Eagle Tree Systems Flight Data Recorder Review - RC Groups

Eagle Tree Systems Flight Data Recorder Review

How high was that flight? How fast was I in that speed run? What's the RPM with this battery and prop combination? Does the EagleTree flight data recorder accurately answer these questions and much more? Sure does!

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Flight Data Recorder V2:
Size:1 7/8" x 1 3/8"
needing 1" height clearance for wires & Pitot tube
Servo Data:Logs 16 channels, via the 4 included Y connectors, including glitch counts
Altitude Data:Sensor built into recorder, to 25,000+ feet
Temperature Data:Separate sensor plugs into recorder, dual, to 424F
Revolutions Per Minute:Separate sensor with magnets, to 40,000+
Airspeed:Built in sensor connects to external Pitot Tube, 9-290MPH
Voltage:Receiver battery voltage read from servo Y connectors
Accessories:"Expander" units available for additional data
PC Requirements:Windows 98SE/M/2K/XP, USB port
Manufacturer:Eagle Tree
Available From:Eagle Tree

I was considering buying an altitude recorder to use in my planes (gliders especially) when I learned about the Eagle Tree Systems Flight Data Recorder (FDR) from our RCGroups.com Fun Manager, AnnMarie Cross. This little "Black Box" not only recorded a plane's changing altitude during a flight, it recorded much much more. It recorded the speed of the plane during the flight; the voltage of the radio battery; the temperature of the motor (gas or electric), battery pack or speed controller. Information on each servo and if there were glitches during the flight was recorded. Even the revolutions per minute (RPM) of the prop throughout the flight was recorded. As a reviewer and a pilot, access to all this information was appealing. As I investigated the product further I learned that accessories were sold individually so that multiple planes could be set up for use of the FDR by simply swapping the Black Box. Eagle Tree also sells additional, different types of sensors as "Expanders" to allow pilots to obtain even more information on the operation of their planes if they wanted it.

This device was great! Or was it? It obviously recorded data during a flight and that data was obtained by connecting the Black Box to a computer with a special USB cable that came with the unit. The user can download a lot of data after a flight. But how accurate was that information? If it said my plane climbed to 800 feet, how accurate was that 800 feet? Was my top speed in a speed run really 86 miles per hour? I had no way of knowing if the data was accurate or not if I just reviewed the FDR in a plane. And I wanted to know for certain that this unit really WAS accurate. I decided this had to be a scientific review even though I had no test lab, no scientific equipment and no budget for testing. I designed tests that could scientifically confirm or disprove the accuracy of the Eagle Tree FDR's measurements.

Kit Contents

The Eagle Tree USB Flight Data Recorder kit came with 1 FDR -- that is to say, one "Black Box." It came with 4 "Y" cables, 3 feet of Pitot Tube hose and one plastic Pitot Tube extension, 1 RPM sensor, 4 tiny magnets, 1 Temperature Sensor, 1 custom USB cable, CD-ROM, 1 battery backup harness and one instruction manual. I went to Eagle Tree Systems website and downloaded the most current windows compatible software for use with the FDR. At the time of this review the complete kit sells for $169.99.

The individual senors and equipment mentioned above are also sold separately so that multiple planes can be set up and only the Black Box need be switched from plane to plane. Optional equipment they refer to as expanders are available for measuring G-Force, Exhaust Gas Temperature, Electric Motor Current/Voltage and other parameters are available on a custom basis. These additional "expanders" were not tested as part of this review.

The Computer Software

The software was extremely user friendly! I connected the hardware, the FDR, to my computer using the custom USB cable that came with the unit. Once connected it was easy to program it as to what sensors I wanted the FDR to record by just checking the sensors box. After I selected the data I wanted for one flight, I then had to select how often I wanted it to record data. For the review I recorded data 4 times a second and 20 times a second. That sure was easy and it was ready to use. After the flight, I simply reconnected the supplied USB cable and hit download. (There is even an expander unit available that provides for an external plug outside of the plane.) Once the data was in the computer, I viewed it in graft form as well as had it play back on digital readout and circular gauges. The data was easy to save and recall and I easily cleared the FDR's buffer with the push of a button or completely reprogram it for the next flight. I was very pleased with the ease of using this software. (Not convinced? Read the instruction manual on line or downloaded from Eagle Tree System's website.)

Of course, the more sensors recorded and the more frequently I record readings, the shorter time the recorder had in flight before it would be full. (I didn't fill it in my testing.)

My first test was on the accuracy of the speed recorder so I turned the other functions off with the exception of the battery voltage recorder. The programming and reprogramming of the FDR was so simple that even this "old dog" mastered the use with ease. The instruction manual was very helpful.

Scientific Testing!

How accurate is the information from the FDR? Is it "sort of accurate" or is it "dead on accurate"? How do I know? With a little reflection I came up with four scientific tests that I could perform with the FDR, and none of the tests involved flying a plane. My tests would check the accuracy of the FDR's readings on speed, altitude, temperature sensing, the RPM sensor and the battery voltage data. For all the scientific tests I recorded the data at the rate of 4 readings a second.

The FDR came with a battery backup harness. I utilized the harness to power the FDR in the first three of these tests, so I didn't even use my radio gear or a plane for the first three tests. My tests results should be repeatable by anyone with an FDR who duplicates these experiments. Thus the test for empirical or scientific testing of being reproducible has hopefully been met.


The first test was to determine the accuracy of the FDR's speed readings. For this test I taped the Pitot tube to a metal yardstick as shown in the picture below. The FDR is supposed to be able to measure speeds above 9 miles per hour up to 290 miles per hour. For this test I checked its accuracy on speeds from 10 miles per hour (MPH) to 60 miles per hour. With a friend holding the yardstick with the Pitot tube out the window of my car, I drove down a remote abandoned runway. I increased my speed in increments of approximately ten miles per hour. With the wind at our back I accelerated my car up to ten miles per hour then twenty and topped off at thirty four miles per hour. The car coasted to a stop and we turned around for our return run into the wind. The wind was blowing approximately 10 mile per hour. I accelerated the car up to forty MPH and after a few seconds accelerated up to 60 miles per hour. After completing the two test runs I went home and downloaded the data from the FDR using the supplied USB cable and my Compaq Presario computer.

The results were quite interesting. On the first trip with the wind at our backs there were a few glitch readings while I was still stopped, but once under way the readings were right on with my car's speedometer with a top speed of 34 MPH and then braking and a pause. On the return trip down the runway the readings into the wind were higher then my actual speed. When I was going 40 it recorded 48-52 and when I was going 60 the readings were from 66 to 74. The difference I attributed to the headwind I was driving into on the second test run. Thus the information on speed would be accurate in calm conditions or flying downwind but into the wind considerations of the wind's speed are necessary if ground speed is the desired measurement, as the wind added to the reading. I was very pleased with this result and that the FDR passed my first test. My thanks to Jeff Hunter for assisting me.


Testing the accuracy of the altitude readings occurred while driving in Southern California during Thanksgiving weekend. Highway 74 out of Palm Desert to Helmut and then onto San Diego California is called the Palms to Pines highway. It rapidly climbs out of Palm Dessert. Cal Trans posts altitude signs for every 1,000 foot change in altitude. Trusting that they are accurate I started the FDR at one sign (1000 foot elevation) and my wife stopped it at the next sign (2,000 foot elevation). The pictures of the signs below show where my test started and stopped. At about 2,150 feet altitude there was a scenic lookout that allowed me to view most of my test course. I had to wait until I got back home in Stockton to download the results of that test and a couple of others. According to the readout the altitude climb was measured at 996 feet. That was certainly acceptable for my use and I don't know if it was Cal Trans, the FDR, or a little of both that was off the total of four feet, or .4%. I tried to measure a descent. Starting at the top of a hill and going down about 2,000 feet (exact distance unknown) I got no reading on the FDR for altitude when I later hooked it up to the computer. I did't know if I made a mistake or if the FDR couldn't record below its starting point. This would not be a problem for most pilots but some of us slope pilots sometimes like to know: "How low did I go?" (I have since learned that my unit doesn't record below the starting point but the new units can record negative readings.) I will test this aspect again in my next review after I upgrade my system.


Test three was performed using our electric grill. It has a "temperature gauge" for settings to cook different items. I took readings using the FDR temperature sensor as I turned the grill on and heated it up to three different settings. The temperature sensor was simply resting on the grill as shown in the pictures below. The temperature settings on the grill were 200 degrees, 300 degrees and 350 degrees.

As you probably determined from the above pictures my data readout on the temperature readings were nowhere close to the settings on the heating element for the grill. This was a test design failure on my part. During the test I held my hand about six inches above the grill and I could feel the heat was very different over different parts of the grill. Additionally I just had the outside part of the sensor lightly sitting on the grill...the sensor may be on the inside part of the wire. When the heating element turned off at the "200 degree" setting the readout on the FDR was only at 132. For "300" the FDR recorded about 190 degrees and for the "350 degree" setting on the grill the FDR topped with a reading of 225 degrees. Although the FDR readings did not match up with the "settings" on the grill heating element, I don't know what the actual temperature of the grill was at the various times where I had the temperature sensor resting. On a positive note the sensor held steady at the same time the heating element indicated that the desired temperature had been reached. It moved higher when I set the element to a higher setting and it cooled down when the experiment ended. I will do more testing with this sensor, determine how it works and come up with a better test to be covered in an addition to this article or in the next review. This test result with the temperature sensor was inconclusive.

Temperature, Round 2

Back home in Stockton after I had finished all of my original scientific tests I thought up a new way to test the temperature sensor. I would take it from room temp and the place it in the freezer for enough time to cool it down and include an outdoor thermometer for comparison. I was going to use the back-up wire harness to power the FDR directly with a four cell Nicad flight pack. All was ready to go and I plugged the battery wire harness into the FDR. I almost immediately noticed I had plugged it in backward with red to black and black to red...just what they warned me not to do in the instructions. I immediately unplugged it and hoped nothing bad had happened despite their warnings that doing what I had just done could damage or ruin the FDR. Nothing I could do about that now so I connected the battery in the proper way to the FDR and put the heat sensor into the freezer with my outdoor thermometer. A half hour later the outdoor thermometer read zero degrees Fahrenheit. When I connected the FDR I was able to download data and the sensor also went from 64 degrees down to zero, taking about 11 minutes in the process. My test was a success! I reset the buffer and was ready for my last test, a video taped flight in Stockton.

Battery Voltage and RPM

Tests four and five were performed as bench tests utilizing my old Multiplex Brummi as my test bed for these experiments. The final two tests were performed together and the results were downloaded at one time as part of a complete readout of my entire system. I noted the voltage of the battery before and after the test with my Hobbico voltage meter. I was only measuring the voltage supplied through the Battery Elimination Circuit (BEC) as that was the voltage the FDR would be monitoring. (An Expander would allow monitoring of the entire voltage in the motor battery.) The fifth test was of the RPM data. Set up is shown in the pictures and described in the section below. During the three minute bench run of the plane's motor I ran it at three different speeds. I used my Cermark Tachometer to get readings of the RPM at those three speeds. I got my second and final Hobbico voltage meter reading and then took my plane's fuselage with the FDR installed to my computer room. There I hooked up the USB cable between my computer and the FDR and downloaded the data. The good news was that I had voltage readings within 2 hundredths of those with the Hobbico Voltmeter, thus the receiver voltage data test was another success. The bad news is that I had no RPM readings on this first attempt. (No fault of the FDR -- read on.)

RPM Sensor Round 2

The "Live Mode" of the FDR gives instant readings from the FDR to the computer for reading data for bench testing. With my computer still connected to the FDR I went and got my transmitter. I bench tested the unit in Live Mode in my computer room. While the altitude and speed readings were crazy in this mode, the voltage readings were steady and there were still no RPM readings. I repositioned the RPM sensor closer to the magnets very slowly and still no reading. I then tried to get readings with the backside of the sensor as suggested in the manual might work if the magnets were installed upside down. SUCCESS! (I didn't have any red markings on my earlier version of magnets and I installed them backward. Using the backside of the RPM sensor worked perfectly.) With the help of the Live Mode I found and corrected my problem with the magnets and the correction with the RPM sensor mounting it backward to read the magnets.

I performed my bench test of the RPM sensor a second time using my Cermark Tachometer. At half throttle I got a reading of 310 on my Cermark tach and times 10 it means 3100 RPM. Three quarters throttle gave a reading of 412 or a total of 4120 and full throttle was 518 or 5180 RPM with the Cermark tachometer. The readings from the FDR were 3130-3138 at half throttle. The second reading was 4180-4198 and the top speed reading was 5225 but it was steady at 5218 for most of the time on full speed. Thus the FDR passed yet another accuracy test.

Installation into test plane

The basic installation of the FDR required that the fuselage have sufficient space for the recorder, wire and sensors. I chose an old and familiar member of my air force to be my test vehicle. It was sold by Multiplex as the Brummi. The plane had lots of room for the Black Box as well as the wires and I had easy access through the motor covering/windshield for the RPM sensor and the Pitot tube for measuring speed. My plane was equipped with a brushless Astroflight 020 motor with a super gearbox and an Astroflight ESC. It had two Jr 241 sub-micro servos for rudder and elevator control and a Futaba receiver. The ESC had Battery Elimination Circuitry (BEC) so there was no separate flight pack battery.

The Y harnesses were used to connect the servos to the FDR. I simply unplugged the servo from the receiver and plugged it into the Y harness. I plugged the appropriate wire of the Y harness back into the receiver from where I just unplugged the servo, and the servo was again connected to the receiver. With or without the FDR, the servo worked through the Y harness just as it would through a servo extension wire. Next I connected the third wire of the harness to one of the four plugs in the bottom right corner of the FDR, just above the LED. I could've connected up to four servos to the FDR using the four plugs available. It made no difference which servo was connected to which plug initially. However, the instructions recommend that once I established a pattern, I should stick with that pattern. Since the majority of my planes are flown with a JR transmitter I used the pattern for receiver plugs with that system. In that system plug three is elevator and plug four is rudder and number 1-4 from top down. I used the bottom two plugs in the FDR for my test plane.

The Pitot Tube is the speed sensor and it works on pressure differential. The tube plugged into the center of the flight data recorder onto the nipple designed for it. The other end of the tube had to be secured to face directly into the direction that the plane is flying. I secured the tube (with the insert in the tube facing forward) to a metal yardstick for scientific testing and to the bottom of the test plane's wing for flight testing. In both cases I used tape to secure the tube. The manual says that shortening the tube doesn't affect the accuracy, but that being too close to the transmitter or mounted in the line of the prop-wash can adversely affect the reading. (The Pitot tube would normally be inside the wing with the end coming out on the leading edge facing forward. This way it would be out of the way. However I wanted to use it on a number of planes before I mounted it permanently, mounting a couple extra Pitot tubes that I will buy into permanent homes in my planes.)

The RPM sensor plugged into the FDR in the bottom slot in the lower left corner. Actual installation of the magnets and the RPM sensor will depend on the type of motor or engine as well as type of plane. But in any case they recommend that two of the small magnets supplied be firmly secured(glued) to opposite sides of a part that will spin with the motor and the sensor be secured 1-2 mm away from the magnets. This was the only step that was in any way challenging to perform. The pictures below show where I glued the magnets and how I secured the sensor using a wooden dowel. (I looked over my fleet of electric powered planes and this would be even harder to set-up on many of them, but relatively easy to set up on a gas powered plane. FYI.) The corrections to my installation of the RPM sensor were discussed above and after they were performed the sensor worked fine.

The temperature sensor plugged into the FDR in the lower left corner, right above the RPM sensor. An additional temperature sensor can be purchased and used in the same plane. The instructions describe how to install the sensor to a cylinder head to monitor it for temperature. In this review I used the temperature sensor with several items in my plane, including the electric motor, the speed controller and the battery pack. I used tape to secure the sensor to the various items per the pictures below, one at a time. For an electric pilot like myself, buying an additional sensor to have two in the plane is a smart idea.

There was no installation procedure to obtain the altitude readings or the voltage of the flight pack battery. The equipment for determining the altitude is built into the FDR and the voltage readings of the flight pack battery are taken off of the servo Y harness connectors.

Double Check for Safety

The manual clearly and forcefully warns that there is a possibility that the FDR and its equipment may cause radio interference and that a range check should be performed for safety reasons before flying with the unit. They indicate that the servo signal inputs are opto-isolated from the rest of the recorder circuitry so interference is unlikely and no case of interference has yet been reported, but it is best to be safe. Therefore I did a range check after installation. With my transmitter's antenna collapsed and both the transmitter and receiver on, I still had control of my plane with no twitches or glitches from 100 feet. That range has always worked with my radio gear in the past so that was a success.

Flight test

Test Flight in Palm Desert.

Three of the Scientific tests had been completed and only the RPM test had not been tried at all by the time our vacation in Palm Desert was nearing an end. I decided to install the magnets and RPM sensor into the plane after I got home from the vacation. I would take a test flight and check out everything other than the RPM sensor and its data.

My test flight in the Palm Desert was in windy conditions. I got readings on my two servos, temperature readings on the motor, altitude readings, speed readings and voltage. The altitude readings appeared accurate throughout the flight with a start at zero and a high of just over 350 feet. The speed readings were consistent but read higher than actual "ground speed" when I was climbing into the strong headwind. (This of course is accurate, as the unit's job is to read airspeed, but feels 'odd' to the user on the ground. This same result was noted in the scientific test as well.) The readings going downwind again seemed reasonable. Voltage was of the BEC supplied power and showed a slightly lower voltage when the motor was running full speed or the servos were being used a lot vs. when the motor was off and the plane glided in one direction. Battery reading through the receiver with my Hobbico voltage meter matched the readings from the FDR to within a few hundredths of each other. Temperature reading on the motor started at 74 degrees Fahrenheit, the actual temperature at the time, and went up during the flight to just over 100 degrees and was cooling down when I turned the recorder off. The motor didn't feel very warm to the touch but the gusty breeze may have helped keep it cool. This test flight supported the accuracy of the FDR on all the standard tests with the exception of the RPM sensor which had not yet been installed at that time.

Test flight in Stockton

I met my friend Dick Andersen at the local park and he videotaped me doing a quick version of my RPM bench test and then a test flight with a steady climb, a dive from altitude, a loop de loop and then another climb at full, 3/4s, and half throttle followed by a glide to landing. Dick lost my plane for a bit with the camera but the flight was a success. However, when I downloaded the data I had four good readings and two worthless readings...apparently, I did damage the FDR with my battery mistake in the freezer test performed the morning of the flight. Voltage readings were normal and temperature readings off of the battery went up from 72 degrees to 106.4 degrees. The servos were working fine but I had spotty but accurate RPM readings and according to the altitude I went from zero to 62,000+ feet instantly and then a few seconds later went right back down to zero. My speed data while still on the ground doing RPM tests read 280 miles per hour but appeared accurate in flight even though the altitude readings were now zero.

Using my computer I cleared and turned off all readings and settings and reset for 20 pieces of data per second from the previous 4 per second and turned all the readings I had been getting back on. I went back to the field alone to try and repeat my previous flight that was videotaped. I had a short but successful flight where I climbed a couple hundred feet and performed a speed dive and did a loop. Then after a little more flying I turned down the power and glided to a landing. Then I came home and download the data. It now looks more and more like I damaged the FDR (at least temporarily) when I plugged in the battery harness the wrong way with a live battery. In this flight data it indicated the flight started at 122 feet of altitude and landing at 122 feet of altitude instead of the normal zero setting.. Other than that it seemed to be working fine. RPM at full throttle was about 5,225 as it fluctuated between 5218 and 5225. Battery temp started at 60.2 degrees and warmed up to 74.8 in the short flight. Top speed in the dive was 46 miles per hour and I could see the loop in the altitude graph that documented a climb to 336 feet but started at 122 feet. (Thus the suspected damage.) Receiver voltage as read through the voltage supplied by BEC showed a lot of changes from about 5.1 down to 4.9 due to motor and servo use etc. It still seemed to be working correctly. I will be sending my FDR back to the manufacturer as part of my upgrade and he will determine if I damaged it. But I did complete my testing. The pictures below show how I graphed the individual results.

It Worked, so what does all this data do for me?

The FDR, while a lot of fun, is not "just" a toy. It supplies a wide variety of usable sophisticated data. What data is important to you may depend on what you fly and how serious you are about your flying. You don't have to use all of the components all of the time. The more data you record and the more frequently you set the FDR to record readings (up to 20 times a second) the quicker you will use up it's memory on a flight. Everyone should be interested in how their servos are working for voltage efficiency and safety. Readings out of the normal range could lead to an investigation of the linkage and possible binding during flight or too weak a servo for the stress during flight based on servo data at high speed vs. low speed. Probably every pilot would like to know how long their radio battery can safely work under load. Beyond that it is probably a matter of individual choice as to what information is important. The glider pilot probably wants to see the battery readings and the altitude graph and possibly learn something for future flights. The pilot with an electric motor may be most interested in getting the Electric Expander to gather data on his battery pack voltage use and the RPM and speed with different props. Those readings could help maximize performance or diagnose a problem. The temperature sensor on a speed controller may help diagnose an over heating problem as I once had while reviewing the Great Planes Dr 1 electric conversion. The pilot with the gas engine might be more interested in engine temperature and RPM readings as he/she looks for the best tuning and prop combination. Or the expander measuring exhaust gas temperature may be the information they desire or the expander measuring G-force may help them get the best acrobatic performance out of their plane.

The next four pictures of expander items were downloaded from the Eagle Tree Sytems website.

The Flight Data Recorder can supply you real time data for bench testing purposes. Per the tests in this review the data is real information that has proved accurate. Hooked up to a desk computer or laptop and the plane it can supply information in real time as the plane is running. Very helpful in tuning the motor and making prop selection!


The USB Flight Data Recorder performed excellently, proving its accuracy in my "scientific" studies and it provided usable data from the tests and test flights. I will no longer have to guess how high my plane flew or how fast it went in a speed run. More importantly I can use it when I set up a new plane to make sure everything is working as it should and I am getting the most out of the plane. It handled my original desire for altitude readings and did so much more. The altitude sensor, the speed sensor, the RPM sensor, the voltage sensor and even the temperature sensor proved in tests to supply accurate and sophisticated data that was previously not available to the average modeler. If used properly it will let us fine tune our planes to get the most we can from them in performance and duration. The FDR lets us get all this information in a very easy and user friendly manner.

To answer my own questions from the start of this review...that 800 foot reading of altitude appears to be withing 3 1/2 feet per my test. That speed was probably 86 miles per hour on a calm day or down wind but maybe only 76 MPH into a ten mile per hour wind. The Eagle Tree Systems, Flight Data Recorder is a scientific instrument!

What's next? REAL TIME LIVE DATA ala Seagull!

I am flying my glider and I have been lucky enough to catch a series of thermals and have stayed up for an hour and forty minutes. My full house glider has six servos in it and I had one shorter flight earlier in the morning. Does my battery have enough juice to make it safely to two hours? Am I in sink or lift right now? With the FDR, I could get that data from my recorder when I land, but do I push it and possibly lose my plane or is it safe to keep flying? If only I had that data now in real time!

The newest product from Eagle Tree Systems will give you that information while your plane is still in the air and it supplies the information in real time. They call it the Seagull Wireless Dashboard Telemetry System. It comes with a monitor to attach to the transmitter and a very small and light transmitter to place in the plane, attached to the FDR. Best of all those that already have the FDR can upgrade their unit to get the wireless system. Now I would know if I was in sink or rising air, what voltage is left in my receiver battery and much much more. I haven't seen it in person but I am upgrading my FDR with the Seagull and I plan to get the Electric Motor Current/Voltage expander and a second temperature sensor as well. Look for my review of the Eagle Tree Systems Seagull with the Electric Expander unit in the near future. The photos below of the Seagull were supplied by Eagle Tree Systems. Thanks to Seagull, the FDR is not just for post flight or bench review anymore. It can also be used with RC helicopters and RC cars.

DEDICATION: I dedicate this review to Don Herbert and the staff of the "Mr. Wizard" early TV show that gave me a life long interest in science and helped teach me to think outside the box. I am sure that show played a part in my creation of these experiments.

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Dec 03, 2004, 07:53 AM
Registered User
radfordc's Avatar
The author has a fundamental misunderstanding of the what airspeed really means. He confuses indicated airspeed with ground speed.
Dec 03, 2004, 10:52 AM
Closed Account
Originally Posted by radfordc
The author has a fundamental misunderstanding of the what airspeed really means. He confuses indicated airspeed with ground speed.
Re-read the article, he clearly states that the headwind accounts for the difference in his findings between the car's speedo and the data recorder's readout.
Dec 03, 2004, 05:26 PM
Registered User
radfordc's Avatar
While doing a test in the car he said: "Thus the information on speed would be accurate in calm conditions or flying downwind but into the wind considerations of the wind's speed are necessary as the wind added to the reading."

He seems not to understand that driving downwind the speed of the wind will make the indicated airspeed less.

Later, when talking about a test in the air he said: "That speed was probably 86 miles per hour on a calm day or down wind but maybe only 76 MPH into a ten mile per hour wind."

Here he seems not to understand that the indicated airspeed of a plane in flight is affected at all whether the plane is going up or down wind.

Maybe you also don't understand fully?

Dec 03, 2004, 08:42 PM
Registered User
Michael Heer's Avatar
I do understand the difference between airspeed and groundspreed. And I have experienced the benefit of a 100 mile plus tail wind in the jet stream. In the speed experiment I videotaped the speedometer in both runs and played it back in real time and noted the speed at different intervals on my stopwatch in viewing back the video. Those times were then compared with the FDR data readout on playback. On the down wind trip the speed recorded on the FDR matched up almost perfectly with the digital readout on my speedometer which has been checked for accuracy by doing a marked mile stretch at 60 miles per hour with cruise control on and taking 60 seconds (plus or minus one or two tenths of a second.) to run the mile. I was reporting ground speed readings from my cars speedometer and the FDR matched those (not higher or lower) going downwind. I only did one test run downwind and one into the wind. My FDR has been mailed back for diagnostic testing to see if I fried the altitude meter but when it is returned with the Seagull telemetry unit I will do further tests on speed and hope to include more test data and compare readings with a radar gun at the slope.
I hope you enjoyed the article. Mike
Last edited by Michael Heer; Dec 03, 2004 at 08:46 PM.
Dec 06, 2004, 02:18 PM
Registered User
BEC's Avatar

The thing is, a pitot tube can ONLY be used to calculate AIRspeed - via comparing the static air pressure sensed wherever it is (on the FDR box itself, right?) and the dynamic pressure from the pitot tube.

So where you mention a "problem" because the airspeed reported into a headwind was higher than the groundspeed is not really a problem - it IS the AIRSPEED after all that the unit is measuring. It cannot measure ground speed.
Last edited by BEC; Dec 06, 2004 at 02:23 PM.
Dec 06, 2004, 05:00 PM
Registered User
Michael Heer's Avatar
From my experience pilots want to know how fast their plane is going compared to ground speed and not the airspeed that the device measures. The FDR does measure the airspeed in the unit itself and the Pitot tube connects to a nipple in the center of the unit. I created a possible misunderstanding in trying to keep my discussion on the matter short and I was not precise in my use of language. Mike
Dec 07, 2004, 02:35 PM
Registered User
BEC's Avatar

Perhaps they do, but that requires some kind of measurement that can see the ground, which is beyond what the FDR can do. Besides, as is often argued in "downwind turn" discussions - the airplane cares rather more about airspeed than groundspeed regardless of what a ground-based pilot may care about. In other words, this unit is no replacement for a radar gun for those who want to know how fast their plane is relative to the ground.

In reading the manual on their site I can see that the static port is on the FDR box itself somewhere - they talk about making sure that there are no pressure fluctations inside the fuselage (such as from a cooling air intake) to mess up the static pressure sensing, and describe bringing a static line out to the side of the fuselage if needed (as is done in full scale practice).
Feb 02, 2014, 10:22 PM
Registered User
hi michael,

i still confused about several parameter panel in eagle tree system GUI. What does the glitches means on servo glitches? and how to calibrate the servo or the brushless motor? why do my throttle panel doesn't work properly. ?

thanks for helping

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