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PSS Dash-7 (DHC-7) build blog


Ben-Erik Ness
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After quite a fee hours in the production hangar, another milestone has been reached, the airframe is now glassed. To allign up the tail, and to construct a solution to make it detachable took some time but now it's all in place.

The fuse and tail is now glassed, ready for some sanding, and construction of 4 crying detacghable engine pods...

Some photos of the process and result so far:

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It has a good size...

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Glassing...

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Posted by Mike Chantler on 11/11/2020 23:27:14:

Lovely build, fuselage and wing saddle look great. Simple carbon reinforcement really appealing. But how did you get the white foam carved so well? When I've tried it, the white EPS beads go everywhere and ruin the surface.

Thanks!

I use a very very sharp fishknife, with a long blade that gives me the ability to "shave" off small thin peices at the time...
https://www.marttiini.fi/Condor-Filleting-Knife23

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  • 2 months later...

Hello there!
Christmas and a hectic december is over and we are still in "stay home mode"
The project is now slowly movinf forward. Before X-mas I used way too many hours figuring out how to make the 4 engine pods. I did find a solution that can be incorporated with the huge flaps, but I have decided to put them aside and focus on the plane itself.

To put the pressure on mysel I had this caps specially made!

caps.jpg

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So this is the status post:

  • Fuselage and wings etc has been primed and given a light sand
  • I have now cut loose the big flap, and the ailerons and midle flap has been cut and are moving on the built in mylar hinge
  • The elevator is also cut so it moves on the mylar hinge line built into the wing

Next...
Well, I would like to continue with radio and servo installation. Hope to get the garrage heated to a level that allows me to start spraying the fuselage.

Some photos!
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There are a number of things that we come across in our hobby that stand out for me Ben, and your project includes

quite a few of those.

Big beautiful aircraft,

big beautiful propellers

Long nacelles

And spraying.

I will spray anything from 1/76 scale to 1/5th.

You realise that temperature is important and I can t wait for the weather to warm up again.

For me, I never spray below 10°C but prefer 15° and above.

Indoors, I work on 1/76 to keep my interest, but in summer anything goes, as I can work outdoors.

Keep up the good work

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  • 2 weeks later...
  • 4 weeks later...

Out of the paint shop!

I hate rattle cans, I have never got the hang of it. So, it's far form perfect - but good enough!

Before having my decals made by a mate (who runs a signshop) I usually test them fist, printed on paper, and attach them to the model.

Pretty happy how it turned out.

 

Next now is to get the decals cut, and in the meantimehook up all servos and connections again. The slope where I intend to maiden the Dash is still coverd in snow, so I got a few weeks before it can fly...

 

Pretty happy with how it presents is self ?

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That is a great looking model Ben and I think it will look fabulous in the air. Regarding your comments about your flaperons and adverse yaw, differential aileron usually takes care of adverse yaw (I take it the wings have some wash-out built in). I don't think landing your model slowly in tight spaces will be a problem, with it's big wing and huge flaps. What I would say is drooping the ailerons with the flaps may provoke a tip stall which would be most unwelcome, especially close to the ground when landing, so personally I would not bother. In fact reflexing the ailerons, 'crow-braking' fashion, might help with accurate hilltop landings as well as giving you a measure of protection against a tip stall. The only downside being that it might not be very scale. Just my view.

 

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2 hours ago, Piers Bowlan said:

That is a great looking model Ben and I think it will look fabulous in the air. Regarding your comments about your flaperons and adverse yaw, differential aileron usually takes care of adverse yaw (I take it the wings have some wash-out built in). I don't think landing your model slowly in tight spaces will be a problem, with it's big wing and huge flaps. What I would say is drooping the ailerons with the flaps may provoke a tip stall which would be most unwelcome, especially close to the ground when landing, so personally I would not bother. In fact reflexing the ailerons, 'crow-braking' fashion, might help with accurate hilltop landings as well as giving you a measure of protection against a tip stall. The only downside being that it might not be very scale. Just my view.

 

Thanks for your input!

There is some washout built into the wing yes, and I will mix ailerons up when landing, like a traditional butterfly setting we use on the 3m F3F gliders.

I don't care too much about scale, that's why I don't have any undercarrage ?

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Hi Ben-Erik, can you check the dimensions of your wing again please?

 

It looks to have symmetrical taper but 70 mm (sweepback) 165 mm (tip chord) and 70 mm (sweep forward of the trailing edge) only adds up to 305 mm (should be the same as the root chord, 420 mm).

 

I estimated the sweepback of the tailplane at 55 mm.

 

Using the drawing as it is the calculated CG with stability margin is 171 mm aft of datum (AoD, wing root at leading edge).

 

Assuming an untapered plank wing (420 mm chord at root and tip) the CG is 128 mm which I would expect to be the same for a symetrically tapered wing.

 

Eppler 205 works very well at 38% (for optimum sailplane performance which might not be stable enough for a slope model).

 

38% of 420 (root chord) is 160 mm.

 

     Cheers

 

         Gary

Edited by Gary Binnie
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20 minutes ago, Gary Binnie said:

Hi Ben-Erik, can you check the dimensions of your wing again please?

 

It looks to have symmetrical taper but 70 mm (sweepback) 165 mm (tip chord) and 70 mm (sweep forward of the trailing edge) only adds up to 305 mm (should be the same as the root chord, 420 mm).

 

Very well observed, I think I have to go back and meassure on the wing and not the drawings. I have so many versions of drawings, and I think I might have used the wrong edition here... Back later this afternoon with updated and dependable meassurements....

 

Ben-Erik

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21 minutes ago, Gary Binnie said:

Cool.

 

I use a mixture of drawings and actual measurements, if you have laminate flooring in your house you can use the join lines as datums and measure sweepback etc from them. 

I think you read my mind.... ?

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The "distance to the tip leaning edge is 15cm and the equivalent distace from the tailing edge is 10cm. The corde at the tip is approx 17cm (rounded curve)

 

Again, very well observed!

The floor is nice too...

 

Ben-Erik

Edited by Ben-Erik Ness
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Sorry, I didn't see the numbers at the bottom of the last post.

 

So the taper of the wing is more swept back than swept forward?

 

CG with static margin would be 193 mm, 41% MAC (Mean Aerodynamic Chord).  Neutral point 203 mm (no stability). 

 

I would test fly around 180 mm where it should be safely nose heavy and remove nose weight in stages if required.

 

I was given a guided tour of a Dash 7 of Tyrolean Airways at Innsbruck, by pulling a handle in the cockpit each pilot had independent control of the aileron on their side in case of a control jam. The pilots were very skilled in maximum crosswind take-offs and landings, Innsbruck is usually calm until lunchtime then the Foehn wind starts, blowing about 25 knots straight across the runway.  

Edited by Gary Binnie
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Calculations.... Maybe I shouldn't have started this discussion with myself ?...

 

eCalc says: between 19,7 - 20,6 cm from leaning edge

Aircraft Center of Gravity Calculator: 18.8 cm from leaning edge

 

When measuring the root at the wing and listening to my gut feeling i'm more at 16 ish centimeters from the LE at the root.

I'm considering various options: Make a chuck glider and see how it flies, maybe find a gentle slope and try the plane somewhere else than the grand big slope...

 

Any input will be appreciated!

 

CG_1.jpg

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CG_2.jpg

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