Blenheim operating limits and checklists

[phoenix1963]

Thanks for a very informative reply Robo
As well as mixture at altitude, the heat flow still seems off. The manuals clearly state that gills should be fully open on the ground, but closed on takeoff and flight.

This is not plausible with the current model, the sensitivity needs some adjustment.

56RAF_phoenix

[IvanK]

The Prop pitch selection in the Blenheim IV was I believe straight out Fine or Coarse without any "wiggle room". In the case of the Spitfire MKI the Wiggle room and technique on how to get benefit of it is clearly stated in the Spit Manual. To all intensive purposes it provided similar pitch control to what we see in the 109E though ergonomically not as well set up. No such mention of this wiggle room is mentioned in the Hurricane I manuals though. Here is an excerpt describing its operation from the Spit I pilots notes:



In the case of the Blenheim MKIV (and MKI) there is no mention at all of any wiggle room in the propeller pitch department in the Pilots notes. Neither is their any mention of it in Graham Warners exquisite book that covers engine handling in great detail. Nor is there any mention of it in the RAE Flight test reports available in the National Archives which cover engine handling in reasonable detail. Two of these reports are in relation to achieve Max possible climb performance and max level speeds.

As to handling with particular reference to Take off as we see it in the Sim the Yaw on take off is grossly over modelled. Again the Pilots notes state ... "Turn into wind, straighten up and opent the throttles together,taking only two or three seconds in doing so. ..... There is a slight tendency to swing to the right which is easily overcome by the rudder." Whats more telling is that the recommended Rudder trim setting for take off is neutral. There is no way we should have an aeroplane that we struggle with maintaining directional control with asymmetric power and stabs of brake.

With respect to Engine RPM in SIM versus Real world there is a large mismatch. Again the RAE reports give good details here. I "think" the issue in the Sim is how propeller pitch has been set this results in out of wack RPM values for a Given Boost and TAS. There is a fair bit of discussion in the RAE reports on setting up the Prop pitch stops for coarse with the intent that Full Coarse at Full throttle height should provide max RPM i.e +5Lbs Boost Prop Full Coarse around 2700RPM:



Here is the test data on RPM Versus Altitude V TAS again Coarse pitch



The RAE reports also provide copious data on Engine cooling. Clearly the Sim is way to critical in this area, I think Phoenix is spot on. Cylinder head temperature and Gill position is way to sensitive/critical.

A great insight to the Blenheim IV and its handling and engine operation etc is the Flying Machines "Flight of the Blenheim" DVD.

http://www.flyingmachinestv.co.uk/page2/page2.html

Warning slight but related thread drift follows.
With respect to Propeller pitch issues this imo is a common oddity in the Sim that may go some way to explaining the shortfall in performance in the 2 pitch Spits even at only 6Lbs boost (avoiding the 100 Octane debate . Looking at multiple RAE reports that provide RPM versus IAS/TAS V Altitude for the early Merlins then repeating the tests in the SIM will see the SIM RPM consistently 300-400RPM less than real world.

[Robo.]

Originally Posted by IvanK

The Prop pitch selection in the Blenheim IV was I believe straight out Fine or Coarse without any "wiggle room". In the case of the Spitfire MKI the Wiggle room and technique on how to get benefit of it is clearly stated in the Spit Manual. To all intensive purposes it provided similar pitch control to what we see in the 109E though ergonomically not as well set up. No such mention of this wiggle room is mentioned in the Hurricane I manuals though. Here is an excerpt describing its operation from the Spit I pilots notes:

Brilliant info, IvanK, thank you very much for that! The quote I provided above origins from this very same document. Older version of Spitfire Mk.I Pilot's notes didn't contain such info because it was assumed that pilots would only use fine pitch for take-off and switch to coarse pitch thereafter. This was apparently discovered later on. In the very first phase, when these fighters were new with their VP, some pilots used to fixed props kept forgetting about it:

''It was easy to forget the propeller adjustments that had to be made to the Spitfire, the same as they did to the Hurricane. Brian Considine (...) had only flown fixed-pitch propeller biplanes when he was sent to join 238 Squadron at Tangmere. (...) He 'took off in fine pitch and promptly forgot to put it back into coarse pitch, and did a few circles round the field thinking how marvellous it was... I made a nice landing and as I taxied in I could see the CO jumping up and down like a monkey in a rage. When I got out he told me U had wrecked the thing. I hadn't but it was all covered in oil.''

Then they found out what was later incorporated into official pilot's notes. Now the question is if the airscrew had the same bicycle pump mechanism (and bracket), can it be assumed that a bit of wiggle space has been available on Mk.I Hurricane and Mk.IV Blenheim, too? I agree that if there is no mention at all anywhere, there is not much space for speculations. It was perhaps the particular control lever allowing such a practice in Spitfire only.

Originally Posted by IvanK

In the case of the Blenheim MKIV (and MKI) there is no mention at all of any wiggle room in the propeller pitch department in the Pilots notes. Neither is their any mention of it in Graham Warners exquisite book that covers engine handling in great detail. Nor is there any mention of it in the RAE Flight test reports available in the National Archives which cover engine handling in reasonable detail. Two of these reports are in relation to achieve Max possible climb performance and max level speeds.

I am reading through the Mk.IV pilot's notes - it says ''the aircrew pitch controls should be pulled out to put the airscrew in coarse pitch'' (obviously) and it mentions later that the RPM indicators are not very precise. I wonder how much resistance these airscrew controls had when pulled and if it was at all possible to set them inbetween. Even if it was, it is clear that it has not been used then and it is indeed wrong in the Sim.

Originally Posted by IvanK

As to handling with particular reference to Take off as we see it in the Sim the Yaw on take off is grossly over modelled. Again the Pilots notes state ... "Turn into wind, straighten up and opent the throttles together,taking only two or three seconds in doing so. ..... There is a slight tendency to swing to the right which is easily overcome by the rudder." Whats more telling is that the recommended Rudder trim setting for take off is neutral. There is no way we should have an aeroplane that we struggle with maintaining directional control with asymmetric power and stabs of brake.

Absolutely! You need full left rudder trim for take-off and almost full left for climbing at the moment. It also says it can be airborne in about 400yards (14.5000lb. long range full load in still air) which is also quite impossible even on +9PSI.

Originally Posted by IvanK

With respect to Engine RPM in SIM versus Real world there is a large mismatch. Again the RAE reports give good details here. I "think" the issue in the Sim is how propeller pitch has been set this results in out of wack RPM values for a Given Boost and TAS. There is a fair bit of discussion in the RAE reports on setting up the Prop pitch stops for coarse with the intent that Full Coarse at Full throttle height should provide max RPM i.e. 7200ft +5Lbs Boost Prop Full Coarse around 2700RPM:

That explains a lot then - at the moment you're pretty much climbing with engines idling at odd 1800RPM even at full +5lbs., coarse pitch. Unfortunately the manual only provides very vague figures. On the ground (few seconds engine start-up).

+5lbs - 2300-2400RPM (static)
+9lbs - 2500-2600RPM (static)

And only refers to Boost from then on, saying that pilot should switch to coarse pitch at the speed of 120MPH and then climb at 150MPH at coarse pitch. Coarse pitch + full boost were not recommended unless necessary. None of these is possible in the Sim at the moment. But I am only repeating what you have said already anyway...

Originally Posted by IvanK

With respect to Propeller pitch issues this imo is a common oddity in the Sim that may go some way to explaining the shortfall in performance in the 2 pitch Spits even at only 6Lbs boost (avoiding the 100 Octane debate . Looking at multiple RAE reports that provide RPM versus IAS/TAS V Altitude for the early Merlins then repeating the tests in the SIM will see the SIM RPM consistently 300-400RPM less than real world.

It seems some of these are global FM issues concerning more planes in the Sim.

At the moment (beta 1.03) - the temperatures and failures are far too aggressive, mixture is not working at all (except when starting the engine and is still animated other way around on Hurricane) and the RPMs are, just as you say, far off at given boost / TAS / alt. 300-400RPM is a lot and in case of Mk.IV Blenheim we speak about 500-600RPM difference to the real life data!

Regarding the grills, it says that even with these fully closed, there was enough air streaming to keep the engines cool. CHT limit was 210C.

Thanks for your post, IvanK, that was excellent.

[phoenix1963]

The pitch does now seem to be variable in the one third portion closest to coarse setting.

Right or wrong, it proves quite useful, I can now climb at about 2150 rpm, +2lbs boost, +1000 ft/min. But I still have to have the gills open ~70%.

As Robo says, shaking sets in at almost 5000 ft, indicating the need for carb (intake) heat.

Best news (unless I missed it before the Beta) is that the sight now has sideslip adjustment!

56RAF_phoenix

[Blackdog_kt]

I think sideslip correction was only mentioned for the German Lofte sights? I could be wrong, but i didn't see it with the mechanical sight in the Blenheim.

In any case, the correction that does get applied automatically in the Blenheim is an angle of attack correction. In reality i guess it was manual, what happens in the sim is that it needs some time of straight and level flying while the bombardier automatically adjusts this. In short, it's just a matter of correcting for how up/down your nose is pointing when on level flight due to weight differences between sorties (a heavier aircraft will need more nose up trim than a lighter one to maintain level flight, assuming they are flying at the same speeds).


As for the propellers, i was under the assumption that the method of obtaining semi-adjustable RPM didn't involve setting the prop controls mid-way, but manually and constantly alternating between the two positions, ie a case of increased pilot workload and as such, useful only for specific phases of flight.

There's a video on youtube by A2A simulations (the guys who made the Spitfire add-on for FSX) aptly titled "propellers" which demonstrates the method. I tried it in CoD with a Spit Mk.I and it works, but you have to be wary of your boost: coarsening the pitch as much as the two-stage props do results in a substantial rise of manifold pressure, so set your throttle for an in-between boost value that won't exceed maximums when at coarse pitch.

[IvanK]

"As for the propellers, i was under the assumption that the method of obtaining semi-adjustable RPM didn't involve setting the prop controls mid-way, but manually and constantly alternating between the two positions, ie a case of increased pilot workload and as such, useful only for specific phases of flight."

I think that assumption is incorrect Blackdog Kt The Spit manual implies that its just a matter of using the Prop pitch control as a Vernier device that enables you some additional control of Prop pitch other than just the Coarse and Fine stops. The location of the Prop pitch control in the Spit I makes it a little easier to manage.

As to the Blenheim with the controls mounted behind and under your left elbow and 2 to fiddle with that would be imo virtually impossible. As indicated in my earlier post there are no references at all to the Blenheim IV (and I) props being capable of intermediate settings other than Fine and Coarse.

[phoenix1963]

Originally Posted by Blackdog_kt

I think sideslip correction was only mentioned for the German Lofte sights? I could be wrong, but i didn't see it with the mechanical sight in the Blenheim..

Blackdog - There's an adjustment knob/nut on the right hand side of the Blenheim sight that rotates it left or right to allow for wind/sideslip. I don't know much about sights, so maybe I simply missed it before!

56RAF_phoenix

[Blackdog_kt]

Good to know, i'll try it out next time i'm flying that temperamental coffin
I have all the bombsight functions mapped to my numeric keypad with shift and ctrl combinations, i'll have a look at it.

Also, thanks to IvanK for the renewed feedback

[lane]

Originally Posted by IvanK

[…] In the case of the Spitfire MKI the Wiggle room and technique on how to get benefit of it is clearly stated in the Spit Manual. To all intensive purposes it provided similar pitch control to what we see in the 109E though ergonomically not as well set up. No such mention of this wiggle room is mentioned in the Hurricane I manuals though. Here is an excerpt describing its operation from the Spit I pilots notes:

I think that assumption is incorrect Blackdog Kt The Spit manual implies that its just a matter of using the Prop pitch control as a Vernier device that enables you some additional control of Prop pitch other than just the Coarse and Fine stops. The location of the Prop pitch control in the Spit I makes it a little easier to manage.

That’s very interesting information IvanK, thanks for sharing!

Regarding the de Havilland two position propeller on the Spitfire I: "If the two position control is fitted on this aeroplane it can also be operated to give various airscrew pitch settings between fine and coarse; this is obtained by slowly moving the control between its range of movement until the desired r.p.m. are obtained. […] This in effect will give a similar improvement in performance to that obtained by means of a constant speed airscrew."

Are the devs aware of this?

Hmm, come to that; are the devs aware that Spitfire Is were equipped with constant speed propellers during the Battle of Britain?

[IvanK]

"Are the devs aware of this?

Hmm, come to that; are the devs aware that Spitfire Is were equipped with constant speed propellers during the Battle of Britain? "

Yes the Devs are aware of both these facts.