In light of the "beat Streaga" thread, and seeing far to much stuff on Concorde lately, I thought I might bring this subject back to the table. Well, at least some variant of the subject: Breaking Mach, in a homebuilt airplane. So how would it be done? How would you do it? The only limit I want to put on this, is we need to talk about ~available powerplants~. And we're not going to talk about buying used military aircraft. To cut to the chase, you can break mach with a balloon and a pressure suit. EG: Felix Bomgartner jumping from 70,000'. But that's not exactly controlled flight. The BD-10 was supposed to be the answer, but I can't find any record of one actually breaking mach, and they seemed to like to shed control surfaces. Serious Options So lets talk about how this could be done. I'm going to start with powerplants. Powerplants: Somehow, we need to get this plane up to altitude. And unless we're just doing a stunt, we want to sustain the speed for a while. If "just hitting mach" was the goal, maybe just climb and dive? Props: Since most of us have familiarity with props, lets start there. Doing some research, shows that the XF-85 Thunderscreach hit mach .83. There's reports of at least one spitfire hitting mach .95 in a dive. And the TU-95 Bear flies in that ballpark too. I'm not sure anyone, other than boaters, have really considered airfoils for use above the speed of sound in their working fluid. Would wedge type blades work? Would it help when prop tip speeds are over mach? Would it reduce drag? Or is going with a propeller just nonsense. Between trying to deal with high prop speeds, interference drag from the prop, and piss poor prop efficiency at low speeds? Maybe that's just crazy. Now.. someone was trying to break mach with a prop, but the machbuster project was dead in the 90's. Ducted Fans: So, ducted fans have the advantage of not having all those tip losses. And a good duct design can keep the airflow through the fan under mach, even when the airframe is above mach. The fan could be used to drive engine cooling as well. However there's a big weight penalty from all that ductwork. And wetted surface drag. Sadly, I don't have the math handy to calculate a ducts efficency. Does anyone want to tackle that? I'm really curious. Jet engines: Well, why not? Small jet engines are available on the market. They produce quite a bit of thrust. As I understand it, the magic to going over mach is to get the intake just right. Allowing for good pressure recovery, and low losses, no matter the airflow speed. Could.. a small plane get enough thrust from say, the engines that Sonex sells? Or would we need to look at "real" engines? This is the conventional answer, and probably the easiest of the bunch. There's the least guessing using an actual jet. I think that's the direction I'd go in. Airframe Materials: I'd love to hear your thoughts on this. I.. have no good answers, but I have a heavy preference for aluminum. Retracts: I think that anything that might want to break mach, would need retracts. This starts to get complicated, because all of the "usual" methods for dealing with retracts start to have real issues when we start talking thin wings for low drag, and then having a fuselage that wants to have air ducts in it, instead of space for wheel bays. This has lead to some really oddball solutions on military aircraft. Such as outword retracting gear, specialized thin wheels and tires. Wheels that pivot at the end of the landing gear so they can sit upright in the fuselage. Tiny, but tough tires. ... I suppose that's best re-examined after the wings. Wings: So what to do about wings? They're definitely not going to be wood. The plane, should still manage a 60-70kt landing speed, so we'll need a lot of wing area, or lift adding devices. Frontal area, starts to matter more than airfoil as you go faster, so the plane should have some very slim wings. Delta? Straight wing? Swept wing? Tailed Delta? I have a thing for tailed deltas (aka, Mig21) Fuselage: Now things get interesting. Essentially all popular home-built designs have room for two, ideally two, and luggage. Frontal area matters monumentally when it comes to flying faster than mach, so this means we're talking a very cozy side by side, or tandem seating. What's it take to build a good, smooth duct? Should that be fiberglass? Is area rule going to be a concern? Maybe just aim for a scaled down copy of a F104, or F106 and be done with it? Mission: Because it's important, why would someone want this. First, bragging rights. Second, time compression, sure you can't actually break mach over most of the US, but if you go offshore a bit, you could make some quick trips up and down coasts. It also looks like if you can get the thing above 45,000' you can go ahead and do some machbusting. At least according to this quora article: https://www.quora.com/Are-there-speed-limits-for-aircraft-civilian-or-military That also means building for high altitude flight. 45kfeet means pressurization, and reasonable cabin air conditioning. I believe I just talked myself out of this ~really cool~ idea. But... I'd like to hear your thoughts. and it would definitely give Strega a run for it's money.