03 Jan 2026, 00:47 [ UTC - 5; DST ]
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Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die  Posted: 26 Oct 2019, 12:15 |
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Joined: 10/06/19
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Username Protected wrote:
The minimum number from a data set that included a number of configurations including a number of pusher prop canard designs. In addition to being hung up on the polars, you also seem to be fixated on the drag reduction from laminar flow over the fuselage. In practice it is a lot smaller than you seem to think and is typically offset by other factors. For example, the two big vertical stabilizers on the wingtips of the Raptor. They may have a positive impact on induced drag and increase the effective AR of the wing, but if you look at your polars, that is a fairly small piece of total drag. On the flip side, they add significantly to parasite drag as IAS approaches 200 knots.
Pushers are hardly groundbreaking new technology. The earliest airplanes were pusher designs, so the tractor config is the relative new comer. The initial reason to put the engine in front was for crash survivability with wooden stick construction, but as airframes became stronger, the tractor design still remained more common. Even amongst fighters and air racers where every bit of speed counts. Think about that. If the pusher canard was dramatically lower in drag, wouldn’t pusher designs dominate every class at Reno where they are allowed? They clearly don’t.
The airframe my minimum possible drag number came from was in fact a tractor config with a small area high aspect ratio laminar airfoil wing that had lower overall drag than any pusher design with available data. It was also unpressurized, lighter, and optimized for lower altitudes where cooling drag could be reduced. Based on how that airframe compares to the Velocity line and other pusher configs that are EXTREMELY similar to the Raptor, it isn’t hard to figure out where the Raptor will slot in without some innovative drag reduction approaches that I see no evidence of.
I have given you more than enough. If you remain convinced I am wrong, share YOUR numbers and sources. Explain YOUR reasoning. So far all you have shared are a bunch of questions challenging others, assertions about drag polars but no actual drag polar for the Raptor, and pictures of variable definitions and formulas with no numbers.
Well stated! +1 Best, Tom
Hi Matt,
I am fixated on polars. Specifically the power curve (which is just the polar inverted yes?)
I am not so much fixated on drag reduction from laminar flow over the fuselage (though that is one of the advantage I think this bird has given its clean nose) so much as the reduction of parasitic drag over the fuselage, wing root and empennage given the lower air-speeds/resistance given you do not have add the thrust velocity from the prop in a pusher configuration. (You lose something in that the prop does not get as clean a bite, but I think the advantages will far outweigh the disadvantages.) That drag squares with velocity. The other factor I know will factor in, (but have no idea how to accurately handicap it) is the amount of the lift the fuselage itself will produce (and corresponding reduction in induced drag from the wings.)
I think this bird is going to have a significantly flatter power curve than the Lancair Evolution, which is already slick as snot.
https://www.lancairowners.com/developin ... mance-data
Cheers
--Chris
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Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die Posted: 26 Oct 2019, 13:27 |
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Joined: 11/22/12
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Username Protected wrote: I am fixated on polars. Specifically the power curve (which is just the polar inverted yes?) No. A drag polar plots Cl vs. Cd, it's dimensionless. Lift and drag each go up by the square of v but power required is drag x TAS so it's a cubic function of speed. Very different curve. Peter Mueller didn't understand that either, which is why his speed estimates were so wildly unrealistic. https://en.wikipedia.org/wiki/Drag_polar
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Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die Posted: 26 Oct 2019, 13:49 |
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Joined: 02/20/16
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How much is air passing through the propellor accelerated typically at cruise speeds? I recall that it is not very much, but the tractor/pusher question has me curious regarding parasitic drag for the two configurations.
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Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die Posted: 26 Oct 2019, 13:54 |
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Joined: 10/06/19
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Username Protected wrote: I am fixated on polars. Specifically the power curve (which is just the polar inverted yes?) No. A drag polar plots Cl vs. Cd, it's dimensionless. Lift and drag each go up by the square of v but power required is drag x TAS so it's a cubic function of speed. Very different curve. Peter Mueller didn't understand that either, which is why his speed estimates were so wildly unrealistic. https://en.wikipedia.org/wiki/Drag_polar
Thank you for technically correcting me on that. I misspoke. Yes... The inverted polar times TAS is correct...
I should have said the power-curve is a derivative of the inverted drag polar integrated over speed.
But are you making my point for me? (And Peter.) TAS is TAS for any ship. The polar is the multiplier!!! And that is why it matters so much!!! And that is where the performance is going to come from in my opinion.
Last edited on 26 Oct 2019, 14:05, edited 1 time in total.
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Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die Posted: 26 Oct 2019, 13:58 |
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Joined: 10/06/19
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Username Protected wrote: How much is air passing through the propellor accelerated typically at cruise speeds? I recall that it is not very much, but the tractor/pusher question has me curious regarding parasitic drag for the two configurations. Just a simple mass balance equation right? F=MA How much drag do you have in lbs. You need an equal amount of thrust to match it. So weight of air times volume of air gives velocity. Add that to ship speed.
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Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die Posted: 26 Oct 2019, 14:02 |
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Username Protected wrote: Matt Fine,
was that "optimum" airframe catbird? No, it was a modified experimental with no canard, but I will have to look to see if I have or can find enough data on Catbird.
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Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die Posted: 26 Oct 2019, 15:09 |
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Joined: 05/01/14
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Username Protected wrote: How much is air passing through the propellor accelerated typically at cruise speeds? I recall that it is not very much, but the tractor/pusher question has me curious regarding parasitic drag for the two configurations. Just a simple mass balance equation right? F=MA How much drag do you have in lbs. You need an equal amount of thrust to match it. So weight of air times volume of air gives velocity. Add that to ship speed.
Mdot or mass flow rate is density times Vp times prop disc area (simplified). Vp is the velocity at the prop and is the average of the exit velocity and free stream velocity.
T = D = Mdot(Ve - Vo) = r * .5 * (Ve + Vo) * A * ( Ve - Vo)
At higher velocities, the flow rate is higher so the difference between Ve and Vo gets smaller. For a plane cruising at 300 knots in the flight levels, it’s going to be quite small.
Density of air is around 0.035 lbs/ft3 and figure prop area around 38 feet for an 82” prop. 300 knots is close to 500 ft/s. Someone can plug the math into a spreadsheet and figure it out for the 275-300 lbs force (vs lbs mass) of thrust that would be a minimum for the Raptor. It’s not much.
Edit: if I did the math right away from a computer, it is going to be somewhere around 8-9 knots extra velocity. Someone pls verify
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Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die Posted: 26 Oct 2019, 17:20 |
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Joined: 02/20/16
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Username Protected wrote:
Mdot or mass flow rate is density times Vp times prop disc area (simplified). Vp is the velocity at the prop and is the average of the exit velocity and free stream velocity.
T = D = Mdot(Ve - Vo) = r * .5 * (Ve + Vo) * A * ( Ve - Vo)
At higher velocities, the flow rate is higher so the difference between Ve and Vo gets smaller. For a plane cruising at 300 knots in the flight levels, it’s going to be quite small.
Density of air is around 0.035 lbs/ft3 and figure prop area around 38 feet for an 82” prop. 300 knots is close to 500 ft/s. Someone can plug the math into a spreadsheet and figure it out for the 275-300 lbs force (vs lbs mass) of thrust that would be a minimum for the Raptor. It’s not much.
Edit: if I did the math right away from a computer, it is going to be somewhere around 8-9 knots extra velocity. Someone pls verify
Matt, I think your math checks out, thanks. So at high cruise speeds the parasitic drag penalty for tractor configuration due to prop exit velocity increase only just isn't that significant. Chris or Matt or anyone who cares to comment; fundamentally, is the Raptor doing anything differently aerodynamically than the Velocity series that it looks so similar to?
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Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die Posted: 26 Oct 2019, 17:32 |
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Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die Posted: 26 Oct 2019, 18:16 |
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Joined: 10/06/19
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Username Protected wrote:
Mdot or mass flow rate is density times Vp times prop disc area (simplified). Vp is the velocity at the prop and is the average of the exit velocity and free stream velocity.
T = D = Mdot(Ve - Vo) = r * .5 * (Ve + Vo) * A * ( Ve - Vo)
At higher velocities, the flow rate is higher so the difference between Ve and Vo gets smaller. For a plane cruising at 300 knots in the flight levels, it’s going to be quite small.
Density of air is around 0.035 lbs/ft3 and figure prop area around 38 feet for an 82” prop. 300 knots is close to 500 ft/s. Someone can plug the math into a spreadsheet and figure it out for the 275-300 lbs force (vs lbs mass) of thrust that would be a minimum for the Raptor. It’s not much.
Edit: if I did the math right away from a computer, it is going to be somewhere around 8-9 knots extra velocity. Someone pls verify
Matt, I think your math checks out, thanks. So at high cruise speeds the parasitic drag penalty for tractor configuration due to prop exit velocity increase only just isn't that significant. Chris or Matt or anyone who cares to comment; fundamentally, is the Raptor doing anything differently aerodynamically than the Velocity series that it looks so similar to?
Hehe.. Right but <comma> :-)
As Matt will tell you, we are less than a hog's tether away from a dog's breakfast here....
A.) Ve - Vo changes as you move out the radius (given hub radial velocity versus tip velocity AND the changing pitch/chord/airfoil of the prop)
B.) Ve changes immediately (increases) on a tractor due to the fuselage/cowling/what ever cross-section the air has to flow across. And that has to be calculated across the full fuselage profile, wing root, and empennage... antennas/pitot tubes/hinges/etc.
C.) Not all changes isometrically scale as cross section changes due to compressability.
D.) In any instance of laminar flow being interrupted (turbulent flow induced) all bets are off. The energy input to push through the phase change immediately accretes as drag. Think gap seals, wheel pants/retracts and speed kits in general.
and so on... :-)
You quickly get to an Archimedes/crown fable type approach as being nearly the only solution (i.e. Measure the whole in the real world i.e. Fly the necessary mission profile to construct the polar) ) Expect is it harder... given things are happening in real time (i.e The 4th dimension as opposed to three.) Would be analogous to Archimedes trying to measure the volume of gold in the crown by throwing it in a stream and calculating how much the stream rose as opposed to tossing it in bucket.
We shall have to wait and see I suppose... Unless you are good a guessing. :-)
Last edited on 26 Oct 2019, 19:57, edited 1 time in total.
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Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die Posted: 26 Oct 2019, 18:57 |
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Username Protected wrote:
We shall have to wait and see I suppose... Unless you are good a guessing. :-)
The thing is, there's really nothing new under the sun aerodynamically. Have we really discovered anything new since the 60's (or even earlier)? Yes, we are all guessing at this point about the Raptor because there're so many unknown variables, but not guessing about the past 100 years of aviation that have brought us the configurations and shapes that we have today.
Last edited on 26 Oct 2019, 19:09, edited 1 time in total.
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Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die Posted: 26 Oct 2019, 19:11 |
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Joined: 10/06/19
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Username Protected wrote:
We shall have to wait and see I suppose... Unless you are good a guessing. :-)
The thing is, there's really nothing new under the sun aerodynamically. Have we really discovered anything new since the 60's (or even earlier)? Yes, we are all guessing at this point about the Raptor because there're so many unknown variables, but not guessing about physics or the past 100 years of aviation that have brought us the configurations and shapes that we have today.
Right... the issue is most folks are REALLY REALLY REALLY bad about guessing on this kind of problem (especially conventional pilots?) given non-linear relationships and counter intuitive engineering truths... Even folks educated in the space who may be able to do the math don't understand what that really means in the real world.
Will give you an example... If you have a 3 inch ID pipe with water running through it at continuous flow and pressure at 80 psi and it goes through a reducer to a 1 inch pipe
1.) What will the pressure be in 1 inch pipe?
Most folks can't guess within a 200 PSI of the answer and about 98% will get the direction of the change in pressure wrong. Aerodynamics (i.e Fluids) are counter intuitive as hell.
And when you get into phase change energy paradigms and their implications people loose their mind.
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Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die Posted: 26 Oct 2019, 19:26 |
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Username Protected wrote: 1.) What will the pressure be in 1 inch pipe? 8.888 PSI?
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