ArtHobby Thermic RES

[sblckwd]

Just finished and flew an ArtHobby 2.5 Thermic RES with conventional tail. Wondering what a good flying weight is for this ship. I'm around 800 grams right now and I suspect this is on the heavy side. Anyone have any experiance with this one?

[emersunn]

I have the non-RES thermic and it is 822 grams. I have trouble getting it back if it goes too far downwind, or if it gets specked out. It is very light for a 2.5M. I will be adding weight for better penetration and I suspect you will too, unless you live where there is little to no wind.

[wingsnapper]

Are either of you speaking of the new Poly version? I have been waiting to hear some details about it. Thanks JS

[sblckwd]

Yes it's the poly. Same wing as the others except you cut it to make the two dihedral breaks. I've only flown mine once so far. I need to get some more time on it before I can form any judgement. Seems to need speed in order to function. Guess thats 'cause of the narrow wing.
I had to put a bit over 2oz of lead in the nose and was thinking that might be excessive. I have the spoiler servos mounted rather far aft in the wings so I'm sure that contributes to the need for nose weight.

[wingsnapper]

Let me know about the next flights. Does it tend to tip stall? JS

[sblckwd]

One thing I was impressed with on the first flights was it's ability to make steep turns. One of the ways I would get it to land next to me was bring it back rather fast and then set it in a low tight circle until it ran out of energy (I think my spoilers are too small). It was pretty impressive so I think the dihedral set up is about right. But I need to put more time on it to be sure.

[sblckwd]

2nd set of flights today. Windy and gusty. Added 40.2 grams of weight (thats 4ea. 38 cal lead wad cutters + tape) to keep it heading into the wind.
Impressions are the rudder is way to small for those long wings. It's ok if you have a head of steam up but when you hit a wall of air and slow down the rudder is useless (conventional tail on this one) and the wings take control.
No tip stall no matter how hard I cranked it around.
The wind died down later and I took the weight off. Got a couple of great launches off my highstart then I stepped in a gopher hole, fell down and broke the boom off at the end of the fuselage. Oh well.

[emersunn]

wingsnapper: the one I have is not the poly

sbickwd: Ouch! that stinks. Mine was dragged by an errant horse/rider running through the winch line. still flys.

[sblckwd]

It's repaired and ready to go again. I had a dog eat the tail off one a while back. That took a while to repair! Landed too far away from me and he got there before I could. You're lucky all the horse did was drag yours.
I think if I can figure out how to keep the speed up I'm going to like this one. Might tweak the rudder/stab though.
I got this to fly while I build a new wing for my Majestic.

[sblckwd]

Did some more flying today. Turns out my spoilers work great. They're 25x200mm with the L.E. located 100mm forward of the T.E. Used HiTec 55s to actuate them. Used a Brents Electronics Servo Reverser on one so the throws would match.
Still have trouble getting the weight right. Emmersun, you were right. It's hard to fly against the wind.
The rudder is still problematic. Throwing some elevator in after the turn is initiated helps a lot but it sure is hard to get it to react to the initial rudder input.
Thermals are few and far between on the coast so wind is the way to get lift.

[wingsnapper]

Are you used to ailerons? Is this your first RE ship? The rudder problem really troubles me as a prospective buyer. Just have to have a plane that turns right cause I do a lot of cranking in those low level thermals. Thanks JS

[sblckwd]

I have 3 ships, all RE (2 are RES). Never tried ailerons. Ailerons and poly wings don't work. Keep in mind I've only flown this one for three sessions and I still need to get the speed and weight right. A bigger rudder/fin, if needed, is no big deal. A little balsa and some glue and presto it's done.

[Ollie]

Ailerons cause adverse yaw if not properly yaw compensated as in a coordinated turn. With adverse yaw and polyhedral you get adverse roll as well, which renders the ailerons less effective.

However, if adverse yaw is properly compensated, then ailerons work very well with polyhedral.

[Bernie Wolfard]

I built an Poly RES Thermic about 2 years ago. I never weighed it but it was really light for a 100” ship. I never ballasted it because it has such a wide speed range as it is. At slow speed it mushes but is very hard to stall. However it likes to go a little faster than mush speed to thermal well. At slow speed, like all RES ships, it turns slow but speed it up a bit and it will turn very fast. Put the nose down and the Thermic will scoot, especially compared to older RES designs.

I could never get my spoilers to work right because of the problems imbedding small servos in such a thin wing but I could land it pretty well without them. I am thinking of building another Thermic RES and would appreciate any info on how you are setting up Thermic spoilers.

Bernie

[sblckwd]

I put the LE of my spoilers 100mm from the TE of the wing and the inboard edge of the spoilers 200mm from the center joint of the inner wing panels. They are 25x200mm CF. They are held closed with a small rare earth magnet, from Radio Shack, on each TE corner. The hinge is clear packing tape. Servos are HiTec 55s buried in the wing forward of the cutout. One has a reverser circut so the throws will be the same. I just use the servo arm to lift the panel. The airstream and gravity close them and the magnets keep them closed. Simple. I mounted them as far aft in the wing as I could to get them away from critical airflow but couldn't get all the way back to 60% cord 'cause the wing gets to thin to house the servos. Ended up working quite well.

[Bernie Wolfard]

sblckwd; What are your spoilers made from? Sounds like you cut the wing out below them so they fit flush with the top of the wing or do they just sit on top? How is the servo connected?

Better yet do you have any pictures?

[sblckwd]

No pics. I'm probably the only person on the planet that doesn't own a digital camera.
I cut out the spruce wing covering for the spoilers. Use a long thin knife to separate it from the foam. The spoilers sit flush with the wing skin. Coat the exposed foam with epoxy. The sevos are glued into a cavity forward of the spoiler which was created by removing foam. The spoiler panels are 2 layers of CF. Servos are not hooked to the spoiler panels. The arm of the servo simply pushes against the bottom of the panel to open it. The little rare earth magnets from radio shack are very strong and do a great job of holding them closed.

[Bernie Wolfard]

sblckwd, thanks. What kind of servos did you get to fit inside the wing that are strong enough to overcome the magnets? I had a similar set up with the addition of a short piece of elastic cord from the end of the servo arm to the spoiler to keep the spoiler closed. I burned out 2 GWS Pico servos,:mad: I think because of the effort of keeping the panel closed. After that I taped the spoilers closed and adjusted my landings accordingly.

Bernie

[emersunn]

Flutterbug,

I blew up my Thermic wing on a windy launch. I want to re-build it poly like yours. Could you post the length of each panel and angle of each break? You do not have to give degrees, just give me mm off the tips to the workbench for each break.

Thanks in advance. Paul.:)

www.casl.net

[sblckwd]

Here's a scan of the Thremic Res wing plan.

[emersunn]

Perfect! thanks!

[emersunn]

OK I converted the old broken aileron wings into a slightly heavier poly version. It flies fine, but one problem: it wallows back and forth (dutch roll) I have the v-tail version, and the guys say I need to increase the rudder area. I think I will build a standard rudder and elevator. How do i calculate the size? can someone post the dimensions of a 2.5M tail section?

[Ollie]

You can't go wrong by following Dr. Drela's tail volume coefficient guidelines.

"Ch = (A_hori/A_wing) * (tail_arm/avg_wing_chord)
Cv = (A_vert/A_wing) * (tail_arm/avg_wing_span )

A well-sized tail will be in the range...
Ch = 0.35 - 0.50
Cv = 0.02 - 0.035
If the Ch and/or Cv are below the minimum values, the handling will suffer."

[emersunn]

Great.

[tclark]

There is also a DOS-based program on the CRRC ( www.charlesriverrc.org )site that computes coefficients based on your measurements of span, chord, tail arm, etc. This allows you to adjust the size of the tail and see how it will affect stability. I think it is called 'Design Assistant' or something like that. It was very helpful to me in computing polyhedral angles to improve one of my planes.

-Tracy

[sblckwd]

Here's the conventional tail.

[emersunn]

Again, thanks. I will soon have a very different Thermic!

[TailWind]

I'm seriously considering the Thermic for my next RES plane but wonder how strong the wing is? What kind of a spar does it have and could it be reinforced with CF to take a mild zoom off a winch launch?

Also, how easy is it to get the wiring to the spoiler servos?

[tknuutti]

The center panels have a 5mm-thick glass/balsa/glass spar with thin carbon caps.
No spar in tip panels.

The tip panel joints are probably the weakest points, 4mm rods in glass sleeves in short balsa boxes. One could add some glass over them for extra strength.

The wing panels are the same as in the aileron-version kit, so they have the wire channels cut in the foam - no trouble to wire the spoilers.

[TailWind]

Many thanks for the info. I've checked the posts and didn't see any reports of any problems with the wings. My preference is to use a Hi-Start rather than a winch and it looks like they will be able to take it OK.

From what I can see the AUW is around 30oz which makes the wing loading just under 7oz/sq. ft so it should be a great floater but with the ability to penetrate given the thin wing.

Looks like this is going to be my next RES plane!

[tknuutti]

Mine is only about 25.5 oz. AUW, poly-version with spoilers and v-tail. Kind of feels like flying a supersized handlaunch, it can make very tight turns :)
The cg in the plans is way on the noseheavy side, one can move it back 20mm or so.

Only complaint I had was the radiotray, its molded way too high for any servos to fit. One has to cut it open and place servos deeper inside. Not a big thing of course, just a little extra work...

[TailWind]

That makes the wing loading around 5.9 oz/sq. ft. , pretty impressive for a 100" wingspan plane. In fact you probably could hand launch it! Obviously moving the CG back helped with less nose weight.

I'm interested in knowing more about your spoilers. Did you have any problem fitting servos in the thin wing? What servos did you use? Did you use a linkage or just use the servo arm to push them open? What keeps them closed on launch, magnets?

Also, is the wing built as a three piece with removable tips or one piece?

[tknuutti]

I had no problems with the spoiler installation. The servos do need to be pretty thin though. I used some GWS servos, Naros I think, not the best servos, just had a couple laying around.
I used servoarms to push them open and small magnets keep 'em closed. This way there is no load on the servo when spoilers are closed. Linkages with small servos are kind of critical, as even a little binding in the closed position can easily burn the servo out.

The wing is 3-piece, wouldn't wanna haul a single piece 100" wing around..
The instructions had a neat way of cutting the polybreaks, cut just through the upper surface and foam, then sand the gap a little bigger and bend the tip up - the bottom surface will easily bend enough. Very easy to make the breaks and no alignment problems.

Like emersunn posted earlier the vertical tail area at least in the v-tail version is a little small for a 100" poly-wing. Very flyable, but shows tendency to dutch roll somewhat. Maybe conventional tail has a little more area, I haven't checked.

[TailWind]

Many thanks for all the valuable information. The Thermic is definitely top of the list for my next RES plane.

One last question! Is there any room to add some ballast if needed?

[tknuutti]

One could fit some ballast in the fuse under the wing, if you use a small enough receiver to keep it out of the way. Not too much space in the fuse though, its pretty narrow.

[TailWind]

Thanks. I contacted Art Hobby and Andre told me the Thermic RES is sold out and it will be 4 weeks before they receive the next shipment. I think it will be worth the wait!

FYI, he also emailed me some drawings and photos. One of the photos shows the Thermic with one polyhedral. The file name is ThermicRES25M_T.Knuuttila.jpg, could this be your plane?

[tknuutti]

Yeah, that would be mine.
Took a little shortcut and made only one polybreak..

[sblckwd]

Something you'll want to do, if you plan on using a Hi-Start for launching the Thrmic Res, is beef up the center wing joint.
I found out the hard way!
I'm sure I used overkill for the beef up but it will take a hard launch into the wind with no problem now.
I used epoxy mixed with mill fiber and Cab-O-Sil in place of the wooden blocks and also used a short peice of CF rod as a joiner in each cavity. I also epoxyed a small joiner of 1/8 ply to the center spar.
I used CF cloth to cover the bottom joint, instead of glass. A patch of CF on the top joint over the wing mounting screw area and a patch over the top of the LE . Then covered the top joint with glass cloth.
I also reinforced the area inside the pod, where the LE pin goes, with CF.
Sucker goes up like a bullet now.

[TailWind]

Thanks for the tip.

I was planning on glassing the center section to add some strength.

Any idea how much weight you added?

[sblckwd]

Nothing measureable and it's all center of mass anyway.

[Guilherme Pace]

Hi,

I decided to buy the Thermic, but before I do that I have a few questions...
Should I buy Poly or normal wings?
V-Tail or Convencional?
What servos to use? If I decide to adapt flaps what servos should I use for those?

[sblckwd]

Finally got some time and still air to set up my Thermic Res properly. Wow! the thing really flys now. Set the decalage by shiming the front of the wing up about 1/16 and back of the stab up 3/32. In other words the wing has a higher angle of attack and the stab less of an angle of attack. The CG is now at 78mm instead of the initial 65mm as called out on the plans. Tow hook is still at 60mm but could probably be moved back a few mm. Didn't have time to experiment with that yet. With the elevator dead neutral it has a shallow recovery from a high speed dive. Flys hands off with neutral elevator. Stays up in the slightest breeze and handles absolutely great.

[ChuckW]

Just ordered a thermic RES poly to go along with my Boar 2M. Is everyone still happy with the thermic? Any new mods to discuss?
I actally plan to use a larger fin / rudder and might go with a full flying stab. Any comments / suggestions?