KidEpoxy

Well, I guess I made a commitment now that I've signed up. Maybe I should have looked into the flight killing physics before picking this model . In theory, I'm trying to get a Variable Sweep plane, but I'm hitting problems with the CG no longer being over the wing when the wing sweeps back... considering tyeing a sliding RX & battery(front) & fuel(rear) to the sweep servo... try to move weight to slide CG with the wing sweeping.... hmmm

Perhaps the variable sweep is better left to larger models carrying a whole passal of servos- we'll see

I hacked out a draft, saw this immediate problem, and came up with Beta & Gama drafts.

KidEpoxy

Have made a twin Norvel .074, and can get the engine to behave ok, but I have no idea how to run a cox.

Since there is a good chance this thing will only get off the ground high enough to utterly destroy itself on an immediate return to Terra, I'm going to try the $7 Sure-Start .049 . Doing my research on the bladder, but saw someone say the needles are junk on Sure-Starts, bladders bode bad for them. But I need something to compensate for the fuel being 3-10" in front of the engine... If this thing flies at all, it will be fast, and is supposed to be like a fighterjet, funny pitches & G's that a tight needle bladder system would cope better with.

ptulmer

My Feedback: (5)

The Cox reedies DO NOT have thrust washers! Be careful with electric starters and pusher configurations are out of the question. Sorry. TeeDees do have thrust washers and should do OK as a pusher.

KidEpoxy

So the main problem I have with Surestart Pusher is that you can't use Surestarts as pushers... Must admit, with all the other challenges this model posed, I hadn't considered Incompatable Engine to be the project killer. Looks like I'm gonna have to massage the plans with a chainsaw or 9iron.

Kinda changes the budget, from $15 for 2 engines to gobs more than $15.

Thanx for the warnng, I guess that is why I dont see a lot of them around.

Tim Wiltse-RCU

KE,

Clutch the pearls ...all is not lost. All you need to do is score a couple of steel washers to go between the prop driver and crankcase. If you were planning to order the engines from Cox then while you are on the phone just order the Killer Bee thrust washers while your at it .

LAter,
Tim

BMatthews

....or just make your own thrust washers from some steel or brass shim stock.....

It may be worth filing a very slight groove in the front edge of the crankcase as well. That'll provide a path for the oil to leak out a bit and lube at least one of the running faces that way. Just a bit more than the size of a scratch is all you need.

KidEpoxy

ok, I grabbed a pic from cox of the crank, case, & driveplate. Gonna take up this line of chat in the COX Reed FAQ thread so others can gain from my questions.

ptulmer

My Feedback: (5)

The problem I had has the crankcase itself is too long. Or the crankshaft is too short... After using the electric starter on them for a while, it fits nicely though. BTW, you can get the fiber washers from Home Depot. I like those cuz you can modify them with an exacto knife.

BMatthews

Oh, and BTW.....

One reason the swing wing idea works with the full size is that the fuselage with the big engines provides a rather sizable portion of the lift with most twin jet airplanes. Expand your "fuselage" and LEX area and the wings pivoting back won't be nearly the problem they are with the sketches you are showing. Make the center section about 8 inches wide with a strong delta wing influence and make it so the swing wing area is only about 50% or less of the total area of the fuselage "delta", wings and stab and I think you'll find that with a bit of a compromise you can get by with the swing wing. The wing's won't weight much I know but with them swinging back the CG will shift a little on it's own thanks to the swing. I'm tempted to suggest adding some weights to the tips but that would be a bad thing in so many ways that it could not possibly have a net positive effect.

And for 1/2A's sake keep the swing wing actuator servo light. Some form of very light jackscrew mechanism that uses a light pager motor or similar.

KidEpoxy

And for 1/2A's sake keep the swing wing actuator servo light.
I'm in the mind to run hs55 or cirrus 9/10g servos on the controls, and considering a standard servo on the swing. The control surfaces, 2 elevators(maybe eleverons) & 2 Vtail, will be flying, with a whol lot of counterbalance ahead of the axle. The twin drive should be way more than enough power, but the small wing area may... who am I kidding... wing area WILL require crazy speed to stay off the ground. Loading may be high, but this should have the power.

Expand your "fuselage" and LEX area and the
ok, you got me. LEX ?
I am assuming that is the part that I have called the shoulder plate, the green thing above & across the "jets" that the wings pivot on, & the fuse floor. I have the Fuse floor above the floor of the "jets", this is from the F14, but I'm not above changing to a flat plate bottom if that's what it take to stop faiilg out of the sky. Should be ok as a channel, your wider idea makes sense, maybe a squeze- what was the 6pack that had tip-droop compression lift, the valkyre?

BMatthews

LEX= Leading Edge Extension, these are the long strakes you see on the F18, F15 and many Russian aircraft . They look like long delta wings that blend the fuselage into the engine area. Their chief function is to help generate body lift and to generate a strong vortex flow over the central wing and body area to help delay the center section stall at high angles of attack. This is a subsonic effect that can also be used with our models.

Even a regular servo likely won't have the torque needed to deal with the wing sweep loads. That's why I recoment a home made solution with longer transit time but VERY high torque or thrust. A jack screw servo would be ideal. Basically you can make one from a set of mini servo replacement gears, a small motor that will run well on 4.8 volts and a long length of 4-40 threaded rod. Drill and thread through the output gear with a 4-40 tap and mount the next gear in that is intended to drive the output gear onto the motor shaft. This will require that you modify this by cutting off the inner small pinion part and drill it so it's a tight fit on the motor shaft. That will drive the output gear and the gear ratio plus running the threaded rod through about 2 to 3 inches of length will provide the high thrust force needed to deal easily with the wing sweep loads. An old and non working servo will work well or go buy a cheap small hobby motor.

KidEpoxy

To keep the drag on the wing down for the servo, and to keep the airspeed up, I was thinking a thin, 5-8% symetric/planky wing... the lift will have to come from AoA. I don't want the thing to become a Dirt Finder when inverted. I'll get into wing construction & foil later. I'll post a foil sketch in the morning, after 1am now.

KidEpoxy

The wing swinging pannels:
I'm thinking I want to keep the drag down and have good inverted as stated in prev post, so a symetric 5-6%. The short aspect, just 11:8 = almost Aspect 1, should reduce the demand for heavy spar-ing, so the 5% shouldn't be to snap-in-halfy. Also, they need to slide into the shoulder, so I should keep them thin to reduce overall shoulder / top plate thickness, too.

I need a lot of the cord at a constant thicknes to have the pivot bear on even surfaces in the shoulder, the pivot disk area, so I figured to just keep the flattop foil the whole way. Constant foil thins at tip to wafer, which should slice ok foward & swept.

For construction, I'm leaning toward the Flanksteak Flyer technique: ElmersWashed copypaper on foam meat tray, but skinning a little forming hardwood spars. Add some geometry of spar layout to consider the swept loading, and reinforced pivot disk area.

The pic represents cross section views, concept draft, not actual / proposed ribs.
Also pictured is a widened shoulder plate (green) for more unsweeping sq"
Hmm, perhapse taper in the "jet intake" to make the shoulder LE more effective...

BMatthews

At least look for one of the 70 to 100 in-oz servos so it has a fighting chance. Looking at the Hitec and Futaba sites I see that there are quite a few high torque servos that are right around 2 oz and have 100 or more in-oz of torque.

The standard servo may do the trick at 45 or so in-oz but what if it doesn't? If things start moving around and the servo draws it's stall torque then the system may fail due to low voltage and then it crashes. If you don't want to spring for a new servo for one use then at least plan on one regular sized servo for each panel. Expecting one to move both wings is just playing with fire IMHO.

KidEpoxy

Just occurred to me, the sweep is done for high speed flight, and foward for lowspeed, and the high speed is when there is more drag force pulling the wings back against the sweep servo...

What if I sprung the wings forward instead of servo?
play with the tension, but I could have a spring/rubber holding the wings forawrd in normal flight, and as speed & drag increase they just start sweeping back on their own against the spring. When the speed drops back down, they come forard on their own. Possibly I could put a servo as a inline cam type augment to assist the spring... or just the spring.

Anyhoo, I will first try to get it in the air with a fixxed wing mounted on the pivots, then we'll see about getting the sweep to sweep.

KidEpoxy

Grrr...

I moved and my Visa expired just before christmas, filled out form at bank, still waiting for a new visa- Can't order anything till it shows and it's killing me. Gonna have to head back to bank & crack some skulls.

I was living about 20mins from Sheldon's in San Jose, now I have to find a LHS in San Antonio, TX. Heading to Rebel in a few minutes to check them out.

Any help out there for a good / cheap LHS for a guy north of SA,TX ?

combatpigg

My Feedback: (3)

A sprung system would give the servo a constant high current draw when the wings are retracted. Why not just direct drive the wing panels with a single standard servo? The load on the servo during both modes of flight wouldn't be much. The key will be making a pivot joint that allows the wing to glide with ease as it moves in and out. Contact cementing something light and slippery [ like plastic sheet] to all rubbing surfaces will help. The actual pivot doesn't have to be anything other than 2 different slip fit sizes of brass tubing, with a #6 screw and nylock nut to clamp it all together.

RC_Pattern_Flyer

My Feedback: (1)

Kid.. welcome to SA. Another great hobby shop is @nd Chance hobbies on Wright Blvd in Converse off Pat Booker rd near he base.

If you need any help being new in town let me know.

Chuck Hochhalter

ps, love your design.

Cirrus has a high torque sevo at .9 oz in weight.

KidEpoxy

A sprung system would give the servo a constant high current draw when the wings are retracted. Why not just direct drive the wing panels with a single standard servo? The load on the servo during both modes of flight wouldn't be much...
My original musings about it was a single standard (read $10 hitec) servo, possible a pair if needing the extra torque. but that is way heavy, not too heavy for a twin SureStart, but too heavy for the wing 180-190"" I have in mind. As Bruce pointed out, constant stress on the servo is a bad thing. I thought up the sprung pivot to ease the load, then considered how that would just fight the servo too. That's why I'm now looking at a pure sprung sweep- get enough drag & they start sweeping back. Some well placed rubberband anchor points on the wing & fuse, maybe with a camover like a compund bow to let them stay swept ~20% easier than getting swept back. The rubber solution requires linking the wings as to make sure they sweep the same rate, no biggie. And the bennefit of a few light rubbers rather than a standard servo weight... ok, the real benefit is it's $10 cheaper, and this is a $14 Switchblade after all.

...making a pivot joint that allows the wing to glide with ease as it moves in and out...
the wing skin I have in mind is copypaper & Elmers wash- I did something like this a long time ago, and had a hard shell. depending on a lot of stuff, I may go with a shot of graphite /slicon /white lith to ease the rub... may be the elmers'ed plate will be fine plain.

ZoomZoom-RCU

[8D]Sounds cool.



ZZ.

KidEpoxy

Well I just drew some HS55 type servos & linkage in. The stabs are going to be full flying eleverons, and the tail I'm not sure of. I will start with Tailerons, and if the roll control is good, I may at some time go Vtail mix. Since I dont have any ailerons I want as much roll surface as I can get, so both Eleveron & Taileron to make sure this 0-dihedral plane will not go spiraling earthward.

I figure with shafts thru / into the "jet" top & bottom for the axle of the vtails, I'd want the linkage geometry to reduce throw for force gain. That will be good for the highspeed & for the whole surface turning, even though I have a ton of counterbalance in mind. Mid servo hole to 'outer' crank hole. Also, I have the vtail shafts canted outward, and the motors will be sticking up thru the 'jet nozzles' canted inward. This will help, but I may still need to trim some clearance off the bottm of the Vtails.

I'm planning on epoxy a short brass tube stub to the floor of the 'jet' for the vtail shaft to slip into for assembly & dissassembly, the linkage crank shouult hold the shaft to the roof of the 'jet'. Similar brass stubs for the stab axles, again the crank will hold them inboard & the fin/stab will hold them on the outside.

Going to have to make some test wing pannels of built vs bluefoam & skin. May go with a 4-5% thick wing if I can get decent results from the tests. Ballpark weight better be under 2 lb, but the pannels are short span, so we'll see what kind of stress they can take. Will mount in a jig like the shoulder & pin, then load them up with pennies along the span for wt.

With Vtail pitching up, the tails squeeze in at the rear & over/next to the eng cylinders. Will exhaust blast give me problems? Will having two cylinder nubs in the squeezed airstream give me problems? Will having the stabs close to the plane the wing is in, give me wing wash problems? Will typing with poor posture give me problems? This project is a headache already, and I haven't even bought the wood yet. One task at a time. I'll look at some of thsis other stuff once I test some wings.

Pic with the servos (may slide for balance), and I improved the fronts ofthe jets for better airflow. Also stretched the inboard ends of the wing pannels & located spar.

KidEpoxy

Drew an elevation view to go with the frontal & top views.
Drew some bulkheads / formers: Gonna notche the formers & fuse sides to lock together Eggcrate style so the same former will extend for the jets sides too. Planning to do the wet & bend on the fronts of the jets in 1/16 sheet, and morph from square inlet to octagon beveled tail ends. Drew thru jet airway & rear vents to blow past the engines.

I figure to use balsa for the formers mostly, but the F8 firewall one will be 1/16 Ply, 3/8" breather holes: Must have airflow thru jet to cool engine. Butts against 1/8x3/8 hardwood frame rails, 1/8x1/4 hardwood as stiffener & gussets across frame tops . Balsa block firewall shim at 3-4deg out.

The others will 1/16 balsa grain from side to side, 7/8" jet airflow hole, Vertical 1/16x1/4 stiffeners, Holes along bottom for pushronds

As for the foam wing pannel test- oops, I for some reason thought I would just but up 2 pieces of paper rather than get a large enough peice, so I have a faulty test piece... good thing I'm testing this proceedure A piece of 1/4" blue foam blew into the yard, & that's what I would like to use... but driving around I can't find the site it blew in from, and the blue at Home Deopt is the 3/8 stuff... makes me go hmmm.

D Bronk

KidE.I think you got a real, cool, project going here.I was, Thinking for your sweeping wings you might want to do something like this,in these drawings.."GEAR"(meshing teeth),your wings together.Pivots from Aluminum or Brass tubes(piece inside, of a piece).I should be working on my own stuff ,,,,,but..

KidEpoxy

With the plain tension aspect of a ruber sweep control, I can use one rubber pulling on a single string, that then Y into a string to each wing... if one wing gets stuck or has less drag forcing the sweep, the other wing can't keep going because of the Y to the Tesnsion string. The wt savings and ease of aplication looks appealing over the servo control & geared wing inners. Less Ply more Fly. I waas considering the gears, but would go with just another linkage to the servo from the other spar to beat friction & wt of gears.

Amazing how you wipped out them color drawings in no time flat... you must really be snowed in

KidEpoxy

Ok then, I finally broke down & cut something & took a pic. A crummy webcam pic, but a pic none the less.
um, maybe I should wait till I get something noteworthy accomplished next time, I just wanted to get something started & photod.

I cut a fuse side, Notched halfway for the former, and cut some formers with counter notches. Since the bluefoam scraps keeps blowing into my yard, .25" foam formers it is. I'll run some 1/16 sqr front & back for extra binding to the fuse sides. Right now I just slid the notched pieces together & pinned a jet side on the outside. Pic 2 you can see the next former notch and the breezeway holes in the blue formers jet area for blowthru pusher engine cooling