2026 Speed Challenge - Telnar1236

[MadMonkey]

One of my main sources of inspiration. My design was mostly inspired by wanting to minimize the impact of the motor's torque, but I also remember seeing somewhere that WW2 twin fuselage designs were something like 20 mph faster than their single fuselage counterparts - as you see with the Twin Mustang (F-82G) having a top speed of 461 mph vs. 440 mph for the P-51D.
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The other one was the Pond Racer which isn't really a twin fuselage design but still has a similar look to it. There's a pretty neat 3D printed version of it that I saw a video of a while back and I've been itching to try my hand at something similar.

Pond racer 1200mm

This replica of the Pond racer is designed for quick and easy construction and printed using regular PLA. Designed to suit the 3548 900kv motor this model has a significant amount of power and is happy to cruise around at 50% power on 3s. Utilizing 6 channels; Ailerons, Elevator, Flaps...

cults3d.com

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Think I mentioned it before but that Pond Racer was my first attempt at a 3D printed plane. It flew great until one of the spinners decided to explode 👍🏻

I'm about ready to give it another try I think.

 

[telnar1236]

Can't say that I've read EVERY word in this thread, but it certainly is interesting. I also think it kind of highlights that having 3DP aircraft and DTFB aircraft competing against each other is bit....skewed?

I would like to ask, what CAD software are you using, and what are you using for CFD? Simscale perhaps?

In general, I agree - foam board cannot compete with 3D printing for what is possible aerodynamically. That's part of why I'm building EDFs instead of building a prop plane and trying to have a more generally capable design with long flight times and good aerobatic capabilities instead of something purely built for straight line speed - I'm relatively confident I could blow through 200 mph using a 3D printed design if I built something that wasn't restricted by those limitations I have self-imposed. I also don't really want to win so much as have fun with this competition and give myself a reason to finish my Super Duper Sabre.

That said, it is a give and take with 3D printing. The big limitation for 3D printed designs is weight. So I might have a design with a fraction of the drag, but I probably need 1.5x the wing area to support it or to spend a lot of effort on high lift devices to give me more lift. It is worth it, in my mind, since you do lose less drag than you gain weight, but it isn't as cut and dried as you might think.

I fully expect Mr. Man, or Houndpup Rc to go faster than the Super Duper Sabre with a foam board design and for that matter, I doubt the Super Duper Sabre will beat what Mr. Man did last year.

 

[telnar1236]

Can't say that I've read EVERY word in this thread, but it certainly is interesting. I also think it kind of highlights that having 3DP aircraft and DTFB aircraft competing against each other is bit....skewed?

I would like to ask, what CAD software are you using, and what are you using for CFD? Simscale perhaps?

I'm using Fusion 360 to design the planes and XFLR5 for preliminary analysis going into Simflow for more detailed runs containing the fuselage. I've also been playing around with Baram since it doesn't have a 200k node mesh limit, but in general Simflow with its mesh limit is good enough for building RC planes (in other words far more than anyone needs in the first place. There's no reason you couldn't analyze a foam board design in Simflow too, but in general, CFD data isn't super useful for getting drag without some form of calibration data so you need to test a number of planes to figure out how your models correlate to real life.

 

[telnar1236]

Suggest you get in contact with APC props on the west coast.
Ask to talk with the teck person and explain your situation and this guy should give you a handle on what to do.

Years ago, I was interested in 4D flying and asked him about reversible props. They designed one and he stated that it was about 80% efficient in both directions. Never even expected that. So give them a call. Also they have quite a data bank on their props and what they can do. May have to hunt their site to find info. Pylon racers are always trying different engines and need different props.

With dual engines, agree like others, that you will need cw/ccw props. On my 2 motor VTOL, ran just CW props, then CCW props and then CW/CCW and best result was CW/CCW with the FC. Also flew a big flat piece of blue foam doing cw/ccw and would not with 2 cw motors with a FC..

Frontal drag is the biggest culprit, if you are looking for speed, if the tail feathers can be V-tail, it will add big gains. Pylon racers proved that.

Might be worth doing if I really decide to try and push things with this design at some point, but at this point I don't even know if I'll build this plane much less how much I'll feel I can push it in terms of speed.

Definitely, yeah, having counterrotating props is the whole point of this design. I built a single motor 3D printed pylon racer last fall to test my laminar flow airfoil, and it flew relatively well (till the ESC exploded) and I got it up over 100 mph, but I never felt confident enough to push it over about half throttle on 4S due to the torque from the prop, much less to fly it on 6s which it was capable of.

I'd have to disagree about minimizing frontal area being the best approach to reduce drag. It's the easiest way to reduce drag, but having a smooth streamlined fuselage with continuous curvature will get even less drag still. It's why if you look at real planes, the fuselage isn't just a straight line back from the engine but instead tends to bulge out a bit. Same for the tail - a V tail isn't inherently less draggy than a conventional or T tail and is actually higher drag in a lot of situations. In the case of the foam board design, having a flat horizontal surface in the wake of the wing and two small vertical stabilizers is actually better than having two large V-type tail surfaces.

 

[telnar1236]

Was curious how a 3D printed version of the twin fuselage racer would fare relative to the original foam board concept and it's definitely the biggest number I've gotten so far without assuming an 8s power system costing hundreds of dollars - predicted top speed is 196 mph which probably means it's possible to push this design over 200 with some more tuning. And I'm assuming pretty small drone motors so going to a bigger power system and larger props is also definitely a possibility if I decide to pursue this design at some point.

However, it's not as much of an improvement as I might have guessed - only 13% lower drag which is still a good bit, but not anything that couldn't be trimmed off the very simple foam board design too

 

[telnar1236]

Got the flaps and elevators and canopy latch installed and the internal linkages for the elevators set up.

The flaps are pretty straight forwards and should have gone into place without too much trouble. I needed to reprint a whole wing because I somehow managed to break one of the filament hinges when installing the flap, but the exact same design went together perfectly on the second try. The elevator control linkages, however, were very much a matter of trial and error. The amount of space available is quite small and the linkage needs to be very stiff to avoid excessive slop or flutter at high speeds.

I ended up needing to go with a ball link installed into the elevator control horn. I still need to replace the rubber grommets on the servos with solid plastic grommets too, since those continue to allow a bit too much give in the system. I also designed a slide in place deflection gauge with the correct throws for the elevator based on CFD and testing of the 50mm model.

The throws are 3 degrees up for level flight trim, 10 degrees up for trim with full flap deflection, 15 degrees up max throw for flight with the flaps up, and 20 degrees up max throw for flight with the flaps down.

I can also now start to check the balance and thrust for the airframe. It looks like it should balance well with a 4000 or 5000 mAh pack all the way forwards, or up to my planned 9000 mAh Li-Ion pack a bit further back. The lessons from the Ghost definitely helped make everything go more smoothly with the CG this time. In terms of thrust, it doesn't fit on my thrust stand, but even with a mostly empty 3300 mAh pack it's probably producing around 2.7-2.8 kg of thrust (weight was 2.3 kg when I tested it and thrust to weight was easily over 1), so I think the 3 kg of thrust with a fully charged 5000 mAh pack I assumed as a design number should be achievable. Again, all the testing with the 50mm version, the laminar flow wing sport jet, and the Ghost as well as numerous static tests really helped make it possible to get a relatively small inlet that has very low losses and barely decreases the thrust at all.

 

[telnar1236]

Most likely I will be able to attempt a maiden flight this weekend or the next though there will still be a couple refinements like gear doors and some fairings after that before it can achieve its full speed

 

[telnar1236]

Got the servos remounted using hard plastic standoffs instead of the rubber grommets, but it turned out that was only half the source of the remaining flex in the system. The other half comes from the control horn twisting due to the ball link having the force offset from the centerline.

I now need to figure out if there's a way to stiffen up the control horn through the small access window or if I'm stuck with it and will just need to hope for best. I think it would be fine as is since the design is quite stiff at this point, the control surface should be almost aerodynamically balanced, and I've used a similar dimension of control horn with a larger unbalanced control surface on my F-106, but I'd still rather not risk it if I can avoid it.

 

[telnar1236]

Finally got my nose gear designed. The nose gear bay is so tight that I couldn't get very good suspension on it - it will work if it runs into something that produces forces backwards, like if it runs into a small bump but won't be as effective for forces pushing up into it due to the small angle. I may end up redesigning it at some point, but the nose gear in general experiences fairly small loads, so I'm not all that worried.

Unfortunately, the strut still doesn't quite fit inside the gear doors.

So I needed to add a bulged fairing to fit it. Again, something I may redesign, but good enough for now and it won't substantially impact the speed, it's just a bit ugly.

 

[Mr Man]

Wow, that plane looks AWESOME

 

[Gadeirus]

Agreed, I love it!

One thing, though, just eyeballing it, do you have enough vertical stabilizer area? Looks kind of small?

 

[telnar1236]

Agreed, I love it!

One thing, though, just eyeballing it, do you have enough vertical stabilizer area? Looks kind of small?

It's definitely on the smaller side - the 50mm version and some CFD give me the confidence to attempt to fly with it sized the way it is. Externally, the 80mm version is exactly scaled up from the 50mm with the only change being a slight increase in the angle of incidence of the wing relative to the fuselage to compensate for trim forces from the elevator. One thing the side view somewhat hides is how big the ventral fins actually are.

And they are definitely a big help - one big takeaway from the 50mm versions was that without ventral fins, the plane flies well, but stalls very dangerously (my first stall test of the 50mm version resulted in the thing sideslipping at almost 90 degrees). However, with the ventral fins, the 50mm version was capable of a reasonable amount of high alpha flying and while it could be forced to spin by keeping it in a stall with full elevon deflection in both pitch and roll, it gave you a lot of warning and opportunity to recover prior to that, and it also recovered fairly quickly on its own if you let go of the stick after letting the spin develop.

 

[telnar1236]

Here's the thread where I developed a lot of the ideas that led to the Super Duper Sabre and did the testing of the 50mm version and some other experiments with its laminar flow wing/airfoil if you're interested

Experimental EDF Jets and Other Ideas

EDFs are cool but compared to prop designs they are inefficient and lack thrust. Beyond that, as a whole, the performance of small RC planes has not significantly improved since the switch to lipo batteries and brushless power. Top speeds are still around 120-130 mph unless you want to buy...

forum.flitetest.com

 

[MadMonkey]

I was wondering what y'all were talking about and figured out I somehow had telnar1236 on ignore 🤦🏻‍♂️

 

[telnar1236]

Landing gear are on the actual plane now - all that remains is the rudder and control linkages

 

[telnar1236]

Got the flap servos and controls installed. The linkages have a bit of play, but I think they should be fine.

 

[telnar1236]

Had AI mockup a picture of an F-100 with a NASA paint scheme, and I think that something along those lines is probably what I'm going to go for with this design - it's very visible and it's going to be less easily damaged than a gloss silver scheme even if it isn't quite as pretty.

Might go for a thunderbirds scheme if I'm feeling adventurous but with the fairly different proportions of my design vs. the F-100 it could be annoying to adapt. And of course, scratches are very obvious in silver paint

 

[Houndpup Rc]

Had AI mockup a picture of an F-100 with a NASA paint scheme, and I think that something along those lines is probably what I'm going to go for with this design - it's very visible and it's going to be less easily damaged than a gloss silver scheme even if it isn't quite as pretty.
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Might go for a thunderbirds scheme if I'm feeling adventurous but with the fairly different proportions of my design vs. the F-100 it could be annoying to adapt. And of course, scratches are very obvious in silver paint
View attachment 259385

That would be awesome!!

 

[MadMonkey]

I love that NASA scheme, do it!

 

[LitterBug]

I love that NASA scheme, do it!

That thunderbird theme is awesome too!