sensei

What is your method of slowing before touchdown?

ahicks

My Feedback: (2)

Another great question...

My own planes are generally flown with the CG back far enough where cutting the power is like hitting a set of air brakes? The tails starts settling as speed drops off (which happens fairly quickly), AOA goes up, and if you don't push the nose back down or get on the power, the plane will literally stop mid air?

For those not set up like that, a forward slip is always fun?

bogbeagle

Reduce power ... resist the pitch change ... flap as appropriate ... trim.

karolh

All depends on the particular model I'm flying, but normally it's throttle management up to just before touchdown then a little back pressure for a smooth touch and roll out.

BMatthews

Hmmmm.... to me that suggests that you're either setting the CG back TOO far and it's behind the neutral point or you're using too much downthrust for the wing to tail trim and CG location. Generally models should not respond to a chopped throttle by nosing up.


Back to the original question..... Too many of us tend to make our landing approaches by going into a steep glide path or even a shallow dive (your guess as to where the point is that it's one or the other). By making the approach with the nose down in either manner we build up a lot of speed. And on a clean model this typically means when we go to flair for the touchdown that the model shoots along the length of the runway with no sign of touching down. Or we push the model onto the ground anyway.

If done right we make the approach with a nose up slow glide. The drag from operating the model ins this sort of higher lift style flight speed sets up a steeper and predictable glide slope that lets us set up for a predictable touch down point.

Another way that I've used to bleed off speed is to come up to the approach turn in, chop the throttle and perform a steep banked pylon turn to bleed off the excess energy. As you recover from this turn you exit with a slow nose high glide setting and make the last part of the approach with that same slow glide speed. With a clean sporty model the pylon turn might need to be a full circle and then some to bleed off all the speed. But used well and with the proper exit from the turn the model can be set up with the sort of slow glide you want to see. A variation of this turning to bleed speed is a low throttle tight banked spiral dive with a nose high gliding exit just off the deck and lined up for touchdown.

sensei

I guess for the most part I just idle back far enough that the fan up front becomes a break and if I need more to slow up then I just cross it up and side slip it in using power as/if needed to extend.

Bob

ahicks

My Feedback: (2)

BMatthews -
I generally do not use the conventional "neutral point" a lot of guys prefer? Mine are set for enhanced knife edge performance, which is adjusting CG to allow flying with a flat elevator? This does often leave me a hair in back of what others call neutral, but I find it very controllable? They slow quickly but I wouldn't describe what they're doing as nose up w/chopped throttle. Not like a plane with too much down thrust at all.

chuckk2

To me the trim and CG should be such that a power off glide without the chance of stalling should be the default. Landing then is nothing more than a small up elevator command/setting.
I believe this is a safety factor, in that when the control surfaces, etc, go to default, the model glides nicely, instead of stalling or nosing down. The smoother the approach, the more likely that a smooth landing will result. I often use a steeper and shallower angle of descent to manage the approach, much like you might do in a full size aircraft. With practice, it's possible to project the landing spot, based upon the approach speed and descent angle/rate.
Another way of looking at things has to do with wind gusts. If your approach speed is low, a 5mph gust in the wrong direction can be bad news.
(Low, slow, and no time to recover from a stall.) Let's assume a 25-30 mph airspeed. A five mph gust blowing from upwind towards the front of the model isn't a big deal. A tailwind gust on the other hand, can cause a stall. (I've heard "The wind drove it into the ground" statements after a really rough pancake landing! )

I also play around with the CG, usually to get the elevator to be in line with the horizontal stab when the model is "trimmed" for 1/2 throttle level flight.
One trainer, an Alpha 25 (electric powered) had a CG problem that required significant nose weight. I decided to relocate the wing towards the rear about an inch.
This allowed me to remove almost all of the nose weight.

speedracerntrixie

My Feedback: (29)

Al This is exactly the way I set mine up too. Here on RCU as soon as you suggest moving CG aft from the current position everyone seems to want to think your telling someone to make his airplane tail heavy. Truth is 90% of R/C pilots fly nose heavy, I've just been trying to convince them to correct that condition.

acerc

Ohhhhh! The horror!!!!

lopflyers

My Feedback: (12)

Better nose heavy. There is a saying: a nose heavy plane flies bad, a tail heavy one flies once.

speedracerntrixie

My Feedback: (29)

But it a well trimmed, well maintained airplane flys forever.

BMatthews

Fair enough. From this last post it sounds a lot more normal too. Your earlier one made it sounds like the trim was very extreme or the angles messed up.

A flat foamie electric I've got tends to slow down like it hits a brick wall when the power is cut as well. And I've got the CG back as well. I haven't done it as much as what your setup sounds like but I'd like to try it that way.

Mostly with this style of model I suspect it's the big diameter and low pitch prop which acts like a big drag chute when cut back to low RPM's.

I remember one time I was gliding it along and the prop stopped windmilling. I kept gliding for a little more and then bunted to a vertical dive. It sped up pretty good until the prop overcame the motor cogging and started windmilling. When it did the dive speed slowed down by a noticeable amount. Another sign that the big low pitch props make a very effective speed brake.

ahicks

My Feedback: (2)

Sounds like how you arrive at the CG you like/use would make for a hot topic here as well?

It's funny. When the CG topic comes up, and you mention how far in back of suggested CG your plane is set up, peoples eyes just kind of glass over is disbelief (or fear of the unknown?). It's pretty obvious further discussion isn't necessary.

IMHO, it's not just about KE, setting up for a flat elevator is also pretty easy to justify with an eye towards minimizing stall speed? For those not familiar, all you can do is present the concept, and from there people need to be curious enough to do some research/experimenting on their own. It's certainly not the way to set up a plane for a "landomatic" (trainer?) flying style if that's your preference?

I think a lot of people read that manf's suggested point in the directions (or plans if anyone is still using those?) and forget the rest of the suggestion. The part that says recommended CG.... "for test flights"?

Is anyone here trimming their elevator so on low rates full up stick cannot stall the plane? Expo to minimize ballooning while flaring?

speedracerntrixie

My Feedback: (29)

One thing we look for when selecting a prop for a pattern or IMAC airplane is how much brake action we can get out of it in a down line.

Al, my rule of thumb when setting up an aerobatic airplane for sequence flying is to use just enough throw on normal rate to get through the sequence. When I get to a maneuver that requires different throws I set up an additional set of rates. I end up with 3 rates in all. Normal, snap roll and rolling circle/spin.

acerc

I never balance a plane for sake of being balanced per on the table. I balance for flight and at that point the ele is almost always inline with the stab.
I also have a landing trim on the dual rates that I switch to on approach. Of course these things take several flights to get ironed out but really make flying much more enjoyable.

sensei

+1

Bob

acerc

I come in on approach at about 3° nose up and use the throttle to control rate of descent. There is no flaring in the process. Unless the nose up is considered flaring.

thailazer

That is close to my process. On downwind I will crank in 4 clicks of up trim on my DX6 after I reduce throttle and let it settle into a stabilized long final. I'll slow it up more for a noticeable nose-up attitude with another click our two of up trim, and try to fly that attitude all the way to the runway using power to compensate. At the runway I reduce throttle and increase back pressure until it settles to the runway, desirably in a full stall. Done well, the nose gear doesn't kiss until several feet after the mains. CG is really critical for being able to fly a plane properly on approach, as is a lot of practice.

HighPlains

My Feedback: (1)

So many ways to burn off excess energy. If I've been flying a lot and have the right airplane, I do rolls on final to kill excess airspeed and altitude. Or do a forward slip or a side slip, which can end up looking a lot like knife edge flight losing altitude down to the threshold of the runway. Easier methods would be "S" turns which any trainer can do, or flying on the back-side of the curve to enter a high drag condition which is useful when dead stick and the airplane is not very agile (like a pylon racer). Just so many methods.

As to the old saw that a tail heavy airplane only flies once. Just not true, it can be done. It's just that most pilots have never flown a airplane that responds in complete divergence to pitch. By divergence I mean that if it starts pitching up, then the rate of pitch change starts increasing very quickly, and if it starts pitching down, the rate of that happening also increases rapidly. So you have to pulse the elevator constantly both up and down just to fly level. You will not have a trim setting with the elevator that allows the airplane to fly level. It has a high pucker factor for the pilot however, so returning to the ground quickly is the best option.

Lifer

My Feedback: (1)

ahicks,

You and I set up our planes the same way. I gave up trying to get people to try their airplanes in a non-nose heavy balance point. Fast landings are as much a result of balance as anything else. There are issues of center of gravity and center of pressure involved and for those who don't understand, or are unwilling to learn, let them continue slamming into the ground at a high rate of speed holding full up elevator, hoping it doesn't snap-roll before the wheels reach dirt.
In my youth, I flew free-flight airplanes that had large, lifting stabs that moved the center of pressure WAY back, and they balanced at 65% of the m.a.c. Those planes flew great and landed real slow. Nose heavy planes came in fast and suffered damage as a result. The C/G isn't some critical precipice that causes a plane to suddenly become uncontrollable if breached. Rather, it is an area where pitch gradually becomes more sensitive as it is neared. Simply reduce the pitch authority to tame the beast. I have a lot of planes that use less than 1/4 inch of elevator travel and they fly like a dream. Many are more than a decade old.

Nose-heavy planes do serve one purpose, they keep the local hobby shop in business.

Let those who like to flame others begin, but attend a free-flight contest first so you can learn something others already know!

CafeenMan

I tend to fly pretty close to a stall and then use throttle for altitude management. Sometimes I just like to grease it in fast and that's what I do, but that's for fun, not my usual method.

da Rock

And that saying suits a lot of flyers who will never do anything but bore holes in the sky. Unfortunately it is interpreted by way too many as, "any CG that isn't nose heavy is deadly."

It is simply way too shortsighted advice.

Lifer

My Feedback: (1)

Amen, Brother!

speedracerntrixie

My Feedback: (29)

About 2 years ago I built a tribute airplane in honer of my mother in law. She had just gone through cancer treatment and we had a cancer awareness race. The airplane was a vintage kit of a Cassut racer. The airfoil was really thick and had an ice cream cone shape much like a full scale Extra or Edge. I followed the 25% rule thinking I would be pretty close and then make a battery location change if needed. Right after lift off she snapped to inverted. I eased forward on the stick and managed to gain some altitude and rolled upright. The next 5 mins were a real battle. I managed to get it down safely in the tall grass. The CG that ended up working was right on the LE. Something to do with that airfoil and large cheek cowls that I did not think about.