September 24, 2018, 05:25:29 PM


Author Topic: It all makes my head hurt  (Read 4154 times)

Offline D45/70

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It all makes my head hurt
« on: April 01, 2018, 01:51:19 PM »
Been trying to find some Information that make sense to me.
As close as I can find My little bug motor with a 59" three blade prop and 12* pitch blocks at 3000 rpm delivering around 50 hp. to the prop make 200 to 250 pounds of thrust.

 OK SO what the heck does that mean?

Is that a lot or is that so small it would make a good hair dryer?

The calculations and calculators are very abstract to me and tell me nothing this simple Montana head can understand.

About half the calculators refer to water props and SOME flat out tell me that a 55 pound thrust trolling motor is around 3 hp. I can understand that. But air is way different I know.

Can any one help?

 My head hurts.
DO to the increasing cost of energy, Gas,and Electricity. The Down turn in the economy.
The light at the END of the TUNNEL is Now TURNED OFF!!!

Offline MOSPARKY

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Re: It all makes my head hurt
« Reply #1 on: April 01, 2018, 07:42:04 PM »
I have no idea what any of that means either. but my bosses best friend comes to the shop from time to time. He is an engineer in the wind tunnel at Boeing here in St. Louis. I will try to ask him next time I see him. Also a friend of mine had/has a Private pilots license and was real big on avionics and the associated math. I will see if I can get in touch with him as well.
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Offline D45/70

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Re: It all makes my head hurt
« Reply #2 on: April 01, 2018, 08:12:28 PM »
COOL
DO to the increasing cost of energy, Gas,and Electricity. The Down turn in the economy.
The light at the END of the TUNNEL is Now TURNED OFF!!!

Offline John Andrews

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Re: It all makes my head hurt
« Reply #3 on: April 02, 2018, 02:54:27 AM »
You need someone smarter than me to figure all that, D!
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Offline MOSPARKY

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Re: It all makes my head hurt
« Reply #4 on: April 02, 2018, 06:18:04 PM »
I copy pasted your post and sent it to my friend, his responce follows :

"Hey Sparky, the volkswagen engines have been usind in homebuilt aircraft for years.  When driving a propeller however they tend to run no more than 2500 rpm as much faster the propeller tips go supersonic and loose the needed thrust. As far as the thrust, 250 pounds of thrust is quite a bit.  The BD-5 J can fly at 200+ knots on 300 pounds of thrust.  The weight of the boat and therefore the draft are a big part of the calculations.  Realistically, have your frind contact a UNiversity that has an aerodynamics degree and ask the department professors for help.  They usually are happy to do so."

Hope this helps. Sounds quite promising to me, might want to throttle back the rpms tho. I guess that is largely going to depend on prop radius.
John Andrews is my hero !

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Offline D45/70

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Re: It all makes my head hurt
« Reply #5 on: April 02, 2018, 07:04:48 PM »
Cool thanks.
 Answered most my concerns.
The prop I'm using can be turned up to 3100 rpm before it goes supper sonic.
 
DO to the increasing cost of energy, Gas,and Electricity. The Down turn in the economy.
The light at the END of the TUNNEL is Now TURNED OFF!!!

 


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