Lap times are irrelevant!

[steven yampolsky]

Who invented this messed up measure of seconds per lap? This is one of those sneaky measures that up until recently I did not fully understand. For most of my models I tended to set up the model for a 5.2 sec lap times never realizing how drastically the number changes when the lines change just by 5 feet! Did you know that if you cut the lines from 67 down to 62 feet, all other things being equal, the model speed will go down from 5.2 to 4.8 sec/lap!

to help me understand the impact of line length and lap times, I created a spreadsheet that I would like to share with you:

https://doc-04-84-docs.googleusercontent.com/docs/securesc/ha0ro937gcuc7l7deffksulhg5h7mbp1/agf7jrllbfsfu405qfa3svk1rmq3lupb/1351310400000/13116471100394470931/*/0B9jqv0bA7wfdOHV4TjVVWlBCTG8?e=download

I've included things like wing span and length of pilot's arm in order to experiment with the impact model size or the style of holding the handle(against the chest or streched out). Turns out, model wingspan is irrelevant and how you hold the handle can impact your lap time by AT MOST 0.1 sec/lap.

Enjoy

[Brett Buck]

Who invented this messed up measure of seconds per lap? This is one of those sneaky measures that up until recently I did not fully understand. For most of my models I tended to set up the model for a 5.2 sec lap times never realizing how drastically the number changes when the lines change just by 5 feet! Did you know that if you cut the lines from 67 down to 62 feet, all other things being equal, the model speed will go down from 5.2 to 4.8 sec/lap!

    Changing the line length by 5 feet is a HUGE change and I don't think it's very surprising that it would alter the lap times significantly.

    To first approximation your title is right, but it is useful to help in the trimming processes. Change something, fly it, pulls harder - but oops, the engine sped up, too, and the lap time went down .1 sec, so you learned very little about the trim change

     Brett

[Jim Thomerson]

The usual rule of thumb is a change of one foot in line length makes a change of 0.1 sec in lap time.  I think that is about right for the line lengths we usually use to fly stunt airplanes. I couldn't get your spreadsheet to load.

[Igor Burger]

may be you have to slow it down little bit on shorter lines ... or even better, you have to find proper line lenght for particular model

... BTW I fly the same lap times on 15ft lines and also on 65ft lines :- ))))))))) (no, not the same model :- P)

[Bill Little]

Hi Steven,

I think Brett said it best.  Lap times are very useful in trimming.  I fly the model, and once it is flying as I like it, I get a lap time.  This is for checking it later, to see if I am in the ball park under different conditions.  Each model needs its own "air speed" to fly well so once that is found a lap time helps to get it right each time.

BIG Bear
RNMM/AMM

[RandySmith]

 Lap times are irrelevant!
 

Hi Steve
lap times are not irrelevant     they are really relative, what I mean by that is they are relative to the model, and used in that manner can be a big help.
 Trying to compare plane to plane is not really ideal unless the planes are similar in size and line lenght, even then it is best to keep it to one plane.
Example is ,a large modern ship running 5.4 lap times , on near 70 ft. lines , is world's differant than a small classic ship on short lines running 4.8 on smaller lines.
maneuver times maybe a better measure to compare with.

Randy

[steven yampolsky]

lap times are not irrelevant     they are really relative, what I mean by that is they are relative to the model, and used in that manner can be a big help.

I like your definition better Randy. I stand corrected.

[Randy Powell]

As a subjective measure, I like to fly as fast as I can comfortably control. On my planes that's usually around 5.3 second laps. But it's sort of like using hinge to hinge moment measurements. From an aerodynamic perspective, it's a mostly useless measure, but it useful for a sort of rule of thumb or general idea point. Same with lap times. Gets you in the ballpark, then you have to trim for what works for you.

I flew a friend's plane awhile back. He and I trim planes very differently. I found the plane almost unflyable. He does very well with it. It depends on what you are used to and what you expect.

[Dave_Trible]

I find establishing a lap time is more about me than the airplane.  You can usually trim the airplane to fly well at any airspeed within a range.  (Note I said airspeed). The difference is at what manuver speed am I comfortable and in sync with the airplane.  (You can tell how your medication is doing-HA!).  Once you have determined where its working for you, you can accurately repeat it.

Dave

[steven yampolsky]

The problem with lap times as I see it is that it is typically the only number people give when they talk about their model setups. anyhow, I am attaching the spreadsheet I've created to play with line lengths and lap times. I hope someone else will find it usefull

[Jim Thomerson]

I think an airplane has a flying speed at which it is happiest, so adjusting lap time with line length is, I think, the best thing to do.

[Chris Wilson]

I thought that models have a 'judging' speed which is more or less an expectation.

Lapping quickly will more than likely draw comments like 'lack of time for appraisal' and subconsciously being marked down.

(I know, it should have no bearing on the score (like the type of noise an engine makes, but I bet that it does.)

[phil c]

Most everybody seems to trim out stunters somewhere between 52 and 55 mph- 75-80 fps.  At 88 fps you start to hear comments about flying really fast.  Much over 55mph precision starts to go down because we have a pretty much fixed reaction time.  Once you've got the model trimmed, as Randy pointed out, checking the lap time will stay very close, flight to flight, unless something changes.  If it constantly changes, flight to flight, you've got problems to fix.

Igor also has a good point.  Using the longest lines possible gives the plane more space so some maneuvers may present better(i.e. squares look squarer, even though the corner isn't all that tight), but a particular plane/engine combo may not do well on long lines.  So part of the trimming process is finding the right length of lines for a particular plane.  That is the reason for 48 oz. Noblers.  On 60-62ft. lines it takes that much weight to keep .015 lines tight enough not to mess up the plane's trim.  A lighter plane needs shorter lines and can fly a bit slower for good effect.

[Randy Powell]

Well, ideally, I'd love to be able to fly 6.5 second laps with all the power in the world and have plane be impervious to conditions. Nothing to do with the airplane. Having to do with my reflexes. Haven't seen that as possible yet, but hey, you never know.

[steven yampolsky]

Well, ideally, I'd love to be able to fly 6.5 second laps with all the power in the world and have plane be impervious to conditions.

We would then get bored and move onto something more challenging.

[phil c]

I've always toyed with th idea of building something like Charles Mackay's Monster-  600 some squares, maybe 32 oz.  the engine offset 30 degree for line tension.  It just might be able to do 45 mph on 69 ft. lines and give you your 6.5 sec. lap Randy.

Spectra lines would help too.  With virtually no weight swinging around on the wing tip would make it much easier to trim.

[Chris Wilson]

Well, ideally, I'd love to be able to fly 6.5 second laps with all the power in the world and have plane be impervious to conditions.

Fly indoors then.

[RandySmith]

Well, ideally, I'd love to be able to fly 6.5 second laps with all the power in the world and have plane be impervious to conditions. Nothing to do with the airplane. Having to do with my reflexes. Haven't seen that as possible yet, but hey, you never know.

Hi Randy

Built a Scott Bair Stuntfire, they fly at a normal 6.2 sec laps as a standard setup, you should be able to fly 6.5 with them, just have a strong 65 to 75 engine

Randy

[Jorge de Azevedo]

As a beginner I feel lap time as one of many interacting and interdependable variables .
To me looks better when level flight speed is egual to maneuvers speed and permitis easy control of the model.
I am wrong or right ?

[Bill Little]

Hi Randy

just have a strong 65 to 75 engine

Randy

Or an .80"something" with three glow plugs and bit the DEVIL out of my finger! LOL!!

BIG Bear
RNMM/AMM