Huntster

I am building an Ultra Sport 46 (OS 46 FX) Without a pipe for now. I haven't built the Fillets yet but am wondering if they are worth the pain? Is it an astetic thing or do they actually serve a perpouse?

Rudeboy

Wing fillets will get you some extra speed on a fast plane... but I doubt you'll notice the difference on an ultra sport...

buzzingb

My Feedback: (2)

Flying, you need a larger engine. I have been flying an Ultra Sport as my primary plane for about a year with 3 different engines (OS 61FX, Saito91, Saito 80). All of these engines will balance on my Ultra Sport without lead being added. They do wake this wonderful airplane up and make it really haul also. There is no negative aspects that I have found with any of these larger engies. I am sure that a OS 46 will pull this plane but why settle for that when you can have so much more. The wing fillets won't be needed with a 46, that is for sure.

bob27s

My Feedback: (19)

The short answer is that Yes, wing fillets (in general) do afford a substantial aerodynamic improvement - for a few reasons (which I won't go into here).

For this aircraft, you probably will not notice the difference.

One nice thing about the fillets on the UltraSport is they provide a bit more wing saddle surface area, and some strength to that area of incorporated properly. Plus I think they kinda look nice

Huntster

Buzz ------ You put a .61 on an Ultra Sport 40? WOW that would really wake it up!!! The trick there would be to keeping it slowed down to a walk on the flight line area.

Bob --- Thanks for all the inputs! I think that I might leave them off this plane because they are a bit of work unless get more info on this. I would rather have a real nice flying bird and unless something like this would add more performance that is noticable I will leave it off.

Good gosh----- A .61? ON THIS SMALL PLANE????? Now that I'd like to see!!!!!!

buzzingb

My Feedback: (2)

Yes Flying, Indeed a 61 will fit with ease. The wing on this airplane is plenty large to handle it in flight without giving too much wing loading. It will idle low enought to putter out of the grass pits easily and accelerate wonderfully becoming airborn in a short distance. Landing is great also, it slows down and lands better than my trainer. The 61 is flown with a 12X8 prop and with the small airframe it handles it well and really unloads in air. I am planning on trying a 11X11 11X10 prop soon to see how it likes those. I would recomend beefing up firewall with triangle stock and epoxy just for security and adding one size larger blind nuts and screws(I think 8-32). However, I would like more power for this airplane but for the price the 61FX that I bought used here on RCU for $90 is ok. If you are buying new I would recomend a 90 size engine it the weight is about the same as 61FX.
If you use the larger engine also use as large as fuel tank as will fit. I think I used a 10 or 8 oz. and my flight time is a little short about (8minutes).

Huntster

That sounds like a posibility for later on. I was noticing that the wing is rather large but Since mine is a scrach-built I'll have to see what sort of charateristics the wing has before loading it up. If it is good I'll keep my eyes open for some motors.
That 8 minute flight might be all you need if this thing will really howel in the air!

Julian537

My Feedback: (9)

BoB27,

Can you go into more detail on why wing fillets are faster? I am building a small plane for speed, and i need every advantage.
Is it worth my time to put some wing fillets on it?

Julian

WMB

My Feedback: (1)

bob27, I would like an education on wing fillets as well. They do look good, that's for sure.

Mods-R-Me

My Feedback: (1)

Wing fillets reduce Interference Drag. Interference drag is caused by the disturbed airflow over an unblended/un-streamlined surface (i.e. dowels, open cockpits, landing gear legs, etc). The wing fillets allow the smooth airflow to travel over the area without becoming disturbed, thus reducing drag. Less drag = faster plane. This is also one of the main reasons why we use wheel pants and cowls. Plus they look cool .

Mods

bob27s

My Feedback: (19)

Thanks Mods.....

yep, he pretty much covered it.

Another way to consider part of the reason ..... 90deg angles are bad. The fillet allows you to avoid the 90 deg angle. (very simplistic here).

Also worth noting, that fillet design is somewhat of a science and art combined. There is a potential to do it incorrectly and create drag. I won't even try to go into the details behind this, but for the most part, if you look at the fillets found on older pattern planes, pylon F1/QM40, some jets, etc.... emulate those designs..... you will be ok.

rjbranchii

Talking of fillets, we are not talking here little 1/8 inch fillets. We are talking really big fillets. The bigger the better as far as aerodynamic drag reduction is concerned. Lest you think they are only for ultimate speed planes, look at 100% scale Ercoupe. The fillets are huge. The trailing edge fillet is about a 10 or 12 inch radius. Granted that one also controls airflow over the horizontal stab and prevents the plane from being able to be spun, but try to find a modern plane that will cruise at 114 mph with 85 hp. You won't. Aerodynamically it is a very highly developed plane and much of it due to the fillets. Want to go really fast? make anything attached to a flying surface just a fillet and add two really big motors. Its called an SR-71.

And folks thought big fillets were only for control line stunters.

Bob Branch

combatpigg

My Feedback: (3)

At what point does it matter? What point does it not matter might be of more interest? It makes sense that just a little microballoon fillet will not make any difference, especially on models that barely get up to the lift off speed of full scale planes. I think the difference that is made is relative to the size, power and speed of the plane in question. The P-51 has some good looking fillets to use as a reference. Study the shape of the extremely fast fish in the ocean and you can see that the designers of the really fast jets haven't invented anything new.

Ed_Moorman

My Feedback: (1)

John Northrop is credited with first using wing fillets that were developed at Cal Tech. Shortly thereafter, the Douglas DC-1 & DC-2 used fillets.

Due to the taper of the fuselage from the thick point toward the tail which creates a low pressure area and the rear of the wing on a low wing plane, also a low pressure area, the airflow detaches in the corner between the trailing edge and the fuselage. This causes drag and also a side-to-side yaw. Early pattern planes, like the Kaos, which did not have fillets, were known for their "tail dance." A fillet fills in this double low pressure area reducing both drag and the slight yaw instability.

HighPlains

My Feedback: (1)

That's really not difficult. A Van's RV-9 cruises at 166 mph at gross weight at 8000 ft with the 118 hp engine running at 75% power. The Ercoupe with the same power would only do 127 mph.

Running the RV-9 at 55% power (65hp), it still achieves 150 mph. Which is the same power as the Ercoupe 85 hp engine running at 75% power (64 hp).

KC36330

i was having problems with my Jett 90LX last year between idle and 1/4 throttle so i put it on my US40 ARF (because it dead sticked much better then the F-16) while i worked the problems out. i did have to mount it upright because of issues with the engine mount but it defiantly wasn't lacking in the power department.

kc

rjbranchii

HighPlaines

No arguement there. The a number of modern experimentals will do a good bit better. They a primarily flying much lighter weight airframes and much smaller wings with higher wing loadings. As has been mentioned though fillets can do alot. The Bonanza's are responsible for a good bit of its performance as another example.

Bob

Julian537

My Feedback: (9)

I think KC posted in the wrong topic? Or does that ultra sport have fillets?

KC36330

yes the US has fillets on the kit built and if you had read the whole thread you'd see i was responding to another comment.

kc

blw

My Feedback: (3)

I didn't know about the fix for the older Kaos models. Interesting. Was this fillets just on the tail section or the wing too?

proptop

My Feedback: (8)

So...just as an example...let's say I have a Sonic 500 that I want to put fillets on.

I'm thinking maybe a 1/4" radius from the leading edge back to the high point of the airfoil, then gradually increasing the radius as the fillet travels rearward?
I'm thinking that by the time I get to the T.E. area it should be about double that? (about 1/2" R.?)

daven

My Feedback: (1)

Proptop, it wouldn't hurt, just not sure it would help all that much.

Its also not legal in Q500 racing

proptop

My Feedback: (8)

"Its also not legal in Q500 racing"

We don't need no steenking rule book
It's run whatcha brung brudda...
Ask Nitro Junky, Coydog, and FlyinBR what they're bringin' to the party...[8D]

Chuck and John, is Benny a member of RCU? Benny has a Webra .50 with full len. pipe on his Sonic...and you've already seen Nitro Junkies...and mine has a K&B 6.5 FIRE...so we are expecting speeds above the typical Q500 realm.

BCarter

All this talk about fillets and speed got me curious and hungry. I'm currently building a 40 shrike, I was considering putting fillets on the sides of the fuse to blend into the wings, I simply thought it would look cool. Now I get the impression there might be speed advantages as well..... SO, my question is what the easiest way to make fillets ? Should they be top and bottom? How big?

rjbranchii

I use epoxolite. It is a dark brown color. Aeropoxy lite is a light blue color. Depending on your finish method one may be easier to deal with than the other. Both are good products though. If you are looking to increase speed I would do at least a half inch radius all the way around the wing. While you are at it scrap that nose wheel, scrap the wing mounted gear and make it a taildragger with aluminum gear, use thin racing wheels and thin wheel pants. There is a seperate thread on how to do this. Be sure to take off with high rate elevator so you can keep the tailwheel planted til you have airspeed for the rudders to work or you will have a wild ride to the left. The plane does do inetesting cartwheels though if you forget.

Bob Branch