TopModel Samsara 3.2 meter glider, build thread on Aloft's Forum.

[Konrad]

Flight report.
With the aileron to flap mix set at 20% using Mike Shellmin's Open TX templet "E-Soar Plus V3" I now get good aileron (roll) control.
http://rc-soar.com/opentx/setups/esoarplus/index.htm

The Samsara with the CofG set at 91mm (95mm April 2019) stalls straight ahead. I also don't need any motor to elevator compensation with the CofG at this setting. The rudder roll coupling is very benign making cross controls (rudder aileron) very nice while flying tight thermal coring circles.

The elevator response is very nice!

When coming in under full crow, with the aileron flap mix set at "0" (dead) in full crow the roll response is now good. (I still like to manually add rudder).

Set up values are as follows () factory recommended values:
Elevator:
Up, 12mm (17mm)
Down, 17mm (17mm)

Rudder:
50mm (50mm)

Ailerons:
Up, 22mm (25mm) [24mm up April 2019)
Down, 11mm (14mm)
Crow, 13mm (18mm)

Flaps:
Aileron, Up 10mm, Down 8mm (N/A) [10mm up&down April 2019]
Reflex, Up 3mm (3mm)
Camber, Down 4mm (5mm)
Crow, Down 80° (70mm) [Down 90° April 2019]

Flap servo arms 12mm long
Aileron servo arms 6mm long

Thrust lines are perfect when centering the firewall to the factory cut nose opening.

The airfoil responds OK to camber changing. Reflex response is not as great as I've come to expect with other popular airfoils.

The long fuselage magnifies, makes it easy to read, the aircraft's attitude changes to the air's movement. It is well worth the added mass needed to balance that tail, that is way out on the end of the tail boom! At 2.06KG (1.965 kg April 2019) the Samsara is no light weight by today's F5J standards. But she is very responsive to the air. That is what we are really concerned with when we talk about wing loading. I'm really liking the 1.8 meter fuselage compared to the standard 1.5meter fuselage that is standard in this class of model.

Airframe report.
Like I said I really like the fuselage. It is long and more than adequately reinforced with carbon to make the boom stiff. There is extra carbon around the elevator rocker opening, this opening is not the week point in the fuselage. The fuselage weak point is in the battery opening. Add some carbon tow hoops that span the fuselage seams. With the tail post installed the vertical fin is rigid making it more than adequate as a mounting platform for the tail servos.

I like that TopModels has left adequate flange material around the wing and battery openings to allow one to size the flange as we see fit. I choose a 5mm wide flange as there is a lot of stiffening carbon to be found just under these flanges.
The fuselage comes with the elevator rocker pin bore pre drilled. Also the wing hold downs are glued in at the factory but not pre-drilled for the hold down bolts.
(The fuselage is why I purchased Samsara).
The canopy should not be made of carbon in the modern age of 2.4 gHz.

The wings are a mixed bag, but overall more than adequate.
My main complaint is that the wing hold downs are misplaced by 2mm or 3mm forcing one to have to place a threaded insert dangerously close to the fuselage side in the wing fairing.

I don't like rib cap strips They just add work during building of the wing. The film covering actually offers more than enough lateral support to the rib. I hope TopModel gets rid of these. The labor credit from the removal of the cap strips should be applied to making the ailerons hollow.

The bottom of the wings (transparent covering) should have a lot more color to aid in high altitude visibility.

The glass wing joiners are far too heavy for this class of glider!

The spar is great! It is made up of 2 spruce spars with a full width shear web between them. On ether side there are 3mm shear webs that come up fore and aft and are glued to the side of the spruce spars. These side shear webs are reinforced with 50gram glass cloth to keep them from splitting as the wing flexes. I forgot to mention that there are also 0.3 thick carbon strips just inside the spruce spars!

Now my particular kit appears to have had a soft center section wing panel. As shown by the center panel going into flutter far too early (less than double the stall speed). I think most of this can be attributed to the poor glues (hot glue) used to assemble the wings.

My rudder had the hard point misplaced for the rudder horn.

General quality issues.
The holes in the control horns are too small for the supplied clevis pins. Wing hold down through holes are misplaced, The film covering over lap is too large. The wings are built with soft hot glue, and too much of it at that (The spar looks not to be built with this glue). Wing joining rod made from the wrong material (heavy). The canopy is made out of the wrong material. Hard point for rudder horn misplaced.

Now comes the difficult part. That is training the owner/pilot to get the most out of the Samsara .

 

[Konrad]

Flew the Samsara for another 2 hours. This time there was a lot of thermal activity. Actually had difficulty getting out of a few thermals. May need to work on the speed mode programing (reflex) to get the Samsara to move faster (way from thermals).

She signals lift great. She may be the best signaling ship I've ever thermaled. Really love the long fuselage!

Roll rate is now OK to good. I upped the aileron flap ratio to 35% and adjusted the differential so that the flaps as ailerons are going 1:1 up and down.

Adjusted the elevator crow comp curve so that 75% of this comp happens in the first 1/4 of crow stick movement. The last 25% of the curve is pretty linear over the rest of the 75% stick movement.

I did get the wings to flutter but I really had to try*. I only got the outer tips to flutter. The reworked center section did not flutter. All planes have a do not excced velosity. With the reworked center section this is now well outside the speed we should see while hunting and playing with thermals.

* Please recall that I'm using Ultracoat light on the bottom of the wing tip panels. This may or may not be a contributing factor in the tips going into flutter at the speed they did.

 

[Konrad]

Jim I think you want to post that here.
https://forum.alofthobbies.com/inde...rge-a-hole-and-keep-the-hole-in-position.185/

Gun drills are used for deep boring where the flutes can be used to guide the cutting edge of the drill. Generally not used with thin materials.
https://en.wikipedia.org/wiki/Gun_drill

True one wouldnt want to use a utility reamer (as shown for final sizing). As mentioned a barrel reamer would be better for hand sizing the hole.

 

[Konrad]

Expensive tooling, that is the point. While you and I have thousands of dollars of tooling in our tool boxes. The average modeler does not. The use of twist drills is counter productive to having any hope of keeping the wing aligned after enlarging the hole for the threaded insert. A utility reamer will keep the hole in position while opening it up and is a readily available from ones local hardware store.

While I haven't mentioned what are acceptable tolerances, the work Jim is doing sizing the holes for oversized rivets is rather demanding. Remember that a rivets' holding power is the expansion of the shank to fill the hole. So the hole needs to be on size, round and in position.

 

[Konrad]

Please let us know about these UV Adhesives and suppliers. This would make another great how to post. I'm thinking of all the time (7 hours) I could have saved on this model to install the rudder post.

 

[Konrad]

Flew another 2 hours with the Samsara, getting to like her more and more. Still moving the Center of Gravity aft, but the biggest change this time out was in the reflex setting of the ailerons and flaps. Today I was NOT able to get the wings to flutter. I attribute some of this to the reflexing of the airfoil at speed. (The pitching moment of the airfoil is greatly reduced in reflex, speed mode. This reduces twist on the spar).

I have to admit its been decades since I last flew (had) a 3 plus meter gas bag glider. It is taking me a bit of time to learn how to control the altitude speed and sink rate with this type of model. I'm so pleased with the crow function. It opens up a whole world of control options that the classic RES ship of the 70's just didn't have. And with a modern airfoil (one that doesn't look like a banana) the modern gas bag can still move around the sky looking for lift, or as was the case today move getting out of lift.

If you are looking for a gas bag to rekindle some spark from your youth? Look at the Samsara as a good model to rekindle what we remember from ships like the Windfrees and Wanders. Unlike the Radian XL the Samsara is much more durable and should you have an issue, rather easy to correct as it is built with classic model airplane materials. It is a wooden wonder so don't be looking for the strength of a carbon ship.

Today I speced her three time. To get her down I flew tangent to the thermal in speed mode. One time I tried full crow full rudder and full aileron and full up. The Samsara just went into a slow spin never gaining much speed. If I had an RES ship I think I would have had to fly inverted if I hoped to get out of those thermals and keep the wings on. With the Samsara one has a lot more control.

Flew the Samsara back to back with my Multiplex Heron (another 6 servo ship) I'm glad to report that the Samsara makes the great foam glider that is the Heron look like a brick. There is nothing wrong with the Heron being the best 2.6 meter class (2.4 meter actually) foamy there is, but it is still a foamy. Now for a little less than double the price of a fully set up Heron the Samsara offers more that double the performance!

If looking to move away from the 2 meter entry level foamies, many of the TopModel gliders offer a low cost look into performance gliders.

 

[Konrad]

If I was to build another Samsara, and I might very well, I'd do a few things differently.

First I'd go for smaller (lighter) servos, as the Samsara really can't build up speed like a carbon ship. The tail servos would both be the KST X08, the ailerons would have KST X08 servos and the flaps would have KST 135.
To get even more weight out of the tail (read need less nose weight) I would use 26AWG on all 4 servo leads to the back servos.
https://alofthobbies.com/kst-x08h-servo-2-8kg-38-oz-in-09-sec-8-grams-wide-voltage.html
https://alofthobbies.com/kst-ds135mg.html
https://alofthobbies.com/servo-wire.html

I'd look for a heavier motor as this would put the mass further out on the moment arm. (I'm thinking of an Aveox 1415-3Y) With a heavier motor I could drop to a lighter battery. No need to have more than 600 watts of power.

With this change in equipment I should be able to get the Samsara to weigh less than 2 kg.

I would still use a common bus bar for all my servo extensions in the wing and in the fuselage. I would still add some carbon hoops across the fuselage part lines at ether end of the canopy opening. And I'd change out the carbon canopy for a fiberglass one.

 

[Konrad]

Flew the Samsara for another 2 hours. Specked her out 3 time never got her to flutter.

I lost some weight going to an EF-1 battery (335 gram and pushing it all the way forward to keep the balance (91mm maybe 92mm). AUW is 2.02KG. I think this weight loss is pushing the flutter speed further away from the stall speed. I think I can now go 4 times the stall speed and not flutter the wings. I did loops and rolls, no high speed dive and she was well-mannered.

I think the roll rate is unacceptable at the low setting in the manual for the aileron throw without the flap mix. Even adding aileron to flap mix has issues. One needs to make sure that one maintains the aileron differential even in the flaps. That is the flaps as ailerons move up more than down. To maintain this differential I can only mix my flaps as ailerons at about 25% to 30%.

I'm thinking of re-rigging my flaps to allow more aileron function. If I do this I'll take the opportunity to re servo the flaps with a lighter set of servos, I'm thinking KST mini X-10 or even KST X0-8. Yes, the Samsara doesn't go fast enough as to tax the X0-8 servo.

With the prop I'm using 17x9 I'm only drawing 37 amps I'm thinking of dropping down to a Castle Creation Talon 35. I may need to add a few grams to the nose near the motor, but should actually lower the weight.

With a new set of flap servos and smaller ESC I should get below 2Kg. I could make a lighter rear wiring loom, but I'm not quite that rabid in my thinking that I need to loose weight.

Had the elevator pivot back out. Do glue it in or at least tape both sides of the pin hole and check it each time before flight!

Edit
The mini X-10 is out if using the CC Talon 35 ESC as the ESC has a low voltage BEC.

 

[Konrad]

I've been flying the Samsara a lot over the last 6 months. In fact I take her with me every time I'm out flat land flying.
I'd like to give an assessment of the bird now that she and I have had some time to get acquainted.

I really like the long 1.8 meter fuselage. This is well worth the shipping cost! The way the fuselage signals lift is almost as good as many 4 meter ships.

After the initial set up issues, the wings have been trouble free. I think a lot of this can be attributed to proper radio set up. I use a bit of reflex (aileron and flaps up) in all my speed runs jumping from thermal to thermal. I also don't fly the Samsara like a high dollar molded ships. After all the wings are wooden with a bit (very little) carbon.

I have to admit I'm a bit surprised at how much aileron differential in required. I'd have thought that the vertical fin being so far aft would have controlled the adverse yaw more than it does. I have to admit I do like a bit of adverse yaw in my thermal gliders. I like to control this with the proper rudder inputs.

Love how this ship cores a thermal. I attribute a lot of this to the long fuselage but also to the rather flat wings. This will be an issue for guys coming from an RES background. To properly core a thermal with the Samsara you will use the ailerons and rudder to find the center. Then once coring the thermal you will need to apply opposite aileron to flatten out the bank. This is where I find the adverse yaw helps align the fuselage to the relative wind as the Samsara is circling in (fuselage slip angle is greatly reduced). While this style of glider does put a bit more pilot load on the pilot the benefits are that when you get the glider set up coring the thermal the drag is minimized.

The only operational issue I've found is the the bottom of the wings are easily damaged at the third dihedral break if you aren't flying off a sod farm. During the winter maintenance I'll have to add some kind of armor to this area.

I've also found that the roll rate is a bit on the low side. This is to be expected as the Samsara is a light ship and flys rather slowly. This slow flight makes powerful ailerons response rather difficult. So while I'm complaining a bit about the roll rate. It actually is a good indication that the Samsara flies real nice and slow just what we want in a thermal hunter!

Some misconceptions about this model are that she builds tail heavy. Not so, with 8 to 9 gram tail servos it is easy to meet the 90mm to 92mm balance point with no added nose weight using a 335 gram battery. I think with the heavier (recommended) motor it will be even easier to meet the Center of Gravity and get the AUW below 2Kg. I'm using a rather light Hacker A30-18-M 6.7:1 motor (105 gram). This is why I need a heavy 335 gram battery. (With a heavier motor I can use a lighter battery getting the AUW weight below 2 kg. I'm also carrying 50 grams of repair weight).

I've read that some guys are forsaking the rudder servo in hopes of saving weight, This is a very bad idea, sacrificing controllability for weight. And with the wings of the Samsara you need rudder inputs if you hope to gain any efficiency in coring out the thermal. While weight is an enemy of gliders it is the least of the enemies a glider has to address. Drag and controllability are far more important than weight loss! With 2 servos in the tail it is still easy to get the flying weight down to 2kg or even lower.

CAUTION: WITHOUT RUDDER INPUTS, THE SAMSARA WILL FLY LIKE A PIG!

If you have seen my landing you can attest to the fact that the fuselage is more than stiff enough and that the elevator rocker is more than adequate for the job.

While 2 kg doesn't make the Samsara an effective FAI F5J model it is a nice model in the style of an F5J ship. Lets be honest here, it only cost 1/5 the price of an F5J model. And at that price point with all 7 channel at your disposal it is a great ship that can give the full blown F5J ships a run for their money.

The performance price point of the Samsara makes her a great entry level ship to full house thermal flying. If you are bored with the bent winged (RES) type ships it might be time to move up to a full house ship. The Samsara is great for experimenting with learning how to set up (program) such a ship.

All the best,
Konrad

 

[Wayne]

Thanks for the update! Good stuff!

 

[Konrad]

I've been reading a lot of misinformation about this great Top Model 1.8 meter long fuselage.
https://www.rcgroups.com/forums/showpost.php?p=40971931&postcount=9

While I don't know what constraints this RCG poster had. But I can tell you that the aft servos are working great! I've had the elevator servo in and out 1/2 a dozen times fine tuning the elevator response. ( I don't like to use trim offsets to make up for improper linkage geometry).

Please note that the CofG shown in the manual is way way too nose heavy. Aim for about 92mm as the desired balance point for the Samsara. I think the Element has the CofG at about 117mm.

 

[Konrad]

Woo, just found this photo on the web (I annotated it). It looks like this poster is having the same issue with his Topmodel "Element" as I had with my Samsara. (See post 81 of this thread)

Wayne, have you invited Topmodel to look at this thread? I think it would help them greatly with the few production issue we see with this family of model.

All the best,
Konrad

 

[Konrad]

One of the ways I can tell if a guy actually likes his model is by way he maintains it.

As I've said earlier I take this Samsara with me every time I go out and flat land soar. OK, no big deal, you might say it is the only thermal glider I have. To give you all a better indication of how much I like the Samsara I've just spent the time and money to change out the KST DS 225 MG servos for a set of KST XO-8 plus servos with output shaft supported mounts.

The KST DS 225 MG servos really were way over kill. When I was first building this Samsara the XO-8 plus wasn't out on the market. Also KST wasn't selling the gear sets for the XO-8 servo as a replacement item. I didn't think the standard XO-8 was up to the task and that there were no gear sets made the XO-8 unsuitable as a flap servo. But now less than a year later the XO-8 plus with spare gear sets and that servo mount that adds a support to the output shaft are available at Aloft Hobbies, the XO-8 plus looks viable as a flap servo. So while I have the Samsara down for her winter maintenance I thought I'd upgrade the gal.

I hope the upgrade will have at least two benefits. First will be a reduction of 34 grams. This will bring my Samsara's flying weight down to 2kg. But what I hope to see is a wing that is a little more responsive at signaling lift. And as I'm removing mass aft of the spar, I should move the flutter speed higher. (I haven't had any problem with flutter after the initial radio programing issues)

I have to admit I'm a bit concerned with the small gears in the XO-8 plus as a flap servo. But I really think the added output shaft support should contribute a lot to the durability of the gear train on these small servos.
https://alofthobbies.com/kst-x08h.html
https://alofthobbies.com/kst-x08-gear-set.html
https://alofthobbies.com/external-bushing-servo-tray-for-kst.html

All the best,
Konrad

P.S.
The XO-8 gears are NOT suitable for use on the Samsara's flaps.

 

[Wayne]

Wow, you are fast.. I usually collect parts and let them sit in bags on my bench for way too long!

 

[Konrad]

What???

You forget I still have a dozen gliders I bought from Aloft Hobbies within the last year that haven't seen the light of day.

My problem is that I start a lot of projects but rarely finish them in less than 5 years. This was a maintinance upgrade. If the rains stop, and I wanted a ship to fly, that means bite the bullet and get the job done!

You know it took the better part of a day to fit and rig the new servos and support mount. So really I'm slow.

It was just that this time I was motivated.

(I had stopped by Aloft Hobbies on Friday to gathered up a lot of servo mounting stuff; to keep me amused during the rainy 3 day weekend).

All the best,
Konrad

 

[Konrad]

Looking for input from the Aloft forum hive mind.

Now that I've re-servoed the flaps I'm looking to get more roll rate (one of the few complaints I have). While recallibrating the servo I've added a lot more up aileron. I'm trying to get at least 1/3 as much up aileron in the flaps as I have in the ailerons. ( I think I'll need to re tape the flaps and bevel the flaps for more clearance). I want to get the same (equal movement) downward as I have upward movement. That is have no differential in the flaps as ailerons.

My observation is that with the flaps coupled as ailerons I get a bit of downward pitch, if I have aileron differential in the flaps. What scares me is that on my maiden flights I actually had reverse differential in the flaps and could NOT turn the ship if the flaps where coupled as ailerons.

As of now I have a lot of flap differential trying to control the adverse yaw. But with the clearance issue limiting the upward flap movement the amount of actual aileron flap mix is very limited.

I'm trying to maximize the roll rate from the flaps. While at the same time controlling adverse yaw. Right now my attempt at controlling adverse yaw in the aileron flap mix with flap differential is causing a bit of pitch down coupling.

Am I thinking correctly, that the differential in the flap aileron mix is acting like a bit of camber reflex causing the net airflow over the stab to pitch the ship down?

 

[purview]

reverse differential in the flaps and could NOT turn the ship if the flaps where coupled as ailerons

I've done this for the thermaling task. It works, but it is not as response as the classic differential (more up less down). I liked the way it flies in a thermal with some more or less deflection that causes the overall "down movement" of a ship.

the differential in the flap aileron mix is acting like a bit of camber reflex causing

I know that I didnt understand you properly. The best solution I realized nowadays is to set the differential of the ailerons without the flaps. Then I couple the flaps to aileron. Flap goes exactly the same way down with the AIL and the upward movement is increasing the roll authority. My observation is that it is not affecting pitch; axis only roll (the flight line axi) if AIL diff previously set to minimize effexts on other axes.

There are some reasonable thoughts to try to set up the AIL DIFF in a way* that it induces some pitching moment: upwards or downwards -> how u can do this? For which flying task it is recommended? You can increase the roll rate if you move more than 2 servos on a 4 servo wing.

Happily Yours
Chris

*and in the next step also coupled with the rudder to a specific task or flying style (more or less to cover several effects to tune the flight path properly)

 

[Haoyang Wang]

Set the differential to maintain the pitch, and use aileron->rudder mix to rid of adverse yaw.

 

[Konrad]

So you concur with my assessment that flap differential can influence pitch trim? I have to admit that this is the first 4 servo wing gas bag I've tried to trim (write a program). With faster heavier ships I don't like aileron rudder mix. I tend to core out my thermals with a bit of opposite rudder. That is after finding the core of the thermal. I like to flatten the bank with the ailerons. I then add rudder to maintain the circle and align the fuselage to the relative wind. This results in me coring a thermal with cross controls (actually opposite ailerons).

 

[Haoyang Wang]

Yes, both aileron and flap differentials can affect pitch. I like to trim the differential so that it won’t affect pitch, thus makes the roll axial.

The amount of aileron->rudder mix is just enough to eliminate the adverse yaw, and make the roll axial. The rudder mix is not for turning with one stick.

Use aileron differential to control the pitch, and rudder to control the yaw.