Can’t remember where I read it, certainly wasn’t in “The great big book of
Dive-Bombing Spitfires" though ;)
Maybe in my Flying Guns of WWII, Williams & Gunston.
Witch
On 31 Mar 2019, at 5:30 pm, 56RAF_phoenix <phoenix@xxxxxxxxxxxxxxxxxxxx>
wrote:
Thanks Witch, where did you find that?
I knew about the "100 mph sight", but the muzzle velocity (though the bullet
slows) of the Browning 303 was 739 m/s and 100 mph is 44.7 m/s (x2 for
diameter), arctan(444.7/739) = 6.92 degrees = 120.8 millradians.
So that's consistent.
56RAF_phoenix
On 31/03/2019 17:24, Lee Fisher (Redacted sender l.fisher for DMARC) wrote:
RAF GM2 MKII Reflector Gunsight
6 degrees, 44 minutes ~(117 milliradians)
It was a '100 mph ring', which meant the radius of the circle represented
the deflection allowance for hitting a target crossing at 100 mph.They had a
system for it and the '50 mph ring' used in bombers for various types of
shooting.
It wasn't initially meant for judging range.
witch
On 31 Mar, 2019, at 03:47 PM, 56RAF_phoenix <phoenix@xxxxxxxxxxxxxxxxxxxx>
<mailto:phoenix@xxxxxxxxxxxxxxxxxxxx> wrote:
You wouldn't believe what a mess the information on Spitfire gun sights is
in. Unfortunately, the right two columns of my calculations rely on getting
this number right.
Various sources claim that the Spitfire gun sight (which model? I suspect
an early non-gyro) brackets a 109 wingspan at 200 yards.
But wait! The RAF didn't even know what model of fighter they were facing
when war broke out. Hence the weird reporting of other makes.
But here goes, that's arctan(9.87 m / 182.88 m) = 3.089 degrees = 53.9
milliradians = 54.915 NATO mils (just don't ask....)
But on the ED forums, Sokol (who I rather trust), says it's 118 Mils
<https://forums.eagle.ru/showpost.php?p=2997142&postcount=1>= 6.6375
degrees (from NATO Mils) = 6.761 degrees (from milliradians).
This website <https://forum.axishistory.com/viewtopic.php?p=156892#p156892>
has lots of info (including the incredible story that in 1938, after the
Anschluss, 55 Type II sights were delivered to Germany via Austria!), but
apparently no details on the circle angle.
Does anyone know of authoritative info?
56RAF_phoenix
On 31/03/2019 12:50, 56RAF_phoenix wrote:
I finally discovered how to set the bombing assist on to help analyse my
bombing at various dive angles and speeds. I was hoping the HUD would also
show a flight trajectory marker, which would have given me a correction
for the angle between that and the pipper for my spreadsheet calculations,
but it doesn't.
The results were somewhat discouraging in terms of getting a systematic
method based on things you can control or measure easily.
You really have to dive at something like 75 degrees and very fast >400
mph (as Roblex says) to get the bomb-drop circle at or above the nose. The
trouble with that is that with a 75 degree dive you're still getting
faster, ie. you've not reached terminal velocity (which will vary a bit
depending on loadout). This will make for inconsistent drops because
you're not managing your velocity accurately.
It might work with a more draggy 'plane that reaches terminal velocity, or
with air brakes.
The trouble with diving at a more shallow angle is that it helps because
you may reach your terminal velocity, but the bomb-drop position will
always be below your nose and invisible.
So Roblex's method may be as accurate as you can get by being fast and
close to the target when he drops. But that makes the pull-up low
(dangerous for risk of impact and escape from defending fighters).
The table below shows the angle below the pipper with Roblex's solution in
green. It's not corrected for the difference between flight path and the
pipper, which is why he's at 0.7 pipper-to-nose multiples, rather than 1.0.
Now corrected for a re-measured pipper-to-nose angle of 2.845 degrees. The
calculations assume a 6.6375 degrees gunsight ring size I found on a DCS
forum.
Dive angle Theta (deg) Altitude (ft) Speed (mph) Angle below
(deg) Angle difference (deg) Gunsight ring multiples Pipper to nose
multiples
60 4000 300 66.6 6.6 1.0 2.3
320 66.0 6.0 0.9 2.1
340 65.6 5.6 0.8 2.0
360 65.2 5.2 0.8 1.8
380 64.8 4.8 0.7 1.7
400 64.4 4.4 0.7 1.6
420 64.1 4.1 0.6 1.4
440 63.8 3.8 0.6 1.3
460 63.6 3.6 0.5 1.3
480 63.4 3.4 0.5 1.2
500 63.1 3.1 0.5 1.1
520 62.9 2.9 0.4 1.0
45 4000 300 55.5 10.5 1.6 3.7
320 54.7 9.7 1.5 3.4
340 54.0 9.0 1.4 3.2
360 53.3 8.3 1.3 2.9
380 52.8 7.8 1.2 2.7
400 52.2 7.2 1.1 2.5
420 51.7 6.7 1.0 2.4
440 51.3 6.3 0.9 2.2
460 50.9 5.9 0.9 2.1
480 50.5 5.5 0.8 1.9
500 50.2 5.2 0.8 1.8
520 49.9 4.9 0.7 1.7
75 4000 300 78.2 3.2 0.5 1.1
320 77.9 2.9 0.4 1.0
340 77.7 2.7 0.4 0.9
360 77.5 2.5 0.4 0.9
380 77.3 2.3 0.3 0.8
400 77.1 2.1 0.3 0.7
420 77.0 2.0 0.3 0.7
440 76.8 1.8 0.3 0.6
460 76.7 1.7 0.3 0.6
480 76.6 1.6 0.2 0.6
500 76.5 1.5 0.2 0.5
520 76.4 1.4 0.2 0.5
56RAF_phoenix
On 25/03/2019 22:40, Rob (Redacted sender robinhj for DMARC) wrote:
I did some testing on Klems mission and got some good results though not
using the exact method recommended.
I did approach at 10,000ft and tip in near the target but I did not have
much luck dropping at 6000ft and 60 degrees. It was just not fast
enough and the parabola meant the impact point was below the nose. What
I found was that buy diving steeper, nearer 75 degrees and waiting until
4000ft I was reaching 420mph and getting the much sought after 'drop when
the target is on the end of the nose' . I repeated it three times and
it was fairly consistent ie always within 5-7m which is enough for most
targets if not tough tanks.
I put the pictures of one such drop into a fake diary entry as it is the
easiest way to post large photos.
https://roblex56raf.livejournal.com/32265.html ;
<https://roblex56raf.livejournal.com/32265.html>
I initially tipped in too early so immediately levelled again and pulled
up to 10k and tried again two seconds later by which time I was right
over the target. The second & third photos were both taken just at drop
point. The speed after dropping from near stall speed at 10k down to 4k
(engine off) was only 420mph and easily enough to allow an easily
recovery. Obviously it would be better if I could get the same accuracy
from a 6000ft drop as my lowest point was about 2000ft I believe (I
forgot to check that but still can) which is dangerous with defenders
around but it was only my first trials so maybe I can do it higher.
As I said in a previous post though, it is unlikely that the method that
works for one person will 100% work for another so really we all need to
do our own tests.
Rob
