swampyankee
Chief Master Sergeant
- 3,993
- Jun 25, 2013
Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
What is the tip speed of turbo jet rotating parts?
And it's tip speed relative to the airflow that's important, not relative to the rest of the engine, which should be a bit higher, but not supersonicIt depends, but typical is probably 350 to 400 meters per second. Greater tip speeds permit greater stage pressure ratios
Please note that most, or almost all (leaving myself an out) jet engines in supersonic aircraft have ducts that are shaped/configured to reduce the incoming airflow to subsonic, even if still high, speeds. There may be a few exceptions like the SR-71?
Please note that most, or almost all (leaving myself an out) jet engines in supersonic aircraft have ducts that are shaped/configured to reduce the incoming airflow to subsonic, even if still high, speeds. There may be a few exceptions like the SR-71?
The intake had to supply air to the engine with minimum pressure loss and distortion and at the speed dictated by the engine, namely about Mach 0.4. It had to do this at all flight conditions.
The SR-71 is a dual-cycle engine - changes operation from a turbo-jet to a ram-jet at high speeds.
Doing a search comes up with many super sonic propeller experimental planes.So a 1 meter diameter rotor, at 12k rpms would have a tip speed of 628 meters per second. Bit faster than speed of sound.
Centrifugal forces are crazy in turbine / jet engines.
An interesting article.
http://www.energy.kth.se/compedu/webcompedu/WebHelp/media\Lecture_notes\Papers\Srinivasan_97-GT-533.pdf
Doing a search comes up with many super sonic propeller experimental planes.
I'm always amazed that folks will say it can't be done, with out any effort to think maybe it can be done.
Doing a search comes up with many super sonic propeller experimental planes.
I'm always amazed that folks will say it can't be done, with out any effort to think maybe it can be done.
Large reciprocating engines can certainly save fuel in the airline industry by reducing people's desire to fly in planes powered by them and vacationing closer to home. Fewer flights means more fuel saved
Longer fights with more noise/vibration in the plane and more noise near the airport are not what customers (or airlines) want.
The high performance fuel that allowed the R-3350 and R-4360 to make the power they did is not coming back.
Trying to make the same power at lower boost levels to suit available fuel means either higher rpm or larger displacement engines (bigger cylinders or more of them) or both.
Modern material might mean somewhat lighter engines (Titanium connecting rods and Titanium crankcases? )Modern fuel injection may help, modern ignition systems may also help. Modern sparkplug technology may help with less frequent sparkplug changes but aircraft plugs are not the same as car spark plugs.
but start to be competitive you need 5-6000hp engines for a 4 engine plane for long distance.
last big western turboprop airliner.
View attachment 506028
four 5730hp engines.
cruising at 320 kt T.A.S . (25,000ft) , 13,500 r.p.m. ; 2,780 s.h.p. ; 3,033 e.h.p. ; 0.398 Ib/e.h.p./hr . From Flight magazine 1958 article.
The EHP is a bit of an exaggeration as that is counting exhaust thrust. However it helps explain why the big reciprocating engines faded away for new aircraft.
It also shows that the target for a new reciprocating engine would be much harder to hit.
That was late 1950s turboprop and weighed about 2400lbs (less than 2/3rds what a R-4360 or turbo compound R-3350 did).
A new PW 150A turbo prop makes a bit over 5000hp and weighs under 1600lbs.
They also have a considerable amount of reserve power ( engine is flat rated to 37 degrees C, not the old 15 degrees C) and is allowed to use the 5 minute rating for 10 minutes in the event of an engine failure on take-off with no engine life penalty.
https://www.easa.europa.eu/sites/default/files/dfu/TCDS PW150 series issue 01_20141119_1.0.pdf
This is what a new reciprocating engine in the airliner market would have to match or beat.
View attachment 506029
You would have to reduce the weight of the old reciprocating engine by a factor of 4 while keeping the same power and vastly reducing the maintenance requirements and vastly increasing the overhaul life.
Oh boy,
http://www.continentaldiesel.com/typo3/fileadmin/_centurion/pdf/Datenblaetter/DS_CMG_2_CD-155.pdf
View attachment 506072
155hp max power and 97hp best economy power from a 294lb engine (weight does NOT include coolant or radiator)
WOW! I am impressed!
Of course the Continental Io-360 (360 cu in air cooled) can make 195hp max from 305lbs dry
http://www.continentalmotors.aero/u...gines/Gasoline_engines/300AvGas-SpecSheet.pdf
and the Lycoming O-320 series can make 150-160hp from 280-307lbs dry weight
Both gas engines have been around for decades. Some of the Lycoming O-320s have an overhaul life of 2000 hours.
Both engines can be made in models with slightly reduced compession to suit less than 100LL fuel.
I also like this tidbit.
"Through key improvements, continuous testing and field experience, both the CD-135 and CD-155 are now rated to a TBR of 2,100 hours. The TBR of the CD-155 increases from 1,200 hours to 2,100 hours, the CD-135 from 1,500 to 2,100 hours. In addition, the gearbox and timing chain will be rated for 1,200 hours once EASA issues the final paperwork for these components."
Highlighting by me. The old flat air cooled engines don't use a gear box in the basic models (or any that have been made in decades, the reduction gear versions were put to sleep decades ago if they ever existed in these sizes).
In a number of ways, the maintenance costs are less for piston engines. When I worked for a helicopter company, we used to budget around $135 per hour for lifed items and overhaul on the 250-C20 (420 shp)(that was cheap, because we did all the work in-house) in 2008. The turbine had a heavy inspection and lifed components at 1750 hours. The compressor was 3500 hour TBO
Now, with inflation, I see that an IO-720 (400 shp) base exchange price is around $66,000, with a 1800 hour TBO. This equates to just under $37 per hour. Although the TBO is greater for the turbine engine, the lifed components effectively nullify this.
It is on the Continental diesel engines. And offered on some of the gasoline ones as well. Personally not sure if I would want electronics controlling the engine in a plane I'm flying, but thats me.Those costs above look like purely overhaul costs to me and therefore ignore the periodic maintenance costs of each type.
. I am not aware of any FADEC piston engines but I have not worked on pistons for years.
Just as long as the FADEC system doesn't use Windows everything should be OK
Just as long as the FADEC system doesn't use Windows everything should be OK