Slope MOMs Racing - Lets get this going!

[Andy Lincoff]

I had a good time and am really impressed with the stoutness of this plane. I lost control and crashed on the beach but had minor repairable damage. I need to tune better because when the lift got light some planes definitely flew better. I set the cg at 55 but it was still looking a little tail heavy.

 

[smirkracing2024]

At the risk of opening Pandora’s Box, I’d like to hear the feedback you guys have on using 3D-printed models for the event. I’ve built and crashed more most. I am pretty cognizant of the pluses and minuses. The good is an almost molded-like airframe at a fraction of the investment in time, $$$ and materials. We never could have achieved the event yesterday without 3D printing. Kudos to Aloft for making that possible. But, several of you discovered the downside: a serious crash likely means a new airframe.

Without changing anything about the plane as printed by Aloft, there are ways to make the airframe a bit more robust. But, there aren’t any miracles that can overcome the fragility and brittleness of the most commonly used materials, PETG and PLA. The fuselage can be made a bit stronger, but the wing is a challenge.

There’s not much that we can do this season but there’s always the next one . So, what say the rest of you guys? What would you like to see going forward? More 3D-printed airframes or…? No promises

I see three important components:

1. design (thank you @OribaSJ88 )
2. printing (thank you @RafaelAvila )
3. kitting (thank you @Wayne and Aloft)

All three components are important (to me anyway). I have multiple half-printed projects from free designs I downloaded. I have some Soarkraft planes too (not an open design per se but you get the files once you pay $20) which are also half-printed / incomplete. I even have some fully printed airframes that have been awaiting assembly for months and months because I haven't gotten around to getting all the little bits and bobs necessary to complete them.

I would not have been able to join this adventure (which has already been a ton of fun and we've barely gotten started) without all three of the above. Getting a ready-to-assembly kit from Aloft was so convenient and easy.

With that said, I agree that printing replacements is an issue which needs to be addressed in the future. For now, @RafaelAvila is being very generous about helping people with whatever they need, but that raises the bigger point: this is only working because multiple people have basically donated time/talent/skill/labor.

I also have a printer, but I doubt I'd have found the time to get the airframe printed over the last few weeks. Assembling it from a kit was probably the most I could have accomplished in the time we had. However, I do wish I could print replacements on my own when parts get damaged.

Zooming out, am not aware of a better/cheaper option that would have gotten a dozen or more pilots out flying a single, good quality plane. $75 is hard to beat.

On the issue of an open vs closed design, I wonder if there's some hybrid option that basically says "you have access to the STLs if you agree to some set of terms (no distribution, no selling, whatever else is required)." That would resolve the only issue I have, which is the inability to print replacement parts.

 

[OribaSJ88]

Thanks for the feedback guys. It's all good. As the designer, I don't want to put my thumb too much on the scale, but I'll share opinion. I'm sure it won't come as much of a surprise to some of you.

• Wayne and I, among others, share the goal of getting people out to fly together. MoM racing is something we'd both like to see take hold again and it offers a chance to kill two birds with one stone.
• In order to promote the event and have any chance of holding one this year, we needed something that could get into the hands of people FAST. Aloft had already printed the Slingshot for their own use and it was really the only option. Aloft making printed airframes available was the only way to move things along quickly and the results speak for themselves.
• Asking people to print their own would have guaranteed that the level of participation would have been less. Even for those people with 3D printers, there is usually a non-negligible amount of work to get a design to print well on a given printer. Some designers offer profiles for Bambu Lab machines which seem to have a high level of consistency. What if someone doesn't have one? I don't, for example. The designer of the Roughgen, Waynsie, and some of Geode's designs (for those who know these guys) come with a high level of support and it's a great service that they offer. But, it opens a whole can of worms to offer a design for general consumption. It's just not in the cards for me.
• The good news is that, despite it diminutive size, it does fly like a slope racer. To those new to racing it may not be quite as obvious. Also, for its small size, it doesn't have a lot of the "questionable" flying characteristics that often accompany small model. For anyone in doubt, see the Destiny and its derivatives. Also, MoM racers can have short lives. Even molded models can disintegrate in a midair. The low investment in time and $$ to put one together is a plus in my book.
• The less good news, as several have already discovered, is the they're fragile. PETG and PLA reinforced with carbon fiber provide a reasonably stiff structure but the material itself is brittle. A rough landing can easily total a model. Also, even simple repairs can be a bit of a challenge because the parts don't hold their shape when broken. I had been reluctant to promote a 3D-printed model to get into MoM racing for all these reasons. I would hate to think that people get discouraged because the models are too fragile.
• For those who have the inclination, fiberglassing the inside of the wing saddle area will help a lot. A lot of stress from landing goes through this area and it is where I most often see breakage. I also don't use a removable wing. I glue it on and treat it as a structural element.
• The concern I have about foam models , as robust as they may be, is that aren't a stepping stone into real MoM racing. Just my opinion. I love my Ahi but would never consider racing one.
• Where I'd like to see things go...with a magic wand of sorts
  • In order to have any chance at success, I think there has to be a slope racer available to participants for purchase.
  • I don't think the racing class needs to be a "One Design Rule" type of event necessarily. I also don't think an "anything goes" event is going to get new people into the sport. Look at F3F/F3B as an example.
  • I had hoped that we would find a reasonably priced model with a fiberglass fuselage and maybe sheeted foam wing that we could base a competition around. Ideally there would be more than one to choose from. Perhaps something like this one: Spin by Blejzyk. This type of model is usually fairly robust and often fly well. I have no particular experience with that model, but it seems reasonable. It likely can take a bit of ballast and won't explode in a crash. I don't have a proper workshop, so having a relatively high level of prefabrication is important to me and, I'm going to guess, to others, too.
  • I'd love to see a 60" all-out MoM level of competition using whatever model a pilot wants to use. Modeled racers would be the obvious choice. No limits other than the span.
  • There's always the stretch goal of getting an Unlimited MoM race at Davenport going again. There was an effort made this year but didn't get the level of interest required. Perhaps that will change going forward

What happens next is up to all of us. Whatever we decide to do, I'd like to try to keep the momentum going and hold a event on a regular basis.

Ollie

 

[OldElectric]

Hi,

Sadly I crashed mine before the races. (I couldn't come to the races because I was out of town, would like see them go!) I would like to suggest experimenting with PCTG, it is less brittle has better "impact flexibility" than PETG. Perhaps just the fusealage?

I am going to print Geode's MR60 in PCTG.

-Glen

 

[Wayne]

On that front, I hinted at a new program that might be of interest:

This is an early beta program one of my friends has been working on for about 6 months. I'm blown away with how far has managed to get on this project. The app just loads up on your browser, you do not need any CAD experience, it does all of the hard work for you. You get to modify most anything you would like, airfoils, planform, dihedral, fuselage shape, basically everything. Once you have the design looking how you would like, you then click on the structures tab and start adding your servos and carbon fiber and even the control horns. For the servos is has a little database and sets up the servo pockets for you. Lots of neat stuff. Then you hit the print tab and it will solidify all the features and spit out printable files with parts designed to fit your bed size. In the end you have your own custom design.

I sort of love the idea of using this for a race series where we just have one limit, wing span and let people make whatever they like. Could be fun.

 

[smirkracing2024]

On that front, I hinted at a new program that might be of interest:
View attachment 26928

This is an early beta program one of my friends has been working on for about 6 months. I'm blown away with how far has managed to get on this project. The app just loads up on your browser, you do not need any CAD experience, it does all of the hard work for you. You get to modify most anything you would like, airfoils, planform, dihedral, fuselage shape, basically everything. Once you have the design looking how you would like, you then click on the structures tab and start adding your servos and carbon fiber and even the control horns. For the servos is has a little database and sets up the servo pockets for you. Lots of neat stuff. Then you hit the print tab and it will solidify all the features and spit out printable files with parts designed to fit your bed size. In the end you have your own custom design.

I sort of love the idea of using this for a race series where we just have one limit, wing span and let people make whatever they like. Could be fun.

Mind. Blown.

This is amazing. Would be insanely fun.

It might even cause teams to form. Some who are better at design, and some who are better at piloting, could form teams to experiment and iterate and compete.
And once @Wayne sees which designs are working the best, he can even kit those!

 

[zeo0nie1]

But, it opens a whole can of worms to offer a design for general consumption. It's just not in the cards for me.

To be clear, as someone who has supported open source software projects, there is no judgement from me whatsoever regarding not wanting to support an open model.

My suggestion (pipe dream?) was to have a community-supported model, be it Slingshot or something else out there. People can order from Aloft or print themselves. The parts kits are essential, I'd probably buy those even if I printed it myself.

Anyways whatever happens I'll get the plane and continue to be an easy heat win for whoever I'm paired with

 

[Wayne]

The app above will actually be able to fill a shopping cart with the needed items to build out the plane.

With this said, I like what Ollie had to say. Very valid points.

I would like to thank Ollie very much for sharing his design. I don't know we could have picked a better model. I love that it responds like a larger model and allows pilots to learn so many new skills. There are other designs out there like the MR60 that look really promising, but after flying it, it is nothing special in the air. There are a lot of models out there that fly, but are not special. The Slingshot has some magic in her.

As for durability, I like the bolt on wing as it allows me to swap my busted wing for a new one. But the planes do seem to me a lot more durable in the fuselage when the wing is glued on. Somehow I have been really lucky as I have yet to have any major fuselage carnage despite a number of bad landings. I think I had a crack that I CA'd closed.

Changing filaments - The downside of changing filaments is usually costs and or some other tradeoff. I know we have used a wide range of different materials and we always come back to PETG for planes. Mostly for the temp range. But maybe worth a try with one of the newer materials.

 

[OldElectric]

Changing filaments - The downside of changing filaments is usually costs and or some other tradeoff. I know we have used a wide range of different materials and we always come back to PETG for planes. Mostly for the temp range. But maybe worth a try with one of the newer materials.

IF one ChatGPT's PETG vs PCTG you get this (I use PCTG exclusively, unles high temp resistance is required, then ASA):

PCTG is essentially an upgraded, high-performance cousin of PETG that offers drastically superior impact resistance, higher optical clarity, and better chemical resistance. While both materials are polyesters modified with CHDM (cyclohexane dimethanol), PCTG contains a much higher concentration of this compound (often over 50%), which fundamentally elevates its mechanical properties. However, it comes at a higher cost and is less widely available than standard PETG. [1, 2, 3, 4, 5, 6, 7, 8]

---

Core Performance Differences

Feature	PETG	PCTG
Impact Strength	Moderate (can shatter under extreme force).	Extreme (up to 20x–30x tougher than PETG; deforms instead of shattering).
Optical Clarity	Good, but can have a slight yellow tint in thick layers.	Excellent (highest clarity among copolyesters, closer to Polycarbonate).
Chemical Resistance	Fairly good against water and mild acids.	Superior (highly resistant to hydrocarbons, fuels, oils, and industrial solvents like IPA).
Heat Deflection	Softens around 70°C.	Slightly higher, stable up to 74°C–78°C.
Moisture Absorption	High (highly hygroscopic, requires constant drying).	Lower (absorbs up to 3x less moisture than standard polyesters or ABS).
Cost & Availability	Very budget-friendly ($15–$25/kg); massive color selection.	Premium pricing ($35–$55+/kg); limited brand and color options.

I think its worth experimenting, be happy help with the printing. I estimated the cost difference to be less than 10 dollars in cost of goods for the SlingShot. I use 3DFuel ProPCTG at $30/kg.

-Glen

 

[MBR]

I was pretty lucky to race at all after I dorked my first landing and cracked the fuse at the front of the wing saddle pretty badly. I was able to fix it with some borrowed glue and masking tape, thanks Wayne and Jarron! To prevent this kinda damage (catching the wingtip on less than level landing) the Nybolts included are not forgiving enough. A taped on wing would be more forgiving possibly? Picture maybe a shallow v shaped saddle with about 3/4" tongue on the wing center leading and trailing edge, which can be taped to the fuse with a wrap or 2 of electrical tape? There would be a matching V shaped saddle on bottom of wing to lock into the V saddle on the fuse for alignment reasons. Tape would give hopefully instead of the fuse cracking. For me, this was my weak /fragile spot.
Otherwise, this Slingshot is a great performer!! From light winds to Heavy winds! Believe it or not, it is easier to land in heavier (30-35 mph) winds !

Congrats to all who showed up and raced. It was great to see so much interest! I had fun in helping out anyone who asked for it, as well as being a caller for anyone who needed it.
It was an very enjoyable day! ( course the wind could have picked up a little more! Lol)

Hats off as well to our volunteer scorekeepers and flagmen who kept the racing moving like a well oiled machine ;-)
Thornton for our next race is my vote.
Till next time, Mike R

 

[RafaelAvila]

Being work with pctg for the last couple weeks still trying to fine tune, the filament on my option doesn't seem to be a better option, keed in mind is different to result from printing 2 layers and a solid body, so no much gain in structure reinforcement just yet, ill keep working in temp/speed/colling, BTW before anyone suggested it, my first print was with the recommended printing perfil, downloaded from the 3d fuel website. Its kind hard to fine tune materials its takes time, 1 or 2 degrees in temp makes difference, 5% more in cooling fan makes difference, finding the balance between speed/temp/cooling is a real challenge.

 

[smirkracing2024]

Being work with pctg for the last couple weeks still trying to fine tune, the filament on my option doesn't seem to be a better option, keed in mind is different to result from printing 2 layers and a solid body, so no much gain in structure reinforcement just yet, ill keep working in temp/speed/colling, BTW before anyone suggested it, my first print was with the recommended printing perfil, downloaded from the 3d fuel website. Its kind hard to fine tune materials its takes time, 1 or 2 degrees in temp makes difference, 5% more in cooling fan makes difference, finding the balance between speed/temp/cooling is a real challenge.

This is why I probably would not have been successful if we had started with a design file instead of a kit. Thank you @RafaelAvila for putting in all this hard work. It is easy once someone documents all the settings for a given print... but getting all the settings takes a lot of trial and error.

 

[JJ Colorado]

Yes, Rafael has one just about ready, he will be getting more going very soon.

So where do we want to go for the next race?

If someone flew out from Salt Lake, then you could certainly consider bringing these out to Wilson Kansas to fly. The September fly in event doesn't have formalized racing, but lots of the people will likely have ODR racing gliders, and there is always the Dream Flight racing class. And I believe Andrew (Canuck) has some receiver reacy ODR planes available. We do one on one racing for big unlimited gliders, but fly four up for ODR.

 

[gnichola]

I thought the race and the plane were great. I lost focus during landing after my race and ended up on the beach. When describing what happened to Patrick on the way home, he said I should consider taking Adderall to combat my ADD
What I will say is that the having to "rebuild" the plane is not a huge deal and won't take long, but as was said earlier, how long can we expect the donation of time and effort into producing the kits.
The Spin that Ollie mentioned looks simple enough to build and I am sure it is much more repairable.
Personally, I like the One Design type racing in that then it becomes a pilot issue and not as much a design/setup/tune issue.
In my powered club we started racing with T-28's. It was a cheap $130 foam kit and you could change nothing, and we had a good deal of participation. Then we split that group in two, so the consistent winners were in their own category. Participation was still pretty good.
Inevitably the "real racers" wanted to do something more, so we added an unlimited class where we spec'd something pretty minimal, like wingspan and cell count (it was a while ago so the specifics escape me). When we did that, the participation dropped dramatically as it required people to be much more serious about it.
All that being said, I want to fly something that will keep the Mike R's interested while making it easy for the Guy N's to participate by throwing together a simple kit that can continue to be supported throughout a season, or two, without causing undo effort on the part of the provider.

 

[JJ Colorado]

If you are considering Dream Flight racing here is a video of the "all up" race at Wings Over Wilson, WOW. Note that WOW is MOM upside down.

Google Photos

photos.google.com

The contest rounds for DF racing are 4 up at a time, and you need to fly around the pole at each end. When the regular contest is done, we go all up for one elimination round.

While any DF plane is allowed the Ahi is the primary choice.

 

[JJ Colorado]

I fully support the printed plane concept thought the ODR racing we do at Wilson every year is nice in that:
A. the planes are very durable,
B. with an 11oz per sq ft wing loading they can fly in a wide range of wind conditions, and
C. 60" span with a 6" chord is easy to see compared to smaller airframes.

OK, so the DF racing blows all that out of the air and had the highest participation of any racing class, and foam bounces best of all building materials.

 

[OribaSJ88]

Guys, can we pencil in a date and a site for next month's race? I heard rumblings from Red that his arm might be twisted to join us next time if we hold it on Saturday. I'll propose the following:

• Date: Saturday 8/15
• Where: Thornton Beach again
  If we can scout out another site and confirm its suitability for racing, we can change this. I do think there is an advantage, especially for newbies, that we stick with a known site for the racing. Just my two cents.
• We should be able to schedule another event in September before the autumn winds put an end to most slope soaring in the Bay Area. Any opinions?

Ollie

P.S.: What say you, Red?

 

[OribaSJ88]

That's a lot of good discussion about where to take the racing going forward. I'd be super happy if we can get a regular event going with a given design. Whichever design we choose, I'd like to hope it has some or all of the following:

• Good availability: There is a dearth of airframes these days. Wayne, what can you source?
• Modestly-priced: MoM slope racers can have a pretty short lifespan
• Relatively durable airframe: A crash shouldn't mean starting over; should be capable of ballast
• High level of prefabrication: Best way attract the maximum number of participants
• Not so basic that experienced pilots don't want to join the fun

As far as an AI-enabled 3D-printed racer design program...call me skeptical. The devil is in the details. Has anyone tried generating a model using it and then printing it out? How did it go? What does the 3D-geometry look like with all the stiffeners, servo pockets, alignment features, etc? Is the airfoil properly preserved (this is a huge issue with Fusion 360 & elliptical planforms). Even if it works great, they'll be fragile and will (probably) require people to print their own.

 

[Red]

Guys, can we pencil in a date and a site for next month's race? I heard rumblings from Red that his arm might be twisted to join us next time if we hold it on Saturday. I'll propose the following:

• Date: Saturday 8/15
• Where: Thornton Beach again
  If we can scout out another site and confirm its suitability for racing, we can change this. I do think there is an advantage, especially for newbies, that we stick with a known site for the racing. Just my two cents.
• We should be able to schedule another event in September before the autumn winds put an end to most slope soaring in the Bay Area. Any opinions?

Ollie

P.S.: What say you, Red?

If I'm in town I'm in!

 

[Wayne]

Saturday 8/15 at Thornton Beach sounds like a solid choice.

I would very much like to have the group visit some other slopes though. Just the experience of getting to fly different spots helps to keep things interesting. But I also am frustrated with the lack of actual flying sites we have in the bay area. We have lost some decent sites in the last 10 years and gained zero new ones. I'd like to see that trend reversed. I am actively on the hunt for old and forgotten sites as well as new possible sites. I have set out of some explorations to locate possible sites. (Maybe this should be a new topic as I have a few I want to do that will require some camping and exploring and maybe others are interested in that sort f thing too?)

For this season we will stick with the current plane, but lets keep our eyes out for what we might want to use for next season. If you all are OK, we can allow Rafael to make improvements to the Slingshot to address the weak spots. Seems like a lot of the carnage I saw this weekend was mostly fuselage at the wing mounting saddle. Is that correct?

(We resisted making any changes once we starting printing the airframes as to keep them all the same.)