'Correct' Coarse Pitch Setting...

[brad617]

Hello,

After contacting Historic Flying Limited, the operators of P9374, and having read Andy Saunders's book on P9374, I have found the 'correct' coarse pitch setting for the DH 5/29 propellor as fitted to early Spitfire I aircraft. This is a setting in the simulator of "coarse, 44%" and a virtual redline of 92% on the throttle. These settings give the same performance as John Romain describes in a in the book detailing the test flying of P9374. He describes having to perform CAA required maximum speed dives to 405 mph from 9,000ft. After countless dives from this height in the simulator to the 405 mph required I found the simulated Spitfire performed as Romain outlines in his account. He said, however, that the VNE for the Spitfire I is 450 mph but this would require an over speed of 3,400 rpm to achieve. Being a simulation, I proceeded to dive to the 450 mph VNE speed - the simulated Spitfire over speeding to 3,400 rpm as described!

On contacting HFL, John Romain said that he uses the Spitfire I in either fine OR coarse. He doesn't juggle in between the settings for the required rpm. With this in mind I set off for another test flight which involved climbing and level cruise checks (at 0 boost, around 2100 rpm and 230-240 mph) using a maximum power of 92% power and the coarse 44% propellor settings as established in the dives, I found that once again the simulated Spitfire performed as Romain described P9374 to perform.

So, if you want to fly how Romain describes, coarse 44% and a limit of 92% throttle is the way forward. (92% gives the stated '+6 1/4' boost figure).

I take off in fine and at about 180 mph switch to my coarse pitch setting, giving me an average of 2060 rpm for the climb at 160-180 mph. If the rpm drops too low, lower the nose until sufficient speed has been reached. I cruise at 0 boost giving 2000-2100 rpm and 230-240 mph. On landing, I use the coarse setting until under 140 mph with gear down (I always wait until under 120 mph for flaps). So far as aerobatics go :- +6 1/4 and coarse always used with, generally, a 250+ mph entry for most climbing manoeuvres which gives a sufficient rpm (2400-2600). The only situation in which I do not use this setting is during a half Cuban eight or a loop, as the speed drains off towards the apex and the rpm gradually falls through 1900, I pull the power back to -1 to avoid over boosting the engine.

Hope this helps and happy flying,
Brad

[Bradburger]

May thanks for that info Brad.

Much appreciated.

I have an account of flying P9374 written by John Romain in an issue of Aeroplane Monthly (possibly the same article you read) from a couple of years back, and this info helps fill in some of the blanks as regards power settings in the A2A Spitfire I.

I see you mention the power/rpm settings you use for aerobatics.

Did John give you the settings he uses for aeros as well? (I wouldn't have though he would use the full 6.25 lbs of boost).

(Just waiting for the implementation of the automatic boost control, which I always thought would make engine management a tad easier, and how it should be!)

Cheers

Paul

[brad617]

Hi,

Glad you found it helpful. And yes, the Aeroplane article is the same as I read. Andy Saunders's book is a must have though!

He didn't unfortunately but I made an informed guess. The BBMF use +6 and 2650 which is practically climb power. Civilian operators of specifically small, 'baby' Spitfires (I-V) use generally the same settings. So it's reasonable to assume that John uses a similar setting. It must be noted, however, that to start his display routine, John dives in from crowd rear thus enabling a higher rpm from the offset. If you do this, from cruise speed and from about 1,000ft AGL you'll have no problems. I usually enter my 'routine' at 330mph with 2600+ which is more than enough really. The key, especially with the Spitfire I - and without wanting to sound patronising - is to manage the energy from the first pass as Alex Henshaw explains in his book. You may notice if you watch the YouTube video of John displaying P9374 that he does a low topside pass after a series of half Cubans and barrel rolls, possibly to gain momentum for the next set of aerobatics. But without wanting to go on too much...stick with +6 1/4 and coarse and you should be alright

+6 1/4 is by no means the limit of the engine, just take off and climb power. I belive that the Merlin III goes all the way to +9? I never use more than +6 1/4 so I'm not really sure, I'll get back to you on that one though. The BBMF certainly engine ground run to +12. And as you say, the automatic boost control will help with engine management no end, I found during the dives that as the rpm increased and the altitude decreased that the boost began to rise, I can't remember the final figure in honesty. Wasn't past +10 anyway.

Regards,
Brad

[Bradburger]

Thanks again for the info/comments brad.

As for power settings on various engines on Spits.

I've just had a look at the engine limitations for the Merlin II & III listed in the MK I Pilots Notes/Maintenance Manual (A.P.1565 A Vol 1) and unlike the later Merlins, there is not a Max Continuous rating (which is +7lbs/2650 RPM for a Merlin 60/70/266 series), and is generally what most Spitfire operators/pilots would use today during a display for a MKVIII/IX/XI/XVI powered by such an engine.

It's worth remembering though that the BBMF MKII & V (along with several other 'Baby Spits' flying today) are fitted with post war Merlin 35s, as opposed to the engines they were originally fitted with, which is rated at 1280 HP @ +12lbs/3000 RPM @ take off. It's max continuous rating is +4lbs/2400 RPM, and with an intermediate, or climb rating of +7lbs/2650 RPM (1hr limit).

I recall reading a while back that for a display, BBMF normally use +6lbs for the Merlins ( +7lbs for the Griffons), so that's somewhere between the Max Continous figure and Climb figure for the Merlin 35.

As you probably know, the Merlin III is rated (87 octane) at 6.25 lbs/3000 Rpm for take off (up to 1000ft or 3 min), climbing (@ 2600 rpm), and all out level (@ 3000 Rpm, 5 min limit), whilst the maximum cruise power setting (Rich) is +4.5lbs/2600 RPM, and +2.5lbs/2600 RPM (Weak). With 100 octane fuel, it could of course go all the way up to +12lbs if needed.

I know John Romain mentions the delicateness of the early Merlins with their one piece heads and banks in the article, so with that in mind, I would say he uses somewhere between the two cruise boost settings for a display, rather than the full 6.25lbs of boost available.

I must say, that I've found somewhere around +3lbs (rich or weak mixture) boost sufficient for a low level aerobatic display in the A2A MKI.

Cheers

Paul

[brad617]

Thanks for your information Paul,

Your settings do seem more probable only, I'd expect John Romain to use a climbing power setting for the type of display he flies. Especially with P9374 being heavier at take off than the A2A Spitfire. I am not disagreeing with you at all, just putting through my thoughts. I again think you're right about P7350 using a Merlin 35 but I'm sure AB910 uses the standard Mk. V Merlin 45?

Either way, I'll try contacting ARCo again to get a definite answer...

Brad

[Bradburger]

Thanks again brad, and I meant to say that I might well be wrong regarding the power settings for a display in P9374!

But it will be interesting to hear what John Romain says regarding power settings he actually uses.

I'm pretty sure AB910 is/was still using a Merlin 35 at present, but I guess one can always check with the BBMF to be sure! (That said, I know they are now using a 266 in MK356, as opposed to a Merlin 500 that was fitted during the original restoration).

Whether they will fit the correct type of Merlin during her rebuild at ARC (I believe she originally had a Merlin 55M), we'll have to see!

As for MKIs', both AR213 & X4650 are using Merlin 35s at the moment, although I know that when they rebuilt AR213, they had acquired and restored a Merlin III, but used the 35 because of it's later mod standard, improvements, and reliability etc.

I'm pretty sure that one was also rebuilt for X4650 as well, but they decided on the 35 as well (along with a modded Hamilton Standard propeller) for the same reasons.

Interestingly, I recall reading that after AR213 had it's rebuild, both of the regular pilots who had flown her said that she flew at least 30 mph faster than before she was put back to 'stock' condition, despite having the same engine, four blade prop, and internal armour windscreen!

Cheers

Paul

[brad617]

Paul,

Your settings do seem more logical considering the reasoning. I'm still awaiting a reply from Historic Flying Ltd on the power settings used so we'll see.

I actually visited the BBMF regarding a collage project a couple of months ago...AB is set to return with the 'correct' 3 bladed prop as opposed to her Mk. IX 4 bladed one she was flying with - though I always liked that she had a 4 bladed one personally, it made her even more unique. She may even return with a Merlin 45 too...

I forgot to mention about AR and X4 too...I'm certain AR has had the 35 for a while now, even before the restoration, when she was with Tony Bianchi. I think I'm correct in saying that both AR and X4 both use the bracket props but modified for constant speeding?

Also, I did another dive from 9,000ft today in the simulator - only got 2860 passing 390 and a steady 3050 at 450. I didn't do another dive to confirm as I was short of fuel, what figures are you getting?



Brad

[brad617]

Historic Flying Ltd's Martin Overall has replied to my query:

Take off +4 2400rpm.
Climb +2 2600rpm.
Cruise 0 2000 rpm
Display +4 various rpm.

Seems you were more on the mark than me Paul!

Brad

[Bomber_12th]

Great information! Thank you for finding it out and providing it here, as well as your own studies/varifications. I have been flying this aircraft in FSX quite a bit lately, more so than I was able to when it was originally released, and it is probably the most beautifully flying aircraft I've ever experienced in FSX - such ease and grace (and rightfully so). I recalled in this video a few shots of the tachometer in-flight on P9374, indicating an RPM at just under 2000 and at 1800, on this, one of its earliest post-restoration flights: http://www.youtube.com/watch?v=Oh1S-C1r_mA

ARCo/HFL are of course now operating another early-mod Mk.I as well, in the form of N3200, with the same early Merlin III, DH bracket prop, and manual undercarriage as P9374.

[Killratio]

Great info, thanks.

It is gratifying that the performance figures on our Spit came out so close, particularly since all of the working out was done from engineering drawings and old accounts and before Andy's book came out. I was desperately hoping he would get his act into gear BEFORE the A2A Spit was released!! (not Andy's fault but his publishers I believe):)

A note re aerobatics....it is always safer to set a variable prop at maximum rpm (fine pitch) and then treat it as a fixed pitch.

On the subject of pitch, I can understand why John does not "fiddle" with the in-between settings as this is only really useful in a full on climb or long range cruise, neither of which a modern Spit is likely to engage in often or at all.

regards

Darryl

[brad617]

Darryl,

Aerobatics, the fully variable prop (as seen on the Mk.IIa) is usually set around 2650/2700 for a display. If it's the DH two pitch prop John uses it in coarse and treats it as a fixed pitch unit. Basically, everything other than take off, the initial climb to 500ft or 2700 rpm and landing is done in coarse pitch apart from slow flight under 120 mph

According to Mo at ARCo. The in-between fiddling isn't used. I didn't ask why, but I assume it's something related to the fatigue of the propeller unit and the tensioning cables.

Regards,
Brad

[Killratio]

Hi Brad,

The Mk II is a constant speed, so yes, you set an RPM. Interestingly enough I often get the comment from much better aeros pilots than me "how can you fly aeros with fixed pitch?? Much too hard without a CSU. " My answer is always suitably "modest"

Sorry, I was talking about the true "variable" of the Mk I. Interesting that they use coarse pitch but then I guess in the Spitfire the fine setting is really a "take-off and landing gear" as you have said and coarse for everything else (except full combat power). Usually though you would want all your power instantly available for aeros but then I fly a lot lower performance aircraft that NEED everything there. The Spit is very capable at +2 and 2200 I would think, let alone +6 2600!!

I suspect you are right about the cable tension considerations...fine is taught cable, so not desirable for longevity.

Damn, I wish I could stop thinking about her as a +6, 2600 warbird for 5 seconds and use the BBMF/John type settings for a nice leisurely cruise. One day perhaps I'll keep the red tab pulled back and see if I can get more than 2 hours out of an engine

D

[brad617]

It's all about establishing a flowing aerobatic routine I find. Enter at the highest speed needed and drain off the energy gradually. The Spitfire will perform most aerobatics at just over 200 mph if she's flown right, as I'm sure you're aware Although I generally like to add 10/15 mph just to be safe.

I really hate thrashing it about everywhere - they're grand old ladies after all!

Brad