voodoodb

My Feedback: (98)

Is there an advantage to useing a bypass system on our turbines over the conventional bell mouth pipe?

thanks

jason

My Feedback: (1)

you will get a few answers that differ on this subject but my experience shows that if you had two models the same sat on the runway, one with a bypass and one without, you will find generally the one with a bypass has a faster top end speed and also carries the energy better in the vertical, out the bottom of a loop and so on. A lot also depends on the airframe being used. A good argument for a model that would make good use of a bypass could be one with big inlets and lots of internal formers acting as air brakes. Some also say that a bypass forces high speed cold air into a hot tailpipe which makes it expand and gives better high speed thrust. Others will say that you will get a better static thrust without a bypass. Maybe this is true because the engine could get a better supply of air through gear doors etc and not sucking up though possibly long inlets without the ram air effect you get in the air.

One experience that springs to mind was about 12 years ago when me and a friend both built BVM Mavericks. My friend had a very good 12.75lb Wren 54 and mine was a 12lb Wren (I built and tested both engines so I know the figures were correct) My maverick had a bypass and my friends didn't. Although he had 3/4lb more thrust than me, my Maverick was way way faster. Also this was in the days of regular flame outs and mine was seen to retain it's speed much better.

I don't think anyone on here can honestly give you proper calculations on what the difference will between both installs as there are so may variables in so may airframes, although some may try and baffle you with bullpoo pretending they can..

Jason

Kevin_W

My Feedback: (1)

I dug up my response to this question from several years ago.

Pro's
1. Less drag, smoother airflow through the inside of the airplane than a non-ducted installation.
2. Cleaner install (if done properly)
3. Less chance of equipment inside the plane coming into contact with the turbine (either fod in the intake, or melting onto the side of the case).
4. More protection for the turbine in a crash
5. Might also help avoid having fuel spray come in contact with hot engine parts in some crashes (less chance of a fire)
6. Easier for inexperienced builders to set up a bypass system that is pre-engineered without making mistakes.

Con's
1. More difficult turbine access.
2. Much more difficult to scratch build using a bypass because the ducting and fuel tanks need to be designed and built to fit the airplane.
3. After engine shutdown the radiant heat from the turbine will be contained inside the bypass, necessitating the use of a fan to help with cooling (yes I realize this is a good idea even if you don't run a bypass, but it is pretty much mandatory with one).
4. Takes up more space inside the airplane.
5. Higher cost.
6. Some propane start turbines are more likely to "BANG" on startup inside a bypass (usually doesn't hurt anything, but it gets everyone's attention).

I'm sure there are more on both sides...

Springbok Flyer

I have been flying these things since 1997. Initially I too built them without a bypass, but for the past 10 or so years I have only built my jets with bypasses.

I concur whole-heatedly with the previous two guys and will add only the following:

Pro's:

- During a hot start you have far more chance of saving your airframe and may at worst have to replace the bypass.
- During a hot start you only have to direct the fire-X into the intakes and don't run the risk of damaging anything else during the process.
- Jets with a bypass, uses less fuel, I have done the test and proved it - timed, startup to dead stick.

Con's:

- Sometimes I don't get to build a jet I like because I cannot fit a bypass.....too bad, I won't be buying it.

Cheers,

Jan