T-80 rubber flaps

Over half a year ago, I promised to write an article about T-80 rubber flaps and their purpose, which would have completed the trifecta article collection: T-80 aerodynamic features and T-80 MBT engine air filtration and dust prevention systems. This article builds up on the T-80 aerodynamic features topic and will conclude this series. 

Unfortunately, I have come across zero primary sources, that directly mention the purpose of these rubber flaps, which makes it difficult to write an article with primary sources. There are 2 disputed arguments on this topic; one argument states that the flaps on the T-80s are meant to redirect airflow and reduce air contaminants like sand and dust from entering the engine. The other argument is that these flaps are used as additional protection to prematurely detonate HEAT warheads. I will discuss this topic by only talking about the presence of the flaps on T-80s.

Firstly the rubber skirt, present on the lower frontal plate of T-80s. Its primary function is to dampen incoming airstreams and prevent vorticity around bottom hull protrusions and chassis components. Without a skirt on the LFP, the incoming airstream is split at the UFP/LFP midpoint, where a part is directed beneath the tank by the LFP. The UFP carries the majority of the air upwards, towards the turret, where it is diffused/redirected by the turret. As air streams flow around the suspension, roadwheels, and tracks, they begin to vortex and kick up contaminants (see image 4), such as sand/dust, which becomes a problem during crosswinds. By dampening the lower airflow streams, the LFP reduces vortices. This reduction in vortices is assisted by the rubber side skirts, which also act as a dampening feature. 

Image 1: Rubber skirt and splitter rubber skirt placed above it

T-80BV and T-80U variants also have an integrated rubber splitter mounted above the rubber skirt. This splitter catches and redirects some airstreams downwards, where the lower skirt dampens the airflow, reducing airflow that can be used to cause vortices around the running gear. 

Image 2: Simplified T-80 aerodynamics drawing. The diagram depicts normal airflow streams with no crosswind. Completely transparent arrows indicate clean air while dotted arrows indicate contaminated air.

Image 3: Simplified T-80 aerodynamics drawing. The diagram depicts airflow with a crosswind from the left side, with speeds above 4m/s. Completely transparent arrows indicate clean air while dotted arrows indicate contaminated air.

T-80U mobility performance during winter. It is worth pointing out that the front mudguard dampens some of the snow, which directs it downwards. This can also be applied to sand/dust. This phenomenon can also be observed in images 2 and 3. 

Image 4: Tunguska aerodynamics for reference. Airflow begins to vortex around the 3rd and 4th roadwheels. This model can be partially applied to vehicles like the T-80.

The turret flaps require a more complex explanation. T-80U MBTs and their later variants were the only vehicles with rubber flaps on their turrets. Rubber flaps were not fitted to the T-80B and BV MBT turrets due to the complexity of mounting them on the Kontakt-1 ERA layout or simply because they were not considered necessary at the time. 

It is important to note that the rubber flaps on the T-80U are mounted in a way that corresponds to the shape of the turret ERA blocks. Flaps extend downwards and match the angle of the top ERA block to close the visible gap between the hull and turret. 

Image 5: Visible gap between the hull and turret with rubber flaps. 

When crosswinds occur, the narrow air gap between the hull and turret allows airstreams coming up the UFP to merge with the turret. These airstreams can be redirected upwards above the turret or around it. 
This feature works in conjunction with the air intake snorkel. This air intake is used in contaminated air conditions. The air intake extends to the top edge of the turret, allowing it to capture cleaner air from above, which the rubber flaps help with generating. 

Image 6: T-80U without rubber flaps mounted on the ERA block.

Without the flaps, air streams travelling up the UFP or crosswind from either side would get caught on the lower ERA blocks of the turret and be diverted downwards. This creates some problems, in environmental conditions where an air intake is used. A lack of clean air directed to the air intake could affect engine performance. 

The problem becomes noticeable in image 3, which depicts the crosswind and how it is redirected by the turret towards the air intake. In this situation, the rubber flaps help guide contaminated airflow at a larger curve, outside the air intake zone, preventing a higher density of contaminants from entering the filtration unit and resulting in less mechanical stress. The larger and longer curve prevents crosswind air from entering the reverse airflow zone, which is located behind the turret around the air intake. 

Image 7
Displacement of reverse airflow streams based on different cross-wind angles. 
No.1: 20° crosswind angle, No.2:14° crosswind angle, No.3: 7° crosswind angle 

Image 7 does not explicitly state the use of rubber flaps, but it is obvious that the large turret cheeks are indeed rubber flaps placed around the frontal turret arc. It can be observed that the various incoming crosswind breezes are gradually redirected to have a much larger and longer outer curve after coming in contact with the rubber flaps, resulting in reduced contaminants present in the reverse airflow zone behind the turret. 

Comparing images 3 and 7, it can be seen that the crosswind breeze carrying contaminants is deflected outwards by the rubber flaps. Without the flaps, the curve of the crosswind breeze is sharper, following the turret outline and is directed towards the air intake. 

Image 8: Drawing of T-72 aerodynamic features, created at the Central Institute of Aviation Motor Development (ЦИАМ). Can be observed that a reverse airflow pocket develops behind the turret above the engine filtration unit. This phenomenon is also present in the T-80.

Using the T-72 aerodynamic features as an example, air streams follow the UFP and merge close with the turret, following the outline towards the back, where a reverse airflow zone is present. The T-72 and T-80 share similar aerodynamic phenomenons, but due to the T-72 air filtration system using a 2-stage cassette-cyclone system and marginally lower air consumption, T-72 tanks don't need to have rubber turret flaps. 

To conclude the assessments made. The rubber skirt located on the LFP is used as a dampening tool for incoming air streams and prevents vortexing around the suspension of the tank. Rubber flaps on the turret are there to ensure that direct or crosswind breezes are diverted above the turret or outwards to prevent the reverse airflow zone from accumulating too much dust/sand, causing unnecessary mechanical stress on the air filtration unit. 

References: 

1. Вестник бронетанковой техники, № 1, 1985 - МОДЕЛИРОВАНИЕ ПЫЛЕВЫХ ПОТОКОВ ПРИ ИССЛЕДОВАНИИ ВОЗДУХОЗАБОРНЫХ УСТРОЙСТВ ТАНКА Т-80 
2. Вестник бронетанковой техники, № 9, 1987 - АЭРОДИНАМИЧЕСКИЕ УСТРОЙСТВА ДЛЯ ПЫЛЕЗАЩИТЫ ВГМ
3. Вестник бронетанковой техники, № 8, 1989 - ПРИМЕНЕНИЕ ФИЗИЧЕСКОГО МОДЕЛИРОВАНИЯ ДЛЯ СНИЖЕНИЯ ВОЗДЕЙСТВИЯ АЭРОЗОЛЬНОГО ПОТОКА НА ДВИЖУЩИЙСЯ ТАНК
4. "Броня России" - Серия 9 из 10