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Chris McG F-86 Sabre Dog build blog

my first attempt to a soaring bird for the PSSA MB 2020?

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McG 696920/11/2019 18:48:08
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2714 forum posts
1017 photos

Hi again,

As I only had a short session at La Grotte, I decided to leave the wing halves alone and to prepare some other bits.

Both WP1 are not entirely conform to the side view plan where they seem to meet the former behind them.

I decided to modify them slightly - cutting off about 5mm and gluing it back at the other side - so they could but against the former (F7?) later. The final adjusting will be done when getting the fuse halves together.

536_wing_plate_wp1_900.jpg

The battery box was a pleasure to assemble - thanks Martin - and I decided to make it a bit lighter as my ‘longer’ Dog fuselage will gain some weight anyhow. I only drilled a few holes in the ‘side’ parts.

538_batterybox_900.jpg

QUESTION please, gents > do PSS aircraft generally need some extra weight at the front and is it necessary to foresee some ‘lead’ box there?

Hakuna matata

Chris

BRU - BE / CTR Bits Control

Martin Gay20/11/2019 18:58:47
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260 forum posts
230 photos

Chris,

The prototype Sabre now has the CG at 172mm back from F4 (was 165mm on the plan). This is acheived with 110g of lead in the battery box front of the 4 cell Nimh battery.

You may not need any lead in your longer version.

Martin.

McG 696921/11/2019 08:44:55
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2714 forum posts
1017 photos

Thank you for your fast reply, Martin.

With the Dog, I could even bring the balance weight closer to the radome nose, allowing for some weight reduction.

Now you mention "4 cell Nimh battery" and I thought about using a 2S Lipo w/ UBEC to feed the RX... indecision

I suppose one of the reasons being that the Nimh pack can be charged in situ, but then I need some switch and charge socket on board, do I?

Can someone please bring me some light in the newbie- tunnel with the specs of the electrical bits & pieces I need for the Sabre build. Thanks in advance. enlightened

If I can order them from HK, it should be a lot easier/cheaper to get those to BE.

Cheers

Chris

Andy Meade21/11/2019 08:50:16
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2671 forum posts
681 photos

If you want to avoid the use of a nimh battery, I'd recommend a 2 cell LiFe. All my fleet now use these, and are perfectly safe to charge in the aircraft. What's more you don't need a UBEC (potential failure point) as they are 6.6v nominal.

Martin Gay21/11/2019 09:07:13
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260 forum posts
230 photos

Most modern (2.4GHz) receivers can handle higher voltages, my Jeti ones can go to 8.4v.

Just make sure your servos will handle more than 6v. Some can't, so make sure to check the specs!

McG 696921/11/2019 11:14:39
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2714 forum posts
1017 photos

Thank you both for your info, gents.

When looking for a battery, should 1500 > 2000 mAh be OK? And where to order one (Zippy/HK?).

I still need to find a switch/charging socket device !

Regarding the LiFe voltage of 6,6V, my projected X8R receiver can handle up to 10V, so no worries there.

But I'm planning to use analog Corona 929MG or digital 939MG servos and I can't find their maximum voltage spec...

@ Martin > can your TGY-9018MG servos handle 6,6V ? ...

Thanks in advance for your guidance.

Cheers

Chris

Martin Gay21/11/2019 12:50:07
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260 forum posts
230 photos

Chris,

The Hobby King website lists all three servos as 4.8V / 6.0V, so they are probably not able to handle 6.6V.

The Corona DS939HV, from Hobby King is rated for 6.0V / 7.2V though.

**LINK**

McG 696921/11/2019 17:50:15
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2714 forum posts
1017 photos

Thank you for the link, Martin.

I saw those Corona HV servos but didn't pay enough attention to them. blush

Now the jury is still out there...

But, as your battery box's internal dimensions are 42 x 42mm and the LiFe 6,6V are larger, I guess I'll stick to a 4,8 or better a 6V Nimh receiver pack, enabling me to use the Coronas or your TGYs.

Could you please tell me what you're using regarding battery & switch/ charge socket. I mean brand, specs and where to get them...

Thanks in advance & cheers

Chris

 

Edited By McG 6969 on 21/11/2019 18:06:24

Chris Barlow22/11/2019 01:17:18
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1858 forum posts
1266 photos

Chris

I tend to use 4.8v 2000mah NiMh packs for PSS simply because they usually last for a full days flying and add sufficient weight where it's usually needed. On some models I have a 4.8v sub c size 3300mah for extra nose weight!

The LiFe batteries are good at delivering a consistent voltage but will drop off rapidly when exhausted (and may even be damaged) The NiMh will drop off gradually and an X8R won't be affected too much. You'll notice the servos starting to slow if you let the battery drain too much but you'll still have control to bring the model in safely.

Remember though 4.8v NiMh is a 4 cell pack but 6v NiMh is a 5 cell pack and won't fit in the battery box.

McG 696922/11/2019 11:49:08
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2714 forum posts
1017 photos

Thank you for your kind advices, Chris.

I guess I'll keep it simple (& cheap...) and go for the Nimh solution.

The 4 cell 4,8V (in two rows) would be perfect for the battery box but I think a 5 cell 6V version in two rows as well (3 + 2 on top), could also fit the box if they are slightly 'tilted' in diagonal. I'll have to check that before committing. indecision

Any additional guidance is always welcome of course... yes

Cheers

Chris

Chris Barlow22/11/2019 12:49:08
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1858 forum posts
1266 photos

If you want to experiment you can tape some simple AA size batteries together to see what fits.

McG 696922/11/2019 13:12:56
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2714 forum posts
1017 photos

That's exactly what I had in mind, Chris. angel

I'm having a session at La Grotte this afternoon, so we'll rapidly have the answer, I guess.

Thanks again for your assistance.

Cheers

Chris

John H. Rood22/11/2019 16:38:48
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242 forum posts
347 photos

Captain Barlow, your happiness with the 4.8V NiMH route is glad news for me -- as 4.8V NiMH is really the only thing I know how to use nowadays -- so seeing as it works for you, I believe I can just stay lazy oops I mean "keep it simple"!

Cadet McG, kudos on your fine workmanship and meticulous ways thus far.

"Now GO, and commit this sin no more."  smile d

military_woman_china_army_000495.jpg_530.jpg 

Edited By John H. Rood on 22/11/2019 16:44:09

McG 696922/11/2019 20:27:35
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2714 forum posts
1017 photos

Hello to all,

Following Chris B’s advice, I made up a pack of 4 AAs in two rows and obviously they fitted the battery box easily.

Next was to try a 5 AAs combo (3+2 on top) and they will fit provided they’re a bit lifted on one side. So we have the choice of 4,8 or 6V. I will post some pics later.

I started making a rib sanding jig to have some ‘repeatable’ progress with the ribs.

544_starboard_ribjig_900.jpg

The ply I used is from a Spanish ‘mandarines’ (tangerines) tray and is totally ‘junk’ material, but at least the fruit was delicious. cool

As I will be using some paper tubes for the servo wires, I had to foresee some holes in R2 up to R9. This makes the process quite a bit slower especially because the swept angle dictated some bevel sanding. Only about half a dozen ribs finalized so far. blush

548_balsa bit_r1_900.jpg

Thanks to my “note to self”, at least I didn’t forget to add the bit of balsa strip above the wing jig R1s. The little ‘deviation’ of the red line is purely due to my mid-finger being a bit to long…

Hakuna matata

Chris

BRU - BE / CTR Nimh Control

ps > this Cadet will very probably have a lot more sins to hide, John… wink but thx.

McG 696923/11/2019 20:48:12
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2714 forum posts
1017 photos

Hi again,

As promised, here are some pics of the Nihm test.

549_nimh_4.8v_900.jpg

Two rows of 2 AA batteries are obviously not a problem at all.

A 3+2 combo is a touch to wide at 12,5mm each, plus taking in consideration that there will be some heat shrinking ‘envelop’ around them.

551_nimh_6v_900.jpg

However, if slightly ‘tilted’, it becomes easy enough to get them in without binding.

Some plan is to foresee a Depron ‘wedge’ to slide the pack maximum forward.

I guess this is quite workable?

Hakuna matata

Chris

BRU - BE / CTR Depron Wedge Control

John H. Rood23/11/2019 21:49:03
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242 forum posts
347 photos

Adjutant McG, I am no expert, but one thing that might help set one's mind at ease with regard to battery DURATION (using 4.8V NiMH) is that, at least in my experience of powering just two servos with 4.8V 300 mAn packs, THEY LAST ALL DAY. And I mean, ALL day! Like, flying pretty much non-stop from mid-morning until dusk in warm and halcyon Southern California. Same is true for 750mAh packs

True, the airplanes I've been flying flying are relatively small and lightweight, ergo the batteries are likely driving less powerful servos than we might use now on our 1/10th scale Sabres, but there it is. As a PSS flyer, you might wanna ask yourself, "HOW LONG AM I GONNA BE OUT THERE IN A STRONG CHILLY WIND, ANYWAY? And be chilly, I mean ICE-COLD, like, you begin losing touch with your face, your fingertips, the works!

hot Junior Aircraftman Cadet Rood

McG 696924/11/2019 11:00:39
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2714 forum posts
1017 photos

Thank you for promoting me to 'Adjudant', Junior Aircraftman John. cool

You might well be totally right in Southern California & with small and lightweight models.

But as Martin is using 4,8/2000 mAh, I might at least stick to that for the Welsh climate (even in June...).

My idea to use 6V might allow my analog MGs to operate a bit better regarding torque & speed.

Also he uses 100gr lead in front of his pack, so I thought it would be better to ad some 'useful weight' there if possible. angel

I don't really need "ice-cold" weather to loose touch with my face, finger tips and especially... neurons. blush

Cheers

Chris

McG 696925/11/2019 19:16:49
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2714 forum posts
1017 photos

Hello out there,

As we are now bashing some balsa wood, albeit quite slowly, I can finally get the feeling some bits are coming together.

All starboard ribs are finally ready to go and I started gluing them in using Superphatic.

554_topspar_dryfit01_900.jpg

So far, the top spar is just a dry fit to check things out before committing with some glue.

As you can notice R1 isn’t glued in yet as I have to fit the servo wires paper tube first.

556_topspar_dryfit02_900.jpg

The ribs are really glued square to the sheeting, I swear…

But I guess the wide-angle lens is trying to make me look even more stupid than I am…

Hakuna matata

Chris

BRU - BE / CTR Distortion Control

Danny Fenton25/11/2019 21:08:20
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9289 forum posts
4116 photos

Great progress Chris, I will watch and learn for when I am up to bat

Cheers

Danny

Mark Kettle 126/11/2019 05:11:13
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2471 forum posts
1492 photos

Looking neat and tidy Chris.

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