2 stroke thread (with occasional F1 relevance!)

[saviour stivala]

A six cylinder twin-row radial, a ten cylinder twin-row radial, a fourteen cylinder twin-row radial, an eighteen cylinder twin-row radial as well as a twenty eight cylinder four-row radial are all designed as an ‘uneven’ cylinder count engine per-row. Meaning the ‘even’ number of total cylinder count in the design does not classify them as an ‘even’ number of cylinders engine.

[coaster]

The timing gears for the cam in the Rotec ran 1:6, the cam was the size of a small plate.
I thought the uneven cylinder count was due to the master rod holding the remainder of rods and their pickup positions were a simple mirror flip to cut down the math required for their locations.

[J.A.W.]

As explained, an even number of cylinders 4-stroke radial would not be feasible to have an equally timed firing cycle. As such the Nordberg radials being of even number of cylinders configurations were of the 2T cycle mode.

The Nordberg radials were 2T, & as noted in the linked article, of 11 & 12 cylinder configuration.

If 4T, things may become 'blurred' with nomenclature, with 'radialine' multibank 'star' configurations.

[saviour stivala]

The timing gears for the cam in the Rotec ran 1:6, the cam was the size of a small plate.
I thought the uneven cylinder count was due to the master rod holding the remainder of rods and their pickup positions were a simple mirror flip to cut down the math required for their locations.

The 'Rotec' running 6:1 crank/cam ratio is the 7-cylinder R2800 radial. The 'Rotec' 9-cylinder R3600 radial runs a crank/cam ratio of 8:1.
5, 7 and 9 cylinder radials that uses '2-cam rings' on an internal tooth gear, with each of the 2-cam-ring, one having exhaust lobes only and the other having intake lobes only. information as follows:- 5-cilinder = 2-lobes on each cam-ring = crank/cam ratio 4:1. 7-cilnder = 3-lobes on each cam-ring = crank/cam ratio 6:1. 9-cylinder = 4-lobes on each cam-ring = crank/cam ratio 8:1. The 4-T radials having an 'uneven' cylinder count is due to consistent every-other-piston firing order providing for a smoth operation.

[Tommy Cookers]

... The 4-T radials having an 'uneven' cylinder count is due to consistent every-other-piston firing order providing for a smoth operation.....
'a 6 cylinder twin row and a 10 cylinder twin row radial ... are designed as an uneven cylinder count per row ....'

but eg the Bristol Hydra, Curtiss Chieftain, Smith Static and the later A-S Wolfhound etc had even nos of cylinders/row
they (well at least the Hydra) had master rods each with an odd number of slave rods
https://enginehistory.org/ModelEngines/ ... ydraFO.jpg gives its firing intervals

anyway radials all have some things apparently non-ideal (unless having weird complex crankshafts)
there's no magic kinematics magic for them - just empirical methods

and presumably propeller vibration would exist even without engine vibration

[saviour stivala]

The ‘even’ number of cylinders per-row 4T radials design attempts mentioned ‘the Bristol hydra’, ’Curtiss Chieftain’, and ‘Smith Static’ as well as others, success story was as good as to have never entered production, they all suffered of ‘severe distractive vibration’. The solutions was simply for a 4T radials regardless of cylinder count per-row, design with uneven number of cylinders per row, and this also regardless of the number of rows.

[Tommy Cookers]

The ‘even’ number of cylinders per-row 4T radials design ,,,, all suffered of ‘severe distractive vibration’. The solutions was simply for a 4T radials regardless of cylinder count per-row, design with uneven number of cylinders per row, and this also regardless of the number of rows.

no - the designers weren't fools
pages c. 55 - 62 of this thread include much information and references
odd numbers could produce bigger differences in piston motion
and see www.enginehistory.org/Piston/Curtiss/Chieftain.pdf

odd numbers of course fit the typical stagger of cylinder rows - and are easier to forge the master-rod
even numbers are of course for non-stagger engines and ohc and higher cylinder counts

[saviour stivala]

I personally don’t subscribe to the notion of a designer of a 4-T radial engine with an even number of cylinder per-row as being a fool. It is just that no such designs were ever as successful as the 4T radials with an un-even number of cylinders per row. In fact as far as I know no one of the 4T radial engine designs having an even number of cylinder in a row ever made it to production line.

[coaster]

Resonance appears in so many areas of engineering and it is avoided at all cost, but I have a feeling one day a great mind will harness resonance as a form value adding energy.

[Slo Poke]

Resonance appears in so many areas of engineering and it is avoided at all cost, but I have a feeling one day a great mind will harness resonance as a form value adding energy.

Good post Coaster!
However swop out the word ‘adding’ for ‘controlling’ and it’s even better,.. erm for brake magic that is!

[coaster]

Controls agreed, self limiting.
Silly me, power pipe 2 stroke is resonance.
The ramjet, a whistle, wind instruments such as flute, trumpet all use resonance.
F1 geartrain for the camshaft added dampers to eliminate resonance, also the rubber mounting of stepper motors.
Resonance seems to work great with gases, not so with mechanical loads.

[gruntguru]

AFAIK the main reason for the odd cylinder count in each row of a 4T radial is even firing. Firing order simply follows the crankpin around - every second cylinder fires.

[J.A.W.]

Check out the geometric sophistications/conrod convolutions utilized by that Curtiss-Wright mill:

[saviour stivala]

AFAIK the main reason for the odd cylinder count in each row of a 4T radial is even firing. Firing order simply follows the crankpin around - every second cylinder fires.

Yes. Exactly. Why design otherwise (an even number of cylinders in a row) when at design stage one can already achieve less vibration and provide for more even pressure pulses in the exhaust, that’s apart from having an engine that sounds smoother.

[J.A.W.]

AFAIK the main reason for the odd cylinder count in each row of a 4T radial is even firing. Firing order simply follows the crankpin around - every second cylinder fires.

Yes. Exactly. Why design otherwise (an even number of cylinders in a row) when at design stage one can already achieve less vibration and provide for more even pressure pulses in the exhaust, that’s apart from having an engine that sounds smoother.

Evidently you haven't heard a large single-row radial (such as in a T-28, for example), they sound 'staccato' rough.

Indeed, training units would - on the report of 'rough running engine' from neophyte fliers - check each 'pot' was hot
(@ cyl-head), to ensure it was running on all of 'em, & if they were, then the classic - 'They all feel rough like that..'
rejoinder was trotted out - as a truism/stock-in-trade...

If you can be bothered to look - well Bill Pearce in his article site, gives the firing order which enabled the USAAC
NVH engineers to 'sign off' that Curtiss-Wright 'hexagonal' even numbered 'radialine' - as meeting airframe spec...