"Gross" and "Net" rotaries power outputs.

[Greybeard]

KACEY

you wrote: "But you can ONLY measure 'NET TORQUE' with a Dynometer set-up".

AFAIK, just that is impossible for me. Apart I do not understand what a dynamometer is intended here (it is literally an instrument to measure FORCE; a force at a given distance is a TORQUE, but I do not know a dynamometer which measure directly torque), a test bench (that I used in the past) "simply" measure torque by a device like that illustrated by FlyXwire, that is force developed by entire engine trying to rotating on its stand and measured by a leverage at a given distance, thus giving a torque. Torque multiplied for RPM gives HP. "Gross" HP, since you cannot avoid to include all kinds of friction developed, let we say, into that "box" which is engine when "view" from external by mentioned devices. To purge those losses and get "net" horsepower you must measure them apart, like you told about Liberty engine, and then subtract from previously described "gross" power". To measure "at a glance" net power output, you should act, I think, by some kind of torque converter, applied to crankshaft; I believe this is now certainly possible putting a strain gage, for instance, on a joint between crankshaft and brake, not sure they could do the same at that time by mentioned torque converter or something similar. Certainly not by a "dynamometer", at least as I intend this instrument.


BLETCHLEY

you wrote: "You certainly seem to be on to something here, GB!"

Not sure to have understood what do you mean.

"I am still not convinced by your net/gross argument..."

why, since you are responding yourself?

"...but the early BR1 (AR1) certainly does not appear to have the performance to justify its 150 hp rating or its reputation - it is clearly only marginally better than the 126 hp Clerget 9B, and has a performance clearly inferior to that of the 148 hp Gwynnes/Bentley Clerget 9BF. The later high compression BR1 is also, clearly, only marginally better than the 9BF."

S!
GB

[Bletchley]

GB, I mean that there is something clearly 'wrong' with that 150 hp rating for the early A.R.1/B.R.1 engine listed in the Data Sheet, but I am not convinced that this is evidence that the British recorded rotary engine output differently from the French. If they did, would they not have recorded the (HC) B.R.1, the Clerget 9BF and the B.R.2 with a similarly much higher rating (all of them British built Bentley rotary engines)?

It is odd that the British used this early A.R.1/B.R.1 from June 1917 onwards in preference to the Clerget 9BF, even though it appears to have been clearly inferior to the Clerget 9BF (which preceded the A.R.1 in design). And why was the A.R.1/B.R.1 given its flight test in a Camel prototype (presumably this is the Martlesham acceptance test) before the 9BF? So was this early Bentley rotary rushed into production too early by Humber (as so many British aero engines were) to fill a gap left by delays in the production of the Gwynnes Clerget 9BF?

Bletchley

[Machinbird]

Originally Posted by Greybeard

KACEY

you wrote: "But you can ONLY measure 'NET TORQUE' with a Dynometer set-up".

AFAIK, just that is impossible for me. Apart I do not understand what a dynamometer is intended here (it is literally an instrument to measure FORCE; a force at a given distance is a TORQUE, but I do not know a dynamometer which measure directly torque), a test bench (that I used in the past) "simply" measure torque by a device like that illustrated by FlyXwire, that is force developed by entire engine trying to rotating on its stand and measured by a leverage at a given distance, thus giving a torque. Torque multiplied for RPM gives HP. "Gross" HP, since you cannot avoid to include all kinds of friction developed, let we say, into that "box" which is engine when "view" from external by mentioned devices. To purge those losses and get "net" horsepower you must measure them apart, like you told about Liberty engine, and then subtract from previously described "gross" power". To measure "at a glance" net power output, you should act, I think, by some kind of torque converter, applied to crankshaft; I believe this is now certainly possible putting a strain gage, for instance, on a joint between crankshaft and brake, not sure they could do the same at that time by mentioned torque converter or something similar. Certainly not by a "dynamometer", at least as I intend this instrument.


BLETCHLEY

you wrote: "You certainly seem to be on to something here, GB!"

Not sure to have understood what do you mean.

"I am still not convinced by your net/gross argument..."

why, since you are responding yourself?

"...but the early BR1 (AR1) certainly does not appear to have the performance to justify its 150 hp rating or its reputation - it is clearly only marginally better than the 126 hp Clerget 9B, and has a performance clearly inferior to that of the 148 hp Gwynnes/Bentley Clerget 9BF. The later high compression BR1 is also, clearly, only marginally better than the 9BF."

S!
GB

GB, I knew there was some communication problem, and here it is. Although a dyne is a unit of force (metric), a dynamometer is a machine to measure horsepower. Normally a dynamometer is coupled to the engine under test with a shaft and consists of a brake of some sort with a means of measuring the reaction at the brake stator required to keep it from rotating. This reaction is a force over some distance from the center of rotation. As I mentioned earlier, you could also measure this reaction at the engine mount, as with a torque stand, and you could compare the two measurements in the case of a rotary engine to come up with a measurement for windage torque.
Once you also measure the rate of rotation of the engine, you have the necessary data for horsepower computation. Please examine the following picture of one of Sir Harry Ricardo's early test rigs consisting of a test engine and a dynamometer.


Now back to the subject at hand. Since all of you gentlemen are used to calculating aircraft performance, you must realize that Bletchley's last post with the rate of climb performance of the camel with 4 different engines is sufficient to calculate relative engine performance once you adjust for the slight difference is gross weight due to the different engines. Climb performance represents surplus power from the engine above that required for level flight. You can probably assume that the propellers of all 4 aircraft under test were equally efficient. The altitude gain per unit time represents the surplus power available. If you know how heavy the aircraft is you can can pretty well cross check advertised horsepower with this data. And yes, climb rate for any climb segment is not constant, but altitude is the integral of climb rate.
I certainly hope this little spiel is not lost in translation.

[paolomiana]

.....like what appens to mine....
So if you have the ceiling times of Camel with both engines is possible to verify my hypothesis of two different spinners…….

Sorry for my bad english......

[Kacey]

GB,

Your talking about a Torque Stand measurement where torque of the engine and shalf are being measured.

I'm talking about a (at this point in time WWI most likely a water-brake) DYNAMOMETER which measures BRAKE (net) torque from the shaft.

(Excuse me I was not spelling it correctly in previous references)

Well I believe that "most all" the data we are conversing about were from a Brake Dynamometer since they almost always reference BT or BHP. This is also the REASON we call it Brake Horsepower!

This is why the Rotary Engine Manufacturers wanted there engines tested with a Torque Stand.(such as the one shown in Dave S. picture). So the output ratings would go UP by including the rotating engine torque.

Which means to me that the reported figures were the lower ones (net) from a dynamometer test.

Machinbird, thanks for the picture of the dynamometer setup. (not sure what kind that is but thanks)

But, I was also pointing out that the benifical effects of a rotary engine cowling and a rotating propeller infront of it moving thru the air at 120mph,
displayed lower (windage) resistance than the same engine mounted open(without cowling) running in no-wind(zero-velocity) without the propeller. (which is the manner in which it would have been tested on the Brake-Dynamometer).

So, in an actual aeroplane, the actual rotary engine BHP(net) that makes up the reported data is somewhat on the low-side during the low RPM stages but is a fairly good approximation of MAX output (max rpm).

That's what I was most concerned about!

Respectfully Submitted,

KC

[Machinbird]

Originally Posted by paolomiana

.....like what appens to mine....
So if you have the ceiling times of Camel with both engines is possible to verify my hypothesis of two different spinners…….

Sorry for my bad english......

Paolomiana, no need to apologize for your English. Your math in your earlier post was quite understandable. With regard to spinners on Camels, I haven't found pictures of a spinner on a Camel yet. Do you have such a picture? In addition, I suspect the drag reduction from a propeller hub sized spinner on a Camel would be small and hard to measure by performance effects. Or were you referring to some other aircraft?
Sid

[paolomiana]

no, I really need to apologize you for my terrible English, because I write spinner instead of propeller....... D'OH.

bad transaltion software.

Paolo

[Greybeard]

Bletchley

Unfortunately, I can't help you about 9BF and AR1 question; performances in Data Sheet speak clear about difference in HP while different dates of introduction may be explained by what you guess (another apparent contradiction caused by war urgencies).


Machinbird and Kacey

Now I see what you mean!

Indeed there's a different meaning commonly given to "dynamometer" word, as you can see from english and italian explanation into Wikipedia:

Dynamometer - Wikipedia, the free encyclopedia

Dinamometro - Wikipedia

Thanks for test bench photo (btw, in Italy so we call all the apparatus, while your dynamometer is our "brake"); it looks to me like a water brake (it seems to me a radiator is slightly visible in background). At any rate a sophisticated one for that era.

[Bletchley]

Apologies for resurecting this thread, but I have just come across some information that KC and Greybeard will probably want to see

From previous post be KC:

"It appears the Admiralty Radial is being "misquoted" as a BR.1(HC)!!

I've cal'd what it's actual output "most likely" is, hope someone can confirm or dispute these figures:

Admiralty Radial AR.1, misrated 150hp@1250,with actual output of 127bhp@1250rpm and 128@1300rpm, with a 4.7 - 5:00:1 CR.

Basically, I took the BR.1(HC) and reduced it's compression to arrive at these figures for a AR.1/BR.1(LC)."


From L.J.K. Setright's 'The power to fly' (Allen & Unwin, 1971):

"the BR1...engine of 150 hp rating at 1250 rev./min. [had] an actual test figure established at the Royal Aircraft Factory (S. D. Heron did the work) proving a gross hp of 142 from which 16.5 could be deducted for windage losses despite the standard aircraft cowling"

Bletchley

[YavorD]

Originally Posted by Machinbird

.......
Now back to the subject at hand. Since all of you gentlemen are used to calculating aircraft performance, you must realize that Bletchley's last post with the rate of climb performance of the camel with 4 different engines is sufficient to calculate relative engine performance once you adjust for the slight difference is gross weight due to the different engines. Climb performance represents surplus power from the engine above that required for level flight. You can probably assume that the propellers of all 4 aircraft under test were equally efficient. The altitude gain per unit time represents the surplus power available. If you know how heavy the aircraft is you can can pretty well cross check advertised horsepower with this data. And yes, climb rate for any climb segment is not constant, but altitude is the integral of climb rate.
I certainly hope this little spiel is not lost in translation.

Hi, Machinbird!
This is a sound idea. It should be implemented. The real problem is with engine and propeller data. There are several prerequisites to follow this trail.

• reliable torque (power) vs rpm data at various altitudes, or assumed shape function (with hidden assumption engine carburettor being properly tuned and engine controls properly used);
• reliable propeller data, or assumptions (diameter, pitch, blade chord; thrust or efficiency and torque coefficients plotted against advance);
• reliable aeroplane lift and drag data (lift and drag coefficients plotted vs incidence).

Reasonable doubts about any input data (or assumptions) will affect results of such an exercise (quite costly in terms of manhours too).

Regards,
Yavor