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HomeAircraftHelicopterMain Discussion › Calculating Output Horse Power At The Disc, 1HP to 1 lb
03-12-2015 04:42 PM  3 years agoPost 21
Flyin for Jesus

rrVeteran

Troy, IL. 62294

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The 1hp/lb was just a number calculated from a 700 size Heli weighing like 12 lbs and has a 12 hp motor...
The flaw in your calculations is that you're calculating at a constant HP requirement.
If you have a 12lb heli with a 12hp motor... You simply will not get a 3 minute flight if you're pulling a constant 9000 watts.
I can easily believe that you can get a heli with 1hp/lb but speaking at a peak HP output to match the weight... Not constant.

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03-12-2015 05:03 PM  3 years agoPost 22
AirWolfRC

rrProfessor

42½ N, 83½ W

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I was talking about peak power
. . . and if you hold that power, you only run for 3 minutes.

In a nut shell, with a battery that's only good for 1/2 lb/HP (peak output - 20x), the airframe can weigh no more than the battery to get 1 lb/HP

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03-12-2015 05:06 PM  3 years agoPost 23
icanfly

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ontario

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I can easily believe that you can get a heli with 1hp/lb but speaking at a peak HP output to match the weight... Not constant.
that's what is a fact of the matter, not using the entire output power, the drain on the battery when in high hp mode soars.

Weighed my 550 shuttle an hour ago(old bird with a few new twists), weighed in a 5.6lbs (with aluminum boom, cf being half the weight of alu it should be changed out soon) The shuttle has a few excesses due to dated engineering and design. I'm beginning to think Nitro is where the one to one ratio will shine keeping endurance numbers high compared to electric.
Beyond shortend flight times, the quest for better power to weight will also affect reliability.
this is true

Not everyone is on a mission from god to rinse as much water from a stone as possible, my quest was born years ago when a certain mtb I had reduced from 19lbs to 16.5lbs at a cost of three times original value, you get what you pay for.

I like the YEP esc because you can set very low throttle from the tx without governor and not burn it up. CC is great and all, lets see logging in a freewheeling esc now folks that is where the future is, love to make a heli and include it as oem. YEP esc cost is twice that of standard hq offerings.

The OPTIONS are getting better out there, from all sides of the rc world, great days.

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03-12-2015 05:28 PM  3 years agoPost 24
FNFAL

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Dayton OH

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I really don't see nitro winning the power to weight ratio over advances in electric. But it does have that "burning fuel weight off" as you go to increase P/W.

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03-13-2015 01:29 AM  3 years agoPost 25
icanfly

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ontario

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that's a very good fact of the matter.

So happens when I did my 550 weigh in it has fuel in the header and main tanks, mostly full. It will loose a little more weight here and there as the days progress. More than a 450 weight challenge success has happened lately, another success is ballast less blades, NO LEAD, cog at 50/50. Experimenting is fun as all hey,,,,,,,,,,hey.

I can absolutely recommend reading the first post and link.

HEY

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03-13-2015 01:59 PM  3 years agoPost 26
FNFAL

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Dayton OH

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Like you, I've done some thought before on this too, and it seems to me at this time, what is offered (off the shelf), the 700 class bird is potentially easiest to get a high power to weight.

That is with the big 4540 style motors you can use, and a frame weight essentially not much heavier than a 550. I calculate a 160 to a 200A ESC running around 14-16S.

That is if you can crank up the headspeed and also not have the rotors/blades self destruct. Otherwise, without head speed you can't extract all the power your motor is capable of.

But just my 550 at idle up has the blades pulling at over +700lbs of force...so imagine what the 700 does.

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03-13-2015 04:09 PM  3 years agoPost 27
icanfly

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ontario

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the 700 blades pull about 800(and a little)lbs doing 400+mph at the tips at 2200rpm, from a posted report on the net, I think that info was over on hf btw. The topic came up back in January or there-abouts. 700mm blades weight 200gr while the 550's are only 150gr on average (and I think those are fb specific blades)

What is the idle up rpm of your 550? My Shuttle is something like 1600rpm, 1800 at 100% throttle (nitro so the rpm is low compared to electric, a conversion to electric is a strong consideration however)

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03-13-2015 04:24 PM  3 years agoPost 28
FNFAL

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Dayton OH

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~3000+ running the newish Align HD spindle with 12.9 flanged M5 bolts and a non-stepped feather shaft and safety wired blades.

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03-13-2015 04:28 PM  3 years agoPost 29
AirWolfRC

rrProfessor

42½ N, 83½ W

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the 700 blades pull about 800(and a little)lbs doing 400+mph at the tips at 2200rpm, from a posted report on the net,
I think that number is on the light side.
How far out from the main shaft is the CG of those blades ?

I had a link to a RR post where I showed the calculations for centrigugal force but Mark has been messing with my gallery and it's no longer there.

EDIT,
Here it is https://rc.runryder.com/p2243030/

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03-13-2015 04:36 PM  3 years agoPost 30
GyroFreak

rrProfessor

Orlando Florida ...28N 81W

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Your link provided interesting reading, thanks.

I think about the hereafter. I go somewhere to get something, then wonder what I'm here after ?

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03-13-2015 04:45 PM  3 years agoPost 31
prototype3a

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Christiansburg,VA

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Otherwise, without head speed you can't extract all the power your motor is capable of.
The thing about spinning the blades very fast is that the hover load on the motor increases exponentially.

Jan Henseleit said the following about the TDR during development.
So more than 1800 rpm at the main rotor are unnecessary when flying this helicopter. The logger data show that the efficiency of the blades decreases rapidly with increasing head speed, so that most of the energy is wasted. For the same flight condition "Hovering at one position" 570W is required at 1300 rpm at the rotor and at 1850 rpm you already need 1000W. At more than 2100 rpm 1500W are required, i. e. nearly the triple amount, although you do nothing more than hovering.
Now consider that some people are running 700s at 2600rpm. I would guess they're using almost 2500w JUST TO HOVER. Now consider that they're using motors and escs capable of 5400w continuous. So that leaves ~3000w of power for aerobatics.

Personally, I'd rather run a light setup with a moderate headspeed (~1800rpm) with a 4200w motor like a 4035-560 or 4235-520 and still have ~3000w for aerobatics but with far less stress, wear and tear.

~Drew

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03-13-2015 04:57 PM  3 years agoPost 32
FNFAL

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Dayton OH

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Indeed that makes very good sense. But there will be nothing practical left about this hypothecial project bird, but a knife-edged tool.

When you have a +10kw motor you have to dump that energy somewehere. If your goal is heavy lifting then longer blades or multi-blade I'm thinking. If it's speed, then to me I think higher headspeed???

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03-13-2015 09:29 PM  3 years agoPost 33
icanfly

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ontario

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thanks for the replies everyone, an unexpected and welcome inclusion of good info from Henseleit, can't question those guys much. The info suggests if you wanted another 150 rpm it would cost another 500w, so this falls in the law of diminishing returns.

Jeeze, I got so used to my little back yard 300 with 5000 rpm it doesn't sound as F1 anymore with a 4280kva at 98% at around 3800rpm, (pre downgrade motor and battery were always very hot upon landing) I miss it, lol.

does everyone equate low rpm to slow action? probably.

Doesn't sound encouraging to hyper rpm a heli just to see it move so fast you almost can't see it, like the P51 Mustangs who's motors were burned out quickly at high rpm, speed costs some serious energy.

If there was a full size Bell 500 with 1800 rpm I know it would be able to 3d, lol.

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03-13-2015 09:35 PM  3 years agoPost 34
prototype3a

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Christiansburg,VA

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I wish I had a good video of my Logo500 Ultralight flying. I run 550s on it at just 1500rpm and I wouldn't call it 'slow'.

This is from almost two years ago when it was 'new'. These days, I fly it much more aggressively. Back then I was still sort of feeling it out to see what it would and would not do.

Watch at YouTube

~Drew

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03-13-2015 09:59 PM  3 years agoPost 35
AirWolfRC

rrProfessor

42½ N, 83½ W

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The laws of physics still apply.
The best performance from the blades is with an Angle of Attack around 8º. Anything less than that and you loose efficiency of the blades (and increase the "responsiveness" ).

As light as the disk loading is on these models (0.5 lb/ft²), you don't need faster heads or multiple blades. A tip speed of around 300-400 fps is very slow compared to the full size with much higher disk loadings.

You want efficiency/endurance, slow it down. You want to fly like a mexican jumping bean on crack, spool it right on up there.

PS

Here's what I posted to calculate centrigugal force back in 2006.
https://rc.runryder.com/p2243030/

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03-14-2015 12:38 AM  3 years agoPost 36
AirWolfRC

rrProfessor

42½ N, 83½ W

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Here's another apporach . . .

If you want better performance for the power on board . . . try smaller blades.

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03-14-2015 02:27 AM  3 years agoPost 37
icanfly

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ontario

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I'm impressed by the Logo 550 flying there prtotype3a, some shining moments every so often. One can only imagine what two years of going through the motions has done.
If you want better performance for the power on board . . . try smaller blades.
Interesting, 8* pitch best, 1500 to 1800 rpm best, Pump up the rpm and flight time suffers, pitch events are quicker, parts are stressed sooner, bearings wear quicker, links, servos, gears, probably a few things more, all in the name of a hyper active 3d flight. Obviously not for everyone, like the rev of 7500rpm of a Nascar on the highway in a daily driver, 100% passing power until something fails.

Alright, tune the machine to best pitch, blade length and rpm, hp, weight, gearing, combination and be satisfied then go fly, fair enough.

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03-14-2015 02:53 AM  3 years agoPost 38
AirWolfRC

rrProfessor

42½ N, 83½ W

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When I say 8º, I mean Angle of Attack . . . not pitch angle.
That angle gives about the best efficiency.

For a NACA 0014 profile blade which is the most common blade shape for these model helis (http://airwolfrc.com/NACA%204%20digit.png), the best L/D (best efficiency AoA is about 7º. back off from that by at least 1/2 to accommodate a pull up of up to 3G's with blade AoA up to 12º. That's an estimated blade pitch angle of 16º

I guestimate that the downwash through the rotor disk is good for about -4º so the AoA plus 4º gives a blade pitch in hover of about 11º.

If your hover pitch is less than that, your head speed is likely too fast or you have too much blade.

Setup your collective to accommodate ±16º and give it a try.

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03-14-2015 04:58 PM  3 years agoPost 39
FNFAL

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Dayton OH

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16 and 16...whoa...you mean on the bench?

I understand how you're working backwards to derive your values but why do all the manufacturers suggest collectives grossly short of that....

I have motor/esc headroom. I'm willing to try it though....but you throw in a little cyclic too and now you're talking some serious a of a.

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03-14-2015 05:30 PM  3 years agoPost 40
icanfly

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ontario

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Something I had to adjust for on a heli when lowering the head to the barest minimums where clearance between the swash, frame. and hub were 0, had I not reduced some servo rate in the tx , I know the 450 pro v2 dfc would go a total of 18* in one direction before hitting anything, just don't want that much.

Interesting again because I rarely ever use full collective, aka stick banging, to get the heli to move around quickly. I'll have to keep this in mind when flying the 550, how much is too much when a costly crash is always nearby should the limits be ignored.

Every time I fly lately I'm doing quick direction changes in a stationary 180 (wall stop) and listen for drag which in turn is waste energy. It should be that you fly the machine in the most efficient manner possible and not stick bang the collective with high g force loading on the rotor, rpm being thought of as the element overcoming stall in those maneuvers.

It's one thing to do a tic toc, it's another to integrate it into every other move, tic toc'ing piro flips, lol, that would be something .

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