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Old Dec 13, 2012, 09:18 AM
Horizon Hobby Employee
United States, IL, Mahomet
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Challenge declined. The engine provides excellent performance in its intended environment IE: installed in an airplane, operating outdoors.
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Old Dec 13, 2012, 09:27 AM
Complete RC Idiot Savant
The Netherlands
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Quote:
Originally Posted by DarZeelon View Post
The output curve is pretty flat... It is turning out .95 HP (709W) on the 12x6 APC @10,500 RPM, 1.04 HP (777W) on the 11x6 APC @11,800 RPM and 1.02 HP (750W) on the 10x6 APC @13,700 RPM.

I challenge Craig and Jimmy to show all of us here, how 1.68 HP @ 16,400 RPM, can be extracted from this engine!
There is something wrong with those numbers.... I have never seen an engine with a power curve that flat, over such a wide RPM range. (not saying Dar made a mistake, just saying that that curve is VERY unusually flat for a 2-stroke)

The power output normally shows a greater variation, and especially, a sharper drop after peak power has been passed. So, I doubt those figures to be accurate....

As peak power for a 10 cc glow engine can easily exceed 2 HP at comparable RPM figures, and taking into account that on gas, typically power drops by 20~25%, the claimed 1.7 HP would not be impossible.

Not impossible, is not the same as "the claim is true" though....

Brgds, Bert
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Old Dec 13, 2012, 09:39 AM
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Quote:
Originally Posted by Craig Greening View Post
Challenge declined. The engine provides excellent performance in its intended environment IE: installed in an airplane, operating outdoors.
Why not, Craig?

It is not only Horizon Hobbies with this new engine; it is virtually all model engine manufacturers, who advertise what can only be described as 'tall tales', regarding the output of their engine.

It is time all of them just use the target RPM on given props like in the .pdf file Jimmy posted (or like Dub Jett does for his engines), without bothering to claim the 1.87 HP in the specs.

I am only 'making waves' because you are making claims...
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Old Dec 13, 2012, 09:46 AM
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I was getting about 0.8 HP with the NGH 9cc engines, sometimes a little more, so their 1.04 HP numbers for the Evo 10cc engine is pretty reasonable to me.

I think you could get 1.68 HP using a Evo tuned muffler on the engine along with a 9x7 prop. You might have to advance the timing a little bit more. But I don't think the fad has started for gas engine powered Quickie 500 Pylon racing yet. But that is a possibility though.
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Old Dec 13, 2012, 09:53 AM
Horizon Hobby Employee
United States, IL, Mahomet
Joined Jun 2006
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We have an engine team, and they published real world RPM numbers for a range of props. For the vast majority of modelers, those are adequate to determine if the engine is suitable for an installation.

I'm not even a little bit interested in debating you on theoretical vs. actual HP calculations and output.

Craig

PS: It's Horizon Hobby, not Hobbies.


Quote:
Originally Posted by DarZeelon View Post
Why not, Craig?

It is not only Horizon Hobbies with this new engine; it is virtually all model engine manufacturers, who advertise what can only be described as 'tall tales', regarding the output of their engine.

It is time all of them just use the target RPM on given props like in the .pdf file Jimmy posted (or like Dub Jett does for his engines), without bothering to claim the 1.87 HP in the specs.

I am only 'making waves' because you are making claims...
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Old Dec 13, 2012, 10:27 AM
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Quote:
Originally Posted by Craig Greening View Post

I'm not even a little bit interested in debating you on theoretical vs. actual HP calculations and output.
I am not making it personal.
We are debating your claimed HP number in an open forum; and there is no such thing as 'theoretical HP'.

With a glow engine, the manufacturer can decompress the engine, use 60% nitro fuel, install an adjusted-for-length, un-muffled tuned-pipe and actually achieve the claimed figure.
It might not be as the engine was purchased, as well as in contrary to the engine's warranty; but it is actually achievable with these alteration.


With a gas engine like this Evolution, which I do trust is of excellent quality; you are already using the most potent fuel it is supposed to use. Raising the C/R and using higher octane gas, would very marginally raise the power.

From the APC numbers Jimmy posted, the engine produces as much as 1.06 HP. A tuned-muffler, like the one from Jett that you offer would raise output by ~25%.
It is still some distance below the 1.68 HP that your specs claim.

Why don't you just drop that so-called 'theoretical HP' from this engine's specs; and replace them with those 'props@RPM numbers'?
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Old Dec 13, 2012, 10:38 AM
Complete RC Idiot Savant
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Originally Posted by DarZeelon View Post
We are debating your claimed HP number in an open forum; and there is no such thing as 'theoretical HP'.

Aehm.....

Actually.... yes.... there is....

In fact, I would say, there is ONLY "theoretical HP" as virtually ALL engine builders, from RC engines to big marine diesels need to refer the stated output to some form of standardized conditions, and there can be BIG differences between nominal output and actual output.

Currently (as I am writing this) I am sitting on top of a marine diesel that has 3500 kW on the identification plate, has testbed records stating over 3900 kW (which is probably derived from indicator diagrams which I cannot verify due lack of the actual draw-cards) but which in reality is maybe delivering 3000 kW at best, looking at fuel consumption and its caloric value, and based on scavenging air pressure and max combustion pressure.
But I have no way of knowing how much it is producing actually.

So yes.... the only thing a manufacturer can state is theoretical HP, because actual produced HP can vary too much due to influences outside the manufacturers control....

Brgds, Bert
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Old Dec 13, 2012, 11:51 AM
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Bert,


Does this 'theoretical HP' need to be sourced from something; actual data, perhaps, or can it just be a grandiose number that looks attractive for the manufacturer to advertise, so that his sales will rise???

The example you gave is not so right... The actual power of that marine Diesel is so much greater.
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Old Dec 13, 2012, 12:01 PM
Horizon Hobby Employee
Joined Dec 2012
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Hey guys,

I'd just like to clarify how we obtained those numbers. We have on-board telemetry on all the aircraft we test, so the posted numbers are real-world measurements. They are not theoretical. The horsepower calculations are derived from those numbers and are only meant to give you a general ballpark of what power the engine is putting out. These numbers are theoretical (if that's your definition). We find that it is much more practical to give real-world numbers (prop size/RPM).

That being said, the rated horsepower that is listed on the website is accurate to what we've tested. We have obtained 16,400 RPM on an APC 10x6 propeller. If you run the numbers on the power calculator that was previously posted you will find 1.67 HP. We showed 15,100 RPM on the chart I previously posted because that is a more averaged number that we obtained and more realistic that everyone should be able to measure.

Please only use these numbers we post as a guideline for determining which prop to choose for your given application. That is a much more useful approach to these charts than a power curve. We have found the sweet spot in this engine to be using a 12x6 - 13x6, though it does have a decently flat power curve.

I hope this helps clarify a little bit as to how we determine those ratings and numbers.

Regards,
Jimmy

Horizon Hobby, Inc.
Saito, Evolution & Zenoah Developer
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Old Dec 13, 2012, 12:16 PM
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Quote:
Originally Posted by DarZeelon View Post
BRW,


The numbers posted by Jimmy are legitimate.

The output curve is pretty flat... It is turning out .95 HP (709W) on the 12x6 APC @10,500 RPM, 1.04 HP (777W) on the 11x6 APC @11,800 RPM and 1.02 HP (750W) on the 10x6 APC @13,700 RPM.

I don't have the prop index for the Evo props, so I cannot plot-out the numbers.


Quote:
Originally Posted by Brutus1967 View Post
There is something wrong with those numbers.... I have never seen an engine with a power curve that flat, over such a wide RPM range. (not saying Dar made a mistake, just saying that that curve is VERY unusually flat for a 2-stroke)

The power output normally shows a greater variation, and especially, a sharper drop after peak power has been passed. So, I doubt those figures to be accurate....

As peak power for a 10 cc glow engine can easily exceed 2 HP at comparable RPM figures, and taking into account that on gas, typically power drops by 20~25%, the claimed 1.7 HP would not be impossible.

Not impossible, is not the same as "the claim is true" though....

Brgds, Bert

To compare I do show the three values, 0.95 HP/10.500 rpm, 1.04 HP/11.800 rpm and 1.02 HP/13.700 rpm in the graph of the Super-Tigre G60 Blue Head.
See the blue curve! Flat?

TF
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Old Dec 13, 2012, 12:23 PM
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Prop power calculators are for static RPM only!

Greg
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Old Dec 13, 2012, 12:33 PM
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[/COLOR][/QUOTE] The example you gave is not so right... The actual power of that marine Diesel is so much greater. [/COLOR][/QUOTE]

And how do you know that? Do you have all of the specs of his engine?

Maybe what would satisfy you is if the stated HP was a range, rather than a specific number? That is about as silly as a car company stating the MPG as a range (depending on many outside factors)...
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Old Dec 13, 2012, 12:42 PM
Complete RC Idiot Savant
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Quote:
Originally Posted by DarZeelon View Post
Bert,


Does this 'theoretical HP' need to be sourced from something; actual data, perhaps, or can it just be a grandiose number that looks attractive for the manufacturer to advertise, so that his sales will rise???

The example you gave is not so right... The actual power of that marine Diesel is so much greater.
Of course it needs to be sourced from something.... but what you do with that data.... that's where the trick is.... How you convert to ISO conditions, and how you correct for the different conditions makes a great difference.
Every engine manufacturer has his own theories about how to do those conversions.
Even the way you measure has a very distinct influence on the measured output.
Take those "propcalculator" values for example.... where do they come from? Are they corrected for air density, corrected for what is behind and in front of that prop? Are all 10 x 6 props the same? A very crude measurement at best, and nevertheless you believe them to be true, but the distributor derives his claimed output from the same source....

You are so very wrong assuming that there is a relation between power measurements, and the size of an engine. Basically the same methods apply, and the same corrections/deviations. The same theories and the same calculations.
But then again, I have been MEASURING power output (not guessing based on some "propcalculator") for most of the last 20 years.

I know only very little about tuning engines or getting the most out of it, but I do know a thing or two about how power is generally measured, and generally, I find that the claims of most manufacturers are not far off, if you replicate their measurements accurately, and even not really far off if you correct properly for the specific conditions you are doing your measurements in. And that goes for the full range from model engines, motorcycle engines to big marine diesels that I did measurements on.
I am very sure, that the Diesel currently under my supervision will give the same data on its testbed every time, even if it would be me doing the actual measurements. Still, I do not achieve these values in its current application, analog to you not achieving this 1.67 HP in a real life situation.

Basically all that blahblah means, that if a manufacturer states a certain power output, and you are not getting that figure, than something is really different in the way you measure, or there is something really different between the measuring rig and your actual engine application.

But it does NOT mean, that the engine manufacturer (or distributor) is telling lies or blowing numbers out of proportion.

You could have guessed, that your statement (that this engine would not get its claimed output) does not even stand a chance of being appropriate, looking at the huge difference between your highest used RPM, and the RPM the output was claimed for.

You claiming that my example is not valid because the engine is bigger (my example showed a difference in various output figures of roughly 25% of the highest claimed output) compared to this case, where the difference is roughly 40% of the highest claimed output, shows that your knowledge about measuring, calculating or even estimating power output in reciprocating engines, is more limited than you think.

I have no access to that "propcalculator", but I have no reason to doubt that their claim of measuring 16400 RPM on an APC 10 x 6 prop, obviously equalling 1.67 HP, is not true....
You can not blame a manufacturer or distributor for using the highest values they measured, unless you have proof, those values were never actually achieved.

Brgds, Bert
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Old Dec 13, 2012, 01:10 PM
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Jimmy,


Using the Reivers prop calculator, I calculated for the APC 10x6 on the ground (your number 13,700), with the prop-index 1.23. I got 1.02 HP.

The 15,100 RPM that you achieved in flight cannot be used to calculate HP, since it is an unloaded RPM... As the plane flies forward, the airflow on the prop blades makes them behave as if their pitch is considerably lower than stated.

This is why RPM increases in flight.

When a very sleek plane flies at the calculated pitch-speed, the load of a 10x6 prop is like it is a 10x0 prop. Even if it is quite a draggy plane, the prop would load the engine like a 10x4.

So, it would be ill advised to use the 10x6 dimension for calculating HP from in-flight RPM, for a 10x6 prop.

The prop calculator and its index values can only be used using static RPM numbers.


Using a friend's OS.46AX engine, we wanted to see and to calculate its actual output, when that engine was allowed to rev to 16,000 RPM (claimed by OS to be 1.65 HP at that RPM).

We mounted an APC 8.75x8.25NN pylon racing prop on it and took an RPM reading.
It spun 16,100 RPM, close enough to the claimed peak...
But when we calculated the output with that prop's index (0.9), the output was only 0.92 HP; far from OS' claimed number.

I believe what you should do for reference, is to take the static RPM with an APC 9x6 prop.
If the calculated output is still rising (in comparison to the 1.02 HP achieved on the ground with the 10x6), try next with an APC 8x7, 8x6 and so in, to plot an actual HP curve for this engine.
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Old Dec 13, 2012, 01:33 PM
Grumpa Tom
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United States, CA, Los Angeles
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lol...
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