Thread Tools
Oct 26, 2020, 11:24 AM
Mach One
captain MoMo's Avatar
Quote:
Originally Posted by Evan D
There may be multiple root causes, compounding issues.

Another question MoMo, what voltage was your BEC set at? One reason I ask is that the ESCs with internal BECs seem to be about 5.5V and the externals about 5V.
5.5V or less.
Sign up now
to remove ads between posts
Oct 26, 2020, 11:27 AM
Registered User
Quote:
Originally Posted by captain MoMo
What I can vividly recall is that she suddenly refused to respond to my elevator input and before I could do anything she hit the ground hard nose first - bounced back up in air, rolled as she scrapped on the runway and came to a full stop by the fence. Both elevator rods are disconnected, major scratch damage on both wings and stabs - broken torso, broken nose. No damage to rudders.
Unless both stab linkages came off at the same time, inflight, unlikely but not impossible, what else would cause no elevator response? RF interference or electronics failure.

Did you test the stab servos yet to see if they are functional? Not that that would be necessarily conclusive, because of crash damage possibilities, but if both were no longer working then that may lead to a root cause or at least a contributing factor.

What's the state of the electronics system including the MCB, BEC and Rx? Can you track frame loss to eliminate RF issues or confirm that they may or may not be a root cause?
Oct 26, 2020, 11:28 AM
Mach One
captain MoMo's Avatar
Quote:
Originally Posted by rvincent
MoMo I'm sorry but I never heard, did it still have roll and yaw capabilities? Throttle? I know it happened fast but any additional info is helpful. If it only lost elevators is a whole different set if forensics than if it had nothing.
Honestly I did not get a chance to see what else worked - split second. I did have to unplug the battery as it still had power to the RX. No blinking on the RX either. It seemed to spiral after the initial hit all on its own. Power was on - plus the velocity it had from the approach to the runway. This is crazy stuff.... I used to watch the videos from China and others and think - they must have done something wrong - well - here I am in the same exact shoes. I am not sure what the problem is here - but I can tell you for sure that this one is not pilot error.
Oct 26, 2020, 11:41 AM
Registered User
[QUOTE=captain MoMo;45736885]......instructions, replaced the elevator servos with the 23g upgrades and yes, put the links in the correct holes but on a shallow dive - not even a real dive - just adjusting to do a low pass over the runway - it happened. No control on pitch and ....QUOTE]

I've been following this problem from the F-22 thread, Just felt I shud post a relevant experience that may shed light on this problem. Nearly 20-yrs ago (yes, at the dawn of EDF ) I built a composite 60+inch F-4 w/ twin 90mm WeMo fans at then considered powerful 2.35kWatts total. I dopplered it later at about 100+ mph. While still wringing it out on its 4th flight, my test pilot suddenly brought it back down. It was soon evident its two FF stabilizer panels were at about 30deg different angles!! Am still amazed how he was able to land it in 1 piece

On the bench, I found the 5/32 wheel collar turned actuator arm on the misaligned panel, had distorted & climbed over its flat seat ground into the shaft. Curious, I attached my fish scale to simulate the servo force it took for this collar to distort; IIRC, it was about 65 oz-ins. The kit specified a single 140 oz-ins. servo, so that was okay.

Con't...
Last edited by PhilLin; Oct 26, 2020 at 12:10 PM. Reason: grammar
Oct 26, 2020, 11:42 AM
Retired US Navy
Evan D's Avatar
What do you think of a survey?

What elevator servos did you have?-----Stock low torque-----Upgraded FW stock-----Upgraded other
Did the ele servos go through the MCBe (BB)?----- Yes----- No
If not did you Y them to the receiver?----- Yes----- No
Where the ele pushrods stock?----- Yes----- No
If modified what was modified?----- Metal rods----- Ball links----- Carbon tube
Where the ele horns stock? -----Yes----- No
If modified what was modified? -----Horn itself -----Ball links----- Mounting screws
Did you balance the stabs? -----Yes -----No
Did you use the stock BEC? -----Yes----- No
Was your MiG balanced at the factory marks?----- Yes----- No
If not, where? -----About 10mm aft -----About 15mm aft -----About 20mm aft -----More than 25mm aft
What do you think caused the crash?----- Loss of ele control----- Loss of radio signal -----BEC -----Servos----- Balance----- My fault/ not sure

Additional info I think is important:
Oct 26, 2020, 12:03 PM
low, left, & fast
nuts-n-volts's Avatar
Could add... What voltage from BEC? Flaps: Down or Up? If down what servo?
Oct 26, 2020, 12:07 PM
Registered User

FF stabilizer force, cont;d.....


Herb had sounded the alarm, on the other thread, that the elevator servos were suspect. I think the servos provided with the F-22s were only in the 45 oz-in range. Some were replacing these with the MG servos rated about 65-70 oz-in (5.5v). Those may be okay for the shorter lifespan of a foamie? I took the risk & had 3 flites on my F-22 before severe weather set in on the Midwest; but fully intending to replace those servos in the spring.

This Mig-29 is larger than the F-22. What size servo is adequate? There are several ways for the theoretical types on this forum to work it out. My back of envelop calculations says about 120 oz-in minimum.

Hope that is what the replacement FW provides are rated for. Note I don't own this plane at the moment.

Phil
Oct 26, 2020, 12:20 PM
Instagram: @tcat.rc.creations
T-CAT's Avatar
Quote:
Originally Posted by PhilLin
Herb had sounded the alarm, on the other thread, that the elevator servos were suspect. I think the servos provided with the F-22s were only in the 45 oz-in range. Some were replacing these with the MG servos rated about 65-70 oz-in (5.5v). Those may be okay for the shorter lifespan of a foamie? I took the risk & had 3 flites on my F-22 before severe weather set in on the Midwest; but fully intending to replace those servos in the spring.

This Mig-29 is larger than the F-22. What size servo is adequate? There are several ways for the theoretical types on this forum to work it out. My back of envelop calculations says about 120 oz-in minimum.

Hope that is what the replacement FW provides are rated for. Note I don't own this plane at the moment.

Phil
The Freewing upgraded 23g servos are supposed to be rated at 3.4kg torque.

https://www.motionrc.com/pages/produ...n-80mm-edf-jet
Last edited by T-CAT; Oct 26, 2020 at 01:58 PM.
Oct 26, 2020, 12:28 PM
Still Screamin'!
rvincent's Avatar
Quote:
Originally Posted by T-CAT
The Freewing upgraded 23g servos are supposed to be rated at 3.4kg (~120oz) torque.

https://www.motionrc.com/pages/produ...n-80mm-edf-jet
3.4Kg = 7.93 lbs or 126.88 oz's of torque
Oct 26, 2020, 12:30 PM
Instagram: @tcat.rc.creations
T-CAT's Avatar
Quote:
Originally Posted by rvincent
3.4Kg = 7.93 lbs or 126.88 oz's of torque
I only ran it through a google calculator that does the conversion. I figured it may not be perfect though. .
Last edited by T-CAT; Oct 26, 2020 at 01:59 PM.
Oct 26, 2020, 12:35 PM
Still Screamin'!
rvincent's Avatar
Yep either way I would feel better with 140+ I have planes that weigh 15 lbs and go over 140 and would NEVER trust anything less than the HS 5645 at 143oz's.
Oct 26, 2020, 12:37 PM
Still Screamin'!
rvincent's Avatar
In fact the HS5645 in my Tam Jets A-4 for flaps would burn out after just one flight if I set the flaps down going too fast. And the Taileron or elevator surface on this plane is WAY larger!
Oct 26, 2020, 12:58 PM
Registered User
Well then it's clearly not the elevator servos, as momo replaced them. I don't think it's an aerodynamic thing. The elevators are huge, there should be no way for them to be blanked out. Probably the linkage is the culprit, maybe it can get hung up when there is too much force.

Could another problem by low voltage caused by long wires in the fuselage? Voltage drop under load causing them to shut down, or a brown out isolated to the elevator servos? Maybe the lines need a voltage booster, or add a cap pack at the back somewhere connected to the servo lines.

If this is the case, replacing elevator servos might even make the problem WORSE because a bigger servo needs more power.
Last edited by bandetlol; Oct 26, 2020 at 01:07 PM.
Oct 26, 2020, 01:10 PM
Registered User
I have D85s installed. Would these work?

https://www.weekenderwarehouse.com/s...-booster-2pcs/
Oct 26, 2020, 01:11 PM
I Used To Have More Free Time!
I think if it was electrical interference, then the crashes would not almost all be happening only in dives. Seems like an equal # of crashes would be at level, high throttle conditions too.
Has anyone asked Alpha what exactly the loads are that are put on the FF stabs in a high speed dive? He should have known this # early on into the design. Or maybe not... after all, they specced underrated servos the first time around.
Sorry to hear about the crash MoMo.


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
New Product Freewing twin 80mm F-14 Tomcat Alpha.MotionRC Foamy EDFs 12604 Yesterday 05:11 AM
New Product Freewing 80mm Mig-21 Fishbed xplaneguy Foamy EDFs 8521 Nov 28, 2020 03:17 PM
New Product NEW Freewing F-14 twin 80mm EDF (Vendor-independent) SU-4ever Foamy EDFs 186 Feb 07, 2017 05:47 PM