I am building a plane to be powered by a Saito 180. This plane will not be fast, but rate of climb is important. I know that static thrust is best when using a low pitch, large diameter prop. In this case, I am planning a 18x6 prop. But I have no good idea of how many pounds of static thrust this will give me. Are there any tables or charts that provide this information?

Static Thrust Calculator - STRC

Of course the best way is to connect a fish scale to the tail (with a safety line) and measure the actual thrust under load.

The only accurate way to do that is measuring thrust hanging downward and subtracting the weight of the airframe.

Or you can measure the thrust while letting the airplane slowly move forward (on a smooth surface of course), then measure the thrust while pulling the airplane backward. Split the difference for the true static thrust.

But of course the thrust generated varies as the airspeed of the airplane changes. The only time the static thrust matters is in a hover.

That's not completely accurate. It does not account for gravity which is still acing on the object.

When computing bullet energy, part of the equation is a factor to account for gravity. It would be no different here.

How many pounds of thrust does it take to overcome gravity and move the object?

Quote:

I know that static thrust is best when using a low pitch, large diameter prop. In this case, I am planning a 18x6 prop.

if you go to the "Tach Reading Page" you will see many people posting what their Saito 180 turns for RPM,

for what you said I agree for the most part, that is when comparing 2 props of a given brand and type, such as an APC 17X8 to an APC 18X6. but what you will find is that a good quality Wood prop pulls much harder than a Plastic prop of the same size. for example>, my Magnum 180 4St turns a Xoar 17X6 at 8600 RPM, and an APC 17X8w Sport turns 8800 (both on 15% Magnum fuel) so I suggest on your Saito for you to run a prop in these sizes with 20% Nitro or less (APC 17X8w, or a 17X6 good quality wood prop), I'm betting if you run an APC 18X6 with 15% you will turn around 8200. so with that if you want to run an 18 inch prop you will most likely have to use less pitch than 6" unless you burn more Nitro. don't get me wrong, if you wish to run at a lower RPM, then please do so, many people do, and engines run smooth and constant when loaded like that, they just work a little harder

see the Tach Reading page here,
Tachometer Readings - RCU Forums

Jim

The APC 18x6W produces about 17,8 pounds of thrust at sea level on a standard day on the ground. So as you get moving say 30 mph you are down to 12 pounds of thrust and 60 mph you around 4 pounds of thrust if the engine stays at the same 8000 rpm. With this prop I think you will see around 10,500-11,000 in the air at full power and producing around 8-9 pounds of thrust.
So for max climb this prop may not be the best and you need to try other props smaller and more pitch maybe to find what you like the best. APC makes a 17x8 stnadard and 17x8N that are good props to look at. The 17x8N APC prop makes less thrust at 8,000 rpm on the ground but at 60 mph it is make around 7 pounds of thrust at the same 8,000 rpm. With this prop depending on the plane you can fly as fast as the 18x6W but at a reduced power setting.

That's too many RPM for an FA-180.

I'm going to try a 20x6 on mine, but it's modified for higher compression and it has CDI. It turns an 18x8 @ 8450 static.

Telemaster I bet you will be surprised by your inflight rpm.

Thrust of a propeller has nothing to do with the weight or position of the motor/plane or propeller. It is simply the force that a propeller will exert at a given altitude density and is directly related to its RPM.

Static thrust is just that, the amount of force generated from a static position and zero wind speed in any direction. Measured using a strain gauge with the engine/plane held level in place.

Dynamic thrust is directly related to the speed through the air mass. At a certain point after the prop unloads the max rpm will become constant. The faster the plane moves through the air mass the lower the Dynamic Thrust will be until the sum of the drag on the aircraft balances out the dynamic thrust then maximum airspeed on the straight an level is achieved. We measured this with the same strain gauge with the engine mounted on a sliding test stand in a wind tunnel. Air speed was set with a manometer calibrated for air speed to 60 mph. Dynamic thrust fell off in direct proportion to airspeed.

In a climb or dive the mass of the aircraft will be a contributing factor to the max speed but only as long as the dive or climb is maintained. Returning to straight and level flight will return to the balance of Dynamic thrust and sum of the drag and the previous airspeed.

my numbers were static, on the grown.. if he is going to stick with an APC I still think he would be better off with an 18X5, the 18X5 should keep his engine up around 8800 Static, and that is were the guys have reported their Saito's 180s like to be, as well as my Magnum 180 did

Jim

Why do so many seem to want to over rev their Saito engines.

I estimate about 9500 RPM at 70 MPH air speed.

True speed of a model is sometime difficult to determine without a radar gun. Size, sound and distance from the model can really skew our perception of how fast it’s really traveling.

Rent/borrow a radar gun you will be surprised at the real speed. Most war birds top out at 60 to 80 MPH.

Perception of scale speed vs. scale speed has been an ongoing discussion in judging realism in flight for years.

sorry for the edit !

I don't think 8800 is over Revving a 180 4St Glow engine, then again I think 8000 is a bit low, but that is just my opinion, so I could be wrong,, if some one is up around 10,000 with 10% Nitro then I would agree they are not efficient.

when I researched cams for my friend's 400 Chevy (460HP) I read that an engine's Peak Torque Point is where the engine's Power is most "efficient", yet with that I also read that a racer can benefit if he over Rev's his Peak Torque Point by 200 to 400 RPM (BTW, Mr, Isky said that)

if you go and look on the Tach Reading page you will see some guys where using a Wood Prop that loads more than the APC 17X8w, yet they were Revving their Saito 180s close to what my engine was with the APC, yet some were Revving higher than my magnum would,,, so in my opinion I do not think 8800 is over revving a Satio 180,, plus, Saito gives Prop Size/RPM numbers

example, look at my Magnum 180 4St Static Numbers

APC 17X8w 8800
Xoar 17X8 8200

Note that in flight the APC accelerated my plane faster as well as producing a faster top speed, therefor I knew my engine was over Propped with the Xoar, and the engine's Peak Torque Point was somewhere between 8200 and 8800

but like I said LOL just my opinion I could be wrong

Jim

oops, to add, my engine did run smoother with the Zoar

Jim

8800 RPM is not over revving an FA-180. But that is static and people have mentioned 10,500 and 11,000 in the air after the prop unloads at speed.

THAT is over revving!

You "over rev" an engine when making a 1/4 mile pass to get higher in the power band in the next gear after the shift or you want to get your maximum HP onto the track 300' before the traps. We aren't shifting gears here or over revving for .5 seconds before shutting down..

A better example would be using 4.56 gears in a road race when you know that you will be over revving for extended periods at top speed.

I think I know a little about peak HP and power/gearing.

My 2006 Charger 5.7 Hemi made Maximum HP @ 6250 (426 RWHP and 460'# RWTQ @ 4600) I shifted @ 6500 but the .323 gears (4.55 final drive ratio in 3rd gear) had me crossing the traps @ 6250. I would have liked to have seen 6500 @ the traps. A 3.31 (4.67 FDR in 3rd) would have been near perfect.

Bear in mind this is a 4300# car at the line and it was driven, sometimes as much as 800 miles to the track.It got up to 26 MPG on the hi-way.

What the heck has the family sedan got to do with a model airplane motor get back on topic will ya and keep the bragging about the family putt putt for another forum. Who cares how your clunker limped down the track.

Dennis

I was responding to the post below which refers to peak HP/TQ and shift points.

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

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?

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.

airraptor, I reread his post, and I agree with you, he said he wants "good" Climb Rate, not a Constant Rate

Jim

Hi!
A 18x6 will be just fine for a high wing trainer type plane ! The cut-and-try metod is what most of us use.