But instead we're watching the world slowest train-wreck being played out on Youtube. It's a slow agony.

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But instead we're watching the world slowest train-wreck being played out on Youtube. It's a slow agony.

Cessna did that, then punted.Maybe Icon might want to expand its product line.

BJC

Maybe a smart marketing campaign in the future will end with the phrase..."and it's not a Raptor!"not so long after I hope to be entering the market

I agree with that and suggested moldless proof of concept early in this thread.Generally successful projects start with a bare bones proof of concept and add luxuries to the production version, rather than start with everything you could ever want and later subtract from the production version.

He has a different way of doing things. Either way it would take more than one iteration.

About 6 vortilons along the leading edge seemed to do the trick on the scale model. Just can't figure out why PM only put one on the real plane. It's not an uncommon "band aid" to see on these style planes to help with the headaches of needing a swept wing.

Imagine if it became a "reality"show like Airplane repoBut instead we're watching the world slowest train-wreck being played out on Youtube. It's a slow agony.

For some of us it is the squandered resources.Could Give my opinion of why I think that is,

There are probably a dozen orphaned kit planes that could have been brought back to the market - in improved versions - and the first 50 kits given away and still have cash in the bank. There would be no new tech or advancement of the art but there might be a few more planes flying. Example:

How many new fast build Starlite kits could be produced

I find it interesting that 1) someone could identify dutch roll in a 4 sec ballooning flight, and; 2) that dutch roll is some kind of bad omen. Lot's of airplanes exhibit dutch roll to varying degrees (V-tail Bonanza, for one) as it's more desirable than some other forms of roll / yaw dynamic coupling. Certainly not something I would scrap the plane over.

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Well, there is guessing, and then there is educated guessing, sometimes called 'analysis'.So much speculation and guessing and linearizing accelerations...

Now as to what the power and BSFC really is for the Raptor, well, you are all guessing...Once we admit to ourselves that they are guesses, when will we stop talking about it?

Many of the folks here seem interested in tinkering with ideas about aircraft design, and that also includes Raptor Peter. But let's do a thought experiment: you want to create an airplane that is as good as some known quantity that works well. So where do you start? Do you just wave your hands around and say 'that looks about right'?

Okay, so obviously it pays to do a little preliminary analysis, which is why no airplane is ever designed without undertaking such an exercise.

In this particular case we are interested in the power required by the engine in order to give us the required

Now if we look a little deeper we find that trying to figure out why a Cirrus performs the way it does is due

But the good news is that all of those aerodynamic [and propulsion] characteristics are already

Let's run an example. Our first order of business is always to compile thrust required and power required curves. But in order to do that we need to know a couple of key things that are known only to Cirrus, namely the

How do we extract those?

Well, it turns out that there is indeed a well traveled road to do that. The zero lift drag coefficient CDo

Looking at the POH we see a best glide speed of 88 KIAS [at 3,400 lbm]. There is also a glide ratio given of about 9.6, but that includes propeller drag, which means the

The importance of the CDo is that it

A very useful relation for finding the CDo:

CDo = W^2 / q^2 / S^2 / pi / e /AR

This holds true

We start the analysis by first finding our lift coefficient at this best glide speed using the lift equation, L = q * S * CL, and turning it around to solve for CL we get:

CL = 3,400 lbm / 145 ft^2 / 26.2 lbf/ft^2 = 0.895

[q is dynamic pressure.] We now find our CDo using the long equation above, plugging in a

CDo = 3400^2 / 26.2^2 / 145^2 / pi / 0.8 / 10.1 = 0.032

We know that our induced drag CDi must equal CDo at best glide speed, so we now find our lift induced drag coefficient:

CDi = CL^2 / pi / e /AR = 0.895^2 / 3.14 / 0.8 / 10.1 = 0.032

So it works! We have found our zero lift drag coefficient, and it exactly matches our lift induced drag coefficient at best glide speed. Each one is 0.032, so the total drag coefficient CD = 0.064.

BUT, we need to now double check that result at a different flight speed so that we can verify that our CDo does indeed

We find our drag coefficient by first finding our total drag, which will

Drag = Thrust = power / v = 310 HP * 0.85 * 0.85 * 550 ft*lbf/s / 311 ft/s = 397 lbf

Where 550 is the number of ft*lbf/s in 1 hp, and 0.85 is both our percent engine power and our

Now that we know our total drag, we can find our overall drag coefficient:

CD = D / q / S = 397 lbf / 96 lbf/ft^2 / 145 ft^2 = 0.029

Well, we have a problem! Our total CD is now

So here is where we iterate the two

It turns out for this example that a prop efficiency of 0.9 will give an Oswald number of ~0.9 [0.89565]. Both of those are reasonable figures in line with known quantities: the C182 has an e of 0.84, the 35 Bonanza 0.82. The Oswald number is related to span efficiency from lifting line theory, so the higher aspect ratio will give a higher e, as we would expect in the SR22 with its aspect ratio of 10.1.

We note that the lift coefficient

CL = W / q / S = 3400 lbm / 96 lbf/ft^2 / 145 ft^2 = 0.245

We now find our lift induced drag coefficient:

CDi = CL^2 / pi / e / AR = 0.245^2 / pi / 10.1 = 0.002

Summing our CDo that we found at our best glide speed and which doesn't change, plus our CDi, we get:

CD = CDo + CDi =

Note: as we were iterating our Oswald number and our prop eff, we ended up with a new zero lift drag number, smaller than with our original assumption:

CDo = 3400^2 / 26.2^2 / 145^2 / pi / 0.89565 / 10.1 =

Note that we are using here our dynamic pressure q [26.2] for our

We are all set now, and have what amounts to the

Glide ratio at 184 KTAS = L/D = CL / CD = 0.245 / 0.03 = 8.1

To find our

We can also verify this:

CDi = CL^2 / pi / e / AR = 0.895^2 / pi / 0.89565 / 10.1 = 0.028

Exactly the same as our CDo, as it must be.

Our total CD = CDo + CDi = 0.028 + 0.028 = 0.056

Our max glide ratio is then:

L/Dmax = 0.895 / 0.056 = 16

Thrust required at any speed is: Tr = W / (L/D)

We can now go ahead and calculate the entire drag and thrust required curves at every speed, using nothing more than our CDo, which stays the same, and simply computing CL at each speed in order to find the CDi.

All you really need, aside from this analysis method is to accurately calculate atmospheric conditions, a good calculator here.

So are we merely 'guessing'? Well, yes our actual numbers for the

BUT, and this is a big one, the fact that our two values [e and prop eff] may not be exact is completely irrelevant. They work PERFECTLY in letting us PREDICT

It doesn't really matter that these two variables may each be [very slightly] off, because

So we see that we can indeed perform very useful performance analysis by simply 'guessing' [iterating actually].

Additionally, one can carry this much farther by using more sophisticated methods to estimate propulsive efficiency, as well as the Oswald number. This is done all the time, in both industry and academia, and there are some really clever methods out there. It all depends on just how much accuracy you are after.

So back to the Raptor and engine power. In my earlier analyses of the takeoff performance, the exact same

Slo = 1.44 * W^2 / g / rho / S / CLmax / {T - [D + Rr(W - L)]av}

We see that the entire THRUST term in parentheses on the right can now be solved when we possess the zero lift drag coefficient, plus the Oswald number. [Rr is the friction coefficient for rolling resistance.]

We can now

A difference of even 5 percent is quite acceptable. Say 950 ft instead of 1,000. Or 285 hp instead of 300. That kind of difference is a lot better than nothing. And, as mentioned already, you can get very accurate results, even down to several significant digits, depending on how fancy you want to get with various intricate methods.

The simple reality is that there is nothing new and very little guesswork involved in performing very accurate aircraft performance analyses. This is always done when designing a clean sheet airplane and setting performance targets, as well as extracting those unknown numbers for a competitor aircraft.

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With successful programs the second iteration builds on sound designs.Either way it would take more than one iteration

It's essentially almost identical to a Velocity except the wider width, the diesel engine and pressurization. So what would be the point of building a regular Velocity first? He hired a Velocity expert who presumably built the wings almost exactly as a Velocity anyway. He could have saved time and money by starting with a used Velocity, like Vans did on the RV-1. I doubt the sensible gradual evolving approach would have attracted deposits and the project would have ended early.With successful programs the second iteration builds on sound designs.

The most major apparent mistake was the complete disregard for logical weight estimation. Since he estimated the same 1800 empty weight as a Velocity even with the pressurization, so clearly no sensible weight goal was posted on the website at the beginning. The engine is the second big variable and we don't yet know how badly estimated the engine weight and performance is.

It could be they knew the weight was vastly more but simply neglected to change the web numbers. Nobody knows.

So it is not because americans can't distinguish miles and milesAlways in miles an hour because 170 mph sounds way cooler than 140 kts.

Thanks. Not sure what made me think it was electric, but the issue is the same with it engine driven. If he didn't program it to disconnect the belt pulley clutch at low RPM that will stall the engine when AC kicks on, it wouldn't surprise me at all if he didn't do it for WOT either.

I just manually flip the AC off on my car going up a mountain pass. I bet Peter figures a test pilot could do that on a prototype.

Diesel engines have twice the torque. Since I got a twin turbo Diesel (like the Audi engine, but 2.2l instead of 3l), I can go up mountain highways in the 6th gear. Aircondition can not be felt at all.I drove one once, it accelerated so fast my face hit the windshield.

Dutch Roll is kind of a long period phenomenon to be sure about on a few seconds of ground effect flight...

Vortillons and winglet extensions below the wing have fixed Dutch Roll and increased stall resistance of the main wing on Long Ez and derivatives . I suspect that Dutch Roll can be "fixed" easily enough, as it has in all of the other ships in this basic configuration.

Billski

Only heavier, slower, and take longer to get airborne.At the end it will resemble a Formula 1 car.

Brandon

Uh-oh. That's a red rag to those who can't do physics.But it is power that makes the vehicle move.

[I shouldn’t have done that, but it has been several months since the last debate.]

BJC

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