Shop our Airplanes Products Shop our Surface Products
Thread Tools
Old Apr 19, 2016, 03:11 AM
oneday is offline
Find More Posts by oneday
Registered User
Dorset, UK
Joined Jun 2002
32 Posts
Discussion
Thrust augmentation

Back in the days of the dinosaur, Jetex produced what they called an augmentation tube which increased the mass flow. I wondered if anyone has tried using a standard EDF as the primary jet inside an outer duct. I guess that it wouldn't be practical to get the primary to secondary duct ratio ideal but who knows.

Tony
oneday is offline Find More Posts by oneday
Reply With Quote
Sign up now
to remove ads between posts
Old Apr 19, 2016, 03:17 AM
St. Martin is offline
Find More Posts by St. Martin
Big gov never Works
St. Martin's Avatar
Skunk Water, Rhode Island
Joined Jul 2002
13,471 Posts
Hi Tony, I may be wrong here... I use JETEX back in the 60's. I had 100's, 150, and Scorpions. And aumentation tubes. They are a combustion true rocket producing heat. The tube cooled the exhaust helping the increase in mass flow. This cannot be done with EDF. We get many arguments here on RCG, with people trying to compare true jet and rocket engines with ducted fans. Not saying you are, just keep in mind that there is heat helping the combution versions.

Fuzz
St. Martin is offline Find More Posts by St. Martin
Reply With Quote
Old Apr 19, 2016, 03:21 AM
St. Martin is offline
Find More Posts by St. Martin
Big gov never Works
St. Martin's Avatar
Skunk Water, Rhode Island
Joined Jul 2002
13,471 Posts
Also, the reduction in the exhaust tube outlet area, of an EDF is doing the same as the Augmentation tube, by speeding up the flow.

Fuzz
St. Martin is offline Find More Posts by St. Martin
Reply With Quote
Old Apr 19, 2016, 10:59 AM
oneday is offline
Find More Posts by oneday
Registered User
Dorset, UK
Joined Jun 2002
32 Posts
Thrust augmentation.

Hi Fuzz
Thanks for the reply and I see that there have been other posts on this subject which i shall have a look at. Your suggestion that there would be some benefit from heat transfer is probably correct but the main benefit from the augmenter tube is increased mass flow due to the fact that the jetex motor inside a tube acts as an air jet ejector, which entrains air thus increasing mass flow.
oneday is offline Find More Posts by oneday
Reply With Quote
Old Apr 19, 2016, 12:14 PM
oneday is offline
Find More Posts by oneday
Registered User
Dorset, UK
Joined Jun 2002
32 Posts
Thrust augmentation.

Just to give you some idea of the increase in mass flow that you can achieve with the air jet ejector principle, I have attached a couple of photos from back in the late '60's when I was working at lockheed Georgia company on fan engine duct noise reduction for the L500 aircraft. I had been tasked to come up with a test rig to that would simulate the engine fan duct intake velocities. The fluid dynamics guys reckoned that it would need a specially designed wind tunnel but that was not an economical solution and I remembered my jetex augmenter tube days and we built a small scale mock up which enabled us to predict that a 3/4 full size rig was possible. Tests were conducted for primary to secondary nozzle area ratios of between 1:100 and 1:16, 1:50 turning out to be the optimum. 300 psi air supply to the primary nozzle was provided from large air tanks that were normally used for the company's hypersonic wind tunnel and gave 30 secs of run time. I know that this description is opposite to what we want as it sucks and not blows but what comes through the front also goes out the back as thrust!!! It would be interesting to conduct some tests to find out if the very low primary to secondary ratios, that would be possible when using an EDF as the primary nozzle are worthwhile.
oneday is offline Find More Posts by oneday
Reply With Quote
Old Apr 19, 2016, 03:10 PM
killickb is offline
Find More Posts by killickb
killickb
killickb's Avatar
The Villages. Florida
Joined Jan 2005
2,423 Posts
Still have Jetex motors, fuel and augmenter tubes ----- no wick ! Want me to fire them up ? As I remember we used the augmenter tube more to prevent the doped tissue catching fire than for thrust .

Interesting project there one day ----- which pocket protector clad engineer are you, in that photo ?
killickb is offline Find More Posts by killickb
Reply With Quote
Old Apr 19, 2016, 04:08 PM
efflux RC is offline
Find More Posts by efflux RC
efflux RC's Avatar
United States, CA, Santa Clarita
Joined Aug 2009
10,394 Posts
Quote:
Originally Posted by oneday View Post
Back in the days of the dinosaur, Jetex produced what they called an augmentation tube which increased the mass flow. I wondered if anyone has tried using a standard EDF as the primary jet inside an outer duct. I guess that it wouldn't be practical to get the primary to secondary duct ratio ideal but who knows.

Tony
Having used Vortex tubes for cooling electrical enclosures and air multipliers in my work many years ago, I feel this (increasing static thrust) is quite achievable. Entrained air is exactly the principle (Coanda effect) of operation.
I thought about building one a number of years back, I just don't have the time to invest for development.

Good luck with your project.
.................................................. ..........
efflux RC is offline Find More Posts by efflux RC
Site Sponsor
Latest blog entry: Updated blog Oct 2014
Reply With Quote
Old Apr 20, 2016, 11:34 AM
oneday is offline
Find More Posts by oneday
Registered User
Dorset, UK
Joined Jun 2002
32 Posts
Thrust augmentation

Hi killickb
I'm the guy with my arms folded. Can't believe it was taken 37 years ago & also that I worked in the aerospace industry for 50 years, time certainly accelerates as you get older. I was lucky to work on some interesting research projects during that time and I've attached a few photos of one of them that was more like my hobby than work. A couple of years after the photos in my last post, I returned to UK to establish an experimental engineering division for Westland Helicopters to investigate co-axial rotor systems and ended up managing a rotary wing surveillance drone program. Back in the'70's there was very little equipment that was available "off the shelf" and we had to design and manufacture just about everything. Now days you can buy a multi rotor drone with GPS and HD video that can do most things better, except that the flight duration is much less, for a couple of grand whereas Wideye , the large one in the photo cost at least $300k and weighed 160 lb. I also got to test fly all three variants. The initial version used Veco 61 engines and started out weighing 10 lbs and ended up weighing 32 lbs and was used to develop the flight control system.
oneday is offline Find More Posts by oneday
Reply With Quote
Old Apr 20, 2016, 06:41 PM
Quorneng is offline
Find More Posts by Quorneng
Registered User
Joined Feb 2007
615 Posts
A thrust augmenter tube works on the principle of using a small volume, high pressure jet to entrain airflow to increase the overall mass flow.
A Jetex produces a small volume relatively high pressure jet. This is the exact opposite of an EDF.
Quorneng is offline Find More Posts by Quorneng
Reply With Quote
Old Apr 21, 2016, 10:22 AM
oneday is offline
Find More Posts by oneday
Registered User
Dorset, UK
Joined Jun 2002
32 Posts
Thrust augmentation.

I realise that there is a difference in the exit nozzle velocities between the Jetex and EDF's and that the entrainment efficiency would be significantly less if using an EDF as the primary nozzle but my original question was whether any worthwhile increase in thrust could be achieved. I guess I might just get around to checking it out but maybe any increase in mass flow, that is gained, would be counteracted by reduced exit velocity.
i.e. force/thrust = mass X velocity squared.
oneday is offline Find More Posts by oneday
Reply With Quote
Old Apr 24, 2016, 02:12 PM
tom bacsanyi is offline
Find More Posts by tom bacsanyi
Registered User
tom bacsanyi's Avatar
farmington hills mi.
Joined Sep 2006
926 Posts
Ok lets assume...........

Ok lets assume that we have an edf with an efflux V and a mass per second of M .

Then we fashion an "augmentor" tube that increases the mass flow per second to 2M..

Momentum in equals MV. and momentum out equals 2M times one half V if there are no losses in momentum

Thrust of the edf alone equals MA. We are taking a one second slice so A equals V divided by one second. What we said was that one second of mass flow accelerated to V. In the one second slice, thrust equals MV.

Similarly, thrust of the edf with "augmentor" would 2M times one half V which simplifies to MV. No gain!

So, augmentor means flow augmentor. Years ago it was fashionable to empty exhaust into an augmentor tube that was often referred to as a thrust augmentor. A little research revealed that it was to increase cooling airflow thru the cowl. A FLOW augmentor. Turbines often use an augmenter tube set up for cooling with no appreciable change in thrust.

In this example, the energy in the edf efflux is equal to M times V squared divided by 2. In the edf with augmentor, the energy in the efflux is equal to 2M times V squared divided by 4. Half of the energy was wasted in this example.

You need to recover high velocity efflux energy efficiently as in a turbofan to increase thrust. An edf is not a good candidate .
tom bacsanyi is offline Find More Posts by tom bacsanyi
RCG Plus Member
Reply With Quote
Old Apr 25, 2016, 11:52 AM
Erik v. Schaik is offline
Find More Posts by Erik v. Schaik
My project: FAIREY DELTA 1
Erik v. Schaik's Avatar
Uden Volkel, Netherlands
Joined Dec 2003
5,062 Posts
Quote:
Originally Posted by tom bacsanyi View Post
Turbines often use an augmenter tube set up for cooling with no appreciable change in thrust.

An edf is not a good candidate .
Interesting thread. It took me a while to understand the argumenter tube and while reading I thought it would be similar like a pool vacuum cleaner...

I think one needs to adress the P=M*V (power=mass*velocity) and this is where edf shows it's weakest side. The thrust/efflux ratio is far from desired and there are solutions to engeneer this already if one really wants to.

However, if you look at the thrust it'll be better to understand how thrust is generated. If you can increase the friction causing the thrust you'll be on track and this is a ARF product availabe (but not recognised as thrust increaser)
Erik v. Schaik is offline Find More Posts by Erik v. Schaik
Reply With Quote
Old Apr 26, 2016, 07:06 AM
stumax is offline
Find More Posts by stumax
The blade numbers go up to 11
stumax's Avatar
Sydney, Australia
Joined Aug 2002
4,497 Posts
Unfortunately the laws of physics are against us in the EDF world. Thrust requires power. For a given amount of power you can change the amount of thrust you get but you also change the speed of the exhaust blowing out the back - one goes up the other goes down, no defeating that basic rule of propulsion.

To produce thrust there is an infinite amount of options but basically it can be stripped back to going in one of two directions: efficient or really cool. Efficient means accelerating the largest possible disc of air by the smallest amount, relative to the aircraft's speed. This would be done using a large diameter prop. Really cool means accelerating a small disc of air a huge amount relative to the aircraft's speed. This is what an EDF unit does. Someone told me chicks dig EDF pilots, that's why I fly EDF.

Most EDF systems will have an exhaust velocity much greater than the aircraft's airspeed. Because of the small diameter exhaust it will need this high exhaust velocity in order to generate enough thrust. Make the inlet, fan & exhaust larger and the system will usually work better, just as long as there's enough exhaust velocity to maintain thrust at speed. It's always better to use the largest fan your inlets will feed (but no larger), and by "feed" I mean minimum of 100% FSA inlet area at the tip of the inlet (ie the "catchment area", not the area inside the duct). Size the exhaust to give you the in flight performance you want.

Stu.
stumax is offline Find More Posts by stumax
Reply With Quote
Old Apr 26, 2016, 09:14 AM
jumo004 is offline
Find More Posts by jumo004
Registered User
jumo004's Avatar
Joined Apr 2010
654 Posts
Quote:
Originally Posted by stumax View Post
Unfortunately the laws of physics are against us in the EDF world. Thrust requires power. For a given amount of power you can change the amount of thrust you get but you also change the speed of the exhaust blowing out the back - one goes up the other goes down, no defeating that basic rule of propulsion.

To produce thrust there is an infinite amount of options but basically it can be stripped back to going in one of two directions: efficient or really cool. Efficient means accelerating the largest possible disc of air by the smallest amount, relative to the aircraft's speed. This would be done using a large diameter prop. Really cool means accelerating a small disc of air a huge amount relative to the aircraft's speed. This is what an EDF unit does. Someone told me chicks dig EDF pilots, that's why I fly EDF.

Most EDF systems will have an exhaust velocity much greater than the aircraft's airspeed. Because of the small diameter exhaust it will need this high exhaust velocity in order to generate enough thrust. Make the inlet, fan & exhaust larger and the system will usually work better, just as long as there's enough exhaust velocity to maintain thrust at speed. It's always better to use the largest fan your inlets will feed (but no larger), and by "feed" I mean minimum of 100% FSA inlet area at the tip of the inlet (ie the "catchment area", not the area inside the duct). Size the exhaust to give you the in flight performance you want.

Stu.

Hi Stu,
GREAT info !!
I'm trying to understand the 'catchment area' that you speak of.
In the attached sketch,

Is the catachment area shown correctly ?

If the catchment area is, at minimum, 100% of the FSA does that make the inlet area even smaller and if so does that require a tapered inlet to get back to the diameter of the fan shroud ?

...or am I missing something ...

Thanks for your time !
jumo004 is offline Find More Posts by jumo004
Last edited by jumo004; Apr 26, 2016 at 11:34 AM.
Reply With Quote
Old Apr 26, 2016, 10:51 AM
ex-racr is offline
Find More Posts by ex-racr
AKA Terry Till
ex-racr's Avatar
Alexandria, VA
Joined Apr 2002
1,722 Posts
That's correct Jumo004. FSA is the area of the annulus defined between the motor tube and shroud.
ex-racr is offline Find More Posts by ex-racr
Reply With Quote


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Mini's augmented display glasses dll932 Life, The Universe, and Politics 3 Apr 10, 2015 02:17 PM
Discussion Aero Glass augmented reality dll932 Life, The Universe, and Politics 2 Aug 03, 2014 07:55 PM
Discussion Augmented thrust for EDF? sumobob Electric Ducted Fan Jet Talk 23 Mar 28, 2009 05:31 PM