That’s a good idea. Also interesting to find out whether prop rpm was ever monitored in the cockpit instead of engine speed. I suspect that if max rpm was proscribed as 2,700 then that’s a red herring too. That would equate to an engine speed of over 4,000 rpm.

..and my response was deleted.

I have been researching variable pitch props for years now, so two minutes Googling may not in fact be all that relevatory 🙂

In the full understanding of ‘how it works’ the question remains.. a pitch control in the Yak-1 cockpit suggests the prop was not constant speed. If in fact it was an rpm control then it suggests it was. I may be missing something here, but it’s not the principle of CSU operation.

You gotta love this forum. Thanks Nii – where else could one find the specifics of Soviet props so quickly? One thing to add – technically there’s no such thing as a constant speed propeller, though we all use the term. A variable-pitch propeller only becomes constant speed when it is governed by something to be so.

Edit – GB, our posts crossed. I was thinking that too. There are different optimum prop speeds for different situations, so essentially that’s what you’d want to do – have a say over the RPM. But not via direct control of pitch – that’s the job of the CSU/governor.

Nii, as Graham says, surely if the 61P needed a pitch lever, it wasn’t constant speed. Are you sure it wasn’t an RPM control?

Ah, wait. Nii, Reading your post again, especially the bit emphasising prop rpm as being distinct from engine rpm – are you thinking there is some sort of variable-ratio gear between engine and prop? There isn’t. ‘Gearing’ is all done by prop pitch. Raise the pitch, and all else being equal you lower prop rpm. And engine rpm. The reduction ratio between the two is fixed. Apologies if not, but reading it back it looks like what you say about being constant speed and having a pitch control would make sense if you didn’t appreciate that the pitch was essentially the only means of varying ‘gearing’.

Thanks Andy.

If they were doing August 1940 through to the end of hostilities I can see how it might have taken longer than the first tranche, 1939-40..

Looking forward very much to the forthcoming ‘release’ of records – there might be some interesting results to a proper reading of some of these files.

Hi Kye

Not a strange question on a forum like this 😉

First of all the people who say the angle couldn’t be adjusted were wrong – but they might have been getting at something else.

The crucial difference is between variable pitch/controllable pitch and constant speed. These are used interchangeably far too often, but they are very different things.

A constant speed propeller will not show variation in load on any gauge. This is because for any given settings, the blade will automatically correct for changes in load – which would otherwise manifest itself as a change of RPM – by changing its angle. This has the effect of maintaining a constant load.

The Vish 105sv fitted to the Yak1m was, according to all the sources I have found, just such a constant speed unit.

However, a controllable or variable pitch propeller allows the pilot to alter the blade angle manually in flight. This will have an effect on load, and therefore rpm. It is possible that the vish 61 originally fitted to the Yak1 was in fact one of these – the interchangeable use of CP and CS makes it impossible for me to tell from what I have at my fingertips (which I admit is mostly Google).

The picture is further complicated by the fact it is possible to turn a CP prop into a CS one by fitting a ‘CSU’ – Constant Speed Unit. The prop itself doesn’t necessarily need to change to do this. This was done with Spitfires in 1940, for example.

I think the Artificial Horizon gyro was powered by a vacuum (certainly the usual Sperry Mk1 type was). This was probably maintained via a venturi, which might ice up?

Ah. Sorry. Different interview. She did say ‘of course’, didn’t she? Oops!

Not sure now, Stu. I am looking for the footage, as there are two different written versions, one with the ‘Of Course’. I thought I had seen it, and I remember her as being more evasive..