SPEED MEASUREMENT:

Have you ever wanted to know the speed of your model, and all you really have to go with is the sound it is making.

This can be a definite problem. Just because the aircraft sounds good - it does not really mean that it is fast. This system uses a sound recording and Doppler effect of noise going away and coming to you to determine the speed of the aircraft. This system also calculates the RPM in the air. All this is very handy.
The spectrogram that I have loaded into my computer does all the work.

What equipment do you Need!
The main thing is that you have a sound recording device. Anything will do. I had a pocket sound recorder that was a left over from my student days. When I used to record a whole lecture at the University. The only problem was my recorder was mono, and the computer was stereo - so I had to purchase a special lead - this cost me about $12 I think for two bits of cable. This was my total out lay. You will also need Microsoft Excell on your computer.  Well I suppose just about everyone has that.

Getting the programs!
So this is what you do - First install all the software - just contact me over the Internet from my web site and ask and I will e-mail it back to you. No cost. You will have to Unzip some files. There are two active programs One is the Spectrogram and the other Excel program. Just nominate whether you want the Basic or Excel programs for performing the calculations . I must thank Stu Sherlock and George Angelov for their assistance in getting me the programs and telling me how to use them. I believe that Stu got this idea from Australian CL news.

Installing the Programs! (Take Notice) Note there are two alternative methods.

MS EXCELL Spread Sheet. (To do the Calculations)

I suggest that you do not use the Basic Program listed below as I have now a MS Excel  spread sheet  that will do the calculations for you.  I have had that on my list of things to do for some time and now it is working.  It is very easy to use.  All you have to do is key in the values and the answers come out automatically:  I love it.   Just e-mail me and I will forward the Excel  Spread Sheet to you.

BASIC (To do the Calculations)

This is where a number of people have been getting into trouble.  It is essential that you have Quick Basic (QB) installed on your machine. If I have not given you this program please contact me and I will send it to you.

The Spectrogram should be no problem - however the RPMSPEED  program must have QB installed.  You do it this way.  Install the QB.exe  file that I sent you first.  Then restart your computer.

Then Install the Spectrogram and RPMSPEED programs - place these in a folder that you can get at easily.  I have mine in a folder called "Speed Measurement".  In fact I have created an Icon on my Desk Top so that all I have to do is click on either of them to open the programs.

The Spectrogram program can be accessed very easily - it will open up without any problem.  

The RPMSPEED program is another matter - It will have to be ASSOCIATED with the QB program.

You do this by first clicking on the RPMSPEED program that you have installed and your computer will recognize that it does not know how to run this program.  A small window will appear and ask you what program do you want to associate the RPMSPEED program with.  

Just scroll down and you will see QB  just select that and the program will run.

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Now this is another way - I did this the other night at Gary Davidson's house when I could not get his computer to do it using the above method.

Copy all the programs into the same folder.  Unzip the two zipped files.

Open the Quick Basic Program.

Open the Folder in which you have RPMspeed program.

Then open the RPM Speed program - and then you will be able to use it to do your calculations.

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Make the recordings
The next step is to do the recordings. This must be done in a certain way to get effective results.
The recordings can be taken from anything. You can play a sound recording into a telephone, and have someone at the other end make another recording of it. I have done this. Some people have rung me up and played the sound of their model over the phone - I have recorded this on my little recorder. Then I went to my computer - called up the Spectrogram program and fed the sound into that. In that way I was able to tell that person what speeds and RPM his model was doing.
There is no reason why I cannot get hold of old videos - taken years ago and find out what speeds we were doing then. This would be very interesting.
There is a problem with this measurement. It should be done correctly - otherwise you can get strange results.
Firstly it is best that you stand between the two back pylons (2&3) but about 50 to 100 meters down wind. This will give you some good frequency graphs. You can also stand at the side of the base pylons - but not close to them. You do not want the model to be flying over your head. If you do this, the Spectrogram graphs will have a funny shape. You should be getting a shape similar to that displayed in the picture shown in this article. This is a recording of a small half A model - the graph has nicely shaped hills and hollows. In fact it was a flight made by Brian Steele at Lilydale,
Now this is what happens. The spectrogram will show a plot of your model coming to you and going away from you. If you decided to get in a position eg. Between 1 and 2 pylon. It will record two peaks per lap - instead of just one. From number one to half way down the straight (Coming towards you) and then half way down the straight to no 2 (Going away from you). What you want is only two reading per lap ( From No3 to No 1 and No 1 to No 3) Just like what is shown on the graph in this article. Each peak and Trough represents one lap. So if you count them you will notice that I have on the screen five laps.
Not only do you have to position yourself correctly to record the laps but you must tell the pilot what he has to do - in order to get correct measurements. He must fly level and preferable low - he must fly the same course for each lap. He should try as much as possible to simulate the actual pylon course. It is no use flying a very short lap and then a real long one. This is possibly the major problem we have with a measurement system - including that done with a radar gun. A longer straight will give you a faster speed. This is a problem we have had earlier - on occasions I would get increased rpm with the same prop and slower air speed. Why is that so! Well the pilot was to blame he started to fly a shorter course and hence the slower speed. The aircraft must be faster as the RPM has increased, because he is still using the same prop. I feel it is much better to simulate the course longer than shorter. We do not all have the luxury to have the pylons set up at our field for practice purposes - so we have to guess the course. Anyhow any measurement is better than none.
So here we are at the field standing in the correct position about 50 meters down wind from No2&3 pylons and have the sound recorder in our hands ready to record.
The pilot then starts his engine. You then start the recording - you then speak into the recorder stating what you are going to test. Eg "This will be Jim Orenshaw testing his new Rex 8 port QM engine - using a QM02 prop - Weather condition 30 degrees and humid". You can read off those ground revs later. The model take off and your are recording its sound. When you have enough laps you can stop the recording. You can start it up again if you want.

Note if your Scan Input page does not look like this contact me and I will send you the latest program:

Use Your Spectrogram Program:
When you get home you can plug the recorder into your computer. Bring up the Spectrogram program. Click F4 Scan Input Option - Then a further screen will be displayed. Do not alter the settings as displayed. Then Click OK.  Use setting shown above.
The Spectrogram will be displayed - and the spectrogram will start recording.
Then Start playing the sound recorder. You should hear the sound and after a while you will see the sound waves appearing on your screen. When you have enough click the STOP button.
Now by moving your mouse you are also moving a set of cross hair.
On a piece of paper draw up the following columns - High F - Low F - Speed KPH - RPM
With the cursor on high peak record on this piece of paper under High F the Frequency (Hz) that is displayed in the Scanned Input box.
Now do the same for the low Frequency at the bottom of the curve and record it in Low F column.

You can also record the time for the laps if you wish just place the cursor on the top of each peak and read off the time displayed in mille seconds - subtract one from the other to get the lap time.

Do this for the remainder if the curves that you have selected. In the example you could have taken 5 sets of frequencies.
Now exit the Spectrogram program.

Hit F5 to run . Then fill in all the readings that you have recorded from the Spectrogram. One Pair of frequencies at a time. Also add in the correction factor. I use a standard 10% for that because this factor is to adjust for the height the model is flying. Being a pylon model it is very hard to fly exactly at the same altitude so who knows how high. Each lap is usually all over the place. 10% is okay!.
When you have entered the correction factor the program will produce speed and RPM figures
Record the readings on the sheet of paper against that lap.
Then Hit F5 twice and you will be ready to get another result.
When you have finished you will be able to analyze all the results.

Excel Method of doing the Calculations:

Just key in the coming and going frequencies as detailed above and also the correction factor and the answers will come out automatically in the appropriate columns.

This system is ideal for testing changes to your set up - new against old settings - perhaps the actual speed is only a guide - the main thing is that you are able to see if you get improvements from the changes you make.

Trust you have fun with this - I know I have - perhaps if you have a small lap top or a cheap computer you can take it down to the field and get first hand information.

The answers that you should get with a 5% factor are 30,000 rpm and about 300+ kph speed: I only took one lap as I could not let the file get too large.