not positive but i think tower makes a 11x5 plastic prop for their 46 OS FXI for their nexstar engine that runs very well.
http://www2.towerhobbies.com/cgi-bin...&I=LXGAK9&P=ML
10 by 7 pusher http://www2.towerhobbies.com/cgi-bin...?&I=LX1500&P=7

Eventhough we all called the Cessna 337 a "Mixmaster" at the airport and that's the name we remember them by.....

The real name of the plane was "Skymaster" as Dar said.

The Continental IO 360 didn't have but an average 800 hr TBO (published TBO was 1500hrs) even in the front of the plane. This was at a time when other engines had a pulished 2000 hr TBO and it would seem to do more harm than good to take one down then.

The name "Mixmaster" came about from "Skymaster" due to the fact that if you ever heard one, it sounded like the engines were out of sync.

Cooling is a real problem with pusher engines in our models. A friend had a big pusher model with a Fox 78. The first time he went to fly the plane, he was making sure everything was OK and was taxing around the field when the engine quit. It melted the head button around the glow plug and the glow plug was gone.

Pete,


Here, in Israel, this plane was used to 'seed' clouds (silver-iodide) and later augmented by an Aero-Commander 680 as the 'rain-makers' squadron...

The Kanaf-Arkia crew rightfully called each of them a Cessna 'Push-Pull'...


...At least it is the easiest plane to fly with one failed engine...

Of that we can be sure[8D] and ditto for a twin scale model.
Some years back I witnessed a tractor engine failure on a Skymaster at an airshow (Solberg, NJ), very strange sight at first glance, seeing what would appear to be a single, deadstick, flying a normal landing pattern[8D]
Pete