Advantages/Disadvantages of a Bypass on turbine installs
12-09-2012, 12:20 PM
#2
RE: Advantages/Disadvantages of a Bypass on turbine installs
my opinion.
advantages:
-better case cooling (forced flow)
-smoother, quieter sound in the air (= higher efficiency, but not really notable at our scale) (My BARF with a P-80SE probably quieter than an equivalent size EDF)
-keeps loose crap from the cabin from being sucked by the inlet
-cleaner, neater install
-if there is an engine fire, the bypass gets it before the airframe. May not be able to to save the engine, but save the airframe.
disadvantages
-dead weight
-can be a pain to make it work
-in order to get true beneftis, you need the right size for your engine. There is no true one size fits all. Then again, if not sized correctly for the application, why use it a all (see #1 disadvantage)
-Only one supplier with multiple sizes to match your engine/airframe (but please correct me if Im wrong)
-in the case of an engine fire, you would only see it by the paint blisters forming on the cap
advantages:
-better case cooling (forced flow)
-smoother, quieter sound in the air (= higher efficiency, but not really notable at our scale) (My BARF with a P-80SE probably quieter than an equivalent size EDF)
-keeps loose crap from the cabin from being sucked by the inlet
-cleaner, neater install
-if there is an engine fire, the bypass gets it before the airframe. May not be able to to save the engine, but save the airframe.
disadvantages
-dead weight
-can be a pain to make it work
-in order to get true beneftis, you need the right size for your engine. There is no true one size fits all. Then again, if not sized correctly for the application, why use it a all (see #1 disadvantage)
-Only one supplier with multiple sizes to match your engine/airframe (but please correct me if Im wrong)
-in the case of an engine fire, you would only see it by the paint blisters forming on the cap
12-09-2012, 12:49 PM
#3
My Feedback: (1)
RE: Advantages/Disadvantages of a Bypass on turbine installs
My reply from this thread several years ago: http://www.rcuniverse.com/forum/m_67...tm.htm#6747797
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).
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).
12-09-2012, 08:59 PM
#5
RE: Advantages/Disadvantages of a Bypass on turbine installs
Do bypasses imporve performance? At very high speed, if they are designed correctly.
You have to make sure the turbine, bypass and tailpipe are working together correctly, In my experience you can do this statically by checking operating temperatures, not so easy to do in the air.
You have to make sure the turbine, bypass and tailpipe are working together correctly, In my experience you can do this statically by checking operating temperatures, not so easy to do in the air.
12-09-2012, 10:36 PM
#6
RE: Advantages/Disadvantages of a Bypass on turbine installs
ORIGINAL: DiscoWings
If it was strictly in terms of performance, do bypasses improve performance?
Thanks
If it was strictly in terms of performance, do bypasses improve performance?
Thanks
From an aerodynamic point of view, a well designed bypass installation can considerably reduce the overall parasite drag of the airframe. This will improve several performance indicators including increased speed, decreased fuel consumption, reduced noise levels, better glide ratios etc.
Most turbine models today have bags of excess power, more than enough to overcome the increased drag of an open system at the speeds we fly at. We don’t worry too much about fuel consumption, noise or efficiency’s in general.
However, as Matt says, if you really want to go fast, you need to keep parasite drag to a minimum, and a correctly designed internal bypass system is a good way to do this.
As an aside, full size aeroplane designers place a lot of emphasis on cruise speed, fuel consumption, noise, glide angles, and airframe efficiency, which is why the type of open installation we use in models would never be seen on a full size aircraft.
Just my thoughts..
Roger
12-10-2012, 06:16 AM
#7
RE: Advantages/Disadvantages of a Bypass on turbine installs
I actually went through a step by step process on the SR-71, where early test flights were just the engine firing into the tail pipe.
Then 3 flights with inlet liners, and bypass.
Then added the inlet spikes infront of the engines.
Each step along the way added 10-15 mph, and let me pull the engine throttle back 10% or so on each step.
The inlet liners and bypass's I would have expected. I was a bit surprised how adding the spikes in front of the engines not only improved performance, but changed the sound when rounding a corner, and hearing the front of the plane. Just a good example, of you need only a certain amount of air for a certain engine, plus a certain amount for cooling, and anything beyond that scooped up, is just drag.
Lance
Then 3 flights with inlet liners, and bypass.
Then added the inlet spikes infront of the engines.
Each step along the way added 10-15 mph, and let me pull the engine throttle back 10% or so on each step.
The inlet liners and bypass's I would have expected. I was a bit surprised how adding the spikes in front of the engines not only improved performance, but changed the sound when rounding a corner, and hearing the front of the plane. Just a good example, of you need only a certain amount of air for a certain engine, plus a certain amount for cooling, and anything beyond that scooped up, is just drag.
Lance
