boat plans for ENYA 90-4C?

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Ian_Timshel
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boat plans for ENYA 90-4C?

Post by Ian_Timshel »

Hi all.
I was just given a little four cycle engine that needs some work. I'm hoping to get inspired to fix it by figuring out what I might do with it if it turns out to run nicely. I don't have much experience with these little guys so any commentary is welcome.

The engine has had valve guides put in poorly I think and at the very least need to be trimmed back to make more clearance for the springs and such.

I don't have a whole bunch of time to sink into this project but a boat with a prop on the back sounds about as simple as it gets. What do you guys think?
I would like some ideas for something fun and not too time consuming to drop this engine into. No I don't want to learn to fly.. ;^) This engine did good service in a plane before I got it though.

Thanks for hearing me out.
Cheers! Ian.
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Doug_C
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Re: boat plans for ENYA 90-4C?

Post by Doug_C »

Ian,

Without first hand inspection of the engine, I couldn't say what it suffers from. Enya's are not exactly creme of the crop. Definitely getting better and giving the competition a run for the money. I can't say I have had any bad experience with them though. The only things I have heard was that longevity was never one of their strong points.

As to using it in a boat. You would need to put a water cooling system on the head. I doubt these are available and may need a custom made unit since the head is not round. These are made to have air cooling and plenty of it, provided in the prop stream. It still needs to get to running temp (250deg'z or so, but not over 300), but protected from over temp or thermal run away.

Sizing the correct prop for water thrust may be a challenge. It should run in the 8-10,000 rpm range with plenty of bottom end torque. These are only 70% as efficient in power output as a 2 stroke of the same displacement, so that should be taken into account when sizing the application.

DC
Ian_Timshel
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Re: boat plans for ENYA 90-4C?

Post by Ian_Timshel »

Thanks Doug.

I"m not so concerned as to the merits of the engine design or it's repariability as I am with finding something other than flying that I can put it to work in. Any ideas?
Cheers! Ian.
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Doug_C
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Re: boat plans for ENYA 90-4C?

Post by Doug_C »

Your imagination is the only limit.

How about a flat bottom everglades fan boat? At least it still has an airscrew with proper cooling?

Radio gear would still be a nice feature for control. It should be a fast monster swinging a 16x8 prop.

On Home Improvement a few years ago. Tim made a gas operated cordless screwdriver with a pull start! [img]/ubb/images/graemlins/grin.gif"%20alt="[/img]

DC
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Re: boat plans for ENYA 90-4C?

Post by Ian_Timshel »

A flat bottomed boat sounds like a good idea.. although the screw driver is sorely tempting.. ;^)

When you say "16x8 prop" what does that mean and how did you come to that conclusion? Is there a link I'm missing for newbies and propellors?

Do you know where I might find details of a simple boat appropriate for this engine? The radio stuff is next for sure. I expect this thing will really move along quite quickly. < g >
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Doug_C
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Re: boat plans for ENYA 90-4C?

Post by Doug_C »

Oops, I mis-stated that prop size. I use a 14x6 on my Saito .80 engine and a 13x6 on my Saito .65. I was thinking it would a 90 would be a natural for a 15-16" prop. After reading some of the responses around the web, I see folks using a 13x8 12x7 for 10-11k rpm?

That seems really weak for a .90 size engine!

13 would be the diameter and 6 or 8 would be the pitch in how far it moves forward for each revolution.

I do not know of any specific plans for a fan boat, but I did see a good sized one earlier this year at the local RC show. Look around the web and in the plans section of some of the boat RC mag's.

DC
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Re: boat plans for ENYA 90-4C?

Post by Ian_Timshel »

Even with the reduced power of the four stroke you think the larger props appropriate?

Does a 13x7 have less "pitch" than a 13x8?

Thanks for all your input here Doug. My kids are investing their interest already.. ehh

Cheers! Ian.
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Doug_C
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Re: boat plans for ENYA 90-4C?

Post by Doug_C »

Well, the prop is a load on the engine. Four strokes have a lower rpm wider power band compared to the screaming two stroke. Even though the torque is there to compensate some, the 4 stroke has 1/2 the power strokes. It is not always an equal trade, but the sound of a four stroke is oh so nice and not nearly as annoying! LOL!

Yes a 7" pitch is less than 8", which tells you that there will be less load on a 7" pull in the same diameter prop. There is a slight overlap in power requirements for a 14x6 vs a 13x8 due to the surface area increase of the airfoil on the larger diameter over the pitch of the smaller diameter. Part of the gain with a larger prop is the flywheel effect to attempt to get a lower idle rpm to keep the engine ticking over its high compression near TDC. An increase in diameter usually means a lower pitch to get the same load characteristics for thrust, while gaining other attributes as desired.

DC
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Re: boat plans for ENYA 90-4C?

Post by Ian_Timshel »

Thank-you very much for the brief and concise primer. I'll be scouting some boat plans now.

Your comments on the sound of the four stroke exhaust note was what tweaked my interest in this engine to begin with. The fellow who gave it to me said that it sounded pretty sweet.

I'm curious as to how it was that one comes to determine the range of diameters in propellers for a given two or four stroke engine. I say so because I was told to use a 12 inch prop. on this engine but knowing nothing leave me open to learning. [img]/ubb/images/graemlins/grin.gif"%20alt="[/img] If you have the time and patience.

Thanks in advance. Ian.
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Doug_C
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Re: boat plans for ENYA 90-4C?

Post by Doug_C »

Ian,

In keeping it simple enough for me to understand. Selecting a prop is like selecting gear ratios for a differential on a race car.

The engine and craft perform work together. That match of weight to motivation should extract available power as efficiently as is practical as the power plant allows for its performance limit. There is plenty of data available on engine sizing that should help to keep power to weight ratio expectations realistic.

If power is work done over time. Then think of the prop pitch distance traveled at 10,000rpm for one minute. If a 7" pitch goes 70,000 inches and a 8" pitch goes 80,000 inches in the same measure of time at 10Krpm. The 8" pitch did more work in that time, which takes more power.

As you vary the load on the engine via pitch, you will notice a point that power peaks, then begins to fall off. You want to stay on the rizing edge with a little room to spare.

In many light aircraft with variable pitch props, it is the prop that controls the engine in this manner, more so than the engine controlling the prop.

Using gears/prop improperly suited for the engine either never uses its full capacity or lugs it down over its capacity.

Finding the happy medium takes trial and error in selecting a prop within the suggested guidlines of the manufacturer. After you have had some exposure to various engines and props, you gain an idea of what props go with a certain engine displacements as a general rule.

DC
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Re: boat plans for ENYA 90-4C?

Post by Ian_Timshel »

gracias..
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Eggit41

Re: boat plans for ENYA 90-4C?

Post by Eggit41 »

Hate to get in the middle here, but I went the 4stroke in a swamp boat and can definatly say dont do this. Theres too much torque and not enough air flow over the rudders. What you wind up with is a boat that will steer better with the engine torque than the rudder input, and constantly turns right.

Its possable to make it work O.K. but the effort is not worthwhile.


As far as putting it in a boat you will not need to water cool it at all. A simple scoop directing cooling air twords the engine is plenty as the fuel its self does a partail job of cooling the engine. The fuel is alchol and actually cools the engine while burning.

If you dont believe me, talk to some drag racers who run alky cars. They actually want the long warmup and burnout period while on the starting line to help the engine build more power. were taling running an engine with NO cooling for 3-5 min then screaming it down the track at 10,000rpm while burning 6-9 GALLONS of fule.

I would reccommend a 36-45" hull, deep V and somewhere in the neighborhood of a 2.250" to 2.750" prop. This should put you in the 35-40 mph neighborhood.


Your best bet is to find some R/C forums and find their video section. they will be glad to help you get this going with a minimun of trial and error and very little guessing.

Good luck to you. [img]/ubb/images/graemlins/cool.gif"%20alt="[/img]
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