9 replies to this topic

[Mark Crowley]

I was setting up Trackmate on a new 55' Oval track at Raytown International Raceway today.  When setting up the scale speed I noted we were running scale speeds of 250 mph or so.  I  checked the Trackmate setup on the 155' Ogilvie Blue King and we had it set to 1/24 scale speed but the track length was set to the default 30' so mph.  I changed the King track length to 155' and now instead of laps at 100 mph they are 500 mph.

Do other tracks use the high scale speeds setting or do you artificially set a more realistic speed?  We ended up setting the scale of both tracks to 1/8 scale instead of 1/24 to make the speeds appear more reasonable.  A 5 second lap on the King is now 169 mph.

I personally don't don't pay attention to mph and only look at lap times when I practice, but a lot of people like to quote their speeds.

Thanks

Mark

[jimht]

How long is a scale hour?   

Anyway....to get a sort of relevant mph in the SRT program, I double the track length.

[gjc2]

How long is a scale hour?   

 

 

When someone at the raceway asks me how fast the cars go I'll point to one running on the track and say "that fast" 

[Samiam]

To get a perspective on how fast various types of cars go I'll run them on the Drag Strip. It may not glean the top performance of these non drag cars but it does give relative actual MPH numbers.

 

As George pointed out, people want to know numbers. They see a Retro car going around the track and are impressed with it's speed. Then a Gp-27 Wing car zips by and they're speechless. It would be nice to have accurate and  real MPH numbers. Be it average MPH for the lap or top speed. 

 

I brought up the idea of having so called "trap speed" options for a new race control program. One could be top speed on the main straight. The other could be the entire  back end. Say from the entrance of the Dead Man to the exit of the Lead On.   These numbers could give racers important info for tuning their cars. Even if it is just on Orange. Readout of both time and real MPH would be ideal.

[Mark Crowley]

Unless I have my math wrong.  A slotcar that travels 155' on a King in 5 seconds is traveling at a real speed of just over 21 mph. x 24 = 507 scale mph

 

A 155' King at 1/24 scale represents a 155 * 24 = 3720 scale feet. / 5280 = .70 scale miles long which in Nascar terms would be a short track = to Richmond that is .75 miles long.  IIRC Richmond speeds avg about 115 mph

 

Jim:  Not sure how SRT measures scale speed but doubling the length of the track but Trackmate that would give a scale speed of 1014 mph.

Mark

[Phil Hackett]

No such thing as "scale" times as Jim H. hinted.

 

Some quickies for ya....

 

Multiply the FeetPerSecond by .6818 to get MPH.

 

Multiply MPH by 1.4667 to get FeetPerSecond.

 

Since time is not scaled and track/cars are, the slot cars should traveling the same times over the same distances as the real things. They're not. Slot cars are MUCH faster.

 

Richmond's (.75 mile) lap record is 176mph (IndyCar), run in 15.3 seconds... current King tracks (.7 scale mile) are routinely lapped at 4 seconds or quicker.

 

HO cars are insanely faster than 1/24th.

 

Now for "scale" g-force.....  

[Robert BG]

The preference I've seen across the board from RC to slots is for real MPH.Scale speeds are associated with cheap RC/toy sets trying to look faster than they really are.

[Marty N]

For 24 scale drag racing we multiply the measured speed by 2.4. The time by 10. It works out like this.

 

Real AA/FC running 4 flat runs @  330 mph.

 

Scale AA/FC runs .400 seconds at 137.5 mph.

 

.4X 10 = 4.00 and 137.5 * 2.4 = 330 mph.

 

Rule of thumb in real cars is track length divided by ET will be pretty close to the mph.

 

Real car 1320 / .4 = 330 mph

 

Scale car 55 / .4 = 137.5

 

The math works and the rule holds.

 

155’ in 4 seconds by this method is a lap average 63.4 scale MPH. Seems it could be a fair representation for 7/10 mile and that many turns.

 

155 * 24 = 3720 scale feet. 4 seconds times 10 equals 40 seconds. 3720 feet / 40 seconds = 93 fps which is again 63.4 mph scale. So where does the 10 come from? Kinematics. Just a ratio of time to the scale distance for linear acceleration.

 

Australian Blue King record of 1.592 seconds gives a scale average lap of 159.31 mph.

 

A 220’ high banked oval run in 1.72 seconds would give 209 mph. Scale mile at scale speed.

 

Not saying it’s a scientific fact. Saying it’s fun. Gives it some realism.  

 

[zipper]

With scale  models in liquid environment the speed is multiplied by square root of the scale , 1/24 factor is about 4.9. (Froude)

[Marty N]

With scale  models in liquid environment the speed is multiplied by square root of the scale , 1/24 factor is about 4.9. (Froude)

 

It's speed divided by the square root of the length X body force. Body force it the force that acts within the entire volume of a body. Inertial force​ of liquids are affected by temperature and rate of shear. Viscosity. aka, a fictitious force. That quality that makes it look as if it isn't following Newton's second law of motion when in reality it is. It just has to be accounted for.

 

It, the Froude number, is used in determining the ratio of the flow inertia to the external field. Study turbulence and drag ratio in incompressible liquid systems like ship hulls and drive screws. Like the Reynolds number for gasses it used to determine the velocity point where flow shifts from laminar to turbulent under a particular set of conditions that effect the "external field" or body force. Not for scaling speed. In doing so such things as propulsion screws can be studied in scale to note the cavitation point of a screws shape for instance.