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air boat prop question

Old 08-15-2014, 12:04 PM
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dontrinko
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Default air boat prop question

I have an air boat with a 380 size motor. ( T400). I an using a 5.5x4 prop. I would like to try a prop with more pitch. Is 5x4.5 more pitch? any recommendations? Are there props that are "close" to being balanced from the factory?
The motor I have is turning about 11,500 rpm with the 5.5x4 prop. Thanks, Don

Last edited by dontrinko; 08-15-2014 at 12:15 PM.
Old 08-15-2014, 12:54 PM
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arcdude
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Hi Don, The first number is the diameter of the prop and the second number is your pitch so the 5x4 is smaller in diameter yet the same pitch. Usually the rule of thumb is if you go down a size in diameter you can go up one increment in pitch. By increasing the pitch it will have less pull at the bottom end and higher speed at the top end and vice versa the other way around. From your previous post in having to boat in algae I would suggest the higher torque the bottom end will give you rather than the top end speed to get you through the gook a little easier. I'm no expert so just offering my experience which is usually following the manufactures recommended prop for the applicable motor and electrics are quite sensitive to heat so any changes will likely have a negative effect on the motor. All you have to remember is high pitch = high speed, low pitch = torque, Cheers

Last edited by arcdude; 08-15-2014 at 01:05 PM.
Old 08-15-2014, 01:04 PM
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dontrinko
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So if I understand you correct a 5.5 x 4.5 would lower top speed but have more power at the low end? The props i have seen are cheap so I don't mind buying a few to try. Thanks for the quick response. Don
Old 08-15-2014, 01:13 PM
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arcdude
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Originally Posted by dontrinko
So if I understand you correct a 5.5 x 4.5 would lower top speed but have more power at the low end? The props i have seen are cheap so I don't mind buying a few to try. Thanks for the quick response. Don
What you need is less pitch to give you more torque at the bottom end. What does the manufacture suggest? They usually suggest a couple.
Old 08-15-2014, 01:23 PM
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arcdude
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Hi Don I edited my earlier post, not sure if you saw it or not.
Old 08-15-2014, 02:29 PM
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dontrinko
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I do not see a recomendation. This motor ois normaly used with a gear box for a specific plane. I am turning 11500 rpms with the 5.5x4. I thought maybe a higher pitch would lower the rpm. Don
Old 08-15-2014, 02:48 PM
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arcdude
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A higher pitch will lower the rpm but it may cause overheating by taxing the engine or other components too much, at least that's my understanding of electrics, I'm sure there's some latitude there. What you really need to do and if I were in your shoes is find out what the recommended rpm is for the motor? That would be the place to start and work from there. Maybe you could send an email to the company with your questions, I've done so in the past and most are more than willing to respond.
Old 08-15-2014, 04:48 PM
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dontrinko
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I did email them just a few minutes ago. Thanks for the idea.
I did some more digging and i found this is the same as the Graupner Speed 400 6v. No load rpm is aprox 16,000.
I thnik I'll buy a couple props and see what works best. Don

Last edited by dontrinko; 08-15-2014 at 05:11 PM.
Old 08-15-2014, 05:38 PM
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arcdude
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Hi Don, I read a little bit and found that the lower pitch props will give you the best torque which I'm assuming that is what your looking for and at the same time the motors don't work as hard and have a better time cooling. So as long as you keep the load on the motor reasonable and monitor your heat you should be o.k. A suggestion may be to pick up a few props in lesser pitch and see how they perform. Let us know how it works out for you, Cheers,
Old 08-16-2014, 04:16 AM
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dontrinko
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Thanks. The motor stay cool compared to my car motors for a similar time. I need to try it in the water before i try to much more. I'm having trouble getting the props ballanced.
I was using 2 razer blades. I have a balancer on order. I have one prop with only slight vibration. It is an acceptable level for now but still a little vibration. 11,500 rpm is most of the problem. Ther is almost no vibration at 2/3 throttle but at full it is still apparent.
The factor prop was horrible, even at 8400 rpm (stock motor) it had bad vibration. With the new motor ( 11,500 rpm) the wires were braking and the prop was vibrating 1/4".
When you looked at the two motor wires it looked like 4 wires! LOL Not good1 Don
Old 08-19-2014, 09:50 AM
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dontrinko
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8-19-14 new prop(2nd one) fairly well balanced . Very little vibration at full throttle.
A little faster than stock. Started with full 2s 1100 mah lipo.(8.4 volts) Motor temp after 5 minutes was 97. I stopped after 7 minutes. ( I was done, no problems) Lipo was 7.8 volts after 7 minutes .
Went over small algae patches at 1st but would not towards the end. ( Battery voltage lower?)
Old 08-19-2014, 05:51 PM
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arcdude
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Looks like your going to have to change ponds there Don or trade in the boat for something with a little more get up and go, it's all in good fun
Old 08-20-2014, 03:46 AM
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dontrinko
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In the spring there was no algae. With the wind there is always a fairly large clear spot for the air boat. Boats But under water propellers seem to find algae under the surface.
This fall most of it should disappear. i have another pond i can go to that is kept clear but it is 15 miles away, this pond is about 1 mile.
I found some static thrust calculators and the bottom line is I need a bigger prop,( no room) and/or a lower pitch (higher rpm, harder to balance prop)
The difference between pitch of 4,3.5, and 3.0 is small. (aprox 50 grams thrust)
Without major mods I probably should use it like it is. I'll be lurking on Ebay for an airboat that I can put a large electric motor and a large prop. The problem is most of the bigger ones are gas and do not have a lot of room for a battery.. Oh well this is a hobby. Don

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