Two questions about FM

[vertical1]

Hi all,

I have two question about FM in Il-2:

First: Have flying in VVS birds with open canopy (Yaks, LaGGs, La-5,7) any impact on max speed? Me think in real life it should resulted in speed loss by 20-30 km/h (about 5%),

not case in Il-2..

Second: Is taken into account volume of fuel tanked into plane? It should be noticeable difference having 200 kg or 400 kg fuel on board in fighter like Yak or Bf-109...

 

 

[Gavrick]

3 часа назад, vertical1 сказал:

First: Have flying in VVS birds with open canopy (Yaks, LaGGs, La-5,7) any impact on max speed? Me think in real life it should resulted in speed loss by 20-30 km/h (about 5%),

Yes. 20-40 km/h - approximately.

 

3 часа назад, vertical1 сказал:

Second: Is taken into account volume of fuel tanked into plane? It should be noticeable difference having 200 kg or 400 kg fuel on board in fighter like Yak or Bf-109...

Yes. Contrary to what might be expected, this weight difference has only a minor impact on top speed. It does, however, become very apparent in turns and during climb.

[312_Lazy]

Top speed loss resulting from open canopy is about 15 kph in most VVS planes. Not noticeable in dogfights, certainly noticeable in chases.

[R33GZ]

On 8/3/2026 at 1:01 PM, Gavrick said:

Yes. Contrary to what might be expected, this weight difference has only a minor impact on top speed. It does, however, become very apparent in turns and during climb.

Depends a bit on the aircraft too. The P47 is very sluggish with a full fuel load, it takes a lot of runway to get her off the ground when she's fat and heavy 

[Avimimus]

13 hours ago, R33GZ said:

Depends a bit on the aircraft too. The P47 is very sluggish with a full fuel load, it takes a lot of runway to get her off the ground when she's fat and heavy 

A lot of that is the lower acceleration though! This sluggishness doesn't really impact the top speed (which is determined by drag vs. thrust only).

Weight only impacts speed due to the fact that it requires flying at a slightly higher attitude to generate more lift, which generates more induced drag.

But most of the aircraft's lift is required during takeoff and climb, so in cruise conditions (or at top speed) the wing area is larger than necessary, so the aircraft is flying almost flat with a very small attitude relative to the horizon which means that the effect are usually quite small (at least compared to what one might intuitively expect). It'll still impact cruise efficiency though (even if top speed isn't strongly effected).

[R33GZ]

On 8/8/2026 at 9:25 PM, Avimimus said:

A lot of that is the lower acceleration though! This sluggishness doesn't really impact the top speed (which is determined by drag vs. thrust only).

Weight only impacts speed due to the fact that it requires flying at a slightly higher attitude to generate more lift, which generates more induced drag.

But most of the aircraft's lift is required during takeoff and climb, so in cruise conditions (or at top speed) the wing area is larger than necessary, so the aircraft is flying almost flat with a very small attitude relative to the horizon which means that the effect are usually quite small (at least compared to what one might intuitively expect). It'll still impact cruise efficiency though (even if top speed isn't strongly effected).

Slightly off topic, but I've noticed the P-47 gets a wicked case of the shudders at around 400mph, with a full bomb load. Is that drag from the bombs? Or have I left something open I shouldn't have. I'd usually have the cowls closed and the radiator and intercooler vents at default, what ever they are when you spawn in

[FuriousMeow]

29 minutes ago, R33GZ said:

Slightly off topic, but I've noticed the P-47 gets a wicked case of the shudders at around 400mph, with a full bomb load. Is that drag from the bombs? Or have I left something open I shouldn't have. I'd usually have the cowls closed and the radiator and intercooler vents at default, what ever they are when you spawn in

Prerty sure the intercooler shutters need to be completely closed In a high speed dive. 

 

 

[MaxPower]

On 8/7/2026 at 1:19 PM, R33GZ said:

Depends a bit on the aircraft too. The P47 is very sluggish with a full fuel load, it takes a lot of runway to get her off the ground when she's fat and heavy 

This is especially true in the P-47 D-22, which has a larger fuel load compared to the razor back version we also have in the sim.

On 8/8/2026 at 2:25 AM, Avimimus said:

A lot of that is the lower acceleration though! This sluggishness doesn't really impact the top speed (which is determined by drag vs. thrust only).

It affects it but only a little.  Increasing weight increases the lift required, which increases induced drag at all speeds.  At high speeds angle of attack will be low but somewhat higher than the plane in a lighter configuration.  This is a very small percent of the total drag at high speed, and like you say, it's very minimal.

[MDzmitry]

10 минут назад, MaxPower сказал:

It affects it but only a little.  Increasing weight increases the lift required, which increases induced drag at all speeds.  At high speeds angle of attack will be low but somewhat higher than the plane in a lighter configuration.  This is a very small percent of the total drag at high speed, and like you say, it's very minimal.

I'd also like to add that the opposite is possible with the plane being too light for its wing! Surprisingly, it was one of the points Pokryshkin noticed/critiqued about the Spitfire. Believe it or not, he described a trial/mock dogfight and flight performance comparison between a P-39 (piloted by him), a Spitfire V and a "new, lightened" LaGG-3. 

In a dive both the Cobra and the LaGG steadily pulled away from the Spitfire, mostly because its small wing loading produced excessive lift, causing additional drag. 

[MaxPower]

20 minutes ago, MDzmitry said:

In a dive both the Cobra and the LaGG steadily pulled away from the Spitfire, mostly because its small wing loading produced excessive lift, causing additional drag. 

Yep that sounds right.  The only alteration I would make is that drag that is involved in producing lift at the time is induced drag.  Drag that's not directly related to lift is parasite drag, even if it's produce by the wing.  Aircraft with big wings have relatively low induced drag at low speed but relatively high parasite drag at high speed.  The opposite case is the thinking that's responsible for the Focke Wulf and it's tiny wings but very nice high speed performance.  Also I'm no aerodynamicist so take what I say with a grain of salt.

[JollyJack]

Fuel load also has a big impact on a He111 with a full load of bombs. REV up the engines and hold on to the brakes might be of help.