Can a Flite Test plane break the Sound Barrier?

[Shorty Hassfurther]

In case you hadn't seen this before, Boom Supersonic and some other big shots released the following competition:
https://boomsupersonic.com/prize

The contest promises an award to the first amateur team to break the sound barrier without diving, using an air-breathing engine (no rockets).

When I saw this, I really had no questions other than: Where on Earth will someone let us fly a model airplane at Mach 1?

Other than that, I think that a supersonic model plane is very much within the scope of the Flite Test team.

The design hurdles will be:

The engine, which almost definitely needs to be crowd funded. Do any commercial RC designs have the power? How about with an afterburner added on?
The aerodynamics, which I'm sure have been researched by N.A.C.A./NASA for missiles, and
The metal structure, which John Overstreet may be a lot of help with.

Either way, I hope Flite Test takes a crack at this and that we don't get beaten by some rich kid or WhistlinDiesel. To me, the big prize isn't the money: it's the excuse to fly a model airplane past Mach 1.

 

[telnar1236]

In case you hadn't seen this before, Boom Supersonic and some other big shots released the following competition:
https://boomsupersonic.com/prize

The contest promises an award to the first amateur team to break the sound barrier without diving, using an air-breathing engine (no rockets).

When I saw this, I really had no questions other than: Where on Earth will someone let us fly a model airplane at Mach 1?

Other than that, I think that a supersonic model plane is very much within the scope of the Flite Test team.

The design hurdles will be:

The engine, which almost definitely needs to be crowd funded. Do any commercial RC designs have the power? How about with an afterburner added on?
The aerodynamics, which I'm sure have been researched by N.A.C.A./NASA for missiles, and
The metal structure, which John Overstreet may be a lot of help with.

Either way, I hope Flite Test takes a crack at this and that we don't get beaten by some rich kid or WhistlinDiesel. To me, the big prize isn't the money: it's the excuse to fly a model airplane past Mach 1.

Quite the challenge - this would need to be quite the plane. I'm not sure there's even a legal framework for an amateur team to break the sound barrier.

 

[Shorty Hassfurther]

Quite the challenge - this would need to be quite the plane. I'm not sure there's even a legal framework for an amateur team to break the sound barrier.

I was thinking about the legal side of it and was going to say "it certainly wouldn't be flying below 400 feet", but now that I think of it, you might get the most fuel savings from doing takeoff - supersonic - landing at low altitude on a very long straight line. Somewhere like Bonneville. It seems Jared Isaacman of NASA is involved, so that might help clear the legal cobwebs a bit

 

[Mr Man]

In case you hadn't seen this before, Boom Supersonic and some other big shots released the following competition:
https://boomsupersonic.com/prize

The contest promises an award to the first amateur team to break the sound barrier without diving, using an air-breathing engine (no rockets).

When I saw this, I really had no questions other than: Where on Earth will someone let us fly a model airplane at Mach 1?

Other than that, I think that a supersonic model plane is very much within the scope of the Flite Test team.

The design hurdles will be:

The engine, which almost definitely needs to be crowd funded. Do any commercial RC designs have the power? How about with an afterburner added on?
The aerodynamics, which I'm sure have been researched by N.A.C.A./NASA for missiles, and
The metal structure, which John Overstreet may be a lot of help with.

Either way, I hope Flite Test takes a crack at this and that we don't get beaten by some rich kid or WhistlinDiesel. To me, the big prize isn't the money: it's the excuse to fly a model airplane past Mach 1.

I highly doubt whistlindiesel would do it 😂

 

[telnar1236]

Did a bit more looking into what would be required and it seems right on the border of what is physically possible with the engines and materials available today - you would need a ridiculously well-designed aircraft with barely any margin for error - I think you could physically make an airplane with enough power and low enough drag to do it while keeping enough lift to slow down and land at a somewhat reasonable speed, but I don't know if that airplane would be able to hold itself together at those speeds - the wings would have to be ludicrously thin and rigid to give low enough drag while still avoiding flutter.

 

[Mr Man]

Did a bit more looking into what would be required and it seems right on the border of what is physically possible with the engines and materials available today - you would need a ridiculously well-designed aircraft with barely any margin for error - I think you could physically make an airplane with enough power and low enough drag to do it while keeping enough lift to slow down and land at a somewhat reasonable speed, but I don't know if that airplane would be able to hold itself together at those speeds - the wings would have to be ludicrously thin and rigid to give low enough drag while still avoiding flutter.

Yeah, carbon fiber would be a must

 

[Shorty Hassfurther]

Here's a basic drag estimate (in pounds force) of a 55 lb transonic rc airplane. I'm using NACA wind tunnel data because the test articles they use are are very close in scale and speed to a potential Boom Prize contestant. The best documentation I could find so far is Effects of Body Indentation on the Drag Characteristics of a Delta-Wing-Body Combination at Transonic Speeds, which involves a delta-wing aircraft with a 4" fuselage diameter.

----- NOTE: this is an edited version of what I sent before, which had several calculations out of order ----

Drag is dependent on lift coefficient, with lower lift meaning lower drag. Thus, we can figure out what lift coefficient (C_L) would give the test article 55 pounds of lift force = 245 Newtons at Mach 1. Lift = C_L * q * S, and this test article's wing planform area (S) is 1.625 ft^2 or 0.15 m^2. I was a bit lazy to calculate dynamic pressure (q), so I just Googled "q air dynamic pressure at mach 1.05" and was told that it equaled 78 kPa.
We can find the required C_L = L/(q * A) = 245 N / (0.15 m^2 * 78 (10^3) N/m^2) = 0.21.

The NACA document has a drag coefficient plot at a C_L of 0.2, which is close enough.
At an airspeed around Mach 1.05, the drag coefficient peaked at 0.0375. Drag = C_D *q*S. I double-checked that the S being used was based on the wing planform area and not the wetted area (full surface area), which would be much larger.

Thus, the object's drag at Mach 1.05 is C_D *q*S = 0.0375 * 0.15 m^2 * 78 (10^3) N/m^2 = 438.8 N = 98.6 lbf.

That is significantly more than the thrust a 4 inch turbine can produce, which is around 40 pounds. An afterburner might get that to 60 pounds.

Meaning that either an extremely souped-up turbine would have to be used, or a whole different type of propulsion may be necessary. I'm looking into ramjets: they seem capable of delivering enough thrust, but they're useless at low speeds.

 

[Shorty Hassfurther]

One thing I missed in the above calculations is the effect of supersonic ducting on the performance of a turbine. If I remember right, this should improve thrust performance. Also it would be necessary--without ducting, the turbine will encounter all sorts of compressibility issues from supersonic intake air. Come to think of it, the changes in airflow properties will place the turbine in a completely different environment than what it was designed for, so a different rotor/compressor would likely be needed.

 

[telnar1236]

I will say, it looks like they're using quite a low fineness ratio for supersonic flight in that article so you can probably do better in terms of drag. It also looks like they aren't getting to take credit for the inlets or nozzle which lowers your total area.

It also looks like you can buy more powerful turbines pretty easily - here's a 54 lbs turbine with a ~4.5" diameter and I'm guessing you could package it into a plane with about 80 lbs of drag at Mach 1.05.

AceX-240 Brushless 240N / 24KG Turbine Engine

ACEx Turbines has raised the bar in standard and excellence! Bridging the gap between ordinary and extraordinary! At ACEx Turbines, we bring to you a top tier product with unparalleled customer service and support! ACEx is not just another turbine company. We exist through our love for RC...

globaljet.club

And here's a 67 lbs engine with a ~5" diameter - probably closer to 100 lbs of drag with this one but also more thrust.

AceX-300 Brushless 300N/30KG Turbine Engine

ACEx Turbines has raised the bar in standard and excellence! Bridging the gap between ordinary and extraordinary! At ACEx Turbines, we bring to you a top tier product with unparalleled customer service and support! ACEx is not just another turbine company. We exist through our love for RC...

globaljet.club

And finally, a range of engines up to much higher thrust levels from China

https://www.alibaba.com/product-detail/Turbojet-Engine-23kg-60kgf-80kgf-Reliable_10000043608572.html?spm=a2700.prosearch.normal_offer.d_title.7d2367afeQdzwN&priceId=9098cc11c33b410aa84d1214120cbfa9

Somewhere up around 132 lbs = 60 kg is where I think the combination of aircraft size, engine thrust and drag would be most practical for a sub 55 lbs aircraft intended to try and get this prize.

You might also want to look at stall speed since per the terms of the contest the aircraft has to fly on aerodynamic lift - a 55 lbs aircraft with a 4" fuselage like the one shown in the article would be landing at 100+ mph. I don't think it would weigh 55 lbs at that scale - even the 132 lbs thrust airplane would probably only weigh in around 30 lbs - but that's still a stall speed in the 50-60 mph range.

 

[Mr NCT]

I will say, it looks like they're using quite a low fineness ratio for supersonic flight in that article so you can probably do better in terms of drag. It also looks like they aren't getting to take credit for the inlets or nozzle which lowers your total area.
View attachment 259371
It also looks like you can buy more powerful turbines pretty easily - here's a 54 lbs turbine with a ~4.5" diameter and I'm guessing you could package it into a plane with about 80 lbs of drag at Mach 1.05.

AceX-240 Brushless 240N / 24KG Turbine Engine

ACEx Turbines has raised the bar in standard and excellence! Bridging the gap between ordinary and extraordinary! At ACEx Turbines, we bring to you a top tier product with unparalleled customer service and support! ACEx is not just another turbine company. We exist through our love for RC...

globaljet.club

And here's a 67 lbs engine with a ~5" diameter - probably closer to 100 lbs of drag with this one but also more thrust.

AceX-300 Brushless 300N/30KG Turbine Engine

ACEx Turbines has raised the bar in standard and excellence! Bridging the gap between ordinary and extraordinary! At ACEx Turbines, we bring to you a top tier product with unparalleled customer service and support! ACEx is not just another turbine company. We exist through our love for RC...

globaljet.club

And finally, a range of engines up to much higher thrust levels from China

https://www.alibaba.com/product-detail/Turbojet-Engine-23kg-60kgf-80kgf-Reliable_10000043608572.html?spm=a2700.prosearch.normal_offer.d_title.7d2367afeQdzwN&priceId=9098cc11c33b410aa84d1214120cbfa9

Somewhere up around 132 lbs = 60 kg is where I think the combination of aircraft size, engine thrust and drag would be most practical for a sub 55 lbs aircraft intended to try and get this prize.

You might also want to look at stall speed since per the terms of the contest the aircraft has to fly on aerodynamic lift - a 55 lbs aircraft with a 4" fuselage like the one shown in the article would be landing at 100+ mph. I don't think it would weigh 55 lbs at that scale - even the 132 lbs thrust airplane would probably only weigh in around 30 lbs - but that's still a stall speed in the 50-60 mph range.

Wow, and the acex240 is on sale!!
$3,294.95 down from $3,395.00
You Save 2% ($100.05)

 

[telnar1236]

Wow, and the acex240 is on sale!!
$3,294.95 down from $3,395.00
You Save 2% ($100.05)

Yeah, whoever does this will need far far deeper pockets than I have

 

[Mr NCT]

I bought a used Mercedes wagon for less 🤣🤣🤣 and thought twice about it.

 

[Shorty Hassfurther]

I will say, it looks like they're using quite a low fineness ratio for supersonic flight in that article so you can probably do better in terms of drag. It also looks like they aren't getting to take credit for the inlets or nozzle which lowers your total area.
View attachment 259371
It also looks like you can buy more powerful turbines pretty easily - here's a 54 lbs turbine with a ~4.5" diameter and I'm guessing you could package it into a plane with about 80 lbs of drag at Mach 1.05.

AceX-240 Brushless 240N / 24KG Turbine Engine

ACEx Turbines has raised the bar in standard and excellence! Bridging the gap between ordinary and extraordinary! At ACEx Turbines, we bring to you a top tier product with unparalleled customer service and support! ACEx is not just another turbine company. We exist through our love for RC...

globaljet.club

And here's a 67 lbs engine with a ~5" diameter - probably closer to 100 lbs of drag with this one but also more thrust.

AceX-300 Brushless 300N/30KG Turbine Engine

ACEx Turbines has raised the bar in standard and excellence! Bridging the gap between ordinary and extraordinary! At ACEx Turbines, we bring to you a top tier product with unparalleled customer service and support! ACEx is not just another turbine company. We exist through our love for RC...

globaljet.club

And finally, a range of engines up to much higher thrust levels from China

https://www.alibaba.com/product-detail/Turbojet-Engine-23kg-60kgf-80kgf-Reliable_10000043608572.html?spm=a2700.prosearch.normal_offer.d_title.7d2367afeQdzwN&priceId=9098cc11c33b410aa84d1214120cbfa9

Somewhere up around 132 lbs = 60 kg is where I think the combination of aircraft size, engine thrust and drag would be most practical for a sub 55 lbs aircraft intended to try and get this prize.

You might also want to look at stall speed since per the terms of the contest the aircraft has to fly on aerodynamic lift - a 55 lbs aircraft with a 4" fuselage like the one shown in the article would be landing at 100+ mph. I don't think it would weigh 55 lbs at that scale - even the 132 lbs thrust airplane would probably only weigh in around 30 lbs - but that's still a stall speed in the 50-60 mph range.

Stall speed would be a big factor for sure. I imagine that the easiest way to get past that would be to fly a long straight line all the way from takeoff until landing, with minimal altitude gain. That way, less fuel needs to be used, and the wings don't need to create extra lift to climb and turn. I imagine that once a giant space to fly in has been found, a 100 mph landing won't be that difficult relative to some of the other challenges of this aircraft.

 

[Shorty Hassfurther]

Yeah, whoever does this will need far far deeper pockets than I have

As they say...
"The easiest way to make a small fortune in aviation is to start with a large fortune"