SU-27 Build Guidance and Pictures

[RobertCL]

What an awesome jet I spotted this thread a while back and started building one. I should have probably have posted some pictures along the way as I was working on it as it's taken me a while. Definitely one of the more time consuming and challenging foam board planes I've built. I think I struggled most with the final steps of gluing on the vertical stabilizers and getting the elevons on reasonably level and symmetrical, but after much thinking and staring and test fitting time I eventually went for it and it turned out okay.

Anyway, took it out for a maiden flight today, got someone else to launch it for me and wow does it fly well! I have the FT Viggen and the FT X-29 both in EDF as well and they always feel quite mad and on the edge to fly, but this is so calm and smooth compared to those, an absolute pussy cat I was being fairly careful and just did a few rolls, and climb outs, but it was very well behaved.

Part of the maiden:

2nd flight landing:

For the electronics I used these; all from Banggood (but they took quite a while to turn up!)

• Freewing 70mm EDF Ducted Fan 12 blades 6S E7217 with 2300KV Motor for 70 EDF RC Airplane - CCW + CW
• Hobbywing Skywalker 2-6S 80A UBEC Brushless ESC With 5V/5A BEC
• EMAX ES09MD Digital Servo

All up weight is 1970g (4.4lb) including the battery and I'm flying it on an HRB 4S 3300mAh 60C lipo, which gave me about 3mins flight time with a little left in the pack at the end. (Seems to be about average for jets in my experience)

The watt meter says:

• 36A at 50% throttle => 5.5mins flight time (60(m/h) * 3.3(Ah) / 36A)
• 76A at 100% throttle => 2.6mins flight time (60(m/h) * 3.3(Ah) / 76A)
• 1135Wp (peak watts) => 258W/lb (which is supposedly "sporty")

It'll just about "hover" at full throttle when held vertically, but it feels like it'd be nice with a little bit more power when flying and it did seem to run out of steam in a vertical climb, so I might try a 6S battery at some point, but I'll need to look at weights for that and see if it's worth the trade off. I have some 6S 5000 packs, but I think they'll be too heavy and probably physically too large as well. So I'll try them on the watt meter, see what it says the peak Watts is and then work out if it's worth buying some 6S 3300's (see if the extra watts will give me more W/lb with the extra weight of the 6s)

Next task is sort out a paint job now I know it flies well

Many thanks for making the plans available and I'll report back if I get anywhere with 6S.

 

[Flitedesign 3d]

What an awesome jet I spotted this thread a while back and started building one. I should have probably have posted some pictures along the way as I was working on it as it's taken me a while. Definitely one of the more time consuming and challenging foam board planes I've built. I think I struggled most with the final steps of gluing on the vertical stabilizers and getting the elevons on reasonably level and symmetrical, but after much thinking and staring and test fitting time I eventually went for it and it turned out okay.

Anyway, took it out for a maiden flight today, got someone else to launch it for me and wow does it fly well! I have the FT Viggen and the FT X-29 both in EDF as well and they always feel quite mad and on the edge to fly, but this is so calm and smooth compared to those, an absolute pussy cat I was being fairly careful and just did a few rolls, and climb outs, but it was very well behaved.

Part of the maiden:

2nd flight landing:

For the electronics I used these; all from Banggood (but they took quite a while to turn up!)

• Freewing 70mm EDF Ducted Fan 12 blades 6S E7217 with 2300KV Motor for 70 EDF RC Airplane - CCW + CW
• Hobbywing Skywalker 2-6S 80A UBEC Brushless ESC With 5V/5A BEC
• EMAX ES09MD Digital Servo

All up weight is 1970g (4.4lb) including the battery and I'm flying it on an HRB 4S 3300mAh 60C lipo, which gave me about 3mins flight time with a little left in the pack at the end. (Seems to be about average for jets in my experience)

The watt meter says:

• 36A at 50% throttle => 5.5mins flight time (60(m/h) * 3.3(Ah) / 36A)
• 76A at 100% throttle => 2.6mins flight time (60(m/h) * 3.3(Ah) / 76A)
• 1135Wp (peak watts) => 258W/lb (which is supposedly "sporty")

It'll just about "hover" at full throttle when held vertically, but it feels like it'd be nice with a little bit more power when flying and it did seem to run out of steam in a vertical climb, so I might try a 6S battery at some point, but I'll need to look at weights for that and see if it's worth the trade off. I have some 6S 5000 packs, but I think they'll be too heavy and probably physically too large as well. So I'll try them on the watt meter, see what it says the peak Watts is and then work out if it's worth buying some 6S 3300's (see if the extra watts will give me more W/lb with the extra weight of the 6s)

Next task is sort out a paint job now I know it flies well

Many thanks for making the plans available and I'll report back if I get anywhere with 6S.

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Awesome, thanks for sharing! Also I'm very interested to see how it performs on 6s. With 6s you will definitely have a lot higher w/p as giving 50% more voltage should a bit more than double the wattage, but the thing is that efficiency drops quite dramatically on those numbers. What you could do is measure the static thrust with the 6s 5ah because it will be almost the same on the smaller one and decide the worthiness of the smaller battery this way

 

[RobertCL]

6S update: I did some testing with the watt meter using the 6S 5000mAh batteries I already have (which are unfortunately physically too large and also, at 745g, too heavy to achieve balance without adding tail weight!). The watt meter measured:

• 57A at 50% throttle (1400W) => 5.26mins(?)
• 126A at 100% throttle (2700W) => 2.38mins(?)
• 2700Wp (peak watts) => 519W/lb

And at full throttle it would easily climb when I held it vertically in my hand.

So based on that I bought some 6S 4000mAh batteries from HobbyRC ( https://www.hobbyrc.co.uk/gnb-4000mah-6s-70c-lipo-battery-xt90 ) which seemed to be the lightest I could find at "only" 495g (and also reasonably priced). These just fit in the battery compartment and the plane balances at the COG point with the battery towards the rear, but not quite all the way back, which is nice.

Finally after a month of "British summer weather" there was an acceptable flying day, it was a bit gusty, but the extra power from the 6S worked really well. It's still super easy to fly, it'll cruise around on just under 1/2 throttle, it still glides in for landing and seems to have pretty much unlimited vertical climb now, much more jet-like It did trigger my low battery alarm in the full power climbs, but that's hardly surprising really! On the 2nd flight I managed about 3 mins and still landed with about 18% in the batteries, so could probably have pushed another 30s, maybe 60s, but I was trying to be kind to my new batteries on their first flights.

So if your electronics (and bank accounts!) can support 6S I can highly recommend it. Oh and it sounds great as well especially when you cruise into a low pass and then power out on full throttle

And finally some pictures of my new paint job as well (mostly based the pictures here because I though it looked so good)

 

[iwpublic]

Hi there,
I have signed up to just build this amazing masterpiece. Thank you for sharing.

My idea is to scale it down to 71% in order to give it a try with 2x 50mm edfs (50/70mm=71%). So I scaled the printouts to 71% and started the cutting process. Will keep you posted.

I also thought of moving the EDFs a little further back and to cut slots into the upper side of the air intake in order to increase Air Intake even further.

I am, however, curious whether there are updated plans available like announced. It was also mentioned to drop the main plate as structure would be strong enough to build it without it. This, obviously would save additional weight.


Again, awesome masterpiece, thank you!

 

[cosmocop]

I'm in the same boat. Printed plans out for a twin 50mm setup. So far, just have templates cut out. Hope to finish before Thanksgiving.

 

[Flitedesign 3d]

Hi there,
I have signed up to just build this amazing masterpiece. Thank you for sharing.

My idea is to scale it down to 71% in order to give it a try with 2x 50mm edfs (50/70mm=71%). So I scaled the printouts to 71% and started the cutting process. Will keep you posted.

I also thought of moving the EDFs a little further back and to cut slots into the upper side of the air intake in order to increase Air Intake even further.

I am, however, curious whether there are updated plans available like announced. It was also mentioned to drop the main plate as structure would be strong enough to build it without it. This, obviously would save additional weight.


Again, awesome masterpiece, thank you!

Awesome, good luck on the build, both of you! Just be aware that as you scale it down the bend radii of the parts gets smaller which makes it more challenging, so be prepared to do some patient crafting.

For the update on this model, yes, there is a sequel coming. It's not really an update to this model but rather a whole new model based on the same design but almost completely remade.

 

[iwpublic]

Yes I have noticed that one already. Another sidenote is to cut the holes wider as the material stays 5mm thick...

 

[iwpublic]

First status: when scaling down to 71% the 5mm ft foamboard cannot be used anymore for the tight bends. I use 3mm Foamboard instead.

Insane piece of engineering. Really enjoying building it.

Looking fwd to the next version of the su-27 plans.

 

[Jermaine123]

Greetings .. I too have been wanting to add to tye discussion ... Sms ... So five months later I finally maiden this beautiful bird .... Many thanks from me as well ..it went surprisingly better than expected cg refference was on point ... Having been a huge fan of bens jets most of which I ve done fly great by the way I expected some hickups .. But everything went well it flew great .. Sadly I only had a 2200 6s pushed a bit past the former in the cockpit but it was fine for I only needed to test it ans get it trimmed so hopefully I'll.get aomething a bit bigger for the next flight .. But .. Thanks again ..

 

[iwpublic]

Update…
While building the intake I realized that the print scale of 71% (50mm edf / 70mm edf) is slightly too small. I noticed that by the thrust tube not fitting the edf + the edf part of the intakes are not U-shaped but more pointing outwards on the top side which then does not fit into the main plate attachment points anymore.

After measuring the edf to be 51.5mm inner & 54mm outer diameter the updated scale results in 73.5-74%.

As there is some buffer space in the intake I will rebuild the edf part of the intake with adjusted inner formers.

Lesson learned: measure edf, test print the thrust tube, do some tube/edf fitting before finalizing the final print scale.

 

[iwpublic]

Question: is there any particular reason why the edf is lifted upwards by the former which then requires the 3d printed air ramp?

 

[Flitedesign 3d]

Question: is there any particular reason why the edf is lifted upwards by the former which then requires the 3d printed air ramp?

The fan is slightly elevated to make it horizontally level with the thrust tube exit, thus making the thrust line horizontal. The 3d printed air ramp is optional, but it makes assembly easier as it also functions as a former

 

[iwpublic]

The fan is slightly elevated to make it horizontally level with the thrust tube exit, thus making the thrust line horizontal. The 3d printed air ramp is optional, but it makes assembly easier as it also functions as a former

Makes sense. Also serves as efd protection in case of rough landing.

 

[Mutley]

Love this build!

 

[iwpublic]

Thanks to +++ flitedesign 3d +++ I have a build log & some experiences to share.

My scaled down project:
I had two 50mm cw / ccw EDFs laying around, so I decided to scale the plane down (50mm / 70mm = 71.4%) including some margin of 74% in order to fit 50mm EDF into the nacelle when using 5/6mm foam.
As 5mm foam board is quite difficult to bend - in particular considering even smaller radiuses - I chose 5mm for nacelles, wing bottom and structure only. For the other surfaces I used 3mm simple paper coated foam.
When scaling the plan down I also had to consider that some cut-outs had to be still 5mm wide for the parts.
Same applies to the 3d printed parts: Some parts are to be scaled down but thickness must remain the same, e.g. for the control horn.
Scaling also gave me a little headache with the servo size as the EMAX09MD would interfere with exhaust tube. So I went for EMAX08MD and minor modifications.

Material:
Not sure why fitedesign’s plane looked so smooth and ripple free - apart from being laser cut - I always had the issue that paper-coated foamboard ended up with squished foam inside and lines outside.
See pictures.
5mm Kraft foam board is significantly stronger and therefore heavier than the white paper coated foam board but I had to accept some compromises.

Electrics:
ZOHD Kopilot Flightcontroller with GPS (return-to-home) and stabilisation
2x EDFs 50mm 12 blade with 4600KV motor, approx. 700g each static thrust according to manufacturer @12.6V, which I never get in real life
2x ESC 40A with 5V BEC
I wanted both ESCs to supply the flight controller with 5V for some redundancy in case one BEC burns out. And I wanted to get some current margin in case a servo draws too much.
So I used 2x Schottky diodes in order to avoid current flowing back to the BEC.
2x EMAX08MD servo
1x 6ch light weight Receiver
1x 2200mAh 3S Lipo, 176g
Two of them would be way too much weight

For the wiring I went for one thick cable from Batt to ESCs instead of two individual ones in order to save weight.
As the Cable from Batt to ESCs is quite long I also added capacitors as voltage ripples effects become worse the longer the cable is.

Some Measures:
Full throttle flight time (on ground) would be around around 3 mins with 3s 2200mAh - depending on Battery age, cell health etc. So this would give me around 4-5mins real flight time.
Weight of the naked plane is around 800g and 1300g incl electrics and battery.
Unfortunately the thrust was not enough for power-to-weight-ratio of >=1. Even with two cheater inlets per nacelle.

Next Steps:
I am currently re-building the SU-27 without Main Plate + I use Depron instead of Coated foamboard. This will save me around 300g-400g of weight.
It’s not as rigid, i.e. it bends easily but it’s nearly indestructible. So I’ll add the one or the other re-inforcement. Thinking of 29g/m2 Fibre Glass Coating or Carbon rods where it’s needed.
Will keep you posted!

 

[iwpublic]

Again, many thanks to Flitedesign 3d for sharing this plan!
I am very curious when the version 2 will be published to your followers

 

[iwpublic]

Material comparison. Have a look for yourself

 

[iwpublic]

Maidenflight
Maiden was a little challenge due to the relative high weight compared to the thrust.
But I managed to have her airborne and gosh she looked pretty in the air!
Landing was again a little rough due to the speed needed due to the weight.

What I have noticed was the need to pull elevator up quite significantly during the entire flight despite the perfect CoG.
When pushing the battery further back, she was then very nervous due to tail weight.

Any idea?

 

[Flitedesign 3d]

I have a build log & some experiences to share.

That's awesome, thanks for sharing! This isn't an easy build in normal scale let alone scaled down, so good job on that

Not sure why fitedesign’s plane looked so smooth and ripple free

I'm using the flite test foam board, it bends very well once paper is removed from the inner side. For the bending I use more or less the same techniques that are being used on any ft ms kits. I have little to none experience on different foam board types, especially ones outside europe, so getting the real stuff is the only advice I'm able to give...

Thinking of 29g/m2 Fibre Glass Coating or Carbon rods where it’s needed

You can trade lightness with strength or the other way around, it will always be a compromise. I myself like to make my models as light as possible as I find them to be the most enjoyable to fly that way

I am very curious when the version 2 will be published to your followers

I will build the next version, the su-30/37, most likely in the upcoming summer. The design is pretty much complete.

What I have noticed was the need to pull elevator up quite significantly during the entire flight despite the perfect CoG.

If the cg is on spot, why don't you just trim the stabilators to make it fly level? Having a slight positive angle on the stabilators relative to the wing bottom surface is normal.

 

[iwpublic]

I'm using the flite test foam board, it bends very well once paper is removed from the inner side. For the bending I use more or less the same techniques that are being used on any ft ms kits. I have little to none experience on different foam board types, especially ones outside europe, so getting the real stuff is the only advice I'm able to give...

Having no access to ft foam board I suppose its depron with kraft paper coating as it bends really nicely with no braking. Guessing though...

I will build the next version, the su-30/37, most likely in the upcoming summer. The design is pretty much complete.

Can someone please put me to sleep or severance me (referring to an Apple TV+ series) until summer?

If the cg is on spot, why don't you just trim the stabilators to make it fly level? Having a slight positive angle on the stabilators relative to the wing bottom surface is normal.

Makes sense to me. I had the stabilizers aligned with the wing bottom like on the pictures of the real SU-27 also in order to deduce drag.