Author Topic: Brodak T-Bird wing offset (Read 2319 times)

Tom Weedon · « **on:** August 27, 2007, 09:31:37 AM »

Hey Fellows,

I'm working on a Brodak T-Bird wing and I noticed that the plans have a note that states wing offset is not necessary on the T-Bird. I guess that the original had a 1" longer inboard wing. The note on the plans state, "equal span wings do not exhibit an adverse roll characteristic in tight maneuvers and have the bonus of better line tension over all."

Now here is my problem, I'm getting back into C/L after 30 years layoff and I remember being taught that the inboard wing should always be longer than the outboard wing. Has anything changed over these years that I missed? Should I build this T-Bird with equal span wings as suggested in the plans?

Tom Weedon

Bill Little · « **Reply #1 on:** August 28, 2007, 08:19:57 AM »

Hi Tom,

I would put the C/L of the wing on the inside edge of the fuselage as Bob did the original. It flies great like that!

Equal span panels have been used on some of the "top line" ships, but it requires more tip weight and really needs the outboard flap to be increased in area.

Most every design I see now still has about 1/2"-1" of asymmetry.

Tom Weedon · « **Reply #2 on:** August 30, 2007, 09:59:56 AM »

"I would put the C/L of the wing on the inside edge of the fuselage as Bob did the original. It flies great like that!
Equal span panels have been used on some of the "top line" ships, but it requires more tip weight and really needs the outboard flap to be increased in area. Most every design I see now still has about 1/2"-1" of asymmetry."

OK, on the answer. I'll do as you suggested, but why should the outboard flap be increased in area, and by how much? I guess I'll have to put a weight box on the outer wing tip so that I can get it trimmed right.

Thanks, Tom Weedon

Bill Little · « **Reply #3 on:** August 30, 2007, 11:18:30 AM »

Quote from: Tom Weedon on August 30, 2007, 09:59:56 AM

"I would put the C/L of the wing on the inside edge of the fuselage as Bob did the original. It flies great like that!
Equal span panels have been used on some of the "top line" ships, but it requires more tip weight and really needs the outboard flap to be increased in area. Most every design I see now still has about 1/2"-1" of asymmetry."

OK, on the answer. I'll do as you suggested, but why should the outboard flap be increased in area, and by how much? I guess I'll have to put a weight box on the outer wing tip so that I can get it trimmed right.

Thanks, Tom Weedon

Hi Tom,

On "equal panel" wings, you increase the outboard flap area to help carry the extra tip weight, that you can carry, through the corners.

For the "stock" (offset build) *by the plans* is fine. The Brodak kit has provisions fo rthe tip weight box and adjustable lead outs. Use them both!

Balsa Butcher · « **Reply #4 on:** September 13, 2007, 11:22:34 PM »

Would building a T-Bird with equal span wings be grounds for disqualification for classic competition? All the T-Birds I have built have had unequal wings span but I'm really tempted to do the next one with equal span wings.

Bill Little · « **Reply #5 on:** September 14, 2007, 06:38:41 AM »

Quote from: Pete Cunha on September 13, 2007, 11:22:34 PM

Would building a T-Bird with equal span wings be grounds for disqualification for classic competition? All the T-Birds I have built have had unequal wings span but I'm really tempted to do the next one with equal span wings.

Hi Pete,

"By the Rules", there is no function for a *Disqualification*. Nothing in the rules about it.

It would defeat the "Spirit of the Rules", and if the contest is awarding Fidelity Points you should take a hit there.

PatRobinson · « **Reply #6 on:** September 14, 2007, 10:20:24 AM »

Hi Guys,
Tom, I am not going to advise you or contradict Bill but this has bugged me for years.

If Line tension is your goal for unequal wing panels then based on my experience this "would be" benefit is a myth. Years ago I remember reading Al Rabe writing about the benefits of tip weight and how it always produces line tension. I had a straight wing at the time so I cut off the extra area of the inboard wing and added tip weight till it hinged in the corner and then backed it off till it stopped and presto I had a dramatic increase in line tension. Later that year I scratch built a Profile with a long outboard wing panel and carried more tipweight and I had line tension everywhere at 5.5 lap times on 63 ft lines and it turned flat and tracked evenly. It is ironic that the long outboard wing had far fewer roll wobbles than my long inboard planes. At that point, I decided that a long inboard wing has no benefit to line tension in and of itself and on the negative side it limits how much tipweight I can carry which actually does work to increase line tension.

I know everybody has different experiences but to me I don't see any benefit. I had a conversation with Tom Dixon about this subject on classic planes and his advice was to shorten the inboard flap and slightly widen the outboard flap to reduce the problems with classic unequal panel designs.
I think his point was it reduces wobbles and with more tip weight to increase line tension, or at least that is how I remember it.

I remember reading Bob Hunt's article where he was the first "Name" flyer who advocated for equal span panels and de-bunked the theory for un-equal panels. I said out loud ATTA-BOY!!

I realize that people try some assemetry in order to reduce overall airplane weight by reducing the amount of tip weight and that is a understandable goal and people have made it work acceptably over the years but if the overall primary goal is line tension ,then I ain't buying it.

We live in an era where heavier airplanes and faster airspeed is more the norm than in the past so perhaps tipweight is less important to overall line tension than it was in the past. HIGHER SPEED + HIGHER WEIGHT = PULL which may negate some of my objections to unequal panels and render it a moot point on some airplanes.

My opinions about unequal panels and line tension in smaller and lighter planes of 45-56 oz. flying at 50-53 mph are based on empirical testing rather than heresay and myth. I haven't really tried out the big planes, very much, yet so, I will refrain from spouting any untested opinions about them.

Guys, I apologize if this came off as a rant but this topic has been a pet peeve of mine for years and I guess it brought out the "Mythbuster" in me to finally say something.

Tom, if unequal panels works for you great!! and wonderful!!, but if you need more line tension you might look at Tom Dixons advice on fairly easy fixes that will let you add tipweight and increase line tension.

Okay, I am done now and I feel better now that I have done my part for Truth, Justice and the American way.

Tom, and guys I appreciate you all listening.
Best wishes,
Pat Robinson

Balsa Butcher · « **Reply #7 on:** September 15, 2007, 09:25:40 AM »

Pat's post brings up something that I've believed for a long time. What we fly are not wings as in airplane wings but rotor blades, as in helicopter wings. In our spinning flight they are subject to the same aerodynamic idiosyncrasis as those beautiful two or three or four or five fiberglass, foam and titanium airfoils that have suspended my sorry carcass in the air for the past 29 years and around 8,500 hrs. What the larger inboard wing does is compensate for dissymetry of lift. The inboard wing has less area to cover so it is flying at a relatively lower speed than the outboard wing ergo is develops less lift. Larger inboard wing area helps compensate for this. It is compensated for in helicopter rotors by blade flapping. So far sounds like a good idea but I feel many vintage designers overdid it - see "All American" or even the offset in the Brodak Smoothie I am currently building. Offset wing effectiveness is also dependent on airspeed, the slower the airspeed, the less effect it has on the flight of the airplane, so when you need it the most, it's not there.

What some may not realize is that helicopter rotor blades, like CL airplanes have wingtip weight. Around 5-15 pounds (depending on the type) in most light to medium turbine helicopters (Bell Jet Rangers, Eurocopter A-Stars). Reason for this is to increase rotor system inertia during unpowered flight (autorotation) making it easier to maintain rotor RPM. The increased inertia on the spinning blades (along with centrifugal force) makes the blades stiffer as they rotate - kind of like line tension. Without this, the otherwise flimsy blades could not support the weight of the rest of the helicpter...and its occupants!

In our airplanes, this combination of increased inertia plus centrifugal force results in line tension. To demonstrate, take a small styrofoam ball, attach it to a string and twirl it. There will be little line tension. Now replace it with a ball bearing or marble - instant line tension, not wing offset necessary.

This is my simple explanation that may not make sense to anyone but myself as to why tip weight is more efficient than wing offset in our models. I continue to use offset in Classic designs because that is in the spirit of the event. In modern stunters I agree Tom Dixon and many others who feel that no or very little offset is necessary as tip weight is much more effective in developing line tension.

PatRobinson · « **Reply #8 on:** September 15, 2007, 03:53:55 PM »

Hi Pete,

I would say a big ATTA-BOY!! but I have already use that line ,so I will just say thank you for bringing a new and unique perspective to this discussion.
I never would have drawn the comparison between helicopters and control line. Interesting.

I guess the reason that I get so intent on this topic is when I was learning to build and fly, I wasted time doing things the so-called "right" way and getting no results and so I spent a lot of time doing empirical testing to find what works for me in the real world, so I don't have much patience for what I call "Stunt Myths". Fortunately, today there is a lot more information available to give beginners a wider perspective on what to do.

Pete, I thank you for your interesting point of view.

Pat Robinson

Dennis Adamisin · « **Reply #9 on:** September 15, 2007, 06:42:38 PM »

Classics should be built as designed - like the Sterling Sptifire I just built tith about 2" assymetry! However I would LOVE to build another - with symetrical span, thicker airfoil, about 4" longer tail plus a slightly larger fin moved aft a little...but I digress!

I have built with wing offset, then went back to equal, then back to offset and back to equal, and that is where I still am. I have not tried a tab on the o/b flap but will add that to the things to try list. I would note because the o/b wing is flying a slightly larger (& faster) circle it creates more lift and drag automatically.

PatRobinson · « **Reply #10 on:** September 15, 2007, 08:47:48 PM »

Hi Dennis,

I have no problem with building a classic as designed but I personally would apply Tom Dixons modifications because I don't think they violate the spirit of the event anymore than your flap modifications to the Oriental. The changes are visually subtle but could hopefully be effective. Dennis, if you think about it almost nobody uses Bob Palmer's tricked out Thunderbird flap setup which was a part of that design but that doesn't mean that guys aren't honoring the spirit of event.

I remember Bob Hunt saying that even though the outside wing flies faster the fuselage flying at a tangent angle shadows the inner part of the wing so the overall lift of the outboard is not that much more if at all.

Equal panel wings obviously work so Bob's "theory" could be just as valid an explaination as the "theory" behind the long inboard wings.

Dennis, the deal breaker for me is, if the a long inboard wing is a better concept, then why did my long outboard wing airplane NOT fly "poorly".
I had great line tension and had less roll/yaw wobbles than my long inboard
airplanes produced. The day I flew that plane was the last day I believed in long inboard wings.

Dennis, my MAIN point is if your goal is line tension then tip weight is a more effective tool at generating that line tension than assymmetry will be which I believe is also the point that Pete was making.

If your primary goal is to reduce overall weight by reducing tipweight then a little assymmetry could be a useful tool to use and you would adjust trim to account for the assymmetry. Obviously guys make unequal panel planes work
and have for years.

If a guy is flying a big and heavy plane with a "hoss" motor or if he is flying Fast then tipweight becomes a smaller piece of the overall line tension equation, of the total tension that is being generated.

However, if a guy like you, who has flown smaller wing area planes of less than 60+oz. in weight with a strong but not "Hoss" engine then I think tipweight plays a bigger role in the overall line tension equation so running equal panels and having the option to add tipweight, if you need it, is better than having that option blocked because you have unequal panels and the plane can't handle the extra tipweight.

Dennis, I hope I made my point with a little less hyperbole and a little more clarity this time.

Best Wishes,
Pat Robinson

Balsa Butcher · « **Reply #11 on:** September 15, 2007, 10:50:20 PM »

Re Pat's post: Affirmative, weight being more effective than asymmetry in maintaining line tension was the only point I was trying to make. I actually side with Dennis regarding classic competition planes. You have to draw the "Spirit of the Event" line somewhere and for me, it is altering the wing symmetry of a design, sort of like moving the landing gear location of an OTS design - a definite "No No". for competition. That's just where I draw the line, others may feel different (and that's OK too). But don't mind me - I also don't think electric power in Classic or OTS is in the "Spirit of the Event" either

Dennis Adamisin · « **Reply #12 on:** September 16, 2007, 12:04:28 AM »

Pat:
As always your posts are spot-on and perfectly clear - I always learn something.

Can you elaborate on Tom Dixon's mods for Classic? I expect my CLassics I will routinely be guilty of the the usual structural and control system upgrades, plus sealing the hingleines and (if needed) clipping the flaps!

The unequal speeds of the wings are a "fact" but whether that fact matters or not is up for grabs. I mentioned it because it enables the use of more tip weight. Seems like adding a tab to the o/b flap goes a little farther down that same path. BTW - the fuselage blanketing is a viable concept but applies to both equal span wings and those with assymetry - so I am not sure it really applies to the span discussion?

Good catch on Palmers "differential flap" system - I just re-checked that on the Skyscraper plans. He made the inboard flap move farther AND used assymetry - PLUS used over/under leadouts! The greater throw in the i/b flap, plus assym, plus up-line in bottom position would all ROLL the airplane out. However the drag component from the asym and extra flap throw would YAW the bird IN! He must not have liked the idea of tip weight???

Here's my take on the Big Power statement. This summer I saw two otherwise superlative PA76 powered birds - with the wings not level with the lines! That is a pretty fundamental trim step and it seemed odd it was missed. Makes me wonder how many times the big power actually MASKS trim issues. I will argue that the BETTER the trim is the LESS power is required. More to the point, the power reserve goes UP for fully trimmed airplanes! (Historically I am not sure I have always trimmed out all my birds to their max potential...)

Pete:
Uh-oh, maybe I should not tell you about my new classic ship where I plan to take advantage of the E-Power battery weight to correct a vertical CG issue...!

All seriousness aside, when I see 46's in Noblers and 65's in Sharks the "spirit of the event" thing seems to take a serious hit. Heck even my LA40 powered Oriental was probably 25%-50% MORE powerful than the original.

Certainly E-power is here to stay. I also hope that using e-power will let me practice fly in my back yard...

PatRobinson · « **Reply #13 on:** September 16, 2007, 07:07:09 AM »

Hi Dennis,

The changes that Tom Dixon suggested to me for unequal panel wings was to shorten the inboard flap at its tip till it equals the out board flap, on wings that don't have full span flaps, and for those wings with full span flaps to cutoff and glue on a greater portion of the tip area similar to the way you do your flaps but make the spans equal. Now, on the outboard flap, in addition to having the flap span on the outboard flap the same as the inboard flap span, you also, widen the flap chord by 1/8" to 3/16"+ at the tip, but you leave the flap root chord the same. I doubt most people would even notice the difference in chord.

I think his logic is by having both flaps the same span you avoid any "lift imbalance" caused alieron-like effects and wobbles and by using a slightly wider chord on the outboard flap area ( both fixed and moveable areas) you increase lift to carry needed tip weight without adding an ugly tab on the tip.

Tom is a clever guy who does things his own way and his classic planes fly good enough he could use them to fly in PAMPA Expert so I give his idea creedence.
Visually , the planes overall planform shape configuration is only changed subtlely at the outboard flap area but otherwise it remains unchanged. The advantage is to give you the flexibility to add tipweight if you need it. To me,having trim options is better than not having them.

So, Dennis, I hope that helps clarify Tom's ideas for unequal panel airplanes.
Sorry, I wasn't clearer and more complete earlier.

Dennis,it is good talking with you again and I hope you have a great day.

Pat Robinson

P.S. : I just now saw Pete's second post , Duh! Well my only excuse it is "Oh-My-God-early". Pete, using Tom Dixons ideas you can still retain the wing assymmetry and also keep the planes overall planform shape almost the same with only a subtle difference ,but at the same time you can increase your tipweight trimming capability. So what do you think? Pat

Balsa Butcher · « **Reply #14 on:** September 16, 2007, 09:08:12 AM »

Pat: Thanks for the information on Tom's technique. I like it. I've acually built a few of Tom's designs (Phoenix, Charisma, Stylus, T-Bird 46) and other designs off his plans. All have flown GREAT except the T-Bird 46 which I mistakingly built with original style wing/flap assymetry. I suspect this may have been why it was difficult to trim out (of course mis-aligned wing tips don't help much either-DOH!). I am just sorry that my current Smoothy project is too far along to incorporate these subtle modifications. Next time.

Dennis: I know electric is here to stay and anything that opens up new fields from which to fly is good. I will probably build one myself...soon, for just that reason. Still, I hope electric does not become toooo popular w/ classic fliers. I would miss the 4/2/4 engine run that is an intrinsic part of the event. But to correct a trim issue - that's different. RE: big engines in classic planes. Not a good trend either IMHO - People wondering if an LA-46 (or ST-51) will be enough power for their Nobler; Uhhh ya,- Spirit of the event; that would be "no", and probably waaay too much line tension - but were'nt we just talking about that?..

PatRobinson · « **Reply #15 on:** September 16, 2007, 12:37:33 PM »

Hi Pete,
You are most welcome for the info and I am glad you liked it.
Like I said Mr. Dixon is a clever fellow who has been flying for a long time and comes up with own way of doing things. The credit is his.

Pete, I see your point about electrics in the Classic event changing it's ambience . Overall, I think that reduced noise and the opportunity to make available more convenient flying locations will become a driving force moving guys to electric.

In regards to bigger engines in a Nobler & etc., the OS LA46 and ST 51 are to some extent "budget priced" engines with acceptable runs which makes them popular. On the down side they are heavier than classic engines by several ounces and if you run heavier stock mufflers - Oh my, it is really
"tail-weight-city". Tounge mufflers or light tube mufflers are needed.

The other side of this story, is, I see much less concern about airplane weight
than in the past with more acceptance of the idea if it is too heavy then bolt on "MO Power". I think more appropriate choices for more power for classic planes are the Aero-Tiger-36 and the PA-40 Ultralite. These are "Lighter-Hoss" engines that are very powerful and capable but also higher priced.

The other thing that has changed in recent years is I see many classic planes flying 5-5.2 sec. lap times on 63+' lines, instead of 5.4-5.5 lap times and going from a speed of 50-53 mph to 55 to 58+mph as a common practice. In the past these increased speeds were reserved for use in turbulence and wind.

In reference to what Dennis said in his last post about trim in bigger engine airplanes, it seems that if you have a heavier airplane and you fly it faster with more power and as a result you have lots of line tension, I agree that it will mask trim problems. When you fly slower ,even if you have more power , I think you need a better quality of trim to maintain having even line tension everywhere.
Now, this is just my opinion at this point and I am open to empirical data
to the contrary.
Let me just say, that if you fly a heavy plane fast with a powerful engine, with the result that you have good line tension and the plane turns okay, you may be de-motivated to pursue a more nuanced trim that would be required by a slower or lighter airplane in order for it to perform well. This does not necessarily apply to top level flyers who always strive for an advantage.

Now, to be fair, having a big ole PA-75 doesn't necessarily mean flying fast,
I think it was Doug Moon ( or Steve, sorry) ,anyway, he stated on SSW that he was running a 14/3+ pitch, 4-blade prop and was flying about 50 mph on max lines, even in wind. THRUST WORKS- yes indeed it does! On more than one occasion I have judged Randy Smith flying his Drednought and other designs with a PA 51-61 engine on pipe at a fairly slow speed and that plane cut through nasty turbulence as if it wasn't there. THRUST WORKS.

I personally don't like to fly fast and I don't think a fast plane looks as graceful doing the pattern as a slower airplane, case in point I think the slower flying "Shark" with the Retro Discovery engine "presents" better than the faster "bang-bang" fast and crisp style of flight. Both styles can be flown correctly and score well if the maneuvers are correct, but the slower plane just looks better doing it as long as it avoids sagging slowdowns from insufficient thrust during maneuvers which usually will mar the shapes.
In that case, fast and correct beats slow and flawed.

So Pete, how do you feel about a PA-40 ultralight rear exhaust engine using a rear muffler in a classic plane in order to avoid having a side muffler hanging out , with the goal of having the plane look closer like the original planes that didn't use a muffler. Is this modern solution in the spirit of classic? ( No tuned pipe just rear muffler )

Pete, this has been an interesting discussion. Good Stuff!

Pat Robinson

Balsa Butcher · « **Reply #16 on:** September 16, 2007, 03:14:37 PM »

Pat: No arguement with anything you said. Classic wise maybe the trend toward modern engines on older designed was probably brought to the forfront by Bob Hunt @ VSC 2(?) when he flew his Tucker Special with a high RPM Webra 32. (Bob Hunt, trying something different - who woulda thunk it?

) At the time many purists felt he was pushing the envelope but hey, it worked, quite well in fact. Spirit wise, I have noticed that many of the modern high RPM engines still have a 4/2/4 break, a good thing both spririt wise and function wise. My only regret regarding your proposed PA 40 ultra-light w/ rear exhaust set up is that I don't have one

Bill Little · « **Reply #17 on:** September 16, 2007, 06:00:44 PM »

As to engines, I have always heard that the main reason for not specifying a "period" engine in OTS or Classic was because many people do not have them.

Dennis Adamisin · « **Reply #18 on:** September 16, 2007, 10:13:42 PM »

Good point Bill. Gets even tougher when you try to install a muffler on an old engine. Still, ANY modern engine of equivalent displacement will show a clean set of heels to any of the classic era engines - the power-up is free. Most of the modern engines are also heavier - but with a few big exceptions as Pat pointed out.

I dunno, using modern engines AND increasing the displacement is a real case of overkill. I just got a handyman special Fox 35. But I am not really planning on building a Classic for it. I guess we'll see.

Bill Little · « **Reply #19 on:** September 17, 2007, 08:04:54 AM »

Quote from: Dennis Adamisin on September 16, 2007, 10:13:42 PM

Good point Bill. Gets even tougher when you try to install a muffler on an old engine. Still, ANY modern engine of equivalent displacement will show a clean set of heels to any of the classic era engines - the power-up is free. Most of the modern engines are also heavier - but with a few big exceptions as Pat pointed out.

I dunno, using modern engines AND increasing the displacement is a real case of overkill. I just got a handyman special Fox 35. But I am not really planning on building a Classic for it. I guess we'll see.

Hi Dennis,

I like the idea of using the Brodak 40 and the DS 40 (with the venturi enlarged!) in the Classic planes, since they are light and give a touch more power, yet also give a pretty classic run.

I just wish I could run my McCoy 40s more! LOL!! (but I have been star struck by the Aero Tiger 36....

)