SEN 2458 - Stop your watch, check your battery, listen to your motor
- Category: Archive 2018
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Table of Contents – SEN 2458
Stop your watch, check your battery, listen to your motor
- Class F1C. Maximum duration of motor run in 21st century.
- Timer battery Testing
- On stopping the watch
Class F1C. Maximum duration of motor run in 21st century.
Nowadays without exaggerations F1C model aircraft should be considered as a work-of-art among highly technological objects. With ultimate aerodynamic parameters and advanced design of high-power piston engines F1C models are built from composite materials and could utilize variable wing and airfoil geometry, geared engines and flight control mechanisation based on electronic timers and servos.
Evolution and dynamic development of technical characteristics of F1C models were accompanied with new technical restrictions throughout the years. Since the beginning of F1C class in early fifties one of the most important regulated characteristic is Maximum duration of motor run which was reduced from 30 sec to 5 sec in 1998. Starting from 2016 this characteristic has been farther truncated to 4 sec.
Due to obvious reasons the precision of 4sec motor run timing should be very high in order to accommodate contemporary rules. Possible systematic errors should be eliminated or minimized.
However over the years the methodological approach for timing the motor run for F1C models has not been changed. In practice the old-fashion “acoustical” method of timing is used which requires from competitors an additional reduction of motor run by 0.4-0.6sec for compensating sound travel from about 150m altitudes.
With simple calculations everyone can verify that for 4sec motor run only this systematic error takes in average 12% of total motor run. It sounds as an unacceptable value.
A lot of improvements and developments in terms of timekeeping were successfully implemented for FAI control line models such as F2A and F2C but nothing in F1C where timekeeping is a crucial part of a competition process as well.
Nevertheless a simple solution to this problem could be suggested for the models equipped with electronic timers.
Together with the embedded software an electronic timer by itself is a precision digital device with time resolution at least 1/100 sec and an extremely high level of repeatability. Contemporary electronic timers have standalone pieces of equipment (programming modules) where all parameters could be visually checked and verified. Based on these facts the following validation procedure for maximum duration of motor run could be proposed for F1C models with electronic timers:
1 During the registration process together with other technical parameters a competitor should indicate in the Registration card the duration of engine run and correspondent timer settings for each model.
2 During Model Processing Procedure the compliance with the requirements for F1C engine run will be verified by taking readings from the timer of the engine cut-off time for each model with correspondent logging of the results.
3 During competition timekeepers will have rights to check settings of a motor cut-off time before an official flight and verify them against correspondent logged parameters during processing.
3? The contest Jury will have rights to perform a spot check of timers settings on participants models before and after official flight. In special cases Jury could request competitor to perform a control engine run on a ground.
For F1C models with mechanical timers the following procedure could be proposed:
1 During registration process a competitor should indicate technical characteristics of his models in the Registration in order to demonstrate compliance with FAI rules.
2 During Model Processing Procedure the compliance with the requirements for F1C engine run could be verified by spot check of engine runs on a ground. Two timekeepers should measure the duration of engine run. In order to confirm the actual engine run duration one timekeeper should take measurements near the model and another one should time from 150m distance. Their readings shouldn’t exceed 4sec and 4.5sec correspondently.
3 During competition the duration of engine run will be controlled by two timekeepers who should only verify that their readings are within 4.5 sec in order to confirm compliance with the rules.
3? The contest Jury will have rights to spot check the duration of an engine run on participant’s model during an official flight. The readings should be within 4.5 sec in order to confirm compliance with the rules.
Note that such amended option to the rules allows using full potential of F1C models within same regulations, mitigating errors during timekeeping, demonstrating flying results that correspond the level of a competitor, and will not discriminate the rights of modellers who still flying F1C models with mechanical timers.
We are proposing to support this amendment to the FAI rules for F1C models.
Timer Battery Testing
A number of SEN issues back we talked about LiPo capacity and some testing we had that showed that in some cased the labelled capacity was sometimes optimistic.
We got this follow up question.
From Terry Kerger
How can I test my timer battery without investing in a battery cycler/charger?
Does it make any sense to charge the battery, measure the voltage, then cycle the timer several times and see how much the voltage drops?
How much voltage drop is safe? What is a safe voltage range to operate the timer
Am I just waring out my servo cycling the timer to test voltage drop?
The best way is to do a series of simulated flights, including time for retrieval.
This is best done while doing some other activity as it takes some time.
It is a good idea to do this before you first start start flying a new airplane.
As an indication Igor Vivchar has done ground tests of Magic Timers with Dymond servos in his F1B models with the buzzer turned on and LiPo of about 120 MA - that gave 50 simulated flights before the voltage got down to any where near danger.
Note that testing a non-towline-glider timer e.g. F1B, C , P, Q, S and E is easier tham F1 A and H. Because with a glider the battery capacity is affected by the time the glider is spent on tow so that part of the flight should be simulated too. The notes below with voltages apply to timers that run off a single cell LiPo, they need to be adjusted if the timer uses a different battery.
Use a simple digital voltmeter
Charge the battery
Measure voltage with timer on and off
wait for 20 minutes.
Do a series of simulated “flights” as follows- for example 7 to simulate a 7 round contest.
If you power other devices such as flasher, altimeter, GPS or tracker from the timer battery that should be connected to0, just as you would when flying.
In these notes we refer to Magic Timers but the principles apply just as well to other timers too.
turn on timer
wait 30 seconds
start timer and "fly" 3 minute flight
wait 20-30 minutes for retrieval
turn off timer
repeat above for seven timer, or a bit more if you want to simulate fly off too.
Measure voltage at the end -
Watch for fall off in servo performance - such as slow movement or servo jitter.
Note that if it is a single LiPo timer as used in most non-glider models the battery voltage of a freshly charged battery will be 4.1-4.3 volts. Most just under 4.2 volts.
Magic Timers will run on 3 volts, servos will not.
LiPo batteries have a nominal voltage of 3.7 volts. Most servos used in timers will run at 3.6 volts.
Under most circumstances the battery voltage at the end of a days's flying should be 3.8 - 3.7 volts If you do the test early in the life of the airplane it sets a standard you can use as a check. Typically the battery will either be bad from the start of fail after a extended period of use.
If the performance of voltage at the end of the day starts to fall off, replace the battery otherwise following Murphy's Law it will fail at the most inopportune time.
LiPo manufacturers say the expected life is 3-4 years. This does depend a bit on how often it is used and it it is well maintained and not allowed to discharge to a dangerous level.
Always charge the timer before a day’s flying no matter when you last used it.
On stopping the watch
From: Aram Schlosberg
When a model disappears behind an obstacle, one is suppose to count to ten. If the model reappears the timing continues, otherwise 10 seconds are deducted.
Does this rule apply when models disappear into over head? Case in point was the ‘15 Eurofly near Bern, where C models disappeared into a low hanging cloud. The timers (who belong to a hockey club and rotate poles each round) waited for about a minute for the model’s to reappear under the cloud ceiling. With the count to 10 rule they would all have had attempts (under 20 seconds).
Another case is when my B model disappeared into the sun in Sweden last year. Fortunately the iCare tracked the altitude every 10 seconds and it indicated that the model DTed from 100 meters in 4 minutes. Fortunately I was awarded the max.
A day earlier, under a low cloud and rainy conditions, Mike Woolner was clocked at 40 seconds going into a cloud. Others were more fortunate.
Two rule recommendations. First, counting to 10 would only apply to low flying models.
Second, for models disappearing overhead or into a cloud, the flyer should be able to establish their flight time with altimeter data during or after the flight. The default is the 10 second rule.
It’s true that not everyone has an on-board altimeter as part of a timer, stand alone or as feature of a GPS. But deploying one is can prove to be a max saver in cloudy/hazy circumstances. ////