confusing imperial system
 

I need a spinner nut for one of my planes but I do not understand the measurements given by tower hobbies

for example

SPECS Shaft Size: 1/4-28
Weight: 4oz
Diameter: 1"
Length: 1.5"

( http://www2.towerhobbies.com/cgi-bin...8&I=LXL715&P=K )

what is 1/4-28 in metric and is this both the shaft diameter and lenght?


also


SPECS Shaft Size: 8x1.25mm
Weight: 2oz
Diameter: 7/8"

( http://www2.towerhobbies.com/cgi-bin...8&I=LXL736&P=K )

I'm guessing that the eight is the diameter but what does 1.25mm describe?



The engine I need this for has a 6.2mm diameter and without the prop and all it´s 32.8
in length, what would that be in that system?

(also I know the links to those nuts isn´t maby what fits the engine but they are examples)

RE: confusing imperial system
 

Yes..it is all too confusing.....

which engine is it for.... that might be quicker....

I'm sure someone here has it and would know right away which spinner is better.....

RE: confusing imperial system
 

¼ - 28 is a standard SAE thread, with a quarter inch shaft diameter and 28 threads per inch. No metric nut will fit those threads.

M8 x 1.25 is a Metric standard for an 8mm diameter shaft. The thread pitch is 1.25 mm per thread.

Are you sure that 6.2mm shaft isn't actually a quarter inch? There are thread pitch gauges made in metric and SAE, with which you can determine the threads.

Good luck,
Dave Olson

RE: confusing imperial system
 

well I can't be sure 'cos I don´t have the engine or the manual but if my memory serves my right then it is a .52 4-stroke engine


well now that you say so it is probably a quarter inch shaft



that about covers it, thanks people

RE: confusing imperial system
 

Yeah, they don't make a 6.2mm... just a 1/4" and a 6mm... take a look at these two Dubro spinner nuts, Tower lists the compatible engines on each of these pages... these Dubros are one of the best spinner nuts IMO...

[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXE158&P=7]Dubro 1/4-28 Spinner Nut[/link]

[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXE160&P=7]Dubro 6mm Spinner Nut[/link]

RE: confusing imperial system
 

Hmmm...might be putting the cart before the horse......

I would think you would want the engine....or at least know which one it is, before you bother with the spinner.....

but that is just me

RE: confusing imperial system
 

Umm... sounds to me like he's already got the engine...

RE: confusing imperial system
 

Now I'm confused


From post #4:

RE: confusing imperial system
 

Haha! Me too... didn't see his second post... my post hit 40 seconds after his second post, so I never saw it until now! :)

RE: confusing imperial system
 

what I meant to say is that I can't be sure because I don't have the engine with me or the manual

RE: confusing imperial system
 

Hi
I'm Swedish and have he same dilemma with the Imperial vs. metric conversions.
If you buy both the engine and spinner nut from Tower hobbies, you don't need to know the meassurment in metric, just buy the 1-4/28 spinner nut if that's th same meassurment as the prop shaft of your engine. (You can find many engine manuals online on the manufacturers websites)

Something I must advice you to buy if you'll ever build a kit is the "Hobbico builders ruler".
This thing is the most useful builder tool for us 'non-imperial' kit builders building a US made kit.

Just pick up a dowel or wood part and testfit it in the ruler, until it fits a slot, all slots are marked with the Imperial meassurment, perfect!



http://www.hobbylinc.com/gr/hca/hcar0482.jpg

RE: confusing imperial system
 

Hi!
Well, nearly all 3,5cc-8,0cc engines use this 1/4x28 axle tread dimension. It is only MVVS and Rossi (Nova Rossi) that use a metric thread (6mm, 7mm or 8mm).
As has been said before; 1/4" is the diameter of the axle in inches and 28 is the treads per inch.(Inch is tum in Swedish).
Hope the world could get rid of the inch system soon;)!
If you want an aluminum spinner nut I can make one for you.

Regards!
Jan K
Sweden
http://hem.passagen.se/airracing

RE: confusing imperial system
 

1/4-28 means that the outside diameter of the shaft is 1/4 inch. The 28 means that there are 28 threads per inch, i.e. if you turn the nut 28 turns it will progress up the shaft 1 inch. Gosh, wouldn't it be nice if everyone adopted the metric system, life would be so much easier.

RE: confusing imperial system
 

I bet if the French wouldn´t have invented it then the Americans and the British would be using it


and I found an old nut that is 1/4-28 and it fits perfectly, now I know for sure what size I'm looking for

also put one of those rulers in my order, it'll come in handy

and one question since I have this thread here, do heavy spinner nuts make much of a difference on idling?

RE: confusing imperial system
 

.

RE: confusing imperial system
 

I can just say that you'll find that ruler handy many times when you read an instruction book or blue print and it says "use the 1/16-28 XYZ Dowel" :)

I think a heavy spinner nut is more for balancig (and good looks), than having any major impact on idling.
A longer prop though shoud improve idling since the engine gets loaded with more g-force and want to tick over again and again and again.... (Inertia? )

RE: confusing imperial system
 

well my airplane is also tail heavy so....

and isn't inertia sorta the same thing as momentum?

RE: confusing imperial system
 

Yes a heavy hub does slightly help lower the minimum idle speed.

RE: confusing imperial system
 

Lesson 1: Newton's Laws of Motion
Inertia and Mass
Newton's first law of motion states that "An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force." Objects "tend to keep on doing what they're doing." In fact, it is the natural tendency of objects to resist changes in their state of motion. This tendency to resist changes in their state of motion is described as inertia.


Inertia = the resistance an object has to a change in its state of motion.
Newton's conception of inertia stood in direct opposition to more popular conceptions about motion. The dominant thought prior to Newton's day was that it was the natural tendency of objects to come to a rest position. Moving objects, so it was believed, would eventually stop moving; a force was necessary to keep an object moving. But if left to itself, a moving object would eventually come to rest and an object at rest would stay at rest; thus, the idea which dominated people's thinking for nearly 2000 years prior to Newton was that it was the natural tendency of all objects to assume a rest position.

RE: confusing imperial system
 

I did a little search about momentum

"Momentum can be defined as "mass in motion." All objects have mass; so if an object is moving, then it has momentum - it has its mass in motion. The amount of momentum which an object has is dependent upon two variables: how much stuff is moving and how fast the stuff is moving. Momentum depends upon the variables mass and velocity. In terms of an equation, the momentum of an object is equal to the mass of the object times the velocity of the object."

sorta the same thing isn´t it

RE: confusing imperial system
 

Sure sonds same but there's gotta be a twist to it.
I guess we'll get some more input on this one as soon as a RC-flying, physics professor dropps by :)

RE: confusing imperial system
 

Momentum is energy that a mass has that is in motion.
Inertia is resistance to a change in velocity.
A heavy hub doesn't have alot of inertia for its weight(mass) because it is small in diameter. A hub that has more of it's weight(mass) in it's outer circumference has more inertia(like a flywheel). The heavy hub does not effect the idle much because of it's relatively low inertia.[&:]