F100 Profile Glider Beta Builder Needed

[Hudsonduster]

Been watching the thread from a distance, and I think we're getting off track here. We have to remember that every hobby has its own specific boundaries, and what works in one might not in another.

Experience with R/C models does not naturally translate into a skill set with these small flyers, let alone naturally-heavier paper flyers. The aerodynamics may seem the same, but it comes down to an issue of motive power, mass, and area available for the air to work on. A better area of homework would be in free flight instead of R/C: those guys are, as a class, way ahead of the R/C crowd because they don't got nice big engines to pull 'em out of trouble AND no trim settings on their Rx - when a F/F model leaves your hand, it's out of your control and you better've prepared right!

We face three big challenges here, and all three do not play well with the others. First, we limit ourselves in size by trying to work in paper, one of the worst structural media we can pick, so we gotta make the planes small enough that the paper won't just bend & flop. Second, paper is comparatively way heavy as a structural component, so now you're both small and heavy, and - Third, you're trying to build a SCALE-looking model of a much larger aircraft, so you don't have an "optimized" planform at all, you got stubby flying surfaces and big draggy fuselages; even the shape of the wings & tailfeathers produce drag and turbulence, it's a curse of the scale model.

So, as the size of your aircraft goes down (and remember, available surface area diminishes as a square of the overall), your ratio of surface in turbulence rises and you get less & less efficiently "flying" air; while simultaneously your mass of structure to area rises as well, making a heavier aircraft with less to hold it up. This is what beginning modelers, building peanuts because "smaller is easier to build," have to learn the hard way.

Basically, it's a wonder you've got anything left flying at all. Even when built by master craftsmen and minimally light & ballasted to top efficiency, small scale flyers have barely better aerodynamics than a dry leaf. I am serious. I've made 'em, I know. Trust this, you have a challenge.

So, what can you do with that challenge?

First, know when to give up: you will not be able to add sufficient fin area to any jet profile to counter that enormous front, because you're also increasing parasitic drag AND blanking the stab with added turbulence. Also you've gone & defeated your "scale" look entirely. You can grow a little, but in this case you can't grow enough. Same goes with the wire probe idea, you're just making a lawn dart and you're into guided ballistics and not flight.

After that, work with what you got. The F-4 will fly as a small glider in nearly-scale configuration, it's been done often in balsa, but you have to know what you're doing:

Once again, consider foam sandwich wherever possible for a light, stiff structure (and if you must build in paper, work out the aero bugs in foam or balsa first).

And give yourself every gimme you can - use a polyhedral configuration, like tips 1/4" to break (and angle the line of your fold to give washout!), then 1/8" per side under that tip break. This will give you back some directional stability to help with the barndoor vertical area. the more polyhedral you use, the better that will get. Remember, your model isn't flying "straight" through the air, it's flying "down" - sloping through air that's rising to meet it, and your dihedral is stabilizing the model around that vertical area, if you give it half a chance. Don't fear dihedral. Or washout, for that matter.

The anhedral stab isn't the problem, it's that the stab is too small. Make it at least 25% of wing area, and it won't burn your eyes if it's 30%. The turbulence off that big dirty wing and its corner with the fuselage is blanking the flow over the stab and it's like the stab don't exist. You may try raising the anhedral 5• to help a little, it'll still look right; and try a degree or two of down elevator. (See, this is the kind of stuf that's a snap when we're working with a foamie test horse!)

Figuring C/G on a flat plate is no worse than on a 'foil, it's just more pitch-critical, but that only applies to decently large surfaces. We're so small that it's lousy no matter what we do. Better in our size to toss and see what it's doing, really - don't spend time worrying the theory, the theory's already lost in the turbulence here! How many of us here know how to find center of lift on a tapered swept wing? Answer: we don't gotta know anyhow. Now go throw and test.

And, be prepared to go make another. Unlike just paper modeling where there's just the one goal of a finished pretty thing, WE are multitasking, and there will be lessons to grow upon (lessons: NOT failures!) - making a flyer is a process, a sequence. Redefine your goals, and you got a whole new hobby.

[mbauer]

Hi Hudsonduster,

Read through what you have to say. Some very good thought provoking thoughts. Some sage advice it looks like from someone who has done this before!

Explains things in a way that is fairly easy to understand. Like mentioned above, thought provoking!

Been thinking about what you've said. Then it came to me. The F4 seems to be the problem child, why not redo it using everything that has been suggested.

Will be modified as follows:
1) One version to stay the same except for 25% larger stabilizer
2) One model with 3 deg incidence
3) One model with both changes
4) One model with bigger wing (the version that was shared looked to have a much bigger wing-this one was from the Mcdonnell Engineering dept on a single sheet of cardstock)
5) One model with bigger rudder (no other changes)

These mods should be quick to do and fairly fast builds.

Plan to stay with Index 110lb cardstock, because not everyone has access to foam.

Personally have some 1mm Depron that could be used, but not everyone has a resource to get it. Here in Alaska not many foam egg cartons, plenty of meat trays, but they seem dense and to thick.

Here is a link to someone I have always found to be an inspiration, Wallis Rigby, this link is to an article that was printed in 1951. In it Wallis describes why he uses cardstock for his design media. Jetex.org: Archive - Jetex Paper Models (Wallis Rigby)

Once again, Thank you for taking the time to post what more than likely is the issues I'm trying to overcome!

Best regards,
Mike Bauer

[thepaperguy]

i never said tha my RC skills would help here. just that i knew what washout was and how it works. i added a strip of clear acestate from the upper tip of the exaust nozzel to the upper tip of the rudder following the same angle as the TE of the rudder and it flew 10x better. not perfect but better. i could get 90ft before it would start to wobble and spin. i am going to get a slightly larger piece and try it again and will get photos for you.

[thepaperguy]

ok Mike i got a winning combo with the clear tail extension on the F-100 . . . . . . . un fortunatly after a rather vigrouus baseball throw it now resides tle length of a full sized bus and a 1/4 up a tree and flew about 40ft fwd to get there lol if i can get her down in one piece i will get a pic for you and thankfully i drew the outline of the template on a spare fuse segment so i will still have you covered lol. its a bit bigger that i expected. before i got "treed" i did put in a nice flight somewhere in the 85 to 90ft range with a flat gentel bank to the left this morning

[thepaperguy]

heres my only pic befor the tree ate the model. i threw it at to high a nose attitude( 30 degrees up) and she snapped to the left and nosed straight down she survived to fly again. glad i re-enforced the nose with super glue. useful weight lol

[mbauer]

Originally Posted by thepaperguy

ok Mike i got a winning combo with the clear tail extension on the F-100 . . . . . . . un fortunatly after a rather vigrouus baseball throw it now resides tle length of a full sized bus and a 1/4 up a tree and flew about 40ft fwd to get there lol if i can get her down in one piece i will get a pic for you and thankfully i drew the outline of the template on a spare fuse segment so i will still have you covered lol. its a bit bigger that i expected. before i got "treed" i did put in a nice flight somewhere in the 85 to 90ft range with a flat gentel bank to the left this morning

Excellent! I can see the shape of the clear, gives a good starting point when I go to address the F100.

Working on the F4 changes for now, got quite allot done last night, finish up tonight and will be printing three out for building and testing.

Mike

[Hudsonduster]

Originally Posted by thepaperguy

i never said tha my RC skills would help here. just that i knew what washout was and how it works. i added a strip of clear acestate from the upper tip of the exaust nozzel to the upper tip of the rudder following the same angle as the TE of the rudder and it flew 10x better. not perfect but better. i could get 90ft before it would start to wobble and spin. i am going to get a slightly larger piece and try it again and will get photos for you.

Okay, I came on pretty fierce there, but with "never said" you are still skirting around the fact that what you are saying, all well-intentioned I'm sure, is still heading in the wrong direction. The reality is, we gotta approach this like a free flight model.

Here's the "Catch a clue" moment: "i could get 90ft before it would start to wobble and spin." Ah-HAH! Let's examine this.

This is what's called "glide test:" toss the model at a point about 30ft. away (meaning, just slightly nose-down) and watch it. It should fly stably and straight, sloping down but flaring out as it approaches the ground and going well past that "30ft" you pointed it to: you need to see that slight "up" curve as it ghosts in to a landing. Did that? That's a smooth glide. That's telling you the model is actually flying, and self-correcting its attitude to sustain flight.

But the model didn't do that: in your description, it went straight and then - plopped. What's happening? You gotta ask that, you gotta answer it, and you gotta fix it before going further.

What I'm reading in the "wobble and spin" is, the model is flying "too straight" - you got it trimmed pitch-critical. It's losing forward momentum and just stalling & dropping. A properly set up model won't do this: what it says is, this model is basically unstable despite the fact that you can get that straight flight. What the model should do as it drops below flying speed is to just-barely drop its nose and go into a shallow dive and pick up speed until it's flying again.

The way you accomplish this is by setting up a "seesaw" with wing's center of lift as the fulcrum and the stab and nose weight being the beam ends: the lifting wing needs to be kept at a positive angle of attack in order to sustain lift, so you set incidences between the wing and stab (popularly & wrongly called "decalage") to make the stab pull the wing "up" - which will make the model stall, except that you counter it with nose weight. The center of gravity, then, needs to be just forward of the center of lift, so the model's "up" tendency is pulled down - but then, as it goes down and picks up speed, the stab's extra "down" rotates the model back to the optimum flying attitude - and if everything's working right, you get stable flight. The model is actually "flying downslope" through air that's providing it lift.

I'm guessing that there isn't enough decalage in this model: if you add noseweight, will the model just dive? Okay, crank a little more up elevator in and try again. Did that cure it? We shouldn't go straight and then drop.

Once we got that good behavior, we can go to the next step. These things gotta be one-at-a-time. Sorry, but they just do.

The next stage will be to get dihedral and washout set right, so you don't need that enormous extra fin. You wil find you don't need near as much as you're using: a little maybe, not a lot. Have faith.

(You can find this procedure in mind-numbing detail by searching "Flight Trimming;" here's one of the best versions by a very cool fellow, John Koptonak: Free Flight Tips )

[thepaperguy]

it went up at a 30 degree angle and stalled when it lost airspeed. just like an actual aircraft the moment between the TE of the wing and the LE of the elevator is so short they cancel out. since there is no insindence it wont try to recover. it just happened to drop the left wing this time before nosing in. i frew it rite after that and i got a flat glide to the rite. i bent the right tip down a few degrees and i git an even shallower bank to the left. that and with them being so close together the air seperating from the TE of the MAIN wing is to dirty for the elevator to bite and pull out. the tree gave my plane pack and after one flight across the yard i tried using the rubber band hook im willing to bet i topped the 100ft mark. it was a flat eye level launch that woulda been further but a bush stopped it at the heigth it was flying. im 5ft 11in tall and my eyes are 5ft 5in above the ground. i wear a size 12 shoe and got 118 heel to toe steps from where i took the pic to where it landed. if you want mike im willing to put it in an envelope and send it to you for futher testing.
( first pic is the extension scotch taped to the tail. it is a help with the trimming by being flexable. Pic 2 is the distance looking from the launch point top the bush it hit. pic 3 it slightly zoomed showing the position of the glider)

[thepaperguy]

Hudsonduster i grew up building HLGs as a kit of various aircraft out of what i could find. Meat trays, Balsa, Plastic sheets, i even made a "paper" airplane out of sheets of aluminum foil. i know there is a magic formula and such but untill i turned 16 i never knew that it was always trial and error ant after a week of trying i would scrap a project and move on. i used what i had and taught my self the rest. so my post are after dosens of flights with a little bit of tweaking here or there untill i get the performance i like. as the saying goes " to each his own"

[Hudsonduster]

Dude, I am not singling you out (well, there at the end maybe) - but we can't be there seeing what you are seeing, which really is the ONLY way to do these things: we gotta rely on what you describe, and I addressed your exact words. From what you've subsequently described, I stand by the assessment and encourage anybody building these gliders to take a hard look at this entire discussion for the data it contains.

In any case, the result is the same: the short tail moment here, 'tho it's a challenge, is not a deal breaker and it certainly does not translate to "cancel out" - you have two distinct surfaces, and while you must deal with the limits of the model in specific ways, you still can win. - We said at the start, it's a scale(-like) model, and you can't set it up like an optimized glider.

But we got some good guidelines to work with , and Mike is incorporating good, much-needed revisions into the iterations he's presenting. Win-win.

And also, now you got a few places to go & get more information, so that should be a plus.

Me, I gotta go back to my day gig now! See ya, guys.