Today I was buddy boxing with my instructor for the second time and lost my plane. It was a very calm day. My instructor took off and checked the trims again and said he thought there was some sort of radio interference. The plane would loop very tight as if someone had applied full elevator. This didn't happen in the next 2 or so minutes of flying and he gave it to me. I made one gentle turn and was headed back in the opposite direction when it did it again. He immediately took it but had no control over it. I watched it spiral to the ground from way up. He said he had no control at all. The battery showed almost a full charge (tx and rx) and all the servos are working. After we brought the plane back, we watched the servos for interference but didn't see anything. The rubber grommets were in place, the receiver was wrapped in foam as was the receiver battery. There was no fuel near the receiver.
I think my engine is ruined. It is hard to turn and took a hard lick on the spinner nut. The needle valve broke off too.
Any ideas? This plane flew fine 4 days earlier on a much more windy day.

Was it just you two there at the field? Maybe some one else was on the same channel and shot you down. I dunno.

I'd say something or somebody else was on the same frequency. I guess I would have to have been there today to say for sure, but it the plane was doing perfect loops looks like some ******* was screwing with you on the same frequency.


Wings

Geez, that's too bad. Definitely sounds like radio interference.

Check the switch, they some times are intermitent. Radio interference different thing not like a loop or role. Loose plug in, that loose conection are hard to find and are some times never found check these very close, with lock up like that , it is power related. All so rubber bands on wing if you use then.

Do pcm receivers help prevent interference? I thought that I had read that somewhere on this forum. I bought an ultra stick for a second plane and have an xp8103 radio. I'm not going to buy another trainer. Cruz, there were alot of people out there that day. Probably 4 heli pilots, and probably 15 airplane pilots. The frequency board had about 9 checked out freq's. It looks to me like someone else would have had interference if that was the cause. Can there be another source of interference besides another tx?

PCM discriminate better against other kind of interference but if some idiot still turn their TX on while in your freq then there is nothing you could do. []

I always kinda wondered what kept people from just driving by, in their car and getting close to the field and doing that kinda stuff on purpose. If you wanted to be a diick it would be so easy to do.

I am sure there has to be butt heads out their doing that stuff.



Wings

I used to race 1/8 scale buggies and occasionally my car would go "nuts" and I would have no control. I eventually discovered there was a small fracture in a printed circuit board trace in the receiver. Apparently it had been intermittent for quite some time. I would try lightly tapping on the receiver to see if you can make it "go crazy" again. Maybe just flex the receiver case a bit to see if you can duplicate the erratic behavior. I sent mine back to Hitec and they fixed it for free. (After nearly destroying my car several times). Sorry you lost your airplane.

I don't think it's power related. If you lose power, everything freezes. It won't go into a sudden loop, it will just stop responding to the controls.

In regards to the engine .....

It is almost 99% just fine. Will need some significant cleaning though.

DO NOT Turn the engine over if you can help it. There is dirt inside, that does damage every time it gets ground between parts.

I had an OS46FX (just like yours, I believe). I buried it nose first into the ground at about 1/2 throttle. Needed both hands to pull it out of the dirt. Just like yours, the needle valve had sheared off.

Strip the engine down. Remove the carbeurator, cylinder head, crank cover, etc. Strip down every part you can get to. It is a lot simpler than it looks.

Here is the breakdown routine.
1. remove both carbeurettor screws (one on each side of carbeurator). Put whole carb assembly into a jar of fuel.
2. Remove 6 SHCS (Socket head cap screws) from cylinder head. Careful, because there is a copper gasket in there. Don't loose it). Also, the head can be mounted in either direction. There is a dimple underneath the cylinder head that is off to one side. Take noe of whre that dimple is so that when you reassemble the engine later, you can put it back the same way you found it. This is not really critical though. Put it in the fuel as well.
3. Remove the 4 SHCS keeping the (now broken) Crank case cover at the rear of the engine. Careful again, because there is another (some type of plastic) gasket. Put it in the fuel.
4. Put your pinky into the back of the crank case, and push up against the cylinder sleeve. It should move with some pressure, and slide up. You will see that there is a pin at the to p of the cylinder, and a notch in the cylinder sleeve that matches up with the pin. Thus, there is only one way for the sleeve to go in. No need to remember it's orientation. It will get tight just before the sleeve is all the way out of the cylinder. This is normal. Just force it gently (that is not an oxymoron). Put it in the fuel.
5. I have found that the piston can only go in one way. I am not sure exactly why though. It is hard to see a difference between the front and back other than at the bottom of the con-rod. One side is slightly larger than the other.... Anyway, with the sleeve out, the piston rattles around a lot, just pull gently at the bottom of the con rod, and the piston/conrod assemply will come out (you have to make sure the crank shaft is as far forward as it goes as well). Just fiddle with it, it is not difficult. Pull the piston/con-rod out the top of the cylinder. Put it in the fuel.
6. Pull out the now free crank shaft. Put it in the fuel.
7. Put the now-empty engine block in the fuel.
8. take the carb out again. Loosen the screw with the spring on completely. Count the approximate number of turns required to remove that screw (write it down). The carb barrel (the part with the throttle control horn on it) will fall out the side. There is a spring in there, which you must not loose.
9. Get an old tooth brush (or someone elses current one ....), and scrub every part using the fuel. Rinse all parts in freesh fuel. The difficult part is cleaning the bearings that are still in the engine block. Use the crank shaft to check them, and just keep rinsing them until the crank shaft spins without being gritty.
10. When all parts are clean, re-assemble in the reverse order of dis-assembly.

I was anxious when I did this the first time (see [link=http://www.rcuniverse.com/forum/When_excited%25%25%25%25_take_a_step_back%25%25%25/m_1188099/tm.htm]My Crash thread[/link]). But, engine is now running fine.

I decided not to spend the money on a new back-plate/crank case cover to repair the broken remote needle mount. Instead, I fabricated ou of balsa and ply a "harness" in which the broken part of the remote needle is sandwiched in. I then attached this to my cowl. I did misjudge one thing, and put the needle on the wrong side of the engine, so there is quite a lone tube between the needle and the carb.

See this picture...

Engine now runs just fine....

gus

For the record, I did not remove the con-rod from the piston. Decided it was OK to clean as-is.

gus

hmmm....

That crash both sounds and looks very sad. PT-40's are very nice-looking.

Dah!! I wish i had gone Computer and PCM.

Sounds like Radio interference or a vibration interference, but what in the HECK WAS YOUR INSTRUCTOR THINKING anytime you have a loss of control or problem of any unknown kind YOU HEAD FOR THE AIRPORT LAND , and check things out. , have saved many aircraft with attitude.

Sorry for your loss

Thanks everyone, especially you gus for the engine info but I believe the shaft is bent. I've pecked and shook everything again and can find nothing. The radio gear seems to be working like it should. It's not the lost plane that bothers me as much as not knowing what caused it. If I had made an obvious mistake like putting 2 rubber bands on, I would feel better. As it is I haven't learned anything. I'm afraid of using this radio gear in another plane.

If the wing slipped for not anough rubber bands you will never know. My plane done funny things when band broke seen it happen did not get it down fast anough. One thing about this hobby , most of the time we can rebuild!! They some times fly better the second kit around.
Sorry for the loss!

You're welcome.

A new shaft can be bought for a fraction of the cost of the engine. Contact OS, or even maybe your LHS. They may have replacement parts.

OS will probably do a complete overhaul for you, and fix all problems, for part of the cost of a new engine.

gue

My thoughts exactly checklist! First sign of trouble with mine or a students plane I declare an emergency and head for the runway and no more flying till it's sorted out.

zetor
The worse kind of crash is when you didn't do anything wrong[:@]
Take your switch and receiver and send them back to the manufacturer with a note explaining what happened. They can check the out and put the parts on a shaker table to see iv any problems show up. They may find something maybe not but may help you feel a little better.

Sorry for your loss
Been there done that....Don't need the T shirt I have the tail

DEG

glue is cool.

I had the identical thing happen to me a couple months back on my Hobbistar 60...it started doing loops and rolls at full throttle...had no control to get it back to the runway. Mine was doing loops so hard and fast that the wings sheared right off. Now I had a missle heading to the ground. Plane was in splinters but was able to salvage the engine. I took what was left to a guy who does forensics on planes and he came up with nothing. He thought it was either someone on the same channel or possibly "harmonizing" of other frequencies. It's rare but does happen. In my case, there was a club member who just bought a new radio on my channel. Personally, I don't think he turned of the tx when it put it in the impound...oh well...now I check his radio before I get mine from the impound rack.

Does your club keep track of who uses what frequencies? It's too late now, but if you know who else is on your channel, and if something does happen, you have a starting point as to whose transmitter to start looking for. Just a thought. Plus if someone is looking to buy a new radio, they can see what channels are being used the least.

real sorry about your pt40, i just love the heck outta all my ww2 warbrds. as was said b\4 IF it was outside interference, (as took place lastyear across the big pond @ a jet rally) then you must do eveything you can to prevent another incident like maybe checking out a flight system receiver that locks onto your frequency and rejects all others, even supposedly on the same channel. if im to cart my plane home in a sack then i want it to be my doing, as i have alot more than mere $$$ invested in my bird! other than this i think your idea of a detailed autopsy is going to be your best bet for answers good luck, Ted aka flip-flop-fly!!

rc outlaw I think you may be onto something there. Well I checked everything out and found nothing wrong. The battery had a good charge, both tx and rx. I screwed the servos into a board and held it against a lawnmower engine along with the receiver to provide vibration and could not reproduce anything that happened yesterday. Something did occur to me. The windy day we flew, I noticed that the wing had slipped back a little. My instructor was in the clubhouse looking for a new tx and I forgot to mention it. I just added a couple more rubber bands and realigned it. I think that maybe my wing mounting technique is suspect. I never thought of this before but I have been going in one direction with the rubber bands (always back to front). I was thinking this may be putting a constant rearward pulling force on the wing. If it were to slide back, the wing incidence may be changed enough that a loop might occur. If a loop does occur, the problem could magnify itself because the force generated in the loop could would act to separate the wing from the fuse and cause a release in tension creating an even more rearward movement of the wing. What do you think about this theory? Is it possible? Or is it just plain crazy?

DEFINITELY...you need to put at least half your bands in a criss-crossed direction. On my trainer, I use 18 to 20 bands with 10 or 12 being crossed. Then to test, I hold the leading edge of the wing and try to bounce or "swing" the fuse to see if there is any wing movement. If there is, I add more bands.

The bands were crossed. What I meant was starting in the back, stretching them over the wing, and putting them on the front (always back to front) The engine is trashed. I took it apart and there is a crack in the crankcase. The prop-shaft is bent too. The camshaft is hitting the side of the bellhousing too.

I'm a RF telecomunication engineer and I think wouldn't be a big deal to these radios manufactors to install some small receiver scan in their radios that would check for any signal in the air, within the RC spectrum, right when you turn your radio ON which wouldn't allow it to turn the TX power on if your frequency is being used already!
Besides, it wouldn't be also a big deal to have a dual frequency mode radio and receiver, auto switchable, in case interference is experienced.
In the mean time, I have a JR radio X378 that like many other I guess, has the feature of "safe mode" or something like that, which assign specific positions to all servos if any interference is happening. This would give you, maybe, some time and with luck, the interference could vanish before your plane hit the ground.


Nilo