davideboracay

Hello,

An year ago I bought a Hangar 9 Funtana X 50. I had powered it with a .46 2stroke engine.
Recently I bougth a Saito .82 4stroke engine and installed it in the plane.
The first time I went to fly it I crashed at take-off.
I had given half throttle and after 50 metres it lifted off a couple inches and rolled sharply to the left and hit the ground immediately.

THERE WAS VERY LITTLE WIND!!

Can anyone help to explain what happened so that next time I can get it right?


Thanks

alan0899

G'day Davide,
You stalled it, lack of airspeed = stall, try full power next time, & throttle back when you are at a decent altitude.

da Rock

The prop was flying and lifted the model into the air before the model had airspeed enough for the airplane to be stable. The prop is flying before the tail is "flying". The tail keeps the airplane going straight. When it's flying fast enough.

And the tail has to keep the wing's AOA under the stall AOA, as well as keeping the airplane from yawing around behind the engine/prop when those two decide to swing left.

Very often, the kind of crash you described can be avoided every time by a simple technique. Roll the throttle in at a controlled pace. Don't throttle up too quickly. How quick is "too quickly"? You just found out for that airplane.

The first couple of takeoffs for a new model/engine combination should use A LOT of the runway to get off. Learn how the airplane reacts to throttle on takeoff with a safe, even throttle up. Give the wing a chance to get all of itself flying, and the tail a chance to "get a grip on the air".

davideboracay

I gave slow progressive throttle to half and didn't touch the controls after that.

Some guys at the field said it was the torque effect.

I think it could be a combination of the torque and a tail heavy/badly trimmed plane. The plane just lifted off after roughly 20 meters and rolled sharply to the left.

MinnFlyer

My Feedback: (4)

It probably WAS torque effect - and it was caused by what da Rock said. You lifted off the ground before the plane was ready to fly.

jetmech05

sounds like a stall to me also...I always and I teach my students to always use full power on takeoff/go around..I know you said that you didn't touch anything after you applied throttle...just because the airplane lifted off the ground on its own doesn't mean it's ready to fly..plus if it was just above stall speed the controls would be really sluggish and take alot of throw to be effective....remember you might have too much up elevator trim causing the aircraft to lift off on its own..you haven't had a chance to trim it yet.
You didn't mention if you checked the CG after the engine change..if you didn't you should

aerowoof

how did it become tail heavy?most 4 strokes of the size you installed weigh more than the 2 stroke you replacerd?

fozjared

thats what i thought as well!

Insanemoondoggie

The OS .46 AX weighh 17.2 oz and the Saito 82 weighs 17 .6, both with muffler.

jetmech05

you are sure that everything was replaced in the exact same spot as it was before, that there is no way anything shifted. you used the same engine mount. and the distance from the cg is the same? I check CG after changing anything that has as much effect on CG like an engine does.....then again it may have nothing to do with CG.
You asked for possible explainations....

davideboracay

I sure did check the C.G.
It wasn't tail heavy actually. I was just suggesting possible causes of the crash.

bla bla

It sounds like you snapped on take-off.
To much elevator throw, to little airspeed.
Bang. the rest is history.
Torque isn't an issue here.

Mode One

Uncertain how you can unequivocally make the above statement. Torque most certainly could be an issue. Best question; Why didn't you use full throttle at take off?

Essentially a new engine makes this a new test flight. I always go to full throttle with my thumbs on the sticks ready to make any and all corrections needed to keep the wings level and the airplane in a shallow climb-out. With a significant change to the airframe (which an engine change would be, for me) I'm back to handling the airplane with "Kid Gloves" for at least the first few moments of a test flight and for the first landing.

MinnFlyer

My Feedback: (4)

I agree with Mode One - I think this is a textbook case of a torque roll on takeoff. I've seen it happen too many times.

bla bla

Because it's a normal sized engine in a normal sized airframe!
Are you thinking that engine torque will rotate the airframe in a split second?
If it could, it'd do it all the time! You'll be flying a constant rolling plane, having to hold in opposite aileron, perminatly!
Even with massively overpowered and superlight 3D airframes it take some seconde for engine torque to become evident. As in a torque roll.
Even then the rotation isn't that fast.

For all you people that have experienced this on take off (and who hasn't)...it's a snap.
Stop imagining it's something else.

MinnFlyer

My Feedback: (4)

Ok, let's look at the facts:


Ok, NORMAL sized engine? An 82 4-stroke is the largest size recommended for this plane. This is a 3-D plane which means that it will be grossly over-powered. Also, they list this plane for a 32 - 46 2-stroke. It is generally accepted that the 4-stroke equivelant of a 46 is a 70. Yet, they recommend an 82. So I wouldn't call this a "Normal size" engine.

Now let's review what happened:




If he's not, I am.

I have seen it happen 4 times in the last two years.


No, there are physical forces called Momentum and Inertia that keep it from happening.

You're right, it DOES take a second or two for the plane to start rotating - but that plane is stable and you're waiting for the torque to take effect. When you are rolling down the runway, the torque is at it's peak, and at half throttle, you're not generating much airspeed. So the plane is TRYING to roll to the left, but the ground is preventing it from doing so. IF you lift off before you have suffucient airspeed, the plane that has been wanting to roll to the left all the way down the runway will do so - and immediately.


Note: He did NOT say it snapped. It rolled sharply. This is a CLASSIC example of a low-speed takeoff torque roll.

bkdavy

My Feedback: (1)

I have to agree with bla... A Funtana will snap very easily, which is good when you want it to happen. Too little speed combined with up elevator on take off is a recipe for disaster.

There was no discussion of the change in prop associated with the change in engine. Most times the change described ends up with a larger diameter prop, but little or no change in pitch. The 4 stroke is no doubt turning fewer RPMs than the two stroke. There fore half throttle take off with the 4 stroke is going to have significantly lower speed. While the wings obviously were generating lift, the addition of either elevator or rudder (or both) was probably enough to push the wing into the stall and generate the snap.

Chalk it up to experience.

Brad

bla bla

Torque roll on take off?[sm=lol.gif]
What you've seen happen 4 times in the last couple of years... is a snap. To much elevator, to little airspeed. Boom, you're in the ground.
Now, people may well be happier blaming it on some uncontrollable act of God, a shot from the blue... out of there control... poor, unlucky, bast#rds! And thats fine.
But it really is nothing other than pilot error.
Sorry.

da Rock

If it wasn't a snap, it was a torque roll.

If it wasn't a torque roll it was a snap.

The probability of either happening on takeoff when the prop is flying and the airplane isn't yet is huge. The probability of it being something other than those two is almost nil.

How would an observer know? Beats me. Maybe get a clue from the AOA.

And it's quite possible the roll is both happening at the same time.

Bottom line............... the pilot let the airplane fly itself. He certainly didn't let the airspeed build safely. And control the throttle to allow the airframe to catch up to the prop.

And FWIW, I just got in from flying today, where I had the misfortune to witness a really nice 40size U-Can-Do execute what I'd say was a torque roll on takeoff. I'd call it a torque death roll. The airplane never showed what I'd call a nose up AOA on the takeoff. But the sucker was going pretty slow. Maybe not as slow as it'd need to be to hover, but certainly slower than it'd be doing in a climbing torque roll. And that's a favorite maneuver of the pilot of that airplane. Lots of 3D airplanes can be pulled along at almost zero airspeed. They're usually pointed up most of those times. But up, down, sideways, the wing and airframe see the same airspeed no matter what the direction. And if it'll torque roll at almost zero airspeed pointed up, it'll torque roll at the same or less pointed any which away.

Where do we cast our votes?

Mode One

Torque roll or snap, it is still pilot error and the error is using only 1/2 throttle. Davide makes no mention of ANY control input, rudder, aileron or elevator. He also doesn't adequately describe the airplane's condition, warps in the wings and a million other details it would take to quantifiably determine the cause of the crash. Could it be possible for the cause to be a torque induced asymmetrical wing stall (snap roll)?

All I am only saying is; none of us has adequate information to declare we know the answer! However, I hope Davide didn't do much damage and the next time, if you have the power, use it.

My Funtana S 40 snaps well; however, it is also very docile at slow speeds.

davideboracay

The plane was perfectly fine because a few months ago i had the old 2stroke in it and it was flying well.

The plane survived well and the damage is not that big and easily repairable.

Now I see the significance of nylon bolts!! They broke!

Mode One

Davide, All I'm aluding to is; from the small amount of information you gave on what happened, it is impossible for us who were not there, to make a sound judgement on the cause of the crash. I meant no disrespect towards yourself, your model, or your model building abilities! You have never responded to the question why you were only using 1/2 throttle, however.

bla bla

Amazing that people actually believe theres such a thing as the dreaded, the scary and not to forget, the highly ellusive....Torque roll on take off.
Not to mention the "They happen, I've seen 'em" (but not all the time as they sneek up on you and roll your airplane, occassionaly) mentality.
You've got to laugh.

As they say, for every action theres an equal and opposite reaction.
BUT NOT in the case of the one in a million... Torque roll on take off action.
IT only raises it's head every now and again, prefering to remain hidden 99% of the time.
Lurking in the back ground waiting, like a preditor, ready to POUNCH on anyone that's going to slow and is giving to much elevator on take off!

"Hey buddy, looked like you snapped on take off there."
Yes it appears like that to some... but to us believers...we KNOW it was really....a torque roll!
It's FUNNY!

da Rock

Hate to judge such a kewl theatrical performance, but.............

To get a stall you have to have AOA greater than the wing's ability to fly without stalling. So unless the wing had enough AOA, it won't stall, any type of stall. And unless it's flying, it's not going to stall. And flying takes airspeed. Without it, the wing isn't lifting. And until it can lift, it isn't flying. Without speed, it's neither flying nor lifting. And until it's doing that, it can't stall. Stall is what happens when it has passed beyond the most lift it can create (and it's gotta start creating before it can create it's max) and the airflow over and around it checks out and the wing stops creating it's lift.

And if you are experienced enough to be able to judge a models AOA on takeoff, you will see an awful lot of them that are moving ahead with way less pitch than the wing's stall AOA. And no matter how cutely you describe snap roll, it takes the wing stalling to do it. And the wing won't stall when it isn't pitched to the stall AOA.

Theatrics aside, when the wing isn't flying, and the prop is, whatever happens isn't going to be because of a snap roll. And 3D airplanes are easily dragged in the vertical with nothing on the airplane flying, just being pushed around by prop blast. And they're also easily dragged horizontal. And the 4Ds are held vertical pointing down. So it ain't hard to see that they'd easily be carried into the air with nothing but the prop flying. Heck, "2D" planes are every day. We had a trainer taxii out, stop, and FIREWALLed into bits a pieces yesterday about the same time the U-Can-Do was firewalled to death.


Speaking of mentality........... the red lettering over the message box all of us use when typing our posts starts off with:
Please resist the urge to curse, flame, degrade, insult or embarrass someone in your post.

davideboracay

I used half throttle because this was the first time I flew a 4 stroke and i thought it would have much more power than my previous engine.
Also in reviews it says " it took off in only 50 feet at half throttle".