Guys guys guys, you've got it all wrong. You're not appreciating the awesomeness of CFD.
Bullet: thanks for treating us to your fantastic CFD analysis though at this point I’m not sure which CFD that is: Completely Fictional Dynamics, Confusingly Faulty Dynamics, or Clearly smurfy Dynamics.
But I digress with having a little humor at your expense. You’ve tossed out some flight model zingers. Here’s the deal- FM zingers are a dime a dozen and people toss them out on here all the time thinking that they’ll get noticed. Don’t fall for that trap! You’ve got to distinguish your FM zinger from the rest of the herd mind you, sort of like the techniques a girl will use to stand out at the Miss Universe Pageant (and it’s more than putting lipstick on a pig…well, you get the idea). What’s the difference maker for FM zingers? Your analytics of course. The ones that really stand out are the ones that are strong analytically.
So here’s a helpful guide in order to construct analytically strong FM zingers. Let’s just look at your manifold pressure statement as an illustrative example how differently you might have approached it analytically.
STEP 1: CLEARLY STATE YOUR HYPOTHESIS½ of all FM zingers fall off the rails at the start because the hypothesis is unclear leaving the rest of us trying to figure just what exactly is the cause and effect relationship someone is trying to make. You’ve actually did well here because it’s pretty clear what you’re saying about AH manifold pressure. It’s much better than other statements like:
“I got shot down in a Spixteen by a freakin’ Mustang in a turn fight yesterday. That’s impossible! There’s something wrong with the Spixteen or Mustang FM!”.
See, with such a statement it’s totally ambiguous as to what is wrong since the cause and effect is left open to interpretation. What is wrong could be pilot suckage as much as an FM problem but we don't know which. However your statement is clear. I’ll restate it in my words:
HYPOTHESIS: “The AH FM is frapping wrong because it doesn’t model engine manifold pressure change with altitude!”
Well, having a clearly stated hypothesis isn’t enough however. If ½ of all FM zingers don’t have clearly stated hypothesis, that leaves ½ of the other FM zingers that actually do so you still have to go beyond that to stand out analytically so don’t stop there!
STEP 2: SUPPORT THE PRINCIPLE BEHIND YOUR HYPOTHESISSort of a corollary of the Step 1, the 2nd place FM zingers quickly become train wrecks is that the principle behind the hypothesis is not explained or proved. Of the ½ of FM zingers that have a clearly stated hypothesis, only 10% of them actually explain the principle behind the hypothesis. Don’t make this mistake either, otherwise your FM zinger looks just like the rest of them. Remember, the goal is to get noticed! In your manifold pressure case, let’s give you a B+ in your statement because you actually state your principle:
…once the Spitfire Mk 16 reatchs an altitude of 18,000 feet its manifold pressure drops…
Not bad, but it could be better. How? By demonstrating this principle either through aero physics math or with data, or both. How might have this looked instead? Maybe something like the following:
“PRINCIPLE: Piston aero engine performance is affected by the reduction in air density as the altitude increases reducing the manifold pressure of the engine. Superchargers can address this but they too eventually are not immune to decreasing air density. For example the following Spitfire Mk VIII (Merlin 66) flight test data demonstrates this:
(courtesy wwiiaircraftperformance.com)
As evidenced by the chart the manifold pressure or “boost” level fluctuates between +18 lbs/sq in to 0 lbs/sq in as altitude and supercharger gearing changes.”
If you can do this with charts, even better. People love charts even if they have no clue what the chart means. It helps to add to your level of credibility and authority! But supporting the principle behind your hypothesis still isn’t enough though. We haven’t sealed the deal yet. After all supporting your principle only gives us an idea that perhaps you know what you might be talking about but it doesn’t do a lick to prove anything yet.
STEP 3: TEST YOUR HYPOTHESIS TO PROVE (OR DISPROVE) ITThis is where the rubber meets the road when it comes to FM zingers! Infact people realize this as much that they rush off from STEP 1 to STEP 3 and totally leave out STEP 2. Don’t make this mistake. STEP 2 is important because it gives you a basis for the principle that you will be testing against in STEP 3. ½ of ½ of all FM zingers with clearly stated hypothesis fall for this trap. Assuming that it hasn’t and that we’re in the 10% that haven’t skipped STEP 2, we’re now ready to do the testing and to demonstrate the hypothesis.
In your manifold pressure case, we’ll be generous and give you a C- for it. It’s hard to tell what kind of testing you’ve done and you make some statements in the affirmative as if you or someone else did but clearly HiTech thinks you haven’t. Why is that? Well you’ve not presented the data of your tests of course! But the trick here is NOT ONLY PRESENTING YOUR DATA, the trick is to do this COMPARED AGAINST YOUR PRINCIPLE IN STEP 2. See a lot people will throw out data in a form of test but not against any principle. And when they do we don't have an inkling of the cause and effect relationship they are trying demonstrate.
Here’s how you could have done this much much better, in fact without even actually flight testing it!
TEST: We’ll examine the Aces High Rate of Climb to see if it demonstrates the similar pattern found like in the actual flight test report listed above. Let’s examine the Spitfire Mk XVI in Aces High. I could have chosen the AH Spitfire Mk VIII to match the figures above but since you were talking about the Spitfire XVI we’ll just do that for the heck of it (Nevermind that the Mk VIII uses the Merlin 66 which is what our Mk XVI uses because it’s really just a Mk IX LF with a Merlin 66. Why are the Brits so confusing anyway???? Centre vs. center, colour vs. color?? Really.). Here’s the published RoC chart compared between a Spitfire Mk IX and Spitfire Mk XVI (WEP Power):
Well crap. Sure is funny that the AH rate of climb chart exhibits the similar raggedy lines that the real flight test RoC chart shows, especially as altitude increases RoC decreases. What does this all mean??? Well one possibility is that the AH Spitfires engine power output (and thus manifold pressure) actually does decrease with altitude. Huh, fancy that.
But we all know that AH can’t be 100% right right??? So there must be other possibilities of why the AH FM is screwed up and wrong and the manifold pressure goofed! We just have to go fish for some more data to prove our point or repeat steps 1-3 as necessary until we do!
So there you go, 3 E-Z steps to positively make your FM zinger stand out from the rest of the rabble! I’ll let you go figure out how you can apply this to your “drag” question!
Peace, Out!
Tango
412th FS Braunco Mustangs
