More damed lies

[mik]

I thought I would post these facts which were hiding in my book collection.
The Raf engine in the RE8 is variously quoted as 140hp or 150hp. With this power rating if you do the maths the RE8 has less drag at any speed than the PFalz D111. with 160hp engine. I assummed the RAF engine to be doing about 1500 rpm. I found a reference to the earlier 80-90hp version doing 1800rpm. Then discovered that the RAF 140hp engine actually produces 160hp at 1800rpm. I have not recalculated the maths yet but I knew something had to be wrong.

[Chock]

Quite a few pilots familiar with WW1 aero engines and the aircraft you find them in have claimed that the original power estimates of old aero engines are too low. They may be right, or may simply be misled by the fact that such engines are usually fitted in fairly compact and light airframes, but it is something you hear from time to time.

Al

[mik]

I personally feel the allies are often lieing about German aircraft (perhaps for propaganda reasons). "The winners write the History" The RAF engine Data came from an encyclopedia of aeroengines.

[Chock]

That too is quite common, one of the reasons for doing so was indeed propaganda. For example, the cutaway illustration of the bf109F which appeared in 'The Aeroplane' magazine in 1941, was drawn from a shot down belly-landed example. The Allies had a few in their possession and managed to piece together the wreckage of one or two in order to test fly them.

Clarke, the guy who drew that illustration, deliberately put on the details of the drawing that the cowling guns were '7.7mm' in calibre, when he knew very well they were really 7.92mm. Stuff like that was done to mislead the enemy into thinking that no intact examples of the aircraft had been recovered and tested should they examine a copy of the magazine, which they almost certainly would have done.

All very clever stuff, but sometimes confusing for historians!

Al

[Dan_San_Abbott]

Hello Mik:
I don't have the data at hand, The RAF4 developed 140 hp,at 1800 rpm, but the RAF4A was rated at 150 hp at 1600? rpm. It produced 170 hp at 1800 rpm.
Off hand I don't know what the rpm standard was used by the Royal Aircraft Factory. For example all German rotary egines were rated at 1200 rpm and other in-line or V type engines were rated at 1400 rpm. This is not necessarily the enginges maximum rpm or hp. For example the BMWIIIa was rated at 185 Ps at 1400rpm, but at 1600rpm it produced 260Ps.
Too many authors do not do sufficient research, the RAF4A was a RAF 4 with the fly wheel and fan removed in addition to other improvement to the engine to develope more power.
Blue skies Mik,
Dan-San

[Greybeard]

Mik,

the key point of this matter is that WWI engines DO NOT have a max power as we're accustomed with: believe it or not, they were limited BY ALLOWED RPM!

You can see graph about Salmson engine on Jane's 1919 reprint to see what i mean, for instance.

So, if we took a RAF4a or everything else at that time, probably we could get even 200 or more horsepower, but simply its mechanical resistance couldn't allow related RPM's and stresses.

As a consequence, it was matter of CONVENTIONS, like those mentioned by Dan-San about germans. Each engine had a "nominal" power that was in general, lower than power output at dynamometer, although got at rated RPM. Only exception I know was Daimler early DIII which developed 150 PS at test bench, instead of nominal 160 PS (developed then by later DIII).

According Air Ministry's Data Sheets, RAF4A developed 170 HP at 1800 RPM.

Hope this helps.

GB

[Bletchley]

As KACEY has pointed out in a previous thread, and confirmed by Ricardo after the Great War in his tests on many of the Allied aviation fuels in use during this period, many of the aero engines of this time would have been suffering from mild detonation problems because of the variable quality and knock resistance of the fuels. If you build a replica engine today, or restore an original to its full working condition, and fill it with modern aviation fuel (or even fuel that meets the RAF's specifications of the early1930s) then this mild detonation will not be there and the engine will produce more power than expected as a result.

The British didn't have a wartime Type acceptance procedure (a Type Test) for engines until after the war. They allowed the engine manufacturers to specify average power output and test each engine, under the watchful (but sometimed not so watchful) eye of an AID Inspector. Spot checks were done on individual items (component parts as well as fully asembled engines), and an acceptance test was then done on the aircraft and its engines once they had been matched together (often, after orders had already been placed). This led to disasters such as the ABC Dragonfly, and the system was changed after the end of the war. Also, many wartime manufacturers sub-contracted work to other companies, and engines could be of variable quality (and even power output) depending on who built them - this was a particular problem where the whole engine was licence-built by a manufacturer other than the original company.

As Greybeard has pointed out in another thread, when you get to the rotary engines there is also the problem of 'gross' and 'net' values (with or without the windage effects). Manufacturers liked to quote the larger 'gross' value in their publications.

The Royal Aircraft Factory at Farnborough tested engines, both Alllied and Central Powers, and these tests are, I think, generally a better guide than manufacturers' figures (although the tests on German engines were often skewed, I think, by the difference in Allied and German fuels).

Bletchley

[YavorD]

Hello!

From "Notes on R.A.F. Engines. Types 4A and 5 (3rd edition) 1917.
The engine is rated 160 bhp at 1800 rpm (normal revs). It was a geared engine, gear ratio 1:2.

... All motors are tested for 3 hours at 1,800 R.P.M., and must give a minimum of 150 H.P. during the whole time.

From "Air Board Engine Data Chart (Sheet 5)"

Rated H.P. 150
Normal full speed (maximum for long periods) 1,800 R.P.M.
Maximum permissible speed (for few minutes only) 2,000 R.P.M.
Torque 437.5 lb-ft

Both sources made available by Bletchley.

Regards,
Yavor

[Greybeard]

Yavor,

first of all, sorry: going on memory, I confused RAF4A with Beardmore, so RAF4A horsepower is not 170 HP.

Now, about "rated" and "normal" (to use same Air Board terminology) RAF4A power outputs, I would integrate your detailed info with attached collage I did with sheet 5 and Table of Performance of Air Board to show both.

So, Mik, actual HP to use for computation is 160.

GB

[mik]

Thank you gentlemen.
My calculations with 160hp 150hp and 140hp all seem way off. When calculating for newer aircraft it seems to work. Perhaps the problem is "there really is no accurate hp measurement.