About the bubble in the bombsight of the Pe2...

[coconut]

... What is it used for?

[JtD]

Aiming.

[coconut]

The bubble is for aiming? How so?

 

Doing a search on google, I found this: http://forums.ubi.com/archive/index.php/t-416531.html

 

 

While the plane is positioned horizontally, the bubble visible in the bombsight lenses should be in the centre of the reticule

 

The plane is maintaining a constant altitude while I'm using the sights, but I suppose that does not imply it's flying horizontally. If the bubble isn't in the center, I should adapt the speed so that the plane can fly level and keep its altitude. Right?

Edited September 5, 2016 by coconut

[ShamrockOneFive]

The bubble is the slip indicator isn't it? So you can see if your aircraft is drifting. Usually its pretty much close to centered on a normal bomb run.

[coconut]

The bubble is the slip indicator isn't it? So you can see if your aircraft is drifting. Usually its pretty much close to centered on a normal bomb run.

In my case, it's usually centered horizontally, but not vertically.

[JimTM]

In my case, it's usually centered horizontally, but not vertically.

 

I wonder if the bubble was meant only to level the bomb sight before dialing in all the bomb sight settings. Of course, we don't have any sight leveling controls, so I think the only use for the bubble would be to correct any slip.

Edited September 5, 2016 by JimTM

[DarkFib3r]

I had the same question. When the bubble is low in your sight, you need to slow down slightly to center it for the bombs to hit at the middle of the sight. This guy's video shows an example: https://youtu.be/1mTnQpz2fbs?t=350

Edited August 21, 2017 by DarkFib3r

[FTC_Frederf]

On 9/5/2016 at 1:59 AM, coconut said:

... What is it used for?

It is used for leveling (plumbing) the sight. Sight units are not bolted directly to the airframe in a fixed position. Instead they are adjustable in a small range in order to be oriented vertically even if the airplane is not, perhaps by 5 or 10 degrees. The spirit level in Pe-2 is a gas bubble trapped in a fluid-filled cavity with a curved upper glass in the vertical sight tube. Movement of the sight tube (by holding in the hand?) which produces a centered bubble and allows the entire sight to be calibrated such that supposed vertical is actually pointed toward the center of the Earth. Sighting in directions other than downward is accomplished by twisting of the tube relative to the mounting (azimuth) and a rotatable prism below the tube which can look -15+75 degrees elevation.

http://www.airpages.ru/book/instrument_45.shtml

 

We recognize that the sight is a simple numerical computer. It takes input i.e. height and speed and outputs a solution angle. It will always give out the same angle given the same inputs regardless of the airplane's actual attitude. The real Pe-2 has no such computer. The solution would be derived by other means.

 

Given the two items of information above it's clear that Il-2 Sturmovik's generic bomb sight mechanization does not obey these principles. The sight is behaving in an unexpected way and the computer gives solution angle varying according to the actual aircraft pitch. The bubble appears to respond only to acceleration/speed(AOA?)/slip. The result is the only unaccelerated level flight the thing manages to center the bubble is one particular speed ~425 km/h corresponding to an AOA of about 3°. It is also possible to combine acceleration with higher speed or deceleration with lower speed to produce an untenable centering. The combination of the way the sight and solution computer are working means that the bubble can be largely ignored. Constant unaccelerated bubble bias (usually less than a bubble diameter below the indicated zero mark) produces complete precision in delivery and is no cause for concern. There is absolutely no benefit to a longitudinally centered bubble.

[1./KG4_OldJames]

I am assuming this is the same for the A20 as it has a similar sight.

[Herne]

3 hours ago, 1./KG4_OldJames said:

I am assuming this is the same for the A20 as it has a similar sight.

 

no need to slow down in the A20, the bubble stays centred 
 

[LukeFF]

6 hours ago, 1./KG4_OldJames said:

I am assuming this is the same for the A20 as it has a similar sight.

 

It's the same bombsight.