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Old Jan 13, 2011, 07:53 PM
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Required Thrust

Would anyone positively know , the mathematical formula , that would calculate the required thrust for the total wieght of an rc aircraft ?
Please...no guesser's...Eather you know for sure...or or not !
Thx.
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Old Jan 15, 2011, 01:36 PM
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There is no actual formula, there are several other factors that come into play. There are some 'general rules' for power to weight ratios, but apparently that won't work for you. If you need actual numbers, do some experiments. Keep loading your plane until it won't get off the ground. Then you know the 'mathematical formula' for that plane. Repeat on each plane (as there are many variables for different planes) that you fly. Problem solved.
Martin
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Old Jan 15, 2011, 04:23 PM
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Quote:
Originally Posted by mcjustis View Post
There is no actual formula, there are several other factors that come into play. There are some 'general rules' for power to weight ratios, but apparently that won't work for you. If you need actual numbers, do some experiments. Keep loading your plane until it won't get off the ground. Then you know the 'mathematical formula' for that plane. Repeat on each plane (as there are many variables for different planes) that you fly. Problem solved.
Martin
Rediculas...lol
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Old Jan 17, 2011, 06:17 PM
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Commercial aircraft static thrust requirement ( just to get the plane flying ) !
Reportedly to be 0.2 to .4 % of the total plane weight.
In other words 2 to 4 lbs. of thrust is needed for a 10lb. aircraft to get off the ground and start flying.

Now that that's been determined , you can now consider the areodynamics of the type of aircraft your using etc. & decide what performance's you want and upgrade your thrust ratio from there. But you need to know what the eng/prop thrust capabilities are , before you can choose a suitable match. Otherwise , it becomes just trial and error. I don't believe the trial and error method is the way to do it. There has to be a genuine formula out there somewhere.
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Old Jan 18, 2011, 10:33 AM
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Wow, if you're so smart, why ask the question. You seem to have the answer right there in front of you. Although not correct.
Your % usage needs a little work. 2% - 4% is different than .2% to .4%.
Also just to be sure, 2 % of 10 pounds is not 2 pounds, it's .2 pounds which is 3.2 oz. I'm no aeronautical engineer, but I've flown enough planes to know 3.2 oz. of thrust will not fly a 10 lb. airplane.

Example for you...

I did some calculating on your (I'll give you that you intended to use 2-4 %) figures. On a Boeing 747 with a takeoff weight of 358000 lbs (that's the very low side of it's take off weight) you say it'll fly with 14320 lbs of thrust. I guess at 56000 lbs of thrust per engine (224000 lbs total) that's major overkill. I think you need some math help before you start in with a "genuine formula".
By the way, if you're going to insult what I have to say, you could at least get your spelling correct.

Martin
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Old Jan 19, 2011, 06:26 AM
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mcjustis


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QUOTED: Wow, if you're so smart, why ask the question. You seem to have the answer right there in front of you. Although not correct

Your % usage needs a little work. 2% - 4% is different than .2% to .4%


Hey Martin....Take another look ..." YOU NEED SPECTACLES" ! Never , did i quote 2% or 4%...lol. Must have a tough time flying those planes of your's...lol.
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Last edited by rc-air; Jan 19, 2011 at 06:29 AM. Reason: forgot quote
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Old Jan 19, 2011, 06:43 AM
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pe reivers
Bad-ass Super Contributer!





Join Date: Apr 2007
Location: The netherlands
Age: 67
Posts: 1,054 Re: Prop/eng thrust Requirement

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

gliders 10kg/hp
Any bomber will fly well with 8 kilo/hp
sports planes 4kg/hp
warbirds 2kg/hp
Aerobatics 1kg/hp
3D 3/4kg/hp
__________________
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A BASIC ENG. HP FORMULA PROVIDED FROM AN ENGINEER ON ANOTHER FORUM , WHICH WORKS JUST FINE AND WILL PROVIDE ALL THE THRUST NEEDED.
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Old Jan 19, 2011, 09:02 AM
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Old Jan 19, 2011, 09:09 AM
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Busted for flatulance, removed the offending flatus.
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Last edited by mcjustis; Mar 20, 2014 at 10:16 AM. Reason: to get rid of my violation point... Three years later
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Old Jan 19, 2011, 10:17 AM
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Would this be of some interest?

[Edited]
rc-air, , , no offnce but with only 7 post, you sure do come on pretty stronge.

I'll guess your very technical savy.
I think maybe I should edit out whatever link I posted.
Hate to get slammed for try'in. I'm just a simple guy.
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Old Jan 19, 2011, 10:36 AM View Post
rc-air
A moderator felt this post violated the following rule: Personal Attack. It is temporarily hidden while rc-air edits it. Show it to me anyway.
Old Jan 19, 2011, 11:18 AM
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Dude,
.2% of 10 pounds is (like I stated earlier) 3.2 oz. Way too small to fly any (10lb) plane. You should learn where to put a decimal point.
You are a fool.
20% of 10 pounds is 2 pounds.
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Last edited by mcjustis; Jan 19, 2011 at 12:55 PM.
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Old Jan 20, 2011, 05:56 AM
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mcjustis

Yep..your right mcjustis...i've been misplacing that darn decimal...My apologies...i guess 2 yrs of constant chemo treatment is starting to take it's toll on the memory cells...sorry.

On a new note...check this formula ( using a 10lb plane still ).
we'll go for a 2:1 static thrust ratio in choosing an eng. ok.....so we'll double the plane's weight to 20lbs.
Now i'll use the general static thrust rating for an eng ( 1hp = appr 6.6 lbs thrust)to decide what eng. hp is needed for my desired 2:1 thrust ratio.
And...(if i place my decimal right...lol )it should work out like this.
.............20lbs /6.6 lbs thrust = 3hp....required for this plane , disregarding areodynamic's for now.
And...for a 1.5 :1 ratio (for the same plane) it would need a 2.3 hp eng.
Seems to me,that this formula works out pretty good i think , except for the fact that eng hp ratings are known to be somewhat unreliable.
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Old Jan 20, 2011, 06:19 AM
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I feel all better now. Not to start another bickering feud, but how do you get that 1 hp is 6.6 lbs of thrust? It does sound about right, but again, there are more factors that come in to play. Just curious.
Martin
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Old Jan 20, 2011, 06:43 AM
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Mike Emilio
LOL...hang in there mike , 108 posts just makes a keyboard cowboy,,,no offence..lol.
Not much logic in using the number of posts as a reference to one's knowledge level.I usually don't bother , because of all the self acclaimed experts , in one fashion or another. Your link is not needed LOL.
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