# Making a boom, before Boom Aerospace - Messing around with breaking mach.

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#### TFF

##### Well-Known Member
Migs are cheap on the open market, but I think getting a DC-8 is the best idea. That way you can take all your friends.

#### bmcj

##### Well-Known Member
HBA Supporter
If you had a mothership to launch then not much wings would be needed.
Might need a dry lake bed to land on skids.
Or if you had a big enough rocket, you can leave the wings off and launch vertically, then land under a parachute (albeit a very strong one that can survive a high speed deployment).

Side note: SpaceShipOne was supersonic, yet was not terribly sleek or pointy.

#### Lucrum

##### Well-Known Member
Log Member

Ducted Fans:
Driven by a IC engine? Forgetaboutit

Jet engines:

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.
There's more to it than that. The airflow to the engine has to be slowed to subsonic speeds, usually through controlled shockwaves.

Could.. a small plane get enough thrust from say, the engines that Sonex sells?
IMO ........NO!

There's the least guessing using an actual jet. I think that's the direction I'd go in.
Yes, either a pure turbojet or very low bypass turbofan
And what's more, if it's not oversized you'll also likely need an after burner
Airframe Materials:

I'd love to hear your thoughts on this. I.. have no good answers, but I have a heavy preference for aluminum.
You'll need to factor in the temp rise and skin temps on the leading edges
Retracts:
Absolutely
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)
Without even crunching numbers, I'd plan on a much higher stall speed.
Some form of delta with a tail would probably be the easiest approach.
But certainly not the only one

Fuselage:

side by side, or tandem seating.
Tandem You're goal is so far out of reach to begin with why make it harder with more drag area?

What's it take to build a good, smooth duct? Should that be fiberglass? Is area rule going to be a concern?
I don't think the area rule would apply to the internal section of the engine intake
You will want to apply it to the fuselage shape though.

You'll also need to study compressibility and possibly high speed instability
You'll probably want an experienced aerodynamicist on speed dial as well

0.98 Mach indicated is the fastest I've ever been

#### Hephaestus

##### Well-Known Member
Lol.

Actually wouldn't a spitfire be a good starting point? .92 in an emergency dive.

NACA actually had some neat papers on the theory of going supersonic with a prop.

#### Topaz

##### Super Moderator
Staff member
Log Member
The really big issue here is that, given you had a supersonic homebuilt, you couldn't fly it that way. FAR's strictly forbid it outside of a very few MOA's and military restricted areas. There's no waiver you can get, no special permit, and no class of "experimental" that makes it possible. The only non-military exception I can think of is Scaled's SpaceShipOne, and likely the only reason they got it was because the aircraft was going straight up and no sonic boom would ever reach the ground.

It's all well and good as a fun thought exercise, but to what end?

#### Riggerrob

##### Well-Known Member
Options:

Engine - The least expensive answer is a low-bypass jet engine already in production.
The second option? If you have to ask, you cannot afford the development costs. Hah! Hah!

Propellers - Skyshreak's biggest problem was that it's propeller was constantly exposed to supersonic airflow before it even started turning.
Perhaps if you mounted the propeller(s) farther aft and used area-ruling to reduce boundary layer airflow to sub-sonic .... Imagine a 21st century version of the area-ruling applied to Convair F-106 with props turning aft of the wing.

Ducted fans - are most efficient when hovering and their advantage decreases with speed.

Drop tanks - are used to compensate for poor conceptual design. They are very draggy and far more difficult to design than conformal fuel tanks.

The greatest opportunity for innovation is in nose aerodynamics. Adjustable BOOM technology is just a crude first step. Perhaps a Soviet high-speed torpedo can provide inspiration because it ejects a bubble of air around the nose of the torpedo. That bubble prevents the solid nose from touching supersonic water. The next aerodynamic step uses surface layer sucking and blowing to artificially tune nose shape for the gentlest sonic boom possible.
Reviewing nose inlets on F-100 Super Sabre and Mig-21 could help us better understand supersonic airflow around noses. Did F-100 suck enough to disrupt the sonic shock come originating at the nose?

Yes. I know that I ask too many embarrassing questions, but my goal is to encourage you guys to think up redneck-engineer solutions to problems that have stumped degreed engineers for decades.

#### bmcj

##### Well-Known Member
HBA Supporter
Can anyone think of a really small supersonic aircraft?
It’s been awhile since I’ve been up close and personal with it, but IIRC, the X-43 is only about 10 feet long and it is hypersonic.

#### pictsidhe

##### Well-Known Member
The really big issue here is that, given you had a supersonic homebuilt, you couldn't fly it that way. FAR's strictly forbid it outside of a very few MOA's and military restricted areas. There's no waiver you can get, no special permit, and no class of "experimental" that makes it possible. The only non-military exception I can think of is Scaled's SpaceShipOne, and likely the only reason they got it was because the aircraft was going straight up and no sonic boom would ever reach the ground.

It's all well and good as a fun thought exercise, but to what end?
How far do you go to get into international waters, 12miles? Anyone for a quick island break?

#### pictsidhe

##### Well-Known Member
It’s been awhile since I’ve been up close and personal with it, but IIRC, the X-43 is only about 10 feet long and it is hypersonic.
Cockpit is a little on the small side.

#### gtae07

##### Well-Known Member
The really big issue here is that, given you had a supersonic homebuilt, you couldn't fly it that way. FAR's strictly forbid it outside of a very few MOA's and military restricted areas. There's no waiver you can get, no special permit, and no class of "experimental" that makes it possible. The only non-military exception I can think of is Scaled's SpaceShipOne, and likely the only reason they got it was because the aircraft was going straight up and no sonic boom would ever reach the ground.

It's all well and good as a fun thought exercise, but to what end?
Well, technically...

FAR 91 said:
§91.817 Civil aircraft sonic boom.

(a) No person may operate a civil aircraft in the United States at a true flight Mach number greater than 1 except in compliance with conditions and limitations in an authorization to exceed Mach 1 issued to the operator under appendix B of this part.

(b) In addition, no person may operate a civil aircraft for which the maximum operating limit speed MM0 exceeds a Mach number of 1, to or from an airport in the United States, unless—

(1) Information available to the flight crew includes flight limitations that ensure that flights entering or leaving the United States will not cause a sonic boom to reach the surface within the United States; and

(2) The operator complies with the flight limitations prescribed in paragraph (b)(1) of this section or complies with conditions and limitations in an authorization to exceed Mach 1 issued under appendix B of this part.
FAR 91 said:
Appendix B to Part 91—Authorizations To Exceed Mach 1 (§91.817)
Section 1. Application

(a) An applicant for an authorization to exceed Mach 1 must apply in a form and manner prescribed by the Administrator and must comply with this appendix.

(b) In addition, each application for an authorization to exceed Mach 1 covered by section 2(a) of this appendix must contain all information requested by the Administrator necessary to assist him in determining whether the designation of a particular test area or issuance of a particular authorization is a “major Federal action significantly affecting the quality of the human environment” within the meaning of the National Environmental Policy Act of 1969 (42 U.S.C. 4321 et seq.), and to assist him in complying with that act and with related Executive Orders, guidelines, and orders prior to such action.

(c) In addition, each application for an authorization to exceed Mach 1 covered by section 2(a) of this appendix must contain—

(1) Information showing that operation at a speed greater than Mach 1 is necessary to accomplish one or more of the purposes specified in section 2(a) of this appendix, including a showing that the purpose of the test cannot be safely or properly accomplished by overocean testing;

(2) A description of the test area proposed by the applicant, including an environmental analysis of that area meeting the requirements of paragraph (b) of this section; and

(3) Conditions and limitations that will ensure that no measurable sonic boom overpressure will reach the surface outside of the designated test area.

(d) An application is denied if the Administrator finds that such action is necessary to protect or enhance the environment.
Section 2. Issuance

(a) For a flight in a designated test area, an authorization to exceed Mach 1 may be issued when the Administrator has taken the environmental protective actions specified in section 1(b) of this appendix and the applicant shows one or more of the following:

(1) The flight is necessary to show compliance with airworthiness requirements.

(2) The flight is necessary to determine the sonic boom characteristics of the airplane or to establish means of reducing or eliminating the effects of sonic boom.

(3) The flight is necessary to demonstrate the conditions and limitations under which speeds greater than a true flight Mach number of 1 will not cause a measurable sonic boom overpressure to reach the surface.

(b) For a flight outside of a designated test area, an authorization to exceed Mach 1 may be issued if the applicant shows conservatively under paragraph (a)(3) of this section that—

(1) The flight will not cause a measurable sonic boom overpressure to reach the surface when the aircraft is operated under conditions and limitations demonstrated under paragraph (a)(3) of this section; and

(2) Those conditions and limitations represent all foreseeable operating conditions.
Section 3. Duration

(a) An authorization to exceed Mach 1 is effective until it expires or is surrendered, or until it is suspended or terminated by the Administrator. Such an authorization may be amended or suspended by the Administrator at any time if the Administrator finds that such action is necessary to protect the environment. Within 30 days of notification of amendment, the holder of the authorization must request reconsideration or the amendment becomes final. Within 30 days of notification of suspension, the holder of the authorization must request reconsideration or the authorization is automatically terminated. If reconsideration is requested within the 30-day period, the amendment or suspension continues until the holder shows why the authorization should not be amended or terminated. Upon such showing, the Administrator may terminate or amend the authorization if the Administrator finds that such action is necessary to protect the environment, or he may reinstate the authorization without amendment if he finds that termination or amendment is not necessary to protect the environment.

(b) Findings and actions by the Administrator under this section do not affect any certificate issued under title VI of the Federal Aviation Act of 1958.

So, if you can show that a sonic boom won't reach the ground, you can apply for the waiver. And you can apply for a waiver for purposes of determining that.

The problem is that there's no specific definition of "sonic boom". The "low boom" designs currently being proposed would reduce the audible signature of that boom to being something like a car door closing. I've been in an acoustic simulator that can reproduce the boom from Concorde and an F-18, and the predicted "low boom" aircraft. The latter is hardly noticeable. But until the restriction is written more in terms of a measurable threshold rather than just any boom signature at all, it's essentially impractical.

Of course, I live within hearing distance of an artillery range that likes to practice at night. So my threshold for annoyance may be different than someone else's.

#### Swampyankee

##### Well-Known Member
How supersonic do you want to go?

If the speed is less than about M=1.4 to 1.6, a simple, fixed-geometry inlet like the F-16 uses is practical.

The powerplant is going to be difficult. The two most likely to be practical are the Adour, from the SEPECAT Jaguar and the J-85 from the F-5/T-38. I believe the Adour had to pass bird shot tests, so that may be a factor. It's also a low-bypass engine, so it's more fuel efficient when not in afterburner.

Flight controls will be a major pain; it will have to be irreversible hydraulics.

#### BBerson

##### Light Plane Philosopher
HBA Supporter
Perhaps a very small single place EA-B with the pilot prone in a tight pointy tube could have a minimal sonic boom?

#### Himat

##### Well-Known Member
There was at least on long thread about the same subject a few years ago here on HBA. To find it, well.

For inspiration on a small supersonic airplane, the Folland Gnat and Saunders-Roe SR53 come to mind. Restricting the speed goal to Mach 1,4 to 1,6 make design easier, both the jet engine intake and heating of the airframe. Actually studying the Folland Gnat is a good exercise as the plane was quite clever packaged.

Small supersonic airframes have been made as both target drones and recognition vehicles. The USA made was smaller than their Soviet counterparts I think.