T-Hunter Discussion & Planning

[Andy M]

My T-Hunter had its maiden flight at Burford today. A few test glides went fine with no trim adjustment necessary.

The tow hook holes are replaced with a slot and I started with the hook at the most forward position. I stretched one of the club F3RES histarts to about 55 paces. I don't know what tension this provides, I'll measure it at a later date. Two launches at these settings resulted in somewhat weak launches. I didn't note the altitude on telemetry but I'm guessing about 150-200''. I then moved the hook about a third the way back in the slot and launched with about 60 paces of tension. This was a good launch to about 320'. HOWEVER, the wing tips had extremely severe flutter, so much so that I would not launch this strongly again for fear of immediate wing failure or eventual fatigue failure of the wing structure with repeated launches.

I also extended full spoiler at altitude with a resultant dive. The wing tips also fluttered in this condition. There is no apparent damage to the plane but BE AWARE that the T-Hunter is subject to wing tip flutter at high airspeeds.

I've moved the tow hook to about the 1/4 back from front position, but haven't tried it yet. I have a Lemon Rx that needs 4.5V and I was getting readings close to that and didn't want to push my luck. I think I need to use a 5 cell NiMH (currently 4 cell) or go to a LiPo with a BEC.

It was also quite windy at times and the plane bounced around quite a bit, even though mine is heavy at 600g with the steel wing joiners.

For good turn response you also need as much ruddervator deflection as you can get

Andy

[Andy M]

Judging by Ann and Tim's final weights I think I must have got unlucky with the weight of the wood in my kit. Or Superphatic is a lot heavier glue than I always thought it was. My final weight came in at 585g as follows:

326 Fuselage and tail inc. servos, Rx, ballast and battery (4 cell AAA 54g)
74 left wing
71 right wing
108 centre wing
6 carbon wing joiners (the steel joiners are 21g)
-----
585g

I used Ultracote Lite or Parklite everywhere except on the fuselage forward of the CG, - which incidentally is at Bernard's recommended position which I calculate as spot on. My ballast added was 48g.I used 0.032" music wire pushrods in 2 mm OD teflon tube. I also used aluminum wing joiner tubes.

I would surmise that the advertised weight is without battery, servos, Rx and ballast.

PS I just weighed the amount of Superphatic in a bottle. 50g, same density as water. I used nowhere near a full bottle, so I don't think that explains all of the gross weight. Particularly as Superphatic loses weight as it dries.

[Lyle J]

Andy:
Congrats! It turned out nicely! I like your covering scheme! Shouldn't have any issues with orientation when she in the air! Thanks for all your input. I'm surprised that it required so much lead in the nose to balance! That is a bit disappointing to read. So that's the second T-Hunter completed out of the original shipment of 16. Who's going to take the third spot? Ann?
Btw....I've dinked up my centre panel build, not sure if it is salvageable.....we will see.

Cheers!
Lyle

[Andy M]

I'm done, photos below.

I changed a few things, mentioned previously:-
- Moved the rear wing bolt forward to where the wing is not so thin
- Changed the wing bolts to M4 steel. Heavier I know, but I've written off a plane due to nylon wing bolts.
- Filled the gap between the wing bolt blind nut ply holders and the underside of the wing
- Made up my own smaller control horns with the pivot point at the hinge line
- Changed the pushrods to 0.032" music wire in 1 mm ID teflon tube
- Changed the wing joiners to 4 mm CF rod in Aluminum tube (see Ann's previous post)
- Made a slot for tow hook position adjustment, and added reinforcement at the hook position inside the fuselage
- Added magnets at the corners of the spoiler TE to ensure the spoiler when closed stays snug over its entire length
- Replaced the rearmost fuselage former with a rounded off piece of balsa, see pic of tail
- Made a hole in the nose block for nose weight, but turned out insignificant to the amount of ballast needed. That might be worthwhile if you use Tungsten instead of Lead

RC hardware as follows:-
Wing servos Futaba S3114
Spoiler servo Hyperion DS09-AMD
The servos were what I had from previous models that were suitable and fit
Rx Lemon 0052U
Battery 4 cell NiMH Eneloop Pro AAA, 950 mAh

I put the CG exactly where Bernard recommended at the rear of the spar. I input the model geometry into Tailwind Gliders spreadsheet for V tails and static margin came out at 4.7% with the CG at this position, 65 mm from the LE, which is 33.8% MAC. The neutral point is at 73 mm, 38.5% MAC, so don't go with a CG rear of this. I would appreciate it if someone else input the geometry and checked these results.

AUW is a lot heavier than expected, 587g including 48g of ballast needed. But anyway should be better on windier days. I had a 2 m sailplane that weighed about 850g and that still thermalled fine on good days.

[Lyle J]

Evening!
I finally got going again on my T-Hunter build! I started to build in June, then my progress stalled, always something requiring my attention it would seem. Then before you know it summer & fall have gone by and now we are entering the winter months! Geez, eh? Where does the time go? I got thinking about this build and I surmised the biggest problem is actually starting the build! To that end, I prepared a step by step build manual for the centre section in the hopes that other members who haven't started their builds might be coaxed in to doing so.

I''m not an experience builder by a long shot but I am getting through this build. For those of you that have procrastinated, I urge you to make an effort to start building. There has been enough accumulated experience building this sailplane from within our group, that you should have no problem getting answers to any problems you may encounter.

I will add more build guides as I work my way through the build.

Best,
Lyle

[Andy M]

UPDATE Nov 18. When I started covering the wing on the underside I found the thread protrusion on the covering by the excess thread was not to my liking and was not confident that on the top, the protrusion, although only 0.25 mm, would not be detrimental to the airflow. So I removed the thread. BUT; the washout was still there, so I think that after 4 days the washout has settled in. Both wings are covered now and have 3 mm of washout at the junction between the end rib and the tip piece. See the photo of the tip TE with a 3 mm piece of balsa at the tip. I don't yet know whether it will stay that way.
[attachment=0]20221118_092859.jpg[/attachment]

============== end of Nov 18 update=============

So as my previous method of introducing washout seems to have relaxed out here is another method.

Essentially it comprises putting the washout twist in the outer wing section and then placing a taut thread from inboard LE to outboard TE on the upper surface to lock it in. I used a strong nylon thread 0.25 mm dia. So it should have a negligible affect on the airflow. This is how I did it:-

- Drill a ~1.0 mm hole for the ends of the thread at the positions shown in the photos. Thin CA on the ends of the thread helps to insert the thread through the holes.
- Secure with thin CA the inboard end of the thread through the hole at the inboard LE. Leave some excess under the wing to further secure the thread later. Insert the outboard end of the thread through the outboard hole leaving some excess under the wing. Do not glue it yet.
- Hold down the entire wing tip on a flat surface. I used a rice bag.
- Place a 5 mm shim under the outboard TE. Make sure the entire wing tip is flat on the surface at 3 corners and the 4th corner with the shim.
- While keeping the wing flat and on the shim, and pulling the thread as tight as you can, secure with thin CA the outboard end of the thread.
- Secure about 15-20 mm of each end of the thread under the wing. Also secure the thread where it runs over the top of the spar.

Another way of doing this may be to use a strip of covering instead of the thread before covering the wing.

[Ann T]

Bernard has confirmed there are 5 balsa canopy pieces plus the kit rectangular magnets.

First photo shows the kit parts.
Second shows them assembled
Third is a bottom view of the assembled parts.

Note you will need some scrap sheet balsa (I used 1/8" thick) for the top of the canopy, between the uppermost curves of the sides as the middle laminating sheets are not quite thick enough.

Once assembled, the canopy will need to be planed & sanded to shape & size. Would have preferred it to fit without all the shaping & sanding but 🤷.

Photos:
[attachment=0]PXL_20221026_004550431~3_copy_759x756.jpg[/attachment]

[attachment=1]PXL_20221026_004717420.PORTRAIT~2_copy_1013x494.jpg[/attachment]

[attachment=2]PXL_20221026_004750314.PORTRAIT_copy_768x1020.jpg[/attachment]

[Ann T]

Thanks Andy, for the towhook idea.

When I shaped my leading edge, I sanded the plywood too. Came out okay.

[attachment=0]PXL_20221026_014341349~2.jpg[/attachment]

I've posted a series of photos on the rcgroups t-hunter thread of how I imagine the canopy assembly goes & I'm waiting to hear from Bernard. I will post here once I confirm the correct method.

[Andy M]

A question arose on the oval piece of ply with 3 holes in it. I believe it is intended for tow hook area reinforcement. This is what I did:-
- Elongated the holes to a slot in the oval ply and the fuse
- Attached the oval piece to the underside of the fuse
- Reinforced the slot on either side of the slot with ply inside the fuse
- Put the blind nut in a double ply block

So the hook can be removed and is adjustable in position over the entire slot length. See attached pics. Sorry a couple of them are a bit out of focus.

Andy

[Andy M]

I've just got around to shaping the leading and trailing edges. No problem with the TE. However, my understanding with the LE is that the front of the plywood core should end up being the LE at the vertical centre of the LE, with no or little material removal from the ply. Well on my centre panel (I haven't got to the other panels yet) it doesn't work out like that. After shaping the balsa surrounding the ply, the front of the ply, without any material removal from it, is a good 3 mm (1/8") short of the AG35 airfoil template. To achieve an accurate AG35 LE I'm going to have to add a strip of 1/8" balsa onto the leading edge.

I think what has happened here is that the ply insert into the ribs is not accurately dimensioned and is short of where the front of the LE should be. I don't yet know whether this will be the case on the other panels.

I've previously expressed my thoughts on the LE structure. I'll say no more.

Andy