Project XR3 Phoenix (WIP)

[Loru]

Progress on rear landing gear, and SCRAM tunnels are in place (hard to see as they're 1 sided faces:

---------- Post added at 05:21 PM ---------- Previous post was at 05:12 PM ----------

and better shot:

 

[RisingFury]

I suppose this is a bit of a bad moment to tell you that, but that landing gear is too far back. With the new Orbiter's ground contact model, the elevons won't have enough torque to push the nose of the craft up.

The landing gear should be close to the CG, but behind it. That'll ensure the plane doesn't tip back on its own and the the air control surfaces have enough force to turn it over. You'll have to resort to moving the CG back and the touchdown points forward.

The other very ugly cheap trick you can do is to extend the length of the front landing gear, so when the craft is on the ground, it sits at about 5° nose up attitude, so as it rolls down the runway, it already has an AOA of about 5°. As the plane picks up speed, the wings start to produce lift and the effective weight of the plane decreases (that is, the force required to turn it).

The reason this trick is very ugly is because the engines will also face down - unless you vector the exhaust - and dig a trenches into the runway. It also makes for very difficult landings, as you're landing with a 5° nose up attitude, so I'd recommend you avoid that.

Pretty much all DG class ships suffer from that.


Notice how far forward the landing gear on the X-48 are. At least a third of the length of the aircraft is behind the landing gear and that way the control surfaces have a long enough lever to produce the required torque.

On the F-22, you can see the landing gear is about 3/4 of the length back, however, there's still considerable distance between the elevator and the landing gear. The elevator - the flying tail - is also huge and produces a lot of force, so the F-22 can afford to have its landing gear further back.

But in the case of the XR3, we're not exactly talking about a maneuverable fighter jet... It's tough to see where the landing gear is exactly, but I'd say 1/5 to 1/6 of the spacecraft's total length from the back...


Some more images:

 

[Loru]

I'll consult that problem with dbeachy1 - I can move it forward and in fact I was planning to to it - with my new modelling aproach (make systems and bulid fuselage/wings skin around it) it should be a problem

here is side view:
edit: actually they're around 1/4 total lenght from the back so it's not that bad at all

and logo:

 

[Donamy]

JATOs ?

 

[Grover]

how about RATOs?

 

[Hlynkacg]

Nice work so far, but I still feel like it needs a little extra "bulk in the backside" the mainmounts still look like they're behind the COG.

That said nice job on making them proportional and look like they could actually support the mass of the spacecraft. The ridiculous single bogey mainmounts of the XR5 have always driven me up the wall.

Excellent work on the pheonix patch as well. I'm looking forward to further progress.

Keep up the good work and

 

[RisingFury]

JATOs ?

how about RATOs?

No no, you're missing the point. The problem isn't that the engines are weak or that the runway is too short. The problem is that the spacecraft couldn't turn its nose up. No amount of speed would help out there.

 

[BruceJohnJennerLawso]

No no, you're missing the point. The problem isn't that the engines are weak or that the runway is too short. The problem is that the spacecraft couldn't turn its nose up. No amount of speed would help out there.

A giant balloon? Helicopter blades? :lol:
Sorry couldnt resist.

If I might make a design suggestion, I think it would be nice if the XR-3 had its VC windows slightly longer than the XR-2 had, so as to give the pilot a wider field of view if he needs it. Nice work though :thumbup:.

 

[jangofett287]

Ahem, Gentlemen I have the solution. We simply build the runway with one end terminating at a very tall cliff. That would solve the problem of needing to pitch up. In fact if the cliff is tall enough it also solves any acceleration problems as well.

Unless the terminal velocity of the ship is so incredibly low the wings couldn't generate enough lift and the ship just plunged straight down onto the rocky desert below. But hey, small problems.

 

[Urwumpe]

What about simply building a massive hydraulic actuator into the main landing gear for pushing the nose up? :lol:

Also, as example, remember the Space Shuttle, which is much closer to the Phoenix in its aerodynamic configuration...

Again, the main landing gear is about one third from the aft of the space craft... or better: one third of the distance from CoG to Elevator.

 

[Hlynkacg]

What about simply building a massive hydraulic actuator into the main landing gear for pushing the nose up? :lol:

Also, as example, remember the Space Shuttle, which is much closer to the Phoenix in its aerodynamic configuration...

Again, the main landing gear is about one third from the aft of the space craft... or better: one third of the distance from CoG to Elevator.

That is a fair point but it is worth noting that the Space Shuttle never had to make a powered take-off. Did the elverons have sufficient authority to lift the nose at a reasonable transition speed?

 

[elcpt]

The solution is a runway ramp like this one:

 

[Urwumpe]

That is a fair point but it is worth noting that the Space Shuttle never had to make a powered take-off. Did the elverons have sufficient authority to lift the nose at a reasonable transition speed?

That is correct, but the elevons are far from inactive after main landing gear touchdown. The FBW system still controls the shuttle until it has stopped. If you would put the landing gear too far back for that, the nose would simply slam down uncontrolled.

 

[Hlynkacg]

Well ok then.

Just how much of the shuttle's mass was in the engines/OMS pods. (I'm just trying to visualise where the COG actually is)

 

[Urwumpe]

Well ok then.

Just how much of the shuttle's mass was in the engines/OMS pods. (I'm just trying to visualise where the COG actually is)

A lot of it.

It is between X0 = 1080 and X0 = 1100 depending on payload mass, if you look at this drawing for reference:

Z0 is about 370 during all landings (+/- 2 inches)

 

[Hlynkacg]

Ok that makes a bit more sense.

 

[kuddel]

That is a fair point but it is worth noting that the Space Shuttle never had to make a powered take-off

...but Buran did !

 

[Ghostrider]

Ahem, Gentlemen I have the solution. We simply build the runway with one end terminating at a very tall cliff. That would solve the problem of needing to pitch up. In fact if the cliff is tall enough it also solves any acceleration problems as well.

That however could be a little dangerous. So, I say we launch the craft unmanned with the pilot following on a motorbike. Then, if everything goes well and the spacecraft goes over the cliff and in a dive, the pilot jumps as well and freefalls to an open port on the spacecraft, takes the controls and begins normal operations. Absolutely foolproof.

I say we call it the "Goldeneye takeoff"...:lol:

 

[Loru]

...but Buran did !

Yes, and Buran had 4 jet engines in the rear. XR3 will be similar in this manner as it will have 4 main engines on the back. Those thick nacelles will host mostly gear mechanism with engines far back. I may move main gear 1 or 1.5 meter to front since current fuselage/wing mesh is just reference for putting systems first.

Urwumpe: Thanks for Shuttle reference pictura and schematic. That will help a lot.

Hlynkacg: I doubt I'll be making those gear more massive. They're already bigger than in Shuttle.

---------- Post added at 11:40 AM ---------- Previous post was at 11:29 AM ----------

And with gear moved 1.3 meter to front I have 17.5 degree AOA maximum at landing

---------- Post added at 02:20 PM ---------- Previous post was at 11:40 AM ----------

Engine pods remodelled and prepared to integration with wing, gear stowed in place and added main engine nozzles

 

[RisingFury]

I can't exactly see in the image, but does the landing gear fold back-to-front? When stowed, does the landing gear face forward? If so, I recommend you turn it around.

If it faces back when stowed, then it'll be a bit more forward when deployed - for the length of the landing gear.