SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old May 08, 2013, 07:17 AM
Registered User
Joined Oct 2004
2,759 Posts
You could supplement a turbine or a prop with a statoreactor, but you'd have to shut down and feather the slow speed engine during the high speed portion of the flight.
Brandano is offline Find More Posts by Brandano
Reply With Quote
Sign up now
to remove ads between posts
Old May 09, 2013, 04:48 AM
Registered User
Denver, CO
Joined Dec 2005
6,246 Posts
I couldn't find much info on statoreactors, other than the similarity to a ramjet. Wonder if anyone here is up to designing a supersonic ramjet.
Roto Rob is online now Find More Posts by Roto Rob
Reply With Quote
Old May 09, 2013, 09:18 PM
Registered User
United States, VA, Manassas
Joined Dec 2007
120 Posts
Legalities aside! Don't over complicate. Build an airframe around a 54mm Aerotech J180 motor casing. Find a Tripoli certed rocket guy, they make good consultants. Just keep in mind that it will be burning almost a pound of fuel in about 4 seconds. Can you say "CG shift"? Almost 100 pounds of thrust for 4 seconds should get you there if the airframe can stand up to it. FPV is the only way I could see it happen as at max V it will be traveling almost a 1/4 mile per second.
bpbrinson is offline Find More Posts by bpbrinson
Last edited by bpbrinson; May 13, 2013 at 10:04 AM.
Reply With Quote
Old May 11, 2013, 09:33 PM
Lear 35, GII, GIII pilot
Hazlehurst GA
Joined Jan 2001
387 Posts
I agree with you, bpbrinson, but I must publicly denounce the idea as it opens more than one can of worms that we, as modelers, do not ever want opened.
That being said, my theoretical calculations match yours. Good luck finding a Tripoli member that isn't offended at a launch angle of less that 90 degrees...lol.
Physics can be overcome by a properly designed machine...politics cannot.
agpilot24 is offline Find More Posts by agpilot24
Reply With Quote
Old May 11, 2013, 10:03 PM
I'm slow but I'm expensive
Ken Lilja's Avatar
United States, GA, Snellville
Joined Nov 2003
575 Posts
model turbjet

To make a turbo jet go supersonic we have to play games with the intake and exhaust. This general information for an axial flow turbine the engine and I will work from there.
The actual airflow in the compressor section only travels about 500mph, and as slow as 5 to 6 feet per second through the burners. So do this we need a variable geometry intake system. On a normal airline engine we use a fixed divergent duct. If the engine is moving at 650mph. the airflow entering the compressor needs be slowed by 150mph. Luckily Mr. Bernoulli shows the way. After the air enters the front of the nose cowl the sides of the intake duct move away from the center (diverge). The volume that the air moves through gets bigger. This increasing volume does 2 things for us: it causes the speed of the airflow to drop and the air pressure to rise. We now have an airflow speed that the engine can handle and the first stage of compression.
So, if a divergent duct slows sub-sonic airflow and raises the pressure what would a convergent duct and super-sonic flow do?
More tomorrow if there is intetrest.
Ken
Ken Lilja is online now Find More Posts by Ken Lilja
RCG Plus Member
Reply With Quote
Old May 12, 2013, 02:22 PM
Registered User
Denver, CO
Joined Dec 2005
6,246 Posts
I think if it was kept within about 3/4 miles it might be possible to fly without FPV. I don't know if that's possible though.
The stall numbers, and g force is not terrible at a 1.6 mile diameter turn. But slight changes in turn radius makes fairly dramatic changes to the stall speed, and g force. Looks like it could be very easy to overturn at these speeds, and stall. That might make FPV, the way to go.
Roto Rob is online now Find More Posts by Roto Rob
Reply With Quote
Old May 14, 2013, 12:42 PM
HyperFlight Support
Neil Stainton's Avatar
United Kingdom, England, Stratford-upon-Avon
Joined Feb 2001
3,891 Posts
Quote:
Originally Posted by Roto Rob View Post
Yes, your correct that the exhaust velocity must be higher than the flight speed, for all practical purposes.
This is correct for a jet, but not for a rocket. In a rocket the thrust is caused by the momentum of the exhaust gasses. F=MA. The exhaust gases may still be going forward relative to the ground, and give thrust. But you may need a multi-stage rocket to get there.

Neil.
Neil Stainton is online now Find More Posts by Neil Stainton
Reply With Quote
Old May 14, 2013, 12:50 PM
HyperFlight Support
Neil Stainton's Avatar
United Kingdom, England, Stratford-upon-Avon
Joined Feb 2001
3,891 Posts
Quote:
Originally Posted by Ken Lilja View Post
So, if a divergent duct slows sub-sonic airflow and raises the pressure what would a convergent duct and super-sonic flow do?
Trick question? A convergent duct will slow supersonic flow, a divergent duct is required to accelerate it. It is probably the only bit of incompressible aero I remember.

I saw an old V2 nozzle at a a museum recently and identified it from the shape immediately. It is funny how some things from half a lifetime ago stay clear.

Neil.
Neil Stainton is online now Find More Posts by Neil Stainton
Reply With Quote
Old May 14, 2013, 02:28 PM
Registered User
Denver, CO
Joined Dec 2005
6,246 Posts
Quote:
Originally Posted by Neil Stainton View Post
This is correct for a jet, but not for a rocket. In a rocket the thrust is caused by the momentum of the exhaust gasses. F=MA. The exhaust gases may still be going forward relative to the ground, and give thrust. But you may need a multi-stage rocket to get there.

Neil.
Yes that was an answer to his specific question about a turbine engine.


Another thing I think would be needed is a bunker to stand in. For the close supersonic flyby.
Roto Rob is online now Find More Posts by Roto Rob
Reply With Quote
Old Aug 09, 2013, 11:21 PM
Lear 35, GII, GIII pilot
Hazlehurst GA
Joined Jan 2001
387 Posts
While in my 'office' at 45,000' today, I was thinking..... If a properly ballasted delta winged model was dropped(from a balloon) from 45K or higher, would it reach mach 1? FPV would be required. Maybe drop the whole rocket idea, and use gravity as the propulsion? Just a thought. Gravity is nearly the same force up there, but the air is quite thin.
Supersonic glider....say it ain't so....
At nearly 20 kt. per second acceleration rate, 600 kt would be achieved before having to level out...dropping higher(like 90,000') would insure insane mach speeds.
agpilot24 is offline Find More Posts by agpilot24
Last edited by agpilot24; Aug 09, 2013 at 11:35 PM.
Reply With Quote
Old Aug 10, 2013, 02:00 AM
Registered User
ShoeDLG's Avatar
Germany, BW, Stuttgart
Joined Mar 2012
787 Posts
Another feature of the atmosphere working to your advantage is that the temperature (and therefore speed of sound) gets lower as you go higher (as long as you stay below about 50,000 ft).

At 45,000 feet:
Speed of sound: 574 kt
Dynamic pressure at 574 kt: 216 lb/sq. ft

At sea level:
Speed of sound: 662 kt
Dynamic pressure at 662 kt: about 1,481 lb/sq. ft

Suppose you put a glider in a steep dive and it just barely went supersonic near 45,000. In order for the same glider to just go supersonic near sea level, the force pulling on it (gravity) would need to be more than 6.8 times higher (6.8 = 1481/216). In other words, the glider would have to weigh almost 7 times as much to reach the same Mach number.

For a powered plane, the thrust to go supersonic at sea level can be almost 7 times what it is at 45,000 ft.
ShoeDLG is offline Find More Posts by ShoeDLG
Reply With Quote
Old Aug 10, 2013, 07:14 AM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
13,050 Posts
Next time -- Felix Baumgartner -- does one of his free falls, ask him to take a model plane with him.

Red Bull Stratos now says the maximum vertical speed was 843.6 mph, or Mach 1.25, ever so slightly faster than the earlier reported 833.9 mph, or Mach 1.24.

He could check if the model 'falls' faster than he does, (appears to accelerate way from him).
eflightray is online now Find More Posts by eflightray
Reply With Quote
Old Aug 22, 2013, 06:42 AM
Registered User
MoFl's Avatar
Espaņa, AL, Sevilla
Joined Apr 2007
515 Posts
Quote:
Originally Posted by Brandano View Post
[edit] Come to that, if someone has a scale B52, flying a small scale rocket powered X15 from it would make for a neat show. But this sort of stunts would only be manageable in a desert.
Something like this:
R.C. B-29 launches rc X1 (7 min 54 sec)


But maybe with these bigger models?:
1/10 Scale High Power X-15 Model Rocket (6 min 10 sec)

Giant RC 1:5 Scale B-29 Superfortress Crash - Byron's Striking Back (3 min 44 sec)
MoFl is offline Find More Posts by MoFl
Reply With Quote
Old Aug 22, 2013, 07:57 AM
Registered User
Joined Oct 2004
2,759 Posts
Well, the X1 should have been semi-recessed in the bomb bay, though
Brandano is offline Find More Posts by Brandano
Reply With Quote
Old Aug 22, 2013, 05:40 PM
Registered User
Toowoomba, QLD, AUSTRALIA
Joined Jan 2008
614 Posts
Quote:
Originally Posted by eflightray View Post
Next time -- Felix Baumgartner -- does one of his free falls, ask him to take a model plane with him.

Red Bull Stratos now says the maximum vertical speed was 843.6 mph, or Mach 1.25, ever so slightly faster than the earlier reported 833.9 mph, or Mach 1.24.

He could check if the model 'falls' faster than he does, (appears to accelerate way from him).

Yes, he did reach speeds through the air higher than the speed of sound at sea level and he did exceed his local speed of sound for a significant period of time so technically all is good. However he was never subjected to the magnitude of aerodynamic forces that he would have if he'd been doing 840mph through sea level density air.

An astronaut on a space walk is doing about Mach 22 (seal level) and who knows how high thier mach number is compared to their local speed of sound in a near vacuum.

Not knocking what Red Bull and Felix achieved, but they've carefully realeased enough technically correct facts to allow people's imagination do embelish the rest...
bjr_93tz is offline Find More Posts by bjr_93tz
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Mini-Review HobbyKo Sonic Boom Pusher Jet Review RacerX208 Parkflyers 2 Jun 24, 2012 11:00 AM
Discussion Funjet Sonic Boom timhoffman Foamies (Kits) 2 May 25, 2007 06:39 PM
Discussion Sonic-boom comes to models Ollie Modeling Science 6 Mar 16, 2006 03:12 AM
Discussion Sonic-boom comes to models Ollie Dynamic Soaring 4 Mar 14, 2006 05:42 PM
Not as many sonic booms as in the past? Mike C Life, The Universe, and Politics 42 Aug 07, 2003 08:26 AM