evlwevl-RCU

Hello all

I'm finally getting ready to complete the building of my 99" Pulsar XL. I'm setting it up for full house. I plan on using it for the windier days at our local slope and it will probably not be seeing a winch anytime soon. I dont know what to expect in performance or flight characteristics yet. It is an S3021 airfoil and has a dihedral of about 3 degrees. It is a balsa sheeted foam core wing with a hardwood spars. Does anyone out there know if this is the kind of plane that will do or even handle rolls or loops? or is it more of a floater?

Now that you know what I have, heres my real question.....
I want to know if I should set up individual aileron servos to work with differential or just use one servo for both ailerons and skip the differential. What kind of performance can I expect with either setup?

I'd really appriciate any help anyone has to offer

Thanks
Rob

BMatthews

If you've got coupled rudder or separate rudder control then differential is sorta optional.

But if it's only aileron and elevator I'd use some differential. It'll prevent any unwanted adverse yaw during turn entries.

You can actually get the differential with one servo using the "old way" of doing it with control system geometry. It involves offset linkages that use the differences in the rotary to linear conversion that takes place at the output wheel and control horns and any bellcranks you may have in the system.

It's just that it's so easy to do it with the computer radio these days that sometimes people forget that the other way is possible too.

bjaffee

I'd use at least some differential on a plane with that large a span. Even if you don't use diff, I'd still use two aileron servos on a plane of that size, especially on the slope, where it might end up going pretty fast. It also allows you to do stuff like camber and flaperon/spoileron if you have a computer radio.

I have to ask though, if you build it full house (which presumably means flaps), how would you get away with just one aileron servo?

As for the airfoil, I think the 3021 is more of a thermal then a slope airfoil airfoil, but there's no reason why it still can't be aerobatic.

evlwevl-RCU

Thanks for the help.
As far as the servo setup for this plane. The plans are old and it shows all servos installed in the fuse rather then in the wing.

1 servo controls left/right aileron using a push/pull servo wheel type horn mounted in the fuse using flexible control rods glued into the foam core.

1 servo controls both flaps using a centrally mounted bellcrank

1 servo controls the elevator

1 servo controls the rudder

Now that I think about it, 2 servos for the aileron just make better sense.

As far as my experience with differential, I have a small sloper 50" balsa talon and I set that up with aileron diff using to micro servos in the wing however it always has a tendency to roll very weird. The entire plane does this strange corkscrew pattern when I roll it, its not a pretty sight. Is that the effect of aileron differential? or is it the effect of the shape of the wing and type of plane im flying?

Thanks

bjaffee

Could be you had too much differential on the Talon. I don't think any models smaller then 50" need any differential at all. At 60" you start needing some differential, depending on the plane.

Differential is going to be more of a benefit as you move to higher aspect ratio wings, such as the bigger gliders often have.

kestrel53065

Perhaps someone could clear this up. Aileron differential. When it is said that there is 100% differential. Does that mean that the up and down travel are the same? Or would that be zero differential? Because there is no "difference" in the two measurements. Then, is 80% differential, (eg) 1" up and .8" down.

Just one of those things that the terminology seems to make it unclear. To me anyway.

Thank you for your time.

drone

0% differential is the "normal" mode.
50% differential is full up and 50% down.
100% differential is "split" mode with full up and NO down.

good diagrams on page 30 of the JR PCM10X manual.

esport33

My Feedback: (2)

so... let me get this right. you're setting a plane up using one aileron servo and you're asking about aileron diff? umm what am I missing here? shed the light here... how is that going to happen? PS the talon does'nt need a bit of diff to fly well. just minimal throws will get it more efficiant. my 3 cents

bjaffee

You can get differential with a single servo by using an angled, rather then straight servo arm. For example, if the servo is mounted on the top of the wing, you would use a two sided servo arm that had each side angled slightly backwards, rather then being a straight line. With this geometry, you get less actual travel when the servo pushes the aileron down versus when it pulls the other aileron up.

This is the way people did it before computer radios.

(hope I didn't get that backwards)

BMatthews

Sounds right to me.

The idea of differential through linkages only uses the properties of the servo output wheel moving in a circle and being converted to linear throw.

Normally we set our pushrods so they sit in the hole that is perpendicular to the wheel center. But if you offset it by, say, 45 degrees and then look at the amount of LINEAR COMPONENT to the arcs you'll find that you get more throw as the wheel tries to move towards the perpendicular position than it does when it moves towards the all points in line position.

You can also get the same action by using a 45 or 60 degree bellcrank in the wing(for ailerons usually) or by angling the control horn. Combining two or more sets of angles in this manner at different points in the control system will multiply the differential effect.

esport33

My Feedback: (2)

and it's possiable to get a fixed differential that way. can't see having much adjustability on the degree of differential.. unless you're making control horns. glad I have a computer radio nowb

bjaffee

I think thats why the servo makers still include the big wheel servo arms. It's so you can create any type of servo arm you want.

esport33

My Feedback: (2)

they work for pull pull set up's if you're in a pinch too

rogerflies

My Feedback: (3)

Find someone with plans for the Lovesong. It had differential AND crow with a single servo mounted in the front of the fuse. The same servo could be used to drive the rudder, too. Very light, easily adjusted, and it worked like a champ.

I fondly remember talking to Bob when I placed the order for my second kit. I was telling him about picking up a thermal at head height and working it up till my Lovesong was just a speck. He was just as thrilled about the experience as I was. A genius, and a great guy, too.

Somebody used to make adjustable bellcranks that had a ratchet so the arms could be placed at something other than a 90 degree angle. They could be used with a single servo in the center of the wing to get differential on the ailerons.

Roger

SST

My Feedback: (2)

I put differential in everything from 1/2a to 3-meter stuff. If the airframe really didn't need it because of size, I figure what did it hurt?

KJMDES

The Talon does roll better and react better in tight turns with about 15% differential. This depends on how well you set up the wing to begin with, but if you've got consistant washout (about 8mm) and the wing is clean, you should have a fairly well behaved ship. Experiment with the differential, but you don't need to exceed 20%

This is a reprint from another forum....

Sorry about the short post. I was off to France in the morning and bit tight for time. Relaxing in Italy now, starring at a slope to-die-for and wondering why I left the ship in Scotland.

I thought it was about time to post a little treatment on the Talons history and some inside skinny. And also, to give you the direct URL for the SuperTalon. Go here and then click on New Designs for 2004http://www.kjmdesign.com/kjm_m04_rc.htm. Which, by the way, was of little or no interest to Dynaflite. Not that it’s anything groundbreaking. Seems I had been laboring under the false assumption that there was some interest in an upgraded, high performance alternative. Unfortunately, the ARF scene has pretty much destroyed the kit market as we knew it. This wouldn’t bother me so much if it weren’t for the shear mass of total crap available. Don’t get me wrong, there are some nice ships out there, but they are expensive and are rarely domestic. Seems we are destined to hand this market overseas as well. If this doesn’t bother you, maybe it should. The implications are broader than just loosing another creative asset. It has forced the small domestic manufacturers (who once produced high quality kits) to jump ship and try to compete by consolidating with other junk suppliers. Stripping the supply of building material is just one consequence. Filling trash bins is another. OK, enough said.

Back in 1984, an old friend, Bruce Lewis, and myself, were heavily involved in designing and building RC sailplanes. Bruce was actually the catalyst for many of us getting involved in the sport back in the mid-seventies. Bruce is a master at most anything he tackles and I, well, I’ve got my points.

So, here we are in ’85, I’ve started a new company, Laminar Research, and we are finishing up a new design called the LR-50. A foam and glass V-tail ship that was designed from the get-go to fit in a trunk, assembled. We generally flew at Sunset beach and we packed a lot of big stuff in. Bruce had a competition 2M slope ship design, and so did I. Mine seemed a better starting point to scale down a new ship. So we put our heads together and came up with the new ship. Testing went well and after a year and a half, we developed what was one of the first successful V-tails around. Between a foil section unique to our designs and exhaustive testing of angles, sweep, etc., we ended up with a very solid performer. I have no idea how many LR-50’s we produced, but there were a few dozen to be sure.

Sometime around ’87, I was prompted to design a built-up version of the ship and in that same year I was on a hill in Cerritos, California, testing the proto when someone walked over and asked me some pointed questions about the design. It turned out to be Bob Martin, and we struck a deal to put it into production. I never quite knew if he was pulling a fast one, or genuinely believed that the Talon would not be much of a seller, but, in any event, my royalties were limited to two thousand units. I’m told sales are somewhere over a bucket-load of units at this point. The other thing that was a bit odd at the time was Bobs insistence that I design a conventional tail. We compromised by having two options

OK, lets move onto the nitty-gritty. When I received my first sample production kits, I immediately went ballistic. My original plans and sample kits delivered to Bob had specified spruce spars. He substituted balsa. There were also 1/64th ply doublers running full length, on the inside of the two large fuselage side strakes. The main foil section was also modified. I immediately ripped off a post to all the BBS sites and my own site at the South Bay Soaring Society, listing these changes and the fixes. The final insult came when he sold the kit rights to Dynaflite. The plans now credited him with the design. It took awhile, but now there is suppose to be a change to the plans, sticker, or something to correct that bit of plagiarism.

I will soon put together a list of mods that I have made to the original ship. The SuperTalon is basically the same ship with a 60 inch span, ballast tube and four servo wing. It’s a goer. Too bad Dynaflite is too wrapped up in ARF’s to be interested. Or, for that matter, upgrading the Die-crunch parts. Or even, selecting balsa that is remotely close in weight, side to side. I received two sample kits from them last year and literally thru away half the sheets in order to get one ships worth of semi-matching parts. It’s a sad state of affairs. However, I would suggest that if anything is going to happen regarding kit quality, be it the Talon, or any other kit, you need to email Kevin Burner at Great Planes and lobby for the change.

So there you have it. Good flying
Kevin J. McDonald

Addendum: Answer to where the Talons shape came from
The lines for the Talon were most likely derived from my backgroung in Yacht design and construction. At least thats were my wood sense came from. The ME 262 influenced the shape a bit and the fact that I believed there was both a minor lift and a major structural advantage to the shape. Its pretty common to design in some pre-stress by torturing planks or strakes. In the Talons case, this proved very effective. But, as mentioned above, Bob opted to eleminate the ply doublers, thereby compromising the overall strength.

I don't have much here on the SuperTalon. Sorry. If Hobbico doesn't opt to produce it, it may become history anyway. Who knows. If you go to my site, you'll notice a conversion booklet and info on the kit. I am sorry, but the booklet and kit are not available at this time. I'll keep everyone posted. If you really want the kit, you should email [email protected] and put "Please produce the SuperTalon" in the subject line.

Cheers,
Kevin