90% RUHRSTAHL KRAMER X4 (1944-1945)

Gents,

today I got a big Box from USA, from Proline (THX guys @ Proline for the help!)...

The customs guy was more nasty today, when I told him this is going to be ONE rocket, a 90% scale of one of the most famous German rockets, the first of his art, launched 1944...

They could not believe all these parts for ONE rocket...

Now guess for a few minutes what it could be? This is a 7.5" diameter rocket.....

)

this one..exposed at US Air Force Museum... for real )

Ruhrstahl (Kramer) X4, first air to air guided missile of history... was 6.2ft long and 8.6" diameter... I will build with 7.5" diameter, nearly 90% of real...pushed with 54mm contrail USA K-hybrid motor of course...guess what? it was in real a BMW rocket engine, I think hybrid fits too ;-)

here a few other views of the beautifull parts, near to my 8" V2...

Dang. That is sick.

That's pretty cool!

That might be tough to make stable, methinks. Are you going to upsize the aft fins?

THIS IS AWESOME

Can a hybrid K really lift this, though? Especially with the noseweight probably necessary, I'm thinking more like an M...

Super cool and great subject for those long hybrid motors. Now all you need is one of those semi scale FW 190s to launch it from!

"...That might be tough to make stable, methinks. Are you going to upsize the aft fins?.."

you got it! this is going the toughest challenge for me on this one. The rocket was reported in war time to be very unstable. Of course this is going to be the same issue here, even worse as I do not carry kilos of explosives in the nose...but of course I won't avoid to put an interesting weight in the nose cone...I will need to build the wings and rear fins out of lightest carbon fiber sandwich:
- with expected complications for the wings due to flutter danger
- for the rear fins to preserve weight as much as possible in the front...
Next point will be the deployment issue, of course I will have to eject sequentially from the front in DD process, anything else is silly in Europe as our launch zones are small.
You see a considerable amount of challenges for a reasonably size in fact..7.5" is not that big...to your last point, I do not want to upsize anything, Rocksim says: stable...

I am by the way in contact with the Deutsches Museum in Munich that has got one real piece to make fotos when it is ready.. and guess what..I found a US citizen that..has one of these at home...at his private home..not a joke...

And yes, when it will fly it wil be definitely better than *** :lol: Expected first flight begin of August! Yes this year... of course I need to keep this project secret at home ...do not tell my wife she is going to see me back in 3 months :no:

With you getting all those parts its no wonder Gary can't get the Pro Line V-2 kit out. Just kidding. Make sure you post the build.
gp

Good question. I can get easily 555n/s average from the contrail K casing... means my weight envelope shall be between 10 and 13kg and we are safe on the pad...predicted altitude not that high: around 600 meters but this is enough for a show flight..

CCotner said:

THIS IS AWESOME

Can a hybrid K really lift this, though? Especially with the noseweight probably necessary, I'm thinking more like an M...

Click to expand...

The original rocket weighed 60 Kg and had a 20 kg warhead, and it was designed to be actively guided. I don't see the rocket will be stable without an active stabilization system as the CP looks like it will always be in front of the CG without excessive nose weight.

https://www.luft46.com/missile/x-4.html

https://en.wikipedia.org/wiki/Ruhrstahl_X-4

Bob

Thread subscribed!! looking forward to the build. Please post heaps of pics

V2

bobkrech said:

The original rocket weighed 60 Kg and had a 20 kg warhead, and it was designed to be actively guided. I don't see the rocket will be stable without an active stabilization system as the CP looks like it will always be in front of the CG without excessive nose weight.

https://www.luft46.com/missile/x-4.html

https://en.wikipedia.org/wiki/Ruhrstahl_X-4

Bob

Click to expand...

Massive amounts of stinking, performance robbing nose weight used on Nazi wonder weapons. All that precious thrust wasted to make it somewhat stable. Oh the humanity!

Subscribe. I can't wait for the build and flight reports.

Denis, Glad everything got there safe and sound. I'm sure you'll be able to make it work. I have no doubt you'll get this creature! in the air.

Make a mold, pour the nose cone in lead, and you should be fine Even if this project scribbles across the sky it will be spectacular...mad props sir!

very cool. i'll be watching!

Gonna be an amazing build/flight!

GaryT said:

Denis, ... I have no doubt you'll get this creature! in the air.

Click to expand...

... and that's exactly what scares us over here ... :y: :y: :y:
I'll be watching ... maybe
Wounder when he will show up at LDRS ...:boat:

beezwax said:

Make a mold, pour the nose cone in lead, and you should be fine Even if this project scribbles across the sky it will be spectacular...mad props sir!

Click to expand...

Nah, just spin one out of tungsten.

Way cool project. Keep the pics comeing.

That might be too neat not to be copied.

bobkrech said:

The original rocket weighed 60 Kg and had a 20 kg warhead, and it was designed to be actively guided. I don't see the rocket will be stable without an active stabilization system as the CP looks like it will always be in front of the CG without excessive nose weight.

https://www.luft46.com/missile/x-4.html

https://en.wikipedia.org/wiki/Ruhrstahl_X-4

Bob

Click to expand...

I have supreme confidence that Denis will succeed. I only hope that I am able to plan my work projects in a way that will coincide with the launch! I'm definitely looking forward to this one...

Cheers,
Michael

Daddyisabar said:

Massive amounts of stinking, performance robbing nose weight used on Nazi wonder weapons. All that precious thrust wasted to make it somewhat stable. Oh the humanity!

Click to expand...

He's gearing up to shoot down your Lancaster... LOL
Later! OL JR

Have you considered pivoting forward fins?? That reduces the effective size of them in terms of CP effect, shifting the CP rearward...

Between that and in combination with reasonable noseweight, it COULD be made stable...

Gets a bit more complicated with those fin tip pods, though, but I'm sure it could be worked out...

https://www.rocketryforum.com/showthread.php?21670-Forward-Fins&highlight=pivoting+fins

Later! OL JR

There are some other ways to "improve" the overall stability without adding excessive ballast and killing flight performance.

Don't forget you can add some fin area projecting aft with clear plastic fins. If built neatly, these fins can largely disappear when the rocket is in flight. You can make some significant CP shifts with this approach.

You can also add some drag plates at the aft end of the rocket that will serve the same function. If you fabricate them from clear plastic (like the fins discussed above) you can often "hide" them in the open and minimize most of the visual impact.

For anything with marginal stability, using a longer launch rail allows your rocket to build up more velocity and makes the fins more effective before leaving the guidance of the launcher.

On scale models you can generally distort a few of the external features by a small margin before other people start wondering whether something "looks wrong." Most folks do not have a calibrated eyeball and will not notice if a scale fin is shifted aft a bit, or enlarged by 5 or 10 percent, or if the trailing edge chord is extended by 5 or 10 percent (of the local scale chord). Similarly, the extended nose on your rocket (filled with dense ballast) could probably be stretched a few inches and be more effective at shifting the CG forward.

Agree. And I think by carefully looking at the original rocket that there must be a very good reason why the aft fins are so thick, incredibly thick. It is just about that: more drag at the end move the CP backwards. I am trying to get insight in WWII archives from EADS and Deutsches Museum at the moment. Hopefully I can find old CP calculations. This bird as a very special geometry and was flying straight. No mystery but a very interesting case for me.

Nevertheless I am busy preparing Flight #2 of the Proline V2 and Flight #2 of my big hybrid cluster after severe reconstruction. This is going to fly on saturday with more high speed cams this time. I will post of course. I start the Kramer construction next week. All material arrived, especially the carbon square profiles I will use for the sandwiched wing constructions: ultra light and stiff. This is going to be a vacuum orgy I would say...

CU
Denis
PS: what an interest here, I am really surprised...this confirms it is the right place for me ..and the build after the Kramer...you know, always go to the next level ...

I don't know how expensive this kit is, or how difficult it is to get, but before you spend 100s of hours in build time and finishing it might be worthwhile to build a "boilerplate" version to flight test first.

You could use a similar length of suitable airframe tube and a simple nose cone; I don't think the effects of scale body shape would have as much effect on stability as CG and CP locations. Skip the paint and fancy root fillets. With test fins the same planform as the kit fins, and with the same overall weight and mass distribution, you could get a looonng way to finding confidence with the project with minimal effort. And you won't cry (too much) if your test article bites the dust.

(Edit: Hey! my post count matches my favorite gun!)

Nose weight. Here are some images I've collected, and photos of the X-4 at Cosford in England.