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HelicopterMain Discussion › Calculating Output Horse Power At The Disc, 1HP to 1 lb
03-11-2015 12:00 PM  3 years agoPost 1
icanfly

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ontario

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Let's start here,

http://www.heli-chair.com/aerodynamics_101.html

not certain where I saw this link I began to think about my 450's disc output after reading through more thoroughly this morning. I also want a nice place to refer to the link in future so I'm posting this new topic.

As it stands a 450 with a 1/4hp or 178w brushless motor x 10 through a gearing of ten to one brings a disc output somewhere at about 2hp. Accounting for losses and it would be closer to 1.7 and at the disc. a lot of power moving two ounces or less of mass and at drag (weight of the blades at pitch), this is where the PL factors into the equation.

We could go further to break the hp to watts and amps, amperage being the key factor in converting disc loading of a certain diameter to amperage, round and round it goes, literally and figuratively.

I once asked of a 3500va bl motor could fly a 900 heli with a rotor span of tip to tip of 2m and I think it can be done. A personal challenge will be to devise an ultra light craft weighing LESS than 12lbs.

Appears to be a one to one lb to hp trend in the math, is this correct? It only makes sense since a 700 performs best with a one to one hp to lb ratio. I've heard about disc loading several times but not POWER LOADING.

Alas there are mechanical deficiencies in the standard rc heli configuration that rob power so the disc never gets all the power generated by the motor.

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03-11-2015 12:59 PM  3 years agoPost 2
Peter Wales

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Orlando Fl

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Your first premise is wrong. HP does not change with gearing, discounting losses.

It is the torque which is multiplied, and the rpm reduced. HP = Torque x RPM ÷ 5252

so if the rpm goes down and the torque goes up, the HP remains the same.

I didn't bother reading the rest of your diatribe

Peter Wales
http://scalehelicopters.org

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03-11-2015 01:16 PM  3 years agoPost 3
jake21

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ontario canada

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Very hard to imagine that You could get 2hp output at the blades or 1.7 with losses with only 1/4 hp input. Then You say all the hp cant get to the blades because of losses. Very confusing.
Nothing comes for free.
I must be reading it wrong.

The only way to not crash is up

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03-11-2015 03:24 PM  3 years agoPost 4
Flyin for Jesus

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Troy, IL. 62294

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Peter is right... I did read the rest however.

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03-11-2015 04:07 PM  3 years agoPost 5
icanfly

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ontario

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diatribe
ahh yes, your reply is correct TORQUE is multiplied not hp.
You say all the hp cant get to the blades because of losses. Very confusing
losses in the tail rotor assembly, motor deficiencies, angular losses, mechanical drag, blade drag, add it up and what do you end up with?

If all it takes to fly the snot out of a 700 is a os120 (comfortably with a 90) hp being about 4.5, brushless motors in comparison are wayyyy over powered to their loading, looks great like a top fuel dragster but not everyone wants a 4 second run and a costly rebuild after each race.

fwiw, take the Velos twinny with a combined hp of about 24hp to spin 880mm blades, should be able to lift a few hundred lbs, NO?

read the link before replying then.

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03-11-2015 04:14 PM  3 years agoPost 6
jake21

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ontario canada

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It would be nice if You read My whole reply and quoted the whole sentence that starts with Then instead of cherry picking what You like.

The only way to not crash is up

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03-11-2015 04:18 PM  3 years agoPost 7
icanfly

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ontario

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cherry picking
makes good cherry pie, lol.

all this is probably easier to understand with a graph. Upon re-reading my first post it seems a few notions are in fact incorrect.

A lot of brushless overkill on electric helis is wasted energy, what a gadang waste of wall juice too.

Take my punny 300, step up from a 250, at about 1lb, I did a lift at low rpm test throttling up to a certain point in the curve (you can observe the amount in the throttle curve window of a tx) holding for some seconds while flicking throttle hold while discovering the lowest rpm needed to lift it by adding positive pitch. Working backward it would suggest only a certain amount of hp was necessary to lift the heli. Throw in hard pitch events and the hp demand goes up. If 4g pitch events require 4 times the hp then that at lift then this makes some sense to have a high hp motor.

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03-11-2015 05:09 PM  3 years agoPost 8
MattJen

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UK

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I feel an Airwolf post coming lol
seriously, Dieter Schluters book on Helicopters has all calculation charts to work out power to weight ratio, disc loading, etc etc etc..

Matt

All The Best

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03-11-2015 05:26 PM  3 years agoPost 9
ssmith512

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Indianapolis, IN USA

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Steve

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03-11-2015 06:11 PM  3 years agoPost 10
HeliOCD

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San Diego, CA

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I didn't bother reading the rest of your diatribe
I would hardly consider that a diatribe.

Its all earth!

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03-11-2015 06:12 PM  3 years agoPost 11
Flyin for Jesus

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Troy, IL. 62294

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I agree that most helis are overpowered exponentially. Some people don't understand that changing to a bigger motor won't make your heli faster unless you make changes like increase pitch or HS which would then require a bigger motor.

If you want to do some testing, get a CC ESC with logging. With your big motor, dial down HS and collective pitch to a minimum while maintaining the ability to fly the heli the way your flying style requires.

Log a few flights and the ESC will give you average watts out and peak.
With that data, you can get a smaller motor that will fly your heli to your liking while conserving energy over a big motor.

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03-11-2015 09:37 PM  3 years agoPost 12
icanfly

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ontario

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[quote][quote]

that picture is VERY interesting, a lamb, a wolf, birdy wings. A flying lamb in wolf's clothing? lol. A flying wolf in Sheep's clothing?

Today's topic can be partially blamed on the Military, to which only moments ago a military Hercules aircraft did fly past at a thousand feet due northeast, and a vision projected last summer, a 900.

FfJ, ideally a yep esc with data logging would be utilized. The exercise is about maintaining 3d madness levels while having the ability to mess with speed lift and endurance, can one machine do it all while it is 2m in rotor span?

Its extremely dangerous for manufacturers to supply the market with a race car level machine to first time noobs and ignorant beginners. It would be much more prudent to offer lower power units to assist in learning curves no matter the size rather than what is currently supplied ONE SIZE FITS ALL, no it DON'T.

Here's the diatribe part, rather "anecdote", I go to a waterfront park trail this aft where a woman is flying a dji quadly copter with iphone fpv screen, a babe in a stroller chirps, "Look, a helicopter" I say shyt, people are so dumb, that ain't no helicopter, MY helis ARE helicopters as the quad continuously hovered until I departed minutes after snapping a gopro pic, if they only knew.

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03-11-2015 10:06 PM  3 years agoPost 13
AirWolfRC

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The military full size are as low as 5lbs/HP and some of the light weight civilian stuff is as high as 10lbs/HP

1lb/hp is . . . a tad over-powered.

As for increasing HP with a gear ratio . . . I don't think so.

Except for efficiency losses (drag & friction),
HP in to a gear box is the same as HP out
. . . no matter what the gear ratio.

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03-12-2015 04:37 AM  3 years agoPost 14
Flyin for Jesus

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Troy, IL. 62294

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Sure 1hp/lb is overpowered for full scale... But what it required for some 3D flying? A guy at my flight field drains his packs in half the time that I do... All because of how he flies.
So some may require 1hp/lb to do the things they want to do...

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03-12-2015 05:59 AM  3 years agoPost 15
FNFAL

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Dayton OH

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1lb per 1hp is very high performance...whether you're talking cars, motorcycles, or RC helis. I doubt many things exist in the real world with that power to weight ratio.

I am building a super 550, trying to keep all up weight around ~7lb with Ti parts and all. My super expensive motor can only do 3500w continous or about 4.7hp.

So, for even after spending lots of money, my bird may have a power to weight of 1.5lb per hp...maybe a little better if you consider some motor peak output.

BTW, gearing does not multiply horsepower as many have already said. Sadly when you calculate your 450 number you'll have to stay with your 178w.

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03-12-2015 01:31 PM  3 years agoPost 16
icanfly

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ontario

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it's true my general estimation is out of line with reality, the reality being much closer to 4 to 8 lb per hp in many rc helis.

I think where things get crazy is exactly what FfJ mentions, pack drainage goes up depending on flying style.
I am building a super 550, trying to keep all up weight around ~7lb with Ti parts and all.
yes, the Shuttle 550 nitro in my gallery now weighs under 6lbs due to a few alterations, lol.

my topic comes on the heels of a personal milestone THE ONE POUND 450 INCLUDING BATTERY (weighed in last Sunday at about high noon after a few alterations), who's numbers can be cut even further, at a high cost, SAY YOU WOULD NOT WANT ONE? Are we talking a thousand dollar 450? $1000? something like that. Flew her yesterday for the first time after reaching the milestone, in blustery wind, odd how being dfc it was very stable with a bit of wind ballooning in hover even when the tx has little expo on ele/ail. My 450 is slower to ail/ele than my 300 which I like to fly in my limited backyard space mostly. Dump a KDE 1hp 450 motor in at a weight penalty over standard offerings of +40gr and it almost makes one to one, ooowhee (another $108+) done deal.

Next goal in that respect is to achieve a seemingly unobtainable 5lb 900. Hp to lb ratios and all it gives a sense of what power plant is necessary, 1600w perhaps at a ratio of 1/4hp per lb. If lessons of the past are to be measured upon it will happen, only a matter of investment, that's where this has gone. The pieces of the puzzle are slowly coming together, more money please, lol.
1lb per 1hp is very high performance...whether you're talking cars, motorcycles, or RC helis. I doubt many things exist in the real world with that power to weight ratio.
I used to worship Top Fuel Dragsters. There's the Nitro gal dangit.

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03-12-2015 02:40 PM  3 years agoPost 17
FNFAL

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Dayton OH

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Beyond shortend flight times, the quest for better power to weight will also affect reliability.
I think where things get crazy is exactly what FfJ mentions, pack drainage goes up depending on flying style.

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03-12-2015 03:09 PM  3 years agoPost 18
jake21

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ontario canada

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A 4 second ride in a top fueler would be awesome.

The only way to not crash is up

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03-12-2015 04:00 PM  3 years agoPost 19
AirWolfRC

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42½ N, 83½ W

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Let's run some numbers,

Running at 20x, a 2000mah cell produces 0.204HP . . . for about 3 minutes.

That cell weighs about 1.5oz . . . that's about 0.46lbs/HP
. . . and that's no airframe, no motor, nothing but the battery.

A 6S 5000 pack at 20x produces 3.06HP . . . before efficiency losses.
. . . it weighs about 3.06 x 0.46 = 1.4 lbs

So to get a 1lb/hp bird, your whole rig needs to weigh only 3.0lbs
. . . that's 1.4 lbs for the battery and 1.6 lbs for everything else.

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03-12-2015 04:35 PM  3 years agoPost 20
Funky Trex

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Westerville, OH - USA

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Sounds as likely as that 5lb 900 coming next

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HelicopterMain Discussion › Calculating Output Horse Power At The Disc, 1HP to 1 lb
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