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Micro Rapide


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Looking at either using the guts of or replicating the guts of one of these 3 channel fighter aircraft for something a little more docile 

 

https://www.amazon.co.uk/HAWKS-WORK-Airplane-Stabilizer-Beginners/dp/B0CX8LHPH9

 

As it’s only elevator and twin differential engine for yaw I wanted to go for something that would fit that better. 
 

hoping the gyros makes it a nice little flier but worried about weight (as always) and trying to figure out how I will construct this around the engine pods. 
 

haven’t bought the electronics yet so guessing some sizes (what can go wrong 🤣)

 

IMG_3715.jpeg

Edited by shepeiro
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Obviously at the 3d/design stage so could change a lot if there is any disastrous feedback. 
 

was also wondering about the extra drag causing issues for the motors (above and beyond the weight needing to stay similar) 

backup plan is a more racey scarlet number by same manufacturer. 

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Very neat.

350mm span is pretty small!

What is the fuselage to be made from?

Models tend to have a rather higher power to weight than the full size so extra "form" drag tends not to be to much of an issue. It just means it will fly a bit slower and use a bit more power than it otherwise might. A bit like the full size really! 

Any "guestimate" of the likely all up weight?

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Ah yeah didn’t add a key. 


the cream coloured forms will be balsa (mostly 1/16 with some larger block work for nose and engine pods) and some 1/32 for the fuselage covering (not shown)

 

the orange will be birch ply (mostly 1mm some 0.4mm in pods)


dark grey will be 0.8mm carbon rods (leading edge)

 

for weight I would hope <50g but unsure of electronics weight and pod build up. Doubt I could do it for less than 40 though 

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3 hours ago, PDB said:

Heavy, peanut scale models have a wingspan of 330cm and the successful rc conversions documented are in the region of 20g.


yes but wouldn’t this being a bipe not counter that? I presumed as it doubles the wing area and has a higher ratio than a wider wing this would would give me Leigh way 

 

I currently fly a 40g 260mm plane (very wide and high camber though) and it does feel like it needs slightly wider wing I was going to add another 10cm 😂
 

 

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Posted (edited)

The amazon data for that the 109 I would be stealing the gubbins from has a flight weight of 58g and a wingspan of 380mm which I hope I can at least match in terms of weight but probably have a decent amount more wing area so hoping I can have something that flies slower

 

but I have to still say it’s a timely reminder to try harder to build light

Edited by shepeiro
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Microaces make a nice Rapide kit, larger than your proposed model, but for comparison here are the specifications.

 

If you work out the wing area of your model, you can then work out a suitable weight to give you a similar wing loading. A heavier wing loading doesn't necessarily mean that it won't fly, but it will fly faster.

 

At 350mm wingspan, and assuming that both your and the Microaces models have the same wing outlines, I'd expect your wing area to be in the region of a third of the Microaces one, so a flying weight of about a third of theirs would give a similar wing loading. That means around 35g.

 

Airframe 1/24th Scale
Controls Rudder, Elevator, Throttle, Aileron, Diff. Thrust*
Length 450mm / 17.7"
Wingspan 615mm / 24.2"
Wing Area 6.96 sq dm / 77 sq in.
Flying Weight. 99 - 110g/3.5 - 3.9oz
Wing Load ~14.9 g/sq.dm / 4.9 oz/sq.ft.
   
Brian  
   
   
   
   
   
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Thanks Brian that’s very useful.
my wing shape is scale so would presume it’s same/similar enough to discount as a variable. 
 

Foam construction will win out but perhaps I need to look at reducing mine as far as I can go (not prepared to use this heretic foam stuff yet😆)
 

I feel like mine would fly but less scale like as it should end up somewhere between the hawk 109 and the microaces in terms of wing loading. 
 

really need to get better at calculating elements weight. I use blender (a free 3d app that I use in my day job) it’s not as geared towards engineering as CAD or similar so has no built in way of calculating weight so I need to explore and perhaps write my own. 


I am wondering if I should go cartoon scale and beef the wing chord up a little bit

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Finished off the engine nacelles and also figured out how to work out the material weight and get a CofG looking pretty decent with the motors in. 
 

weight is low though so I’m not sure if something is up with my math/measurements. 
the bare frame came out as 9g which seems a little too hopeful for me. 
 

going to take a look again at everything with fresh eyes tomorrow 

IMG_3749.jpeg

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Weighed all my ply, balsa, and carbon and have some better values for now 

 

13g frame

6g motors

2g covering

1.7g servo 

2g rx?(geuss)

2g for extras

 

so roughly around 27grams if all goes well 

so hopefully that’s correct and my geustimation is wrong

 

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  • 2 weeks later...

Donor plane weighed in at 48g without battery so I think I should be able to have more wing area and less weight so should fly better than the donor which isn’t an acrobat or slow flyer but is very respectable and easy fly docile but quicker than scale. 
 

so hoping it should be able to climb better and fly slower but remain docile

IMG_3820.jpeg

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Unfortunately I took out the donor plane with my three and a half year old and he took quite a shine to it. It’s docile enough for him to take “control” of it at height and me feel confident enough to fix the situations he gets it into. So might have to get another…

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  • 3 weeks later...

Aiming for a 460mm wingspan 45g build. Donor plane has exact same wing area and is 50g. This should have similar front profile area, much sleeker generally but engine pods and wheels (always down) will add a chunk back

high taper wings might be errrrr …interesting. 
 

and this is what the vacume former is for. Never done any scale (ish) model befor what can go wrong!!!

Edited by shepeiro
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shepeiro

Note you donor aircraft has broad chord wings.

Model aerodynamics suggest that below a certain chord the skin friction of air becomes a major factor. In other words as an aerofoil its lift to drag ratio rapidly falls away.

My own experience suggests a chord below 2" (50 mm) is likely to be more "decorative" than "efficient".

The DH planes of the period quite reasonably used relatively high aspect ratio tapered wings that are good for both aerodynamics and structural efficiency but then the minimum chord was measured in feet not inches!

Just an observation but you may find that at such a small scale the performance and handling of your DH based planes may not match that of the apparently "crude" wing of the donor.

Will follow with interest. Keep posting.

Edited by Simon Chaddock
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Hmmmyeah hadn’t considered the effect of the ratio at this scale being negligible if not countered by surface drag. 
going to continue the design but might re-evaluate depending on what the weight is expected at. If I’m well under prob will go ahead if more similar to donor may adjust the wing see what I can get away with without compromising the scale-ness too much

 

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Coming to the end of the design phase, still to remove electronics from donor plane so may need some adjustments. Not calculated weight or cg properly yet but small tests look like it’s in right direction need to get electronics component exact weights and petg molded canopy and spinners weight dialled in. May need more general  lightening  but overall happy with this 

IMG_3939.thumb.jpeg.cfe1340abd52bef81e9ea5cb96030b94.jpegIMG_3938.thumb.jpeg.bd5566bb66cf9eedc95681cfee39c4ec.jpeg

 

images of frame work

Medium-soft balsa is light pink

1mm birch ply in yellow 

0.4mm ply in red brown

1mm carbon rod leading edge (dark grey)

0.5mm petg moldings in white (not wheels though that was mistaken)

IMG_3937.thumb.jpeg.4fd2138ed1b8ec831dc3067517651107.jpegIMG_3936.thumb.jpeg.fe232b7bb4040c7f3dc64ba11880983f.jpeg

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shepeiro

Fair enough but I do wonder if the wings were covered top and bottom in 0.8 mm balsa along with rather closer spaced ribs they would be strong enough without any additional wood of any sort and thus might actually be lighter. The same would apply to the fuselage, 0.8mm balsa skin over formers, but it would obviously be a bit more difficult to do.

Technically a conventional rigid framework is only required if it is to be covered with a material that is shrunk taught like tissue.

Just a thought.

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