MiG-21 MF vs Bis nose lengths : visible ?

[Laurent]

I played a bit with Photoshop Elements with the help of Superheat explanations.

What I've done: I took this LanceR photograph, filled up some areas in red and applied an overlay made from this bis photograph. Matching done on the canopy and fuselage depth.

My conclusion: the nose curvature looks the same but the bis nose is visibly shorter when comparing a LanceR to a MiG-21 bis...

... now I don't know if the LanceR is a modernized early or late MF. The conclusion could be different with late MFs (I presume that the Czech MFNs are late MFs). It seems like the Bis and late MF noses have the same length. MiG-21 bis Vs MiG-21 MFN (photograph taken here).

Taking pollie's post...

MFs were built by two factories: GAZ-30 in Lukhovitsy/Moscow built the early MFs, GAZ-21 in Gorki (which built the bis), started producing the MF in 1975. My guess is the examples built by GAZ-21 are R-60 capable and the earlier ones not.

... in consideration, it seems like the Gorki-built MFs are externally Bises with an MF spine. Yikes !

Edited September 3, 2010 by Laurent

[mirage@enthusiast]

Laurent!

The Bis version has a little bit bigger air intake since the engine was replaced in the bis from the R-13F-300 to R-25F-300. The engine of the bis got an additional fuel pump which gave better perfomance for the aircraft in afterburner mode that caused an increased air consumption in the engine. The engineers solved this problem by incrising the diameter of the air intake.

[pollie]

I played a bit with Photoshop Elements with the help of Superheat explanations.

What I've done: I took this LanceR photograph, filled up some areas in red and applied an overlay made from this bis photograph. Matching done on the canopy and fuselage depth.

My conclusion: the nose curvature looks the same but the bis nose is visibly shorter when comparing a LanceR to a MiG-21 bis...

... now I don't know if the LanceR is a modernized early or late MF.

Lancer-C 5724 is a MiG-21MF-75 from the 'bis factory'. So the theory doesn't work.....

[Laurent]

The Bis version has a little bit bigger air intake since the engine was replaced in the bis from the R-13F-300 to R-25F-300. The engine of the bis got an additional fuel pump which gave better perfomance for the aircraft in afterburner mode that caused an increased air consumption in the engine. The engineers solved this problem by incrising the diameter of the air intake.

I know that but how was the modification implemented ? I thought initially that the Bis nose was more cylindrical but I'm not too sure of that anymore.

If the nose curvature remains the same between the S/R/M/SM/MF/SMT versions and the bis version, if you shorten the nose, the diameter of the intake lip will increase.

Lancer-C 5724 is a MiG-21MF-75 from the 'bis factory'. So the theory doesn't work.....

Unless the MF batches made in Gorky had differences between them.

All I can say is that I've kept the proportions of the photographs. No stretching, just resizing.

[mirage@enthusiast]

[Laurent]

Thank you for the photograph but what's the purpose of posting it ? Do show that intake lip is different ? To show that the bis nose is slightly shorter because of a shorter intake lip ? To show how the RSBN antenna is installed on a bis-SAU ?

[mirage@enthusiast]

all of them. I just want you to see the differnce between the two types nose.... maybe help you. And please check the angle of air intake steel rings. The bis version has 5 degree diference to the mf.

Cheers

[Laurent]

all of them. I just want you to see the differnce between the two types nose.... maybe help you.

Unfortunately it doesn't. Replying to the following question would:

the nose shape is strictly identical between an MF or a bis appart from the fact that the bis nose is slightly shorter ?

My first post is trying to suggest it's the case and Superheat did a demonstration 6 months ago here (... but I find mine more explicit )

[pollie]

I never trusted this picture: the photo of the bis is taken at an angle, because you can look 'inside' the intake, if you know what I mean.

The pitotboom is placed on the righthand side of the intake, so it is natural their will be a difference between pictures taken from the left or right.

I will most likely visit the Krakow museum in Poland in two weeks time, and will try to solve it once and for all (they have both an MF and bis on display).

[Wege]

According to Gordon/Gunston's MiG Aircraft since 1937..

(and note.. this is in gist.. not going into masses of detail)

The dimensions for the MiG21MF and Mig21Bis remain unchanged.

The R13-300 engine for the MF vs R25-300 for the Bis.

Apparently the BIS has a larger 'spine'

The other changes were pretty much internal - the structure and materials were modernised allow for high G stresses/loads to take place.

[dragonlance]

The increased bis intake diameter is irrelevant in any scale, however the downward angle of the whole nose and radome (to give slight look-down capability) are not.

Those Hungarian photos are an excellent example.

The best modeling source seems to be the polish "Pod Lupa" book on the 21bis.

Fair use etc.

[Laurent]

however the downward angle of the whole nose and radome (to give slight look-down capability) are not.

Where did you learn this ? I've never heard about that.

Those Hungarian photos are an excellent example.

When you only see the intake and not the whole nose ? Hardly convincing.

The best modeling source seems to be the polish "Pod Lupa" book on the 21bis.

Drawings suffer the same thing as models: they can be wrong. The roundness of the fin top looks a little strange.

Bonus: Bis Vs PF (here, in red)

Edited September 5, 2010 by Laurent