Blenheim operating limits and checklists

[Vengeanze]

Ok, I can take off and cruise no problem. But I'm concerned about the small margins when I take off.
I've read here that some of you take off when CHT is around 200. If I do that I'll overheat so I let CHT drop to 180 and then decidedly push throttle to max for +5 psi. At 80mph I quickly rotate and retract gear and ease down throttle to 60%ish and dip nose to gain speed to cool engine.
If I pause there and check CHT it's very very close to 240.

I run the cross-country mission so no bombs but full tank.

Any tip on how I can keep CHT down at take off?


Edit:
Btw, is the only way to load bombs to use FMB or online?


Edit 2:
One thing that struck me that I gonna try right now is to slowly increase throttle so I keep temprise minimal while gaining speed. Brb.

[Blackdog_kt]

Due to the small disparities between sim and the manual for the real aircraft, that's what i usually do:

1) Set mixture to rich, prop to fine, open cowl flaps and start up. Sometimes carb heat might be needed, but remember to turn it off after starting as it can rob you of power at low altitudes. Also trim full left rudder.

2) Close cowl flaps to accelerate warm-up, step on the brakes and throttle up in steps: as soon as the gauges start bouncing around due to engine vibration (which indicates engines running rough) i stop advancing throttles and let the temps catch up, once it's warmed up a bit more and the shaking stops rinse and repeat.

3) When you reach 180-200 degrees CHT open cowl flaps, advance the throttle to obtain between 0 and +1 psi boost (about 60%) and start rolling down the runway.

4) As soon as you start picking up some speed your rudder will be effective in controlling the yawing motion caused by the props, so either adjust trim or use manual rudder inputs while advancing throttle the rest of the way.


I think we don't need that much fuel for the current map. One famous wartime raid involved an attack on the Cologne powerplants, that's the kind of distances these tanks were used for but we don't have that big a map yet.

Better to fly only on the inboard tanks and save up some weight, especially since it will translate to a shorter take-off roll and a faster transition into actual flight, where the overheating dangers are mitigated due to the increased airflow at higher speeds.

The inboard tanks are 140 gallons each (280 in total), the outboard ones are 94 gallons each (188 total). The full fuel load is thus 280+188=468 gallons.

To get the fuel percentage we need we can simply divide the gallons in the inboard tanks to the total: 280/468=0.598

So, setting fuel to about 60% should do it. I don't know if the sim will split it evenly across all tanks though but it's a small issue if it does: we might need to change over from one set of tanks to the other but other than that we'll be still flying with the correct fuel load.

I think that adding a more detailed interface for fuel in place of that slider (similar to the one we got for bombs and guns) at some point would be awesome: imagine having complete control over the contents of individual tanks, both in terms of quantity and in terms of octanes. Well, that's one for a future patch, for now just set fuel to 60% and fly

[Phazon]

Thanks for the tips Blackdog. So far I've managed one successful mission with the Blenheim on the Syndicate server but sometimes I still get caught out when starting up either waiting too long for the engines to get warm or not waiting enough.

Taking the fuel down to 60% might help get it moving a bit quicker on the ground for a take-off.

[Vengeanze]

Seems that 50-60% throttle is what most of you use for successfully take off without overheating.
Gonna try that tonite.

xpupx, good tip on using pitch to keep CHT within margins while taxing.
Will try that.

[JG53Frankyboy]

You have only tow pitchsettings, coarse and fine. Just move your pitchcontrol from 100 to 0% when the engines are still off and watch the propellerblades......

[Blackdog_kt]

That's what i initially found out and it's confirmed by the manual for the real aircraft, the Mk.IV had a propeller system similar to the DH hurricane and the early Mk.I Spit we have in the sim with only fine and coarse positions. In the sim however it's possible to move the pitch sliders gradually but only the fully back position switches to coarse and anything above that switches to fine.

On the other hand some people say that while the animation is that of a two-stage prop, it actually works like a fully variable one. I think we need to do some more testing to clarify this.

Xpupx's write up is still good advice though, minus a small inaccuracy: there is no water temp on Blenheim. The engines are air cooled so the gauges display cylinder head temperature

Other than that it's pretty sound advice, especially the part about how each engine control affects certain parameters. I still do some things differently but it doesn't mean it's the only way. For example i don't keep the carb heaters on unless i'm flying close to clouds, because heating the air lowers its density. This means that the mixture is also altered (less air volume for a given fuel volume, it's like running a richer mixture) and i don't know if the semi-automatic mixture systems corrects that.

What i've found out is that you can easily fly up to 10000ft without any carb heat at all. I just turn it on along with the pitot heater when i get fog/icing on my windshield, then turn it off once i'm out of the layer of humidity.

Now, i don't know how close this is to reality, but the current Blenheim in the sim can fly fine with reduced or no carb-heat usage when in clear skies, getting a bit more performance in exchange for having to keep an eye out for potential icing effects.
It's easier to just set carb heat at a certain alt and leave it there but you'll get a bit reduced performance, so it's up to us to individually decide on how to do it.


However, in the real one they probably left the carb heaters on so i guess i should start doing it like xpupx does

The mk.IV manual has no recommended settings about carb heat, but the Mk.V manual does. Since the engines are the same (the main difference is that the Mk.V has constant speed props while the Mk.IV has two-pitch props), maybe we can follow the same guidelines. Here's what it says:

1) Warm intake should be used:

a) For all flying at less than +3.5 psi boost, unless atmospheric temperature is more than +15 degrees Celsius. In that case (more than +15 C), Cold intake should be used regardless of boost.

b) For all flying (regardless of boost used and ambient temperatures), when in conditions of high humidity, in or just below clouds, in rain, snow or sleet. Warm intake can also be used to help warm-up the engines in very cold weather.

2) Cold intake should be used for all other conditions, including:
a) Starting at all times
b) Take-off
c) Landing, unless the bad weather conditions of 1b) apply.


So, i guess it's safe to turn it on and keep it there at the altitude where the ambient temp drops below 15 C. Since we don't yet have the dynamic weather, i guess the sim uses a standard atmosphere model. In that model, the ambient temp on sea level is considered to be 15 C and drops 6.5C for every 1km of altitude (or roughly 3000ft). In other words, if CoD uses an ISA atmosphere and the carb heaters on our Blenheim are similar to the Mk.V carb heaters, we can turn on carb heat as soon as we have completed takeoff, assuming we climb at less than +3.5psi boost. I usually set it to +1 boost for a normal cruise climb, so it would definitely apply to my method.

The easiest way to see what kind of ambient temps the game uses is to spawn a Blenheim in the cross country mission in the QMB without starting the engines, accelerate time for a while to let the engines and oil get up to ambient temperature and see what kind of temps the instruments indicate.

I think that last time i checked this CHT temps were 10-12 C, so it definitely looks safe to turn on carb heat as soon as you climb 500-1000ft after take-off and settle into reduced power settings.

[Vengeanze]

On atmosphere model - if there's a landing strip on a higher alt then one could check ambient temps at sea level then fly (or fix it in FMB) to the strip at higher alt and let the engine cool down.
Then we'd see if there's a change in temps at diff alt at all.
I could do that but I dunno where to check for alt (I never set that on the alt meter).

Btw, anyone checked if temps changes over the course of the day? That should be simple. Gonna check right now actually. Brb.

Ok, back now.

Ran for almost an hour. In game time (tod) was from 09.00 to 23.00.
I checked Oil temp and CHT. No change what so ever at anytime during the test.
A bit funny is that all temps showed different - oiltemp port 17, oiltemp starbord 14, CHT port 10 and CHT starbord 12.

I see this as an indication that there's no atmosphere model at all except for clouds.

[Mechanist]

Originally Posted by Blackdog_kt

On the other hand some people say that while the animation is that of a two-stage prop, it actually works like a fully variable one. I think we need to do some more testing to clarify this.

Allready done:

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

My findings about the carburetor heat

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)

Also mixture doesen't work at all. Just try a mission with mixture at 0%, then refly the same mission with 100% an you won't notice any difference at all, regardless the altitude.