Turbotronic

Correct, but thats not quite all on jets. If the turbine ducting is not perfect the turbine/fan suction lower pressure in the fuselage could add errors much greater than ram pressure. For this reason you MUST have an external static measurement port.
For this same reason we designed a pitot with both ports to interface with our TCU to have an accurate speed "cruise" control function.
Further on a turbine High speed UAV it was absolutely required for the correct operation of the INS.
On the subject of AOA a vanes sensor would have to be rather big and not flutter for accurate measurement.
As per fullsize a servo operated cylindrical probe with ports either side for differential pressure sensor measurement and some electronics would keep the 180 deg alligned pressure ports at zero diff.
The angle of the servo is then AOA.
Andre

stevekott

I agree with all of your comments about the static port but ... IMHO

To be parctical in this application we are looking for something repeatable not necessarily accurate. I can't tell you, with the static port errors, exactly what the airspeed is but it guess it's easily within +/- 5 mph perhaps closer.

In full scale piloting I remember learning that if you exterior static port became blocked (ice, bugs, etc) you could switch to the alternate static source inside the cabin on non pressurized aircraft and have an airspeed reading within 1 or 2 knots of actual.

In practice it its difficult enough to hold a model within +/- 5 mph so I don't feel the static error is all that significant.

I can say with the 4 installations I have flown with the mph indications seem accurate, much more so than with a GPS.

I did one test where I strapped my Eurosport to the rack on top of my wife's SUV and I was getting readings within 1 or 2 mph of the vehicle speedometer. That was with the sensor unit mounted inside the fuse next to the Rx. No special consideration for the static pressure other than that area is not subject to any openings facing forward in the aircraft.

ww2birds

My Feedback: (14)

I've been flying the CB pitotstatic airspeed sensor in my Skymaster Viperjet using the Futaba telemetry system in the 18MZ. First flights with the system (the plane was well tested) were down at FIF recently (thanks again guys for a WONDERFUL event!!)

Since I had previously used the RCATS system, which has the very nice integral static port on the side of the probe (as someone noted above), I was also wondering about the static reference inside the fuse that the CB device uses.

Of course, it's hard to know how to measure "calbirated" airspeed but the readings are sensible .. 1/2 throttle cruise is about 125-130 mph, a little over 160 mph top recorded speed (I don't generally run WOT in level flight). I also have the Powerbox iGyro in the plane and it records the highest GPS-measured speed and it has been within 5 or 10% of the highest recorded pitot speed, which is pretty close given the uncalibrated nature of the pitot system and the variables of head/tailwind.

I also have the Robbe accessory telemetry receiver for my spotter (only in km/sec now, does not do mph .. sigh) .. and we've seen pretty repeatable touchdown speeds just under 50 mph. So I think it's a pretty useful too, certainly fun to have in the plane.

I wonder if it would be easy to connect a separate static reference CB system .. I do have some of the nicer pitot tubes from RCATS that could be used instead.

CB did a nice job of emulating the Futaba GPS sensor, and the setup was very easy, and worked without any trouble.

Dave

stevekott

Congrats Dave - sounds like you've done a great job at implementing this device. Nice to hear you have the Robbe Box working also.

I haven't cut the shrink wrap off any of my boards, but I would guess somewhere on the black sensor item there is a small hole for the Static Sense. Perhaps a small brass tube could be inserted to that hole and be used as a static input. I will email Dirk Bubley and see if he ever thought of that.

Happy Flying!

Steve

Turbotronic

Dave,
Its easy to verify if you have an issue. If you check the airspeed reading on the ground with full power setting on the turbine (preferably with gear retracted/doors closed if any) and the airspeed indicates close to zero youre OK.
I have experienced this myself on a UAV where the engine inlet had a connection to the fuselage where the static reference was. In this case the nosegear opening was sealed of from the rest of the fuselage.
When calibrating we could get 400kph from the suction caused by the engines standing still.
On a regular jet with openings like nosegear close to the static port it may be OK. Point is its not ideal for a reading for approach speed since you will get a HIGHER reading than actual.
Remember the dynamic static pressure is miniscule compared to what a turbine inlet is capable of.
In our case the Autopilot designer neclected to provide the unit with a dual ported sensor making an easy connection impossible. We had to revert to some mayor fiddling to get a static port integrated.
You cant argue with physics.
Andre

ww2birds

My Feedback: (14)

thanks Andre, as a physicist myself, I learned a long time ago not to argue with physics :-)

In the most critical use of the device, to check approach/landing speeds, I suppose that so long as any errors are repeatable, it is acceptable since we'd take the plane up high, put it in landing config (flaps and gear down) and do some stalls to see the reading. For other measurements (e.g. top speed) it's really more of a curiosity.

Next step is to experiment with low speed alarms on the TX and find a way not to "arm" the warning until on the air ... so it's not going off while taxiing! Of course the SM VJ is so easy to fly this is hardly needed, but for heavier scale jets, getting this figured out and implemented is a nice safety feature. In fact too fast is almost as bad as too slow if runway is limited.

My setup does not indicate any airspeed with the engine spooled up on the ground. For those who know the SM VJ, I put the CB sensor on the "floor" of the fuse under the rear cockpit in an area where there should not be much/any airflow, even with the nosegear doors open.

FYI, I used the BVM pitot mount on the side of the fuselage just in front of the cockpit on the left-hand side.

Dave

luckyflyer

If I have an R6014hs operating aircraft functions and then use the R6308sbt for telemetry only will there be conflicts/ interference between the 2? I've been told by Robbe that it will work as long as there is a separation greater than 8 inches between the two but I would like the opinions of other knowledgeable individuals.

stevekott

Hey Lucky Flyer, I'm guessing this is on a non 18MZ Futaba setup using the Robbe Box?.

I'm sure you will probably be OK with the 8" apart solution with the r6014hs/r6308sbt . I understand your concern as the r6308sbt will be acting as a 2.4ghz transmitter (for telemetry) in very close proximity to your 2.4ghz control receiver.

Here's a solution that might make you more comfortable.

Use the R6308SBT as your sole receiver on board. It has 8 PWM (regular servo) outputs on it plus the SBUS.2 connection on the bottom. You could add a couple of these hooked up to the SBUS.2 port along with your sensors to get an additional 6 pwm servo outputs and replace the R6014hs altogether.

www3.towerhobbies.com/cgi-bin/wti0001p

That way you are only dealing with just the one receiver on board and would eliminate any possible RF conflicts.

Steve

luckyflyer

I'm using an older 12z that I like and not ready to retire. I'm sure the 2 decoder modules would be the better way to go. ................Thanks

stevekott

I think you are the exact customer they developed the R6308SBT for. Guys who have existing Futaba transmitters that they like but would like telemetry.

I'll be interested to hear how that setup works out for you. I heard that the Robbe box only does Metric (kilometers per hour). For approach speeds it should still work fine for you, just need to fly high, find out where it stalls in kph and set your target approach in your mind at about 1.3 times that speed.

Best of luck!

Steve

ww2birds

My Feedback: (14)

Steve, correct the Robbe box only reads out in km/hr. I wrote to Emcotec (the dealer I purchased it from) and they confirmed mph not available. They said there may be a software update in August, and it might include the mph setting. Here's hoping that is right!

Dave

luckyflyer

Other than not displaying in mph how has this system worked out for you? Is the link to either your 18mz or the F1666 reliable? I have used the Eagle tree 900 MHz system for telemetry on some of my large gassers and my complaint with them has always been link reliability. I went ahead and ordered the F1666 and the R6308SBT from Robbe today. I hope I'm not disappointed.

ww2birds

My Feedback: (14)

I've only had 3-4 flights with the box so far, and reception seemed to be fine. We did not stress it my flying super far-away and did not see any dropouts. So far, so good for both the link to the 18MZ itself and the Robbe box.

It was interesting to see a voltage alarm on the main RX battery when setting up for landing .. I am using a smart-fly power expander, so the actual RX voltage is regulated, so I made up a jumper to go from an unused servo port to the aux voltage input of the RX so I could read the "raw" battery voltage. I am using a dual 2300 mah A123 setup. With full flaps I was getting an alarm .. I set the limit to 6.0V .. seems the current flow at full flap extension was enough to drag the system down well below 6V .. this is a LOT of current. Not surprising but very interesting. I am going to see about using on the the current sensors from my RCATS telemetry system to measure current and see how many ma are being drawn.

Dave

stevekott

Luckyflyer:

The telemetry link on the 18mz seems VERY reliable. I have never had an instance where I lost signal. I too had used the 900mhz Eagletree system. I did not have the signal loss issues but just having the "beeps" to indicate slow speed was not near as effective as having the voice feature calling out airspeed. It's kind of like a Goldilocks dilemma. Too slow, stall or pancake, too fast over shoot the runway. When I get the 'greased' landings is when I maintain 50 to 55mph on approach and then pull a little power at the threshold. Just having a beep when you get to slow doesn't give you near the control. On days with a strong crosswind is when it really shines because it's so hard to get the airspeed right.

Dave:

I get that same undervoltage alarm on my Flash if I deploy full flaps at too high of an airspeed, that's with A123's through a powerbox regulator. That External voltage port is real handy. I've used it for low ECU battery, low Motor Pack (on EDF's) and I've even used it for a flameout detector on my twin F-14. Have Fun!

CPS

I have one guestion:How can I set the alarm to work above the set speed or below the set speed?

stevekott

Make sure you have the latest firmware, I think it's 2.3.1

Go to the Home 2 screen, If your sensor is not on that display you will need to hit "Select" on the top of the menu to have it display. Click on the Sensor, It should show the alarm screen. Then you need to "Uninhibit" the alarm you want and select a high/ and or Low Threshold value. You can then select Vibration/ and or Speech for the alarm output.

Note: in order to just turn the speech On/Off with a switch you need to click the Home 2 screen then hit select and turn the Timer&PIT&THR "Off" so you can get the speech via switch option to display. (There's probably another way to get to that but I haven't found it). After you set up the switch you can turn theTimer&PIT&THR back "ON" to display the Timer on your Home 2 Screen.

Good Luck!

757Driver

My Feedback: (90)

His email link was no good. Anyone have the proper email? I'm ready to order.

Gonzalo38

[email protected]

757Driver

My Feedback: (90)

Double post removed.

Gonzalo38

Strange. I have been exchanging emails with him using that address. That's even the address used for Pay Pal.

luckyflyer

I talked to Dirk using that e-mail address last Friday and it worked ok.

stevekott

He was on vacation .. er holiday .. you know those Europeans .. anyway he's back now. He was going to call Robbe in Europe to see about the MPH option on the Robbe box. That box was never intended to be sold outside of the KPH regions of the world which is why we can't buy it here in the States. But Futaba left a big hole in the market, guys with high dollar Futaba Tx's, that they love, but wanting telemetry and not willing to take the 3000 steps up to the 18mz. That same hole existed in the European market and Robbe stepped up to fill the need.

I will be interested to see how your non-18mz installations progress!

Happy Flying!

Nhalyn

Hi Lucky flyer !

I've been flying my big Futura for 7 flights till I've installed a R6308SBT with the R6014HS receiver in my fuselage with Powerbox Champion RRS system. Distance between the two receivers is something like 4 to 5 inches and antenae the same distance.

Still no problem after those flights and aerobatics in all positions...

It works !

luckyflyer

That is very good to know. ...........Thanks!

757Driver

My Feedback: (90)

Thanks guys I will try again. Never seen an email with() in it.