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Landships II -> Landships WW1 Forum -> Tanks -> Renault FT and Engine - Misnomers?
Post Info TOPIC: Renault FT and Engine - Misnomers?
Trenchfoot


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Renault FT and Engine - Misnomers?
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I raise this matter because there are some things here I don't understand, and also because in the past it has proved worthwhile to reexamine the accepted wisdom. Please bear with me.

We agreed some time ago that the Renault was called the FT, that FT17 or FT-17 was a confused interpretation, and that the FT18, for similar reasons, did not exist.

This document is, therefore, whilst in many ways extremely helpful, in others rather puzzling, referring to the FT as the Char d'Assaut 18HP: http://www.scribd.com/doc/30292276/Notice-descriptive-du-char-d-assaut-Renault-18-HP-France-avril-1918

Many sources have taken the 18HP to mean 18 horsepower.  However, rather more reliable ones point out that the engine developed 35 to 39 horsepower. Why, then, refer to it as the 18HP?

My first thought was that since the French speak French and are traditionally averse to adopting English expressions they would use the term CV (cheval-vapeur) for "horsepower". Therefore the likelihood is that the HP was just another Renault serial number and referred to the engine itself. On this Renault site they use the term CV in the text, whilst a photo caption refers to the "1906 type G2 18HP".

But on page 24 of the FT manual linked to above, the horsepower (if I read it correctly) is referred to as HP.

The situation is not helped by the fact that I understand horsepower not one bit and could not tell you what horsepower my car is or what it means. Whether 18 horsepower is enough to move a light tank I have no idea, but I note that the MkI, at 4x the weight of the FT, had a 105hp engine and the Mk V 150hp, the Schneider (at 2x) 60hp, and the Saint-Chamond (3x) 90hp.

So can anyone work this out? Is HP a production code, a measurement of horsepower, or, by coincidence, both? Why does the Automitrailleuse ŕ chenilles Renault FT modčle 1917 become, in April 1918, the Char d'Assaut 18HP? Is the fact that it was 1918 a complete red herring?

I do apologise if the answer is staring me in the face and I am being slow on the uptake.



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James H


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Whoops. How have I become Trenchfoot? What happened there?



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Ironsides


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Hi James, on the front cover of that manual which isnt included in the scribe PDf(nor is page 15) the actual descripton is Renault, char D'assaut 18 Chevaux.. inside18HP

Cover

Page 15

manual page by page http://po2260.perso.sfr.fr/FT17/Manuel%20du%20FT/MANUEL-FT17-v0.htm

I mentioned it in this thread http://63528.activeboard.com/t23550844/breaking-news-the-ft-17-did-never-exist/?r=840264

Although the site linked to has moved to the above...

I cant say as too whether or not the engine is 18Horses but this link will take you to a detailed spec of the US M1917 including its uprated variants the M1917A1..

http://afvdb.50megs.com/usa/m1917.html#M1917

If I read it right Maximum HP is 42 at 1460 rpm giving a max speed of 8.9 KPH on roads, but I cant say how accurate this data is without further clarification...I would expect the Renault Ft to have a similar engine power rating...

The uprated variant has a 100HP engine.... the extra power only translated into 14.5 KPH max not sufficient to warrant converting more tanks... something to do with diminishing returns...

my suggestion would be engine ratings are often given as maximums in specs but this is likely rarely used under normal conditions a safer engine speed may give the 18HP mentioned and move the tank at 4-5 KPH its all in the gearing and the size of the flywheel...

On HP ratings you may find this helpful, or not....

http://www.howstuffworks.com/horsepower1.htm

ever seen "Ice cold in Alex"...

Cheerswink



-- Edited by Ironsides on Monday 9th of May 2011 10:57:16 PM

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CharlieC


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The US M1917 used a different engine (Buda) rather than the Renault engine.

I wonder if the 18HP is referring to the "tax horsepower" used in Britain and a number of other countries in Europe in the early part of the 20th century. This is

a simple formula based on the cylinder bore and number of cylinders - the British version of the tax (or RAC) horsepower = Bore (inches)2 * (no. cylinders)/2.5.

The usual quoted horsepower of an engine is the power generated against a load or brake horsepower.

Regards,

Charlie



-- Edited by CharlieC on Tuesday 10th of May 2011 01:52:04 AM

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Ironsides


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Well the assumption is the M1917 would use an engine with similar characteristics to produce a similar performance as the original Renault FT, but that wasnt really the point rather the difference in performance of two different engines in the same Vehicle, only a 50% increase in speed for a 150% increase in power..

See attached image from The Gasoline automobile1915, I would think Renault would have their own formula for power output but I have no info on that one or maybe there a French equivallent...

I seem to recall something about Engines sometimes being rated at a given engine speed (mercedes?) but that this was very much lower than max, different manufacturers would claim different power ratings for basically the same engine depending on the revs, say the engine produces 18HP at 60% of maximum revs and is rated as such but can actually produce 35HP+ at max Revs..

generally without having some idea of what the manufacturers HP formulas/tests and Engine HP ratings were its speculation...

Also you need to take into account mechanical efficiency, I suspect the Renault scores much higher then a rhomboid would and could therefore run on a lower power to weight ratio...

Cheerssmile

 



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Rectalgia


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James H wrote:

Whoops. How have I become Trenchfoot? What happened there?


Most mysterious James, I hope it doesn't mean our host server is acting up - I can see that your IP-address is the same in both posts.

Interesting discussion followed that ... all I can add is that I would expect HP in French military terminology would be Haute Puissance which I suppose could apply either to the motive power or to the armament - in modern usage anyway. I know nothing about either in this context.

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CharlieC


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The Renault and Buda engines weren't very different in performance:

Renault 18CV - 39 hp at 1500 rpm (95mm bore, 160mm stroke)

Buda - 43hp at 1200 rpm (108mm bore, 140 mm stroke)

One of the French equations for calculating tax horsepower is:

P = K n D2 L w

K = 0.00015

n - no. cylinders

D - bore in cm

L - stroke in cm

w - revolutions per second at maximum power.

 This gives 22 CV for the Renault 18CV engine. There were earlier French tax horsepower equations but I haven't found these yet. I guess we could just go along with Renault and call it 18CV which some author (in the first post) translated as 18HP.

The French term for horsepower is CV - (Chevaux Vapeur)

Regards,

Charlie



-- Edited by CharlieC on Tuesday 10th of May 2011 05:20:28 AM



-- Edited by CharlieC on Tuesday 10th of May 2011 09:58:59 PM

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Ironsides


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Hi Charlie, according to the SAE/RAC formulae I make the Renault 22.4hp(so close to the French result) and the Buda 28.8hp or am I missing something?.The Buda does look like a better engine with higher power at a lower RPM with the renault being more stressedwink, but Im not sure if it would be significant, the formulae takes into account loses due to Mechanical efficiency overall at of 25%...

heres a rough and ready calculation from the previously mentioned book.

1.6 D2 = HP four cylinder engine,

gives an equivalent to the SAE/RAC rating and seems compatible with the french one..

D = Dia of piston in inches

In any case I would say the 18hp rating for the Renault engine would be resonable..

Anyone know the piston size for the 105 HP Daimler Knight engine?

Cheerssmile



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CharlieC


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Took a bit of digging but the 105hp 6 cylinder double sleeve valve Daimler-Knight engine seems to have been 81.5mm bore, 134mm stroke gives swept volume of 4.19 litres.

If anyone has been following this - the Daimler-Knight engine has about the same capacity as the 4 cylinder Renault and Buda engines of the FT/M1917 but cranks out

over twice the power. The difference is the much higher efficencies which can be attained with sleeve valves.

Regards,

Charlie



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James H


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Ooh dear. I'm afraid that you would have more success explaining quantum theory to a small child who badly needs the toilet.

The hemisphere that deals with physics never really developed in my case. Can anyone dumb down sufficiently to say whether the engine was 18 horse-power? And what brought about the change of nomenclature?

Have pity on me.



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CharlieC


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We're talking about two different concepts here:

The real world of measured power output of engines (horsepower)

The weird world of government taxation which measures engines by various formulae and produces a number which is translated to a tax on an engine. The tax horsepower has only an approximate relationship to the real power output and is expressed in units such as CV(France), PS(Germany) and HP(English). Renault used the French tax horsepower (CV) to designate his engines - so the engine in the FT tank was a Renault 18CV. This gives only a very crude estimate of the real horsepower output of the engine (39 hp).

Regards,

Charlie

 



-- Edited by CharlieC on Wednesday 11th of May 2011 11:59:23 AM

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James H


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I thank you.



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kieffer


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CharlieC wrote:

 

 This gives only a very crude estimate of the real horsepower output of the engine (39 hp).

 


To my knowledge that was 35 hp...

Kieffer

 

 



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CharlieC


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That's a good way to open a can of worms. Horsepower measurements are dependent on the conditions of measurement. The Renault 18CV engine may have been 39hp measured at the crankshaft but 35hp measured on the gearbox output.

Regards,

Charlie



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