well i thought that was totally up to us. so i just plunked 200knots
Don’t know if I can let you be the fastest.
Cause as we all know, it is not about winning, but about be the fastest, right?
And so has a competition inside competition begun…
yo dawg, I heard you like competitions…so we made a…
Don’t know if I just don’t understand the sheet or there is something that needs a small tweak, but as soon as I select Constant speed propeller My takeoff and climb values are excellent no matter what and cruise at maximum. While that sounds nice and simple I do not believe it is correct? And are the criteria and specifications guidelines or actual rules for the engines? =)
I have like 166 knots. Stop fucking me, guys.
Yes, with a constant speed propeller the propeller can change its angles to give you the best rates for whatever it is you are doing. His formulas in the spreadsheet are set up to show excellent and maximum as long as C-speed is selected.
In this challenge, they are a mix; engine power and planned speeds are more guidelines than anything, but the propeller diameter and the weights are hard and fixed rules.
Bear in mind that due to the laws of aerodynamics, there is, somewhere in that suggested range of engine power and propeller sizes, a combination that gives the best performance while returning the best fuel economy possible. Don’t ask me what it is, though - I literally have no idea, and will have no idea until this round is over.
My entry into this round is a little bit radical - hopefully it won’t blow up in my face!
Ty, that is what I was reading them as. So even though my 850hp beast is not competitive it is still eligible for the landed gentry that can have nothing but a V12 doing 700 knots
Well, you could enter a 700 horsepower aircraft, but bear in mind that it will only be about 25 percent faster than a 300 horsepower aircraft, but with far more than double the fuel consumption. The laws of aerodynamics are cruel indeed
I should also say having now plugged an engine into the sim model, 180 horsepower is as low as I would dare to go for this challenge…even that produces takeoff and climb performance that, if I was confronted with it in reality, would call “scary”.
if the prop tip goes beyond 0.75 mach, that means what?
afaik, it just means the tip is ‘stalling’ right? much more drag but not much more speed?
It has to do with the air speed over the propeller’s surface. I’ve been reading a little as I get time.
Maximum helical tip velocity is an important parameter for propeller selection. In the absence of specific data from the prop manufacturer, it is safe to assume that (a) the maximum prop efficiency will be about 87% (for any metal prop a non-governmental agency can afford), and (b) that the prop efficiency begins to decrease dramatically when the prop is operated at a helical tip velocity in excess of 0.85 Mach. That occurs because the local air velocity over the surface of the prop (near the point of maximum airfoil thickness) will reach Mach 1, and create a shock wave, separating the flow and dissipating prop energy.
TOO MUCH MATHHHHH
but i did get some insight thx to that. so thanks.
now, which is more important… efficiency or longevity…
my engine is… most likely… done
but again. like my first engine, it’s making a weird sound on the lower rev range. the inline 4 sounds like a diesel. my v8 now sounds like… an inline 8?
And now i start feeling panicky because i flat rated my max 183hp engine for this round… Let’s hope fuel efficiency does me favor
The spreadsheet is acting up on me, it’s giving the “#name” for the flight characteristics, gearbox cost, powerplant cost, and engine cost, I’ve filled in all categories and have values for static thrust, required power, and all propeller derivatives. Am I missing something?
Edit, never mind user error I guess, downloaded on my phone and it’s working fine.
Another edit. Question, So would it be reasonable to say that powerplant cost should fall between 10-20% of the stated airframe cost?
Well you want your powerplant to be as cheap as possible while still satisfying both your desires and the challenge criteria, because it directly affects a scored category in this challenge. Nobody’s going to buy an airplane that’s 50 grand more expensive than its roughly equal-performing competition.
The exact percentage of what the powerplant cost should be will vary dramatically based on the challenge; in round one, it was less than 10 percent in some cases, and in some future challenges it could conceivably reach and even exceed 40 percent.
i’m guessing still stable build for this round?
I’ve played automation for years now, and worked as a ship’s engineer for nearly as long, but this was me making changes to the spreadsheet for this challenge.
Yeah, I think I’m going to keep it on the current public release for this challenge - I’ve already had a number of entries so far, and I don’t think it would be fair to them to tell them to start over if for some reason something goes wrong bringing their engines into the beta version. But really it’s a “damned if you do, damned if you don’t” situation.