Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[Drifty]

All you enigneers see my post on RCG I know all you folks with degrees like to over think everything just for fun and thats OK but in my 37yrs of working full scale airplanes I never saw that approach work when trouble shooting malfunctions. I think Evan has the best idea of all. please support him. Yes I do have and fly the Mig (15 flts so far) It is stock except for upgraded servos and 4/40 rod,it is a great flying A/C. I had to stop flying due to the weather here in MI ( to cold for my 83 yr old bones) Good luck to all of you that fly this A/C.

R. Driftmyer CNSgt USAF Retired

[Firebird]

A plane doesn't lose elevator authority on account of a voltage drop if the servos are still exerting a large enough force at their output. I don't recall anything in firebird's data suggesting that the servos quit working except in one case when one servo reversed when stalled. And that wasn't correlated with the voltage drop but with the stalled condition.

Getting overly fixated on a voltage drop is not what is needed. How does the servo behavior change under load is what is relevant, and does that depend on the gauge of the leads?

Also is there any buckling of the pushrods, flexing of the pivots or pivot mounts, control horns, and other parts of the structure when under load.

Thanks to all of you for the feedback!


As i am on duty now, i won’t have time to test at the mig itself. I hope i can maiden until end of november.
I took the time to make a quick calculation of how much servo force you will have approximately available at the outer tip of the elevator.

Objective:

Assuming the stock upgrade servo gives you 3.4Kg at 4.8V - how much force do you have available at the outer tip of the elevator?


Calculation:

Lever arm from pivot point to elevator tip = 22cm

Lever arm from pivot point to pushrod connection = 2cm

3,4Kg / 4,8V force from stock upgrad servo = 33,35N (newton)

Physics leverage law formular: F1xS1=F2xS2

F1=33.35N
F2=X
S1=2cm
S2=22cm

33.35N x 2cm = X x 22cm

33,35N x 2cm
——————— = 3,03N
22cm


3,03N = 308gram



Summary:

Due to the way the servo force is transmitted to the elevator - at 4,8V a force of only 308gram (11x less then servo output) on the outer tip of the elevator might force your servo already to deliver maximum available moment.

Additionally- continues load on the servo during cruise flight (fighting nose done moment due to CG and center of lift correlation) might lower it’s maximum available moment at the end of the flight as the servo might get hot.

[GliderGuy]

Thanks again Firebird. Anxiously awaiting actual flight load telemetry from your upcoming flights.

As another consideration/data point to add - I began flying my MiG during the time when common temperatures were in the high 90F to 100+F (35C to 40C). Generally, I don’t go out if over 95F (too humid/hot with heat index over 100F).

The first several hundred flights were in these heat conditions. CG on the mark and about 4 mm of elevator trim. Very little down time between flights for servo cool down. I rotate batteries pretty fast. Generally, 10 to 15 flights in succession when I go out = potentially a hard workout for the servos in these conditions over a 2.5 to 3-hour period.

Cruising around at 3/4 throttle + acro once I got the MRC upgrade servos installed.

Mean anything? Don’t know! Just more info to consider. I might just have been lucky or the flight loads are not that extreme. Your flight data will show actual loads. Gonna be interesting.

-GG

[GliderGuy]

All you enigneers see my post on RCG I know all you folks with degrees like to over think everything just for fun and thats OK but in my 37yrs of working full scale airplanes I never saw that approach work when trouble shooting malfunctions. I think Evan has the best idea of all. please support him. Yes I do have and fly the Mig (15 flts so far) It is stock except for upgraded servos and 4/40 rod,it is a great flying A/C. I had to stop flying due to the weather here in MI ( to cold for my 83 yr old bones) Good luck to all of you that fly this A/C.

R. Driftmyer CNSgt USAF Retired

We appreciate everyone’s inputs and ideas. Community think is a powerful tool.

Engineers overthinking?....It’s the nature of the beast LOL.

-GG

[kallend]

Thanks to all of you for the feedback!


As i am on duty now, i won’t have time to test at the mig itself. I hope i can maiden until end of november.
I took the time to make a quick calculation of how much servo force you will have approximately available at the outer tip of the elevator.

Objective:

Assuming the stock upgrade servo gives you 3.4Kg at 4.8V - how much force do you have available at the outer tip of the elevator?


Calculation:

Lever arm from pivot point to elevator tip = 22cm

Lever arm from pivot point to pushrod connection = 2cm

3,4Kg / 4,8V force from stock upgrad servo = 33,35N (newton)

Physics leverage law formular: F1xS1=F2xS2

F1=33.35N
F2=X
S1=2cm
S2=22cm

33.35N x 2cm = X x 22cm

33,35N x 2cm
——————— = 3,03N
22cm


3,03N = 308gram



Summary:

Due to the way the servo force is transmitted to the elevator - at 4,8V a force of only 308gram (11x less then servo output) on the outer tip of the elevator might force your servo already to deliver maximum available moment.

Additionally- continues load on the servo during cruise flight (fighting nose done moment due to CG and center of lift correlation) might lower it’s maximum available moment at the end of the flight as the servo might get hot.

Thank you for all the quantitative data and the work you put in to collect it.

Some things come to mind based on your posts:

1. What is the effect of heat on a servo that's under load for several minutes as these FFS servos would be with a forward CG and the pivot point located where it is? With a FFS all trimming is done by the servo, in contrast a regular fixed stab + elevator where the fixed stab (in a good design) takes the bulk of the load. I have had a FW servo in a F-104 that worked perfectly for 3 minutes and then went weird as it warmed up.

2. The FFS pivot seems very far forward on this MiG, so there isn't much aerodynamic balance. This will increase servo loads.

3. With the exception of one servo that reversed itself, I didn't see much evidence in your data that servo behavior was much affected by voltage drop along the wires. And even in the case of that one servo it is not clear that the reversal was due to voltage sag.

[Evan D]

The first percentage was based on their 4.8V spec. I would assume a similar increase would be had at 6V also.

The second percentage was just a ratio between the holes on the servo arms.

Originally posted by Evan D View Post
Some numbers about the servos. The stock 17g servos put out about 37.5 in-oz. The upgraded FW 24g are about 47 in-oz. An increase of 25% of force to the stab.

Moving the pushrod in from the recommended middle hole (13mm from center) to the inner hole (9mm from center) on the FW servos is a 46% increase in force to the stab.



Those numbers for the free wing servos would that be at 4 V or 6 V please?

[Evan D]

When I got my upgraded servos on Sept 21st I did a test and posted the results, note that this was with the pushrod in the inner hole on the stock horn I would say we validate each other...


I got my replacement servos and put them in today. I did a quick non scientific check of force to stall them and got about 300g on the old ones and 400g on the new.

Thanks to all of you for the feedback!


As i am on duty now, i won’t have time to test at the mig itself. I hope i can maiden until end of november.
I took the time to make a quick calculation of how much servo force you will have approximately available at the outer tip of the elevator.

Objective:

Assuming the stock upgrade servo gives you 3.4Kg at 4.8V - how much force do you have available at the outer tip of the elevator?


Calculation:

Lever arm from pivot point to elevator tip = 22cm

Lever arm from pivot point to pushrod connection = 2cm

3,4Kg / 4,8V force from stock upgrad servo = 33,35N (newton)

Physics leverage law formular: F1xS1=F2xS2

F1=33.35N
F2=X
S1=2cm
S2=22cm

33.35N x 2cm = X x 22cm

33,35N x 2cm
——————— = 3,03N
22cm


3,03N = 308gram



Summary:

Due to the way the servo force is transmitted to the elevator - at 4,8V a force of only 308gram (11x less then servo output) on the outer tip of the elevator might force your servo already to deliver maximum available moment.

Additionally- continues load on the servo during cruise flight (fighting nose done moment due to CG and center of lift correlation) might lower it’s maximum available moment at the end of the flight as the servo might get hot.

[themudduck]

When I got my upgraded servos on Sept 21st I did a test and posted the results, note that this was with the pushrod in the inner hole on the stock horn I would say we validate each other...


I got my replacement servos and put them in today. I did a quick non scientific check of force to stall them and got about 300g on the old ones and 400g on the new.

So many posts about measuring the force on the servo under various conditions, and that the servo might stall under aerodynamic load (or because of a voltage drop under load). Maybe overloading the servos due to the geometry (wrong hole)... Its a great discussion, and it could make sense if the failures happened while pulling out of a high-speed dive, or with the flaps down, or in a high-G pull in a turn. And perhaps that did happen in some cases, but look, both of my elevators simply stopped working while I was flying straight and at low power, just cruising by and then I tried to pull up. I want to know why both elevators stopped working while they were essentially idle.

I'm using the MRC-supplied replacement servos and Y-harness plugged directly into the receiver. (and I've done all the other mods, such as balancing the stabs, 4-40 rods, chokes, balance, etc)

[RC Rich]

So many posts about measuring the force on the servo under various conditions, and that the servo might stall under aerodynamic load (or because of a voltage drop under load). Maybe overloading the servos due to the geometry (wrong hole)... Its a great discussion, and it could make sense if the failures happened while pulling out of a high-speed dive, or with the flaps down, or in a high-G pull in a turn. And perhaps that did happen in some cases, but look, both of my elevators simply stopped working while I was flying straight and at low power, just cruising by and then I tried to pull up. I want to know why both elevators stopped working while they were essentially idle.

I'm using the MRC-supplied replacement servos and Y-harness plugged directly into the receiver. (and I've done all the other mods, such as balancing the stabs, 4-40 rods, chokes, balance, etc)

Your experience is very unfortunate and puzzling. After the crash, was your elevator lead still connected to your Rx?

[Doug Fales]

What is we were to use a power safe receiver? So we run all control surfaces on a separate power supply. Would that help?

[CristianMarin]

That's what I'm using. No issues, but still only 3 flight because the weather turn bad. Will see in the spring.

[Edwin-0]

Made use of a rainy day in Belgium to weather and pimp the Mig. Possibly not everyone's thing, but tastes differ.
Upgraded the elevator servo's and puchrods. Printed some décals for the missiles. A full day work 😁. The following will be the maiden.

[themudduck]

Your experience is very unfortunate and puzzling. After the crash, was your elevator lead still connected to your Rx?

Hi there RC Rich, actually in my case it didn't result in a crash! (I posted the full story some time ago). I was flying across the field maybe 100 feet up, and it was just flying straight in a very slight dive just above idle power, when both elevators suddenly stopped working for a few seconds. I only had enough time to think "oh SH** its happening" with that horrible feeling in my stomach - just helpIess with the plane not responding. I cut the throttle just by instinct before it went in and at that moment, control returned and I pulled it up. Everything was working again. Then I lowered the gear, came around, put the flaps down and landed completely normally. And then... I decided to quit for the day while I settled back down!

(Yes its possible that other controls weren't working either, but I don't know. For certain that the elevators weren't working because I was trying to pull up and that was the first thing I noticed.)

Afterwards I was inspecting the model on the bench and I removed the receiver and the plug fell out of the satellite, making me think that it may not have been plugged in all the way. So it could have been a radio glitch. But I have no idea. It happened very fast and the elevators are what got my attention.

[themudduck]

Made use of a rainy day in Belgium to weather and pimp the Mig. Possibly not everyone's thing, but tastes differ.
Upgraded the elevator servo's and pushrods. Printed some décals for the missiles. A full day work 😁. The following will be the maiden.

Edwin your "pimp" looks really great, I love the extra detail you added!! Is the color on the wingtips and fin tips correct to scale? I really like the way it looks.

[janmb]

All you enigneers see my post on RCG I know all you folks with degrees like to over think everything just for fun

There is no such thing as over thinking anything. It is only thinking. And you can never have too much of that.

Nor is it something we do for fun.

Happy-go-lucky is NOT a good way to approach our hobby. Not only is it wasteful in terms of material values, it is also reckless in terms of safety.

[janmb]

Build complete, hopefully maiden on Wednesday.

So tired of the overly conservative CG setup on these models though - even running fairly light 5000 batts, as far aft as possible on the aft and middle bays, relocating the BB aft, and running only a 10g gyro and 2g rx in the front, it is still nowhere near balancing.

The only way to get this balanced without ballast is to drop to at least 4000, maybe even smaller.

[PieterO]

Build complete, hopefully maiden on Wednesday.

So tired of the overly conservative CG setup on these models though - even running fairly light 5000 batts, as far aft as possible on the aft and middle bays, relocating the BB aft, and running only a 10g gyro and 2g rx in the front, it is still nowhere near balancing.

The only way to get this balanced without ballast is to drop to at least 4000, maybe even smaller.

I managed to balance it nice with 2x 4500 admirals 40C. No foam removal needed and no extra ballast. CG is now 10mm aft of the factory CG mark. Only made 12 flights so far (stupid Dutch weather) but so far, this feels at the correct CG spot for me.

[janmb]

I managed to balance it nice with 2x 4500 admirals 40C. No foam removal needed and no extra ballast. CG is now 10mm aft of the factory CG mark. Only made 12 flights so far (stupid Dutch weather) but so far, this feels at the correct CG spot for me.

Approx 10 mm aft of the marks is what I can get too - barely. Would love another 10 though.

[Jet jocky]

Has enyone figured out a mechanism for a parachute for the Mig-29 yet?

[ColtPilot]

The Model Sounds Inc sound system test. The volume is turned up and the speakers placed just behind the CG line. This is loud.

https://photos.app.goo.gl/tDsUrwibZvUoHEYi7