does anybody knows why F3A models have a smaller wingspan than the length of the fuselage???

thanks

What is the F3A? I went to the AMA web site and could not find description?

Multiflyer

F3A is International r/c aerobatics.
I believe the span and fuselage are limited to 2 meters.
The wings look small therefore.
http://www.fai.org/aeromodelling/documents/sc4.asp

many of the F3A have shorter wings - far better roll characteristics than long wings .
In aerobatics the wings should have rapid response, start - stop .
Lift/drag efficiency is of little concern as wing loading is so low that AOA for all but minimum flight speed is very flat.
typical wing loadings are 20/23 ozs per sq ft. avg chord about 14" ---thereabouts .

F3A airplanes are designed for precision aerobatics. They really have "shorter" wings for roll, but the measurement of how short a wing is, shall be related to the shape of itself: the Aspect Ratio (AR) = Span^2/Wing Area

I would reformulate the question as: Why F3A planes have longer tails?

The stability of a plane is related to its "tail volume" V=(Lt x St)/(c x Wa) --> Lt=Tail Length; St=Tail Area (H or V); c = Wing Mean Aerodynamic Chord; Wa = Wing Area.
So, the same stability could be achieved with a "short tail length with large tail surfaces" or a "long tail with small surfaces areas", the second option is used for F3A.... but why?????

Daniel

The shape of F3A aircraft reflects the aerobatic schedule of the competition so as mentioned by Dick and others, the wings have to be good at precision rolling.

The long body with large side area helps in holding knife edge and therefore helps with rolling circles, rolling loops, point rolls etc. The canopy is put well forward to maximise fuselage side area.

The long tail moment arm reduces pitch sensitivity which helps the model to fly stably longitudinally and also seems to reduce the "snappiness" of the aircraft. They don't snap roll like IMAC aircraft - and they don't have to, to win points in an F3A comp. They don't spin like 3D, IMAC or fun fly aircraft either - and they are not designed to.

Over here in the UK the national F3A comp takes place in an extremely windy airbase and light wing loadings are definitely not an advantage. In fact there is a weight limit of 5kg for F3A too because higher weight helps with winning points too. This seems to be related to keeping the aircraft in "the box" even in heavy (cross) winds. A very respected pilot in our club did very well to come 3rd in the "Standard" F3A class last year with a Synergy 90 - which only weighed 6.5 pounds. He said the low weight and high winds put him at a disadvantage to other competitors with much heavier aircraft. This year he chose a much heavier model to compete in the "Senior" competition.

hope this helps

p.s. http://www.fai.org/aeromodelling/f3a/

hey daniel relally interesting what you said, but could you explain me a little better that formula again?
Aspect Ratio (AR) = Span^2/Wing Area


thanks also to all those who responded my question

Basically, the AR defines the shape of a given wing. Two wings (or any kind of surface) may have the same area and differ by their AR.

Here are some typical ranges for AR:
Jets (stunt planes): 3 - 5
Sport / pattern planes: 5 - 8
Sailplanes: 15 - 30

High AR values (greater span and shorter chord) are often chosen for slower airplanes, because these airplanes are more affected by a drag generated by the wing tip vortex (vortex-induced drag), this type of drag reduces as AR increases.
On the other hand, high AR models are slow in roll, and a low AR model may present a wider usable range of angles of attack and lower drag at high speeds.

Area = span x chord. Aspect ratio = span/chord. Simple algebra, substituting terms, gives aspect ratio = span x span/ area. Although I made a D in algebra the second time through, I managed it with only about 15 minutes of scribbling on the back of an envelope.

The heavier model is good only if power is high . recovery from maneuvers is always worse with higher loadings-given same power loading
We find that speed is of far more importance for windy flying
so if one has a set of smaller wing panel for wind -that can be an advantage
better than adding ballast as the model still has same power -just higher wing loading, less drag and goes faster .
We flew pattern/FAI, for many years and that is our take on "best" combo.
Airliners ride much more smoothly with increased weight but for aerobatics --- weight is thy enemy.

yes I agree Dick - that's why ys110's with hatori pipes running 30%+ nitro are used...

another feature of pattern aircraft is attention to reducing parasite drag. They also have small body cross sections and hidden pipes - This will help top speed.

understand that higher wing loadings are going to mean more likelihood of an unwanted stall though...

Today's powerplants develop enough power to drive a model to pretty high final speed if desired. But for F3A (BTW- the event is F3A not FAI; FAI is the governing body) flat out speed is not as desirable as smooth and precise presentation. A slower speed allows easier management of overall presentation parameters such as geometry, stage position, distance out from flight line.

We hide the exhaust systems and engine cylinders and such for clean appearance, then we stick landing gear down below and fatten up the fuselages to dirty it up aerodynamically. Choices, choices!!

MattK

Daniel, the formula calculates the Tail Volume Coefficient, not tail volume. TVC is dimensionless.

Pattern is flown in as precise a manner as is possible therefore the long tail moment allows for significantly greater stability in pitch and yaw than a shorter moment will. Stated another way, the long tail moment allows greater flexibility to make the tail feathers either large for super stability, or medium sized for just right combination between stability and acrobatics. With the end goal being Precision, the long tail will achieve the goal easier than the short tail moment will. And with correct tail area, it will have plenty of acrobatic ability. That's why we use it.

If you want a real flitty model, make the tail moment short and tail area small. Then you would make it do all kinds of gyrations by just breathing on the sticks.

regards
MattK

As a matter of interest - are points deducted for "poor appearance" of an F3A model. For example if the pipe was external, the fuselage un-rounded, no canopy etc. ?

No, it isn't a judging criterion. At flight distance and altitude, it matters practically none at all. BUT it's always a good idea to bring a nice looker to the flightline, and be as profficient as possible where it counts. That always scores points with me, figuratively speaking of course.

MattK

talking about the tail moment, generally speaking of course, how long is the tail moment in comparisson with the wing chord? 1- 1/2 times , 2 times, .....

thanks

The tail moment for reference purposes, is measured WAC to SAC. What I do is determine where the AC's are, and then tape measure. The tail moment to wing MAC ratio is closer to 3 on some modern pattern models. Most fall into the 2.5 area.

MattK

MKT thanks, but i still have a simple question

WAC : wing average chord ?

SAC : stabilizer average chord?

sorry, i dont understand some technic vocabulary

Close. Wing AC and Stab AC. AC, generally for our purposes, 33% of the Mean Aerodynamic Chord.

In general, for the types of wings we fly in pattern, MAC will often be around 13" to 14 1/2" from the root, for a typical wing panel span of around 33-34". Find that chord on the panel, and go in about 33% from the LE. That will be the vicinity of the panel's AC. For purposes of calculating tail volume or its coefficient, that's adequately close.

Good luck.

MattK

Thanks MTK! ... it's clear to me now

Torino....

That "AC" means Aerodynamic Center, the point where we can consider Lift force to be acting and the pitching moment coefficient constant regardless the angle of Attack.

thanks daniel!! now I understand!

really good and clear explanation MTK, but sorry, again, my english sometimes is not enough

I just had an idea , what would happen if I build a 46 size pattern airplane using 3d views from the picture of the oxai pinnacle? it seems a very clear picture ( from the side and from above ) to use the exact tail and nose moments, the wing surface, etc, but of course, in smaller size ( wingspan : 1400 mm )

would it fly ok?
what should i do to make it fly ok?
is it still a bad idea?

http://www.oxai-rc.com/en/showroom/pin1.htm