John Slater Airspeed Tern

Let us all watch your new project progress.
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John Slater
Posts: 52
Joined: 24 Mar 2015, 07:29
Location: Dudley , West Midlands

Re: John Slater Airspeed Tern

Post by John Slater » 18 Sep 2019, 07:27

Hi Barry,
Sorry about delay , we have been on holiday for a couple of weeks, in answer to your question about dihedral I did put a 1" block under the wing tip to give a slight dihedral, in flight this will not be noticed but will aid stability.
Kind regards
John

Barry Apostolou
Posts: 35
Joined: 07 Jun 2019, 15:36
Location: Surrey

Re: John Slater Airspeed Tern

Post by Barry Apostolou » 18 Sep 2019, 07:34

Thanks John,

Hope you have had a good holiday. Yes I will probably do the same re-the dihedral. Not too much progress to report. But both sets of wing spars have been completed and all the ribs have been prepared ready with the cable holes etc.

I have been doing a lot of flying recently while the weather has been good, so my time in the work shop has been cut down. this will pick up as we move into autumn and winter.

All the best

Barry

Barry Apostolou
Posts: 35
Joined: 07 Jun 2019, 15:36
Location: Surrey

Re: John Slater Airspeed Tern

Post by Barry Apostolou » 25 Oct 2019, 12:11

Hey John,

Its been a very busy time flying and refurbishing models, a Fair K8, and a Chris Williams 1/4 scale T21. I am doing as much flying as possible before winter sets in.

I am trying to sell my original T21, a 'Mike Trew plan' 1/5 scale (3.5 meter wing span) no luck so far. No problem - I will just keep it and fly it. I guess that not too many people are into vintage sailplanes. If you know of anyone that may be interested please let me know, I am certain we can negotiate a good deal.

Getting back to the Tern, the wings are now well on the way, see attached pictures. Still to do are the rubber bands supports and the rear wing joiner box. The wing wiring, aileron servos and electric air-brakes (250 cm) will complete the installation. For the ailerons I have Hitec wing servos (HS125MG), at 6 volts they give a torque rating of 3.5 kg. From past experience they will be more than enough for the job.

Still to complete is the the bit of sheeting at the bottom of the wing root, this was left open to give access for the band supports, rear joiner and wiring. Finally I will cover with 'Antique Oratex'. The wing D box was 'sheeted' with 1/16" balsa, the ply was great, but the estimated cost was a bit high, and I had loads of balsa in stock. I might see if I can get a paint or stain to mimic the ply after covering.

Please note that using balsa means that the wing is now 1.2 mm too thick, and needs adjusting to ensure a neat join at the root. The wing tip blocks have a 1/64 ply sheet in the middle, to give a datum line for sanding and additional 'robustness'.

I will now move on to cutting the ailerons from the section and facing them off. I intend to use the covering to make a continuous hinge. thus eliminating any air flow through the gap. they will be hinged from the top and articulated from the bottom of the wing.

I have a question re-the ailerons, do you think they need any diagonal bracing to increase their rigidity, or in your experience are they rigid enough ?

Well, that's it for now. I am getting nearer to completing the model and will keep you posted as and when I finally finish the building.

Once again thank you for your help and advice.

All the best

Barry A
Attachments
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Barry Apostolou
Posts: 35
Joined: 07 Jun 2019, 15:36
Location: Surrey

Re: John Slater Airspeed Tern

Post by Barry Apostolou » 26 Oct 2019, 10:08

Hi all, or any one following this log

I have now started doing the final rear wing joiner box fitting. One side done, as per picture it is a good idea to leave the rear joiner box 'free' till this point then you are able to check the wing incidence v's the tail-plane, around 1.5-2.5 degrees positive AOA for the wing should be about right. This should give a stable sit in the air during flight.

Although you cannot see it from this picture there is also about 2 degrees of dihedral in the wing. This is achieved by lifting the tip 1" during building. Also as per John's plan do remember to build in the 3 degrees of wash out on each wing to ensure good manners in flight. Having checked with John he confirmed that this was important, and should not be ignored.

Spot the 'deliberate error'. I mis-measured the rear fuselage fairing length and have had to add an small infill piece. I hope this will not be too obvious once sanded and stained. It can happen to us all and I take comfort that I am not alone in seeing one measurement on the ruler and noting down another on my plan. Think thrice, measure twice and cut once. Well at least I have not got two right wings !!!!!

All the best

Barry
Attachments
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Jolly Roger
Posts: 298
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: John Slater Airspeed Tern

Post by Jolly Roger » 26 Oct 2019, 10:42

Lovely build Barry. Really enjoying it.

There's something a bit Jules Verne about the Tern... like a fictitious design in some futuristic comic book of the late 19th century. You could have an aerial adventure, or possibly plunge deep into the ocean inside its hull-like fuselage.

In reality, it was built at a time when there wasn't yet a set notion what a glider should look like, so designers were still trying stuff out. These days sailplane design is more gradual evolution than revolution, a little tweak here or there to squeeze small gains. The only revolution I think I can see (no pun intended) is the nose-mounted electric sustainer, which I think will become the norm. And great for us modellers... ;)

Anyway, thanks again Barry.

Rog

Barry Apostolou
Posts: 35
Joined: 07 Jun 2019, 15:36
Location: Surrey

Re: John Slater Airspeed Tern

Post by Barry Apostolou » 26 Oct 2019, 12:49

Hi All again,

I know what you mean Roger it is a very unusual model , it is of its time and reflected the fact that gliding had not really got going. In fact the wings could almost be for a power model, not really the high aspect ratios we consider the norm today.

In the 'head on' picture below you can see the slight dihedral on the wings. Technically speaking the real Tern had a completely flat top wing with dihedral only on the bottom of the wing as determined by the rib size. However it is a good idea to add a couple of degrees 'actual dihedral', please note that you will also need to adjust the root rib to ensure a good fit on the fuselage.

Well despite falling over in the modelling room (I have only drunk tea), I have now managed to get both wings on and ensured that they are the same in terms of AOA. The rear wing joiner boxes need to cure and harden over night so that they are totally solid before we can move on to the next phase. this will be the installation of wiring, servos and air-brakes and then on to preparing for covering.

Just for fun I weighed the wings and they came out at 650 gm for the left wing and 648 gm for the right. Still servos, wire, covering and air brakes to add to this yet.

All the best

Barry
Attachments
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John Slater
Posts: 52
Joined: 24 Mar 2015, 07:29
Location: Dudley , West Midlands

Re: John Slater Airspeed Tern

Post by John Slater » 28 Oct 2019, 08:05

Hi Barry,
The answer to your question about aileron bracing is `yes', and my apologies if it is not shown on the plan.
I have included a phot of my Tern in flight to illustrate this.
Sorry about delay in replying I had been away for a few days, very impressed with the model.
Kind regards

John
Attachments
IMG_6510-A - 2017-04-13 at 12-06-23.JPG
Tern over the Mynd

Barry Apostolou
Posts: 35
Joined: 07 Jun 2019, 15:36
Location: Surrey

Re: John Slater Airspeed Tern

Post by Barry Apostolou » 28 Oct 2019, 18:28

Thanks John,

Yes I do see what you mean about the bracing. I was planning to do this even though it was not on the plan. As yet I have not cut the ailerons from the wing, but they seem to need a little bit more support.I shall do this as per your model, its has been a very satisfying model to do so far. The wing joiner boxes (front and rear) are now fitted, and glued. I will wait a couple of days for the '24 hour' epoxy to cure and fully harden and move on to aileron servos and air brake installation, and finally covering. I will keep you posted on the progress. Had a good days flying my ASW 24 at Bopeep (NE) today, very light wind and lift but great fun.

Thank you for your advice, it is much appreciated.

All the best

Barry A

Adam C
Posts: 8
Joined: 26 Oct 2017, 14:36
Location: Southampton

Re: John Slater Airspeed Tern

Post by Adam C » 30 Oct 2019, 19:47

Can't wait to see it fly Barry. Nice to chat building at mercury on Tuesday.

Found ren Delio pilots but prefer the Jim reeves ones for my Komar.

Barry Apostolou
Posts: 35
Joined: 07 Jun 2019, 15:36
Location: Surrey

Re: John Slater Airspeed Tern

Post by Barry Apostolou » 31 Oct 2019, 09:16

Yes indeed it is nice to talk building as well as flying. I went again on Wednesday and 'maiden-ed' my Chris Williams 1/4 scale T21. We got there early and got in 4 flights before the wind picked up to gusts of over 20 mph. Flying was not the issue it was on the ground where the model was trying to ground loop in the gusts. But all in all a very successful first set of flights. Went home tired but happy !

The advice you took from CW re-adverse aileron drag (more up than down) is so vital to these slower vintage style models, it makes those turns a lot safer.

All the best

Barry
Last edited by Barry Apostolou on 12 Nov 2019, 17:40, edited 1 time in total.

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