Twin row radial engines

[stevehed]

Probably a daft question but I'm no mechanical genius. Twin rows started with rotary engines in WW1 and later in the 30's I've come across Gnome Rhone combining two rows of seven cylinders to make 14 to increase the power. During WW2 there are eighteens and so on. All these engines have equal numbers of cylinders in each row, that is 7 +7, or 9+9. Would it be possible to have a front row of five cylinders and a rear of nine to make 14 or are there technical issues. In my head I'm thinking that five cylinders might allow more air to the rear row to assist with cooling. Regarding the weight the rear row would be heavier and might this help with CoG issues.

 

Regards, Steve

[Vesa Jussila]

One thing what comes to my mind is that two rows share main axle where crankshaft is connected.  5-cylinder have different ignition order than seven or nine cylinder ones. So synchronization would be difficult.

[theplasticsurgeon]

An interesting question.

Another thing that springs to mind is the unequal power from each row - and the stress that puts onto the crankshaft.

Normally with a twin row, each cylinder in the back row will be behind a gap formed by front row cylinder.  All those gaps being equal - the theoretical cooling is equal.

That's no longer the case with unequal rows.

Then there's differing spare parts for each row.

 

[dogsbody]

If it was possible, it would have already been tried by someone. 

 

 

Chris

 

[stevehed]

Thanks Everybody. All good points. I think Chris has hit the nail on the head too. I couldn't find any examples / prototypes anywhere.

[europapete]

short answer...no. many, many, technical reasons why. 

[dov]

Impossible!

• Because of dynamic forces of the engine.
• Because of geometry

In case of same number of cylinder many dynamic forces resullt in a ZERO vector.

Otherwise not.

Each twin radial runs smoothly, in opposition toi a single row one!

 

Geometry: How to lead the pipes of inlket or outlet? 

Symetry too!

 

Same question you can ask for propellers.

On a multi engined a/c to get the number of propellers changed from inner to outer engine!

 

Basic: Make all things as simple as possible!

 

Happy modelling

[Duncan B]

15 hours ago, Vesa Jussila said:

One thing what comes to my mind is that two rows share main axle where crankshaft is connected.  5-cylinder have different ignition order than seven or nine cylinder ones. So synchronization would be difficult.

That's the main issue.

 

Duncan B

[MDriskill]

Also, having a lot of open space between cylinders, does not necessarily help cooling.

 

Early single-row radials had fully exposed cylinders, which was adequate at lower power levels. But most of the airflow thus takes the path of least resistance between the jugs, instead of passing through the cylinder cooling fins. More powerful single-row engines of the WW2 era usually had baffles between the cylinders to force more air through the fins.

 

Closely-fit double rows, with the cylinders staggered, help to do the same job for each other.

Edited November 21, 2022 by MDriskill

[dogsbody]

2 hours ago, MDriskill said:

Also, having a lot of open space between cylinders, does not necessarily help cooling.

 

Early single-row radials had fully exposed cylinders, but most of the airflow thus takes the path of least resistance between the jugs, instead of passing through their cooling fins. More powerful single-row engines of the WW2 era usually needed baffles fit between the cylinders to force more air through the fins. Closely-fit double rows, with the cylinders staggered, help to do the same job for each other.

 

The baffles as used on a Bristol Mercury:

 

 

 

 

Chris