In post #25 you said you phrased your question generally, but spend the next five paragraphs specifically talking about stealth. Particularly:
ISTM (and Ranger Jeff, apparently) that you want to know if you could put an aerodynamic shell over a stealth aircraft that uses flat surfaces to make it fly better, or would performance be reduced.
That question is fairly far removed from your OP.
Um, what I thought I was saying was the OP wanted to put a stealthy aerodynamic shell over a NON-stealthy aircraft to make it stealthy. Either that or the OP has a lot of stock in companies that make carbon-fiber and is looking for ways to make some money off of fat gumment contracts.
If we set aside the issue of stealth, can we all agree that if we picked an aircraft of our choosing (“a little Cessna, a business jet, a cargo plane or an airliner”), and essentially built another frame around that airplane, that it is virtually certain that performance would degrade across the board?
After all, we would start with an airplane that is generally (though perhaps not perfectly) optimized for whatever it is that it does. Then, we build a bubble around it (perhaps with longer wings and smoother skin), and then try to fly that airplane. In all likelihood, all that has been accomplished is to add a lot of mass and surface area in the hopes of getting a little less drag.
If one starts with an airplane that is a cube with stubby wings and a huge engine, one might get a lot of improvement by putting a new wrapper on it. But if you start with a real airplane, how much could it really be improved by adding a bunch of shit to it?
Indeed we can. Hence why I asked how much performance would be degraded, not whether it would be.
Right. That’s sort of what the Original Post seemed to ask (without the stealth stuff). But then in post #25 the Original Poster brings up putting a shell around a stealthy aircraft. The Original Post and the Original Poster’s post #25 are kind of far from each other.
25%.
I was quite aware that I wasn’t going to get a very precise answer. Complex aeronautic questions usually require wind tunnel tests for precise answers. I was looking for ballparks, not snarks.
Sadly, **Ravenman **has nailed the OP’s Q, even as amended and expanded.
How much faster could a car go with a bigger engine?
The only sensible answer is “somewhere between not at all, and 10x faster”. Which is not very informative.
For an aircraft already more or less stealthily shaped you might be able to add RAM coatings at a couple percent of performance degradation. For the Spirit of St. Louis or a Ford Trimotor you couldn’t get it to fly at all at anything resembling modern stealth RCS goals. But you could probably still get off the ground with stealth treatments that’d buy you a few percent improvement in RCS.
Bottom line: Wanting a numeric answer to a question devoid of numbers is silly. I’m reminded of joke. “In partial scores today: NY Yankees - 3.”
Late update:
After
“Which is not very informative.”
continue the paragraph with
“And even that assumes some limitations not in the question. Bolt a warp drive on that sucker and it’ll go a lot faster than 10x normal speed. For another example of an unexpected engine mod to a car, see Citroen Launched off of an Aircraft Carrier - YouTube”.
He could be right. Aircraft are optimized for specific parameters such as payload, range, airspeed, takeoff and landing distance, altitude, etc. Adding anything to an aircraft can rapidly degrade performance. Increasing drag reduces the max airspeed which reduce range, unless you add more fuel but then you decrease the payload. Just the extra weight may require increasing the size of control surfaces which then increases weight again. If the weight added is not at the center of gravity additional weight is needed to maintain that center of gravity. And even you end up with a relatively small performance decrease the cost of adding a fairing to a plane may exceed the cost of a redesign anyway. For what you are suggesting the added weight and drag could easily be characterized as a 25% decrease in performance when considering all the different performance characteristics that would be affected.
Reviving this zombie because an idea came to me:
I agree that micro-scale sawteeth and RAM coating do indeed get the best of both worlds in terms of aerodynamics and stealth. What I am wondering about is if the double airframe setup I’ve described might be well suited to applications where affordability is as high a consideration as stealth and aerodynamics.
Does anyone have some idea of the procurement and maintenance costs of the sophisticated sawteeth and RAM ECM? Is tens of millions for procurement and about as much for stealth-related maintenance reasonable?
If so, what would be the impact of using the double airframe setup for, say, cruise missiles, antiship missiles, drones, stand-off EW planes and bombers? They need good aerodynamics but not as much as a fighter. They need good stealth but again, not as much as a fighter. What they can greatly benefit from, especially the missiles, is greater affordability.
If the reflecting parts of the plane were larger than about 1" and were closer in size to those of the F117, how would that affect different types of radar?
1" sawteeth and RAM coating have very small reflecting surfaces, doesn’t this mean that it’s going to be useful against tracking and guidance radar but much less so against L, S and C band search radars? Don’t the sawtooth and RAM coating designs lose a lot of effectiveness when the wavelength is as larger or larger than the sawtooth/RAM reflecting surfaces?
One point to consider about radar reflection: If your angled panels are significantly smaller than the wavelength of the radar, then for all practical purposes, they are curved. And I think that most radar is in the few centimeters range.
Now, if you’re really clever, you might be able to accomplish something with specially-desiged panels of just the right size, comparable to the wavelength. But that would probably mean customizing just for one specific wavelength, and while radars all use similar wavelengths, they’re not all exactly the same.
This talk reminds me of the Atlantica blended wing kitplane. http://www.wingco.com/
Basically a design effort to increase the size of the fuselage.
You’re right about the impact of having many small angles. This would seem to represent a strong advantage to having very large flat surfaces to reflect the radar emissions away. The fewer surfaces, the fewer angles will make you shine.
As for wavelengths, it would very much depend on the kind of radar and the technology that goes with it. From what I understand, the L and S bands (30 to 7.5cm) appear to be mainly used for search radar. X (3.75 to 2.5cm) seem to be used for both tracking and guidance and it’s likely that planes also use it for searching. Ku (25 to 1mm) to mm seem like they would only be useful for guidance.
With good signal processing and multiple arrays, it may even be possible to use VHF and UHF (10 to 0.1m) for search.
There’s something that happens when a radar wave or its reflector is the same size or some fraction of the other. I don’t remember what it’s called so googling isn’t proving useful.
FYI … Aviation Week is running a nice series of articles on stealth tech. They’re written at about the level of technical complexity that you’d both enjoy and comprehend.
They’re available online behind their paywall. Or you could research their print magazines if you can find a public library with a subscription.
IIRC the first installment was about 6-8 weeks ago and they seem to come out at a rate of about 1/month.
There are a lot of things that happen. The term you’re thinking of might be diffraction, interference (constructive or destructive), resonance, or several other possibilities.
Thanks. I was able to access it up to July 2016. I’ll keep checking.
From what I’ve read, it seems like having several E-2-like planes sending data to a supercomputer from several angles will enable detection and perhaps tracking of stealthy planes at long range.
Fire control would still be a problem. Being able to imprecisely track it could still be useful if the stealthy targets and one’s missile-launching platforms (with their own X-band radar) get within 20-40km of each other, no?
Could integrating VHF to L-band radar data from several sources be done fast enough and precisely enough to provide sufficient fire control data?
Resonance, that’s the one. It’s more precisely known as Mie scattering, right? Mie scattering - Wikipedia
Is it possible for the fins and other control surfaces to be made of radar-transparent materials? Can a material (like fiberglass) which is transparent to X-band become non-transparent if VHF, UHF or L-band radar are used?
The latest stealth article touches on the fire control issues you raise.
Right now the accuracy of the gigantic VHF radars is good enough to get SAM X-band targeting radars looking in the right general area. But not enough to give a direct accurate handoff.
Neither are the small radars on the missiles themselves sufficiently sensitive to bridge the gap between where the X-band says the target probably is and what the missile needs to see to get within the warhead’s lethal radius.
So the “kill chain” has gaps where the target can fall between the cracks in each successive system’s detection / tracking capabilities.
The unclassified working assumption is this is where other physics must be brought to bear. If we can use radar to detect the air wake, or use sound DF or IR or magnetic anomaly or sonar or the Force to bridge the radar gaps, we’d have a robust kill chain.
More computer power enables pulling ever smaller signals out of ever greater noise. It may eventually get like the Navy’s boast of their sonars: we don’t track the sound of the enemy sub. We track the hole in the ambient ocean made by the enemy’s sub.
