Blenheim operating limits and checklists

[Blackdog_kt]

Originally Posted by JG53Frankyboy

AFAIK it has only auto rich and auto lean mixture setting...

Correct. In the Blenheim the levers move all the way (like a gradual, fully manual mix system) but they only have two functions: anything forward of the middle of the lever's movement range is auto lean and anything from the middle and back is auto rich.

This is not a glitch with CoD, the Mk.IV pilot's operating handbook describes how the real aircraft uses such a system.

[phoenix1963]

Well, I've just about tried every combination of mixture, carb heating, pitch, gills (radiator flaps), throttle... and I always get engine failures as I climb out.

I eventually discovered that the lean/rich setting seems to be exactly as labelled next to the lever, fully back seems to be auto rich.

I warm the engine with gills open (as per Klem's excellent pdf posted above), but takeoff with them open, or temps get too high (contrary to Klem's info). I use the 100 octane outer tanks (contrary to Klem's info).

I allow the engine oil temp to get above 40C before revving a little.

I cycle the prop pitch before taking off to circulate oil.

When I take off, I DON'T engage boost override and limit to about 4 lbs boost - that seems to get rid of most of the failures on takeoff - keeping revs below about 2500 and VERY gently increasing throttle.

As soon as I'm wheels-up I reduce throttle to about 0 boost and it seems to run sweetly on about 2200 rpm.

So I get off the ground OK with this recipe, but then I always get gasket failures, governor failures etc at around 2000ft - this is despite closing gills to keep temps up and adding some carb heat.

What am I doing wrong?!

56RAF_phoenix

[JG53Frankyboy]

my only advice would be, try lower rpms and always keep the engine temperaturebetween 200° and 250°.
i personaly never swith to course pitch, i always stay in fine and control the rpm with throttle.

and yes, in the british planes (Tiger Moth i dont know) full rich mixture is 3D cockpit lever full back, with whatevercontrol setting you get this. Digital info mixture reading is 0% (or mixture bar down) than !

[phoenix1963]

My thinking is: governor failures are because oil at the right temperature is not getting to the pitch mechanism; gasket failures are because oil or cylinder pressure or temperature is too high (maybe because I'm running at too low revs for the throttle setting); carburetta failures because it needs heat.

But maybe that's too simplistic?

I did notice, when incorrectly running too lean, that it was impossible to have oil temps and cylinder temps both correct.

56RAF_phoenix

[JG53Frankyboy]

there is no governor (at least that is my understanding how propellers are working......), the Blenheim IV has no CSP, only a two speed propeller.

[Renny]

Ive looked hard at all the advice listed in previous posts please please can someone who is an expert post..a concise..takeoff ,level flight,and combat settings for this plane...TY a head of time

[Mechanist]

I've tested the blenheim for quite a long time, (because it's the only red bomber) and came up with some "interresting" issues:

I've put this results in another bug explanatory thread but I think it will be usefull to put it here aswell

CEM:

Mixture doesn't work at all. I tested it high and low and it's have no effect on temperature, exhaust gas, fuel consumption or anything. And when you set the throttle to 0 no mather what mixture settings you have, it will exhaust black smoke. Also the lever works inversely like in the hurricane.

Prop pitch seems to be two stage in the 3D modell. (on 0 pitch input it turns right to a more featherd position, on anything else than 0 it turns left to its takeoff position. You can observe it when the engines are stoped) However, it have a full effect on rpm in different positions (not just two stages) as I measured:

Throttle 75 %
IAS 200-210 mhp
Height 8000ft
Radiator 100%
Carburetor heat 100%
Pitch % / RPM
100 / 2660
75 / 2520
50 / 2320
25 / 2120
0 / 1760

Carburetor heat seems to work inversely. In 100% you'll get less engine temperature then in 0%

Throttle 50 %
Pitch 75%
IAS: 150-160 mph
Height: 8000 ft
Radiator 100 %
Carburetor heat % / Engine temperature °C / RPM
100 / 201 / 2260
75 / 203 / 2290
50 / 208 / 2340
25 / 221 / 2380
0 / 233 / 2480

Also the carburetor heat controll lever labeld as "AIR INTAKE SHUTTER" (Don't really know how it suppose to work on this airplane)

Boost cut-out doesn't have any effect on engines at all.

Other:

Tailwheel is fixed about 30° to the right when you strat on the ground, making taxiing and straight takeoffs almost inpossible.

Althought the following are not direct part of operation limits and checklist, could be usefull to know:

Blenheim mk IV bombsight problem:

If you fly for example at 6000 ft with 190 mph TAS level flight and you give this parameters to the bombsight, it points approx 3 miles closer then the actual impact point.

So i adjusted the input settings to find the correct impact point and here are the results:

Scenario 1: Adjusting the airspeed with correct altitude to find the correct inpact point:

Fligth conditions 3000 ft 190 mph TAS:
Set height to 3000 ft set speed to 90 mph

Fligth conditions 6000 ft 190 mph TAS:
Set height to 6000 ft set speed to 110 mph


Scenario 2: Adjusting the altitude with correct airspeed to find the correct inpact point::

Fligth conditions 3000 ft 190 mph TAS:
Set speed to 190 mhp TAS the height input is 12000 ft

Fligth conditions 6000 ft 190 mph TAS:
Set speed to 190 mhp TAS the height input is 16000 ft

Also when you set the airspeed you'll see the speed setter wheel turning in the right lower part of the bombing sight. It have a scale from 100-260
I belive it's in mph, but it turns uncorrectly. Althougt the bar/lath in the left upper section of the sight have a scale between 90-310 mph.

The wheel turns like this:

set with keys / Indicated in the wheel:
90 / 258
100 / 120
110 / 155
120 / 190
130 / 225
140 / 258

And so on in the same pattern, so you can turn it arrond 3 times. I belive it is pretty wierd...

The last minor issue I found that when you press shift+F1 to look into the sight it's focusing on the right side bar, which is the "minutes to 60 miles" indicator. I would rather look on the left side bar which is "airspeed in mph x 10" or make it switchable.

Also i tried the BR.20s bombsight, which works just like the Blenheim sight, and it's works perfect. Also the He-111s and the Ju-88s bombsights works as they should in my observations.

These results were taken in the previous 1.01 patch but seems all are valid in 1.02 aswell (in my observation).

[phoenix1963]

My squadmate 56RAF_talisman has answered the question on failures on climb out.
The answer is never to go above 4 lbs boost during takeoff and switch to coarse pitch as soon as 120 mph is reached. Once on coarse pitch, keep to about 0 lbs boost.
It flies beautifully then.
56RAF_phoenix

[phoenix1963]

Originally Posted by Mechanist

Carburetor heat seems to work inversely. In 100% you'll get less engine temperature then in 0%

Throttle 50 %
Pitch 75%
IAS: 150-160 mph
Height: 8000 ft
Radiator 100 %
Carburetor heat % / Engine temperature °C / RPM
100 / 201 / 2260
75 / 203 / 2290
50 / 208 / 2340
25 / 221 / 2380
0 / 233 / 2480

Also the carburetor heat controll lever labeld as "AIR INTAKE SHUTTER" (Don't really know how it suppose to work on this airplane)]

That's exactly what you would expect, the warmer air entering the cylinder is harder to compress, so less power and lower temperatures are expected.

Many car engines use diverted air warmed by the cooling fins or radiator to provide warmer air for the carb. I suspect that's happening here.

56RAF_phoenix

[phoenix1963]

Originally Posted by JG53Frankyboy

my only advice would be, try lower rpms and always keep the engine temperature between 200° and 250°.

Yes Franky, I've just spent a very frustrating hour trying inner and outer tanks because of the conflicting information.

I never got off the ground once (mainly because I have a single throttle and struggle to steer, then overheat one of the engines)! But I can confirm that engine temperature between 200°C and 250°C. Over 250°C and you blow the cylinder head.

Certainly, after taxiing, it often pays to sit and let the engines cool to a little above 200°C to give plenty of margin for takeoff.

I struggle to believe the heat capacity was so low that the temps would vary that much. If it were that important and variable, the gauges would be in front of the pilot!

I also think Mechanist is onto something:

Originally Posted by Mechanist

Tailwheel is fixed about 30° to the right when you strat on the ground, making taxiing and straight takeoffs almost inpossible.

Looking at the behaviour in external views, I think the tailwheel is spring loaded somehow. That would be an easy programming error - forgetting -90° and +90° have the same magnitude restoring force but different signs.

56RAF_phoenix