PDA

View Full Version : Downward spiral of death...


monkey77
09-16-2005, 01:54 PM
I just recently purchased and began flying a Thunder Tiger eHawk 1400. On the first flight I noticed that when I would go into a turn the plane had a tendancy to want to severly drop the wing tip on the inside of the turn and proceed to go into a spin pretty much straight down. Is this a characteristic of sailplanes (http://www.rcuniverse.com/buynow/keywordclick.cfm?bid_id=2608) in general or the eHawk? It has a V tail and ailerons. Do I need to do any mixing in the radio for the v tail? I'm completely new to the v tail setup and it has been about 10 years since I flew any kind of sailplane. Any input would be great.

Thanks
- Dan

Epoxycup
09-16-2005, 04:38 PM
Dan

The cause of the what you describe could be caused from several differant things. Probably not a fault of your particular glider design though.
So with that in mind I will list sevral I can think of for you to check. Set up is everything.;)

Warped wing - It is possible you recieved a warped wing, it does happen. Simply sight down the LE of your wing and look for twist. Dont worry about the tip sections (outer 8" or so) I will talk about that next.

Washout - Most thermal or mild type gliders and other aircraft will have some washout in the tip section of the wing. Put the wing on something eye level, walk about 10' away and look at the tip relation to the LE. The tips should be flexed slightly down (called washout) this helps the glider at slower speeds and in turns. If you have one tip going up (wash in) and one going down that is bad. Generally it can be fixed by flexing the tip down and heating the monokote then holding it until it cools down.

Balance - I will assume you CG is set according to your instructions, if not and you are tail heavey it will make your aircraft very unstable, recheck this and move things or add lead as required.

Lateral balance - Your instructions dont generally address this, but in most kits or ARF's one wing is a little heaveir than the other, after all balsa is a natural product and is subject to variation. Get someone to help and balance the glider at the front (under canopy area) and the back (Under tail section) at the center of the fuselage and see if one wing dropps consistently and fairly quickly. This will be your heavey wing so add some small stick on lead to the other wing until your lateral balance is fairly equal.

Motor angle - If your glider only reacts this way when you are WOT on the motor it may be that your motor torque is causing the increased turn angle. Thrust angle if not given in your instructions is generally a degree or two down and the same to the left (from back of glider looking forward). This offsets the torque of the prop rotation.

Radio set up - Another possibility is your aileron ( if you have them:o ). Check your throws making sure they are equal for both sides down and up. Some people like to dial in (computer radio) some differantial (more down then up). For your pupose just make sure that your opposite aileron goes down as much as the other side goes up. The other thing that goes along with this is that most thermal type gliders like gentle turns so if you have to, reduce your control surface throws (deflection). Aileron or rudder whatever you use to turn.

Well good liuck, some others may be able to think of some oother checks for you. I would kind of expect you to find the trouble in your wing though. ;)

Dan

PS: Sorry Dan just reread your post got the aieron v-tail. So everything above holds true anyway. Goodluck and let us all know how it comes out good or bad, we all learn from these things.

monkey77
09-16-2005, 07:21 PM
Thanks for the information...my CG should be good as I did that per the instructions (I will check it again though). I think you may be right about the wing...I'll go over it carefully tonight and make sure the wing is good. This glider has upturned wing tips...about the last 4 or 5 inches of the wing tips angle up about 30 degrees or so.

I'll post back with my results!
Thanks again

Epoxycup
09-16-2005, 10:14 PM
Dan


Yes upturned wing tips are normal, when I was explaining washout it would lead edge to the back of the wing. It would appear as haveing a slight downward twist as viewed from the end tip of the wing. Hmm hard to describe without a picture but imagine if you took hold od the tip of the wing and twisted it forward, this would be washout. It is generally designed in to prevent the tip of the wing from stalling out. This can happent when turning as the inner wing tip is not moveing through the air at the same rate as the outer wing tip.
Let me know how it looks after you examine it, hope you find something to correct the problem..:o


You dont have to take off ......

But you do have to land...........:eek:


Dan

Heidelberg Germany Flyer
09-18-2005, 04:41 PM
"motor angle if not given in your instructions is generally a degree or two down and the same to the left (from back of glider looking forward)."

Don't you mean a degree or two to the right?

krazykajun
09-25-2005, 02:36 PM
Is your v tail cotrolled by 1 servo to act as elevator only if it has 2 servos it is acting as ruder and elevator and needs mixing you can buy a small on board mixer for around 20 bucks if your radio does not have this capability

krazykajun
09-25-2005, 03:00 PM
If the plne slows down too much it will tend to tip stall one wing will stop lifting. the inside wng in a turn is always gong slower than the outside wing if yuo are going downwind you may apeer to be going fast enough but your airspeed could be a lot slower than you think air speed is only relitive to the wind and not the ground in a 20 ph wind if your ground speed is 25ph going with the wind your airseed is 5ph a turn would likely stall the inside wing even if the plane flies perfectly

monkey77
09-26-2005, 03:44 AM
The glider seems to fly fine with the power to the motor at 3/4 or better. The spirals of death always seem to happen after I cut power and start my gliding. I climb to 200 or 300 feet with the power on into the wind. Once I get up that high I cut the motor and usually start to make a gentle turn back toward where I am standing. When I start to make this turn is usually when I start to notice the plane wanting to spiral. My next question is how the heck can I pull out of the spin? Is it possible? Any tips would be great as I haven't had any luck so far.

Thanks,
Dan

krazykajun
09-27-2005, 02:03 AM
I dont know but at 300 ft you shold be able to just let go of the sticks and the plane should right itself the wings pick up speed and start flying again if this did not work i would conclude that there is more wrong the plane is out of balance. the plane you have I am not familiar with but I had a T Hawk very simalar plane but no v tail and a smaller wing span. It is possible but unlikely to get out of a spiral dive but the only way that worked for me was leting go and hoping I had enough altitude for the plane to right itself. I would check the lateral balance of the plane se if one side of the wing is hevier than the other and also moving your cg a little forward and see if this helps I would start small a dime taped on the nose and work from there.It is also possible that your motor may be at the wrong angle this causes you to use up elevator trim when motor is on when you shut down the motor the plane slows and stalls. I you can find a place to do it glide test the plane motor off just toss it and trim it till you can get it to glide level with no up or down elevator v tails at neutral buy adding weight to the nose or tail. if it will not glide straight but is level try just 1 or 2 cicks of right or left trim. If it flys after doing this give it a go motor on and see how it reacts when you tun the motor on while gliding it should stay straight and start to climb slowly with no input from you other than throttle flying on the wing not the elevator

Epoxycup
11-13-2005, 12:34 PM
Heidelberg


Your right, I mean right thanks for catching that.:o

sparky flyer
12-11-2005, 05:05 AM
I had an Ehawk 1400, and I loved it. Fast and groovy, even with the stock speed 400 motor. It never displayed the tip stall problem you had. I finally lost it when I reversed the elevator servo on the Tx by mistake. I thought it was a neat little plane.

Sparky