Horten Ho 229

[davparlr]

Objects might reflect similar radar waves in similar ways but advances in how those return signals are received and much more importantly how they are processed have moved forward in ways unimaginable to WW2 engineers.
Cheers
Steve

No matter what the processing is, the return radar energy from the front of a row of compressor blades will be very high making insignificant any other RCS reductions available to the Horton Bros. WWII radar receivers would certainly be able to detect this large return if it could detect any aircraft.

 

[stona]

No matter what the processing is, the return radar energy from the front of a row of compressor blades will be very high .

But less than a 10'-15' propeller disc.

Cheers

Steve

 

[l'Omnivore Sobriquet]

[oops sorry, wrong thread.]

 

[davparlr]

But less than a 10'-15' propeller disc.

Cheers

Steve

I don't think you can say that. That also avoids the point that since you have two big radar reflectors in the nose, other RCS reduction features are superfluous. Again, its akin to hunters putting on camouflage clothes and then putting on a dayglo vest to avoid being shot.

 

[GregP]

The propeller is spinning at maybe 2,000 - 3,000 rpm.

The jet engine impeller is spinning at maybe 12,000 - 18,000 rpm.

BIG difference in reflectivity. The impeller will reflect a large percentage of incoming power. Anything that reads reflections will see the jet, assuming decent power to start with. The prop will be seen by anything that impinges enough power to pick up the small reflection percentage from the relatively slow-turning prop disc.

 

[stona]

BIG difference in reflectivity.

It's a far more complicated problem than that. Applying common sense to technical, scientific problems is always fraught with danger

The reflections from a propeller disc (or discs) provide a substantial proportion of the return from such aircraft. The second highest RCS of typical aircraft, after the beam due to the relatively large area exposed, is nose-tail and this is due to the jet engines or propeller discs.

Cheers

Steve

 

[stona]

I've just seen that the NASM team which is restoring the museums Ho 229 at the Udvar-Hazy facility has analysed the lacquers/coatings used on the aircraft (as you'd expect from professional restorers) and reports that their is no evidence of any stealth 'coatings'.

Cheers

Steve

 

[tomo pauk]

The propeller is spinning at maybe 2,000 - 3,000 rpm.

The jet engine impeller is spinning at maybe 12,000 - 18,000 rpm.

BIG difference in reflectivity. The impeller will reflect a large percentage of incoming power. Anything that reads reflections will see the jet, assuming decent power to start with. The prop will be seen by anything that impinges enough power to pick up the small reflection percentage from the relatively slow-turning prop disc.

Could you please provide some source that will back up the quoted stuff?

 

[Gixxerman]

I don't get the notion that the Ho229 was stealthy at all.
As far as I recall it was wooden covered steel tube construction (surely radar waves not 'seeing' the wood would 'see' the steel tube be reflected?) as said it had the most unstealthy engine intake (and exhaust) imaginable.
I also recall it being said that the cockpit is also a major point of return to airborne radar and there is absolutely nothing 'stealthy' about that Ho229's design there.

This myth is a shame really, in my view there is an interesting tale of stealth from WW2. they (the Germans) did try a form of stealth.
But it was on U-boats in the form of anti-radar matting to cover masts such like.

Sadly the real stealth story just doesn't seem to be as 'sexy' as - I'm sorry to say (and I don't mean to offend anyone here) - idiotic notions that the Ho229 must have been 'stealthy' cos it looks a little bit like a B2 in shape (tho it shares nothing else in common - certainly not the billions of $ or the tens of thousands of hours super-computers worked on the actual shape, construction materials testing of the actual B2).

There was a TV show which followed the radar pole testing of the Ho229 (perfectly made, unlike 1945 German manufacturing) they reckoned it had a 20% smaller radar return than an Me109.
Not exactly a huge improvement certainly not 'invisible' to radar, not even the 1945 British radars which aimed the coastal batteries (which was bristling with effective proximity-fused guns thanks to the V1).
I wouldn't fancy the chances of any unit trying to attack targets inland having to get through (and return through) that lot.

It all seems so silly to me frankly.

 

[wuzak]

The propeller is spinning at maybe 2,000 - 3,000 rpm.

The jet engine impeller is spinning at maybe 12,000 - 18,000 rpm.

BIG difference in reflectivity. The impeller will reflect a large percentage of incoming power. Anything that reads reflections will see the jet, assuming decent power to start with. The prop will be seen by anything that impinges enough power to pick up the small reflection percentage from the relatively slow-turning prop disc.

The Rolls Royce Merlin XX had a normal maximum of 3,000rpm and a reduction ratio of 0.42:1, so prop speed was 1260rpm.
The Merlin 66 had a reduction gear of 0.477: for a prop speed of 1431rpm.
The Griffon 65 in the Spitfire XIV had a maximum speed of 2750rpm and reduction ratio of 0.51:1, prop speed 1402rpm.
Early V-1710s had reduction ratio of 0.5:1, engine speed 3000rpm, prop speed 1500rpm.
R-2800s commonly had 0.5:1 or 9:16 reduction on 2800rpm. Prop speed 1400rpm - 1575.
Sabres IIA and IIB revved to 3700rpm and had a reduction ratio of 0.274:1 for a prop speed of 1014rpm.

The Jumo 004B had a rated engine speed of 8700rpm. The BMW 003 had a rated engine speed of 9500rpm.

The Spitfire IX had a 10'9" (3.28m) diameter prop. The BMW 003 was 0.69m in diameter - so the compressor was even smaller than that.

I don't know what this means for RCS. Generally, the turbine compressor is a more solid target than a prop, but it is also much smaller in area.