Pat Barnes

Hi Sid

Didn't mean to imply you were one of the 'sticks in the mud'! I was gently teasing Mick and Mike from this side of the pond! All meant in good humour!

Cheers - Pat

Pat Barnes

And I agree with your comments about IAS over AOA when it comes to models.

Yann

AOA is not difficult to implement. I'm working on two different ways to do it. IAS is not difficult either. Pitot tubes work great.
To have a working auto throttle, of course AOA is not enough, but if you also have an IMU, then it can be worked out.
It's not that I need it, we've been flying our jets without telemetry or gyro for years. It's just that I find it fun to do.
For exemple, making an IMU means implementing kalman filters digitally on a microcontroller, and that is very interesting.

dbsonic

My Feedback: (3)

.. is that really true? correct on the loading, but indicated stall airpseed does not change as a function of air density. My indicated stall speed will remain constant no matter what the altitude/density altitude for a given flap setting. That's the beauty of IAS. Indeed, there are times when I would really like to have IAS for models particularly in less than ideal conditions.

Yann

Well, when air is cold, air is more dense and generates more lift for a given airspeed, right?
So I guess stall speed also depends on air density.

dbsonic

My Feedback: (3)

For true airspeed, yes. But indicated (ram pitot pressure vs available static pressue) is affected by the same air as that is passing over the wing. In other words the ram or dynamic pressure includes the density term. From wikipedia on the subject
"Since it is this same dynamic pressure that drives the airspeed indicator, an aircraft will always, for example, stall at the published indicated airspeed (for the current configuration) regardless of density altitude".

As pilots we almost become too reliant on the airspeed indicator and the ram pitot can sometimes clog due to bugs. Not very often but it is good practice to land occasionally without the use of the airspeed indicator. Something that RC model pilots do all the time.

BlueBus320

My Feedback: (57)

IDK.. Been on 4 different turbojets in my career & will be saving no IAS for the sims!!!..lol. That's why there are 3 air data sensor systems on most modern airliners.
Your indicated stall speed will vary with altitude, but in RC it's a non issue IMO. Not like our altitudes in RC vary by 40000 feet

sidgates

My Feedback: (2)

Pat- Thanks for the clarification. At my age I may be over sensitive the term "sticks in the mud."

sidgates

My Feedback: (2)

Yann - What radio system are you using? I would prefer a unit that works with Weatronic. Do you plan to market your system?

JackD

My Feedback: (4)

Darren,

On my second glider solo (first in a single seater, actually, the SZD junior that sits nowadays at byron), the airspeed indicator got stuck (one of the numbers started to peel off, and the needle got stuck under the paint)
I decided to continue towing all the way to 5000 and spent a long time stalling the glider to learn to judge the stall speed by pitch angle.

It made for an exciting landing haha.

Gonzalo38

Can't a similar thing be achieved with the existing Robbe Futaba GPS ? http://shop.rc-electronic.com/e-vend...&c=2403&p=2403

Can measure speed up to 500 km/hr.



Information can be displayed in the 18MZ or the Futaba Telemetry Box.

BlueBus320

My Feedback: (57)

Definitely not! Example; The GPS will give you ground speed, but your aircraft stalls at a given airspeed. The GPS will tell you your doing 100mph, but if your in a 100mph tailwind your airspeed is zero & airfoils completely stalled

Yann

SidGates,
I'm using a Futaba 12FG system. I designed my own temetry system it works regardless of the radio you use.
To stay away from 2.4GHz, I used 900MHz for temetry. So far it includes Heading, altitude, airspeed and various data from GPS. AOA is on the work as well as a more precise (ultrasonic) altimeter.
No I don't plan on going to market. I just do this for fun and educational purpose.

mr_matt

My Feedback: (10)

Yann how are you going to measure AOA?

Yann

The first way I'm experimenting is using a light sensor from an old computer mouse. You know, those with a ball. The axis goes through the fuselage skin to a vane, like a full scale sensor.
Next, I think I might be able to do it with an IMU.

stevekott

I agree with BlueBus320 about the GPS. In practice, and I tried it first it's worthless unless there is NO wind.

At my field most guys fly early morning and then start clearing out once the wind comes up. I almost always come out later in the day and there is usually an 8-10 knot wind down the runway. You get used to that and spoiled by that. My worst landings have been with direct crosswind, feels windy but not in the direction you think and in conditions of no wind where I have a tendency to land slow. In conditions of high winds down the runway I've seen two guys lose their babies on maidens by stalling on the downwind getting ready to land.

I'm glad we've got some Heavy Iron guys commenting on the usefulness of IAS vs. AOA. I have very limited knowledge of an AOA Indicator. I flew an hour once in a Citation X Sim and that was the only time I have ever used one.

I think on a model we don't need to get too technical or specific. It seems like plus or minus 5 mph will keep us in good shape. Like was said earlier we are usually landing about the same weight every time and pretty much the same Density Altitude. A Pitot Tube will "Self Compensate" pretty much on Air Density. With thinner air you will stall at a faster speed (True Air Speed) but with less air molecules pressurizing it, the Pitot Tube it will show you stalling about the same indicated speed. I think I'm right about that.

flyme2moon

My Feedback: (1)

Hi guys, I am amazed at the level of our technology, however I have trouble understanding abrivations ,

IAS = Indicated air speed,

AOA =

ILS =

IMU

IDK

these are in use within a very small community, please clarify as to meaning and difinition

I once saw an APE in a TRdouble E

stevekott

IAS = Indicated air speed, also referred to as Calibrated Air Speed.

AOA = Angle of Attack. The angle of Relative wind with the Wing Centerline or Chord. It's a good indicator of when a wing will stall. When the Angle of Attack is too great the smooth flow of air over the wing becomes disrupted and turbulent on the top side of the wing. When that happens the wing loses lift and stalls.

ILS = Instrument landing System. On full scale aircraft its a system that shows the pilot an indication with needles on Instruments or symbols on screens whether he is on Glide Slope (proper altitude) and Azimuth (on the runway centerline) on an Instrument Approach. Real handy if you can't see the Runway. You can also couple an autopilot to track this to reduce pilot workload on final approach.

IMU = IDK (I don't know .. sorry)

IDK = I don't know

Eddie P

My Feedback: (4)

IDK

AOA would be really useful for jets or any model airplane. Reason being:

It is a given that a relatively well set up IAS indicator will pretty much always show a stall at the same "indicated airspeed" at 1 G, no matter what model airfield you are at, even a model field at 6000 feet and 90 degrees outside (assuming you aren't flying super high up at 20,000 feet, these are models after all). However, the use of IAS goes out the window when you are flying at G loadings higher than 1 G.

We are above 1G all the time in models. I see guys really yanking on their models, way more than scale G loadings. At a 60 degree bank, that's 2 G's in level flight. Heck, guys are always pulling 2 G's as a matter of just staying in the pattern. Most guys are (in my estimation only) pulling 8 to well over 10 G's all the time when they are barely hot dogging in a model airplane. At only a 2G traffic pattern pull the stall will occur at 1.3 times the normal 1G stall speed. At 8 G's, just barely starting to show off, stall speed occurs at almost 3 times the normal stall speed. Since we don't have G loadings in the seat of our pants or a G meter or a attitude indicator showing bank in level flight it becomes a bit hard to judge stall speed with just airspeed telemetry alone. For models we have all gotten very proficient (or not) usually just looking for wing wobble or mushy response or pre-stall behavior and we judge that on our estimated speed. While telemetry is a great idea at bank angles less than 30 degrees or at any attitude with the knowledge of the limitations, some guys moving to telemetry without an idea of the pitfalls of listening to stall speed in an ear bud may be caught off guard when the jet rolls over onto it's back when they are not even approaching stall speed via telemetry.

This is why AOA might be really nice. Most know a wing will only stall at a critical angle of attack - speed is secondary as a stall can happen at any speed (even at half stall speed, we can make a wing fly, just reduce G loading to near zero and we have stopped the stall - but we still have to recover from the vector if the ground is near) An AOA set of audible beep tones would be awesome information transmitted an ear bud - for me anyhow, it's probably more of a reliable way to think about energy available at any given time on the wing rather than an airspeed call out. Something that starts beeping at a certain rate at anything below Vs 1.6 and below - (close to best glide or corner speed... totally depending on airframe). The beep could be setup to become more rapid, or somehow distinguishably different around Vs 1.3 - and then going to a different set of solid and beeping tone variations below that (VS1.2, VS1.1, VS1.0, etc) would be a really reliable and useful set of feedback especially in the pattern or heaven forbid in a flame out. Some level of familiarity would be required of course to use the system, and this is just my preference... maybe most would be different. A touchdown weight on wheels switch would be a nice touch to kill the tone on the ground.

The ultimate setup for me might be AOA below Vs 1.6 and then above Vs 2.0 I'd like a speed call out every change in speed of 30 MPH or so with a warning set to some level at higher speeds for awareness. Of course I might find that's too much information and take the awareness cues down a notch! I seem to do all right without it but it would be fun to play with.

Related link to speeds, best glide, stall...
http://www.experimentalaircraft.info...lide-speed.php

Pics:

The last picture shows a PDF attachment, it talks about G loading, Maneuvering, Corner speed, etc.

Yann

Sorry guys. IMU stands for Inertial Measurement Unit. It computes aircraft's attitude and orientation based on Gyros, compass, accelerometers and sometimes GPS to recalibrate.
You use complicated mathematical formulaes called "Kalman filters" to put these data together. Kalman filters is used to predict the craft's attitude and orientation from it's previous position in space.
As said before, the interesting point of using AOA over airspeed is that stall speed changes with wing loading, while stall AOA will always remain the same.
Looking for max AOA to land will then assure you to always land at the lowest speed.

chadxp1

My Feedback: (2)

Could you use an inclinometer for AOA?

Yann

Unfortunately no. An inclinometer would give you reference to the ground (or whatever reference you choose) instead of relative wind.

Yann

Very interesting post Eddie,
You seem to be way more educated than me on this topic.
I have one question though from the readings of the previous posts:
Is IAS different from airspeed?
If yes how?
How should I consider my pitot readings since I use a differential presure temperature compensated sensor?
Thanks,
Yann

Eddie P

My Feedback: (4)

I'm not really an accomplished person in setting up model airplane telemetry I only carry over some of the ideas and knowledge I have from my college training and then full scale airplanes ranging from ultra lights to gliders to medium and heavy jet transport to older first and second generation jet tactical planes I've been able to fly and gain experience with. Many of the earlier posts had great ideas and insights, I agree they all had good points. Mostly I am in awe of what you guys are up to so I am learning from you all, not the other way around. But to answer your question about speeds:

Indicated airspeed (IAS) that we would get from a model airplane pitot pressure sensor is very closely related to all forms of "airspeed". For purposes of a model airplane, we operate below 350 mph for the most part and most of us operate at fields below 10,000 feet msl. All forms of airspeed in our model airplanes are "pretty close and pretty related" assuming the pitot tube is precisely and judiciously mounted and the instrumentation is accurate. The biggest deviation we would come to realize would be the difference between indicated airspeed and what ground speed would be, on a CALM day. If you compared one model airplane flying in Anchorage Alaska, sea level, and -10 degrees C and then compare that to the same model airplane flying at Mt. Rose Pass outside of Reno NV at 10,000 feet when it was 80 degrees F outside, it would highlight what I mean. The model plane would be moving at dramatically different ground speeds in clam air and yet be at the same indicated airspeed. The one at Anchorage would be crawling along in a slow flight demonstration, for example just above the stall, and it might read "40 kph / 25mph". Then take that same model airplane to the 10,000 foot MSL flying site and you would see it racing across the sky, but also just above stall speed and you'd hear "40kph/25mph" in the ear bud speed telemetry transmission. Figuring the telemetry was a lie, pulling back on the stick would then demo a stall entry none the less. In this case, airspeed alone is extremely valuable as we are demonstrating a speed and stall range based on pretty close to a 1 G environment. In a model airplane, the indicated airspeed on the same model would be the same for a stall in both locations talked about above.

Since you are interested, the way airspeeds relate to each other is this. "ICE T" Its a way to remember it. The "I" is "indicated Airspeed". You get Indicated Airspeed (IAS) from the airspeed indicator and that comes from the pitot probe with differential pressure measuring equipment. Then you have "C" for "Calibrated Airspeed". Calibrated Airspeed (CAS) is IAS corrected for position and installation errors of the pitot pressure system. Then you have "E" for "Equivalent Airspeed". Equivalent Airspeed is CAS corrected for atmospheric pressure deviations and non standar temperature at the local place and altitude of measurement. (CAS is not going to be much of a player in model airplanes) This correction becomes more significant above 18000 feet and continues to be a bigger player higher up. Then finally we have "True Airspeed" (TAS). TAS is CAS corrected for compressibility (speed effect), usually above 350 mph or so combined with being higher than 20,000 feet, also not a big player in model airplanes.

So as we can see IAS is going to be mostly the only important "airspeed" player for a model airplane telemetry system. Assuming we are careful and set up the pitot system to be accurate as possible and then validate the stall speeds so we can assign some value to it so the speed telemetry has value. TAS (meaning all forms of airspeed from IAS to TAS) is hugely important in full size airplanes for planning longer flights and validating power and speed settings to achieve performance and range for fuel available. It is also critically important for flying high and fast for many more reasons. But not such a big deal in a model airplane.

Here is a neat article talking about it (airspeed.pdf)

Yann

Thank you Eddie. It's all clear now.