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

[bat68be]

I also have the elevator servo installed under the wing. This is a very easy simple setup with light carbon 6mm tube. Quality Savox servo. Zero slop in the system.

Next time I order rc stuff, I will add the 8mm carbon wing joiner in my order.

I did setup with EWD 1,5-2°.
But I'm still a little bit up in the elevator trim. (14 clicks up on Spektrum TX).
Maybe I can move the cg more aft (but I'm happy at 90mm) or the 14 clicks up trim is needed to compensate the negative flap position in flight due to slop in the servo. Only way to find out is to install a mini camera on the wing.
Tomorrow I'll check the 20mm distance at the elevator bed to compare with your glider.

 

[Konrad]

We can discuss the rigidity of a 2mm x 5cm steel pushrod vs a 6mm x 105cm carbon push rod. Then there are the thermal stability issues with these long structures (glass tail boom and carbon push rod).

Also I can't think that a 6mm carbon push rod would be any lighter than one copper 26AWG servo signal wire.

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

Wow, Konrad - do you know anything about gynecology?;) Or like me - just willing to have a go? Nice job Dude!:cool: Doc.

forum.alofthobbies.com

All that aside, I'm impressed you got the mass down to 2050 grams with the under wing elevator servo..

I'm lost by this; "But I'm still a little bit up in the elevator trim. (14 clicks up on Spektrum TX)".
After you get the basic trim set don't you adjust your linkage so that the servo arm is 90° to the push rod? What is this 14 clicks up all about?

I don't care how my ship looks but rather how she responds. Try different aileron and flap rigging to see which one you like best. Who really cares what the camera sees. You might like how a reflexed airfoil performs (I know not likely)?

 

[bat68be]

My elevator system is rock solid. I tried a 4mm carbon tube, but that was not stiff enough (without support somewhere in the middle). 6mm is perfect for the job. As mentioned several times before: it is not a hotliner that flies at 200mph. At the speed this thing is flying, I don't think the glass fuselage is moving at all.
The only gain with servo installation in the tail is the difference in weight between carbon tube and awg cable... a few gramm.
I never said my setup is the lightest, but for sure the different positions of elevator servo is neglectable. Some people think it makes a huge difference... I don't!

About my "14 clicks".
If you are at the correct cg and correct EWD, the glider should fly perfect from the first time, without adjusting the elevator trim. I had to trim up during maiden flight. 24 clicks up at 72mm cg. The clicks is the amount of trim shown on my tx screen near the trim bar.
At cg 90mm I still need 14 clicks up of trim.
Assuming the cg is perfect, my elevator should be at zero clicks (1,5° EWD)
So I wanna know why I still need some up trim, on top of the 1,5°.
The reason could be the flaps going negative in flight due to servo slop. The only way to know for sure is to install a camera.
I ordered the camera today and I really wanna know what's happening in flight.

 

[bat68be]

If my suspicion about the flaps moving negative in flight is correct, this might explain why my flightmode "speed" was not a succes. If the flaps are already bit up and I add more up for speedmode, that would be to much up in total and the glider accelerates untill it hits the flutter speed.

 

[Konrad]

How are you defining "Up Trim"? There will need to be some positive incidence with the AG airfoil.

In my link I show how a few grams in the tail does add up to significant weight being needed in the nose. But as you are at 2050grams it looks like you have a viable set up.

 

[Konrad]

If my suspicion about the flaps moving negative in flight is correct, this might explain why my flightmode "speed" was not a succes. If the flaps are already bit up and I add more up for speedmode, that would be to much up in total and the glider accelerates untill it hits the flutter speed.

With reflex (speed) and thermal (more camber) you need to retrim for level flight in each flight mode. Otherwise you are likely to dive in reflex and stall in thermal modes. In reflex you will be flying faster in level trim than you did with the flaps and ailerons in profile or down (adding camber) again trim for level flight.

You should be able to rig out these slop setting with your camber changing programing. Like I said I don't see the value in a camera. Rig and test fly. Re-Rig and test fly. Try to notice what changes.

 

[bat68be]

My definition of "up trim" is all the extra up elevator I have to program on top of the standard 1,5° EWD.

 

[Konrad]

EWD= Elevator to Wing Dihedral? (AKA, decalage)

 

[bat68be]

Correct. For most rc gliders in this category, ewd is +1,5°. With elevator level at 0°, the wingchord has a +1,5° angle.
Or with wingchord level at 0°, the elevator has -1,5°.
So the elevator is already little bit "up". Off course, extra trimming is normal. It depends on cg in flight and the AUW. I want to get rid of the extra up trim:
- more aft cg
or
- check flaps for perfect neutral position in flight

 

[Konrad]

Depending on the airfoil I like 0.5° decalage. Add that to my liking of the 95mm CG. I have very little trim changes as the model goes through its various speed settings. (To my mind this means a lot less pilot load than the classic nose heavy trim)

I'd like to hear what you think about the long fuse when it comes to signaling lift. This 1.8m fuse was a real eye opener for me.

 

[Konrad]

Here are some of my thoughts on trimming the Samsara. The guiding premise is to lower drag.

Topmodel has given the Samsara too large a stabilizer. This was done to help make the glider easy to fly and be a lot more fault tolerant to control inputs. I point to the fact that guys have lost 50% of the stab and still been able to recover and have a controlled landing. See this post https://forum.alofthobbies.com/inde...er-build-thread-on-alofts-forum.125/post-8922

What an oversized stab allows one to do is trim the model for a rearward CG. A rearward CG allows for less aerodynamic trim drag. (A smaller stab would be better but if staying with an oversized stab I try to take advantage of it) In most of my models I like a CG a far aft as practical (not divergent but very neutral).

This is why my CG is 10mm further aft (95mm) than the manual's initial setting (75-85mm). This is also why my stab is rigged at 20mm rather than the manual's 22.5mm setting.

A big benefit for me is that an aft CG allows the sailplane to signal lift a lot stronger. A down side is that it also signals sink rather aggressively. But for a thermal duration ship the idea is to find lift, even weak lift, and stay out of sink. An aft GC really helps with seeing what kind of air one is working.

 

[bat68be]

Checked my position of the stab on the rocker bed: I'm just under 21mm (at 90mm cg)
Probably could go down to 20mm when I put cg more aft towards 95mm.
For my 90mm cg, I have 21gr of lead attached to the front of my 3s-3000mAh lipo.
Will remove that lead and check how far the cg moves aft.
Will also change the wing joiners for carbon tubes, another 20gr down.
So I should arrive at 2000gr AUW.
I suppose you used carbon tubes 8mm with 7mm inner diameter?

There was only little thermal activity during my flying sessions.
Sunny weather but with only 10°C outside temperature.
However, I managed to gain some altitude from time to time.
The glider signals the slightest lift very well!
The variometer on my rx AR6610T also helps in these very light thermals.
Can't wait for next spring when real thermals show up again.

 

[Konrad]

It looks like I may have used an 8mm x 6mm carbon tube (1mm wall). Note that with pultruded rods one should add the rod end plugs to help keep the joiner from collapsing.

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

Gotcha sorry I went astray there...must be old age..o_O. Well in a perfect situation I guess the rudder should have two seals. For convenience I make them like the wings - 1 hinge and 1 seal. Its not perfect as the hinge is offset but it really does save a hell of a lot of time end effort. But...

forum.alofthobbies.com

I've learned to hate varios as they don't tell me anything that a properly set up glider doesn't. In fact I find them very distracting as I tend to fly the tone rather than the aircraft when using a vario. For cross country gliding at long distances they may have their virtues. But I'd have to really second guess my reasons for fly so far out as to not be able to read the glider directly.

 

[Konrad]

Wow, Is this correct? That Aloft is out of stock on these fine ships. Has there been a rush on these models? Or is this an inventory glitch. Last week I saw 4 in stock.

TopModel Samsara

The Samsara is an excellent thermal ship that features a sleek and long carbon reinforced glass fuselage that is light yet strong with ample room for gear. A traditional built up, 3 piece balsa wing with D-tube does the heavy lifting. The full flying elev

alofthobbies.com

 

[Wayne]

Inventory glitch..

 

[Konrad]

Elsewhere on this forum there was some misinformation given on the effects of aileron differential on pitch trim. It is understood that as a result of the tilting lift vectors there is a strong effect on yaw when giving an aileron input. Aileron differential is used to bias this yaw input to produce a provers yaw response in the intended direction of the roll input.

This results in the changing of airfoil chamber more on one side of the wing verse the other. That is to say the changes in pitching moment are NOT in balance, canceling each other out, when using aileron differential. This change in the wings total pitching moment will result in a change in the pitch trim of the aircraft.

Normally this isn't a concern as you are often using the elevator anyway when making the turn, like in F3F racing. Now in a thermal one often is holding some opposite aileron to the rudder. In this steady state (coring a thermal) you may notice the trim change in pitch from the aileron differential.

With the Samsara I have a rather large aileron differentail and notice that the ship will pitch up ever so slightly with aileron input. This is even the case with the flaps being rigged dead to roll (this eliminated the asymetrical impact of aileron differential on the stab). So to lighten the pilot load the use of aileron to elevator mix often helps. With Open TX there are ample mixes available to add this feature.

 

[Mike W]

What a difference six years makes! My Top Model Prelude wing const. is light years (no glue blobs etc.) ahead as was my Gracia Maxi. I assume my Nike 2 and Thermic Dream are as well though I can't see inside of the sheeted wings? Interesting read!

 

[Konrad]

To my way of thinking the carbon tube is a step backwards. Structurally the tube does not place a lot of carbon where it needs to be to resist bending moments. The LE rod is very susceptible to light impact breaking the LE.

The ribs and multiple false ribs do NOT hold the airfoil shape well (covering sag). The classic D tube wing is far superior to the carbon tube (kite spar) in all respects other than time to build. I'm of the opinion it is best to avoid the carbon tube spar.

Thanks for the photos as they make the points very clearly (see the light dips).

Now if you get the opportunity do try the 1.8m Top Models fuselage, regardless of the wing construction!

 

[Mike W]

I disagree, you are thinking like a sloper where you NEED to overbuild! (When all you have is a hammer everything looks like a nail LOL!) The Prelude is my light wind thermal floater and purposely built that way and with the light wing loading and long fuse it will indicate lift very well. You had to beg my Gracia Maxi to come down and the Prelude will be similar. I'm a flat land thermal seeker and if I feel the need for speed I'll launch my Nike 2 or Thermic Dream on windier days. (much heavier but stronger) My old Aspire was a D-box but at those speeds this would have been lighter. Look at my old FVK Silent Dream(18 years old) from Northeast Sailplane, no D- box. I get your point from an engineers perspective about the accuracy of the air foil. It would be interesting to fly the same bird with and without the d-box to see how much of a difference? On that note will the sheeted wing on my Thermic Dream's cleaner airfoil help to make up for the added weight?
BTW my photos were included to show the cleaner construction with no glue blobs in the newer T/M sailplanes.

 

[Konrad]

I disagree, you are thinking like a sloper where you NEED to overbuild! (When all you have is a hammer everything looks like a nail LOL!) The Prelude is my light wind thermal floater and purposely built that way and with the light wing loading and long fuse it will indicate lift very well. You had to beg my Gracia Maxi to come down and the Prelude will be similar. I'm a flat land thermal seeker and if I feel the need for speed I'll launch my Nike 2 or Thermic Dream on windier days. (much heavier but stronger) My old Aspire was a D-box but at those speeds this would have been lighter. Look at my old FVK Silent Dream(18 years old) from Northeast Sailplane, no D- box. View attachment 14660

LOL, fair enough.

I left the gas bag crowd in the late 70's. I had learned that no matter how light one's wing loading was you were going down in sink. This taught me that the wings efficiency was more (much more) important than wing loading. I now look for glider's legs! That is, how well does she run between thermals. For flat land gliders maximum go is far more important than minimum sink when hunting for thermals.

I too love my FVK Organic (I think it is also 3.2 meter) but this Samsara is the better thermal ship (thinner airfoil and truer airfoil).

Read some of the writings by Dr. Drela, Dr. Selig and Martin Hepperel and you will see that they say fidelity to the airfoil is critical. They also mention that the covering sag between the ribs result is span wise vortices that cause added drag and premature stalls. Drela makes a point with his gas bag airfoils to say to bring the LE sheeting past the 40% chord to avoid this early separation bubble. This is why I love the taco shell LE on my FVK Simply the Best.

BTW; I have far more time as a thermal hunter than as slope speed demon.

All the best,
Konrad

P.S.
As far as the time line, I think the Samsara is the baby (newest design) of the gliders we are talking about.