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My Cub flies way too fast!

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My Cub flies way too fast!

Old 04-02-2010, 03:03 PM
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bibby19
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Default My Cub flies way too fast!

Hey guys and gals,

I need some technical advice. I just took the first flight with my .40 Great planes Cub. The specs call for a four stroke range of .48-.80, i went with a magnum .72 four stroke. If you are'nt familiar with this kit it's very light with a large wing area. Once i got the plane in the air I found that cruising speed was only about 1/4 throttle. I ran into problems on the landing. I had 4 attempts at the runway, i had the abort the first three because the plane was coming in way too hot even at idle at about a 40 degree angle. My last attempt i had no choice but to set it down due to the fuel situation. I made a wide loop, starting my approach about 200 yds out from the runway on idle. Still came in too hot, i ended up bouncing off the grass and flipped it onto its back. Anyone have any advice on slowing this thing down other than buying a smaller engine? Thanks!

Old 04-02-2010, 03:13 PM
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jaka
 
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Default RE: My Cub flies way too fast!

Hi!
There are two ways!
Put on a larger prop with less pitch! Like a 13x4 or 14x4. Second lighten the plane. Light planes fly slower!

But...first I must say that there is no problem using whatever engine on that CUB and still landing it in as low way!
Have you checked the idle rpm? It should be around 2000rpm. The thing is to slow the plane down, and this you do with using a larger diameter prop with not too much pitch (4").

Old 04-02-2010, 04:11 PM
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Default RE: My Cub flies way too fast!

Changing your prop is one way to slow the plane down, but also double-check your CG/balance point - a nose heavy plane will land hot.
Old 04-02-2010, 08:42 PM
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Default RE: My Cub flies way too fast!

Turn sharper, that will use up more energy. A guy at the field told me that once. It works, just don't use it with a dead stick.-BW
Old 04-02-2010, 10:30 PM
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Default RE: My Cub flies way too fast!

40 degree angle.

what does that mean, are you pointing the plane down on for the landing?

stick 40
Old 04-03-2010, 03:12 AM
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Bonified Wingnut
 
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Default RE: My Cub flies way too fast!

Due to the shape of our field I have to make a turn before landing. I never have flown a Cub but the planes that I have that 'float', such as the trainer or my Uproar 60, I usually cut the throttle about half a turn from the runway. I then do a couple of circles as I come down to keep from gaining too much speed. On the final approach I can turn sharper or wider to control how much speed I need. I don't know the shape of your field and I aint no pro but it works for me.

Here is a picture of what I mean.-BW
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Old 04-03-2010, 01:18 PM
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Lnewqban
 
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Default RE: My Cub flies way too fast!


ORIGINAL: gaRCfield

Changing your prop is one way to slow the plane down, but also double-check your CG/balance point - a nose heavy plane will land hot.
I agree with Joe; specially because you stated "Once i got the plane in the air I found that cruising speed was only about 1/4 throttle."

To me, that means that your elevator is trimmed to be up for level flight.
Normally, that is a sure indicator of CG located too forward.

In that elevator condition, the model will balloon for high throttle positions.

I believe that 40 degrees is not normal descending rate and that it is not gliding.
Your elevator must have enough authority as to be able to tip the nose up close to 10 degrees, to the verge of wing stall, where the velocity of the model and sinking rate will be minimum.
Simply, your model cannot flare.

In order to eliminate the propeller-engine-rpm factors, just try a controlled dead stick landing and note the behavior of the model.

Check these good articles about trimming:

http://www.masportaviator.com/ah.asp?CatID=8&ID=141

http://www.masportaviator.com/ah.asp?CatID=8&ID=142

http://www.masportaviator.com/ah.asp?CatID=8&ID=144

And this one about landing techniques:

http://www.masportaviator.com/ah.asp?CatID=8&ID=20
Old 04-03-2010, 01:36 PM
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ES CONTROL
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Default RE: My Cub flies way too fast!

I went thro this with my Goldberg Cub with O S LA65 engine .
I ended up with battery in tail ,14x4 or 13x5 Prop, and lots of elevator . and that fixed It. But I still wish for flaps, just to experiment.
.
Old 04-03-2010, 04:22 PM
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Gray Beard
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Default RE: My Cub flies way too fast!

I built the same plane and installed the OS .70FS and you are correct, it is big gangs of too much power!! I thought it was just about right!! I tend to run long props with low pitch on most everything I own and my Cub slowed down very well for landings so you may want to double check your CG and try some different props.
Old 04-03-2010, 08:48 PM
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Default RE: My Cub flies way too fast!

at idle at about a 40 degree angle.


ORIGINAL: Stick 40

40 degree angle.

what does that mean, are you pointing the plane down on for the landing?

stick 40
no one can answer your question, untill we know what 40 degree
means.

sticks
Old 04-03-2010, 09:18 PM
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MinnFlyer
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Default RE: My Cub flies way too fast!


ORIGINAL: gaRCfield

double-check your CG/balance point - a nose heavy plane will land hot.
Ditto!!!!
Old 04-04-2010, 11:35 AM
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AA5BY
 
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Default RE: My Cub flies way too fast!

My single addition to the good advice given so far, is to be cautious about thinking the problem can be solved by a single item. It could be a combination CG too forward a CG, idle too high, and too much prop pitch.

One other variable not yet spoken to is headwind. A full wing Cub setup right on a still day will want to float forever. They are a blast to fly and do touch and goes in such conditions but the glide slope has to be really gentle and that is a problem for some fields. Remember... landing glide slope angle increases with headwind so without any headwind the glide slope of necessity should be quite shallow for the full wing Cub.

The solution for that assuming the other things mentioned are correct is to create drag in one or two ways. One is to set the wing up for flapperons but be careful to test them for how much roll control is lost and whether they induce any tip stall tendency. I find flapperons slightly effective on a Cub as you describe so don't expect them to do wonders and don't ignore the risk that they bring. The other is to slip, cross ailerons and rudder to create drag... IMHO this it the best method but it takes practice. Of course, once proficient, you would have the true feel of a Cub.
Old 04-04-2010, 02:36 PM
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David Bathe
 
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Default RE: My Cub flies way too fast!

I have a clipped GP .40 Cub. It was well over powered with an OS .46FX... still way over powered with a .46LA! Best prop I found was some rotten old 13(14?) something x 4 I had laying in the bottom of my flight box. Point is, a Cub just isn't pleasant to fly with lots of engine. Everyone thinks it will be, (just look at the threads here when folks are asking for advice, people are recommending FAR to much engine) but in practice... it plain isn't.
What you should do is try moving the CG back some, getting a bigger fine pitch prop, flying at about 1/3-1/2 throttle and last but certainly not leased, learning to side slip her in for landings.
The latter will give you endless hours pleasure learning and once mastered in both directions, seriously add to yor flying prowess. It's a wicked way to land, dropping in from a high and spotting it.
You've got to learn it one day... procrastinate if you may... but a cub is ALWAYS the reason. Try landing one in high wind without slipping it down. You'll be there all day.
Old 04-05-2010, 03:50 PM
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KitBuilder
 
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Default RE: My Cub flies way too fast!

What about the clipped wing version of the GP 40 size cub with approx 6o" span? I have a 52 and 70 4 stroke magnum, I do want it to be aerobatic.
MIke
Old 04-06-2010, 06:09 AM
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David Bathe
 
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Default RE: My Cub flies way too fast!

Mine's a clipped 40 and's over with a .46FX. Sure, I like power but it just don't work well on a Cub.You're aerobatics will have to change to suite the aircraft... and that aint a bad thing. There's nothing more impressive than a cub putting on a slow speed acro show. If you see one in really life, it's kinda scary just how slow the fly aerobatics!Pulling it off with a model is a great challenge, requires some serious stick work, cross coupling and's a real showcase for you skills.Tell you what, strap in the big engine, fly some... get board (because it doesn't fly good unless it's on the wing) and bolt on the smaller version later.It's a laugh either way.
Old 04-06-2010, 07:02 AM
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AA5BY
 
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Default RE: My Cub flies way too fast!

David... I've an Ultra Stick Lite setup with quad flaps/ailerons (crow mode) and it is a hoot to change the whole nature of its flight envelope by hitting the flap switch. It will put around the sky at a crawl without worry of tip stall and land at walking speed. In the closet is a future build of a Balsa USA 1/4 Cub. I don't recall if it is set up for flaps but I'd probably build them into the plane and maybe set the wing up for the quad configuration (crow mode) somewhat similar to Ultra Stick Lite. I wonder if anyone has set a Cub up thus and just how slow they will fly.

Old 04-06-2010, 07:15 AM
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Red B.
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Default RE: My Cub flies way too fast!

The statement ""Once i got the plane in the air I found that cruising speed was only about 1/4 throttle." is an indication that there is a lot of excess power from the engine, not that the balance point is located incorrectly. That conclusion can only be drawn if one knows how the aircraft behaves at other trottle settings as well.

I agree that a large diameter, low pitch prop will help obtaining a low speed, but a controlled side slip is a much more effective solution to the problem. A side slip increases the drag of the aircraft significantly and is usually done by applying opposite aileron and rudder. It is entered by lowering a wing with ailerons, adding enough opposite rudder so the airplane does not turn.

Here is a very good YouTube example of side slipping with a Cub (this is a rather extreme side slip, but it is a good illustration of what it should look like):

[link=http://www.youtube.com/watch?v=wW8GRJI6Kz4]Mikael Carlsson Cub[/link]
Old 04-06-2010, 01:39 PM
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Default RE: My Cub flies way too fast!

That's the way to do it. It's the only way mind 'ld come down... every time.
AA%BY, crow flying a stick is a blast, a unique experience. But try flying the cub as is... that to is an unique experience.
Regarding how slow it'll fly... that's the least of your worries. My little clipped  will almost stand still during landing if there's a decent breeze... just won't come down, just craws along at head height, slow walk speed! Rather disconcerting if you're running out of fuel and need to land. One or two of those occasions and you'll learn that slip real fast.
BTW: Friend of mine has a 1/4 scaler powered by a G23 gasser, not electric ignition, standard stuff. Match made in haven.
Old 04-06-2010, 04:38 PM
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Default RE: My Cub flies way too fast!

Good video clip

http://www.youtube.com/watch?v=sfeML...eature=related
Old 04-06-2010, 08:11 PM
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Default RE: My Cub flies way too fast!

plane was coming in way too hot even at idle at about a 40 degree angle


I will ask again, is this 40 degrees nose up or down?????

sticks
Old 04-06-2010, 09:54 PM
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bibby19
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Default RE: My Cub flies way too fast!

What i meant by the 40 degree angle was the path the airplane was taking to the runway in relation to the ground, not the orientation of the plane in the air.  The plane was level coming in. 
Old 04-06-2010, 11:31 PM
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AA5BY
 
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Default RE: My Cub flies way too fast!

40 deg glide slope as others have pointed out indicates too nose heavy. Dynamically what is happening is that the elevator has been trimmed up to offset the too far forward COG. That means the elevator is constantly leveraging the plane into balanced flight but as the plane slows during landing that leverage is lost and instead of the plane having a reasonable glide slope, the nose falls and as you indicate, the plane sinks at 40 deg having no elevator authority to maintain a reasonable glide slope. The steep glide slope is generating speed rather than bleeding it off.

If unsure of the COG of a plane, experienced pilots choose a flight test procedure to indicate whether the plane is flying in balance. This has been described by others many times much better than I can but here is the rough outline that you can flesh out fully by searching or asking specific questions about it. If you trim your plane for straight and level at half throttle and with plenty of altitude put the nose down and induce a 45 deg down slope with no throttle changes and then remove your hand from the stick and observe what happens one of three conditions will result. The plane will curl up lessening the glide slope, maintain it or curl down making the glide slope steeper. If it curls up and lessens the glide slope... then it is nose heavy because the elevator trim that has been set to adjust for balanced flight will manifest too much up trim in the glide because there is far less balance trim requirement in such a steep down slope.

If on the other hand, the plane curls down then the plane is tail heavy because the down trim in the elevator needed to maintain level flight is not needed during the down slope so it manifest the curl down. Ideally what is wanted is for the glide slope to neither curl up or down. Do this test and share the results.
Old 04-07-2010, 07:56 AM
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Default RE: My Cub flies way too fast!

I don't think that "test" works very well for a plane with a flat-bottom airfoil, like a Cub: with that kind of wing, it will always tell you that you're nose heavy, even if you aren't. It may be better just to go by the feel of the plane. If it's sluggish and very slow to respond to elevator input, move the CG back (just a little at a time) and try that. If it starts to seem twitchy, and needs constant elevator input to fly level, it's probably tail-heavy.

It may be worth noting that many model Cubs are floaters, even when set up just right. It's never going to be as easy to land on a short runway as a lot of other planes. Good plane to learn how to slip with, though.
Old 04-07-2010, 02:11 PM
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jester_s1
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Default RE: My Cub flies way too fast!

Reflexing your ailerons up a little will take some of the float out of the plane. It's best done with a mix on your radio so you can turn it on and off.
Old 04-07-2010, 02:32 PM
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Default RE: My Cub flies way too fast!

These posts are spot on and more than likely you have a fast idle, fwd center of gravity and, possibly, an overweight airplane. Try moving your battery pack to change c of g rearward. Put a wooden prop in lieu of 'plastic' one and alter the pitch a little flatter. Replace the rubber wheels with the foam ones. Have engine idle to spec. I had a Goldberg Cub that had so many hours on it that the engine's bearings wore down to 'chicklets'! That Supre Tigre 60 is still running albeit with new bearings! That Cub could be flown in for a landing in a powered stall attitude (mushing in) where the tailwheel would contact first and rollout would be about 3-8 feet! It was fun to slip and skid for a short field landing. You could 'land' on one wheel, roll down the runway then do same with other wheel. It did mild aerobatics and a hammerhead was especially nice with it! Good luck!

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