3D Printed 64mm MiG 21

[telnar1236]

I'm not so sure I see a logic of why they need a very precise geometry. Mainly they need a very un-confused incoming vector for air flowing. They can't be behind the prop, they can't be next to the body... they have to have some finite (on real plane not very large) distance from other parts of the plane. Any complexity on real planes tends to be based on making them robust... for rain, ice, hanger rash, etc. Beyond that... any special geometry may be because of attempts to make it relatively linear with respect to the ram affect going on... because of the instruments of the day when it was first created (and many decades later) that relied on mechanical bellows, levers, springs and such to turn a mechanical dial.

A straw (as the tube) would never be found on a real airplane... simply not sturdy enough. But it separates the flow from that... that only goes into the tube versus that, that cleanly does not. I would think the leading edge perimeter of the straw is equal to most any (real world) leading edges on a precisely machined pitot tubes after being in the field for a number of years. Not having actually tested it (yet) I believe any malformed non-linear geometries of a simple straw can easily be a corrected in a microcontroller using a mapping function... that NEVER could have been duplicated in a mechanical device.

I can very easily be wrong and will gladly air my failure, but that is my premise going into the experiment.

That is the most important factor but not the only one. It will probably be possible to calibrate the straw to get somewhat usable data, but there are a few major things at play. First, you need a static source from immediately next to the inlet to reliably find dynamic pressure. Static pressure varies all around the plane, so you also need a clean source for static pressure. Pitot static probes are the most common way of achieving this where the static pressure is measured on the sides of the actual probe. You could calibrate the whole plane, but sticking a plane that big out a car window seems sketchy. Second, and a lot less important, the sharp inlet on the straw will be much more vulnerable to changes in angle of attack and sideslip. I don't think that will have a major impact though. Probably the most important thing is just having the ability to precisely calibrate it. If you have a well characterized geometry, you can just read the specs, but when calibrating manually, you're limited by the precision of the measurements you take while calibrating. A 5 mph precision might be 10% or more on an EDF like this. I do think you'll be able to get some data, but it might be too imprecise to be very useful. I would also actually be worried about the rigidity of the straw, even on an rc plane. It needs to stick far enough out from the nose that it gets clean air, but that might be far enough for it to buckle. I had a coffee stir for a while as the fake pitot probe on an Me 163 and it needed to be replaced every 3 or 4 flights.

I think I've seen a 3d printed head with a coffee stir tube used in a pitot-static application, though, so that might be a way to get slightly more reliable results.

 

[L Edge]

@telnar1236, @L Edge

I'm going to put a coffee stir straw through the radome of the F-8 and I have some tubing that should be here tomorrow so I can have a cool test bed for some pressure sensor, altimeter / pitot tube, microcontroller programming project. I'll probably be adding accelerometers and gyros also... just for S&G! I also want to monitor LiPo voltage so I can make better decisions about when to come back down instead of timing like all the other guys use at my field.

Should be a fun project.

A good use of that telemetry is the temp probe. Spektrum has a Rx and equipment for that when set up, reads the temp on the transmitter screen.( Accurate by checking against the Raytek min-temp laser to within a few degrees) and it is an excellent way to break in gas engines and adjust the high/low screws so it doesn't go blurby or lean during half throttle.

When I was doing that pressure stuff with probing the exit of nozzles to see flow pattern and losses, I visited a guy who makes neon signs. After explaining what I wanted about having a micro pitot and showing him my EDF, he went to the scrap pile of broken glass and he made 4 drawn glass pitot tubes so I could measure the exit area flow pattern. Also I bought my small tubing from a gas filled landing gear system) to hook up to the glass ends. I then had him make 2 glass U-tubes to fill with water to measure the difference between static and dynamic pressure. Because the delta P is so small, tubes were inclined 10 degrees up from floor to see the difference. Simple way to check inlet ducting of choking or not.

Question:
Is there a written working program that you can reference me to explaining controlling the FC to have max differential pressure(dynamic-static) and move a servo?

 

[L Edge]

@telnar1236, @L Edge

I'm going to put a coffee stir straw through the radome of the F-8 and I have some tubing that should be here tomorrow so I can have a cool test bed for some pressure sensor, altimeter / pitot tube, microcontroller programming project. I'll probably be adding accelerometers and gyros also... just for S&G! I also want to monitor LiPo voltage so I can make better decisions about when to come back down instead of timing like all the other guys use at my field.

Should be a fun project.

That's what is all about. Actually, FC's stuff is going to enter all the 6th generation fighters. Without rudders, the problems of yaw will need to be solved. Another area is the avian approach.

 

[Inq]

Question:
Is there a written working program that you can reference me to explaining controlling the FC to have max differential pressure(dynamic-static) and move a servo?

I thought it was time for me to quit hijacking @telnar1236 Mig 21 thread with electronic stuff. I've started a thread that I'm going to project on once I get through with FTFC23 planes - https://forum.flitetest.com/index.php?threads/diy-telemetry-and-control.72547/

Could you draw me a simple sketch of what you're wanting to do? The picture I have in my mind is to measure two pressure sensors and move a servo according to some differential algorithm doesn't sound like it be that hard... but I may be oversimplifying it. If interested, please throw it in that thread.

 

[L Edge]

Yeah, LE flaps definitely help a lot. I have them on my 50mm F-104 and they let it slow down far better than it has any right to, although I have not programmed them in to help with turns. Honestly, I don't think automating the flaps with a static pressure sensor will help much beyond what a good curve for deflection vs. angle of attack would give you. But experimentation is a big part of the fun of this hobby, so what you're describing could still be a fun project. Based on the application you're talking about, I think the sensors Inq shared would be perfect, especially with a good low pass filter.

The answer on how it works is this. I use an independent programable gyro. (not talking about gains)
My gyro works off a 3 position switch. Center is off. Rate is one end, head hold is the other.
Now find unused channel and plug in gyro lead that has power. Set switch to that channel. Toggle switch to center, gyro is off, Toggle to rate toggle to hold and gyro is activated. Do not use hold.
Now hook to computer and program the rate mode (just like a servo) of one end to zero(ATV) and the other leave at 100ATV. That means movement allows down servo but will not go above flying horizontal.
Now mount gyro for flying horizontal and insert servo lead into elevator to run moving leading edge flaps.

Understanding what you have done is power up the gyro, it is design only to see movements in pitch and is independent of your plane controls of elevons or rudder or ailerons. It will only act to pitching of aircraft from level to nose up.

I found LEF to be 30 degrees down was max.
So to set flap level, adjust programming setting from 0 to whatever.
Now lift nose of plane up and servo will move LEF down. If it doesn't, and goes up, change ATV from zero to 100 and reverse the other.
Now lift nose way up, and you have LEF deflection down. To set max of 30 degrees down, now move ATV setting back from 100 to what ever number give the max angle. For example, it may be 0 to -46.

Guarantee your takeoffs will be shorter and landings will be slower (and steeper if you like) with the gyro and LEF's. Sharper turns are a byproduct. A safety factor is added if you flip the switch to center, you kill the gyro and the LEF go to zero degrees.

What radio system do you have.

 

[telnar1236]

A good use of that telemetry is the temp probe. Spektrum has a Rx and equipment for that when set up, reads the temp on the transmitter screen.( Accurate by checking against the Raytek min-temp laser to within a few degrees) and it is an excellent way to break in gas engines and adjust the high/low screws so it doesn't go blurby or lean during half throttle.

When I was doing that pressure stuff with probing the exit of nozzles to see flow pattern and losses, I visited a guy who makes neon signs. After explaining what I wanted about having a micro pitot and showing him my EDF, he went to the scrap pile of broken glass and he made 4 drawn glass pitot tubes so I could measure the exit area flow pattern. Also I bought my small tubing from a gas filled landing gear system) to hook up to the glass ends. I then had him make 2 glass U-tubes to fill with water to measure the difference between static and dynamic pressure. Because the delta P is so small, tubes were inclined 10 degrees up from floor to see the difference. Simple way to check inlet ducting of choking or not.

Question:
Is there a written working program that you can reference me to explaining controlling the FC to have max differential pressure(dynamic-static) and move a servo?

I don't think there is a ready-made program that would do that. Like I've said, I don't think there is much reason for it, beyond the fun of it. It should be pretty straightforward to write one, though, as Inq said.

 

[L Edge]

I don't think there is a ready-made program that would do that. Like I've said, I don't think there is much reason for it, beyond the fun of it. It should be pretty straightforward to write one, though, as Inq said.

Did you understand how simple the automation with the gyro?

I disagree about being straightforward to write one program. I asked you what radio you have for if you know about sequencers. Spektrum said real easy, here's a sample. (I used to program in assembly language) The landing gear. Ha,it took me 3 months to do the following.

1) Flip a switch. Do not touch radio.
2) Sequencer then starts left engine on transport and let' it go to idle. Then 30sec later, start 2nd engine and let's it go to idle. Sequencer then jumps out allows you to use throttle as you want.

You need to taxi, so up idle and go:
To control speed, hey you need brakes.
Sequencer program number 2. 3 position switch to 1) no brakes, 2) oscillating brake to control speed, 3)brakes locked
So now you increase throttle and have oscillating brakes to taxi. So match throttle for proper speed.
Get to runway and lined up. Lock brakes. Full throttle and unlock.

Only bad feature, thrust at full is greater than holding brakes lock and you end up having a flat spot on your tire. It started
sliding at 1/2 throttle of both engines.

Do reverse to come back and shut your engine off.

Anyway, my next project is F-117 with an EDF(not prop). Lot's of problems. Have you seen any video that show from launch to landing?
Club member gave me a purchased one and after 2 different flyers crash it. I got 8 flights out of it before when cruising around at slow speed, it rolled over and the ground god's got it.(no rudder) So at least I have the area to work on.

 

[telnar1236]

Did you understand how simple the automation with the gyro?

I disagree about being straightforward to write one program. I asked you what radio you have for if you know about sequencers. Spektrum said real easy, here's a sample. (I used to program in assembly language) The landing gear. Ha,it took me 3 months to do the following.

1) Flip a switch. Do not touch radio.
2) Sequencer then starts left engine on transport and let' it go to idle. Then 30sec later, start 2nd engine and let's it go to idle. Sequencer then jumps out allows you to use throttle as you want.

You need to taxi, so up idle and go:
To control speed, hey you need brakes.
Sequencer program number 2. 3 position switch to 1) no brakes, 2) oscillating brake to control speed, 3)brakes locked
So now you increase throttle and have oscillating brakes to taxi. So match throttle for proper speed.
Get to runway and lined up. Lock brakes. Full throttle and unlock.

Only bad feature, thrust at full is greater than holding brakes lock and you end up having a flat spot on your tire. It started
sliding at 1/2 throttle of both engines.

Do reverse to come back and shut your engine off.

Anyway, my next project is F-117 with an EDF(not prop). Lot's of problems. Have you seen any video that show from launch to landing?
Club member gave me a purchased one and after 2 different flyers crash it. I got 8 flights out of it before when cruising around at slow speed, it rolled over and the ground god's got it.(no rudder) So at least I have the area to work on.

Not 100% sure you I'm following what you're saying here. To be clear, the statement in about it being pretty easy was about writing for an Arduino, not using a transmitter or OTS software. In C++, mapping deflection to angle of attack would be as simple as defining a few arrays and mapping them to each other. Actually maximizing the pressure differential would be harder since there are likely to be two maxima for many angles of attack, one associated with upward deflection and 1 with downward. That's why I was recommending just using a map by angle of attack, but it would still be pretty simple to find a local maximum if you selected specify a bias towards deflection in one direction. The program you're describing for idle and brakes would also be pretty simple in C++ since it would just be a series of conditional statements, delays, and outputs. Modern programming languages are so much easier to deal with than assembly language.

 

[telnar1236]

Did you understand how simple the automation with the gyro?

I disagree about being straightforward to write one program. I asked you what radio you have for if you know about sequencers. Spektrum said real easy, here's a sample. (I used to program in assembly language) The landing gear. Ha,it took me 3 months to do the following.

1) Flip a switch. Do not touch radio.
2) Sequencer then starts left engine on transport and let' it go to idle. Then 30sec later, start 2nd engine and let's it go to idle. Sequencer then jumps out allows you to use throttle as you want.

You need to taxi, so up idle and go:
To control speed, hey you need brakes.
Sequencer program number 2. 3 position switch to 1) no brakes, 2) oscillating brake to control speed, 3)brakes locked
So now you increase throttle and have oscillating brakes to taxi. So match throttle for proper speed.
Get to runway and lined up. Lock brakes. Full throttle and unlock.

Only bad feature, thrust at full is greater than holding brakes lock and you end up having a flat spot on your tire. It started
sliding at 1/2 throttle of both engines.

Do reverse to come back and shut your engine off.

Anyway, my next project is F-117 with an EDF(not prop). Lot's of problems. Have you seen any video that show from launch to landing?
Club member gave me a purchased one and after 2 different flyers crash it. I got 8 flights out of it before when cruising around at slow speed, it rolled over and the ground god's got it.(no rudder) So at least I have the area to work on.

As for the F-117, I have no idea. I think there are some pretty good threads on a foam board version on the forum, and I know Banana Hobby sells a 64mm and 70mm version, but I don't have any personal experience with any of them.

 

[Inq]

As for the F-117, I have no idea. I think there are some pretty good threads on a foam board version on the forum, and I know Banana Hobby sells a 64mm and 70mm version, but I don't have any personal experience with any of them.

I've read that the real F-117 is completely unflyable without the computers (quad redundancy)... to the point that the procedure under computer or power failure is to punch out. I wonder what tweaks to a scale design were required to eliminate that instability in their models.

 

[L Edge]

Not 100% sure you I'm following what you're saying here. To be clear, the statement in about it being pretty easy was about writing for an Arduino, not using a transmitter or OTS software. In C++, mapping deflection to angle of attack would be as simple as defining a few arrays and mapping them to each other. Actually maximizing the pressure differential would be harder since there are likely to be two maxima for many angles of attack, one associated with upward deflection and 1 with downward. That's why I was recommending just using a map by angle of attack, but it would still be pretty simple to find a local maximum if you selected specify a bias towards deflection in one direction. The program you're describing for idle and brakes would also be pretty simple in C++ since it would just be a series of conditional statements, delays, and outputs. Modern programming languages are so much easier to deal with than assembly language.

For the average guy, the sequencer is available to someone that doesn't know about programming or FC stuff. Simple sequencers like brakes can be just about copied from the transmitter and tied to being controlled by a switch.

This was my first project and had it running in an hour. The mode switch turned on/off program and the sequencer was set up with brake, no brake, and oscillating brake(to taxi). The mode switched also let's you do the startup/ get out of it to fly/come back in and shut down.
The start/shut down included 2 mixing programs to set up moving trims for running doing the if/then routine.

All I trying to say is here is a method to use that very few pilots know about. Especially if you are doing scale.
As far as pressure for transducer, I would prefer strain gauges. So, it looks good enough for now. I like to design things that don't exist. Close enough.
This is how I explored control 9 years ago with what you had.

 

[L Edge]

As for the F-117, I have no idea. I think there are some pretty good threads on a foam board version on the forum, and I know Banana Hobby sells a 64mm and 70mm version, but I don't have any personal experience with any of them.

Yes, but the proof of the pudding is the complete launch, flight of the plane and landing being stable. Why do they cut the video short or change views?
The commercial one I inherited(3rd person) the BH one.

 

[telnar1236]

For the average guy, the sequencer is available to someone that doesn't know about programming or FC stuff. Simple sequencers like brakes can be just about copied from the transmitter and tied to being controlled by a switch.

This was my first project and had it running in an hour. The mode switch turned on/off program and the sequencer was set up with brake, no brake, and oscillating brake(to taxi). The mode switched also let's you do the startup/ get out of it to fly/come back in and shut down.
The start/shut down included 2 mixing programs to set up moving trims for running doing the if/then routine.

All I trying to say is here is a method to use that very few pilots know about. Especially if you are doing scale.
As far as pressure for transducer, I would prefer strain gauges. So, it looks good enough for now. I like to design things that don't exist. Close enough.
This is how I explored control 9 years ago with what you had.

Fair enough. Honestly not 100% sure how the strain gauges fit in, but if you have an idea how to use them, it sounds like a fun project.

 

[telnar1236]

Yes, but the proof of the pudding is the complete launch, flight of the plane and landing being stable. Why do they cut the video short or change views?
The commercial one I inherited(3rd person) the BH one.

I really don't have any experience with F-117s, either commercial or not. As Inq pointed out, the real one was extremely unstable. The videos from Banana Hobby make it look good, but they're meant to sell the product. While all my experiences with BH have been good, I know they're famous for quality control issues so you might have run into something like that.

 

[L Edge]

I really don't have any experience with F-117s, either commercial or not. As Inq pointed out, the real one was extremely unstable. The videos from Banana Hobby make it look good, but they're meant to sell the product. While all my experiences with BH have been good, I know they're famous for quality control issues so you might have run into something like that.

As I mentioned, the F-117 was passed down (each had a crash of BH) by the 2 guys. I got a few flights before it totaled. Need to finish up 3 other projects before I attempt. Going to try a different way to resolve issues on F-117. By the way, the reason I was tracking Ing is to glean info with the 8 degree wing and inlet ducting in flight.

By the way, my STOL project has not only high AOA wing up, so is elevator at an angle. Got thread, take any comments from you.

 

[telnar1236]

It's taken a while since I've been pretty busy with other stuff, but the CAD for the version 2 of the MiG 21 is mostly done. Along with improved ducting and reduced weight, there are a number of other improvements including a much simpler hatch geometry that provides better access, a thinner wing that should better take advantage of the ability of deltas to fly at high angles of attack, and a simplified printing process. Hopefully this one actually flies.

 

[Inq]

It's taken a while since I've been pretty busy with other stuff, but the CAD for the version 2 of the MiG 21 is mostly done. Along with improved ducting and reduced weight, there are a number of other improvements including a much simpler hatch geometry that provides better access, a thinner wing that should better take advantage of the ability of deltas to fly at high angles of attack, and a simplified printing process. Hopefully this one actually flies.
View attachment 235972

Remind me... how big is it?

 

[Inq]

If you're interested in getting into the fluids side of things, I can't recommend XFLR5 highly enough, especially for predicting lift. It's a free software and fairly simple to use compared to most CFD tools, but it is limited to just the wings and tail of the aircraft. The lift predictions it makes correlate very well with more complex CFD. For a proper FEA CFD software, Simflow offers a free version that can deal with meshes up to 200,000 nodes. It's easy to use for a full-blown CFD software, but it's still CFD, so a pain. Once you've figured out the setup, the hardest part is getting an acceptable mesh in the node limit. And it forces you to give all pressures in m^2/s^2 instead of some easier unit like Pa or psi.

I've had a project on-again/off-again for decades mainly because of career. Now retired, I need a large workshop which I hope to finish this spring. Which has given me the itch again. I was just using JavaFoil, but the author clearly says the 2D, closed-form methods he uses drastically fail once in stall/turbulent conditions. These two tools you mention... do they have their own CAD or do they import from something like DFX? Although lift/drag are important, I'm looking for after stall conditions and interference problems. I'd also like to be able to export the pressures being applied to the model, so I can suck them back into my FEM to do the structural analysis. Do these analysis programs give pressure data as a function of time? For instance vortex shedding. I think the dynamic fluctuations that might excite natural frequencies in the structure would be far more critical than the ultimate static loads that JavaFoil gives me. aka...

Tacoma Narrows Bridge collapses - History Channel

 

[telnar1236]

Remind me... how big is it?

It's 1:14.7 scale so 39" long. I am designing it to match the scale of my F-104.

 

[Inq]

I recall using some of LLNL (Lawrence Livermore National Laboratory) programs years ago. If you have a need to go over the 200,000 nodes, have you ever looked into either:

LLNL or NASA - https://software.nasa.gov/