ahicks

My Feedback: (2)

Jim,
On the bold, this is where we have differing opinions. I don't view adjusting the CG as extreme at all. No more than adjusting my flight trims or engine mixture/idle speed for that matter. It's where you start? There's no complicated to it. OK, not something you likely want to explore in the days/weeks following your first solo, but pretty basic stuff for guys that have been flying sport/aerobatic/3D for any length of time?

If you like, forget about the landing long argument for a second. Open your mind up to the potential for the suggested CG to be wrong. Just check your CG using ANY of the well known methods for checking that specifically while in flight, then adjust it accordingly. I think you'll find the landing long issue will no longer be apparent when your done... and I'll guarantee you a much nicer flying plane for your trouble to boot! -Al

Charlie P.

I've been doing some head scratching myself as to why the C.G. would effect airspeed.  I came up with further back means you need less control input to effect attitude changes and so reduced drag from deflected surfaces . . . but that is only true up to a point.  Too far back and the problem surfaces again as you fight for stability.  And dirt offers much more resistance than air so there is a n abrupt point of diminishing returns.

I have mine about 3/4" behind the manual's recommended and I am very happy with the performance.  It's not a fast model, and it's not a 3D bird, but it is a splended sport model.

Note that unless your tank is on the c.g. yours will be moving throughout the flight, anyway.

azalner

My Feedback: (8)

Mine came in at 13.5 lbs. Tank is just forward of the CG. Using a single 2300mAh LIFE battery for radio and ignition (IBEC). Carbon fiber landing gear secured to the fuselage with 1" aluminum angle. MY CG is roughly 1/2" behind factory recommendation because that is just how it turned out. Flies fine, no need to tinker with it.

DLE-30 with 19 x 8 XOAR prop. Idle set at 1650 RPM. I fly it right down to the deck and chop the throttle when I get into ground efffect. Beautiful landings every time. Three weeks ago I was challenged by the local peanut gallery to see how many touch & gos I could do. I quit after 25.

Al

ahicks

My Feedback: (2)

Love to practice landings. Boring for anyone watching, but every one of them are different. Did the same thing flying full scale. Try tail wheel first landings when you think you're getting good at them. See how many of those you can do in a row...

PacificNWSkyPilot

My Feedback: (19)

Charlie P,

In a nutshell, it's drag. Pretend you have your plane on a CG machine, and you add enough tail-weight to move the CG back. What happens? The tail drops. The air is a great big CG machine, and when a plane is flying, that balance determines the way the plane flies. Move the CG back, and the tail drops, and the wing (and the plane) is no longer flying straight into the wind. The bottom of the wing is being presented, incorporating it into the angle of attack. Incorporating drag.

For guys like me who have been flying for 35 years, that's not a big deal, and almost a no-brainer to control it and factor in the changes presented. We sense the air speed, we can 'feel' the plane's condition through our sticks. We keep the speed up enough to compensate for it. But that takes a while to learn.

Here's what else moving the CG back does, starting with what it doesn't do. It doesn't increase the lift. It changes the angle of attack, but it doesn't change the shape of the wing to something that creates more lift. It slows the plane down, all right, but it doesn't provide any compensating factors. Since the wing isn't flying straight into the wind, its ability to continue to fly at slower speeds is compromised, making it more prone to tip stalling and other less-than-desirable traits.

It does make the plane more responsive, but at a price, and the price comes when on approach. The plane may slow down, but its stability is compromised. That's basic aeronautics. So what do you do to compensate? You keep the speed up. Not a very effective method of slowing down.

I have guys who had planes that simply wouldn't slow down. I taught them how to crab on approach, and a variety of other tricks. But that was just to get the plane below rocket-speed so it could touch down. Replacing landing gear was a frequent occurrence.

I loved your statement: "And dirt offers much more resistance than air so there is an abrupt point of diminishing returns."

Succinct. Accurate. Amusing! I got a laugh from it.

Mine is moved back some too, for various reasons, but I'm planning on moving it forward some. I don't like the tail flying lower on approach. My gas tank is balanced on the CG, so it's consistent.

I'd have to go back through posts, but I think mine weighed in at 14.5 pounds, with a Syssa. No lead. Adding a little to the nose shouldn't hurt it, as it'll float all day.

For a sport plane, the GSS has it all. It's gorgeous, and it flies like a dream.

~ Jim ~[8D]

PacificNWSkyPilot

My Feedback: (19)

AHicks,
I'm no stranger to suggested CGs being wrong, and that's not what I was arguing here. The CG being wrong was never mentioned. The planes in question were flying straight and true, which was why they didn't want to slow down in the first place.

~ Jim ~[8D]

PacificNWSkyPilot

My Feedback: (19)

I didn't find what the weight was yet, but I DID find an old classic. These are my friends. I love it!

~ Jim ~[8D]

Joystick TX

I also love to do touch and goes. Lots of tail wheel first landings as well. I average about 20-30 per flight. If the field is crowded I don't do many, but there are only two or three of us that fly the "dawn patrol" at our field. Probably did over a hundred landings today alone.

PacificNWSkyPilot

My Feedback: (19)

Joystick,

You could do landing-gear testing for gear manufacturers!

Looks like my GSS weight was right at 14 pounds.


~ Jim ~[8D]

ahicks

My Feedback: (2)

Not arguing wrong here either. There's nothing "wrong" with a manf. suggesting a very conservative CG for test flights. As mentioned, that's pretty typical of the GP kits.

I'm only predicting what you'll find if your mind is open enough to actually check your CG using any one of the many in flight tests designed to do that - as well as the results you'll find if you take the time and trouble to act on your findings. That's it...

If you aren't willing/can't do that for some reason, there's no point in continuing the discussion? You don't sound like you are going to change your mind until somebody demonstrates this to you, and if you aren't willing to actually try this, I'm not driving to Texas to make my point?

Straight and true? That was determined how? By having enough up trim available to keep it flying level?

If the plane is balanced correctly the wing loading is so low it will fly safely at little better than a walking speed - allowing it to settle in in just a few feet. Set this way, the horizontal stab is actually carrying some of the plane's weight at lower speeds.

They land long when they need a ton of air going over the (up) elevator to keep the nose out of the dirt. When nose heavy, the elevator is actually pushing down on the rear of the plane (vs. supporting some of the plane's weight) trying to keep the wing at a positive enough angle to provide enough lift to keep the plane in the air.
-Al

Mpizpilot

My Feedback: (45)

Couldn't agree more. It's simple. Forward cg = higher stall speed, = having to come in faster. I'd rather land at 10mph instead of 20mph. Check the cg, it should be near 30% of the MAC. If not, theres the problem.

On a lighter note, mine has been ordered. Can't wait. Going with DLE 30, HD -1501's for servos.

harttvboy04

My Feedback: (32)

Hey -

I have a 1/4 cub with the 1501's. Work great after 200+ flights - enjoy!

Best,

Chris

Mpizpilot

My Feedback: (45)

I was using the 6001's, but started losing some on a couple different planes, switched over to the 1501's and couldn't be happier. They seem to have more speed and torque plus they center a hell of alot better. Glad to hear they also have some longevity.

PacificNWSkyPilot

My Feedback: (19)

Full scale planes use flaps for landing. Engineers design them that way. The laws of aerodynamics don't change just because it's a model.

There are few full scale planes that don't use them.

But suddenly loading down the tail is a good idea.

I'm an engineer, and my son was a loadmaster in the Air Force. Let's forget me, and just go with his job description, which is to make sure that the CG is kept far enough forward that the planes won't lose the ability to fly due to the CG being too far back.

The only reason I'm not questioning somebody's I.Q. here is because I'm not allowed to. Suffice it to say that anybody who thinks moving the CG back as a first solution to slowing a plane down needs to have theirs checked. Conversely, using a conservative approach to the problem isn't being stubborn, it's being cautious, which I might remind you is something the AMA expects of us, especially now. I think they'd expect it of us in here as well.

Straight and true was determined by the other pilots who asked for help, and I'm going to give them the benefit of the doubt that they knew what they were looking at. Especially considering that if their plane WAS as nose-heavy as you are saying (because it's clear you know what they saw and they didn't), all they'd have to do is let off the elevator to get it onto the ground.

If they said it was flying straight and true, then I believe them. It makes sense.

You're trying to support your argument by talking about trying to keep the nose out of the dirt. So, your statements are that if the tail isn't dragging in flight enough to drag it while landing, that the nose is so heavy that it requires massive up-elevator to keep it out of the dirt? There's nothing in between? WHO is being stubborn? I'm adhering to long-standing aeronautics and aerodynamics, and your arguments are becoming so wild that they hardly make any sense.

You know, ahicks, I've always liked you, but if you were at the field right now and you were there arguing like this, I'd pack up my planes and leave.

I just caught myself sharpening my teeth. Before I say something a bit too accurate that gets me kicked out of here, it's time I pack up and leave.

You new guys. Use flaps, or flaperons. They're designed to slow the plane down using drag AND increased lift. They're designed to slow your plane down and help you land better, no matter what size your plane is, from the smallest model to the biggest Jumbo-jet.

Moving the CG back is for something else. It has its uses. This ain't one of them.


~ Jim ~[8D]

azalner

My Feedback: (8)

Guys

It's time to knock it off. One of the nice things about this thread is that it is subscribed to by a lot of nice folks who get along and enjoy this particular airframe. With that having been said this aircraft is an intermediate sport aircraft. So let's cut to the chase and determine where the CG should be. You can determine the correct CG by simply flying your aircraft.

Start by trimming your aircraft so that it is flying staight and level hands off. Got it? Good.

Now roll inverted. What happened?

If you needed a lot of down elevator to hold level flight you need to add tail weight (or move components back).

If you need a lot of up elevator to hold level flight you need to add nose weight (or move components forward).

I personally don't like slowing the plane to a crawl for landing, it spoils you for other aircraft. My other plane is a 9.5 lb. MXS_R with a DLE-30. It flies 3D quite nicely with the plane balanced using the above procedure.

If you must slow it down use flaperons or learn to use your rudder and crab it in.

Now go outside and play.

Al Z

ahicks

My Feedback: (2)

Al Z, guys -
I'm good with that. Sorry guys. It seems as though I've managed to push the point too far. Consider it dropped.

Mpizpilot- this thing has a really skinny cowl. You might want to consider one of the new rear exhaust engines, or possibly the new DLE 35 w/rear exhaust? Understand they're just starting to ship. That's how mine ended up with a Syssa 30. I think it was the only one available when I was putting mine together. FWIW

-Al

Muttdog

Al I could not agree more. I hate it when forums turn into bickering cat fights and it appears that is where we are heading here. Let's agree to disagree and move on. I subscribed to this forum because of the lack of infightingthat plagues so many forum threadsand over the last 24 hours it seems all for not. I am a firm believer that there is always more then one way to get something done and what works for one, may not work for the other. I have received valuable information from everyone on this thread but that does not mean I will follow it to the letter. Make your own informed decisions and tell everyone what you are doing but don't force your methods on everyone else (no matter if they are right or wrong). just my .02 - MD

Mpizpilot

My Feedback: (45)

Interesting you mention that, I wAs just looking at the new dle 35. UnfortunTley they want another 50 bucks or so. I guess I'll just deal with a bit more of a hacked up cowl for the regular dle 30.

azalner

My Feedback: (8)

You could get an after-market Pitts muffler for your DLE like i did, but it will cost you another $75- $90 depending on where you buy it. When you look at it that way the new DLE-35 is not such a bad deal. Its a shame to mess up the lovely lines of this airframe by chopping up the cowl. But, you gotta do what you gotta do.

You might consider buying a spare cowl if you later decide to get a Pitts muffler.

Al Z

Muttdog

To add to what Al said, if you go with the pitts muffler, DONOTget the Bisson muffler, it will be too wide to fit. Use the J-tec, it fits perfectly. I already learned that the hard way. If you read complaints about the J-tec crushing when you tighten it down, do not worry as those are the old models, the newer ones use tubes welded into the muffler to support the bolts.

ahicks

My Feedback: (2)

Jtec has what they call a "compact" or "P51" style Pitts too. Uses a can section that's not quite as wide. Problem is, with the price of something like this added to the price of the engine, as already mentioned, you could have that DLE35 and have change left over?

Muttdog

I would imagine that with a DLE 35 around the corner, the DLE 30 will have a reduced price. If not I suspect there will be huge unsold inventories of them. You do not need the compact J-tec to fit the GSS, the standard one fits just fine with (minimal) room to spare

Joystick TX

You could go with the Syssa 30cc. It has the single bolt prop hub, comes with two bolts and two pins if you want to use them (I just use the two pins) to prevent the prop from slipping. It also comes with a Pitts-style muffler that fits the GSS perfectly. It is a great running engine, has plently of power,and is easy to hand start. The quality of the engine is second to none. I have over 500 hours of run time on mine and I'm still a happy camper.

Mpizpilot

My Feedback: (45)

I guess I'll give the dle 35 a shot. The dle's I have already have been great to me. Make good sense about muffled price vs new engine Price.

PacificNWSkyPilot

My Feedback: (19)

Had a terrific day at the flying field. My GSS flew flawlessly, and I put flight after flight on it. Over the past year, I've been plagued by gas system problems that ended up grounding the plane each time, further complicated by book deadlines that prevented me from getting back to the field to see how each adjustment worked. I had the engine (30CC Syssa) in another plane before moving it to the GSS, so I knew it ran perfectly. It's an amazing engine.

I didn't know how it was going to go this time, because not only was I flying her for the first time since the most recent gas system adjustment, it would also be the first time since I got the engine back from Syssa with the upgrades. Turns out, I needn't have worried. The engine started right up, and with a minimum of adjustment she was airborne, and running strong. I'd adjusted a few things on the plane as well and was hoping to see how they worked, and was delighted to find all of them had the desired effect. My on-board batteries are pretty good-sized, so I ran them down about when I'd run the Tx down. I thought about field-charging them all and going back for more, but my Mini-Me had broken loose and was rattling around the cockpit. I took that as a sign that it was time to pack up and go home.

The guys were walking out to the flight line to talk about the Syssa engine; how great it sounded, and the power it had. Then I showed them the throttle stick at just under half-throttle. That's all I needed to do everything I wanted to do.

Mpizpilot, I see you're looking around at engines. I highly recommend the Syssa engine. I've had nothing but good experiences with mine, except for one bad spark plug, which doesn't count. Also, it comes with its own pitts muffler and custom-length standoffs included in the price, and the whole deal fits WELL inside the GSS cowl. I know I've posted photos of my setup with it here in this thread at some point. I think this is the link to it:

http://www.rcuniverse.com/forum/m_42...anchor/tm.htm#

~ Jim ~[8D]