Needed: starting specs for a FPV twin park flyer

[UCDWino]

Hey all,

I’m a California-based inventor and product development engineer who is between gigs at the moment, and is looking to invest some time in designing a FPV racing platform that I think is going to be really fun, I could use some advice before I start some first prototypes….

The concept is a simple catapult-launched park flyer. Not So big and fast that it can’t easily stay within the borders of a football field… but big enough to competently carry a DJI air unit.

The desire is to allow a fewbuddies to set up their planes in simple rail launchers, get seated in their goggles, and then simultaneously launch themselves and have a race…. Maybe pylon racing around a football field, maybe with some gate’s in between.

It might perhaps be useful to share this:

That was a FPV racing league that got started just before Covid hit… but I took one look at that and thought: “those planes are way too fast / big for the venue.” If there was a “class” kind of standard that limited the motor size etc… much like many racing disciplines impose…. And slowed those craft down…. Then doing fixed wing racing might be a very tenable proposition.

I have a concept for a simple launcher, but part of the trick to making the launcher simple is that the planes are going to be TWINS…

So, here is my question:

If you were to make an park-flyer twin like this, to fulfill this particular mission, what motor and prop combination would you recommend?

I want these things to be powerful enough to carry the FPV gear, but also not so over-powered that they are scary or dangerous to bystanders in the area, like the wings in the above video were. Bigger props turning slower to reduce noise might also be a plus…

thoughts? Thanks in advance!

 

[Flying Monkey fab]

Kinda some non advice advice. Pick a motor and prop that will produce about 50-60% of the speed you are thinking of being too much and go.
Why do I say 50-60%? Because racers will find a way to make them go faster. If I was doing it I'd just say a double C pack from the flight test store.

 

[Tench745]

That was a FPV racing league that got started just before Covid hit… but I took one look at that and thought: “those planes are way too fast / big for the venue.” If there was a “class” kind of standard that limited the motor size etc… much like many racing disciplines impose…. And slowed those craft down…. Then doing fixed wing racing might be a very tenable proposition.

I have a concept for a simple launcher, but part of the trick to making the launcher simple is that the planes are going to be TWINS…

So, here is my question:

If you were to make an park-flyer twin like this, to fulfill this particular mission, what motor and prop combination would you recommend?

I want these things to be powerful enough to carry the FPV gear, but also not so over-powered that they are scary or dangerous to bystanders in the area, like the wings in the above video were. Bigger props turning slower to reduce noise might also be a plus…

thoughts? Thanks in advance!

I was going to say that the excessive speed is half the fun of the event. But, after watching the video I think you're right that slower/smaller planes would probably be more agile and thus more fun to watch.

Does it have to be a DJI air unit? The website suggests it only weighs 36g. That's not super heavy unless you compare it with something like the Caddx Ant which only weighs about 3g and could be put in a much smaller vehicle.

I suspect you would wind up with something like the FT Arrow as far as weight, size, and power systems go.

Step one will be defining the parameters you want the design to adhere to; guidelines to try to design around.

 

[UCDWino]

Does it have to be a DJI air unit? The website suggests it only weighs 36g. That's not super heavy unless you compare it with something like the Caddx Ant which only weighs about 3g and could be put in a much smaller vehicle.
.

no, it doesn’t have to the the DJI unit, I just wanted to have some starting point for payload requirement. Since the DJI unit can do the HD recording simultaneously, and that it would be good to be able to use that footage in race recap videos… and it’s lighter than having a FPV setup and a GoPro in parallel like I’m used to in quads.

Flying monkey’s point, (I’m hoping) is going to be part of the fun, because as he pointed out, ppl always find ways to tweak.

in this case, what I’m designing is an inner structure for the electronics and the motors which integrate everything that is mechanical and electrical together. It will be a structural core frame that users build foam core around in whatever way they want to create their craft. It also provides the central attachment point for the catapult.

If the motors, props and battery voltages are the same, then racers could have a wide variety of creativity in aircraft form factors…. Flying wings in pusher or tractor configs. Standard airliner layout craft, or P38 style twin-boom tail craft…

 

[UCDWino]

So in searching for existing FPV racing models, I came across this video

If you watch for long enough to see his onboard mobius footage, you realize that even a model like this is going to be fast enough that keeping it inside the bounds of a park or ball field is going to be hard.
that model is this : https://www.getfpv.com/sonicmodell-...ngspan-fpv-racer-rc-airplane-kit-version.html

he is running a 1806 motor on 3s with a 6x3 prop…. If I want less speed than that and I’m going to run twin motors… then I suspect we want even smaller motors and props…. And perhaps keep it to 2s batteries… ?

i Don’t have any feeling for how these things scale…. Are two 3” propellers the same as one 6”. Or much less? (I would assume the area of the disc matters as well as the weight of the marginal motor). there is the hee-wing which seems to get by on two 3” motors…

any sanity checking that can be provided by ppl with actual experience in dealing with small motor twins here (compared to my absolute lack of it) would be appreciated!

 

[UCDWino]

ok…. Did some searching on the hee-wing and found this…. This is exactly the kind of race flying I want ppl to do….

This video is a quad chasing a heewing…. but imagine a racing course like this with 3-4 airplanes…. simultaneous catapult launch, dodging terrain obstacles…. Would be epic. Contrary to the general perception of “racing” most fixed wing planes are just too fast to fly like this. Speed in the absolute sense means the courses need to be huge, which makes it harder to find venues, and less friendly to any spectator.

 

[Paracodespoder]

Smaller motors and therefore smaller props does not equal slower speed. Using the old FT H-pack (1106, 4500 kv) I was getting higher speeds that creates running the F-pack (2205, 2200 kv). To get lower speeds you need to go down in kv or down in prop pitch.
I’m rusty in all this, I’m sure someone else will chime in with more details.

 

[Paracodespoder]

Smaller motors and therefore smaller props does not equal slower speed. Using the old FT H-pack (1106, 4500 kv) I was getting higher speeds that creates running the F-pack (2205, 2200 kv). To get lower speeds you need to go down in kv or down in prop pitch.
I’m rusty in all this, I’m sure someone else will chime in with more details.

Edit: sorry, yes smaller motors can reduce speed, just have to go by motor specs to figure it out.

 

[UCDWino]

Edit: sorry, yes smaller motors can reduce speed, just have to go by motor specs to figure it out.

So that is good news I think, because I can start to design the hardware around a starting, pretty small motor size, and then we can play with props, KV and voltage to determine the rest of the envelope…. Makes sense to me.

T(at would mean that the real first question is: what motor size to pick?
I’d want a size and form factor that is produced in a lot of kv variants by multiple manufacturers…. Any suggestions?

 

[Paracodespoder]

So that is good news I think, because I can start to design the hardware around a starting, pretty small motor size, and then we can play with props, KV and voltage to determine the rest of the envelope…. Makes sense to me.

T(at would mean that the real first question is: what motor size to pick?
I’d want a size and form factor that is produced in a lot of kv variants by multiple manufacturers…. Any suggestions?

Do you have a maximum size and weight for this?

 

[Tench745]

So that is good news I think, because I can start to design the hardware around a starting, pretty small motor size, and then we can play with props, KV and voltage to determine the rest of the envelope…. Makes sense to me.

T(at would mean that the real first question is: what motor size to pick?
I’d want a size and form factor that is produced in a lot of kv variants by multiple manufacturers…. Any suggestions?

Well, going off a plane that seems to fit your mission, I would look at the Hee-wing and its motor/prop combination as a start. 1404 motors with a 3.8x3 prop. Get FPV has over a dozen different 1404 motors listed in their store from 1550kv up to 6500kv.

Doing the math real quick, on the stock 1404 3700kv motor with a 3" prop pitch and a 3 cell battery, the Hee Wing has a pitch speed (no drag, 100% prop efficiency) of about 39 MPH. With the same prop and a 6500kv motor that jumps to 68MPH. Now, you're never going to achieve those speeds in reality because drag exists, but it illustrates the range.

 

[UCDWino]

Do you have a maximum size and weight for this?

Not really. I just want to be able to carry good FPV gear and a good flight recording camera… i recall One of the FT videos where bixler was talking about their micro twin airplanes being light enough to not cross some regulatory weight threshold…. But those planes were REALLY small.. the ones where you climb by applying throttle…. So I’m assuming that if you have a real FPV / camera stack… even an integrated one like DJI or caddix.. that’s not in the cards…. (?)

 

[UCDWino]

Well, going off a plane that seems to fit your mission, I would look at the Hee-wing and its motor/prop combination as a start. 1404 motors with a 3.8x3 prop. Get FPV has over a dozen different 1404 motors listed in their store from 1550kv up to 6500kv.

Doing the math real quick, on the stock 1404 3700kv motor with a 3" prop pitch and a 3 cell battery, the Hee Wing has a pitch speed (no drag, 100% prop efficiency) of about 39 MPH. With the same prop and a 6500kv motor that jumps to 68MPH. Now, you're never going to achieve those speeds in reality because drag exists, but it illustrates the range.

I think this is the answer I was looking for, it makes sense.

i Think I’ll design for 1404’s, and leave the spacing of the motors large enough to clear 3” props with at least 2” of clearance… so that experimentation up to 5” props is possible.

thank you guys for helping me work through this!

 

[JasonK]

Not really. I just want to be able to carry good FPV gear and a good flight recording camera… i recall One of the FT videos where bixler was talking about their micro twin airplanes being light enough to not cross some regulatory weight threshold…. But those planes were REALLY small.. the ones where you climb by applying throttle…. So I’m assuming that if you have a real FPV / camera stack… even an integrated one like DJI or caddix.. that’s not in the cards…. (?)

I have sub-250g FPV fixed wing stuff. my profile pick was one (it is also a resource) and there are some other options also. the FT dart would make a good option (but you would have to cut it yourself as they stopped making the kit).

 

[Tench745]

I have sub-250g FPV fixed wing stuff. my profile pick was one (it is also a resource) and there are some other options also. the FT dart would make a good option (but you would have to cut it yourself as they stopped making the kit).

THAT WAS THE ONE! I remembered FT having a small twin flying wing and I coudn't find it. Thought I was going crazy...

 

[Wingnut pilot]

i was working on this same idea last year but using a flying wing, well more of a delta shape. my reasoning was i wear glasses but not to fly fpv and i figured i could use the catapult to launch w/goggles on. interested in seeing where u go with this.

 

[IgnacioBryan]

I initially believed that the thrill of the event came from the high speeds involved. However, upon viewing the video, your point about slower and smaller planes being more agile and entertaining makes sense. Regarding the choice of equipment, do we specifically need a DJI air unit? The website indicates a weight of only 36g, which isn't very heavy, but compared to something like the 3g Caddx Ant that fits smaller vehicles, it might seem bulky. It's likely that the weight, size, and power systems would resemble something akin to the FT Arrow. The first step, I believe, would be establishing the design parameters to adhere to, guiding the design process. Speaking of which, have you ever considered exploring unique opportunities like online betting using gcash https://gcashgambling.ph/blog/betting-sites/ ?