Spinners Explained?
06-16-2008, 08:52 PM
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Spinners Explained?
I do not really understand the function spinners and what theories I should consider when deciding what size spinner is best for my airplane. I would be interested to know how they work (aerodynamically).
I have a H9 Arrow trainer with an O.S. .55AX and a 12X7 prop and a 2-inch spinner, but I am wondering if I should get a larger one.
I have a H9 Arrow trainer with an O.S. .55AX and a 12X7 prop and a 2-inch spinner, but I am wondering if I should get a larger one.
06-16-2008, 09:39 PM
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RE: Spinners Explained?
I think the main purpose of a spinner on a piston-engined model is to provide a connection to the drive cone of the starter. Secondarily, it is a matter of appearance. Not much concern for aerodynamics among the typical modeler.
06-16-2008, 10:21 PM
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RE: Spinners Explained?
Hi AstroDad,
From an aerodynamic perspective, the root of a propeller without a spinner is a flat surface facing the oncoming air. A flat forward facing surface will generate a large region of high pressure air, called a stagnation region, pressing on the surface (the summation of that pressure is drag). Using a spinner results in a much smaller stagnation region and therefore lower drag.
Since the inner portion of the propeller is not doing as much work as the outer portion of the propeller, a properly sized spinner will not have a major impact on the thrust that the propeller creates. However, if the spinner is over-sized, a useful portion of the propeller is covered, and the thrust is reduced accordingly. On the other hand, if the spinner is too small, drag will increase. If you stick to a spinner that is sized for your engine, it is likely well matched for your propeller as well.
One option that you always have is to experiment a little and fly with a few spinner sizes to see which one performs the best. You may find that the aerodynamic effects are minimal for your trainer, and you may just select the right spinner based on aesthetics alone
Cheers,
Rich
From an aerodynamic perspective, the root of a propeller without a spinner is a flat surface facing the oncoming air. A flat forward facing surface will generate a large region of high pressure air, called a stagnation region, pressing on the surface (the summation of that pressure is drag). Using a spinner results in a much smaller stagnation region and therefore lower drag.
Since the inner portion of the propeller is not doing as much work as the outer portion of the propeller, a properly sized spinner will not have a major impact on the thrust that the propeller creates. However, if the spinner is over-sized, a useful portion of the propeller is covered, and the thrust is reduced accordingly. On the other hand, if the spinner is too small, drag will increase. If you stick to a spinner that is sized for your engine, it is likely well matched for your propeller as well.
One option that you always have is to experiment a little and fly with a few spinner sizes to see which one performs the best. You may find that the aerodynamic effects are minimal for your trainer, and you may just select the right spinner based on aesthetics alone
Cheers,
Rich
06-16-2008, 10:29 PM
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RE: Spinners Explained?
Thanks for the info.
The manual for my OS .55 AX does not indicate what size spinner I should use, only says I should use one.
Since I have a high-wing trainer with typically large boxy fuselage , would it be best to I get a larger than normal spinner, one that is about the same width and height of my fuselage? That would be a spinner 3" to 3.5" with a 12" prop. Or would that be covering up too much of the prop?
The manual for my OS .55 AX does not indicate what size spinner I should use, only says I should use one.
Since I have a high-wing trainer with typically large boxy fuselage , would it be best to I get a larger than normal spinner, one that is about the same width and height of my fuselage? That would be a spinner 3" to 3.5" with a 12" prop. Or would that be covering up too much of the prop?
06-16-2008, 10:52 PM
#5
RE: Spinners Explained?
A 3" to 3 1/2" spinner on a 12" prop is pretty standard. Usually, the nose of the fuselage determines the diameter of the spinner. Your biggest concern is that the cutouts will clear the prop blades. You don't want the prop to touch the spinner at all, except where it seats against the backplate, of course. Just select a spinner than looks appealing on your plane.
So, you have an AX .55 on an Arrow 40? Wow, that's a lot of power. More than you'll ever need, but it should be fun.
David
So, you have an AX .55 on an Arrow 40? Wow, that's a lot of power. More than you'll ever need, but it should be fun.
David
06-16-2008, 11:17 PM
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RE: Spinners Explained?
ORIGINAL: rainedave
A 3" to 3 1/2" spinner on a 12" prop is pretty standard. Usually, the nose of the fuselage determines the diameter of the spinner. Your biggest concern is that the cutouts will clear the prop blades. You don't want the prop to touch the spinner at all, except where it seats against the backplate, of course. Just select a spinner than looks appealing on your plane.
A 3" to 3 1/2" spinner on a 12" prop is pretty standard. Usually, the nose of the fuselage determines the diameter of the spinner. Your biggest concern is that the cutouts will clear the prop blades. You don't want the prop to touch the spinner at all, except where it seats against the backplate, of course. Just select a spinner than looks appealing on your plane.
ORIGINAL: rainedave
So, you have an AX .55 on an Arrow 40? Wow, that's a lot of power. More than you'll ever need, but it should be fun.
So, you have an AX .55 on an Arrow 40? Wow, that's a lot of power. More than you'll ever need, but it should be fun.
06-17-2008, 09:53 AM
#7
RE: Spinners Explained?
Don't rule out taking your fuselage with you to the hobby shop. Like Dave said, the transition is whats important. Spinners in the U.S. come in 1/4" increments and you may find that the 2 1/4" or 2 1/2" is a better looking choice. Those are the sizes I normally use on a .40 size plane
06-17-2008, 10:31 AM
#8
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RE: Spinners Explained?
I read in a '50's Aeromodeller Annual that the most aerodynamically efficient spinner was one 1/5 the diameter of the propeller. i.e. 2 in for a 10 in prop. Sounds about right. @2.5 in for 12 in prop.
06-17-2008, 11:37 AM
#9
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RE: Spinners Explained?
In full scale flight, spinners are used to aid in smoothing the airflow around the nose of the aircraft (along with making the aircraft more aesthetically pleasing). As you know, many aircraft features that are necessary for full scale aircraft are not for our models - spinners are one such unnecessary feature in our small models (unless you're a pylon racer). Choose one that looks nice and meets up with the curve of the fuselage properly.
06-17-2008, 10:15 PM
#10
RE: Spinners Explained?
I like to build 1970's pattern planes. They typically have very narrow noses and were designed to use 2" to 2 1/2" spinners. The old Top Flite Super M 11x7.5's, etc., will fit in these spinners fine, but today's 12" APC's won't without some cutting. Some APC's have very heavy hubs, IMO.
So, I stocked up on NOS Super M's!
So, I stocked up on NOS Super M's!
06-21-2008, 06:08 AM
#12
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RE: Spinners Explained?
ORIGINAL: JimCasey
Check your AMA safety code. Spinners are required. I suppose that getting hit with a spinner is better than being speared with a prop stud. Neither sounds very appealing.
Check your AMA safety code. Spinners are required. I suppose that getting hit with a spinner is better than being speared with a prop stud. Neither sounds very appealing.
Acutally, either a spinner or a safety nut.
06-21-2008, 07:22 AM
#13
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RE: Spinners Explained?
ORIGINAL: da Rock
Acutally, either a spinner or a safety nut.
ORIGINAL: JimCasey
Check your AMA safety code. Spinners are required. I suppose that getting hit with a spinner is better than being speared with a prop stud. Neither sounds very appealing.
Check your AMA safety code. Spinners are required. I suppose that getting hit with a spinner is better than being speared with a prop stud. Neither sounds very appealing.
Acutally, either a spinner or a safety nut.
06-21-2008, 08:26 AM
#14
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RE: Spinners Explained?
ORIGINAL: Nathan King
Yeah, I think the rule is more to prevent thrown props than to make the airplane more pleasant to get hit by.
ORIGINAL: da Rock
Acutally, either a spinner or a safety nut.
ORIGINAL: JimCasey
Check your AMA safety code. Spinners are required. I suppose that getting hit with a spinner is better than being speared with a prop stud. Neither sounds very appealing.
Check your AMA safety code. Spinners are required. I suppose that getting hit with a spinner is better than being speared with a prop stud. Neither sounds very appealing.
Acutally, either a spinner or a safety nut.
For sure..........
Getting hit by the safety nut or the spinner certainly is "just the tip of the iceberg" so to speak. And the iceberg gonna make you feel real bad.
06-23-2008, 03:03 PM
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RE: Spinners Explained?
Shoot, I remember reading about a case from England in the early nineties where someone was hit in the side of the head by a non-powered glider coming in for a landing... the person was killed instantly. There's nothing fun about getting hit by any airplane.
06-23-2008, 04:38 PM
#16
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RE: Spinners Explained?
Some years ago when we were flying Control Line Slow Rat Racers, the first practice flight of the season my son brought the airplane in a little hot for a pitstop and I got a crankshaft end buried in the web of my thumb. Took some stitches, but no permanant damage other than a scar. With a prop nut or spinner I would have gotten just a good bruise.
06-23-2008, 07:56 PM
#17
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RE: Spinners Explained?
Don't let a spinner lull you into a false sense of security. I witnessed a 2" spinner, 40 sized engine, and metal motor mount get buried into the backside of a guy's upper leg to the firewall.
This was a Formula One pylon racer, so it was a rear exhaust / rear intake racing setup, but messy never the less. Although the heat from the engine did stop most of the bleeding.
This was a Formula One pylon racer, so it was a rear exhaust / rear intake racing setup, but messy never the less. Although the heat from the engine did stop most of the bleeding.
06-23-2008, 10:10 PM
#18
RE: Spinners Explained?
If spinners are required by AMA safety code, then how do you explain the 2.7 million AMA sanctioned combat matches that have been flown over the past 50 years with just a bare 1/4" prop nut hanging out?
At 80mph+, which just about any .40 sized sport model is capable of, the difference between getting hit by a spinner nut or crankshaft stud won't have much impact on the outcome.
I'm impressed with photos of the old pre WWII planes with the integral prop/spinners..........and still with all the flying wires and other junk hanging out.
At 80mph+, which just about any .40 sized sport model is capable of, the difference between getting hit by a spinner nut or crankshaft stud won't have much impact on the outcome.
I'm impressed with photos of the old pre WWII planes with the integral prop/spinners..........and still with all the flying wires and other junk hanging out.
06-24-2008, 07:08 AM
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RE: Spinners Explained?
> Check your AMA safety code. Spinners are required. <
Can anyone actually point out where this is found in the AMA rules? I just reread the safety regulations online and there is no mention of this. And the idea that there is some benefit to a pointed spinner entering your flesh versus a crankshaft thread seems silly. Are we dealing with an "aero legend" here?
Can anyone actually point out where this is found in the AMA rules? I just reread the safety regulations online and there is no mention of this. And the idea that there is some benefit to a pointed spinner entering your flesh versus a crankshaft thread seems silly. Are we dealing with an "aero legend" here?
06-24-2008, 07:33 AM
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RE: Spinners Explained?
A little off subject, I fly in my Club Combat League, we fly Avengers with 40-46 sized engines; I know, a little over powered; anyways, we tend to use 2-3" spinners, not for aerodynamics but to help protect the Carb and engine from damage in a midair, the spinners take the hit, not the carb, a spinner is cheaper to replace than a busted off carb.
06-24-2008, 08:04 AM
#22
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RE: Spinners Explained?
Just looked through the safety code. Didn't see anything about spinners or safety nuts. Here's the general section.
2008 Official
Academy of Model Aeronautics
National Model Aircraft Safety Code
GENERAL
1. A model aircraft shall be defined as a non-human-carrying device capable of sustained flight in the atmosphere. It shall not exceed limitations established in
this code and is intended to be used exclusively for recreational or competition activity.
2. The maximum takeoff weight of a model aircraft, including fuel, is 55 pounds, except for those flown under the AMA Experimental Aircraft Rules.
3. I will abide by this Safety Code and all rules established for the flying site I use. I will not willfully fly my model aircraft in a reckless and/or dangerous manner.
4. I will not fly my model aircraft in sanctioned events, air shows, or model demonstrations until it has been proven airworthy.
5. I will not fly my model aircraft higher than approximately 400 feet above ground level, when within three (3) miles of an airport without notifying the airport
operator. I will yield the right-of-way and avoid flying in the proximity of full-scale aircraft, utilizing a spotter when appropriate.
6. I will not fly my model aircraft unless it is identified with my name and address, or AMA number, inside or affixed to the outside of the model aircraft. This does
not apply to model aircraft flown indoors.
7. I will not operate model aircraft with metal-blade propellers or with gaseous boosts (other than air), nor will I operate model aircraft with fuels containing
tetranitromethane or hydrazine.
8. I will not operate model aircraft carrying pyrotechnic devices which explode burn, or propel a projectile of any kind. Exceptions include
Free Flight fuses or devices that burn producing smoke and are securely attached to the model aircraft during flight. Rocket motors up to a G-series size may be
used, provided they remain firmly attached to the model aircraft during flight. Model rockets may be flown in accordance with the National Model Rocketry Safety
Code; however, they may not be launched from model aircraft. Officially designated AMAAir Show Teams (AST) are authorized to use devices and practices as
defined within the Air Show Advisory Committee Document.
9. I will not operate my model aircraft while under the influence of alcohol or within eight (8) hours of having consumed alcohol.
10. I will not operate my model aircraft while using any drug which could adversely affect my ability to safely control my model aircraft.
11. Children under six (6) years old are only allowed on a flightline or in a flight area as a pilot or while under flight instruction.
12. When and where required by rule, helmets must be properly worn and fastened. They must be OSHA, DOT, ANSI, SNELL or NOCSAE approved or comply
with comparable standards.
Academy of Model Aeronautics
National Model Aircraft Safety Code
GENERAL
1. A model aircraft shall be defined as a non-human-carrying device capable of sustained flight in the atmosphere. It shall not exceed limitations established in
this code and is intended to be used exclusively for recreational or competition activity.
2. The maximum takeoff weight of a model aircraft, including fuel, is 55 pounds, except for those flown under the AMA Experimental Aircraft Rules.
3. I will abide by this Safety Code and all rules established for the flying site I use. I will not willfully fly my model aircraft in a reckless and/or dangerous manner.
4. I will not fly my model aircraft in sanctioned events, air shows, or model demonstrations until it has been proven airworthy.
5. I will not fly my model aircraft higher than approximately 400 feet above ground level, when within three (3) miles of an airport without notifying the airport
operator. I will yield the right-of-way and avoid flying in the proximity of full-scale aircraft, utilizing a spotter when appropriate.
6. I will not fly my model aircraft unless it is identified with my name and address, or AMA number, inside or affixed to the outside of the model aircraft. This does
not apply to model aircraft flown indoors.
7. I will not operate model aircraft with metal-blade propellers or with gaseous boosts (other than air), nor will I operate model aircraft with fuels containing
tetranitromethane or hydrazine.
8. I will not operate model aircraft carrying pyrotechnic devices which explode burn, or propel a projectile of any kind. Exceptions include
Free Flight fuses or devices that burn producing smoke and are securely attached to the model aircraft during flight. Rocket motors up to a G-series size may be
used, provided they remain firmly attached to the model aircraft during flight. Model rockets may be flown in accordance with the National Model Rocketry Safety
Code; however, they may not be launched from model aircraft. Officially designated AMAAir Show Teams (AST) are authorized to use devices and practices as
defined within the Air Show Advisory Committee Document.
9. I will not operate my model aircraft while under the influence of alcohol or within eight (8) hours of having consumed alcohol.
10. I will not operate my model aircraft while using any drug which could adversely affect my ability to safely control my model aircraft.
11. Children under six (6) years old are only allowed on a flightline or in a flight area as a pilot or while under flight instruction.
12. When and where required by rule, helmets must be properly worn and fastened. They must be OSHA, DOT, ANSI, SNELL or NOCSAE approved or comply
with comparable standards.
06-24-2008, 08:21 AM
#23
RE: Spinners Explained?
It has been awhile since I looked at the book, but there used to be a recommendation for spinners, not a mandate.
Anything that I've ever found on a RC pylon racer looked like it was there for a very good reason. Last time I saw a FAI version it had a carbon prop with integral carbon spinner. I assume there has to be cast in thread insert of some kind [chunk of aluminum with heli coil maybe] to keep it attached to the engine at 30,000 rpm. It looked like a $100 part that might net a half plane difference at the finish line.
Anything that I've ever found on a RC pylon racer looked like it was there for a very good reason. Last time I saw a FAI version it had a carbon prop with integral carbon spinner. I assume there has to be cast in thread insert of some kind [chunk of aluminum with heli coil maybe] to keep it attached to the engine at 30,000 rpm. It looked like a $100 part that might net a half plane difference at the finish line.
06-24-2008, 12:24 PM
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RE: Spinners Explained?
I prefer the Dubro spinner nuts. They are quick to get on/off, survive most crashes, and give you a good surface to put your starter cone on. They come anodized in different colors too.