On big radials
- Thread starter tomo pauk
- Start date
Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
- Thread starter
- #42
Late (or any) model 190As used no turbos.
The 190B and 190C were without turbos too?
IIRC BMW made the turbo that was used on the Ju 388 version powered with BMW 801, while Hirth was the producer of the turbo used on the 'Kangaroo' prototype.
- Thread starter
- #43
Found this while going round and round reading and watching all kinds of german engine stuff, thank you Tomo for another fascinting topic.
I am a bit puzzled by the phrase below from post nr. 23 on the previous page:
We can note that BMW 801C was rated for 2700 rpm for use in Fw-190A-1/A-2, even when compressor is in high gear, but the question of 'when' remains. See the table for the A-1/A-2 here. The 'Drehzahl uber 5km' column states so.
Also please note on that table that fuel specified is C3 ('Kraftstoff C3'), so now we can bury another myth: that greater compression ratio was needed for higher oct fuel to be used on the BMW 801. Of course, the Merlin and plenty of other engines worked fine with lower compression ratios, that always mean more boost can be used before onset of detonation.
Do you mean the BMW-801C engines were running on C3 fuel as well? Also i can't seem to find the A-1/A-2 table (unless i'm blind or something), the link goes to a topic about dive speeds?
I am a bit puzzled by the phrase below from post nr. 23 on the previous page:
We can note that BMW 801C was rated for 2700 rpm for use in Fw-190A-1/A-2, even when compressor is in high gear, but the question of 'when' remains. See the table for the A-1/A-2 here. The 'Drehzahl uber 5km' column states so.
Also please note on that table that fuel specified is C3 ('Kraftstoff C3'), so now we can bury another myth: that greater compression ratio was needed for higher oct fuel to be used on the BMW 801. Of course, the Merlin and plenty of other engines worked fine with lower compression ratios, that always mean more boost can be used before onset of detonation.
Do you mean the BMW-801C engines were running on C3 fuel as well? Also i can't seem to find the A-1/A-2 table (unless i'm blind or something), the link goes to a topic about dive speeds?
- Thread starter
- #45
Engines will always run on a better fuel. Doing the opposite is tricky.
Unfortunately, I can't find the table that shows the 801C using the C3 fuel to save a life right now.
- Thread starter
- #46
Tomo et al,
I am curious about the idea of the BMW 801 being particularly compact. It is the most compact of the 4 mid sized 14 cylinder WW2 radials, but not by a lot. I see the area of the 801 being about 7% less than the Kasei 21 and 13% less than the R2600 and Hercules. I calculated the frontal area from diameter on the radials. Other data is from Wikipedia and Smithsonian. All of the non german radials have longer strokes.
Diameter or width in inches. Frontal area in parenthesis.
42 liter BMW 801 51″ (14.2 sq ft) 156mm x 156mm
43 liter Wright R2600 55″ (16.5 sq ft) x 156mm x 160mm
39 liters Bristol Hercules 55″(16.5 sq ft) 146mm x 165mm
42 liter Mitsubishi Kasei 21 Ha32 53″(15.2 sq ft) 150mm x 170mm
28 liter Allison V1710 29″ (6.1 sq ft)
37 liter Rolls Royce Griffon 30″ (7.9 sq ft)
27 liter Rolls Royce Merlin 31″(7.5 sq ft)
45 liter DB603 33″
35 liter Jumo 213 at 31″
I have idle curiosity in radial design. Is there a formula on bore, stroke, cylinder to diameter ratios?
Not sure you can get a very exact formula with just a few parameters. But we can try. Define the inner diameter Ri as the distance from the crankshaft center to the bottom of the cylinders. Since you need space for material and the studs bolting the cylinders to the crankshaft you need to add to the bore. Lets say 10mm on each side (more for a slide valve engine, but lets ignore that for now)? So the outer diameter of the cylinder at the bottom is bore B +20mm. Now for Ri we get (assuming a circle to make the calculation simpler) 2*Pi*Ri = Ncyl * (B + 20mm).
Now for the height of a cylinder, in lieu of better data it must be at least the stroke S + the height of the piston. The piston isn't quite square, but the piston + combustion chamber height probably isn't totally far off. Now in addition you need space for material on the top, valve gear, cooling fins etc. Assume that is about the same as the bore. So all in all, the height H=S+2*B.
Thus the total radius is Ri+H, and the frontal area Pi*(Ri+H)^2 = Pi*(Ncyl*(B+20mm)/(2*Pi) + S+2*B)^2
I'm on my phone now, so I leave plugging in the values in the quoted post into the formula as an exercise for the reader.
Simon Thomas
Senior Airman
This is in the SAE paper "Liquid-Cooled Aero Engines" H. Wood SAE Transactions, Vol. 31 (1936), pp. 271
