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RE: Mac 85-SX 21cc
As long as it is moving through the air it will be fine
The problem is trying to set the engine up in the beginning while it is stationary. Some people set the carb needles and tune the engine with pulling prop, then change to a pusher for the action of the model in actual use |
RE: Mac 85-SX 21cc
Iguess going water cooled on the airboat isn't really done because it really doesn't make sense unless your only on the water.
If you go on land the water inlet might get some grass in it and would be pushed through the hole. That makes sense as far as tuning. Everyone just says if you go with a pusher then the motor doesn't get cooled as much so it's getting me worried it will get to hot. If Idon't go water cooled and use a pusher prop Ijust want to make sure it will be ok. |
RE: Mac 85-SX 21cc
I really wouldn't be comfortable with a pusher gasoline powered airboat. I feel it would almost certainly get hot. I know some of the glow guys rig up electric fans to help cool their pusher style airboats, and glow engines run much cooler than gasoline powered engines by their very nature.
The advice here is to run it as a tractor style to assure decent engine cooling and engine longevity, not to mention ease of tuning without overheating the engine. If you go with water cooling to preserve your ability to run it as a pusher, I would run a dedicated water pump for the cooling system. With water cooling, you would have to run it only on water; not grass, ice, snow, etc. But with a dedicated water pump, at least you could just set the boat in the water and do your tuning, while the water pump provided cooling even though the boat wasnt moving. Tractor is really the way to go for all around practicality..... AV8TOR |
RE: Mac 85-SX 21cc
ORIGINAL: av8tor1977 I really wouldn't be comfortable with a pusher gasoline powered airboat. I feel it would almost certainly get hot. I know some of the glow guys rig up electric fans to help cool their pusher style airboats, and glow engines run much cooler than gasoline powered engines by their very nature. The advice here is to run it as a tractor style to assure decent engine cooling and engine longevity, not to mention ease of tuning without overheating the engine. If you go with water cooling to preserve your ability to run it as a pusher, I would run a dedicated water pump for the cooling system. With water cooling, you would have to run it only on water; not grass, ice, snow, etc. But with a dedicated water pump, at least you could just set the boat in the water and do your tuning, while the water pump provided cooling even though the boat wasnt moving. Tractor is really the way to go for all around practicality..... AV8TOR <span class="postbody"> I have been told the motor shoul be putting out somewhere around @ .9 HP at 7500 rpm, the Ignition coil does not allow rpm above @ 10K. </span> |
RE: Mac 85-SX 21cc
I would probably start with a 14 x 6 for that engine on an airboat. If the rpms are quite high, then you could try a 15 x 6.
AV8TOR |
RE: Mac 85-SX 21cc
Iam assuming that is a tractor prop size? Since that is what you were recommending and a 2 blade prop?
It was recommended if Iwent pusher 13x8 which might be a little to big or a 10x7 these were 3 blade props. |
RE: Mac 85-SX 21cc
13x8 is roughly equal to the 14x6 av8tor mentioned, I don't know about the three blade eqivilant
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RE: Mac 85-SX 21cc
Thanks,
How is your project coming? You have any props you would want to sell? Iknow tower has some decent prices on a few. I'm still working on getting things together for my Mono so money is tight but I am getting there. Just a few more things to get and I should be ready to finish putting it together. |
RE: Mac 85-SX 21cc
The general rule is to go down one inch when going to a 3 blade. So a 13 to 14 x 6 3 blade should do it. I recommend a 6 inch pitch for an airboat.
AV8TOR |
RE: Mac 85-SX 21cc
mine is done shy of making a cage for the prop or at least a shield of some form with a handle on top... and maybe cutting the fin off the bottom.
as far as props, those sizes (other than 3 blade) are like $5 at any of the local hobby shops (coyote hobby in oregon city, tammies hobbies in beaverton, and probably some of the hobbytown USA's), I could make you the prop adapter though for cheaper than you could get it from the online places... |
RE: Mac 85-SX 21cc
Thanks for the clarification.
Still debating pusher or puller, Ispoke with somone who built a pusher out of a ryobi weedy motor and he had no issues with overheating. |
RE: Mac 85-SX 21cc
I have an extra lightened flywheel if anyone has a need for it let me know.
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RE: Mac 85-SX 21cc
I wish electric ignitions were not so expensive.
I am thinking I will probably run it as a tractor style just to keep things as cool as possible. Would be nice to be able to do away with the flywheel. |
RE: Mac 85-SX 21cc
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RE: Mac 85-SX 21cc
Good to know but that about $51 more then Ihave at the moment.
Iwill leave it on for now, Ihave a lightened someone gave me so for now that will be good enough and further in the build I'll possibly go that route. |
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