the Wasp

My Feedback: (1)

so, with that above, according to OS, we should be running our engines on the ground around 8500 (even lower), so in the air our engines will unload around 9500/10,000

well I don;t know what i did here, I can't remove the lines

Jim

the Wasp

My Feedback: (1)

note that if we go back a few pages (LOL 30 or 40) we did jaw about unloading in the air

Jim

Rudolph Hart

Jim if you go back to you tube you will see a run in vid for the fa115 using an apc 16x6 which ends up pulling 9300 static.My own fa115 was tached using a mas 15x8 and static was 8800-8900 richened two clicks for a ground speed of 8600,this was directly after run in and minutes before the test flight.Don't skew off on to os two stroke stuff it ignores sr's salient and practical assessments of engine performance between the saito 100/115 and 125.If you have any questions or wonder how the maths stack up...address that directly,otherwise you are spouting suppositories,sorry,suppositions,that are not supported with research,facts,or experience on your own behalf.Therefore clouding the conversation in brown mist.

Does anybody have the math,or is there a formula/table to calculate prop tip speed for a given diameter eg,if you are in a shallow dive towards the ground and the 15x8 mas prop makes a huge boom i reason that the prop tips have gone supersonic,who agrees? or is there some other explanation.The reaction by bystanders to that sound everytime it happened on a low pass was jeezuz h

ps barry that guy flying the cub knew his ass from his elbow friend

Hobbsy

My Feedback: (102)

The first line from the numbers I got from Tachometer Readings, the guy tested two different props. All Saito 1.00's
10% WC fuel APC 15x6 rpm==9,500, same guy, Pro Zinger 15x6 rpm=9,200
15% WC fuel APC 15x6 rpm==9,800
20/20 fuel APC 16x4 rpm====9,800
30% CP fuel APC 14x6 rpm==10,300
15% CP fuel APC 14x8 rpm==9,300
30% CP fuel APC 15x6 rpm==9,900
20/20 ? fuel MA 14x7 three blade=9,500, same guy Graupner 14x7 three blade rpm=8,700

Hobbsy

My Feedback: (102)

http://www.rcuniverse.com/forum/tach...ease-post.html Long Saito 100 thread.

Captcrunch44

SrTelemaster150

Unless one wants to limit their flight envelope to hovering, I don't understand the logic of some guys propping a model aircraft engine at or near maximum RPM static. That would be like having a 6500 RPM stall convector on a street driven car with a mildly built SB Chevy.

In a slow airframe with lots of drag, I might prop for 9000+ RPM static with a medium block Saito. On something that is "slippery", I want more RPM cushion for the prop to unload without over revving as the speed increases. I typically prop my big block Saitos for 7500-8500 RPM static. Medium blocks I want another 1000-1500 RPM depending on the airframe.

SrTelemaster150

You can use the "Flying Speed" and "Perimeter Speed" functions in the calculator below to interpolate when/if your tips go supersonic.
Static Thrust Calculator - STRC

The 16 x 6 propeller turning 9300 RPM in your post above would have a tip speed of Mach .6

That said, a 16" prop would have to turn over 15000 RPM to go supersonic. Just like bullets however, the shape of the propeller tip will determine when the air moving across the surface exceeds 1145 fps.

Some blunt, round nose bullets (like a 45 ACP RN FMJ) go supersonic at as little as 900 fps, nearly 150 fps slower than the speed of sound at sea level.. I once won a $50 bar bet when a pistol shooter stated that the speed of sound was 900 fps due to this very phenomenon.

SrTelemaster150

That post just reminded me of how one of the prolific posters on this forum tried to chastise me in a post for criticizing the FA-125 I was trying to set up with CDI. It was spitting a 16 x 8 prop (even on CDI for crying out loud) after just a few moments of WOT. I've never had any other Saito spit a prop with CDI unless there was a catastrophic mechanical failure.

He emphatically stated that a 16 x 8 was "over propping" the FA-125 yet an FA-120S is sec'ed for up to a 16 x 10 (with GI no less) and the FA-120 has a stroke 1.2 mm shorter than the FA-125.

To be fair, it was -27F outdoors and my shop heater was barely keeping the room temperature warm enough for the methanol to vaporize in the intake. Still, I was not impressed at all with the FA-125 and with CDI it didn't make significantly better RPM, in proportion to the increase in displacement, than my CDI FA-91S when I dropped back to a 15 x 5 prop.

That 125 was the poorest performing Saito I've ever dealt with. In addition to the lackluster power output, it would not stabilize RPM at part throttle unless you advanced throttle a little above the desire RPM range and backed off slightly. I fiddled with ignition timing, as well as HSN/LSN settings but could never get a stable part throttle RPM without jockeying the throttle.

Hobbsy

My Feedback: (102)

Dear Valued Customer:As you may be aware, Tower Hobbies' parent company, Hobbico, declared bankruptcy in January 2018 and has initiated a sale process.We are excited to share with you that the RC brands and Tower Hobbies website that you have come to rely on over the years will continue. The Bankruptcy Court has approved the sale of Hobbico's RC business to Horizon Hobby, LLC. Horizon Hobby has been in business since 1985 and serves customers in the United States and around the World. Horizon Hobby also maintains a strong online presence and warmly welcomes Hobbico customers to its growing family. With this acquisition, Horizon Hobby looks to build upon Hobbico's great reputation for providing quality RC products to customers across the country. More information about Horizon Hobby can be found at https://www.HorizonHobby.com.

SrTelemaster150

Yeah, I got one from Omni Models too, but Horizon already has plenty of my information already.

i don't like the fact that Horizon is beginning to control a monopoly on our hobby.

Hobbsy

My Feedback: (102)

Saito .82 after new bearings, gaskets, spray bar and HS needle.

Fuel===Wildcat 10% full syn.
Plug===OS-f
Exhaust==Stock Saito
Prop= APC 14x6 Pattern Prop, RPM==9,650 Idle ===2,000
Prop=Xoar 14x6 RPM========9,450 Idle====2,150
Runs very smooth
Exhaust valve loosened a little
Intake valve tightened a little
Mike, I'll get it headed west on Monday.

SrTelemaster150

Is that a typo Dave? Your FA-82 is making FA-150 numbers

Hobbsy

My Feedback: (102)

Yes it was, I already changed it, I had 15x8 on the brain. I thought I'd better changed it before someone accused me of anointing it with oil and blessing it.

the Wasp

My Feedback: (1)

Pete, OS using a 2 st in that write up is just an example, all glow engine do have a practical RPM range.
the Cam's that are used in these 4st glow engines are called "High Ratio Rocker Cams", it's very easy to tell by looking at their Nose.. these Cams have less lift than a old style Mechanical Solid Tappet Cam, so they have a broader Nose than the older style Mechanical Cams, so they use a High Ratio Rocker Arm. because of this broader Nose these High Ratio Rocker Cam's utilize "More Area under the Curve",, these Cams are the closes thing you can get to a Roller Cam without the Roller, they create more low end power and more Mid Range than any other type of Flat Tappet Mechanical Cam, with all the reports of these Saito turning big props around 8300 and 8600 I certainly do not believe their peak Torque Point is around 9500,, just my beliefs

Jim

Captcrunch44

SrTelemaster150

Older Mopar V-8s used a larger diameter flat tappet that had a similar effect. By having a wider base they could run more aggressive ramps on the lobes. When hot-rodding the Chrysler slant 6, large diameter International Harvester lifters and modified Buick straight 8 rocker arms are employed to increase rocker arm ratio to maximize lift and duration with a given lobe profile.

blw

My Feedback: (3)

Facebook earned about $12.70 per person, per year. It is estimated each person will bring in $17 this year. That is billions which is what their profit margin is. Oh, that profit comes from selling our personal data. Not from banners or advertising. Just our personal info.

Hobbsy

My Feedback: (102)

Not from me, I dumped them about 3 weeks ago when I started getting reports from them of my PayPal activities. I hadn't OK'd that at either place. FB is just a big nuisance anyway.

Hobbsy

My Feedback: (102)

The Chisler slant six only had 4 main bearings, I always figured that it would be a little iffy souping one of them up. I had one in a 68 Dodge van with double doors on both sides. Other than installing a Holley Econo Master carb and MotoPlatt pointless ignition, I left it alone.

I also had an after market computer system on it I bought in Denver, Colo, it was a combination Cruise Control, fuel meter and outside temperature and engine temp. You don't get to do fun stuff like that any more. To set it up you put it in the Calibration Mode, drove past 3 mile markers, stopped and hit the Cal. button.

the Wasp

My Feedback: (1)

no way would my OS 61 turn those numbers with those props, and that engine must be lighter than my OS

Jim

SrTelemaster150

Captcrunch44

SrTelemaster150

It gets even better.

the Wasp

My Feedback: (1)

Li

yes, and you can boar out the Chevy SB too, and use Chevy BB cam bearings, this is a must-do for the Chevy SB when using these High Ratio Cams, Ford's Lifter diameter is larger than Chevy's, and Mopar's Lifters diameter is larger than Ford's (Cams are made to order) you can get these Cams to use ether Ford or Mopar Lifters, and in some cases Comp Cams do recommend using a mix of Lobe Profiles.. yes>, with these Cams you can use a given Profile on the Exhaust that uses a Ford Lifter while using a more aggressive Profile on the Intake that needs a larger diameter Mopar Lifter (or the other-way-around), you can easily get over .700" of Lift with a moderate Street Duration, but you will have to spend somewhere around $2500 for the Shaft Mounted Rocker Kit that has a Ratio over 1 to 2, and you better have the heads to match, I have always been a big fan of Mechanical Solid Lifter Cams


Jim