afterburner

My Feedback: (18)

I had a issue with my Viper back in the Spring where when flying full throttle straight and level, it would pitch down hard for 1/4 second. Looked like a glitch. Well, before grounding the plane to figure it out I did a low full throttle pass and it pitched down at the end of the runway in the high grass. After wing repairs and a new fuse, I had it ready today and the first flight was fine but the second flight after coming out of a turn, I had the same pitch/glitch down and I throttled back and landed. Now the receiver and crystal were replaced as well as the switch after repairing it. The tail servos are the same futaba standard and the battery is the same. I am cycling the battery as I type this but even under load it is still 5.2 volts. I don't think this is a noise/interference issue as none of my other planes have problems at this field on the same channel. If the battery cycles good, I'm going to change out the tail servos but I was wondering if anyone has ever seen anything like this before with this plane or any other plane? I've got a plastic clevis for the throttle and I'm running a Magnum 46 and a 9 X 7 APC. Thanks.

Marty

[email protected]

check the incidence - wing/engine/tailpllane generally the trailing edge of the tailplane needs to be lifted about 3 mm to get it to fly properly. check this before the servos. trevor hnz

afterburner

My Feedback: (18)

It flies straight and level fine for 99% of the flight. It only takes a pitch down for an instant so I wouldn't think this would be an incidence issue as that would effect the overall flying characteristics?

Marty

djlyon

Had the same thing with a racer2. It was the switch. If you are not using a heavy duty switch, do so.

rmenke

My Feedback: (13)

afterburner:

Check both the incidence and switch. Can never be to carefull with these things. Vipers and others generally do not come with everying right on, especially the v tail setup is prone to miss-alighment. If its not right, will fly strangly. Buy nothing but HD switches and be sure they are truly HD. ENJOY

Ed Smith

Somebody takes the trouble to offer you sound advice and you argue with them. Have you checked the incidence??

Ed S

daven

My Feedback: (1)

I agree with Marty on this one. If its just an occasional blip, and it normally flies straight and level, how could it be the incidence???

If it was an incidence issue, it would effect the whole flight until it was trimmed out.

doesn't sound like the problem to me either, but definately worth checking if he is carrying excessive trim.

I would definately suspect the switch, or loose crystal, or loose module, loose antenna, or possibly bad receiver or battery. Things that are intermittant can be tricky to fix.

afterburner

My Feedback: (18)

Yes the plane has a new HD switch as well as a different Rx and crystal.

Ed, Relax. I wasn't arguing with him(notice the question mark at the end of my statement). I was questioning the validity of this being an incidence issue. I have flown planes with incidence problems and have never seen this kind of reaction. The plane will fly fine for five minutes and for a 1/2 a second of that entire flight, it will nose dive during straight and level flight. Yes, I have checked the incidence. It is 0-0-0. Is that correct? I don't know as Great Planes hasn't listed what it should be in the manual.

Marty

afterburner

My Feedback: (18)

Dave,
I didn't see your post as I was putting my post up, I got two phone calls.

I have a few clicks of up elevator and the the C.G. was set close to the recommended 3". The battery is charging and discharging at it's rated capacity but I'm going to check the current draw while it's in the plane. I might pull some servos from an old plane and swap the 3004's out.

Marty

dwbebens

A had a similar problem a while back. What I found was that I had an antenna routing problem. I had the antenna entirely inside the fuselage, going up to the front on one side, then going back down the other side to the tail. I had been routing my antennas this way in my race planes for 30 years, but with this particular plane and receiver, I had a problem. The problem only occurred when the plane was at the far pylon coming back toward me - - the plane would pitch down for just a moment, giving me a scare each time. It didn't occur every lap, just enough to make me very nervous. I re-routed the antenna and it was fine afterwards. The antenna may have run alongside a metal push-rod, other power wires, or something else to cause this.

Doug Bebensee

Bozarth

My Feedback: (15)

Marty,

Don't worry about Ed S. Just because you ask for opinions, it doesn't mean you have to believe anyone and everyone who pipes in. Discernment is a beautiful thing!

Kurt Bozarth

HighPlains

My Feedback: (1)

After you exhaust all the other options, replace the airborne battery pack.

afterburner

My Feedback: (18)

Doug, I have the antenna routed through the pre-installed antenna tube so there is about 18" hanging out the back of the plane.

Kurt, Good point. I always take advice from anyone willing to offer it. I just felt that it's not an incidence problem but I still don't know yet.

Marty

[email protected]

I have read the thread wwith some amusement, yes I have contributed........I run SPEKTRUM. so long internal aerials are not the problem in my case. I have had exactly the same problem in recent times, and it was the incidence. My previous VIPERS all had JR, and woith a trailing aerial lead.
My test flights are done withoout using a switch, yes call me old fashion but it does eliminate the potential switch problem at an early stage. Its very easy to do with the Viper as you can have manual access to yoour leads thru the hatch allowing for a quick assembly of your power leads.
I answered the question initially on the basis that every 'normal 'check had taken place prior to the call for help via this thread.
I maywell be wrong on your model but to ignore the fact that it may well be incidence is, as we say in New Zealand going out in the rain without a raincoat...........trevor h[:@]
NZ

combatpigg

My Feedback: (3)

My ARF Predator flew the same way and I chased my tail looking at radio equipment, CG, linkage slop, you name it.....until I got home and put the plane up on the table and checked it. Everything was askew, it was a coin toss to see where the major corrections should be made. I ended up raising the trailing edge of the wing a goodly amount and the plane is a solid flyer now [just ugly]. I have to guess that the random pitching down could have been from the constant stress on the ruddervators, IIRC the problem surfaced mostly at top speed.

afterburner

My Feedback: (18)

Trevor,
I do question the incidence theory but I don't dicount that it could be the problem. Like I mentioned, it is 0-0-0 so what should it be?

Marty

djlyon

0-0-0

djlyon

Pssssst. It's the switch or the wiring or the crystal or the receiver or a servo or a battery. I think I had 10 flights with at least 1 incident per before I got it fixed. Somebody up there kept it from crashing.

Denis

djlyon

I know that's not much help but you just have to work your way thru it.

Denis

[email protected]

The incidence on a vee tail is easy to measure and its very easy to get it wrong without knowing- without trying to fuel any answers to the previous mentioned model this is what I do and it has always worked.............before you install the viper tailplane have a look at the dihedral joint and the surrounding balsa block that forms the top of the joint. Measure the distance of the leading edge at the dihedral joint down from that block, and similarly tthe trailing edge, (centre of tailplane thickness) just on memory there is a difference of 2-3mm- they should be the same.
The other way is to scribe a line on the fuselage that is parellel to the datum line, wing seat then set everything up on that.
My mate Ed S has written somewhere on setting up a vee tail- his method works but I can sit down over a cup of coffee, or rum and with my vernier caliper set everything up on the dining room table.
Assuming in the case of the Viper that the top of the fuselage is the datum line then this variance typifies the normal liftup required at the trailing edge of the tailplane to make the aircraft fly properly.
Many of my mates have told me that their models are 000 but have no idea on how to really check the taillplane- they have incorrectly assumed the ailplane seat to be correct- sadly it ain't. hope this helps, trevor h,NZ

combatpigg

My Feedback: (3)

After landing the plane, he should see some compensating trim cranked into the elevators if there is a gross incidence problem. Changing the entire radio system and antenna routing should be tried before the next trip to the field, as well as a manual check of the elevator linkage under a load.

StanDouglas

There have been several posts on various forums in the past on methods for checking the incidence of V-tails. I did a quick search and didn't find any, but in Bill Vargus's article on the NMPRA web site there are pictures of how he does it simply using a standard incidence meter and a a bubble level.
[link=http://www.nmpra.org/Documents/Skinned-hinges/Vargus/v-tail-hinges.html]V-tail skinned hinges[/link]

Here's another a little more complex from Seaholm's site in the building the Bird of Prey write up:
[link=http://www.teamseaholm.com/rcpylon/birdOfPrey.htm]Bird of Prey Building[/link]

As I recall Ed S. has posted a simple method for setting the incidence in the past.

Found it on RCPRO:
[link=http://www.rcpro.org/net/ThreadView.aspx?threadid=475]Incidence meter[/link]
The last post there says "... VIPER the TE has to be raised 3.2mm" on average.

It has been my experience (none with the Viper) that incidence problems usually cause the Q500 to hunt; i.e., it starts to climb and you feed a little down and it pitches down, so you feed a little up and it pitches up and so on.

Steve J

My Feedback: (4)

My $0.02
I had a similar problem on a Scatkat. Turned out to be the pot on the elevator stick in the radio. Had a dead spot on center that was hard to find.

jaka

Hi!
The piching down problem is certainly not a stabilizer /trim problem...it's most likely a servo problem (bad pot or motor).

Jezmo

It may well be the servo but mine was doing it until I moved the CG forward a little and then it stopped. (It doesn't fly as well with the CG forward) I don't know what is happening but it seems a little strange that we all have bad pots in our elev servos. I am thinking of getting a brand new metal gear double ball bearing digital servo and see how that works. That should keep everything centered as perfect as is possible with current technology. When it is pitchy it certainly doesn't inspire any confidence in the plane especially down low around the pylons. The thing I wonder about is, if it is servo problems then, why is the pitchiness always down and not up sometimes.