10/23 Raptor Video

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wsimpso1

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Sorry but drag increases with the square of speed not the cube.

The correct 'rule of thumb' is Power2=Power1*(Vel2/Vel1)^2

ie 140 to 187 knots ==> 1.78 times power
Drag (and thrust required) goes with indicated airspeed squared, so you just computed the thrust ratio increase needed to make that speed increase. Power is force times speed, and so power IS a speed cubed function. Power would have to go up by about 2.4 times to get that bird from 140 to 187 knots indicated.

I do not think any of us buys the theory that Raptor is cruising 140 knots indicated on only 125 hp, and that is what it would have to be to make numbers on 300 hp.
 

BBerson

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Also, do you understand that to go from 150 knots to 300 knots requires 8 times the power and therefore 8 times the heat dissipation? That it's having cooling issues now just shows how far he is away from the claimed eventual specs.

How can the statement "future design is not what you think" be justified when the intent of the design has been clear for the last 8 years, and what he has taken money and the public's encouragement for? i.e. A diesel powered, pressurised, 300 knot, roomy aircraft that can carry 5 across America ...
I was thinking four times the thrust to go from 150 to 300. Chart shows about two times. But that is at same altitude. It doesn't take two or four times if it can get to a higher altitude, say 16,000. It obviously appears all of his wishful estimates must be reduced, including his cruise altitude estimates.
I don't think any of the knowledgable contributors expected any investment return at all. The one example I heard said he "would be happy with 75% of the crazy estimates". Which implies none expected the estimates to be valid.
 

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BBerson

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Power required chart. (Perkins and Hage)
Looks like power required to double speed depends on where on the curve you start at.
 

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mcrae0104

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Right—the parasite curve follows the P2=P1(V2/V1)^3 thing.
 

GotWake

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Did not sell shares. It is a LLC which don't have shares. NO INVESTORS.
Who would invest in a non profit?
The depositors bought ownership in a dream same as PM. None have complained.
Yeah, I worded that incorrectly. He can’t sell shares. But, a LLC can sell percentage ownership. He would send out emails offering to move people up to the front of the line if they would release their escrow with an additional $18k ($20k total). They were guaranteed a set price.
 

cheapracer

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BBerson

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Power required isn't that simple. If you start on the backside of the power curve then power decreases with speed up to best L/D.
 

rv6ejguy

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8 times the HP to double the speed is fairly valid at the same altitude but drag falls off substantially with altitude increase. 130 KIAS at 25,000 feet is around 195 KTAS. This is why supercharged/ turbocharged aircraft are much faster up high than near sea level. If power can be maintained up high, you can really move and get better MPG there as well.
 

BBerson

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Yeah, I worded that incorrectly. He can’t sell shares. But, a LLC can sell percentage ownership. He would send out emails offering to move people up to the front of the line if they would release their escrow with an additional $18k ($20k total). They were guaranteed a set price.
Right. So it's still a premium deposit to get to the front of the line. Hardly what I would consider an investment.
 

mcrae0104

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Power required isn't that simple. If you start on the backside of the power curve then power decreases with speed up to best L/D.
You’re right, BB, it’s not quite that simple. You have to take into account that induced drag is falling off as parasite drag is increasing (power required is the sum of these curves). At the speeds being discussed (140-187kt) it is well above the back side. Because the induced curve is much lower and flatter in this region, the cube rule is essentially valid.
 

BBerson

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I think the idea is to cruise just above best L/D at altitude. So the power required and fuel used would be the same as that same indicated airspeed at sea level. (Lelieve12 was talking about fuel use)
I don't see the cube rule on the chart.
 
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GotWake

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Right. So it's still a premium deposit to get to the front of the line. Hardly what I would consider an investment.
Also, this was in the emails….. sure sounds like an investment.

2) 0.25% (1/4 of 1%) membership in Raptor Aircraft LLC which entitles you to share in the potential profits further down the line. You will receive a Schedule K1 each year with your share of the profit or loss. You are not responsible for any losses but you can write them off on your taxes.
 

cheapracer

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8 times the HP to double the speed is fairly valid at the same altitude but drag falls off substantially with altitude increase. 130 KIAS at 25,000 feet is around 195 KTAS. This is why supercharged/ turbocharged aircraft are much faster up high than near sea level. If power can be maintained up high, you can really move and get better MPG there as well.
Correct, I am just trying to emphasize a point as to how far away this craft still is from the reality of it's claims.

I was going to suggest 4 times originally, but thought what the heck: "Shock Them" ... lol.

All moot anyway, you need pressurisation to fly at 25,000ft, his engine covers are flying off now, imagine what his 'glued on the outside' windows are going to do if (ever) pressurized ...

Someone accused me of hate on PM above, well let me say this: He seems to be a darn competent pilot. He goes by the numbers, stays calm in situations, and flies what is under him when it goes wrong.

See, facts aren't always suggestive of hate.
 

Vigilant1

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Also, this was in the emails….. sure sounds like an investment.

2) 0.25% (1/4 of 1%) membership in Raptor Aircraft LLC which entitles you to share in the potential profits further down the line. You will receive a Schedule K1 each year with your share of the profit or loss. You are not responsible for any losses but you can write them off on your taxes.
Oh, boy. For a lot of folks who formerly had very simple income tax returns, those K-1s will be an annual PITA. Hopefully, the investors will receive them early, but often they don't arrive until late March. And sometimes there are subsequent revised K-1s (often received just after you've filed your return). Yes, investors in Raptor may get a tax benefit (if Raptor LLC has losses 😉), but at the cost of complexity/aggravation.

Talk about adding insult to injury, the annual K-1 will be the little "gift that keeps on giving."
 
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mcrae0104

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I don't see the cube rule on the chart.
It's in the power required due to parasite drag curve. In the Perkins & Hage example, 147 mph requires 340 units of power, and 180 mph requires 810 units of power. The graph in your book is scaled with major units on 1/2" intervals, so you can easily measure and see.

\( {P_2} = P_1 ( \frac{V_2}{V_1} )^3 = 340 ( \frac{187}{140})^3 = 340 \times 2.38 = 810 \)


drag 1.jpg

Or, to look at doubling the speed, as @cheapracer suggested:

\( {P_2} = P_1 ( \frac{V_2}{V_1} )^3 = 360 ( \frac{300}{150})^3 = 360 \times 8 = 2880 \)

drag 2.jpg

The yellow curve is the same for any given aircraft. Remember that \(D=\frac {1}{2} \rho V^2 S C_d \), so changing Cd for a different airplane simply results in a different "scale" of power units and the cube relationship remains the same.

As I mentioned earlier, this "cube rule" does not take into account the diminishing effect of induced drag as speed increases (the other dashed curve). No one here knows what \( V_{L/Dmax} \) is for Raptor (and therefore where its induced curve is located, and further, how much it "offsets" the cube rule). But, the further we are to the right of this point, the more the power required curve matches the parasite curve, and the more it approximates the cube rule.

Again from Perkins & Hage, \(D_i = \frac{L^2}{\pi q b^2} \), so the power required for induced drag curve for an individual plane (at a given altitude) is dependent on weight and span ( \(D_i \propto ( \frac{L}{b} )^2 \) ). Because Raptor is relatively heavy, the induced curve would be relatively higher, meaning that the power increase from 147 to 180 would be something less than 240% (although its power requirement just to get 147kt is quite high due to its weight^2/span^2). But if it were closer to advertised weight, it would be closer to a 240% power increase.

One could reasonably expect that a flight test regimen for a new airframe design (especially where the power output of a new engine is unknown) would include some exploration of these curves.
 
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mcrae0104

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If we apply the same rule of thumb to Raptor...
1624639728864.png
For the reasons explained in the previous post, I don't think we can apply the power required curve for a Cozy to Raptor. Power required for Vmin (lowest point on the curve) will be at higher fuel flow and will occur at a higher speed due to its greater span loading and frontal area vs. a Cozy.
 
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bmcj

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Power required isn't that simple. If you start on the backside of the power curve then power decreases with speed up to best L/D.
But I don’t think anyone here would suggest that he has been cruising on the backside of the curve.
 

BBerson

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The graph in your book is scaled with major units on 1/2" intervals, so you can easily measure and see.
I did that, but I used the solid total curve not the dotted parasite curve which you used (and made yellow).
On the combined curve 150 mph is 1000 units and 300 mph is 3000 units.
 

BBerson

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Also, this was in the emails….. sure sounds like an investment.
Not to me. It sounds like a vehicle for donating and taking a tax loss. My definition of investment is intent for profit not loss. Your milage might vary.;)
When Paul Allen spent $20 million on Space Ship One to win the $10 million X-Prize it was a tax loss.
 
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