“Invisible” Aircraft, (Stealth: The Early Years).

[red admiral]

The show is rather unfortunately (and incorrectly) titled Hitler's Stealth Fighter

Especially when the results indicated it wasn't particularly stealthy....

[AeroFranz]

I have my own opinion on how stealthy the 229 supposedly was, but it would have been nice to have actual tests results. I am not sure that the way the model was made we'll get a meaningful answer. If they are not reproducing an internal structure, I guess then they must be assuming that the OML was not permeable to radar waves. Any other explanation

[Hikoki1946]

What do they plan on doing with the full scale model? Would be nice to see it in genuine colors and put on display somewhere. After all, doubtful we will see the original ever restored.

[AeroFranz]

After all, doubtful we will see the original ever restored.

fingers crossed...I started volunteering at the Udvar-Hazy museum, and once a year the staff is given a tour of the Garber facility. Can't wait to see the real thing. I can't think of a more eagerly awaited restauration. Maybe the documentary will be a catalyst and raise interest in this project?

[red admiral]

I have my own opinion on how stealthy the 229 supposedly was, but it would have been nice to have actual tests results.

The results seem to indicate similar results to the Bf 109 which is not a "stealth fighter". Of course, a lot of the accuracy of the results depends on how the aircraft was constructed (I don't see any large metallic jet engines there) and what radar was shone at it. Its not really possible to design an aircraft that is effective against the wide range of radars in use from the high metric CH to low centimetric AI radars.

[AeroFranz]

given the maniacal attention to detail that is required to reduce RCS to useful levels (the famed fourth power in the radar-range equation), I would be surprised by stealthy-claims. Where does the comparison to the -109 come from?

[Norcrafter]

I’m an advanced projects engineer/manager at Northrop Grumman Aerospace Systems. I was the guy who introduced producer/director Michael Jorgensen to the Northrop Grumman team and helped convince our management to pursue and fund the Ho-229 documentary project. I’ve been directly involved with this project from start to finish and I appear in the show. I’d like to address some of the concerns you guys have raised in this forum.

A number of you have expressed concern that the radar cross section (RCS) testing of the constructed Ho-229 full-scale model is invalid for various reasons, including that fact that the model does not have an internal tubular truss structure, metallic engines, control surfaces, etc. This assertion is simply not true. I’m assuming that most of you are not low observables engineers, but please forgive me if any of the following is tutorial.

At this point in time, the aerospace industry’s low observables (LO) engineering community has considerable experience under its collective belt. Over the decades, countless structures have been illuminated across all possible radar frequency ranges. This includes full-up aircraft and models, down to individual parts, representing all forms of aircraft construction methods and material utilization developed since the Wright Brothers. LO computational techniques have been considerably refined and validated in comparison to empirical testing results.

Before we started the build, we were able to inspect the actual Ho-229 in the Smithsonian Garber facility (an awesome experience!). We were also able to do some testing of the actual aircraft’s surfaces to determine their electromagnetic properties, which you’ll see in the show. In addition, we had at our disposal a comprehensive package of wonderful Ho-229 layout drawings prepared by Arthur Bentley, and Mr. Bentley himself was a consultant to the project.

So, my point is that when we sat down to figure out how to build the Ho-229 RCS test model, we already had an excellent detailed technical understanding of this aircraft and how to effectively simulate it for the purpose of determining its electromagnetic properties.

We discussed the possibility of reconstructing the truss structure, but that would be cost prohibitive and our senior LO engineers determined that it wasn’t really necessary. To obtain the kind of first-order results we were looking for, it would be sufficient to build the model from high-grade plywood with carefully targeted applications of various conductive coatings internally and externally to simulate the interior configuration. Specialized paints and coatings are the key!! We have proven on various projects that this technique works, and that’s the way we proceeded with the Ho-229.

Another key aspect in making the construction method decisions was radar frequency. We studied the British Chain Home air defense radar systems used throughout WW II. We concluded that the use of VHF, UHF and L-band frequencies would be representative for our testing. At these relatively low long-wavelength frequencies, small details on the test model would not be visible or contribute significantly to the overall signature, including the gaps in control surfaces. Also, the coating methodology described above would be very effective at accurately simulating this aircraft at these frequencies without the need to recreate the interior features in detail. To keep things simple, we tested the aircraft in a nominal straight and level flight configuration, which would represent its best radar signature. It would have been nice to include moveable control surfaces on the model, but that was beyond the available budget.

Keep in mind that we built a test model for a one hour TV documentary, not for developing and deploying a real combat aircraft! All we needed in this case was enough engineering fidelity to achieve first order results enabling us to reach some top-level conclusions. I believe our project priorities were properly balanced with this goal in mind, and of course, within the available budget.

As you all know, the Ho-229 was not designed with stealth as a primary design goal. The aircraft has a few obvious stealth “Achilles’ Heels” such as the exposed engine faces. However, a flying wing configuration can nonetheless have inherently stealthy properties compared to conventional aircraft even if LO was not a primary design consideration. This was amply demonstrated by Northrop’s YB-49A. Regarding the Ho-229’s RCS performance, we chose to not get into radar signature reduction specifics in the documentary. Rather, we describe the Ho-229’s capabilities in terms of the resulting reduction in detection & warning time against the Chain Home radar system.

I agree that the show’s title “Hitler’s Stealth Fighter” is somewhat misleading and was certainly not my first choice. The show was produced under a different working title, but the Nat Geo Channel had the final say. Bear in mind that a show like this is created for the general public, not specifically for aviation enthusiasts. Nat Geo is in business to stay in business and I can understand why they chose this title. After more than half a century, anything “Hitler” still sells. All that said, there’s plenty of good stuff in this documentary and I think you guys will enjoy it.

As someone pointed out, the Nat Geo website for this show does state that the Ho-229 RCS model was constructed using “materials only available in the 1940’s”, and that is incorrect. They misinterpreted our statements that we used materials that are, from the RCS standpoint, representative of what was used in the 1940’s. I’ll see what I can do to get that corrected.

By the way, the full scale Ho-229 RCS model is being donated to the San Diego Air & Space Museum. We recently had a great meeting with the museum’s team and we are making plans to get the model down there and on display in time for the documentary’s debut.

All things considered, this has been a fun project.  I appreciate everyone’s interest and I hope you enjoy the show!

[AeroFranz]

Norcrafter,

I appreciate your informative post, and i am even more pleased that from what you wrote care was taken by the Northrop people to do this right (within reason). As mentioned elsewhere, the 'sensationalistic' vibe that forum members got checking out the Nat Geo website kind of worried us for a second that results would be less than accurate. There are many unresolved myths and curiosities in aviation history, and it's not often that you get to find out the truth.
It's really cool that the model will have a home in Balboa park. I can't wait to see the documentary.

[Norcrafter]

Hello AeroFranz,

Thanks for your thoughtful comments. The sensationalistic vibe will probably continue to build over the next few weeks. That's the reality of media marketing in the 21st century, as I'm sure you well know. And some of you guys may not agree with all of the statements made in the documentary. But as I said, I think there is plenty of good stuff in this show that will appeal to aviation enthusiasts, and I think our core methods and conclusions are sound.

I'm looking forward to hearing everyone's reaction to the documentary. And I believe it was you who mentioned that perhaps the documentary will be a catalyst for increased interest in the Smithsonian's restoration of the real Ho-229. That would be the best possible outcome!

Norcrafter

[windswords]

Well, whether it was truly stealthy or not, it was definately the "coolest" looking aircraft the Germans ever made in WWII! Every time I see an illustration, or diagram, or pic of a model of this bird I save it.

There are two aircraft at Garber that I hope are restored before I die. One in Ho-229. The other is the Kyushu J7W Shinden. Would love to see it restored with that 6 bladed pusher prop.

[red admiral]

Thanks for your description of the work carried out.

Was there any particular reason for using Chain Home radar as the illuminator? It wasn't being used a great deal by 1945 apart from long range spotting of V-2 launches. The radar signature against later war radar types would be rather different, e.g. 1.5m GCI, 10cm AI, 3cm AI...

[Norcrafter]

Hello red admiral,
Good question. We specifically mention Chain Home in the show because of its great historical significance and pivotal role in the early air war. Its many variants were in service throughout the war performing the Early Warning (EW) role. The only reason it wasn't being used much in 1945 other than V-2 detection was obviously because THERE WERE NO German air assaults against the UK at that point. If there were, you can be sure it would have been used extensively. Despite the existence of more advanced individual radars at that point, the Chain Home Low and other variants still constituted an entire integrated network, essential to the adequate defense of the UK.

From a strategic standpoint, the most important aspect of the Ho-229's radar signature is it's performance against EW radars, not Ground Controlled Intercept (GCI) and Airborne Intercept (AI) radars. If the Germans were hypothetically able to field the Ho-229 in significant numbers and initiate offensive operations, The EW radar network is the first line of defense and would have been used to cue the defensive response to the attack. This is the reason we chose to test the Ho-229 against VHF, UHF, and L-Band, which covers the characteristic operating frequencies for EW radars during this period of time. These bands cover wavelengths from about 0.9 meters down to about 30 cm.

Of course, we would have loved to test the Ho-229 at higher frequencies as well. We had neither the time nor the budget. I believe that the percentage improvement in radar signature compared to conventional aircraft would be approximately the same order of magnitude at GCI and AI frequencies.

Keep in mind that we have a complex story to tell in about 42 minutes, which is the length of the show without commercials (those of you in Europe and Canada will get a 50 minute version!). We told the radar story as best we could in the time available, in balance with the rest of the story.

[spaced_monkey]

Hello AeroFranz,

Thanks for your thoughtful comments. The sensationalistic vibe will probably continue to build over the next few weeks. That's the reality of media marketing in the 21st century, as I'm sure you well know. And some of you guys may not agree with all of the statements made in the documentary. But as I said, I think there is plenty of good stuff in this show that will appeal to aviation enthusiasts, and I think our core methods and conclusions are sound.

I'm looking forward to hearing everyone's reaction to the documentary. And I believe it was you who mentioned that perhaps the documentary will be a catalyst for increased interest in the Smithsonian's restoration of the real Ho-229. That would be the best possible outcome!

Norcrafter

I wonder with the success of this show if there may be a possibility for  other  such shows to be produced in cooperation with the two companies, maybe a Do 335 or A HE 112 show. (I find that generally speaking when American do WW2 Documentaries there are mostly pro Allied this one was truly a pleasant change from the norm )


the other thing i would like to ask about is why do historians fail to comprehend that the German Nuclear program fail because the German scientists were unable to prove on paper to their higher ups the actual size of a nuke bast. (the heavy water they produced in northern Europe was for their experiment power generators IE nuclear reactor)