Hi

I am hunting for a very slow flying plane (like a cub) and was wondering how to tell the stall speed of a plane by the wing loading?

Does wing loading alone tell stall speed, or do you combine this with the model weight and/or wing area?

Many thanks for any info on this.

Peter

Peter yes the wing loading has a direct affect on the stall speed of the aircraft. Increase the wing load and and the stall speed will increase. There are other factors affecting stall of course chief among them is airfoil design. Weight of the aircraft is not the only way to increase wing loading either. A steep level turn will increase stall speed considerably. In the full scale world this is called an accellerated stall but applys to our models just as well, sudden gust or turbulence will also increase wing loading and stall.

Now what is basic static wing loading? It is just the total wing area usually in square feet divided into the total weight (usually in the case of model aircraft in ounces) to render the wing load. For example a typical trainer may frequently be around 18 to say 24 ounces per square foot. Many types of model aircraft may be much lower or higher than this howerver.

Wing loading figures are often given in catalogs and such and by taking note of these figures you often may get an idea of how an aircraft will fly, fast, slow and how well it will handle turbulance/wind Aircraft with heavy wing loadings will typically handle winds and turbulance better.

John

Divide the weight of the airplane, in ounces, into the square footage of the wing, (stab and elevator should also be considered to be more precise), as they are lifting surfaces at work when in flight, the area of the wing should be in square feet.
For example:
I'm not going to count the tail areas surface.
Wingspan: 72" (inches long) x 10" (inches wide)= 720 sq. inches
720" divided into 144 (one sq. foot, 12"x12"= 144") = 5 (sq. feet)

Weight: 10 lbs x 16 (there are 16 oz in a lb.) = 160 oz.

Wingloading: 160 oz divided by 5 = 32 oz per sq. foot

If you also take into consideration the stab and elevator, the wingloading will be less, of course.

Thanks John and Walter - this is just what I was after.

Any thoughts on a very low wing-loading scale plane? I fell in love with cubs and bipes at our recent warbirds and bibe fly-in, and was wondering what sort of ARF would be suitable.

Peter

You didn,t say peter what your skill level was since you posted in the beginners forum I would assume you are fairly new.

If you are just starting and many may disagree with me but most cub models are in fact poor trainers and it is not because of the conventional gear. While they are slow, they do suffer more than most from a thing called adverse yaw as a result from the high aspect ratio wing (long and narrow) coupled with big barn door ailerons. This is just the tendency for the airplane to yaw away from the direction you are turning simply because the downward moving aileron produces more drag than the side with the upward moving one. Its for this reason they can be problamatical as a primary trainer.

If you are just starting I would urge you to forget the 'scale' thing for now and use one of the many fine trainers out there. If you have already attained some flying skill then great just hang on here and suggestions will start flooding in.

John

Thanks John

Not a total beginner - I posted here because the question seemed pretty basic. I have flown electrics for a year, and a glow powered tranier for 6 months. I'm looking for a second plane that is nice looking and can fly slow and low (to appreciate the appearance) rather than fast and aerobatic.

I guess I would rate my flying skills as good given my time in the hobby (eg. can fly a circuit inverted, land with a reasonable cross-wind etc), but that said I am looking for a plane that is a relaxed flyer. How significant is the yaw characteristic you describe? Could I fix this by mixing aileron and rudder (I think my Hitec Flash 5X has this feature?)?

Thanks again for your help.

Peter

Good Peter by all means go for your cub You will do fine. I think you said you wanted an ARF and in that case the Hanger Nine eighty incher is among the best flying of the cubs. I have flown and tested a fair number of different cubs for folks and the Hanger nine is one of the best ground handling of the bunch. Delightfully easy to do wheel landings with, Not so with some cubs. I have one that I dug out of the trashcan 5 years ago that has served beautifully on wheels and floats as well as a night float flyer. One of the more enjoyable things to do at dry lake that I visit on occassion is to just fly around my self in a continous circle of say a hundred to a hundred and fifty feet then simply let it settle to a one wheel touch down and keep it rollin wing down on one wheel for a couple of circles then increase power a bit an lift off. Some times I have just done this for a whole flight 'just because'!

Back to the Adverse Yaw thing. Indeed AY affects virtually all aircraft big and little and it can be handled in a number of ways. First off we all should practice using aileron and rudder together most of the time as full scale pilots do but for them it is simpler because they can feel it in flight on the other hand it is not so apparent when we can only depend on our eyes at some distance. Many full scale aircraft do 'cheat' however by two differant mechanical means, Differential aileron and or aileron to rudder mix! Yes all you purist out there many full scale aircraft do in fact use some degree of aileron to rudder mix.

Peter you can visually see the effects of AY on any visit to a flying field. just watch any high wing cabin type or trainer (the type that are most affected) on climb out at the first turn, the airplane will turn ok but nose kinda pointing the wrong way and the airplane seemingly skiding sideways, That is Adverse Yaw. There are Three ways of correcting this if you want to impress the Peanut Gallery in the pits. They are: manually using appropriate rudder imput with aileron at all times, using differential ailerons and finally using electronic aileron to rudder mix. In the real world using a mix of all three methods is probably not a bad idea as most of us do tend to get lazy just like full scale pilots.

Aileron Differential is mearly not allowing the downward moving aileron to go as far as the upward moving one, therefore tending to minimise the additional drag from downward moving one. It can be acheived by the simple rigging trick of the angle your aileron servo output arms are set at neutral or it can be done electronically with a computer radio.

As for you last question your Hitec Flash 5X will electonically provide aileron differential or aileron to rudder mix.

I apologize for being long winded, now get busy and go enjoy that Cub.

John

John

This is great - many thanks for your thorough reply.

I had been circling the Great Planes J3 Cub after reading the review in Model Airplanes News. The fabric covering sounded appealing. Do you know how this one compares with the Hanger Nine?

Thanks again for your help.

Peter

I've got a friend with the H9 Cub. His experience hasn't been a positive one. Most of the problems are take-off related. His brother is a good pilot, but just hasn't gotten used to getting the Cub off the ground. You really do have to use the rudder and be gentle with the throttle, keeping it on the ground until the speed has built up. Once it's flying it's a nice enough plane, and the Saito .56 seems perfect for it. It's been through a number of crashes and repairs, and doesn't make it out to the field very often anymore. He just doesn't think it's worth it when he has other planes to fly. He'd had a GP ElectriCub prior to this, converted to glow with an OS .10FP on the nose. That was one nice flying plane, although slightly underpowered. Hand launches were necessary on our grass field. Very slow, and very relaxing.

Have a look at a Tiger Moth and see if that grabs your interest. I've not seen a model, but they are the classic bi-plane trainer and should have very low wing loading. I think Kyosho makes a glow ARF, and GWS makes an electric.

Thanks Mike

I was also considering the Great Planes Tiger Moth ARF. I wondered if I would get sick of the extra assembly time at the field (I'm assuming the additional wing plus fly-wires takes some putting together?). But I will go back and have another look at the TM.

Thanks again.

Peter

Peter first let me address the takeoff problem that Mike has brought up. Most Cubs as Mike mentioned do require vigilance on take off during the throttle up due to the dynamics of a taildragger, among them: 'P' factor, gyroscopic reaction at rotation and spiral propellor wash plus some more subtle ones. Now factor in the vary narrow track main gear with a high deck angle in the three point attitude and you have the makings of a tricky take off and this does apply to most Cubs that are somewhat close to scale even some of the little electrics.

Now does this prevent the average sport pilot from enjoying the airplane? Certainly not. First if you have a lazy left thumb you will need to become more proactive with that thumb and you can do this even with your tri gear trainer, just practice runing the trainer up and down the length of the runway just below liftoff speed and steer with that thumb (by the way if you fly mode 1 down under that would be your right thumb). Lets dig a little deeper Most folks first flying a cub use far to much rudder throw and really compound everything. Just use half the throw as you would a wide track taildragger. Some would say what about aerobatics, snap rolls, knife edge etc. well outside of the fact that all of that is very, very unprototypical for a long wing full scale J3 cub its simple just use dual rates on the rudder. I know your next thought your Flash five X does not have dual rate rudder and you would be right but it does have another bit of magic called expo and its avaliable on the rudder with that radio. Just crank up 40% minus expo on just the rudder and you will be tracking straight as an arrow in no time but can still do all those silly unprototypical things in the air.

I have flown all three sizes of the GP glow cubs but not the arf version which is somewhere between the forty and sixty size kits Most likely the design is very similar. The two bigger kits fly very similar to the hanger nine. Here are the diff's I can recall: the GP has slightly less adverse yaw, the GP is a little more difficult to do a wheel landing (three point is easy), the Hanger 9 is a little less stable in takeoff and the GP will stall just a tad slower.
The GP Peter would also be a fine choice. By the way the three sizes of GP float kits are great floats (pun intended) and I use them for that cub and some other types.


John

Many thanks John - this is very helpful.

Any thoughts on the Cub versus TM question?

Peter