Increasing Wing Size -Effects?

[Murocflyer]

I built a Stevens Aero SQuiRT (http://www.stevensaero.com/shop/product.php?productid=16492&cat=254&page=1) last month. This was my first balsa kit build since I was a kid many, many years ago. I forgot how much fun it is. Now I am building, from plans, a Soarwatt electric glider (http://www.aerocraftrc.com/soarwatt.php), and I thought to myself, what would happen if I put the Soarwatt's wing on the SQuiRT and flew it?

The SQuiRT's wing and the Soarwatt's wing width (insert correct term here) L/E to T/E measurements are the same. The length is what is different. 38" vs. 60" to include a polyhedrahl wing style.

What, if any, would be the negative effects on putting the larger wing on the SQuiRT? Would the CG remain the same since the wing width and mounting area are the same? Are there any other considerations I should be aware of?

Thanks in advance,

Frank

[Sparky Paul]

The effect?
Not much..
I flew these three wings yesterday on the same fuselage...
No changes in anything else, just the wings.
and since these are amenable to modification, why not put the wing on backwards? :)

[Ollie]

You increase the wing area about 50% and span 50%. You decrease the tail power for stability and control for the new wing. You decrease the wing loading and it depends on the new wing weight. You increase the aspect ratio which decreases the induced drag. The new wing moves the neutral point forward. If you keep the CG at the old position, then you decrease stability. The wing spar carries the bending moment. The bending moment increases 50% due to wing area plus another 50% due wing span for total bending moment of 100% increase. The effect decrease of the vertical tail area 50% due to wing area and another 50% due to wing span.

Maybe I forgot something else because, "Every thing effects every else."

[Ollie]

After reading Paul's opinion, I agree that one could make it fly.

In my opinion, the flying handling qualities are poorer.

[Murocflyer]

Putting a wing on backwards? Isn't that sacrilegious? And that doesn't effect lift?

Ollie's post has made me a little nervous, but Sparky's has given me some hope. Based on your responses, I'm thinking this will work. I just need to figure out what the new CG will be AND expect less yaw control?

I know thre must be some formula to determine the size of the vertical based on wing size/span but since I'm not going to change the vertical, I'll just hope for the best. Now I just need to find that CG caluclator I favorited.

Thanks for the replies. I can't wait to give this a try.

[Sparky Paul]

For these non-competition sport fliers, the design finessing is seldom done.
The wing on the Soarwatt is obviously up the task for that plane, and wouldn't be pressed at all on the simpler plane.
.
Backwards, the plane is very sensitive at low angles of attack, but other than that doesn't handle any differently.
For models, a smooth curve from the front to the rear is all that is needed for flight.. not real good flight, but it will fly OK.
The Mirage with the Gentle Lady wing is an excellent airplane, anyway!
It handles well.
With the kit wing, I've flown it rudder only.. turning off the elevator. And it flies nicely that way also.
It's hard to screw up a Goldberg plane.
I also flew the GL wing on these planes yesterday..
I'd built the wing in '92, and it was getting seriously dissed at the field due to the numerous patches, so I recovered it...

[Murocflyer]

I used this site (http://adamone.rchomepage.com/cg2_calc.htm) to figure out my CG and it came out to 1.4 inches with 9% MAC. The SQuiRT measures in about 1.875 inches so I belive I am in the ball park since the Soarwatt's wing is much bigger. Hopefully I'll get my balsa in soon so I can finish the wing up and get it covered. I should be flying before the weekend is out.

Thanks,

-Frank

[Murocflyer]

Sparky Paul,


Here's my SQuiRT with its larger wing.

I checked the CG formula here (http://adamone.rchomepage.com/cg2_calc.htm) and then tried balancing it. According to the calculations, I needed to add a lot of weight for the nose. Do you think the CG calculator is off? I know you said earlier, no adjustments were needed when you went with the bigger wings. What are your thoughts about this?

Thanks,

Frank

[Sparky Paul]

Frank, without knowing what numbers you used, it's impossible to check the c.g. computation.
But..
If the wing is not swept, the c.g. for both wings will be close to the same point, m.a.c. wise, as the chords are the same.
I just returned from flying this one the first time..
A new build fuselage based on the Goldberg Mirage, widened to enclose a Nikon Coolpix 4600 camera.
Uses an eFlite 400 outrunner, and the wing is from a "found item" in a garage. It's a Goldberg Electra wing.. same as the GL, but structurally changed.
C.g. in the usual 3-5/8" aft point for the GL.
It's a sterling performer!
...
Inputing the values for the Mirage and the Gentle Lady versions, that site doesn't even come close to the flying c.g.. it's off by at least an inch in the nose heavy direction for the Mirage with the Mirage wing, the GL wing, and for a standard GL!
Paul

[Murocflyer]

Sparky Paul,

Thanks for the reply, I thought the CG numbers seemed awful small when I plugged them in, glad to know it isn't just me and you got similiar results using the CG calc. Thanks for checking on that.

Here's two photos of the wings, they are very similiar except the longer one has a polyhedrahl wing, but is not swept.

I guess I'm just being a little paranoid making sure I've set everything up right so I have a resonable chance at success.

Thanks again,

Frank

[vintage1]

To an extent CG position is affected by wing profile, but making the wing bigger certainly DOES require a more forward CG.

I would play a bit safe...that calculator errs on the safe side..I would suggest you do to, at least until you can have a few flights and test the stability.

Its easier to remove added lead than to rebuld an entire model. DAMHIKT. :D

[HELModels]

All good advice and I will only add my recent experience. The plane I've been fiddling with used 2 identically designed freeflight wings from 2 long retired freeflight models. The one had slightly more tip dihedral than the other and is the one I now use since the other one landed in a larch tree and is busted up.

Anyway, just this difference is noticable, although not quite the same as changing span. The one with additional dihedral seems faster and definately twitchier response to rudder. I've considered increasing the span on the design for the final version to reduce the twitchiness.

[Sparky Paul]

For flyability, it's the tail volume cofficient (TVC) that counts, not the wing area..
A too-short tail arm has more effect on flyability, as does a too long arm.
With the broad range of an acceptable TVC; from less than .2 to .45, there's a lot of latitude in selecting the wing and tail sizes, and tail moment arm.
The exercise in question has less than a .05 effect on the TVC, so the plane's flyability won't be compromised.

[HELModels]

There is a difference between flyability and just noticing a difference in handling. I took the busted up wing and overlayed on top of the flyable wing. The difference is small but noticeable on the ground as is in the air.

Interesting that tail moment changes were mentioned as I've used different booms that vary only by an inch or so and noticed the change in handling.
My model is only ~30" span and currently 18" from LE to boom end, so smaller changes show up quicker than on models discussed so far.

[Murocflyer]

Fellas,

Thanks for the replies. I am treading on new ground here so all advice is welcomed. Part of me says "just go for it," but the other part like Vintage1 says, "err on the side of caution." I'll add a little nose weight and give it a try as soon as the wind permits. I'm hoping for an extremely calm day real soon.

[Sparky Paul]

The first excursions outside the box can be exciting.. :)

[BMatthews]

Muroc, don't forget that in addition to you needing to move the CG a little forward that there's a lot more wing structure now located behind the CG. That plus the shift forward can easily make for a rather large nose weight addition being required.

[Sparky Paul]

Muroc, don't forget that in addition to you needing to move the CG a little forward that there's a lot more wing structure now located behind the CG. That plus the shift forward can easily make for a rather large nose weight addition being required.
.
I have NEVER found it necessary to add any substantial nose weight when placing a same-chord of any span on a fuselage!

[Murocflyer]

The wind was calm enough today to give the plane a try. Because Vintage1 made me a little nervous, I added an AA battery with double back tape just behind the motor to make it a little more nose heavy. I gave it full throttle and then a little toss. It seemed to struggle to gain altitude, but I did get it up to "cruising" altitude pretty quickly and flew around some. Dinner was ready so I brought her back down.

Emboldened by that first flight, I removed the battery, throttled up and gave it a toss. It climbed real well this time, but like before, rudder response wasn't as dynamic as it usually is with its regular wing. But it seemed to fly fine. It was getting dark already so I didn't make sure it was trimmed out nor did I do any experimenting to see the different flight characteristics of the new wing. It did take a lot longer to bring it down without the extra weight. It wanted to float around quite a bit. Eventually I brought it in low enough to make my final. Unfortunately, I made the final turn a little to tight and it dropped down from about 12 feet onto the road. I bent the motor shaft and broke up some balsa. Totally my fault and not the planes'.

I have a spare motor and the glue is drying on my repairs. I'll recover the damaged areas tomorrow and all will be well again. The wing was not damaged.

I do believe I'll forego any more experimental flights until after I maiden the Soarwatt.

Thanks for the advice in getting me airborne. I appreciate the help.

My next experimental build is going to be a tail dragger with a 60" wing. Looking forward to building that. I'm sure I'll have some more questions.

Thanks again,

Frank

[Sparky Paul]

With the added area, it will float better.. :)
The added polyhedral should have enhanced the rudder response.
These two have identical wings.. both began life as straight dihedral, flying OK as rudder no-aileron planes.
But at slow speeds and high alphas, the rudder effeciency diminishes, and the nose tends to yaw outside a turn, to the point where the plane can stall.
On one wing I sawed off the tips and reglued them with a small amount of dihedral, making the wing a polyhedral.
Swapping the wings between flights yesterday, it was apparent the poly wing response is quite superior.. the plane responds to rudder much faster than the dihedralled wing, which exhibits a perceptible lag between control input and airplane response..
And the nose yaw-stall problem has gone away.
I'd done the same thing on a longer version of the same wing to cure the same problem, and it worked there also.
(The original wing was used on my Baker long-distance plane in 1996, with an OS 26 motor.. Flew 55 miiles in about an hour. Similar sized fuselage. It's flown since with brushed and brushless motors.)

[HELModels]

polyhedral is nice. Whether I get mine down from the pine tree or not, I will forever be reluctant to build R/E/T without polyhedral. Coupled with a V tail, I believe the right thumbs could do rolls. In fact, I have unintentionally rolled inverted with poly. Real slow flight and then hard on the rudder and whoop over she went. Unfortunately, it was only 5 feet up... That is where the pusher design saves props. Polyhedral also recovers quicker from upsets.

murocflyer, dont flirt with the trees or other hazards. Just like full scale, when you think you can handle extra risk is when it might bite.

[BMatthews]

The poly should have helped but the longer wings combined with a "short" tail for those wings means that the rudder isn't working with a very long leverage arm. That may reduce the overall effect to where the better poly response but poor leverage arm length are fighting each other and the results are just adequite.

Looking at Muroc's combo's it seems like the span and area increase are more extreme than your wing switch proportions are Paul. That could easily account for the softer response.

[Tim Green]

It did take a lot longer to bring it down without the extra weight. It wanted to float around quite a bit. Eventually I brought it in low enough to make my final.

You seemed to have experienced exactly what you should have - increased lift - due to having increased the wingspan considerably.

I'd expect that if you flew your normal wing, and then immediately afterward you flew the longer wing, that even with the increased weight of the longer wing, you'd find it a lot more floaty.

[Murocflyer]

The floating part was pretty enjoyable. I can see why glider pilots like it so much! I hope to have the fuselage finished on my powered glider soon so I can see what all the excitement is all about. I'm really looking forward to it.

Frank