Experten109/40

My Feedback: (-1)

your the engineer. I'm joe shmuck.look it up in your notes.
cheers.

ram3500-RCU

My Feedback: (221)

I, for one, would like your explanation of scale weight. You have my attention.

Some people just have a sarcastic way of expressing themselves. Don't need to be offended by it. Ever spend any time on the east coast. It's just the way they converse.

Please continue.

FireBee

My Feedback: (34)

That is the Lift equation. [X(] also in that formula "Planform" is the wing layout of the aircraft: Straight wing (cub) tapered wing (FW-190), swept wing (F4 Phantom aka worlds greatest fighter) or delta wing (mirage or KFIR) as examples.

see this wikipedia link on "wing loading." it is very good / quick read. They also have an interesting comparison chart with the Spit and Me 109 listed.

http://en.wikipedia.org/wiki/Wing_loading#cite_note-0

it states" In aerodynamics, wing loading is the loaded weight of the aircraft divided by the area of the wing.[1] The faster an aircraft flies, the more lift is produced by each unit area of wing, so a smaller wing can carry the same weight in level flight, operating at a higher wing loading. Correspondingly, the landing and take-off speeds will be higher. The high wing loading also decreases maneuverability. The same constraints apply to birds and bats."

I do consider wing loading, somewhat, as I select what scale (1/8, 1/4 etc ) to build my next project, but not as much as engine size, retracts, flaps, cost, size of my field and mostly the "wow factor" of a particular plane.

I love warbirds and far more appreciate all the bells and whistles and this adds weight. I try to compenstae with how I lay out the servos and what gear to use relative to the CG. I read and watch at each warbird rally I go to. You can see what designers planes fly well and what ones are a handfull. I like proven deisigns like Yellow (many are Bert Baker), Ziroli, Meister and Vailly.

I consider reliability and ruggedness far more important these days as 400 plus hours in a project can be wiped out due to a simple low cost part like a single batt switch. I now add weight or as I prefer to call it "ballast" with dual batteries and a single servo with short coupling on each flying surface. I like the direct servo on the tailwheel idea and will try it soon.

My point is everything in airplane design is a trade-off. Knowing how wing loading affects the performance on all aspects such as take-off roll, flying, turning, loops and landing is just another part to this hobby. Keep the full scale info comming too!

I just try to learn how to fly and land each plane. That said, keep using right rudder well past take-off and always put a pilot in the cockpit... no matter what it weighs!!!

dvs1

This is well said for me as well, and a very excellent reason why I do not care how heavy my warbirds are. I am a busy person with work, kids, and wife like many others and it takes me a good year from start to finish of a scale warbird and I for one would gladly throw the extra weight of extra redundant systems, gear and a strong built up structure that I know will not fail under the g-loads the plane will fly at, just to insure that all my hard work, time and money do not end up in a large lump of scrap. It is just very comforting for me to know that the only way I will lose a plane would be to pilot error and the plane is good to go. Like I said previously in the thread for me the extra weight is not even really noticed on landing as it will still land slowly and gently enough, but the heavier weight means all the difference in the air makes for a much more stable scale like flight not effected by winds or pressure and doesnt bounce around like a 15 lb sport or 3d plane.


As for scale weight earlier mentioned, I am interested as well as what formula you can use to get a accurate scale weight. It is just more as a curiousity to see how close my planes are to being a scale weight of the actual plane they are modeled after.

ram3500-RCU

My Feedback: (221)

I checked my model P-47 vs the full scale and found the wing loading to be very similar if you take lbs vs oz. Don't know if this translates properly. I also discovered that the full scale, at a gross weight of 15,000lbs (still under the max gross), in 30 deg temp. and at 3000ft, no wind, and a sod/turf runway, would require 5200' to take off. The formula came to 4000' plus 400' for each 10deg cel. That would be a 1/5 scale 1040' foot long run!!!!! If I'm doing the math correctly. Even at an empty weight of 10,000, it would be 3000' plus the 10% for temp. = 3900' X 20% = 780' at 1/5 scale.

They had to pick their fields carefully, if they wanted to fly back out. They could land in around 2800' at a weight of 13,500, but as shown, they would not get back out, if that was all they had.

frets24

My Feedback: (15)

The P-47's probably had few problems runway wise in Lesina then. The improved "runway" was around 80' X 8,000' covered in PSP or Marsten matting with an additional 20' each side and 1,000' each end in hard pack light gravel with oil or tar mixed in. By mid '44 the taxiways and parking areas had also been pretty well groomed and improved as well. I believe there were B-17's, B-24's and for sure there were DC-3's that operated from the 325th's base along with the P-40's, P-47"s and P-51's.

Here's a few of the 47's for ya Ram, along with a colorized montage of the staging area before a mission. Nice surfaces amid the mud-these guys had it better than most.

MajorTomski

In my opinion from years of couciling it also appears that you have a self-esteme problem too.

[/quote]
I went back over his number and I think it stems from a decade old concept out of the large scale world that was also hinted at one of the other posts here having to do with length area and volume (which, in this case, also refers to the weight, because it can be thought of as a density, a cubic dimention) when scaled down have to be done linerly, by the square and by the cube of the scale factor.

In his 8,000# 1/7 scale P-40 example Experten took 7 cubed or 343 and divided into the original weight 8,000# and came up with 23.32.

When you do this you get what he presented; at that weight this "scale weight" theory you will end up with ball park performance figures for model airplanes.

As a demo lets look at something a little easier to get actual numbers for a Cessna 182
1:1 scale
Wingspan 36' or 432"
Wing area: 174 sqft 25,056 sqin
Gross Weight 3,110#
Stall speed 56 MPH.

Top flight kit
Wingspan 81"
Wing area: 906 sqin kit computed = 25056/28.41 (5.33 squared)=881.9 sqin makes sense that TF would fudge the area a bit
Scale 432/81= 1:5.33
Scale weight= 5.33 cubed 151.5 divided into original weight = 20.53 Pounds, which is twice the listed weight for the TF C-182, but it should be able to fly at that weight but I doubt very much that it will fly as slow as 10.5 (56/5.33) MPH at that speed.

Like I said it gives you ball park numbers to work with

MTC YMMV

Experten109/40

My Feedback: (-1)

" In his 8,000# 1/7 scale P-40 example Experten took 7 cubed or 343 and dividec into the original weight 8,000# and came up with 23.32.
When you do this you get what he presented; at that weight this "scale weight" theory you will end up with ball park performance figures for model airplanes. "

one may try to go with a scale 19" prop & somewhere around 4hp engine will get you a triple in that
ballpark I think.. not quite a homerun though

Johnnie Red

In 1:1 all the airplanes have a weight and ballance envelope. It differs from one type to the other. It has to do with how the pilot will store the lugage and fuel in the airplane prior to take off. All types of airplanes have a weight and ballance chart and is set from the manufacturer.

To cut a very long story short (otherwise we will have to move this subject to aerodynamics)
A simple fact suitable for airmodelling is to keep the centre of pressure behind the center of gravity. That means keep the airplane nose heavy. If the center of gravity comes behind the centre of pressure then the airplane is coming in abrupt conditions that will lead in PIO (pilot induced occilations), a situation that might lead in a crash.

dvs1

This is the final thing I will say about wing loading as I agree with it. I took it off a wing loading website.





How to Calculate the Wing Loading of a Flying Model Aircraft
The wing loading of an aircraft is the measure of weight carried by each given unit of area.

For model aircraft, wing loading is expressed as ounces per square foot (oz./ft2). Experience with different models will make this figure more meaningful to you.

Why Wing Loading is Important
Wing loading is the only indicator of how "heavy" an aircraft is. The actual weight of an aircraft is meaningless.

A 50 lb model having as many square feet of wing area is a lightweight. A 6 lb model having 2 square feet of wing is very heavy and will fly like a sledgehammer (or maybe not quite that well).

The lighter the wing loading, the slower the aircraft can take-off, fly and land. It will also have a better climb.

A larger model can have a higher wing loading and fly comparably to a smaller aircraft having a lower wing loading due to differences in the aerodynamics of different size aircraft.

For example, let's say we have two aircraft that are absolutely identical except for physical size. The smaller model has a 36" wing span while the larger aircraft has a 108" wing span.

The smaller model may have a wing loading of 8 oz./ft2 and the larger aircraft may have a wing loading of 35 oz./ft2. Both of these aircraft may perform nearly identically at substantially different wing loadings due to the difference in size. Note that these figures are off the top of my head and not meant to be taken literally.

It is a good idea to inform the person who is test flying your model as to the wing loading so they have an idea of how long of a take off run it will need to build air speed. This is something that comes with experience because there are no stall warning indicators in model aircraft as there are in full-scale aircraft.

How to Calculate Wing Loading
In this example, we will use an aircraft weighing 5-1/2 lbs (5 lbs 8 oz.) with 600 square inches of wing area. Calculating the wing loading requires that the wing area be converted to square feet (ft2) and pounds to ounces.

1) Convert the area to square feet. There are 144 (12 x 12) square inches in a square foot.

600 in2 ÷ 144 = 4.17 ft2

2) Convert the total empty weight (ready-to-fly with no fuel) to ounces. There are 16 ounces in a pound.

5.5 lbs x 16 = 88 oz.

3) Divide the weight by the area:

88 oz. ÷ 4.17 ft2 = 21.1 oz./ft2

Using round numbers, this gives the aircraft a wing-loading of 21 oz./ft2 or

You can perform the entire calculation in one shot using simple substitution:

(Weight x 2304) ÷ Wing Area

Where weight is in pounds and wing area is in square inches

Plugging the numbers from this example into the above formula gives us this:

( 5.5 x 2304 ) ÷ 600 = 21.1 oz./ft2

For multi-wing aircraft, divide the overall weight of the aircraft by the total wing area for all wings.

rctech2k7

My Feedback: (1)

Thanks, I found that equation already but since pressure is not constant and I don't have illustration how the pressure is varying I couldn't get a function for that required integration. My only option for now is to get the trim from elevator and used that data to get the CP given by existing CG. The reason I'm doing this because most F-18C including mine I believe are nose heavy based on manufacturer's data, the plane flies a lot of speed at 0 angle, if I want to slow like put the throttle to half then I have to set the trim. However I can say that the plane is very solid and stable even on windy. I believe I can reduce the speed if I get the perfect CG which is 25%MAC from leading edge of MAC.

Johnnie Red - Yeah, my worry is when I move my CG backward based on calculated value of CG if I don't have the right location of CP, I might affect the stability of my plane. That's why I also want to know the limit of acceptable CG to make sure if I really need to make an adjustment. Thanks again!

MajorTomski

rctech, please remember that you are working with a 1:1 scale plane that is dynamically unstable in the first place. With out resorting to a pitch gyro to fill in for the flight computer in the F-18 you won't be able to move the CG back to obtain scale like high alpha low airspeed flight as done in the one to one plane. There will be that aft limit that still gives adequate stability that you will just have to live with

Johnnie Red

Very correct said! Only if there were available gyros and fly by wire systems for modellers would be lets say safe to do that.

paladin

My Feedback: (9)

I was taught to fly war birds by someone who flew the real ones and flew models. He said the problem modelers have is due mostly to poor technique. They do not understand stalls, or how the plane acts while heading to a stall. Elevator does not fly at 35mph and stall at 36mph, it gradually looses effectiveness. The key is to recognize this.

It is not about heavy planes are more quirky than lighter planes. But we don’t have the type cert. For the heavier plane. I don’t use wing area, rather wing volume loading to decide what skills are needed to land the plane. The advantage to volume loading is it accounts for aircraft size.

So how is this done? Take your wing area and multiply it by the average wing thickness. I do this by measuring the root max thickness and the tip rib max thickness add them together and divide by 4. Multiply that with the wing area and you have the wing volume. There are 1728sqin/sqft.

Wt. / wing volume in sq.ft.

1 - 0 – 250 trainer / floater
2 - 251-400 light war bird / sport plane
3 - 401-600 war bird
4 - 601- up heavy

If you fly all planes like a type 4 you will have success. If you fly a 4 like a 1 you will rebuild it.

My 2 cents
Joe

crashproof

All this while interesting I suppose would be great to know if you are designing a plane but what you need to fly the plane that you did'nt design ( the ones I have ) is the skills to deal with what ever you got, and make it work. I set mine up slightly nose heavy at the front of the range and the rest becomes feel and technique over time. Kevin.

ram3500-RCU

My Feedback: (221)

Good post Joe.

As for full scale pilots and RC, although many can do both quite well, Matt Chapman comes to mind, most full scale pilots I know can not fly an RC plane if their life depended on it.

There are two main reasons for this.

(1).. 'feel' is much of flying, especially when taking off and landing. You can feel your aircraft through the seat, and stick. Not so in model aviation. You fly with sight, and sight alone. And it is much harder to judge speed and distance (or feel when the plane is creeping up to that stall) if your not sitting in the plane.

(2)... pilot perspective. Everything is in front of you in full scale, and up, down, port, and starboard don't change. They do in RC, and not many full scale pilots, or anyone else for that matter, can make that mental subconscious adjustment in the split seconds it takes to successfully fly RC. Why the average person watches what we do and may be entertained, but has little appreciation for just how difficult it really is. Praise (or condolences) from my peers is much appreciated by this pilot. They well know what it takes.

Beyond knowing 'how and why' airplanes fly, full scale experience does little for the guy wanting to be good at RC, IMO.

frets24

My Feedback: (15)

And in my experience, doubly so for helicopters!! Over 4000 hrs in full scale, 2200+ of that in helicopters, and I still can't get the hang of RC heli's to save my life. Too much of my brain wants the RC heli to behave exactly like the 1:1 and the RC just doesn't seem to be accomodating.

As far as having to judge our planes' performance soley by our perspective view; there really is a definite skill set that needs to be developed and a good deal of that relates to understanding the performance envelope othe plane, good co-ordinated flight skills and reading and understanding the "clues" given by the plane in each phase of flight.

We have one guy at our field who ALWAYS comes in for landing at the same perceived speed(relative to the ground) regardless of wind speed or direction. The result is many stalls, crazy landings and repairs when the wind is down, or lots of long landings and rolling off the end of the runway when the wind is up a bit and near straight down the runway. We won't even go into cross winds!![X(]
This guy just doesn't seem to get it; always says "a gust or breeze shift got it at the last second before landing" on the calm day crack-ups. Can't seem to grasp the concept of reduced control authority when close to a stall and that you just can't get that appearance of a nice slow paced approach and low, low speed touch down on a calm day the same as on a windy day.

Johnnie Red

Well I couldn't agree more with all the last posts; cause they are all right in their own perspectives.

I agree with you according to what you said about feel and pilot perspective.

But I completely disagree on the last phrase. You see a good 1:1 pilot knows how to fly the airplane and make the right desision in life or death situations. The same implies to the 1:4 scale or 1:7 scale model airplane pilot who is capable to fly his model airplane, no matter if it is more difficult than flying the 1:1 because of the lack of cockpit info. A good pilot is a good pilot. It doesn't matter if he is piloting a 1:1 plane or a model airplane.
The quality of a pilot is affected from his natural skills of feeling the airplane that he flies, and of course his knowledge of flying technique, aerodynamics etc. I am a 1:1 PPL pilot, also a modeller, and I have seen modellers that are lacking in technique when its windy even in taxiing their models downwind; one thing that leads always in groundlooping their models even before flying them just because they do not know how to operate their elevators, rudders and ailerons.... I've seen modellers getting in thermal waves while they were shouting "glitch" , "radio interference"...
I've seen modellers that try to fly 3D aerobatics and are missing completely a normal sideslipping landing pattern .....
With all the previous examples and a dozen more what I am trying to tell you is that because it is more difficult to fly model airplanes than 1:1 planes, one thing is certain. Feeling is one part that counts , but the most basic part that counts is aviation knowledge. All of us , the modellers must have our ears and eyes open to Aviation knowledge and this is the only way to get better.
Pride and only leads always in rebuilding r/c models.
Cheers to all
JR

ram3500-RCU

My Feedback: (221)

Good points. I fly full scale as well, (light private aircraft) and from personal experience, I still have problems with the simple slip maneuver in RC vs full scale, and this is after over 40 yrs of flying. I know how it works and why. I just can't emphasize enough, what what the 'physical' link to airplane does for you, vs the radio link. And that was the point I was making. It is one thing to know when and why to do a certain thing. It is another thing to actually execute the maneuver. And with RC, we have so little feedback from the airplane to evaluate, beyond what we can see, and some of see better than others.

paladin

My Feedback: (9)

but rc has its advantages also, in a spin in a trimmed model remove all fingers from the sticks tap the gimbals ring and go back to the sticks and its flying again. in full size the stick goes limp for lack of a better term. so push it away from you while keeping the ailerons centered then step on the last thing to disappear off the wind screen (forgive me its been 30+ years).

Joe

ram3500-RCU

My Feedback: (221)

Biggest advantage to RC IMO..............if you screw up, you don't die.