Were radials usually long-stroke engines?

[[email protected]]

Looking over the available illustrations on the net it appears
that the typical radial aircraft engine had a stroke longer
than the bore (undersquare). Is that right?

It would make sense for high torque at lower RPMs.

--

FF

[wright1902glider]

>From Wikipedia, the free encyclopedia

Pratt & Whitney R-2800The Pratt & Whitney R-2800 Double Wasp was an
aircraft engine, and part of the long-lived Wasp family. It was a two-
row, 18-cylinder, air-cooled radial design. Displacement was 2,804
cubic inches (46 liters); bore and stroke were 5.75" and 6".

Specifications Pratt & Whitney (R-4360-51) Wasp Major
General characteristics
Type: 28-cylinder supercharged air-cooled four-row radial engine
Bore: 5.75 in. (146 mm)
Stroke: 6.00 in. (152 mm)
Displacement: 4,360 in³ (71.4 L)
Length: 96.5 in. (2 451 mm)
Diameter: 55 in (1397 mm)
Dry weight: 3,870 lb (1,755 kg)

Specifications Wright R3350
18 cylinder, air-cooled, two-row radial
displacement: 3,342 cubic inches (54.8 liters)
bore x stroke: 6.125 x 6.3125 inches


I grabbed these specs from a quick Google search. At least in terms of
the larger later-model radials, the stroke is a little greater than
the bore. But as a percentage, its not a huge difference like in some
car engines where the bore exceeds the stroke by 25% or more. I don't
know if radials qualify as "strokers" by those numbers.

Harry "we'll think about and engine next year" Frey



On Apr 19, 9:30 am, wrote:
> Looking over the available illustrations on the net it appears
> that the typical radial aircraft engine had a stroke longer
> than the bore (undersquare). Is that right?
>
> It would make sense for high torque at lower RPMs.
>
> --
>
> FF

[Bob Kuykendall]

Earlier, wrote:

> Looking over the available illustrations on the net it appears
> that the typical radial aircraft engine had a stroke longer
> than the bore (undersquare). Is that right? ...

I think that most radials have bore to stroke ratios in line with
similar engines of other configuration. However, they often have
fairly long connecting rods (which is independent of stroke), which
tends to visually exaggerate the stroke.

Thanks, Bob K.

[wright1902glider]

On Apr 19, 12:37 pm, Bob Kuykendall > wrote:
> Earlier, wrote:
> > Looking over the available illustrations on the net it appears
> > that the typical radial aircraft engine had a stroke longer
> > than the bore (undersquare). Is that right? ...
>
> I think that most radials have bore to stroke ratios in line with
> similar engines of other configuration. However, they often have
> fairly long connecting rods (which is independent of stroke), which
> tends to visually exaggerate the stroke.
>
> Thanks, Bob K.


I'll have to check a few of my Dad's radial engine A&P books from the
50's & 60's. Lots of interesting specs and procedures for tearing down
and rebuilding. Its interesting to see how only the master rod is
connected to the crankshaft, and all of the other rods connect to the
master rod. Very interesting lower end geometry, and I'm sure the
resulting harmonics are even more entertaining when plotted. Its a lot
like music when you think about it!

Harry

[[email protected]]

On Apr 19, 6:37 pm, Bob Kuykendall > wrote:
> Earlier, wrote:
> > Looking over the available illustrations on the net it appears
> > that the typical radial aircraft engine had a stroke longer
> > than the bore (undersquare). Is that right? ...
>
> I think that most radials have bore to stroke ratios in line with
> similar engines of other configuration. However, they often have
> fairly long connecting rods (which is independent of stroke), which
> tends to visually exaggerate the stroke.
>

I think you are right, however:

I found a long list of WWII era radials and scanned through it.
In general (with a couple of exceptions) the German radials were
all close to square (bore = stroke) the British and Japanese were
undersquare and the Americans were all over the place.

--

FF

[Morgans[_2_]]

"wright1902glider" > wrote

> Its interesting to see how only the master rod is
> connected to the crankshaft, and all of the other rods connect to the
> master rod. Very interesting lower end geometry, and I'm sure the
> resulting harmonics are even more entertaining when plotted. Its a lot
> like music when you think about it!

Yep, the first time I saw how the rods of a radial were configured, I was
floored!

Part of the reason for to long rods and long stroke, are _because_ of how
the rods connect to the master rod.

If the rods were too short, the angles at the quarter strokes would be too
great for good efficiency.
--
Jim in NC