Its been a while since I timed the speed of a combat ship.. I'm Just wondering if anyone have the formula to calulate the speed of the plane using 35', 52.3'  & 60' lines?
 
 For example:
Flying at ___ft  from the ground, with ____ ft lines at level flight, ___ lap ___ sec = _____mph.

Thanks in advance.
 

Thanks for the infos. 

 I'll give it a try this weekend or the next flying day. I like the 75mph speed limit combat method with only timing just 2 laps though, I guess thats based on 60' lines, flown no higher then 8'?

I think most places state 10 foot minimum altitude for the speed timing.  Also not over 20 feet.  Amazing how fast 75 is when your get used to flying stunt planes.  DOC Holliday

More years ago than quite a few of the members have been alive, I piloted Rat Racers for a couple of racing teams (a few times -- the engines kept getting better and more expensive quickly -- too much so for limited budgets).  For best speeds, we pulled the handle in close to the chest when flying level, and kept it close in (raised to head level, more or less) for passing, to shorten the lines (at least, when speeds were not greatly different among the planes in the heat).  Most of the pilots already held their handles in two hands in those days (still running three-up at the time).

I can get a copy of an Excel speed chart for 60' lines, with various two-lap timing marks, calculated for speed, if it's wanted, I'll have it forwarded to your eMail, just PM me here with the address you want it sent to.  I think it's a fairly old Excel version, like in Office 97, if that's a problem. 

Yes,  60' lines but there is no height stated (or maybe a minimum of six feet ??) - in fact, you are allowed to walk a 3' radius circle with your arm fully extended to make it look slower.  Of course if you want to fly higher, it will make it look faster, so you  wouldn't really want to do that, unless you were plenty slow already.

I thought that I would take the unusual approach of actually looking up the rule regarding timing for 75 mph speed limit combat -- I guess we all need to read the book more often -- here is the text in the book

Para. 3.3.

 ....... During the timing, the aircraft
must maintain level flight at or above 15
feet. The pilots are allowed to walk
inside the pilots’ circle. If a pilot steps
outside the circle, he is to be warned and
then timed again.

........

So, 15 ft. minimum alt., walk a circle if you wish, as long as it is no more than the 3 foot radius of the pilot's circle. Using that rule, it would be easy to get an actual flight radius of about 66 feet, if you walk the outer edge and hold your hand at full arm extension.

There is no spec. for how many laps or what the actual time must be - the two laps in 6.85 seconds has just been our local spec. since anyone can remember, but there is nothing to prevent anyone from instituting a lower speed limit and enforcing it .... for that matter there is nothing preventing a higher speed limit either, except that shut-off's are required unless a 75 mph or lower speed limit is enforced.

Mike A

Thanks Don. 

It looks to be much more precise.

The point of the speed timing is to keep the speeds reasonable.  The faster the planes are the harder it is to fly a clean match, and the more intimidating it is to spectators.  We use 7.3sec/2 laps(an airspeed of a around 72 mph or so) and the thing I hear most often from spectators is "wow, they really are fast!", and "it must be really hard to fly that fast!".  The second point is to make sure both planes in a match are fairly close in speed, assuming both are running flat out.  75 mph looks really fast when the other plane has a rich run and is only doing 65.  But a plane doing 6.9 with a streamer is a lot faster than one that does 6.9 without a streamer, something like 83-84 mph vs 74mph.  That is what we look for, and the circle marshall has to keep a close eye on things to prevent speed creep and make sure that the matches come off cleanly.  That kind of speed advantage doesn't guarantee anything when you have to avoid midairs, and the circle marshal will be having a talk with you after the match about slowing it down.