CafeenMan

Somebody sent me an e-mail asking what the difference is. As far as I know Brake HP and HP are the same thing, right? Anyone know if there's a technical difference?

DarZeelon

Paul,

Brake-horsepower signifies it has been measured against a brake, in a dynamometer.

This brake (usually hydrodynamic) prevents the engine from speeding up, so the torque is read from the force needed to do this.
From torque and RPM, the horsepower numbers are calculated.

For model engines, a calibrated, known load is spun by the engine, to get the same effect.

One horsepower is equal to 33,000 Lbs. Ft. per minute.

CafeenMan

Thank you for this information. I don't understand it, but that's fine. I will forward it to the person who asked.

- Paul

downunder

CafeenMan...right, there isn't any real difference between them. Brake HP is normally used because of the way it's usually measured. A Brake can be your fingers on the crankshaft (not recommended), a propellor or whatever. There are other ways to determine HP without using a brake but even then it's normal to give the result as BHP.

CafeenMan

Thanks.

Man... your avatar cracks me up.

CAPtain232

My Feedback: (40)

Paul,

I think you know as well as I do, but tell your friend that in this hobby, HP doesn't mean squat.....It's all about torque. This is what info we should try to get from the manufacturers.....Problem is, whether they give us HP or torque ratings, they need to use the same measuring system so that all the information is TRULY comparable.

CafeenMan

Yeah... there has been a lot written about how manufacturers can fudge the numbers without actually lying. He didn't say what he wanted the info for, but I gave him a link to this thread and recommended that he become a member here.

DarZeelon

Paul,

Engine manufacturers do "elevate" their numbers and at their rated RPM, they are usually unusable for actual flying purposes.

But what Jeff wrote is also quite wrong. Horsepower is everything!

If a given engine makes a given amount of torque, at a given RPM level and another engine gives a larger amount of torque at the same RPM, it will be just as high on its horsepower level, in respect to the "given" engine.

High horsepower levels are automatically high torque levels also, but high torque levels are not necessarily high horsepower.

If your car is at a certain speed, for which you can select any of three given gear ratios, its acceleration will be the highest with the ratio that will have the engine spinning at the highest HORSEPOWER level, rather than the ratio that will have the engine at the highest TORQUE level.

Torque and RPM will be translated into horsepower, to determine the available thrust. Torque alone is quite worthless.
This is because horsepower is equal to torque times speed. Torque is a static value and therefore:
HORSEPOWER IS KING!

This is why an engine is best propped, so in high speed flight, it will spin at the RPM, at which maximum HP was measured, (not the "rated" RPM).


The best measure of an engine's relative performance, is the RPM at which it can spin various propellers, not the rated HP levels its manufacturer advertises.

CAPtain232

My Feedback: (40)

so many things that you are saying are similar to what I am trying to say, only I paraphrased to keep from writing a book. The whole RPM thing is true about HP allowing and engine to reach a higher RPM. What I am trying to say is that most of the listed engines here are going to run similar NO LOAD RPM......meaning close HP figures......The fact that one engine can turn a bigger prop than another is closely related to the fact that one engine has a higher torque output than another.



This is a design issue and does not hold true for all situations....I have to revert back to the days when I raced and built car engines (small and big block chevys) It is easy to take a small block chevy and create a workhorse out of it by setting it up so that it creates loads of torque throughout the rpm range....this style of engine does NOT NEED TO BE A HIGH HP ENGINE, so by design you can have lots of torque with relatively low amounts of HP.........................

We could get into a huge debate here, which is fine but we need to start our own thread.....my point is that these engine will be relatively the same HP but their torque will be the deciding factor as to which one spins the bigger prop.....This is why I say HP doesn't mean squat

CafeenMan

Ok, ok...

Guys? This is one of those topics that can get totally lost in semantics, and personally I don't care what the answer is. Somebody sent me an e-mail through my website and simply wanted to know if there's a technical difference between HP and BHP so I'm trying to get him an answer. This could turn into another Flaperon thread if we're not careful.

LearjetMech

Wow I see how this thread can get out of hand. Here is my $ 0.02! Horsepower and torque! Two totally different things that interact with each other. Lets deal with Horspower first. Indicated Horspower (IHP) is the horsepower developed by the engine, that is, the total horsepower converted from heat energy to mechanical energy. If the charateristics of the engine are known, the IHP can be calculated using long drawn out formulas. Brake Horsepower (BHP) is the ACTUAL horsepower delivered by the engine to a propellor or other driven device (car wheel, etc...) It is the the IHP minus the Friction Horsepower (FHP). FHP is the part of the total horsepower necessary to overcome the friction of moving parts in the engine and its accessories. Thus BHP=IHP-FHP.
So to answer your question, YES there is a difference!

CAPtain232

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Paul

Sorry for getting off topic here......BTW LEARJET is RIGHT ON THE MONEY



Any new discussion about HP vs TORQUE needs to be posted in the thread I just started in the GAS ENGINE FORUM......

DarZeelon

Nikolaus and Jeff,

The question asked was if there is a difference between BHP and HP.
BHP means it is the actual HP that the engine puts out through its output shaft (at the flywheel, so to speak).

The term IHP was not mentioned in the question and is of no importance, since it is not what the engine actually gives you.
BHP is and by all likelihood, when HP is used, BHP is meant, because it is the force that drives the plane, or other vehicle.

There are different standards: DIN, SAE, JIS and maybe more, but DIN is the comparable, real HP and JIS numbers are always higher (the engine doesn't drive the water pump, or any other ancillary). SAE is somewhere in the middle.

BHP is usually synonymous with DIN.

LearjetMech

Dar,
You need to re-read my post and understand it thouroghly! IHP, or Indicated Horsepower is simply the amount of TOTAL HORSEPOWER the engine is CAPABLE of making on paper! This is calculated using a complex series of formulas, using engine parameters such as bore, stroke, etc... yada yada yada. You will never see this horsepower number on a dyno, nor will the engine ever produce this HP. BHP, is what you see on the dyno. Your terminology is off!!! I would suspect that engine manufacturers us IHP numbers, as opposed to true BHP numbers. The question was, "Is there a difference...." I answered it, you didn't!!

Flypaper 2

if you were to put an appropriate reduction drive on an engine that allows the engine to turn at its rated hp/rpm with an appropriately larger prop, then it would be the most efficient setup.

ZAGNUT

My Feedback: (1)

i think there was a time in history when IHP was the all important number, maybe back in the 40's or so. cars were taxed according to it much in the same way that they are taxed today by displacement.
i doubt any model engine manufacturer would use IHP today as it involves measuring combustion chamber pressure which would'nt be a whole lot easier than using a brake dyno. i think they either just make a wild ass guess or test the engine under perfect conditions.

Dar, your car only has 3 gears??


dave

LearjetMech

Man, I didn't realize the acronym "IHP" would screw so many people up. Ya'll need to read my first post! IHP can never be obtained, and is calculated using different measurements from the engine when it is not running. All these measurement arte plugged into formulas, and Horsepower is calculated, Subtract the frictional losses, etc.. and you end up with BHP. HP (IHP), and BHP are different!!!

ZAGNUT

My Feedback: (1)

maybe nowadays you can measure IHP without running the engine but in the good old days you used an [link=http://www272.pair.com/stevewag/indicator/indicator.html]engine indicator[/link] to measure cylinder pressure while the engine ran. the "engine indicator" marked an "indicator card" that you used along with various physical measurements to calculate the IHP

and nowhere did i see anybody state that you could attain the IHP as usable power

dave

downunder

OK, settle down guys. LearjetMech is quite right about the IHP compared to BHP and IHP would be the same as BHP in a frictionless engine. I happen to have graphs for torque and HP for a Super Tigre 46 running in 4 stroke mode (which in itself is most interesting) that were derived from the actual internal pressures over several complete cycles. This is the Indicated HP as is pointed out on the torque graph (.51HP before internal losses). If the engine had simultaneously been running on a dyno then it would have shown a lower BHP figure (maybe .4HP?) and from these two figures the actual friction losses could have been calculated.

The graphs can be found at http://www.holdfastmac.com.au/424stroking.html and have only been used after I had permission from Brett Buck (my polite way of saying no one should steal them to use on their own web page without asking Brett first ).

Sport_Pilot

Yet torque wrenchs make poor model engines, even the small light weight engines. Keep in mind that if the prop doesn't turn there is no horsepower generated, but torque can be applied with out turning, as when trying to remove a stubborn bolt. Yet there is no power until the shaft starts to turn.

Flypaper 2

Ever turn a prop by the blade and have it kick in your hand? That's measurable torque but it didn't turn the motor over.

hopkimf

My Feedback: (56)

It takes power to do work, horsepower, kilowatts, or whatever you want to use for units. You need torque and speed to get power. The formula for HP (in US units) is: Horsepower = Torque X Speed / 5252. Torque is in FT-LB; Speed is RPM. For example, an engine that develops 2 FT-Lb of torque at 10,504 RPM would provide 4 HP (2 x 10,504 / 5252). Another engine that produces 4 FT-LB of torque at 5252 RPM would also provide 4 HP ( 4 x 5252 / 5252). So let's not have anymore arguments about torque being the important factor. We need both torque and speed. to develop power. If one engine can spin the same prop faster than another, it sure seems like it's putting out more power.

Maybe someone here has access to engine power curves and propeller power absorption curves. They could be plotted together, with the intersection being the operating point.

Sport_Pilot

Yes Flypaper, and since the kick back produced no work no power was generated.

hopkimf

My Feedback: (56)

One more comment on an earlier note on IHP, or Indicated Horsepower. It should have no part in this discussion. IHP shows the theoretical potential of an engine before friction, pumping losses, etc. come into play. Output after all the losses is what's important, so let's forget about IHP.