Hurricane engine torque

[kimosabi]

This thread is what happens when engineers and theorists sober up.

[Viper2000]

Originally Posted by kimosabi

This thread is what happens when engineers and theorists sober up.

So you're saying that this thread is a massive coffee binge, followed by feverish attempts to catch up on all the work that should have been done during the party?

[kimosabi]

Ya.

[Peril]

Must be 109 pilots throwing in a red herring Hehehehehe.

'Peril looks at the Hurricane tested data posted above and scratches his head'. You guys interested in what 'actually' happened in the case of the Hurricane or what mathematically should have happened but didn't?

Basically, I've not yet been able to find a combination of throttle/prop angle/mixture etc. to get the hurricane flying straight and level. So you have the options of either grab the stick and apply aileron, probably for hours on end, or apply such excessive rudder trim that your plane basically flies sideways.

So, to round that up for you, the plane should trim neutral in roll @ ~130mph, seems you missed the answer or at least the point to the question? (not 42 in this case)

[ElAurens]

Interesting discussion Viper, thank you.

I am a mechanic, not an engineer, and I work on vintage/veteran automobiles.

I have always wondered why you never see Brake Mean Effective Pressure used in modern automobile engine specifications. All the old English cars I work on usually have this listed in their manuals, and it is indeed indicative of their maximum development potential. We race a Triumph TR3, and after all the years of development and money spent on this old design, the maximum BHP that they produce now is still just about what tuners got out of them in the 1960s. Just no way to get around that BMEP thing in any meaningful way. The only thing that has changed over the years is the ability to have much flatter torque and BHP curves, so the engines are more flexible and lap times decrease, even if maximum power is about the same.

Sorry to go off topic, but I rarely get to talk about these things outside of our small vintage racing community.

[Viper2000]

Originally Posted by Peril

Must be 109 pilots throwing in a red herring Hehehehehe.

'Peril looks at the Hurricane tested data posted above and scratches his head'. You guys interested in what 'actually' happened in the case of the Hurricane or what mathematically should have happened but didn't?

So, to round that up for you, the plane should trim neutral in roll @ ~130mph, seems you missed the answer or at least the point to the question? (not 42 in this case)

It's really not that simple, since we don't know very much about the test aeroplane, the power setting (i.e. manifold pressure & rpm) used or the altitude at which the test was carried out.

In fact, for all we know at this point, it could have been a Hurricane II with a Merlin XX, metal wings & ailerons at one extreme, or an early Hurricane I with a Merlin II or III, wooden wings and fabric covered ailerons at the other, and climb power could mean anything from 2600 rpm, +6¼ psi (Merlin II or III) to 2850 rpm +9 psi (Merlin XX; which also has a 0.42 reduction gear instead of 0.477 for the Merlin II & III).

[Viper2000]

Originally Posted by ElAurens

Interesting discussion Viper, thank you.

I am a mechanic, not an engineer, and I work on vintage/veteran automobiles.

I have always wondered why you never see Brake Mean Effective Pressure used in modern automobile engine specifications. All the old English cars I work on usually have this listed in their manuals, and it is indeed indicative of their maximum development potential. We race a Triumph TR3, and after all the years of development and money spent on this old design, the maximum BHP that they produce now is still just about what tuners got out of them in the 1960s. Just no way to get around that BMEP thing in any meaningful way. The only thing that has changed over the years is the ability to have much flatter torque and BHP curves, so the engines are more flexible and lap times decrease, even if maximum power is about the same.

Sorry to go off topic, but I rarely get to talk about these things outside of our small vintage racing community.

I think that the people who produce the brochures these days are afraid that BMEP is too technical for their market.

I think that they emphasise peak bhp because it's a nice big number that's relatively easy to massage in order to sell next year's model.

Really of course you get a better indication of car engine performance around a track by looking at the area under the power curve. This is much harder to massage because generally when you start tuning you end up adding to one part of the curve and subtracting from another unless you either supercharge (and thus increase BMEP) or increase cubic capacity; both of these options are obviously expensive.

Of course, if you improve the gearbox then you can win by tuning the induction & exhaust systems and accepting a peakier power curve. But new gearboxes are also expensive.

If you're stuck with the stock gearbox and don't want to supercharge then really all that you can do is blueprint the engine, perhaps clean up the induction & exhaust systems if possible, and obviously take great care with balancing it. All of this was obviously perfectly possible to do by hand and eye back in the 1960s.

This sort of work might allow you to increase the rev limit a little, but unless you start tweaking the valve and ignition timing this probably won't gain you an awful lot; and of course you'll then find that the gear ratios don't necessarily play nicely with the new power curve.

So in the end you're stuck with the fact that the vehicle is a system of systems, and they all have to work together to produce a fast lap; meanwhile the engineers who originally designed the car (and the tuners who first tried to make it go a bit faster) weren't stupid, and so beating their performance isn't going to be easy.

I think that it's probably easier to improve cars of this vintage by making aerodynamic tweaks; I'd be inclined to pay particular attention to the undertray if there are no rules preventing you from doing so, as quite often old cars are quite poor in this area.

If the track is fast you can probably also reduce drag by cutting down on engine cooling intakes, since they tend to be oversized for road use, based upon the worst case hot-weather uphill traffic jam scenario.

Indeed, if the race is short you could potentially win by going to a total loss cooling system.

Likewise, getting rid of engine accessories that you don't need will save both power & weight. You might also replace the original lead-acid battery with a lithium one, get rid of the alternator entirely and run the coolant & fuel pumps from the battery. And of course you can also down-size your spare tyre (or delete it completely if you don't need to remain road legal).

You can also potentially start playing with the weight distribution by moving the battery around.

New wheels can help to reduce the unsprung mass, and this will open up additional options for tuning the suspension.

But once you start down this path, either you'll run into regulations* if you're racing in some kind of vintage formula, or else you'll be in the slightly unsatisfying position of driving a very fast, very new and extremely expensive car with a vintage numberplate...

PS - glad you enjoyed the discursive part of my little rant. I fear I was being somewhat harsh, but from time to time hecklers get the better of me and I bite...

*Of course, regulations in any serious competition are an exhortation to find innovative ways of violating the spirit of the law without transgressing its letter; if the other teams aren't periodically complaining about aspects of your design then you're doing it wrong.

[ElAurens]

As Kas Kastner, one of America's legendary road racing team managers says, "The rule book is grist for the thinking man".



Actually the biggest gains over the last 7 odd years have been in camshaft technology, at least in the old crocks we race. It's all in the ramps. A true black art. All I know is the valve acceleration with these new grinds has forced everyone that uses them to dramatically increase the strength of the rocker shaft assembly.

Oddly, much of what has been done is a result of studying modern variable valve timing set ups, and a very close look at modern motorcycle practice, as far as cam profiles go.

Cheers.

[Viper2000]

If you go down that path then the next thing to do is to start looking very closely at what the valves are actually doing when the engine is running; you may find that they aren't quite behaving as you expect.

You may also find that the valve springs become unhappy.

There may be some performance advantage to be had from new valves made out of superior materials, especially if you can save weight.

Of course, all of this stuff gets expensive rapidly, and so it's worthwhile to decide what price you're prepared to pay for say 0.01 s/lap. Then you can start analysing your options and rationally allocating budget.

Of course, for this to work really well you need a simulator so that you can investigate the way in which your driver will respond to car performance changes; you may find that changes in power or grip have surprising unintended consequences for the racing line that your driver elects to take around the track, which can either positively or negatively affect the overall lap time.

As with so many things in life, the job is never finished; eventually you just have to decide when to stop.

[Peril]

Your a funny man Viper, you think like an opposing team not wanting improvements.

For info it was a Hurricane II with a Merlin XX, Rotol constant Speed prop, document is 'Measurements of the Flying Qualities of a Hawker Hurricane, by Neilsen and phillips. You could have this test data on your HD already I suppose?? But if you don't and want to improve the sim, 'please supply more data' would be a good start. I tested the Hurricane in game marked as a Rotol prop Hurricane, not sure if that is a definitive match, it's hard to tell based on that description.

So you are aware, I spent the last 6 years building and researching FM for another sim focused on realism, so I have some experience and data to call upon and know what is required. I too didn't modify my FMs without good data but I'm not one to ignore what is logical either. If it is of interest we had to apply on average 0.2 deg of wing twist to obtain an outcome that match reality re roll trims. Sims are great representations but unfortunately they are rarely perfect in result because of using the simplified code they have to use due to the limits of home computing. Before you go off all negative, think about what we have proved here and work backwards from there, I always found the answer could be somewhere in the middle.

Feel free to use any alt, power and the glide test data to confirm, I think you'll find it likely has a problem

That would confirm some changes are needed, some of us are here to 'help' where we can...the only agenda I have is FM realism.