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HomeRC & PowerAircraftHelicopterEngines Plugs Mufflers Fuel › Nitro Engine - best for high torque (NOT gasser)?
05-14-2011 02:56 PM  7 years agoPost 1
Yeager

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Lisbon, Portugal

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I've bought a Robbe Nova Cuatro (5.5kgs) and are considering what Brand 91 size Nitro Engine to install in it?

I am looking for torque and rotor diameter (790-810mm) before headspeed!

OS, YS, Navarossi, etc?? Whats your recommendations?

Many thanks
Y.[B]

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05-14-2011 08:54 PM  7 years agoPost 2
AirWolfRC

rrProfessor

42½ N, 83½ W

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Torque is not what you need. That concept is for those that don't understand power, the energy required to move something. Torque is only a force and does not address motion.

You want HP and gear it properly.

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05-14-2011 10:12 PM  7 years agoPost 3
barely can fly

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oxford ga. usa

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Not exactly, horsepower is how hard you hit the wall and torque is how far you move the wall after you hit it, that is how it was explained to me anyway.
But to answer the question, YS is a long stoke design and as such makes far more torque than other nitro engines.
You can also look at it this way, you can have a million horsepower but without any noticable torque you won't move anywhere.

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05-14-2011 10:51 PM  7 years agoPost 4
AirWolfRC

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What SHOULD have been explained to you is that torque is a force, like how much you squeeze someting in a vise or how much force you apply to a wrench when tightening a bolt. You can have a million pounds of torque but if you aren't moving anything in the process, you have nothing.

Power, like HP, is torque multiplied by speed. half the torque and twice the speed is the same HP. You can take the first and change the gear ratio by a factor of two and have the second. . . . and the power is still the same (minus losses in the gear train).

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05-15-2011 12:53 AM  7 years agoPost 5
barely can fly

rrApprentice

oxford ga. usa

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Sorry professor didn't mean to upset you but with 800 mm blades your target headspeed is probably about 1500 rpm and your peak torque in most 90 size nitro engines is around 16,000 rpm so your target gear ratio is 10.6 to 1. or for those who like math,

torque x rpm x constant = hp
87.5 lb-ft x 60 rev/min x X = 1hp
X = 1/(60 x 87.5) = 1/5250
torque x rpm x 1/5250 = hp
hp = (torque x rpm) / 5250

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05-15-2011 04:53 PM  7 years agoPost 6
AirWolfRC

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Where did 87.5 come from ? ?

If you have RPM and torque in Ft lb . . .
that's 1 lb of torque applied at a 1 ft radius for 1 revolution
circumference = 1 ft x 2 x Pi = 6.2832ft
so . . . one l lb of force applied over 6.2832 ft = 6.2832 lb ft / rev.

one HP = 33,000 ft lb / min

33,000 / 6.2832 = 5252 - - - not 5250 but more accurate . . .

torque x RPM / 5252 = HP

. . . and it turns out that 1 ft lb torque at 5252 RPM = 1 HP

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05-15-2011 11:24 PM  7 years agoPost 7
barely can fly

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oxford ga. usa

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Yes you are right, sorry have seen both 5250 and 5252 used. Came from a book here, possibly wrong because second book uses 5252.

So, let's first go through the numbers to get from torque to horsepower. Pushing with 87.5 pounds (force) on the end of our 1-foot lug wrench applies a torque of 87.5 lbf-ft. No motion yet, so no work and no power. But now let's say the lug bolt loosens slightly and starts to turn, but that same 87.5 pounds of force is needed to keep the wrench turning. For every revolution of the wrench, you are applying 87.5 pounds of force over a distance of (2 * pi * 1 foot) or 6.28 feet, the circumference of the circle that your hand is making, for a total of 550 ft-lb of work. It's only when this system is actually moving that work is being performed. From here, it's a quick step to say that if you work fast enough to turn that wrench once per second, then you are doing 550 ft-lb of work per second, which means you are applying one horsepower.

By the definitions we can see that HP is directly proportional to torque and RPM. "Directly proportional" means there may be a multiplyer involved, so let's find it using our example numbers, remembering that 1 revolution per second is 60 RPM:

torque * RPM * constant = hp

87.5 lbf-ft * 60 rev/min * X = 1 hp

X = 1 / (60 * 87.5) = 1/5250

torque * RPM * 1/5250 = hp

hp = (torque * RPM) / 5250

This is from the second book.
Now if we are measuring torque and RPM how can we calculate horsepower? Where does the equation HP=TORQUE X RPM / 5252 come from? We will use Watts observation of one horsepower as 150 pounds, 220 feet in one minute. First we need express 150 pounds of force as foot pounds torque.

(The * symbol means multiply in the explanations below.)

* Pretend the force of 150 pounds is "applied" tangentially to a one foot radius circle. This would be 150 foot pounds torque.

Next we need to express 220 feet in one minute as RPM.

* The circumference of a one foot radius circle is 6.283186 feet. ft. (Pi * diameter; 3.141593 * 2 feet)
* The distance of 220 feet, divided by 6.283185 feet, gives us a RPM of 35.014.

We are then talking about 150 pounds of force (150 foot pounds torque), 35 RPM, and one horsepower.

Constant (X) = 150 ft.lbs. * 35.014 RPM / 1hp

35.014 * 150 / 1 = 5252.1

5252 is the constant.

So then hp = torque * RPM / 5252

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05-16-2011 12:40 AM  7 years agoPost 8
helixangle

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Mamaroneck, NY - USA

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@ Yeager
The YS 91 SR should do fine, the scale kit should turn 1400-1700 HS with 810 mm blades.

The YS motors develop the most available torque on the market, as stated above, the YS motor comes to peak torque around 16,000 rpm.

If you divide this RPM # by the HS # you want to run you will find your target gear ratio. If your not running at peak torque you will not develop the response and power you will be looking for.

In addition, if money is of little concern and scale is priority...the kit can run a turbine.

@ AirWolfRC, I know barelycanfly, I can tell you that although he may not be able to "Academically Articulate" the point he is trying to make, he used to race two stroke bikes, and 4 stroke cars as a hobby, for at least more than a decade. In addition he owns a heavy equipment repair and machine shop, and has been doing this for at least 30+ years, so he comes with a TREMENDOUS amount of practical experience, which is worth WAY more to me, and most, than some book...

I say this because, as much as I HATE IT when he's right, he's rarely wrong, and this is of course not to say your wrong either.

My 2c -- j

Be sure the juice is worth the sqweeze
Remember life is hard...even harder for stupid people

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05-16-2011 12:41 AM  7 years agoPost 9
AirWolfRC

rrProfessor

42½ N, 83½ W

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Again, where did you come up with 87.5 ? ?
It looks like out of thin air . . .

. . . actually, I know, but do you ?

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05-16-2011 12:49 AM  7 years agoPost 10
helixangle

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Mamaroneck, NY - USA

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5252 is the end equation of a horse lifting 150 lb to a height of 220 feet [for simple purpose of illustration] as observed by James Watt, the inventor of the steam engine.

Be sure the juice is worth the sqweeze
Remember life is hard...even harder for stupid people

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05-16-2011 01:09 AM  7 years agoPost 11
helixangle

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Mamaroneck, NY - USA

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sorry...answered my own questioin not yours.

why do they use 87.5?

Be sure the juice is worth the sqweeze
Remember life is hard...even harder for stupid people

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05-16-2011 01:51 AM  7 years agoPost 12
AirWolfRC

rrProfessor

42½ N, 83½ W

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1 HP = 220ft x 150lb / min = 33000 ft lb / min = 550 ft lb / sec

33000 / 6.2832 = 5252

550 / 6.2832 = 87.54

If you're working with RPM, you don't bother with 550 ft lb / sec or 87.54

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05-16-2011 02:10 AM  7 years agoPost 13
barely can fly

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oxford ga. usa

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Lets play nice children, the first paragragh is simply out of the first book that i picked up, i assumed that 87.5 is simply a number that the author decided to us or pull out of a hat.
But going past the fact that math is always right and that these articles also state that at 5,252 rpm HP and torque will always be the same no matter what kind of power source is used.
I will say this and have already said to helixangle by phone, if you take a 3.5 HP 90 size nitro engine and bolt it to a go kart you probably won't go anywhere, but if you bolt a 3.5 HP lawnmower engine to the same gokart you will move, not taking into account gearing which would have to be pretty radical to make the kart move with the nitro engine.
Or if you have a 300 HP diesel engine with 10,000 pounds behind it you can pull it pretty easily but a 300 HP 4 or 6 cylinder gas engine won't move it very well at all.
There is more at work here than just HP or a simple math equation and that was my point from the beginning and also just to keep airwolf's panties in a bunch for a while.
Hope there are no hurt feelings guys as i am learning by reading what you post.

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05-16-2011 02:15 AM  7 years agoPost 14
AirWolfRC

rrProfessor

42½ N, 83½ W

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Gearing is what makes it all work. Lawn mower engine with a low gear ratio or nitro engine with a high gear ratio, it's the same output.

Formula engines at 10,000 RPM should give a clue.

World War II engines turning an 11ft propeller at 1,500 rpm because of tip speed limits with the engine turning 3,000 rpm is also a clue.

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05-16-2011 02:15 AM  7 years agoPost 15
barely can fly

rrApprentice

oxford ga. usa

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Also fell sorry for the guy that started this post, he probably is just sitting at his computer shaking his head.

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05-16-2011 07:01 AM  7 years agoPost 16
Yeager

rrApprentice

Lisbon, Portugal

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Hi @everybody,

This turned out both funny, interesting and helpful.

I already understand a fair bit of the "power" and "thrust" equations, but have however put most of the basic mathmatics explaining the theoretics behind me. The maths do have their rights in their own.

The YS recommendation is what I was kind of expecting, just wanted to be open to other potential engines suggestions.

I believe the YS will be a great choice.

Many thanks for your explanations and recommendations.
Y

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