I have an EDF-55 from GWS, and I wan't to add working reverse thrusters like the ones on Boeing 717-200's (clam shell ones). Anyone have any suggestions, it may not have been done before, but I would like to create a working prototype.

The way the real turbine reverser's work is pretty simple. It's just something that goes in front of the thrust path and directs it the other way. On real airliners it's, hmmmm, sort of flap like sheets that close in on the turbine and it's thrust. Now all you have to do is figure out a way to configure your set-up. Don't forget you need a passage way for the thrust to go the opposite direction.

Yeah, its a little tricky to configure the set up, but once I get it to work correctly, I will post pictures of it.

I'm not trying to rain on your idea, but a thrust reverser will really only work on a turbine not DF.

DF and turbines opperate differently in obvious ways and some not so obvious ways. With a DF you escentally have a prop turning in a housing. It pulls itself on the air deflection from the blades spinning. It does not move forward from the thrust of the air comming out of the tail. This air is strickly a byproduct of its function. Turbines, on the other hand, do not move forward from a spinning fan. The fan is strickly for compressing inlet air into the turbine. It move forward because of the expansion of gas in the chamber is forcing it forward. To recap, DF has an equal amount of air going in the inlet as it has coming out. The turbine has only a fraction of air going in as it has going out (20 to 1). This makes the difference when using a reverser.

At best, the reverser will only kill the efficieny of the DF and make it not go forward any faster, but it will never make it go in reverse. Obviously the reversing force is what slows the aircraft down.

I'm sure it will look cool, but I wouldn't expect it to slow the aircraft.

correctly put Joe. Curious to know what actual in flight effects would be experienced trying it. I would imagine a level of in flight resistance to some degree could possibly have a weird effect to what he is trying to conceive. Perhaps minor reverse motor rotation??

http://www.youtube.com/watch?v=Vd0zxSxIhOQ

I already have installed clam shell reversers on my EDF already, and tested them, they really do work, although they aren't mechanized yet, but they reversed the thrust.[sm=cool.gif]

That is cool. That is a good explanantion of the reversers, however, it is not how the thrust is made. It is simply reversing the air that is exiting the engine/cowling. Wether the air is made from a jet engine or a prop is irrevelent. Reversers will work great/same on a DF or jet.

There is little loss of thrust when causing a back pressure to the exhaust of any type of pump or fan. Air or water.

Restrict the intake at all, and complete loss of pumping occurs. The intake end, always " stalls " much quicker than the exhaust end.

Edit: The air blast should push the clam doors back to the normal position. So all you need are 2 servo arms Epoxied to the clams which are mounted on a SMALL, REAL SMALL shaft. about .030" diameter. Mount the shaft in some small pieces of drilled out wood to spread the load & wear. . Then have the 2 strings tied to a seperate servo channel. It should be doable.



PM me when you have it done. [sm=thumbup.gif]

Thanks, I will do that, I will be going to the hobby store this week sometime, I will then be able to get some suitable materials.[8D]

I would like to correct a few things here.

I think you are mixing up a few types of “jet engines.” The two most common types of jet engines are turbofans and turbojets or true jets. A turbofan, typical of a modern airliner, produces thrust both by the spinning fan on the front and exhaust from the turbine. The fan is connected to the drive shaft of the engine which is also connected to the compressor and turbine.

Air is drawn into the engine both by the fan and the compressor once inside it is mixed with fuel and ignited, which rapidly expands the mixture, then sent through the turbine blades at the rear which spin the compressor and fan. Air exiting the engine both from the fan and the exhaust creates the thrust.

Turbojets or true jets work on the exact same principle, minus the fan, and create all of their thrust from the hot gases exiting the exhaust.

In any jet the same amount of air (mass) exits as enters. There aren’t any non-Einsteinian processes going on in the engine, mass is not being created. It is true however that the volume of air exiting is much larger as it has expanded immensely, but the mass is the same.

According to Mr. Newton: F=MA, so the mass of the air and its acceleration is what is creating your thrust. It does not matter how that air is being moved, it can be a propeller, ducted fan, jet, fan, flapping wings, etc. Ultimately, if you can put something into the wind stream that directs the airflow in the opposite direction reverse thrust will be created. If you were so inclined, you could create some kind of louvers that redirected the wash from a prop to create reverse thrust.

Hi Joe, Some food for thought here about props and airfoils. A propeller/airfoil never 'pulls' itself forward, it's a low pressure event that lifts or 'pulls' the top of an airfoil. A higher pressure result happens under it which lifts or 'pushes'.

In terms of props, it's ALWAYS called thrust.

http://www.grc.nasa.gov/WWW/K-12/airplane/propth.html

Volume is a function of density (realted to pressure and temperature in compressible flow which definately applies to gas-turbines). Since P2 and P5 (inlet and exhaust pressure) are both very nearly equal to ambient, and more obviously because all the air in has to leave (again, we're not Gods that can void basic physics), the inlet and exhaust gas volumes are equal when the added fuel mass is ignnored.

Thrust reversers work by redirecting the gas-flow velocity vector (momentum of the moving air) so there's a net forward component. In high-bypass turbofans this is done by redirecting on the fan flow by moving baffles with downstream blocker doors. Anyone that's flow a jet manufactured in the last twenty years knows what this looks like. In this type of reverser, the core flow (producing the HP to turn the fan) is unchanged. In low-bypass fans for straight turbojets (think 737-200's and 727's with JT8D's and Sabreliners with JT15D's), 'clamshell doors are used to accomplish the same effect but in those applications the ENTIRE exit flow is redirected.

It's actually only a small net forward thrust that results due to the difficulty in trying to efficiently turn a low volume high-Mach flow or high volumn low-Mach flow. There's also a big penalty in inlet flow stability which is why use of reversers below a certain speed (say around 60 knots) is forbidden.