Eagle Tree Products GPS Expansion Module & RPM Optic Sensor - RC Groups

Eagle Tree Products GPS Expansion Module & RPM Optic Sensor

I had previously reviewed the Flight Data Recorder and was reviewing the Seagull wireless transmission system when Eagle Tree came out with these new add ons for their system. I decided I really wanted the GPS module and was interested in the Optic sensor so I got out my checkbook and ordered these two add ons and here's the review. Don't miss the graphical flight recording images provided by Pete Young!!!

Yet another angle to view the flight path.


The GPS unit comes ready to use.
The GPS unit comes ready to use.
Manufacturer: Eagle Tree

A GPS unit? Huh? Why would I want a GPS on my model? This amazing unit can provide realtime data base to the dashboard at the pilot's hands, for a variety of uses, including cool 3D graphing of flightpath ... information on actual height, distance from the pilot, and so much more. Imagine, for a moment, practicing for pylon racing...and being able to look at a GPS reading afterward to see if you really did or did not cut that pylon? Not to mention finding a downed aircraft after a deadstick landing into rough territory (with another GPS unit to go to the coordinates) ... How cool is that?? Being the scientifically minded person that I am I wanted one because it looked like it would be FUN!

An RPM sensor...that one's easy to explain. What great live data this is, ensuring you don't overspeed in flight, see if the engine is bogging in certain conditions, etc...

I previously reviewed the awesome Seagull Pro Wireless Dashboard system for live realtime data, and before that the basic Eagle Tree Systems Flight Data Recorder (FDR) and won't re-explain all of its great features here.

The GPS unit is an add on module to use with your Eagle Tree Flight Data Recorder, hereafter referred to as FDR. You can see the readings from the GPS unit in real time using the Eagle Tree Seagull system that transmits the data from the FDR in real time and is received by the Seagull receiver that is with you on the ground. The range is reported as 1 mile and I had no range problems with my unit in my glider at about a distance of up to 2,000 feet in previous testing and use. The Seagull can now be bought with an improved antenna and the range is reported at 3 miles and I would recommend serious consideration to getting the unit with the improved antenna. Eagle Tree reports that with the unit you can graph your flight in 2D and 3D. Determine your model's ground speed as contrasted with the air speed that the unit's Pitot tube keeps track of. See your plane's altitude above sea level. They have two models available and I got the one good to about 9 feet for $150.00. More precision costs another $50.00.


1. If you have an older FDR it might not work with the new GPS unit as is. Contact Eagle Tree and see if your FDR and or your Seagull unit needs to be upgraded for the GPS unit to work with your equipment. If you are buying new at the same time it will all work together.

2. The GPS unit tracks and tells you where your plane is. It doesn't fly your plane to a given GPS location. I have had two e-mails asking for that type of equipment since I did my last review. In this day and age I wouldn't tell where or how to do that even if I knew, which I don't.


With the GPS unit, you get a fully assembled unit and a multiple page instruction manual. With the Optic RPM sensor, you get the ready to use sensor and a multiple page instruction manual.


There is no assembly! It is just plug and play. The GPS unit plugs into the FDR in its own slot if you live in North America. If you live in Europe you have a little computer work to do as it plugs into the transmitter slot for European Seagull transmitter units. That is all I know on that subject.

The optic sensor plugs into the RPM socket on the FDR and you install it on the plane so it points to the back of the prop hub that is painted half black and half white. While most optic sensors point through the propeller at a light source to get a reading this one doesn't need a light source. The Eagle Tree Optic RPM has it's own infrared source and receiver built in and it reads the bounce backed infrared light. Simply install 1-4 mm behind the propeller hub.

Both of these can be read live on the Seagull with advanced programing on your computer of the FDR and the Seagull receiver unit. It is very simple to program. All readings are transmitted -- you simply program which ones you want to see on Your Seagull. Since this was covered in my last review I won't go into detail but it is simple to do following the instructions. Just go to the item and select and pick what "page" and "corner" you want to see the readings and what readings you want to see from the unit.

Test Plane # 1

What else but my trusty Brummi would I use to test out the GPS unit? Because they suggest that you separate the units I taped them to the top of the Brummi wing to obtain maximum separation. This location was used for the first two test flights. I plugged the GPS unit into the FDR in the appropriate marked slot and went to my local park and performed two test flights. I turned on my transmitter for the plane and then the battery for the plane that powers the FDR and the FDR powers the GPS module as well as the Seagull transmitter and finally I turned on my Seagull receiver. I set the plane on the ground for five minutes to allow it to link up with GPS satellites and that took about four plus minutes. I had the longitude and latitude readings on the second page of my Seagull and the GPS altitude and speed readings on the third page. During the flight I climbed to over 1200 feet and had constant readings from the GPS module via the FDR. Since my Pitot tube air speed and my altitude pressure readings were on page 1 of the Seagull and I was busy flying the plane during the flight I only noticed that the readings seemed close during the flight. I lost signal for a short period and then got it back as I climbed above 1200 feet to where the Brummi was a speck in the sky. My flying buddies Dave and Dick couldn't see it any more but fortunately I still could. However, I decided to come down so I shut off the motor and slowly glided back to earth. I did have a couple of incorrect readings from the GPS unit. When it first turned on for a second or so it had the altitude as over 50,000 feet and in flight it shot a reading from 1200 feet to 1500 feet for a second. Other than those two short and obvious wrong readings the read outs i saw during the flight were all in line with what I expected. Looking at the chart on the computer post flight there were a couple other wrong altitude readings of a second or so. You will see these spikes in the 2D chart picture below.

I didn't loose the signal again but I had never lost it for more than a fraction of a second in previous tests of the Seagull last year and in regular use since then. I checked with Eagle Tree after I got home via e-mail and learned in flight above me the range with my standard antenna should be one mile. With their new improved antenna (an additional priced option) the range is three miles. While I had no further problems with the unit during test flights for this review I would recommend getting the improved antenna with the longer range. In subsequent flights I did have the Brummi back up to 1300 feet without lost of signal. I don't know what caused the signal lost for several seconds that one time.

While still at the field I turned the plane off and switched battery packs for a second flight. It reacquired the satellite signal in under a minute. After a good climb I turned the plane over to a student pilot who unfortunately broke the propeller during the landing. On two additional flights on a different day the GPS unit and the Seagull transmitter were both in the Brummi fuselage only about five inches apart and they worked fine. In a large cross country glider further separation would be easy to accomplish.

When I downloaded the data from the FDR I found there was no break in the recording of data from the GPS unit to the FDR in any of my test flights. As you can see in the pictures below there can be a fairly large difference in the altitude readings obtained from the pressure reading and by the GPS unit, especially when climbing or diving but they are very close when the plane is flying level. I also found the differences appeared greater when I recorded readings at the rate of 1 a second and less so at the rate of 10 readings a second. It seemed to me (Non-scientific) that the GPS readings may be a second or two behind the other sensor readings.

I was very pleased with the information I was receiving from the Seagull receiver and later the information I got off the FDR when I downloaded the flight information. There were four test flights with the Brummi for this review. Two that first day and two several days later. All information appeared to be valid as to altitude and speed. A graph of the flights in 2D, 2D GPS and 3D was performed but no picture was added to the base for 3D as will be explained below.

Test Plane #2

Since I was going on vacation I decided to take the Eagle Tree unit with me to perform some testing during my vacation. I had this idea before the GPS unit arrived and I read the instructions. It said it might not work in the house and I might have to go outside to connect with the satellites. Well it worked on my Brummi outside as discussed above and so I thought I would at least give it a try in the Alaska Airlines jet. My testing was done while still on the ground at the gate and all electronics were off by the time we pulled away from the gate. In 18 minutes with me next to the jet engine in back (terrible seats by the way) I was unable to connect with the satellites put I did get several readings that it was trying to connect and obtain a fix. When checked later by downloading on the computer the FDR recorded the normal sensors but got no reading for the GPS unit while onboard the Alaska Airline plane. This was to be expected but I tried it anyway.

Testing on the Water

Eagle Tree builds their products to be used in cars, boats and planes and I decided to try it on a boat. My test boat was a big one, the Oosterdam of the Holland America line. Ok so it was a ship technically. In two tries from our room balcony I was unable to get satellite link connection but I did have six floors of ship above me that probably got in the way. However I was successful at getting readings on the ninth deck outdoors by the rear swimming pool and on the observation deck, deck 11, where I was out in the open. The FDR and the GPS unit worked very well together on those decks but I had only sporadic connection with the Seagull transmitter and receiver units to see live data. It was more disconnected than connected, especially on top of the Observation deck. But even I was able to figure out that one when I looked up and saw I was in the middle of three operating radars and the ships communication transmitters. I was lucky that the Seagull, which has low power even on its high power setting, worked at all in that environment. When not swamped by the electrical equipment onboard ship the units worked well on shore in Alaska.

On the stern of the Lido deck aka deck nine I got a constant reading of altitude of 91 feet. I had a changing of latitude and longitude readings and I got a reading of a constant speed via the GPS unit of 26 miles per hour. This matched up well with the reported speed at the time of 22 knots per hour. Later on top of the Observation deck, or deck 11 as I called it and accessible only by stairs in somewhat rough seas I had changes of altitude from 115 feet to 135 feet.

Here four examples of the L/L readings were as follows:

  1. N 57:02 5916/W 135:19:4841;
  2. N 57:02 5883/W135:19:4823;
  3. N 57:02 5852/W135:19:4890;
  4. N 57:02 5862/W 135:19:4905

The charts from the cruise are very boring. Only the GPS sensor was connected to the FDR.

What good are those readings?

I don't need to explain the benefits of knowing your altitude and ground speed via GPS but what good are the L/L numbers? Well if your plane goes down say on a cross country glider flight and you have an assistant tracking those numbers as you fly the last reading can be used with a hand held GPS unit and you can walk out and find your plane in the middle of a cornfield. Or the side of a hill slope flying etc. but it can also be used to track your flight with the use of Google Earth and the optional GPS readings available for $20.00 per year. The basic Google earth is free but the improved version you pay for allows you to get satellite picture to match up with your GPS reading and you can plot your flight in 3D. You may do this simple for fun or to track your flights and see where you are catching lift and where you are finding sink and if there is any pattern to these occurrences. The finding of you plane is of course the big plus should it ever be necessary.

Pictures Behind the Charts

My only disappointment with the GPS unit is that so far I haven't had time to figure out successfully how to load the picture of my clubs flight area into the Eagle Tree program and plot/chart the 3D graph of my flights over a terrain picture. I have the data as you could see above but have not found a decent background photo with the data I need for our flying site. Our Modesto club site does not have a clear picture in Google and I haven't had time to search the web for other possible pictures. Additionally, Eagle Tree is working on new software that will make that aspect of loading the picture easier to use and it should be available in the near future. So for now during the flying season I will hold off and wait for the new software and simply plot my data over open space. For the more computer knowledgeable this is probably easy to do but I can wait on the picture.

Pete Young and 3D graphing of flight over picture

Pete Young seems to have mastered the ability to insert the ground picture into the program and then graph the 3d flights over where he flew using the GPS module. The pictures below were sent by Pete to our mutual editor and E-zone's Fun Manager, AnnMarie Cross. She brought them to my attention and they make a wonderful inclusion in the review in the one area I have to work on with the unit. My thanks to Pete and to AnnMarie.

Optical RPM Sensor

This add on sensor costs less than $15.00 currently and is installed by plugging it into the Flight Data recorder in the RPM slot on the FDR. The working end is flat and has an infrared light source and receiver and it works by the infrared waves bouncing back off of the spinning object that you are timing such as the back of the hub of the spinner. Make half of the hub black and half white and mount the sensor 1-4 mm behind the hub, the closer the better. I had a hub where that was possible and the unit worked when set up behind the hub. The numbers obtained were almost identical to those from my Cermark RPM meter. I also tried it just on a prop on one of my planes and the reading in that later case did not match up with the readings from me Cermark RPM gauge or my friends unknown brand RPM meter. With the hub that was half black and half white (my painting it half flat black) on the back of the hub, the infrared optic RPM sensor worked perfectly and the readings matched up with my Cermark sensor. Unfortunately, set-up inside the fuselage in a hole behind the hub to the side of the motor I wasn't able to take a picture of it in operation.

The benefit from this sensor would be to pick the optimum propeller and energy rate for your plane using the heat sensor and or optional voltage sensor and tracking the performance of your plane in actual flight. It would help you determine how to get optimal performance from your plane. I was actually hoping it would be easy to move from plane to plane and get readings off the prop but I don't think that will work (it hasn't so far) so I will probably continue to use my stand alone RPM meter for most of my needs. I will pick one plane to permanently mount this sensor in just as I did with the magnetic RPM sensor. When installed as recommended it works properly and if you have one plane you really want to dial in it would be great for that and I found it easier to install than the magnetic RPM sensor.


As I have come to expect from Eagle Tree both modules worked as described. I will mount the optic sensor in a large electric glider I have and use it to help me determine the most efficient prop and throttle setting for that electric glider as I want to be able to maximize my motor run time with that plane and for that purpose it will work perfectly. I won't be moving that unit from plane to plane as I first thought I might.

The GPS module is fun to play with and see the ground speed and altitude in real time but I will primarily be using it in my largest gliders when I want to roam the skies or go cross country. Besides the data it supplies with my Seagull in flight I have the improved chance of finding any glider that goes down away from me by using that last reading on the Seagull for location. It was fun to play with on the cruise and to show off to my friends with the Brummi but it will not be used with my Eagle Tree system on every flight but rather with my big gliders when I plan to roam the skies or really want to track a flight in detail such as when flying cross country.

Alaskan Cruise Photo Gallery

Since there really wasn't anything very visual with this review I thought I would share a few of the 300 hundred digital pictures I took on the trip. I have also included highlight video of the whale excursion and by Hubbard Glacier. Ketchikan is worth the trip just to watch the float planes take off and land. I hope you enjoy the glimpse of a very small aspect of Alaska.




Last edited by AMCross; Aug 09, 2006 at 05:21 PM..
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Aug 23, 2006, 09:07 AM
Registered User
Hi, thanks for a great article. I have the micro-logger form eagletree, and I also bought the optical rpm-sensor assuming it would work on propellers. Standalone optical meters work on propellers, so I did not even consider the possibility that the eagletree needed a flat surface to measure from. I have tried contacting eagletree and they have suggested using a setting of 1 in the setup-menu to try and make the sensor pick up on the propeller. Unfortunately I have not been able to test this yet, but I do not think it will work.

Anyways, the setup of the sensor is based on the magnetic sensor and I guess that the reasoning behind the measurement principle is also locked to the magnetic sensor. It is a shame really, because they could have made a truly flexible option here. As it is now I will not recommend the rpm-sensor to anyone. Better off getting a handheld unit.
Sep 12, 2006, 11:36 AM
UN Earth peoples true enemy
treehog's Avatar

RPM infrared dosnt sound able to do f5d or f5b...

RPM infrared dosnt sound able to do f5d or f5b if my understanding it needs flat mounting behind spinner??
Can you opt to use the magnetic insted for those uses

Sep 12, 2006, 12:21 PM
Registered User
Michael Heer's Avatar
I suggest you send Eagle Tree an e-mail and communicate with them directly. Below is a picture of the magnet glued to my propeller shaft and the sensor mounted on a dowel in my original review of the Flight Data recorder.

The optic sensor has it's own infred source. It can be mounted in the front of the fuselage and lined up behind the spinner. Have it half white and half black and it should work. No spinner, then a problem.
Sep 12, 2006, 01:19 PM
Registered User
After a suggestion by Fred, I got the optical sensor to work when looking at the holes in an outrunner motor: https://www.rcgroups.com/forums/show...&postcount=258
The whole assembly needs to be covered so that sunlight does not overpower the IR transmitter.


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