Carsten Groen

During the last year or so, I have been thinking of a device that will help us with this, a little more safety during our landings! During this process, I have had very good feedback from some of my good friends here, Sandor, “andersaa” – Anders, “oliver”, “A343” – Thomas and lately also from “Sid Gates”.
I presented the idea a long time ago to Sandor from Digitech, and he thought it could be a nice product, and we have been discussing back and forth on the design the last few months.

I’m finally so close now, that I’m going to present the idea to you guys, and I hope for some input/ideas/criticism from you!

The ASSI device has inputs for a control switch and the flap channel.
The control switch (typically a 3-position switch), switches between active, off, and teach mode.
In the off mode, the device is inactive, no monitoring etc. is done, the device is doing nothing!
Connection to the sensorhead is done using 3 pieces of 3mm plastic turbing. The pressure sensors are mounted on the device itself. The ASSI board will be very compact, and will be fed by a 2 cell LiPo battery. The device can be left connected to the LiPo battery permanently, it will power itself on when the receiver is powered up. If the battery is drained too much, the device will switch itself off to prevent any damage (deep discharge) to the battery.
The device controls two high bright LED's (Red and Green) that can be mounted (f.ex) on the front oleo.
(Optional, there is also an input and output for a throttle channel, this _might_ be used in the future, no promises !)

The description below is only a "draft" things can and will change, but this is a starting point for discussion

How to use the device.
First, the device needs to be trained, it will record the critical AoA and the optimum landing speed, both will need to be recorded at (up to) 5 different flap settings (remember to do the training at a safe height!).
The training session is done with gear down, and if possible, with less than full tanks (should be as close as possible to a real landing scenario).

The device should be in ”off mode”, with the gear down.

First, the ”no flaps” setting on your radio is selected.
The plane should now be slowed down to what you feel is a ”safe” approach speed.
When that is achieved, bring the control switch from the off position to the teach position for approximately 1 second (not too important), the green light will flash rapidly 5 times when the airspeed has been recorded, then bring the control switch back to off again.

Now, with the same flap setting, bring the plane down in speed, slowly add elevator, and find where the critical AoA is, ie. just before the plane stalls, when you reach this point, bring the control switch to the teach position again for approx 1 second, the red light will flash rapidly 5 times, then bring the control switch back to the off position again (remember to this at a safe altitude!).

The above sequence is repeated for all the flap settings (maximum 5 settings can be trained).
Now, lets say you only teach the system 3 flap settings. You put the device in active mode, but you select a flap position that is in between 2 of the settings you used for the teach session, the device will use the data for the ”lower” flap setting during approach.

After the device has been thru the training process, it is ready to be used actively.

Put the switch in off position, and fly around, just as you used to do.
When ready to land, bring the gear down and put the control switch in the active position. The device will now monitor the AoA and airspeed for the currently selected flap setting (if you change flap settings during the landing, the device will automatically use the settings for the current flap settings)

The device will use the red (for AoA) and the green (airspeed) LED’s for signaling if you are close to the critical AoA and if the airspeed is below/at/above the speed that was trained (for the currently selected flap setting)

Red (AoA):
Off: below critical angle
Slow flash: 5 deg below critical angle (TBD)
Faster and faster flashing: flash rate rises as the plane is getting closer to the critical AoA
Solid on: at or above the critical angle (you really want to avoid this )

Green (Airspeed):
Slow flash: below optimum speed
Solid on: at optimum speed (+/- 5%) (TBD)
Fast flashing: above optimum speed

(TBD: duty cycle of the flash should tell how far you are from the ”optimum” setting/critical AoA)

And the pricing you might ask, and honestly: "we don't know at this point, but very affordable, and certainly cheaper than a crashed jet "

Sorry for the long winded text, and please, don't be too harsh on my english skills

digitech

My Feedback: (10)

Developed by Sandor Kruise (Digitech Electronics BV / Carsten Groen)

Many people have problems with it, we know we have, “guessing” our planes speed when on final, is it too slow, is it too fast ?
Often you find yourself doing a landing with less/more than optimum speed, you’re afraid of coming in too slow, so you tend to go (way) too fast, resulting in many “go-arounds” on small strips.
Now, it’s of no concern for the “Pro pilots” out there, but for many of us “mortals”, it is a real problem.

We know someone might say:
“if you fly jets, you should be able to do this without any helping devices, otherwise you should be flying something else…” .
This may be true and correct, but we don’t want to fly “anything else”, we want to fly jets, and we want as much help as we can get, PERIOD!

So, the next post here, Carsten Groen will explain the idea a little more in detail...
i am doing the sourcing and hardware production....

Carsten Groen

PS: it might be possible that the only thing we actually need, is the AoA indicator, I'm open to that, please give me your input guys

DelGatoGrande

My Feedback: (23)

nice product would be!

i would prefer a head set speaker to give me this info than a light on the plane...since i like to concetrate on the shape of the airframe and how ill touch it down than on the blinking rate of a light..

also what about the hoter or colder days when the air gets thicker or thiner and change lift and stall speed when airspeed can be the same?

insted of an airspeed sensor i would personaly prefer a sensor who will mesure the change of power in flap servos(high load=overspeed low load=stall)

just my thoughts

goodluck!

Carsten Groen

George,
Thanks for the input!

Regarding the earpiece, thats a good idea, I have though my reservations about a transmitter in a plane, will have to make 110% sure that it does not interfere with the control of the plane. Now, if someone suddenly got a glitch, I could easily see what way this could go....

Regarding the temperature compensation, I think it will be ok anyway, the measurements/calculations is based on the factor between AoA and airspeed, so it will hopefully remove itself from the result (but if not, it would be possible to measure the temperature, and do the compensation for that, or worst case, do another training for that "special" day)

andersaa

Since the AOA will be calculated from difference in IAS between 2 inputs in different angels, the density is of no importance.

/Anders

highhorse

My Feedback: (2)

There are really only 3 things that matter with regard to the stall:

1) AOA
2) AOA
3) AOA

Everything else is rubbish :-)

The critical AOA does not vary with weight, temperature, attitude, speed, phase of the moon, or anything else other than flap configuration.

How about a loud piezzo buzzer option? It would be helpful without regard to the model's aspect to the pilot, and in combination with the AOA input, could warn of an impending departure from controlled flight in any attitude, any maneuver, at any speed, and whilst flying in any direction. The 4th quarter of a loop which is being completed whilst flying "away" is perhaps the most useful example.

If you wanted to be fancy about it, use two horns with two tones rather than two lights. The lower freq tone initiating at critical AOA -5 degrees, and a higher, more shrill tone at crit AOA - 2 degrees or so.

The only drawback I see to the piezzos is that it may take a full second or more for the sound to reach your ears and may be drowned out by some 3d goofball hovering nearby.

But I still strongly prefer that to a light.

Thanks for soliciting the input, I'm sure that you will have a winner on your hands !

Rider-60

My Feedback: (17)

An AoA indicator with 3 lights would be perfect and would actually be scale as it is used in carrierborn aircrafts. So we can now be as a landing officer

Carsten Groen

OK,
great with the feedback guy's !
So basically, the device can can omit the "airspeed indication part" from what I read here, it is of no consequence to the hardware needed (other than maybe an LED output that are not used), it's just a matter of if the airspeed training/monitoring is going to be used or not.
The airspeed sensor (transducer etc) is still going to be present, it is used to make the AoA calculation anyway (the system uses two diff. transducers)

Now, regarding the inclusion of a beeper or not, I have my doubts about it, when we fly here, there are usually 3 planes in the air at the same time, and because of that, some noise. I doubt that a beeper could be heard from the plane, unless it is VERY loud, plus there is the delay because of the distance!
But, maybe it could be made as an option, a simple output from the device, then it is up to the user to use it for whatever purpose ?

digitech

My Feedback: (10)

no beepers forget it you wont hear them anyway..
exept on a flame out

mk1spitfire

I was thinking this idea when telematry was invented, hoping new telematry sets linked to airspeed would activate vibration/beep within the tx set as the airframe approached critical stall.
Possibly even a mix that adds power before you realise you have to for desired approach speed.
Good for short fields when you want to bleed off speed.

highhorse

My Feedback: (2)

Perhaps the circumstances at my club are unique, but folks tend to "stand down" while a turbine is in the air and there is little/no competing noise.

Still, given the time delay, sound is probably of little value.

JohnMac

I would say that a true AOA indicator is all we really need, but I suspect difficult to do> Airspeed is interesting. AOA is useful.
I have sent you a PM.

JohnMac

I know one company who are working on a stick shaker.

Rider-60

My Feedback: (17)

Everything you need to know about AoA is here, it's done for full size planes, now if you can make it cheaper... and smaller tha would be perfect
http://www.alphasystemsaoa.com/index.html
http://www.youtube.com/watch?v=DCerL8ljRwk
http://www.aircraftspruce.com/catalo...AngleBuddy.php

and the last one
http://www.google.fr/imgres?imgurl=h...26tbs%3Disch:1

rick hamel

My Feedback: (1)

I've been waiting for years for a deviceI bought one years ago but you had to look at the sceen to know your speed-if you could wear an ear piece an have the speed called out to you every 2 seconds or so that would be the cats behind

757Driver

My Feedback: (90)

I like the earpeice idea...hello bluetooth! The system could be activated with a switch on the TX, low AOA (high speed flight) could be a low tone and as you approach the stall limit AOA it would produce a gradually increasing tone......I'm thinking just like a variometer does for rate of climb in sailplanes.

AOA should be taken via a "vane" just like big birds.

Maby this variometer could be setup to provide changes in ram air pressure (airspeed).... http://www.pitlab.pl/wario_en.html

757Driver

My Feedback: (90)

Just found this and it looks good. Audible changing tone as you get closer to stall airspeed that you set.

http://www.rcaviation.com/fiorenze/ASI%20Kit.jpg

Carsten Groen

Hmm, "stall airspeed", that depends on the current AoA ?
The idea with the tone is however nice! That functionality is already included in Weatronic receivers, they have a Vario sensor, that can be configured as a simple airspeed indicator, and the transmitter module can be programmed to give a warning at low/high airspeed, and can even call the speed every xx seconds (in spoken language, not just a tone)

But, in the long run, I would like this to be a standalone device, and not rely on that a specific product is present..

The idea with the bluetooth is nice, however I don't like the idea with a 2.4 GHz transmitter in the plane (in fact, I dont like transmitters in the plane at all )

And no, the AoA should not (if possible) be taken with a vane, I have an idea, that if moving parts can be avoided, they should ! This device will measure it using pressure instead (and a special sensor head)

Jim Cattanach

The main thing I would look for would be a device that tells the landing approach airspeed. I either come in too fast, or too slow. I think most of us know the landing characteristics of our individual jets, the difficult part is knowing if you are at that ideal speed. A means of setting the device for various speeds, so that the indicator is set for the airspeed you want, is all I would require. Say flashing green if to fast. Solid green if ok & red if to slow. Or any other colours or beeps etc.
Simple is better.

A343

My Feedback: (4)

Well, almost. Without airspeed creating lift, you can have whatever AoA you want. It won't fly anyway!
So Carsten, keep the IAS indication. Maybe a flashing indication for Speed and a steady for AoA. This might be a help for those having a problem separating Green and Red colors.

Regards Thomas

siclick33

I think AOA would be quite hard to fly as guide for approach parameters. The band between ideal approach AOA and the stall would only be in the order of a few degrees. Having a little bit of experience flying full-size aircraft on AOA, I don't find it that easy.

Quite a large number of aircraft (even fairly high performance ones) use airspeed for final approach (not AOA). I think that, in practise, speed would be a much more useable parameter. I would be interested to see if a airspeed comparison, as suggested, would be accurate enough to produce a useable AOA. Maybe this is a reason that the AOA systems that I have encountered all use vanes.

I think that the airspeed system is a great idea. IMO a large number of jet flyers land too fast and wonder why they consistently produce bouncy landings.

HarryC

My Feedback: (1)

re jascat and A343 posts, an AoA meter is more useful throughout the entire flight envelope than an ASI, though I take siclicks point about it operating through a much tighter range so being harder to peg to a reasonable value. But as a previous poster put it correctly, the stall is all about AoA, AoA, AoA! If your model stalls at X degrees, it will stall at X degrees regardless of its speed, regardless of its attitude. On the other hand, a stall speed is only true for the exact G load at which you measured it. At zero G, for example pushing over the top of a climb, stall speed is zero and you can afford to be pushing over at speeds well below the alarm speed, what use is your ASI stall speed indicator then, blaring away when actually you are well above the stall? Or at higher G such as loop or even a steeply banked turn onto finals the stall speed rises dramatically and could be 2 or 3 times the stall speed alarm you have set so the model stalls in the turn and flicks into a spin yet your ASI stall speed alarm never sounded. So an AoA meter alarm will always be true, but an ASI alarm will frequently sound falsely, or not at all when in fact it should.

As to getting the speed right on approach, an AoA meter does this for you, but accepting siclick33's point it may be harder to use in practice. If you have the right nose up/down attitude and a reasonable rate of descent, your speed is correct. You simply swop the AoA for the ASI - where you would watch the rate of descent and increase or reduce airspeed, you watch the rate of descent and reduce or increase the AoA (it goes the opposite way to ASI). So it is possible to still fly a consistent, accurate approach with AoA instead of ASI, if you can make the AoA meter practical to use.

Some of you are probably under the impression that aircraft have a stall speed, after all every full size has a pilots operating handbook with a published stall speed and ASIs have coloured arcs indicating maximum speed and expected stalling speed do they not? Yes, but that is the 1G level flight stall speed, you need to understand that the stall speed at any time is the published stall speed multipled by the square root of the G load at that time, it is not a fixed speed.

H

siclick33

Harry,

Whilst I agree with you 100% on the theory, in practise I still believe that airspeed is easier to fly on approach than AOA. The 'g' argument is somewhat irrelavent as you should be almost exactly 1g on approach (Please bear in mind that I am considering using the system to assist with landing-I agree that g is very important for manoeuvring flight 'stall speed').

In RAF service the Hawk T1 final approach is governed by airspeed (not AOA). Why would they do this if AOA is the be-all-and-end-all?

As for increasing and decreasing AOA on approach, I don't think this is correct as it would cause fluctuating airspeed. You need to hold AOA constant and vary the power to control descent rate.

HarryC

My Feedback: (1)

I was agreeing with you siclick that the nature of the AoA meter having a very narrow range is likely to be harder to use. I will be astonished if they can get anywhere near a useable, consistent AoA meter just from positioning pressure sensors. I think the G argument is relevant if you leave the device switched on all the flight as I expect some people would. Putting aside any practical problem of making a decent AoA meter, it will be the same to use as an ASI on approach - set some AoA, adjust descent, and the speed will be whatever it is, every time. The effect of following the AoA meter and rate of descent to make adjustments will lead to the same outcome as following ASI and rate of descent.