Douglas X-3 Stiletto FSX Native

[Milton Shupe]

The airfoil is quite interesting in shape, my guess is that it was designed to create two shock waves, one at each break and keep them from moving during mach changes. Split flaps were probably used for structural reasons and to keep a shockwave from developing at the hinge line, which on the XF 92A caused considerable local disturbance and hinge line loading. The wing being only 4 1/2" thick needed all the strength it could muster.

A conventional airfoil has the center of pressure move aft as the transonic area is entered. I wonder where the center of aerodynamic pressure is for this airfoil? I also wonder about the pitch change (possible) with varying power settings due to induced flow under the elevator?

Interesting plane!

I do have a NACA research paper on the wing design, plus two others, Stability and Control Characteristics and Landing Loads.

[Sundog]

The airfoil is quite interesting in shape, my guess is that it was designed to create two shock waves, one at each break and keep them from moving during mach changes. Split flaps were probably used for structural reasons and to keep a shockwave from developing at the hinge line, which on the XF 92A caused considerable local disturbance and hinge line loading. The wing being only 4 1/2" thick needed all the strength it could muster.

A conventional airfoil has the center of pressure move aft as the transonic area is entered. I wonder where the center of aerodynamic pressure is for this airfoil? I also wonder about the pitch change (possible) with varying power settings due to induced flow under the elevator?

Interesting plane!

The airfoil will behave the same as a conventional airfoil at subsonic speed, just not as efficiently. But it was obviously designed to be optimized for supersonic flow based on it's shape. For reference, see the F-117A, although that was done for LO, not compressible airflow reasons. At supersonic speeds it should have a compression shock off of the leading edge and two expansion shock waves off of the "angle" changes across the airfoil and then another compression shock at the trailing edge where the flow comes back together.

Here's a diamond airfoil reference https://www.quora.com/How-is-Lift-ge...ersonic-Flight

[Milton Shupe]

The airfoil will behave the same as a conventional airfoil at subsonic speed, just not as efficiently. But it was obviously designed to be optimized for supersonic flow based on it's shape. For reference, see the F-117A, although that was done for LO, not compressible airflow reasons. At supersonic speeds it should have a compression shock off of the leading edge and two expansion shock waves off of the "angle" changes across the airfoil and then another compression shock at the trailing edge where the flow comes back together.

Here's a diamond airfoil reference https://www.quora.com/How-is-Lift-ge...ersonic-Flight

That's an interesting read and comments Sir. Thanks for that.

The X-3 will be a bit more complicated to fly based on this table :-)

[warchild]

I do have a NACA research paper on the wing design, plus two others, Stability and Control Characteristics and Landing Loads.

would you be willing to share the NACA research/?

[warchild]

Ok, so i'm not finding any wind tunnel data graphs on the web so i'll ask here..

As the pressure cone moves back along the wing, the center of pressure ( Mean Aerodynamic Center ) also moves back??
Since the wing is so far rearward on this plane, if the center of pressure moved far enough back along the wing, wouldnt that create a situation where the leading edge of the wing is providing less lift that the trailing edge??
If the trailing edge is producing all the lift, wouldnt that tend to lift the tail section, causing a downward pitch on the nose??

[Milton Shupe]

would you be willing to share the NACA research/?

Pam,

Frankly, I have forgotten what I have shared and not shared with whom.

I will package everything I have and upload for you.

[warchild]

The airfoil is quite interesting in shape, my guess is that it was designed to create two shock waves, one at each break and keep them from moving during mach changes. Split flaps were probably used for structural reasons and to keep a shockwave from developing at the hinge line, which on the XF 92A caused considerable local disturbance and hinge line loading. The wing being only 4 1/2" thick needed all the strength it could muster.

A conventional airfoil has the center of pressure move aft as the transonic area is entered. I wonder where the center of aerodynamic pressure is for this airfoil? I also wonder about the pitch change (possible) with varying power settings due to induced flow under the elevator?

Interesting plane!

I noticed that on the three view i use for measurements, that 75% cord is prominently marked and i have no idea why. According to the research data, the AC/center of pressure is 27% cord at subsonic speed, but travels back through trans-sonicspeeds. Whether the 75% cord is where it ends up or not is something i want to know as well, and i have a buttload of papers on it, but i cant understand a single thing i'm looking at any more.. Perhaps you will have a better grasp of it..

https://ntrs.nasa.gov/archive/nasa/c...9780022113.pdf

If so, please explain it too me as well.. thanks..

[Jafo]

Ok, so i'm not finding any wind tunnel data graphs on the web so i'll ask here..

As the pressure cone moves back along the wing, the center of pressure ( Mean Aerodynamic Center ) also moves back??
Since the wing is so far rearward on this plane, if the center of pressure moved far enough back along the wing, wouldnt that create a situation where the leading edge of the wing is providing less lift that the trailing edge??
If the trailing edge is producing all the lift, wouldnt that tend to lift the tail section, causing a downward pitch on the nose??

I expect that'd be a 'yes'.
Perhaps have a look at whatever you can find re compression lift [and cruise] with the XB-70 ..... another a/c that was instrumental in pioneering multi-mach flight design...

[warchild]

I expect that'd be a 'yes'.
Perhaps have a look at whatever you can find re compression lift [and cruise] with the XB-70 ..... another a/c that was instrumental in pioneering multi-mach flight design...

oooooooo. great recommendation.. thank you..

[warchild]

place holder note for myself: Allison J-71-A-2E

[Milton Shupe]

Facts and Figures

Douglas had expected the X-3 to reach speeds in excess of Mach 2, but it became clear at an early stage to both the manufacturer and the USAF that this would not happen.

Futuristic design Contemporary engine technology could not match the potential of the advanced airframe design.

After completing its test duties the X-3 was handed over to the US Air Force Museum, in Ohio, where it can still be seen.

Even in the company of the 0-558-1 Skystreak and 0-558-2 Skyrocket, the 'Stiletto' looks futuristic. The two earlier Douglas aircraft enjoyed far greater success than the X-3.

Douglas used a long, slender fuselage with low-aspect ratio straight wings for the X-3.

On 15 October 1952 the X-3 made an unscheduled, but brief, trip aloft and an official first flight five days later.

The X-3 used 850 pinholes, spread over its structure, to record pressures and 185 strain gauges to record air loads.

There were 150 temperature recording points spread across the X-3 airframe.

In its fastest flight on 28 July 1953 the X-3 was clocked at Mach 1.21 in a dive.

The X-3 is on display at the US Air Force Museum, Wright-Patterson AFB, Ohio.

The X-3 had one of the fastest take-off speeds in history - 260 mph.
(Note: and that's why the thread kept coming off the tires - and new tire technology was developed to deal with high speed take-offs)

The gloss white fuselage and tail surfaces contrasted with the highly polished aluminum wings.

[warchild]

couldnt resist. I had to go in and give the wings a bright shiny chrome finish after reading that. yeah, i dont know what i'm doing but it doesnt look too terrible..

Thanks to NACA's impeccable data keeping, i'm about a third done with the initial FDE. However, thats the easy third. The hard parts are still ahead.. None the less, a hard roll at M1.05@ causes the nose of the plane to do some interesting things already. Its not what was reported, but its a start..

[fliger747]

Yea! It fly's! That's a pretty fast takeoff, I think my fastest speed in a ground trike was a bit over 210 mph... I'll be the X-3 felt a lot like the woman in the motorcycle at Bonneville!

[Milton Shupe]

LOL Neat!

Today I roughed out a test bed flight model and have been flying and tweaking it.
Liftoff with 3 notches of appropriate flap settings (30*LE-25*TE) at 260 kias.
Tire tread stayed intact ... I guess; haven't modeled them yet. :-)

Scott Thomas is working on a 2D panel and I should have that soon for testing.

[warchild]

i've been using the panel uploaded here. it's pretty nice..

[warchild]

Yea! It fly's! That's a pretty fast takeoff, I think my fastest speed in a ground trike was a bit over 210 mph... I'll be the X-3 felt a lot like the woman in the motorcycle at Bonneville!

i have too much lift on mine. its taking off at 220. Sideslip angle and weathervane is also off.. engie seems ok with top speed just under mach 1 and maxh 1.2 in a dive.. currently my AC is at 75% mac, but it doesnt really seem to matter where i place it on that wing at the moment during subsonic flight.. Thing is, we all know theres a snake in there waiting to bite at the right speed and i havent quite coaxed it out of hiding yet..

[fliger747]

I think the XF 92A was capable of takeoff at lower speeds as well but with the lower power available they were afraid of early rotation and high induced drag preventing a climb out as well as possible control issues low and slow.

: )

[fliger747]

Yes, generally the aerodynamic center move aft as the shockwaves establish in the transonic range. This does usually cause a nose down moment, this is often known as "Mach Tuck". One of the issues in WWII fighters touching into this realm.

I have flown the 747 to high Mach numbers and for some reason it did not experience this effect to any noticeable degree. The considerable thrust requited at high mach from the underslung nacelles may have compensated for this.

With a short MAC and a long arm for the elevator, apparently the X-3 had sufficient compensating control.

[warchild]

I've only flown the xf-92 once so far, but compared to the x-3 it flies like a cadillac. Very amazing job all around on it.. The X-3 reminds me of a pool queue. I know some people will have trouble learning to fly the xf-92, but it fits so well into the delta wings that were prevelent during my childhood.. Hi speed takeoff, high speed landing, dont use flaps or you might somersault, I fell in love with all the delta's at a very young age, especially the skyrray and i think it was called the sky bat?? Not too sure about that last name at the moment..

[warchild]

Yes, generally the aerodynamic center move aft as the shockwaves establish in the transonic range. This does usually cause a nose down moment, this is often known as "Mach Tuck". One of the issues in WWII fighters touching into this realm.

I have flown the 747 to high Mach numbers and for some reason it did not experience this effect to any noticeable degree. The considerable thrust requited at high mach from the underslung nacelles may have compensated for this.

With a short MAC and a long arm for the elevator, apparently the X-3 had sufficient compensating control.

I think maybe perhaps the 747 was a stroke of desperate genius.. Boeing just lost its behind on the 2707 and Tripp wanted a big plane for his company. The 747 i dont think could have been made more perfect, except for oxygen generator locations and cargo door retainer designs..

[falcon409]

i've been using the panel uploaded here. it's pretty nice..

Yep, I recognize that one!

[warchild]

yeahh, you did a great job on the panel.. took a bit to get used to switching from the asi to the mack indicator, but its pretty habitual now..I still think it needs a nose or front wheel cam ::lol::

[Milton Shupe]

Yep, I recognize that one!

Ed, I forgot that you did this panel or I would have used it in my tests. :-)

Fortunately, Scott Thomas should have something for me soon. No hurry as I have lots of modeling to do yet.

[Milton Shupe]

The XF-92A beta release and issues have consumed my time in finishing the exterior X-3 model.

I am still dabbling with the wing flaps actuator housings at the moment.
Then on to the gear bays and gear.

[warchild]

No worries Milton.. The XF-92 is your baby and needs you right now.. The X-3 was unexpected to be honest, and moreso than that, it's as much an experiment in flight sim as it wa in real life, because I'm using Nasa's data. The weight, thrust, fuel, everything including the MOI's I'm just copying out of Nasa documentation and plugging into the fde. The plane flies beautifully, at subsonic speeds. i figure it'll give flight sim enthusiasts the ability to directly study and learn about Aircraft design and in this case, the effects of transsonic inertial coupling, if they want too. Since i'm using Nasa's data, enthusiasts will be able to change the variables in the experiment by pulling the changes directly from Nasa's program and plugging them in. It's not my fde you see. It's Nasa's. We can take our time.. Your making that plane is very special to me. The XF-92 is very special to the entire community. There's a difference