Determining Static Thrust ?
05-31-2017 | 06:31 PM
#26
Senior Member
I'm not trying to fight with you !! I understand that a Drag Race is different, I used-to street race back when a Muscle Car was a Muscle car not a Race Car, I was just making a statement to show a relative to over revving in the air,
as for your statement about over revving in flight at 10,500 and 11,000 "THAT is over revving",, (note that there is a 2,200 RPM difference between the number I used "8,800" and 11,000 that you pointed out for Over Revving),, to me, I don't find 11,000 overly excessive in flight (that is if the reports are truly accurate), look what Saito themselves says in the link, their 180b engine will turn an APC 16X8 at 9300, well you have 3 choices for that number,
1) Peak Static Number for that Prop
2) Tuned for Flight Number, for that Prop
3) an Over Revving Number in Flight for that Prop
So, is Saito suggesting that you tune your Engine with an APC 16X8 to turn 7100 for Flight on the ground so it will unload to a peak of 9,300 in the air, I don't think so. even if Saito is suggesting that 9,300 is a Peak RPM and you should tune around 8,800 for Flight, again it will unload around 10,500 or 11,000 as you say people have reported,, in the link below Saito suggests for a Peak RPM up to 10,000 and I think that is a Peak Static Number,, so we know that 9,300 with an APC 16X8 is a Peak Static Number for that Prop and we should tune a bit below that for flight,
to add, if you think 11,000 is Over Revving in the air, why is Saito saying you can turn a Prop as small as an APC 15X8, I'm betting an APC 15X8 will turn up around 10,000 Static, tuned at 9,600 for flight will git you over revved to 11,800
https://www.horizonhobby.com/product/storefronts/airplane-engines-15042--1/saito-engines/180b-%28new-case%29-aac-w-muffler%3A-bk-saie180b
don't hate me because I'm beautiful, hate me for my opinion
Jim
as for your statement about over revving in flight at 10,500 and 11,000 "THAT is over revving",, (note that there is a 2,200 RPM difference between the number I used "8,800" and 11,000 that you pointed out for Over Revving),, to me, I don't find 11,000 overly excessive in flight (that is if the reports are truly accurate), look what Saito themselves says in the link, their 180b engine will turn an APC 16X8 at 9300, well you have 3 choices for that number,
1) Peak Static Number for that Prop
2) Tuned for Flight Number, for that Prop
3) an Over Revving Number in Flight for that Prop
So, is Saito suggesting that you tune your Engine with an APC 16X8 to turn 7100 for Flight on the ground so it will unload to a peak of 9,300 in the air, I don't think so. even if Saito is suggesting that 9,300 is a Peak RPM and you should tune around 8,800 for Flight, again it will unload around 10,500 or 11,000 as you say people have reported,, in the link below Saito suggests for a Peak RPM up to 10,000 and I think that is a Peak Static Number,, so we know that 9,300 with an APC 16X8 is a Peak Static Number for that Prop and we should tune a bit below that for flight,
to add, if you think 11,000 is Over Revving in the air, why is Saito saying you can turn a Prop as small as an APC 15X8, I'm betting an APC 15X8 will turn up around 10,000 Static, tuned at 9,600 for flight will git you over revved to 11,800
https://www.horizonhobby.com/product/storefronts/airplane-engines-15042--1/saito-engines/180b-%28new-case%29-aac-w-muffler%3A-bk-saie180b
don't hate me because I'm beautiful, hate me for my opinion
Jim
I think its funny a guy that estimates his in flight rpm and tells another guy that has telemetry showing real in flight numbers that is over revving the engine.
To Brian the OP start with the 18x6 get some flights on the plane and then try some other props and see what you like. Sometimes a big low pitch prop doesn't climb the fastest. What I mean by that is if you have a normal big plane like say cub a prop in the 6-7 inch pitch range may climb better than a prop with a 4-5 inch pitch. The plane will fly faster on the large pitch and climb better as it climbs on the wing. Look at the weight lift competition planes built by colleges and most are in the 5-7 inch pitch range on direct drive engines. One other thing to look at here is your flying style is different from everyone in here so find the best prop for your plane and your style and enjoy.
Talking about your mustang and how to shift it from 3rd to 4th, how does that help the OP?
To Brian the OP start with the 18x6 get some flights on the plane and then try some other props and see what you like. Sometimes a big low pitch prop doesn't climb the fastest. What I mean by that is if you have a normal big plane like say cub a prop in the 6-7 inch pitch range may climb better than a prop with a 4-5 inch pitch. The plane will fly faster on the large pitch and climb better as it climbs on the wing. Look at the weight lift competition planes built by colleges and most are in the 5-7 inch pitch range on direct drive engines. One other thing to look at here is your flying style is different from everyone in here so find the best prop for your plane and your style and enjoy.
Talking about your mustang and how to shift it from 3rd to 4th, how does that help the OP?
3rd line up from the bottom. Pretty straight forward if you ask me.
https://www.horizonhobby.com/product...3A-bk-saie180b
05-31-2017 | 06:36 PM
#27
Senior Member
Telemaster- the math works against what you are saying, plus I think your gravity concept errs too since it is only pushing down on the bullet and not opposing travel.
The prop efficiency formula, which leads to prop performance, contains velocity and Velocity. One is what we call static thrust, so you can see that static thrust is only half the story. The other velocity is all the air being rammed through the prop disc area by forward airspeed. The hovering example is valid and is only static thrust. Plus, you have some rotary wing aerodynamics robbing the prop of thrust. The main thing is tip vortices and the other is ground effect when close to the grass.
The prop efficiency formula, which leads to prop performance, contains velocity and Velocity. One is what we call static thrust, so you can see that static thrust is only half the story. The other velocity is all the air being rammed through the prop disc area by forward airspeed. The hovering example is valid and is only static thrust. Plus, you have some rotary wing aerodynamics robbing the prop of thrust. The main thing is tip vortices and the other is ground effect when close to the grass.
05-31-2017 | 07:24 PM
#28
gee, if an APC 18x8 unload's and over revs in the air by 1000 RPM, and Saito recommends a prop as small as a 15x8, I have to wonder how much a 15x8 would over rev in the air
Jim
Jim
05-31-2017 | 10:59 PM
#29
My Feedback: (66)
If telemaster wants to think his engine has never been over 10,000 so be it. I have run many of my saito engines over 11,000 on the ground with no issues in the air and I have run them on 55% nitro too. I think I know their limits lol Some manuals are written to keep engines in a low power safe set up so their isnt any warranty issues. These are bad when a new guy asks a question and gets a million answers and he never asks a question again.
06-07-2017 | 12:45 AM
#31
Senior Member
15 x 8 @ 9300 RPM 68*F generates 11.94# of static thrust and absorbs 2.213 HP
You think that might be a typo on Horizon Hobby's site?
So maybe they meant 16 x 8.
16 x 8 @ 9300 RPM 68*F generates 15.54# of static thrust and absorbs 2.865 HP
Sound more reasonable?
Lets plug in an 18 x 8 @ 7900 RPM as I have observed with my FA-180 with glow ignition.
18 X 8 @ 7900 RPM generates 17.86# of static thrust and absorbs 2.813 HP
Hmmm, 15% more static thrust and more RPM in reserve for higher air speed. Seems the 18 x 8 is more efficient.
So now lets plug in the RPM numbers observed for my CDI stock FA-180 and the various high compression versions with CDI.
Otherwise stock FA-180 with CDI
18 x 8 @ 8000 RPM generates 18.32# of static thrust and absorbs 2.921 HP
FA-180/FG-57 piston 11:1 CR with CDI;
18 x 8 @ 8150 RPM generates 19.01# of static thrust and absorbs 3.088HP
FA-180 .032" deck reduction 12.8:1 CR CDI;
18 x 8 @ 8300 RPM generates 19.72# of static thrust and absorbs 3.262 HP
Same engine with 12mm FA-220 big bore carburetor and ported intake manifold with CDI;
18 x 8 @ 8450 RPM generates 20.44# of static thrust and absorbs 3.442 HP
If I up the nitro from 15% to 30% and reduce the lube content to 8% the same engine will turn the 18 X 8 @ 8850 RPM
18 x 8 @ 8850 RPM generates 22.452# of static thrust and absorbs 3.954 HP
Last edited by SrTelemaster150; 06-07-2017 at 02:13 AM.
06-07-2017 | 02:18 AM
#32
Senior Member
06-07-2017 | 07:07 PM
#33
You think that might be a typo on Horizon Hobby's site?
http://www.saito-mfg.com/single-file...80foreign.html
16 x 8 @ 9300 RPM 68*F
Sound more reasonable?
Sound more reasonable?
Jim
Last edited by the Wasp; 06-10-2017 at 08:05 PM.
06-11-2017 | 03:12 PM
#36
Senior Member
I don't know,,, could be,,,, although Saito's Home Page also suggest the same prop size
http://www.saito-mfg.com/single-file...80foreign.html
no-p, not to me, as I said a few people have reported that their Saito 180 pulled 8,800 to 9,100, I'm sure a 15X8 would rev up higher, I'm betting closer to 9,600,, 9,800, ,, again, I'm just wondering how much a 15X8 would unload in the air
Jim
http://www.saito-mfg.com/single-file...80foreign.html
no-p, not to me, as I said a few people have reported that their Saito 180 pulled 8,800 to 9,100, I'm sure a 15X8 would rev up higher, I'm betting closer to 9,600,, 9,800, ,, again, I'm just wondering how much a 15X8 would unload in the air
Jim
Would you put a 6200 RPM stall converter on a street driven small block Chevy? Same thing as propping a Saito FA-180 @ 10,000 RPM static.
As far as how much ANY prop will unload in the air? That would depend on the airframe. It would unload a lot more on a P-51 @ 80 MPH than it would on a J-3 doing 40 MPH..
I think an 18x8 at 7900 RPM static would unload a lot more than a 15x8 because @ 7900 RPM it would already be in the fat part of the power band ready for more, not gasping for air at the top end.
The 15x8 @ 10100 RPM would generate 14# of thrust while the 18X8 @ 7900 RPM would generate 18#. What's the point in the 15x8 anyway?
I think that the 15x8 would be a great prop for an FA-115 CDI and that's what I plat to try on mine.
At 9300 RPM it will absorb 2.2 HP and that's about what I estimate the FA-115 with CDI and 15% nitro will make.
Last edited by SrTelemaster150; 06-11-2017 at 03:32 PM.
06-11-2017 | 03:35 PM
#37
Senior Member
06-11-2017 | 05:54 PM
#38
My Feedback: (3)
After hearing a few engines unload an experienced person should have an idea of how a jump from 10k to 11k would sound on their engine. I'm sure you have a wealth of knowledge built up over the years Jim and I'm not looking for new arguments to have with someone.
06-11-2017 | 11:43 PM
#39
I'm sure you have a wealth of knowledge built up over the years Jim
After hearing a few engines unload an experienced person should have an idea of how a jump from 10k to 11k would sound on their engine.
I'm not looking for new arguments to have with someone.
Jim
06-11-2017 | 11:48 PM
#40
Would you put a 6200 RPM stall converter on a street driven small block Chevy? Same thing as propping a Saito FA-180 @ 10,000 RPM static.
As far as how much ANY prop will unload in the air? That would depend on the airframe. It would unload a lot more on a P-51 @ 80 MPH than it would on a J-3 doing 40 MPH
I think an 18x8 at 7900 RPM static would unload a lot more than a 15x8 because @ 7900 RPM it would already be in the fat part of the power band ready for more, not gasping for air at the top end.
What's the point in the 15x8 anyway?
sorry for the edit, I just want to get my thoughts straight for you guys
Jim
Last edited by the Wasp; 06-12-2017 at 11:29 AM.
06-12-2017 | 08:30 PM
#43
off topic
I feel he was informed well
Jim
Last edited by the Wasp; 06-12-2017 at 08:34 PM.
06-13-2017 | 01:31 AM
#44
