Seek Advise on How To Keep My "Spite" Cool

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Eagle Spirit
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Seek Advise on How To Keep My "Spite" Cool

Post by Eagle Spirit »

Finally mastered my Civ. "Tang" after a year :D . Now I'm flying the MKll "spit." Have a training flight from Kalispell, MT to Missoula, MT. A little over an hour, at 10,500 ft. All goes well, until I'm parked on the tarmac, then I notice the steam/boil over. I've watched videos and note that pilots can actually finish their flt. w/o over heating. So, whats the trick? I've watched our Scott's fine video's, but haven't found an answer. Does it have to do with fine tuning the prop? Use the three blade. BTW, my RPM around 10:30 relative and prop about 2:30 relative. (sorry I'm not using the correct jargon). My speed is usually around 200 knots., and cross the fence at about 85 knots.

I'm eager to get your input.

Regards, Eagle
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Jacques
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Re: Seek Advise on How To Keep My "Spite" Cool

Post by Jacques »

Are you opening up the radiator enough? I think thats where I might start if the radiator is boiling over after a flight. Or perhaps look at how long you are taxiing once back on the ground.

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Re: Seek Advise on How To Keep My "Spite" Cool

Post by Killratio »

Has got buried deep in history..so here it is again...might help ;)


Radiator Tutorial.
A LOT of time went into modelling and testing this cooling system (and a lot of
research). It is, simply put, "the goods." It is SO accurate that it creates headaches
for the pilot in almost every conceivable way. The radiator is quite small and despite
the large wing area (often used to good effect with large radiators or cooling pipe
runs spread throughout disappating heat well) the design left hardly any room for
cooling in the wings...in fact WARM air and hot coolant from the engine were ued to
WARM the guns!! Then the U/C legs will block much of the airflow through it.
For these reasons, the Spitfire's radiator, as many of you will already have
experienced, is barely adequate on the ground. It also has some strange qualities in
the air....some of them counter intuitive to a non pilot, some even to a GA pilot.
So here is a quick run-down of points to note, tips to use and traps to avoid.


1. Speed is your friend!!
Remember the Spitfire's lineage? The S6 Racer series. The faster you go the more air
you will force through the radiator...MORE cooling. Unlike most modern aircraft,
throttling back and slowing down will actually RAISE your temps in many cases.

So:
a. Keep Speed ABOVE 180mph when ever possible. This goes for cruising, climbing whilst
still at low altitude, or on initial approach to land. A good cruise speed for economy
and cooling is 200mph. Your range at this speed indicated is about the same whether you
are at 100ft, 1,000ft, or 25,000ft.

b. Use the Radiator Shutter AS suggested. In many regimes of flight the drag from the
radiator will mean that more power (and therefore heat) is required to maintain
airspeed...you can actually raise temps by opening the Radiator Shutter and then trying
to maintain speed! Of course if you let the speed drop, less air is forced through, as
per above.
To give you an example to judge by...If you are at 5000ft and you hit the Boost Cut-Out
Override tab, you will usually get an extra 20-40 miles per hour roughly. This
generates a LOT of heat. So you open your radiator FULL to cool down. This will cost
you about 20-40mph of your speed...... In other words, you go no faster but burn 20%
more fuel and you could still over temp.



2. It is called Normal Flight position for a reason.

So if I slow down I get hotter, if I open the radiator I get hotter, if I power up, I
get hotter and if I do nothing, I get HOTTER??

Well, Yes......and no.


This is where the Normal Flight (red triangle on the map box) Marker comes into play.
In GENERAL at all times when you are cruising, climbs at reasonable boost, on descents,
in the circuit on landing...in fact any NORMAL regime of flight, this is the "Minimum
Drag" setting. It is a compromise and balance between volume of air scooped in and drag
caused by the "scoop" size.
The Merlin is designed to run in this range at temps of somewhere between 60C and 95C

So:
a. USE Normal position for most of the time.

b. Treat temp rises early. Diagnose the "why" work out what can be done and do it. THEN
monitor temps closely to make sure it has had the DESIRED effect.
Something we were always taught in the air... "A bad decision is better than NO
decision". That is particularly true here IF you monitor. Try a suggestion from here,
monitor, if it doesn't stop or reduce the rate of rise, try something else. If it makes
things worse, try something else. The only thing you CAN be certain of, is that IF you
chose to do nothing with rising temps, 9 times out of 10 they will NOT cure themselves.

c. Consider moving the radiator shutter ONE position forward of normal and check its
effect. If you are at 200mph, open it one step..you may cool a bit but only lose
10mph...that is worth the trade off. But if you are at 180mph generally that would be a
bad idea.



3. Other than Normal Flight.

a. For a high power climb the Pilot's Notes suggest opening the radiator shutter
SLIGHTLY, in other words by ONE notch. In extreme temperatures (North Africa?) maybe
two MAY help..but this is a definate "try something else", not an SOP.

b. For slow flying open the radiator an extra notch on normal and do NOT reduce speed
below 180mph without lowering your gear (at which time you may let speed fall to 160).
Use power to maintain this speed at the lowest practical boost and rpm WITHOUT being so
low that the Merlin runs rough.

c. Using the flaps for slow flight is difficult. Above 120mph the power setting
required will overheat you due to disrupted airflow from the flaps. Set RPM higher than
in b. above. In this configuration the temperature should stabilise at approximately
100C.



4. Your other friend is Altitude.
Your Spitfire Mk I or II performs best at between 16,000ft and 20,000ft dependant upon
airscrew OAT, load, etc etc. Use these altitudes.
Maybe 10,000ft is acceptable. 6,000ft to 10,000 ft you should be OK if careful.
Extended operation or high power settings below 5,000-6,000ft are just asking for
trouble.
If you are at 6,000 with a hot radiator..try a moderate power climb at 180mph to 12,000
or 13,000ft.
Circuits...well, I'll leave that to you to work out :)


5. Check your Airscrew RPM.
Just as the radiator will indirectly affect the oil temp, so the oil temp can drive up
radiator temp with it.

a. Try reducing RPM with the control, not with the throttle. BUT always be aware of the
affect on your speed.

b. When you have tried everything else and only RPM is left, if you have a fixed pitch airscrew,
you could try leaning out of the cockpit and "blowing" on the hot engine...sorry, best
I can think of. :(

6. Last Resort.
If you really have tried everything else and temps are still climbing, you could try a
moderate power setting dive to increase speed and get some more cooling by opening the
radiator fully and using energy to provide the speed. Make it a SHALLOW one and
remember to bring back the Prop RPM to prevent overseed...
I DO NOT recommend this solution as it can cause a number of problems but as with most
things in aviation, sometimes you must break a rule to survive. I have personally saved
myself on one occasion by doing something as a last resort that was a VERY bad idea at
any other time. You will probably not meet a pilot who has not at one time or another.
The problems to be aware of:

a. Shock cooling of the engine. Rapid descent with a hot engine at low power in
cool air is a bad idea.

b. Prop settings that result in the airscrew driving the engine, not the other way
around. A bad idea.

c. CFIT (Controlled Flight into Terrain)...don't laugh, pilots have died for more
stupid things than getting fixated on watching a radiator temp gauge fall back to
"normal". A bad idea.

d. Uncontrolled Flight into Terrain....the Spitfire must be trimmed into a dive (to
prevent excessive G on pullout). But get too fast in that dive whilst watching the
"pretty green gauge" and you may not get the option of pullout. You guessed it...a bad
idea.

------------------------------------------------------------------------------------


There a any number of wonderful ways to kill your engine, your Spitfire, yourself or
all three at once. There are very few ways fly her correctly.
Prevention is always better than cure. Avoid hot engines in the first place by :

1. Getting your pre takeoff checks and drills learned and then performed efficiently
and quickly but NOT RUSHED.

2. Don't use runways/fields that require extended taxi/hold.

3. As a result of pegging 1 and 2 above, you will get off the ground before temps reach
100C.

4. Climb at moderate power and higher airspeeds unless ABSOLUTELY necessary to go
slower, steeper, climb faster.

5. Watch temps like a hawk below 10,000ft.

6. ALWAYS check coolant levels before flight..remember these levels ARE persistent
between different aircraft of the same Marque.


A final suggestion for those having trouble in the pattern (thanks Dudley). Opening the radiator Shutter to FULL as you turn base may help. The wartime notes advise against it, implying that you aren't doing it right if you have to..however, if you find your temps climbing up...use it to help, if only while you learn.

See how it goes for you.

Clear skys, smooth air and handy tail winds to you all.
Darryl



EDIT...AND get your flaps UP as soon as directional control is established on landing!!!!!!!! (not sure whether I mentioned that in the body of this!
Last edited by Killratio on 20 Apr 2016, 00:02, edited 1 time in total.
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Re: Seek Advise on How To Keep My "Spite" Cool

Post by Killratio »

As to boost and Airscrew..this may help:


From many figures I am seeing people quote, there seems to be a belief (not entirely accurate) that running the Merlin at low boost is somehow "being kind" to it.

The performance of an aircraft is, as you know, the sum of many factors, including but not limited to:

Engine speed and power,
Airscrew size and pitch angle,
Aerofoil design,
Density Height,
etc etc..

An aircraft does not care at what speed it moves relative to the ground. Even a lowly C152 is more than capable of flying backwards from that perspective. I have done it, it is fun, it freaks out the people on the ground and serves absolutely no other purpose in the known universe.

It is therefore little surprise that many performance figures, settings etc recommended do not even mention speed. Thinking back to High School algebra (which I hated with a passion normally reserved only for the Tax Authorities, Meryl Streep, Tom Cruise and anyone in the performing arts with the surname Baldwin...but I digress) if you have 2 of three parameters it is easy to find a third. More complicated formulae track down more variables but all in the search, generally, for a resultant number.

With an aircraft it is, really, that resultant number we are looking for. Now part of the skill is to know WHICH variable is the appropriate one to leave as the "resultant".

So if you want to set up to fly 317mph indicated, you can set 2,600 rpm, open the throttle fully and then find a height (the resultant number, the answer to your calculation) which gives that. A VERY inefficient way to do it. Far better would be to set 2850rpm go to a height where you KNOW the aircraft is capable of 317 mph indicated and then open the throttle until that speed is achieved and adjust the throttle accordingly to keep her there....the throttle setting...the boost... is the "answer" you are looking for in that case. But normally it would be the 317 that would be left as the answer, the other settings would be used and THEY would GIVE that.

In most cases the result of the known performance recommendations is what you are chasing. So in cruise you are looking to set up the power and rpm and take what that gives you (because ground speed is going to still vary anyhow). Sure the performance figures will tell you what you should expect in airspeed at that setting but that will vary anyway with condition of engine etc. Likewise, climb recomendations are generally silent as to FPM...because THAT is the approriate figure to leave as resulting from the settings...(because it will vary minute to minute, foot to foot of your climb).

For these reasons and others, the Spitfire is generally flown on boost and rpm settings NOT to a climb rate, speed etc. (except, eg where speed is part of the setting process..ie on climb).

The Merlin is a high performance engine, from a purebred racing heritage. It is designed to run at high power settings. The best fuel economy will usually be had at low RPM but that does not mean low boost. In fact the Merlin is much happier running at high boost because that is what it was designed to do. It is the normal operating range and any engine is going to be happiest operating in its normal range.

Accordingly the amount of heat generated is in some circumstances much more dependant on RPM than throttle setting. Faster RPM can heat up the oil sometimes and just as oil temp can be indirectly controlled with the radiator...Rad temp can be indirectly helped by lower rpm rather than necessarily just cutting back the throttle. That lower RPM can often result in extra speed..further aiding cooling whereas cutting the throttle will almost invariably slow you down (in straight and level flight).

The recommended settings in the manual are derived from the real world Pilot's Notes or what might be called Operator's Handbooks, POH etc, today. They will give the best performance. Some of them are maxima and it IS suggested that the aircraft be operated "well within" them...but "well within" does not mean toss them out and wrap the thing in cotton wool.

To give one example....climbing at +2 and 2400rpm is far too low for a Mk II to give its best (in terms of cooling, climb and general engine health) where the maximum allowable is +9 and 2850 rpm.

In my opinion, the modern operating limits are a good guide to maximum engine health...+4 and 2400 after takeoff and for normal cruising..... +4 and 1800rpm when flying for range. And for climbing, 2650rpm and sufficient increase in throttle to give correct climb speed. If it is good enough for BBMF who are VERY concerned about engine wear, it is good enough for me. If lower boost settings did any good at all (or at least no harm) then the BBMF would be using them!!

Prunes guide..."Low revs, high boost, will bring you safely home to roost".


regards


Darryl

edit.. I notice that Scott mentioned the other day that relatively high boost (Manifold Pressure) and low rpm is EXACTLY how he likes to operate teh real world A2A Commanche.
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Re: Seek Advise on How To Keep My "Spite" Cool

Post by Killratio »

And one final thought..ditch the 2 blade on the Spit II in favour of the three blade Constant Speed.

The two blade was TECHNICALLY able to be fitted to the Spitfire II (that is why Accusim allows it) but never was, to my knowledge.

The Watts is tremendous fun to fly, inasmuch as it is a real challenge to keep everything within maxima whilst using it, but it is an evil piece of kit until you get to know it. The Merlin II/III of the Spitfire I makes it managable but the higher power Merlin XII on the Spitfire II makes it a nightmare.

During Beta I cost Scott millions in Merlin engines testing the Watts :) :) :)
Last edited by Killratio on 20 Apr 2016, 21:21, edited 1 time in total.
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Tomas Linnet
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Re: Seek Advise on How To Keep My "Spite" Cool

Post by Tomas Linnet »

When you get the hang of it, it flies just as beautiful as it looks.
Kind Regards
Tomas

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Re: Seek Advise on How To Keep My "Spite" Cool

Post by Eagle Spirit »

Well!!....

TYVM for your detailed dissertations. Perhaps the Spitfire isn't the AC for me. I did my four years at USNA, not USAFA, :wink: . I'm just looking for the pleasure I find in uncomplicated simming. Think I'll just stay with "Bush / VFR and business flights to the "city" :lol:, and my P-51 Civ. . It was interesting reading tho. I'll give it a shot. Sincere thanks.

Eagle
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Re: Seek Advise on How To Keep My "Spite" Cool

Post by Killratio »

Eagle,

If you are only overheating once you get to the tarmac..you're already doing most of this instinctively.

Rather than ditch her, try just opening the radiator as soon as you get in the circuit, keep to a tight Mil style racetrack (like the P-51) and getting the flaps up as soon as you are stable on landing.

Other thing is, of course, that Baby Spitfires do occasionally boil, that is what the pressure release valve is for. That is not damaging the aircraft unless you have sustained high temps for a while and they increase beyond the 130C odd range. Don't stress too much about a bit of boil at the end of a flight. Most of the fuss about boiling is at the takeoff stage..because that means you are going to climb and operate with an already overheated engine. In fact, Jeffrey Quill complained that the Spitfire I would happily boil in combat at 25,000ft...not surprising even in supercooled atmosphere given the high power settings and low IAS combat often entails....

Image (AR213 with Tony Bianchi, one of the best, on landing.)

If that solves the problem, great and you will get immense pleasure out of her...I use her for cruising, recon missions AND bush flying in Papua New Guinea with no problems..if you are still having problems and she is not your style, well, that happens :)

But as said..you seem to be doing 90% already instinctively.


regards

Darryl
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Re: Seek Advise on How To Keep My "Spite" Cool

Post by Eagle Spirit »

Improved management seems to have solved the issue. I generally cruise At 12500, keeping speed between 185-90 and keep my rpm managed. I completed a flight from Kalispell, MT to Boeing Field (approx. 2 hrs.) w/o any over heating issue. OORAH!

Regards, Eagle
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Re: Seek Advise on How To Keep My "Spite" Cool

Post by Killratio »

Well done that man!!!!!
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Re: Seek Advise on How To Keep My "Spite" Cool

Post by Lewis - A2A »

Great photo Darryl and glad to hear your getting the hang of it Eagle. It is as with anything just a matter of practice practice practice and if you are ever away from the spit sim for any length of time expect to be boiling over again in no time, as I do again now after a stint of just flying the GA and T-6 aircraft :twisted:

cheers,
Lewis
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