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cbatters
11-13-2006, 03:32 PM
HISTORY
I bought the Ventura ARF to get back into the hobby but only flew it once after it nosed into the grass shortly after launch. I picked up a Challenger and have been successfuly launching / flying it for the last couple months so I decided it was time to try the Ventura again.

SATURDAY
Last flight of the day, I pulled out my Ventura and checked radio range, control surfaces, servo opreation - everything seemed good to go.

Set the elevator slightly up (couple clicks) and gave it a firm, slightly up toss with full throttle. (Was intending to fly it straight ahead and land without turning as a first flight on a new plane.) Instead, the plane rose up quickly but banked strongly to the left. Attempted to add right rudder but it happened too quickly. Cut power and applied up elevator to pull the nose up just before it hit the ground. Rough landing but no damage.

Checked control surfaces again, reduced the amount of up elevator trim and appled 2 clicks of right rudder. (even through everything looked square and rudder was centered.)

Launched it again - firm level toss with with full throttle - and had a similar botched fight.

Two possibilities:

1. Plane may still have had too much up elevator causing the plane to stall and then drop the left wing

2. Torque roll from full throttle. (perhaps it would be better to launch at partial throttle??)

It was getting dark so I did not have any time to try anything else.

Next flights will be

1. Hand toss - no throttle to check/adjust trim (possible the plane was rising too quickly and stalling, dropping the left wing, due to too much up elevator)

2. 1/2 throttle launch and try straight ahead flight


Any other tips on flying the Ventura are appreciated.



Clint

Sky Sharkster
11-13-2006, 05:15 PM
Hi Clint, What you're experiencing is common to just about all E-Powered gliders; The nose pitch-up under power and the torque roll soon after. Understanding a bit about "Why" may help you get this model and any future E-Gliders flying sucessfully.
Most gliders have a (relatively) substantial amount of angular difference between the wing incidence and the stabilizer incidence; The entire stab is angled "up" a few degrees (usually 2-4 degrees) from a datum line straight down the side of the fuselage, front-to-rear. If this difference of angles (called "Decalage") isn't built into the stabilizer, it's built into the wing. The trailing edge of the wing is lower than the leading edge. Sometimes it's a combination of both, but it's always there, and for good reason. Gliders, with a few very-high-performance exceptions, glide better when the wing is presented to the airflow at this angle, called the "Angle of Attack". More lift at low speed, better glide.
The stabilizer, by virtue of it's distance from the wing, exerts a powerful force on the wing. If the stab is "telling" the wing (via decalage) to fly at two or three degrees "Up", that's what the wing will do, as soon as it can achieve a stable flying speed. Again, this will be a low airspeed.
I guess you've figured out where this is going, right? All these things work great at a typical glide speed of 8-10 mph. Now, we fire up the motor and launch...airspeed is 5, 10, 15, 20 MPH. even if the airspeed isn't that fast, the wing and stab are seeing airflow of that speed, because the prop is pushing the air backwards that fast. The stab is still telling the nose (via the wing angle) to come up...and up...and...STALL!
Combine this with a fairly large prop spinning at high RPM, lots of torque, aircraft is stalled or nearly so, the plane reacts to the prop torque more since the normal forces that would counter-act torque (the flying surfaces, wing and tail) are stalled and not helping at all. Nose pitches up, wing stops "flying" (lifting)/ nose drops, torque takes over...pick up the pieces.
There are several ways to work around this; With a computer radio that allows throttle/elevator mixing, most Sailplane pilots mix in "down" elevator in an parallel ratio to the throttle position. If the radio allows rudder mixing to the same elevator/throttle mix, some "Right" rudder, also.
Without mixing electronically, you can do it manually, it just means you have to think it out first, be prepared and use a gentle but steady hand on the stick. The equivilent of 2-3 "clicks" of down elevator and 1-2 clicks of right.
If the model has enough power to launch sucessfully at less than full power, try that; As you increase the throttle, be ready with the other hand to lower the elevator and adjust the rudder. The elevator trim will be constantly increasing; As the model picks up speed into the climb you'll have to stay on the "Down" or even add more until motor cut-off. The rudder correction isn't constant; As the speed builds up, the flying surfaces overcome the torque and the need for "Right" will decrease, towards the end of the climb you may not need any.
This isn't a "vice" or problem with E-Gliders; It's just a function of the design compromises needed to make it fly correctly at vastly different speeds. Once you're prepared and understand what's liable to happen, you can correct it and it will become second nature.
Good Luck!
Ron

cbatters
11-13-2006, 06:37 PM
Many thanks for the explanation.

100% agree. The plane was not moving very fast so it is easy to believe that the torque of the engine could cause the plane to roll. I was just surprised that it happened so fast after launch.

Curious that I have not noticed the same issue when launching the Challenger. It seems to launch pretty level at full throttle and then rises up smartly after I let it build up air speed and pull back on the stick.

Couple obvious differences between the Ventura and Challenger

1. Challenger has a pusher prop and a V tail. Perhaps this reduces the effect experienced on gliders with the motor up front?

2. Ventura has a lot more wash-out in the wing tips. (although I thought this would reduce the tendancy to tip stall)

I was trying to do the same level launch / climb out with the Ventura but it popped up pretty quick and rolled to the left before I could react. I'll try adding more down elevator trim and also see if 50% throttle provides a more controlled launch and get more air-speed before powering up to 100%.

I will also start with a no throttle hand launch to confirm that the plane is trimmed correctly for gliding.

OMT : With both hands on the transmitter (with someone else launching the plane) I might have been able to react in time. Tough launching with your right hand and then getting your hand back on the stick in time to make the necessary correction. Albeit better to find a way to launch the plane so no panic control interventions are required to keep it from crashing.


Again, many thanks.


Clint

cbatters
11-13-2006, 07:03 PM
OMT:

On the Mirage I know the motor/prop (thrustline ?) is angled slightly downward and to the right to minimize this effect. The Challenger prop is also angled downward. Unclear if the motor in the Ventura is angled or if it is in line with the fuse (which might explain why the thrust effects are more pronounced)



Clint

Sky Sharkster
11-14-2006, 12:16 AM
Hi Clint, I believe you've found at least one of the causes, downthrust is a pretty common way of defeating the "Pitch-Up" problem. If it's not a difficult mod to the Ventura, you might try some.
If you visualize the propeller wash as a cone, starting at the prop tips and becoming larger in diameter towards the tail, you'll see the wings are operating in mostly "non-prop" wash, they are more affected by airspeed than prop flow. Obviously, until the aircraft reaches maximum airspeed, the prop wash has a higher velocity than the airflow. That difference is greatest at launch and shortly after; Near-zero airspeed, maximum prop speed. So, the negative effect of the prop (torque) has the least counter force (aerodynamic correction) and the tail has the greater effect.
Now we look at the same cause-and effect but put the prop behind the wing. We still have the same airspeed/prop speed differential, but the wing has none of the turbulance and partial (it's not unbalanced by the cone of air) airflow/speed differential to contend with; The air it "sees" is not a swirling, half-fast/half slow mass. It's a layer of relatively "smooth" fluid. I still don't completely understand the physics of a pusher vs tractor configuration but it seems clear that this is a major difference.
Another factor is wing loading; Although "Lighter is Better" in aircraft, having a greater mass per square foot of wing area may actually help this particular problem; The model won't pitch up because it can't! A lighter wing loading has less resistance to these external forces because it has less inertia. Other factors would be wing airfoil, Center of Gravity, Center of Pressure travel for a given airfoil, tail moment arm and many others.
Anyhow, enough aerodynamics; I sure your eyes are starting to glaze over!
Hope some of this helps, you're already getting a handle on these factors and will solve the puzzle quickly. A "launcher" is a good idea for any test flights, even though the model may seem simple to fly; All these forces work on even the most rudimentry aircraft, in different amounts; More reaction time equals more flying time!
Good Luck!
Ron

cbatters
11-14-2006, 01:42 AM
No glazing over of eyes here - it all makes sense.

Several observations:

1. This explains something I have observed with the Challenger. With a strong toss it would fly straight out/level. With the same trim and a lighter toss, it would nose up and initially climb out at a steeper angle.

Now I realize that this was due to effect of prop on tail.

2. Ventura does have ~5 degree down angle on thrust.

3. Vertical stabilizer may have had a slght twist to the left which didn't help.

4. Checked COG of Ventura. Was flying it toward the front limit of the balance range which might explain why it would nose down pretty quick when stalling.

Next flight will be neutral elevator and hand toss to see how it glides and then a 50% power launch.



Clint

cbatters
11-16-2006, 11:49 AM
Final verdict - BAD TRIM

6 hand launches - each time adjusting for more right rudder and I got it flying straight / true. Amazing glider. Easily getting 100-150' on a firm but not hard throw with zero wind.

Launched the plane with 20% throttle and it began a gentle climb out without touching elevator or rudder.

Launched the plane with 50% throttle and it immediately popped up at a very steep climb angle but was easy to bring the nose back down with some down elevator. (I suspect 100% throttle would be very difficult to control)

Only one crash. Plane was gliding level at about 10' with motor off and I wanted to take it back up again so I pushed forward (too hard) on the throttle. Unfortunately, the nose popped up and the left wing dropped abruptly before I could correct and it crashed. (Minor damage to tail but I broke one of the blades on the folding prop so my AM flying before work was over. :( )

Also my fault for allowing a "new" plane to fly so slow so close to the ground. One or two clicks of down elevator trim and a little more airspeed and it probably would not have happened.

Two lessons learned:

1. ALWAYS hand launch and trim a new plane before attempting powered flight. If it won't fly correctly from hand launching, adding power is only going to increase speed / altitude and cause more damage.

2. Transition from "floating" to powered flight should be done gently and anticipate adding down elevator and possibly right rudder to counter the effects of the prop wash / torque.

Note: I will have to experiment some more with the Challenger to see if abrupt changes in throttle have the same effect. Perhaps the pusher prop / v tail combination reduces the effects of changes in thrust.



Clint

dbourdon
11-16-2006, 01:03 PM
Clint,

Are you flying your Ventura stock?

Thanks,
Don

cbatters
11-16-2006, 01:31 PM
Clint,

Are you flying your Ventura stock?

Thanks,
Don

Yes.

CORVETTER89
12-04-2006, 02:30 PM
i have noticed on the ventura you need all the servo throw of the long side of the servo arm... otherwise your control will be rather limited .. personally i purchased a pair of extended servo arms for the micro servos and cut holes in the side of my fuselage for the extended arms to poke through with the rods close to the sides going back to the control horns... mucho control surface movement and if you want to snap dat sucka around..... it WILL come around!... good luck! vetteman

CORVETTER89
12-04-2006, 03:00 PM
my ventura launches more stable when there is a slight down angle on the elevator if not the plane will almost loop on launch causing a nasty stall then roll, the ventura has so much lift on the wings, if not trimmed down a little it will start to loop on launch... hope this helps....... keep um up! vetteman

cbatters
12-04-2006, 03:02 PM
i have noticed on the ventura you need all the servo throw of the long side of the servo arm... otherwise your control will be rather limited .. personally i purchased a pair of extended servo arms for the micro servos and cut holes in the side of my fuselage for the extended arms to poke through with the rods close to the sides going back to the control horns... mucho control surface movement and if you want to snap dat sucka around..... it WILL come around!... good luck! vetteman

Outermost hole of stock servo and inner hole of control horn seems to work fine on mine. The only mushy control response I have noticed is when the plane is floating very slowly. I either drop the nose to start the turn or give it a little power if I want to tighten up the turn.


Clint

cbatters
12-04-2006, 03:09 PM
my ventura launches more stable when there is a slight down angle on the elevator if not the plane will almost loop on launch causing a nasty stall then roll, the ventura has so much lift on the wings, if not trimmed down a little it will start to loop on launch... hope this helps....... keep um up! vetteman

100% agree. Neutral or down elevator on launch.

50% throttle is also a better throttle setting for first launch for a new pilot - and let the plane climb out slowly and add more throttle as you feel comfortable with the speed / handling of the plane. Less chance of torque roll / stalling on launch.



Clint

wilbou54
01-23-2007, 04:08 PM
I have been flying my Ventura (RTF) for a few months now. I've Had some of the same problems as most of you have already mentioned. In my case the stock speed controller/receiver were not working properly. The throttle functioned from about 50% to 100% of slide position. I didn't realize this until after a couple of weekend trips to the flying field. I would think I was adding/decreasing the throttle by a click or two but in reality I was increasing/decreasing the throttle quite a bit more due to the narrow speed control range with the faulty electronics. Anything less would cutoff the motor. I've since replaced the stock electronics with a Corona RS410 receiver and a Blue Arrow 30-amp speed control. I also purchased a JR-7202 computer transmitter. This arrangement solved many of the problems I was having.

http://www.wattflyer.com/forums/images/icons/icon4.gif I also ran into a problem a couple of weeks back, with the Ventura in that after being launched it pitched up violently, stalled and crashed. After checking and not noticing any damage I reattached the wing and launched again. This time it flew well with no problems. I chalked it up to pilot error. The next weekend I flew the Ventura along with my SkyFly and everything seemed normal. Before my second flight with the Ventura I decided to replace the rubber bands supporting wings. When I launched the Ventura for its second flight, it pitched up violently, stalled and crashed. Upon investigation I noticed upon inserting the wing in its wing slot that It was not quite a perfect fit. If I placed the trailing edge down in the slot first the leading edge would not quite fit down all the way and vice/versa. This caused the wing incidence to change ever so slightly which of course changed the wings angle of attack. I now make sure that the leading wing edge is sitting down all the way before I attempt to fly. Since this discovery I no longer have had the violent pitch up and stall characteristics that had previously perplexed me.

cbatters
01-23-2007, 04:28 PM
Glad to hear that you were able to solve the launch problem. (and I'll have to keep an eye on the wing mount)

I found launching at 100% throttle was touchy - small diferences in throw velocity / angle / wind speed could cause large differences in attitude of the plane immediately after launch.

Launching at 50% is much more controlled / predictable.



Clint

cbatters
01-29-2007, 03:10 AM
Had not flown the Ventura for quite a while so decided to take it out this weekend. Great flight, smooth landing, broke tail on a rock.

1:3 flights I damage the tail on smooth landings whereas I never experience damage with the V-Tails flying at the same field.

Finally decided to do something about it. Bent a paperclip to create a landing skid that raises the tail ~1" off the ground. Should work.



Clint

wilbou54
01-29-2007, 10:57 PM
Great fix with the paper clip for the tail skid. Fortunately I don't have to deal with rocks in the landing area only my poor aviater skills which seem to crop up every now in then.

But I due love my Ventura. I was able to get a couple of flights in Saturday morning before the rain moved in. It flew great and was able to get 16-minutes flying time off of the stock battery.

wilbou54

cbatters
01-30-2007, 12:51 AM
Great fix with the paper clip for the tail skid. Fortunately I don't have to deal with rocks in the landing area only my poor aviater skills which seem to crop up every now in then.

But I due love my Ventura. I was able to get a couple of flights in Saturday morning before the rain moved in. It flew great and was able to get 16-minutes flying time off of the stock battery.

wilbou54

I don't know if I hit a small rock or if the ground was just very hard/frozen but when I came in for a landing, I flared the plane and then saw the vertical stabilizer fly up in the air. I looked on the ground but did not see anything to blame for the damage.

Hopefully the higher landing skid will help.



Clint

Anders0n
01-06-2008, 04:54 PM
My recent Ventura experience :) LINK (http://www.rcgroups.com/forums/showthread.php?t=797154)

cbatters
01-06-2008, 06:20 PM
Nice.

Glad to see someone else have a good experience with the Ventura.

I am just introducing lipo and brushless to my hangar and I can imagine a Ventura power upgrade in my future.


Clint