Strange Quark

[Futura57]

It's been nearly 3 weeks since my little setback with the lipo 'combustion' incident. Since then I've rebuilt the nose, including a better battery box and a whole new removable top fuselage canopy / hatch. I'm much happier with the result. All is now recovered in brown paper. I just need to join the wing tips and she's ready to paint. I have a whole bunch of Halfords rattle cans, so I need to decide on a scheme.

 

 

 

 

 

[Futura57]

I have fabricated, from polystyrene card, a pair of louvred panels for the cheat holes on the sloping underside of the main air intakes, immediately ahead of the fan unit. I also located a couple of air scoops from my box-o-bits to act as nostrils on the nose of the aircraft to allow the ingress of some cooling air around the battery tray. There should be a little suction through the nostrils because the inside of the fuselage is open right back to the fan.

 

 

 

 

 

 

 

 

 

 

[Futura57]

I've started the paint job using Halfords rattle cans.  After a grey primer coat I went all over with a light silver. I then decided on a US flag scheme with metallic steel on the top of the wings as a contrast. My intention is to repeat the pattern on the underside using red and blue. All very time consuming to mask, as I'm sure you are aware. Little sticky backed stars have come in handy with the masking. Perhaps a few panel lines here and there drawn with a 0.5mm fine tip pen followed with some hand cut Oratrim USAF lettering and star and bar decals. Perhaps a final clear coat will be in order for the metallic paint to look its best. I think it will look stunning. She'd better blimin' fly after all this effort.

 

[Futura57]

Close, but no cigar. I'm off to Italy until the 25th. When I return that doesn't leave much time to finish and maiden her before BOB@B at the end of the month 🙉

 

 

 

 

Edited September 13 by Futura57

[Ace]

That is one really fancy and no doubt time consuming ( 3 weeks ) trimming scheme there 👍     

Edited September 14 by Ace
Edit

[Futura57]

On 14/09/2024 at 10:07, Ace said:

That is one really fancy and no doubt time consuming ( 3 weeks ) trimming scheme there 👍     

I've actually spent most of the three weeks working on my driveway. That said, masking everything up and protecting remaining areas from overspray takes hours, and is all about accuracy and symmetry. Spraying takes only a few minutes, then half an hour plus to remove all the masking to get sharp lines before the paint dries too hard. Then it repeats for the next colour, etc. Then a few faux panel lines on the fuselage, finished with a couple of coats of clear lacquer. It all has to be left to dry well between every spray. Fortunately no paint has lifted anywhere and just a tiny bit of overspray in one place which was easily rectified. My favourite bit is applying the decals.

[Futura57]

I was disappointed that I was unable to get the model airworthy in time for the recent Buckminster Best Of British event. It was a missed opportunity for a dogfight with Tony Nijhuis's Tornado 🤣

 

After completing the necessary remedial work I've pencilled in this Friday for the maiden, if the favourable local weather forecast holds up. My main concern is getting her away with a good firm hand launch at a good angle of elevation, then quickly getting my thumbs on the sticks. I usually do it all myself, but I'm thinking I will do the hand launch and get a trusted flyer to man the transmitter. I'm not 100% happy I can trust someone else to do such a critical launch. Although the thrust to weight ratio is disappointing, she feels like she wants to fly out of my hand with a reasonable chuck. A 5 to 10mph headwind should help.

 

Now that the vectored thrust unit, associated linkages, receiver and Eagle A3 Lite gyro are installed, the flying weight with the 40C Zippy 4S 2700 lipo is 1,445g (3lb 3oz). A fair bit heavier than the 1,300g I was anticipating back in July. That said, it compares favourably to the two currently available Motion RC foam jets with 70mm 4S fans and flying weights between about 1,800g to 2,000g. The seven available Motion RC jets with 70mm 6S fans have flying weights up to 2,6000g. Of course, these all have retractable wheels.

 

There are still a couple of niggles in my mind with this Mk2 version. Firstly the C of G is 10mm back from where it was on my Mk1 prototype, not helped by the addition of the VT unit of course. That said, the Mk1 did feel a little nose heavy, though this may have been due to the smaller elevons and their limited throw compared to this Mk2 version. I can always pop 30g or so in the nose for the maiden. Furthermore, when the gyro is switched on it should enable a more rearward C of G without me fighting it.

 

The other niggle is the 60A ESC I've installed. I had in my head a 52A maximum current draw from the 70mm 4S Powerfun fan unit. It turns out this came from the 4-max website which quotes 52.5A, 776W, 1,435g thrust and, to be fair, a 70A ESC. That said, the Banggood website quotes 62A, 1,042W and 1,640g thrust. So who do I believe?

 

This is what I get on a fresh lipo: 72A 😱, 1,100W, 920g thrust 😢 (measured nose down on kitchen scales). Clearly, all the ducting and VT unit have taken their toll. Hopefully, once she's away, the throttle can be eased back quite quickly to draw  40 - 50A and not harm the ESC. I have an 80A Turnigy Plush on order.

 

This could be the last time she's photographed in one piece. Place your bets.

 

ps I must calculate the wing loading too.

 

...In old money - 19 oz / sq ft

 

 

 

 

 

 

Edited October 2 by Futura57
Added wing loading

[Ron Gray]

Hmm, exactly what are you holding it up with in the third shot? 😲

[Futura57]

[Futura57]

Successfully maidened yesterday. Just a short 2.5 minute flight to trim and get the feel. Vectored thrust unit was only enabled on the second flight (not videoed) to do some really tight loops and a manic tumble where a stall turn was expected. Flown on a little over half power because the 60A ESC was under rated for the maximum 70A draw. My oversight during installation. 80A ESC delivered today will be installed for future flights.

 

 

 

 

 

Edited October 5 by Futura57

[Eric Robson]

Flys as stable as the prop driven version you flew at Buckminster. Very impressed with both.

Well done. 

[RottenRow]

That looks excellent and flies as well as it looks.

 

Brian.

[Futura57]

Thanks chaps. On the second flight I turned on the 3 axis gyro along with the VT unit too. She was rock solid. Now I can increase the throws and have some more fun today. Yesterday we had four different models with successful maiden flights. 1 ARTF, 2 plan built, plus mine. It was a great day. Off out again now for some more fun

 

[Futura57]

On 05/02/2024 at 19:54, Chris Walby said:

Hi,

 

I think you are looking to gain too much as items on the shopping list contradict themselves, IMHO

Constraints

Similar model size to Mk1

Similar construction materials to Mk1 – Foam, balsa & lite ply

4S lipo power

1,000g target, bigger/heavier battery, but you want longer flight time?

 

Duration

Increase lipo capacity from 2200mAh to closer to 3000mAh

 

Faster (more thrust)

Increase EDF from 50mm to 64mm (on order), well that should reduce the duration if it has a higher wing loading due to weight, unless you are reducing drag, but not sure how that works with increased wing loading?

Shorter thrust tube & reduce exit area to 90% FSA - calculated properly this time

 

Faster (less drag)

Reduce size of main intakes, no knowledge in this department, but will that actually effect drag as it the sucky bit?

Reduce width of nose, pointy nose might save a couple of % yes it will help, but not by much?

Thinner but stiffer wings, I get the logic so yes it will fly faster, but it will also have a higher stall speed due to the increased wing loading

 

Manoeuvrability

Larger control surfaces &/or greater throws.

Yaw control for knife edge flight, etc – rudders? Won't this add weight and drag?

Vectored thrust (on order) – for pitch and yaw capers, IMO but I found that VT screwed the fan efficiency, added weight and probably adds overall drag

 

How about a SQ 2a and 2b? 

1.  Thin wing light weight low drag sports model
2. Retain original wing and load it up with rudder servo, VT 

IMHO by combining everything it will end up porky with a very narrow flight envelope, but what do I know! 

I have to concede @Chris Walby you were right on some fronts, especially given that I eventually squeezed in a 70mm fan. At a whisker under 1.5kg flying weight I would indeed describe the final result as porky. At least relatively speaking, given my original over optimistic weight target. That said, it still compares favourably to the flying weight of the Motion RC 70mm 4S offerings, which are in the 1.8 - 2.0kg territory. Admittedly those models have retracts and recommend a 4000 - 5000 lipo, whilst I only have a 2700 in mine, giving 2 mins 45 secs with 20% remaining.

 

I've ordered a couple of 3300s to try next week at just an extra 40g penalty. I have 4 mins+ in my sights. I could squeeze in a 4000 if I can find one with the right dimensions, but at an extra 100g+ the CG would require lead in her ass too.

 

Performance wise this Mk2 version is a little more spritely and a little less draggy than the lighter Mk1 with the 50mm FMS fan. It definitely holds its  speed better when I throttle back. Loops are easy from level flight, especially with combined VT pitch.  I'm holding back the throttle a little with the underrated 60A ESC I'm currently using. I just received an 80A ESC to fit.

 

Control authority was sufficient with 50% rates on the maiden flight, with elevons only. For flights 3 & 4 I upped the rates to 75% and enabled the VT and gyro. Consequently, stability and control are superb. So far I've largely restricted my manoeuvres to loops, rolls and knife edge. On the last flight I performed a high alpha (45 deg) high altitude flyby with the VT pitch control augmenting the lift as I'd hoped. No flipping or spinning on her axis yet. Small steps. With a measured static thrust a little over 900g she's never gonna fan hang, but I'm happy with my baby thus far.

 

I think the brown paper covering, pva and multiple coats of spray primer, paint and lacquer haven't help with the final weight. I do think there is a case for a stripped down light sports version with no rudder or VT. This could easily save 200g.

 

For the next version I think I will try flapperons on the front wing for even better roll authority and to help slow her for landing, as is useful on our little jet friends. Clubmates are pushing me to go up in size to 80/90mm and 6S.  All in all I give myself 8 out of 10 so far.

 

 

 

 

 

 

Edited October 6 by Futura57

[Futura57]

Here's a result. A 4S 4500 mAh HV lipo which is only 20g heavier than my Zippy 2700. And it will fit my model. That should boost the performance and give a respectable flight duration of around 5 minutes,  I hope.

 

https://www.hobbyrc.co.uk/gnb-4500mah-4s-70c-lihv-battery-xt90

 

 

 

Edited October 6 by Futura57