Mix Flaps and Throttle to Elevator with OpenTX

[j ferguson]

It looks like this is possible. If someone will confirm that it is possible, I will dive in and figure out how to do it.
The issue is that I can't judge airspeed when I lower the flaps and of course get a big nose-up which I can handle ok. But it is unsightly. When one is inside the plane this isn;'t an issue because you know the airspeed and without thinking about it can push the wheel forward as much as needed and re-trim.
I thought I could tie the amount of down elevator needed by assuming airspeed might have some connection with throttle setting and accordingly I could apply whatamounts to trim to the elevator as a function of throttle setting and flap angle.

If this seems crazy to you, it's ok to say so.
Taranis X9D

john

 

[Wayne]

Yes, you can do this... But with this said, I have never found any great difference in the amount of elevator compensation needed based on flap deployment regardless of the speed of the aircraft.

In other words, when you have the correct amount of elevator compensation for flap deployment, speed does not seem to be a part of that ratio.

I will say the only time I have noticed my flap to elevator compensation needed to be adjusted was when flying my gliders off a mountain that was 10,000 feet tall, and I normally fly at sea level.

Here is the basic mix I use with OpenTX and flaps:
When I deploy my flaps, this automatically adds the same percentage of elevator adjustment. So if I only use half flap, then my flap compensation is also only half. The "weight" of the elevator correction is adjustable via the throttle trim (since I do not use throttle trim on any of my planes.). This allows me to adjust the elevator compensation value on the very first flight and fine tune it so the plane does not pitch up or down when the flaps are deployed or retracted. I can deploy the flaps at any speed and they seem to be right on the money. I usually set up my slope gliders so they are level with flaps out, and my electric STOL planes I will set them up some they are slightly nose down when flaps are deployed.

I have seen many people mess with delays and all sorts of fancy things to try and get elevator compensation, and I originally played with some of that, but I have found just a simple and clean mix does the best.

You can probably setup a flight mode to do this for you, but you would have to dial in each different setting of flaps.. Not ideal, especially if you are like me and use a knob or the throttle stick for the amount of flap you want to use. Yes, I like a variable amount of flap. On our gliders they are used for both drag and glide slope corrections.

For my STOL electrics, I treat flaps much like a glider. I want a massive amount of flap, say 80 to 90 degrees of down flap at full travel and 25 to 30% of up travel on my ailerons. I then can set up a steep dive towards my landing point and flare at the last second onto the runway. I find this works best to give me a very controlled landing with a short roll out. This may not work with a very large model, or a model that has small flaps and can not generate enough drag. If the model only can offer something like 30 degrees of down flap, then I use them like you would in a conventional Cessna. Put them down and float into your landing.. Again ailerons up 25% or so will help cut the lift and make your landings a little smoother and less prone to tip stall or issues from wind gusts on final.

 

[j ferguson]

I cannot thank you enough for sharing all of this. You have probably spared me months of fooling around with this. I need to munch on what you've written for a day or two. try setting up one of my Pandoras and see how it works. I have the Pandoras setup as highwing tail-draggers, they look a little like cessna 180s. They have 3 flap positions, retracted down, and down-more. My flying is mostly flying patterns, trying to maintain constant altitude and turns in which I neither lose nor gain altitude. And then approaches and finals without porpoising. i know this doesn't sound too ambitious, but for me, it is still pretty challenging.

I bought a Timber, flew it for a while but didn't like it as much as the pandoras - they rebuild easier from crashes.

more to follow.

 

[Wayne]

Trust me, we were just talking this morning about flying challenges that make us all better pilots. Things like you just described.

One of my favorites is using the bare minimum amount of throttle to take off and climb out. Rather than mash the throttle and zoom off, I find it much more rewarding to do the very low power take off and make it look at scale like as possible. Think of it as a J3 cub taking off from the Aspen Colorado airport on a hot summer day. I want to use up the full length of the runway and just barely be able to get the plane into the air and very carefully and slowly gain altitude. I find it a fair amount of challenge to do it well. Some models are too heavy to make it look right..

Another super simple challenge is to make a good loop. By good loop I mean it need to be perfectly round and you have the same speed going up as you have going down. The throttle has to be worked, and you will probably have to use a little rudder and elevator adjustments. Once you get that going well, now make the loop much larger and try again. This is when you see how good you are on those sticks. The bigger the loop, and the slower the loop the harder it gets.

 

[j ferguson]

I've learned a lot about accelerated stalls from slow flying, also repairs. I built a flight data recorder which rides along in one of the Pandoras. It uses a u-blox gps and has sensors for heading, barometric altitude, attitude, and position. I found my idea of a rectangular pattern ( the type you fly touch-and goes with) was comical. See attachment.

I've built a newer version which also records control input and airspeed. the micro-controller is Teensy 3.5. I'm having a little bit of trouble just now recording control input - there's a problem with syncing that data, but eventually I'll get it.

I'm a retired industrial architect (factory buildings) and 79, but this is what I really always wanted to do. The beauty of the thing is I'm not very good at any of this so every time I do something, It's better than the last time. This includes the code, the PCB design and fabrication, etc.

 

[j ferguson]

Hi Wayne, If I understand what you've written above, you've mapped throttle trim to the flap-elevator mix. I assume that the trim only affects the mix, not the flaps.
How do you assign throttle trim to flap-elevator mix?
and yes, I have both the opentx 2.1 and 2.2 manuals.

thx much for your help with this.
I have the mix working but haven't been able to figure out how to trim the mix itself.
best regards,
John

 

[Txmustangflyer]

In Ethos, it's quite doable. I'll also mention something Wayne has mentioned to me the "butterfly" mix. If your ailerons are on different channels, you can set up a mix so that your ailerons both deflect upwards a little when flaps are deployed This stops the flare up and helps slow the plane. It would take some fiddling to get it dialed in just right for your aircraft, but something to look at.

 

[Txmustangflyer]

Wayne, what you describe I'll have to ask you on right before maiden on how you set that up in Ethos.

 

[j ferguson]

I've spent a couple of hours fussing with this directly on the X9D and I'm seeing the trim applied to the elevator but not the flaps which is good, but I'm only getting down adjustment and when the trim gets to it's limit it resets. not good.
What is Ethos?

 

[Txmustangflyer]

I've spent a couple of hours fussing with this directly on the X9D and I'm seeing the trim applied to the elevator but not the flaps which is good, but I'm only getting down adjustment and when the trim gets to it's limit it resets. not good.
What is Ethos?

Ethos is the new software from frsky they are using on their Tandem recievers. First out was the X20. About as easy to use as your phone. Along with it, they've released a line if Archer recievers that take advantage of the transmitters ability to use both 2.4 ghz and 900 mhz frequencies to reduce the chance of a brown out or unbind due to interference.
It's a nice setup. One of the best I've used. Aloft supplied, and they made sure it was updated before shipping. Only problem..I think they shipped before the latest update. Now I gotta finger out how to do it myself 8/

Feels good in the hands, very comfortable. Strap eyelet dead on balance point so no flopping one way or another if you are bent down doing something to the plane. Not too heavy so no neck aches, and a good case which the wife has chosen to decorate...
Now, I wouldn't try this without direct input from Wayne and his crew, but I think the X9D can be flashed to Ethos. He'll correct me if I'm wrong. It also would require the reciever to be flashed as well...I think. Not my best area to speak to. But I don't think you'd have to buy a new radio and recievers. If it's possible, he'll be able to walk you through how, or snag Chris to. Or you can send the radio and reciever to them and they can get it all set up as well.
There are some that prefer open TX. Me, I like gadgets. Especially new gadgets. Plus, I've been out if the hobby for eight years. In effect, just getting started like you. Lots has changed.

 

[Txmustangflyer]

Now, Konrad would probably disagree that Ethos is better. But, from a new start point of view, ethos is..simpler. A lot of stuff ethos does on its own, on an open tx radio, it has to be added by the user through scripts etc.
I'm not to where I can get to the radio right now, be almost New Years before I could do that, but Ethos takes all the confusing scripts for mixes, etc, and make it simple point and click.

 

[j ferguson]

Some progress on the flap-elevator trim problem - correct polarity now, but need to figure out how to make a trim adjustment stick.
I see what Ethos is, but I think I'l continue with OpentX. The problem with everthing like this is that one spends an inordinate amount of time with a particular setup thenuses it for a couple of years and cannot remember where it came from.

It's a bit like all the admonitions to comment code. Yup, I do it, but a lot of it doesn't make much sense ten years later. or thirty or forty years later.
My guess is I will upgrade electronics a lot sooner than that though.

 

[Konrad]

In the 7 years of using OpenTX I’ve never written a Lua script. I don’t recall ever saying one was better than the other.

My concern with Ethos was/is that it is a FrSky software product. And historically these early (beta) software products have been riddled with issues that the consumer shouldn’t have to deal with if FrSky actually had what I think of as SW validation protocols.

I’ve voiced concerns that a simplified OS (Ethos) might cost us far too much in programming power (flexibility).

It is still too early in the product life of Ethos for me to make any judgment as to wether Ethos is inferior or superior to OpenTX. But it is looking at this early stage like it might actually be a functioning and viable OS.

Now I have said that the master/slave mixing concept of most other OS if far too restrictive. I’ve also said that FrSky’s other OS (FrOS) found on the Horus line of radio was still born, no better than the master/slave.

 

[HENNY]

In the 7 years of using OpenTX I’ve never written a Lua script. I don’t recall ever saying one was better than the other.

My concern with Ethos was/is that it is a FrSky software product. And historically these early (beta) software products have been riddled with issues that the consumer shouldn’t have to deal with if FrSky actually had what I think of as SW validation protocols.

I’ve voiced concerns that a simplified OS (Ethos) might cost us far too much in programming power (flexibility).

It is still too early in the product life of Ethos for me to make any judgment as to wether Ethos is inferior or superior to OpenTX. But it is looking at this early stage like it might actually be a functioning and viable OS.

Now I have said that the master/slave mixing concept of most other OS if far too restrictive. I’ve also said that FrSky’s other OS (FrOS) found on the Horus line of radio was still born, no better than the master/slave.

Ethos is quite advanced at this time. Performing mixes like above can be done in two different ways. The most common way is almost the same as it's done in Opentx but I think it's easier to setup.

At this time there are not a lot of limitations when using Ethos.

 

[Konrad]

My concern is how did this turn into a an Ethos thread? My post in support of the original poster’s OS, OpenTX. This kind of mix is easy to do with OpenTx. As the flap to elevator response is not linear I map the elevator comp to a curve.
As to throttle, I don’t follow. Throttle has a very weak correlation to airspeed. I guess one could add a speed sensor and then write a script using the sensor as part of the logic.

it is my understanding that what the OP is noticing is an indication of being nose heavy.

 

[j ferguson]

Hi Konrad,

My problem was inability to gauge airspeed visually and not wanting the pitch-up on flap deployment. The planes I flew in the '70s all did this, you had to really push on the wheel if you let out the flaps with too much airspeed. So I thought the same thing might apply to my r/c planes where I'd need mor down-pitch with more airspeed, and ot having any way to guess airspeed I thought it might have something to do with throttle setting. so.....

I've now learned that on these planes, throttle isn't really needed in the mix and having flap deployment add down pitch to the elevators gets the job done.

Wayne mentioned that he'd mixed throttle trim into his mix so that he could adjust the amount of pitch-down added to the elevators and thus ot need to guess every flight. this sounded pretty good to me. I'm able to get throttle trim ( nor connected to throttle itself) to adjust elevator pitch but not incrementallly, either all or nothing and it works wheter flaps are deployed or not.

So I obviously have it screwed up.

 

[Konrad]

Ok, so “throttle trim” is the TX lever used to adjust the elevator compensation? I do this with my gliders. Look at some of the templates by Mike Shelium for haw to do this. With powered ships I’d assign this trim function to a sliders or front knob.
If you are comparing how a full size Cessna responds to a model please be aware that the full size aircraft has a very very wide margin of stability, read nose heavy. I trim my models as close to neutral trim as possible. The closer I can trim to neutral the better I think a model flies. My trimming philosophy is that the only thing worse than being tail heavy, is being nose heavy!

P. S.
The shape of my elevator to flap compensation curve looks asymptotic. That is I need a lot of elevator compensation early in the flap deployment.

 

[j ferguson]

Hi Konrad, I think I'll switch the adjustment from the throttle trim button to one of the knobs. that may make it work for me.
where do I look for Mike Shellium's templates?

john

 

[Konrad]

Try here.

OpenTX/EdgeTX Clinic

Tutorials and templates for OpenTX and EdgeTX

rc-soar.com

 

[j ferguson]

Thanks, Konrad. It occurs to me that I do want the trim control to be a trim control - the system remembers if which won't happen with a slider or knob.