crashed, need help to diagnose problem
 

yea, I was flying at our local airport with a dx7, and my plane was working great for my first three flights.

my next flight, I took off, dove down to do a high speed pass and when I needed to pull up, my plane did nothing, and I crashed.

Now I am scared to fly my other plane, cause this was not Pilot error (I wish it was).

Do you guys have suggestions to try to diagnose.

My plane did do something strange, with everything on before TO, I had no radio response. I turned my radio tx off, checked the rx switch (it was on) turned my tx back on and then it worked. everything worked fine for to, and the first 20 sec of my flight.

Batteries were fully charged, voltage checked!

Thanks

871

RE: crashed, need help to diagnose problem
 

Need more info. What radio equipment, how old what RX, does it have a module, has your TX ever gotten wet, or been dropped? Could be any one of a number of things at this point.

RE: crashed, need help to diagnose problem
 

DX7 spectrum with new 7 ch receiver.

Bone dry, my tx has never been dropped

Thanks!

RE: crashed, need help to diagnose problem
 

You said it was fully charged and checked, was that before the first flight or before the flight where it crashed? Also did you load test the batteries or just check voltage. Just checking voltage is not enough.

We do need much more info:

Type/size of plane and what's installed beyond the transmitter/reciever like servos, battery size/voltage, are we talking about a glow plane, electric plane or gas plane, etc....

RE: crashed, need help to diagnose problem
 

The Battery could have come disconnected. the switch on the plane may not be going all the way on,, is it mounted in the side of the fuse, and if it was, are you hearing it click when you put it in the on position, if the wood on the plane is restricting the switch from clicking into position it could shut off in flight from the vibrations.

The plane could have been too nose heavy, was there are strong wind blowing? you said you were diving, so if you were diving with the wind hitting the top of your wing and a nose heavy plane, this could have prevented it from climbing out fast enough.

I would say a possible bad crystal but does that even use a crystal?

Sometimes a bad receiver will act that way also, it does happen even new out of the box.

Did the elevator linkage become detached somewhere on the servo or the control horn? did you try ailerons and rudder or shutting down the motor during its fall?? if nothing happened then most likely your power got disconnected somehow.

just a few suggestions out of 5 kabillion things that could have happened with out seeing it or flying it myself,,

But I have been there all tooo many times and I'm sure I'll be there again,, LOL its just part of the hobby.. I just put on a smile and get the glue back out. I hope it was at least a cool crash to see[X(]:D thats the only entertainment you get out of your plane during a crash for the work of putting it together. By the way what plane was it. ARF / Kit ?? what size 40 / 60 / bigger
Good luck to you.

RE: crashed, need help to diagnose problem
 

Possibly a high speed stall? Here's the result of mine. 90+ mph straight in. Debris field was HUGE!:D Hopefully you get it figured out before you junk a hundred dollar rx. If you've got a glitchy radio, you could go nuts trying to diagnose it. Better to send the whole thing in to Horizon and have them go through it. Good luck!

RE: crashed, need help to diagnose problem
 

The way you describe it, with the event that happened on the ground, it pretty much has to be the TX or the RX. I'd send both in to Horizon with a nice detailed letter and tell them not to send it back until they find and fix the problem.

Jim

RE: crashed, need help to diagnose problem
 

Did you do a range check after you noticed a problem on ground.
You stated you turned off the Tx and then Rx on then Tx back on. Sounds like wrong sequence for that radio. First Tx to find 2 free Ch then Rx to link to Tx.
With that radio you may want to rebind after a noticeable problem
my 2cents
Bill PTC

RE: crashed, need help to diagnose problem
 

Bill has a good point,

With Spektrum you must follow the right procedure for turning on and off and if you make any changes to the system, it's best to rebind, especially if you do something with the throttle or any surface. If you forget to turn the radio on first, always shut everything off and do it again.

If you do send everything back make sure you send the receiver battery and switch as well. I know I said we need more info and we really do, but based on your statements, you could have had a battery drop a cell which may only show under a load, your switch could have failed, something could have disconnected (you should always tape, heat shrink, etc... connections to extensions or wherever possible)

RE: crashed, need help to diagnose problem
 

Eh this may indeed be pilot error.

When this happens newbies tend to blame the electronics or the plane.

They've forgotten or don't realize that when the plane approaches a high speed, there can be so much pressure on the elevator surfaces that the servos cannot keep the surfaces in the desired position. Particularly if they haven't set up the linkages for maximum mechanical advantage.

This causes the plane to appear to fail to respond.

Typically it happens in exactly the scenario you stated... a dive attempting a high speed pass over the field.

Since you are low to the ground already, and the tail surfaces have minimal effectiveness, the result is that the plane does not have the room to react ( albeit slowly ), and you "lawn dart" in.

I'll bet your plane had big tail planes too.

RE: crashed, need help to diagnose problem
 

I learned a lesson about battery voltage checking (under load). I have a small twin C160 that last week started glitching after take off. I checked my battery voltage and it showed 4.9 volts no load. I checked all the control surfaces etc. and flew it again, same thing happened and I barely got it down in one piece. Somebody at the field asked me if I checked the battery under load. Since I only had a non-load meter one of the guys loaned me his. Under a two amp load voltage dropped to 3.1 volts. This same meter on my other plane recorded 4.4 volts under the same load. Replaced my pack in my C160 and everything is fine. I just bought a new Hanger 9 volt meter with load selection! Good luck, Jerry.

RE: crashed, need help to diagnose problem
 

I rememeber with the DX6 people were having a similar problem and they were losing contact. If I remember correctly it was the receiver not having enough voltage and locking out the radio. Horizon designed the receiver to run on a 6 volt pack and when people used a 4.8 volt pack and it lost voltage from either needing a charge or a high current load it would lock out. Again I dont know if the DX7 is designed the same way but if it is then it is something to consider especially if you were running a 4 cell receiver pack.

RE: crashed, need help to diagnose problem
 

THANKS!

Yes, It is a t34 .40 size. I am experienced enough to realise it was a dead elevator feeling. I was not in a high g situation, just simply lightly pulling up about 10' off the ground. I was messing around with this move all day before the crash. the elevator works fine in is exploded state

I did not load check my batteries. It was a fully charged, virtually new 1100mah pack. When I checked it after my first two flights, the led was still at the highest mark on my gauge.

Everthing works fine here in my shop. should I rebind radio and fly?????, sending it in would take forever!

I will get a new switch

I cant find a more perfect term than lawn dart for my plane.

still searching,

871

RE: crashed, need help to diagnose problem
 

If your receiver gets any voltage drop it will lock you out for up to 13 seconds. I tested a bunch of Spektrum recievers and many would not re-establish a link after loosing the battery for a split second. Most 72 mghz receivers only take a fraction of a second to re-link, but the Spektrum's take much longer and in at leset one case 13 seconds. Most were around 2-3 seconds. Way too long for a recovery at low alt. To avoid this problem always use a dedicated receiver pack and make sure it's fully charged. Another problem is if you are running too many servos on your ESC, if it's an electric plane. The voltage can drop if you are running more than 4 servos and cause the same problem. The 6100 was recalled for this reason.

RE: crashed, need help to diagnose problem
 

As you noticed it was going in, did you note if you had any movement of the other control surfaces.

I know that when something like this occurs, it's next to impossible to pay attention to anything else, but it could help eliminate the radio gear.

e.g. a bad servo or a disconnected servo.

---

I had a Hitec servo recently that would work perfectly on the ground and usually in the air.

However when the engine hit a certain RPM the servo ( which was on the tail away from the engine ) would go nuts.

At first I though that this was flutter or due to excessive speed.

All interconnects were fine and if I reversed the connections ( I had two servos on the tail ) the problem remained with the servo.

Swapping it out for a new one fixed the problem.

RE: crashed, need help to diagnose problem
 

871,

Even new batteries can have a bad cell and the LED things are only showing voltage. While they give you voltage they cannot test the battery and will not show a bad cell. A loads batteris for several seconds to a couple of minutes will show a battery problem and that is something I recommend you do several times during a flying session (AKA flying many times during on day).

It defintely sounds like you have had a receiver dropout.

Also verify no servos are binding in any way. A servo bonding up will put a load opn the battery and if it's bad enough or you have more than one, you can get below minimum receiver voltage fairly quickly.

While Spektrum is a good system, there are certain things you should be aware of and that is insuring your flight battery setup is in good shape

I use a Spektrum module on my 10X and have also had a DX7. I use Li-ION batteries and still check loaded voltage every flight or even every other flight

RE: crashed, need help to diagnose problem
 

yup, I was using the 4.8v nicad pack that came with the system. I am thinking this was my problem. Is this true specs dont work well with the 4.8v packs? that is stupid that they would include it with the system!

So cool, I will get a new rx pack. What would be a good selection.......6v 2000 mah nmh??????????????

rx power sugestions??????????

871

RE: crashed, need help to diagnose problem
 

Unfortunately, you don't say what you found in the wreckage. Most people don't actually do much of an autopsy after a crash, especially if they think they know the answer and it doesn't include a failure in the aircraft. Which is what it sounds like here.

If the elevator pushrod had failed, the connector come loose at the elevator horn, connector come loose at the servo, arm come off the servo, extension come loose from radio, come loose from servo plug, any wires failed internally (broken in previous crashes or whatever) switch failed, battery connection to switch, etc

A good autopsy often finds the cause when it's in the airplane. And it very often is.

RE: crashed, need help to diagnose problem
 

As for condemning that pack outright................

One of the most valuable tools we have available to us nowadays is the smart charger. The Accu-Cycle Elite and the TritonII are examples. Their hidden value is how well they tell when one of our batteries is dying on us. Every time you recharge, if you look at how much capacity had to be returned to the battery and think about how much you used that battery flying that day, you have an idea if the sucker is starting to lose it's capacity. And you can then use the greatest diagnostic function we've ever had. You can cycle the sucker and see if it's really going bad.

Don't trash that battery without a trial. If you don't have a smart charger, it's time to get one. And you have an excellent idea why it's good to have. It's worth putting off the next model or engine to get one.

As for the crash...... who knows, but it could be anything that wasn't looked at.

Like a throttle servo that is stalled at WOT and drains a perfectly good battery in flight.

RE: crashed, need help to diagnose problem
 

Did you check your elevator servo. I had one flutter on me on a prop jet on a high speed pass. Killed my Elevator servo. Went in full speed and couldn't pull up

RE: crashed, need help to diagnose problem
 

on autopsy, yes I checked the linkages....servos....etc. the elevator works well and has plenty of tourque. all the connections were good

Yes, I use a Durtrax ICE charger. It tells me how many mah etc go into the battery before peak......etc

I do have hitech 425's, with my dx7. how can I check for substantial "stalled" power loss on the servos?

Once I get my load tester, how much load should I put on the battery to test, and what is the min safe voltage to take off with for a 10 min flight?

THANKS

871

RE: crashed, need help to diagnose problem
 

sometimes with the new system we forget to rebind......was the fail safe set right.....easy check ....just leave the airplane on and turn the radio off...see if any servo move....if so bingo.....

RE: crashed, need help to diagnose problem
 

After reading through this thread I noticed that nobody has mentioned pointing the TX antenna directly at the model. The TX antenna has a blind "cone of confusion" projecting outward in the direction it's pointing. Most of the time your plane flies through this cone with no problem, but in a low-and-fast condition the momentary loss of signal from the TX is bad. I try never to face my airplane when in the air...always look to the side at it, or angle the DX-7 antenna straight up and then don't fly directly overhead.

Yak

RE: crashed, need help to diagnose problem
 

i have been saying this since they released this radio and all i get is told i am wrong.man am i glad i fly xps---never a doubt

RE: crashed, need help to diagnose problem
 

Been down this road with the Spektrum. The 4.8V that came with it, throw away now. 6V and you might as well get something in the 2000 mA range and be done with it. They are saying that I had the dreaded voltage drop and I was running 2 of a 6V, 2700mA packs for 5 digital and 2 regular servos. I don't know what more I was supposed to do (28% Extra 330 totally trashed). No help from Spektrum at all. Suggest that if you are flying Spektrum on big planes to use one of those power panels and never fly the 4.8V on any plane with it.

read on: http://www.rcuniverse.com/forum/forumid_116/tt.htm

RE: crashed, need help to diagnose problem
 

I load test my batteries with a 2A load using the Hanger 9 volt meter. I'll get 4.2 to 4.6 volt reading on a good pack with a 2A load. I do fly all my planes including my 30% Extra and 33% CAP on Spektrum. The T34 you have would not have caused a battery voltage drop enough to cause your receiver to have a issue unless the pack was bad. Anything below 4.2 under a 2A load I consider unsafe to fly.

Voltage drop in accordance with load is a real science. Some battery technologies work better than others when you have a high load. I run 4.8 on all my large birds but I use SubC Nicad packs at 1400 MH. I use two of them for the receiver running Hitec digital high torque servos. Nicads allow for a higher discharge rate with a lower voltage drop than your typical NMH packs. Its not necessarily the size of the pack that is important but rather the max discharge rates at a particular voltage that is of concern. I avoid the LiPo's due to just adding another failure point with the addition of regulators.

If you have some time check out Hangtime Hobbies web site and refer to their battery section. Some very good information on that site regarding loads.