Help! Need expert input into ideas for upcoming design comp

[Tuttle]

Hi, apologies if this is in the wrong section, but I'm hoping to source some input and suggestions on my ideas for an upcoming indoor flying challenge in my uni class.

The challenge is to build a foamie that can fly within the constraints of an indoor basketball court, with a takeoff then a racetrack pattern, flying through a single (upright) 6ft hoop, and then drop a payload (candybar) onto a small (2ft diameter) target, and then re-land in the same takeoff/landing area.
Some constraints are that we cannot use off the shelf products for the airfoils and body, must use the supplied 2 motors and props, and it must be fixed wing.

My overriding principle is to KISS, so unless deemed absolutely necessary, I'm ruling out things like twin wings (I've also decided against a flying wing), multi-dihedral staged wings, flaps, V-tail etc.

My ideas at this stage are:
- 2 motors in traditional config, counter-rotating (centre line tracking on takeoff is a marked criteria)
- single high lift wing, which would allow for constant slowest possible flight (there's no time limit and flight time will be under 2mins).
The types I've found in my research are either NACA 4412, 6412, or Clark Y (with flat underside). From my understanding, the airfoil itself won't be the biggest limitation, but rather speed and weight?
Which brings me to the next issue - unknown mass. With the main wing-length limitation being the hoop diameter, I'm thinking a max wingspan of 3ft (total) to allow for margin of error when shooting the hoop.
Chord length wise, I'm unsure, but we are provided the foam blocks (if choosing to use foam), so plan was to maximize that?
Whitch raises another question - foam wing vs foam board? We do get rewarded for creativity and enginuity, so nailing a hot wire cut wing with the template method would be great, but if the weight penalty isn't worth it, then foam board it might have to be?
For stability, I was thinking of a simple 3 of 4 degree dihedral (with wings rubberbanded on to fuselage at a rigging angle of 3-4 degrees upward compared to level/tail plane)?
- The fuselage I was just going to make a simply square cross-section box type, to allow for electronics, a bit of a nose in case CoG needs moving forward.
- Tail section I was going to go with standard setup, with rudder/tailwheel primarily for ground tracking (airlerons in flight for turns due to tightish space), and standard elevator.
- For the drop requirement, again KISS is my guiding principle, so a vertical "box" to hold the candy bar, running through the fuselage as close to CoG as possible (so no major shift when dropped), and just a simple servo activated flap at the bottom for quick release (or even just a pin).
-Motor mounts: ??? Only ever built single pusher or pullers, so not sure on the KISS way to mount the two 1700kv brushless motors.. Just bury them into the wing (another plus with the foam wing)?

Phew! So in saying all that, do any experts have any feedback, tips, suggestions, criticisms etc?
My goal is to achieve maximum accuracy by flying as slow as possible, whilst maintaining control and not being on the edge of a stall (we do get practice flights to learn the ideal speed).

My main concern lie in the wing loading at slow speeds in the racetrack turns, the ideal wing length and chord length to achieve this without knowing the overall weight (micro RC, small 2S battery, standard micro servos, candybar, and aircraft weight itself.)

Thanks for any input and help you can provide! Looking forward to the build!

Edit, just attached a (very) rough sketch of what my initial idea would look like, mainly to highlight where the candy bar perils sit prior to drop.

 

[quorneng]

Tuttle
That is quite a target specification!
My initial reaction is it will test your RC flying skill (3" span through a 6" hoop!) as much as if not more so than actually building the plane.
What motors are supplied? The power/weight could be an important factor.
You are quite correct that the all up weight will be critical, then will come aerodynamic stability and finally control.
With such a limitation in span why not a biplane or even a triplane?
There are both aerodynamic and structural advantages in a small span multiple wing layout. More wing area means slower flying speed.
I would however be surprised if you can achieve the best workable configuration first time round. You may have build several prototypes.

If I was doing this challenge I would definitely use foam board, as thin as I could get, and build a proper wing section. At such low speed and small size the actual wing section is not as critical as being able to build light yet structurally just strong enough.
As an example I suspect these flyers could "hover" through a 6ft hoop and they use flat plate wings!

 

[Merv]

The weight of the plane is going to be absolutely critical. With smaller indoor planes, about 20 inch span, the wing loading is in the 1 to 1.5 Oz per square foot of wing area. The normal size FT planes have a wing loading in the 10-15 Oz per square foot of wing. A 10x difference.

I hope the candy bar is microscopic.

 

[Piotrsko]

Which candy bar? Figure located on the CG
For this, airfoil ordinates are relatively meaningless since you won't be going fast enough to be anything but turbulent/unattached. Reynolds numbers aren't big enough for anything else Flat plate is probably easiest as is profile fuselage with wright pusher style undercambered giving a minor advantage. Look to @Silver Surfer FPV for design ideas. Don't forget massive downthrust on tractor, upthrust on pushers.

I could see a 1 sheet DTFB plank flying wing winning this contest 2 sheet if you absolutely must have an airfoil

Biggest problem is the hoop fly through unless you are running FPV. Need something that can bounce when it hits the hoop which it probably will

My tuppence, YMMV

 

[L Edge]

Are you sure you have to use the 2 motors?

 

[Tuttle]

Thanks all for the feedback! I'll get back to each of your great contributions a bit later on, but for the mean time, I've been able to clarify a few things:
We can't use items outside what is provided, that being the electronics, 2 different thickness foam boards, and balsa wood (both sticks/"rods" which teams have managed to use in the past as a centre line fuselage, along with thin sheets of balsa).
There's no requirement to use both engines either, but given the above discussions about Power to Weight issues, would using two be the better option?

Im open to using multiple wings (you convinced me with the shorter length argument), but a biplane introduces more structure/weight which is a concern.

Does having a 2 wing aircraft, with one wing as the tail plane (and therefore an elevator) help? Flitetest have shown these types before, and that would then allow a single or twin balsa wood boom/frame to mount them to.

And finally with engine setup, is the consensus a pusher is a better option? Is there any merit to considering a centreline pusher and puller given the same battery will be on board regardless of 1v2 engines?
And if the props are in a pusher twin setup facing backwards, is there benefit to angling them downwards a few degrees?
Cheers again, the advice is much appreciated!

 

[quorneng]

What you need is the smallest physical weight for a given wing area with a limited span. As stated its the wing loading in oz/sqft that determines the minimum flying speed.
A biplane has twice the wing area therefore in theory 1/2 the wing loading for a given span. Hmmmm.

I did mention the importance of aerodynamic stability. A tandem wing design whilst in theory is more efficient does bring in a whole series of stability issues. The convention wing and tail plane layout is widely used for a reason. The same applies to the theoretically more efficient flying wing. Of course with modern gyro electronics even an unflyable plane by humans can be made to fly but I doubt you would be allowed to use them.
If you are going to use two motors, and can handle the resulting weight, a counter rotating push/pull arrangement can be effective as it virtually eliminates any motor torque effects which can be significant at really slow flying speeds.
Largely built up from thin foam sheet it is no indoor flyer but it shows the principle. With a high wing It is stable and aerobatic. The position of the motors allows the battery to be under a hatch in the nose. Incidentally there is nothing in the fuselage at the CofG!

Note the biplane in my Avatar. Quite a bit bigger and heavier but its wings are still just foam but being a biplane they are cross braced which makes them really rigid. Just like the full size the wings would fail without the bracing.

Nylon thread so it hardly weighs anything at all.
Just some thoughts.

 

[Piotrsko]

Clarification needed: you mentioned you have 2 thicknesses of foamboard. Does that mean only 2 sheets of a certain brand?
How much balsa can you use? I could go off the rails here with just having foamboard control surfaces.

What are the motors/ battery system?

2 wings fore and aft is called a tandem. If you're a Rutan follower quickie comes to mind and it's a viable option.

Odd question: do you know how to fly RC aircraft not in a simulator?

 

[L Edge]

Some thoughts:

Plane- a foam bipe to resolve flying through 6' hoop. A multi or large wing unless flying through dead center, I give you 2% for a fly through. A good stable design offers a best to keep speed down(some high alpha).
It also has to off good prop flow to insure roll, pitch and yaw. Use three servos, the ailerons(both wings need to move) controlled by one servo.

Takeoff and landing is normal. Flying thru hoop requires power on, and slow speed is set by couple of degrees of high alpha and using rudder to steer thru. Flying level to drop candy is tough, so bring bipe to vertical, hover over center and drop. Use a paper cup that is held on by rubber bands. Then land.

Here is my bipe flying inverted and holds a nice inverted flare and rock stable. Good as any

 

[L Edge]

Thinking outside the box, myself, I would try this one. It is a modified STOL approach simplified. From a video, made mine and would fit the bill.

It consist of an inclined flat plate, powered in front with prop, three servos for positive control of pitch, yaw, and roll and has end plates to increase wing stability.
On finds on takeoff, air flow is trapped underneath which helps shorter liftoffs as well as the inclined wing.
If you keep a balanced high alpha wing angle and prop setting, a slow forward flight is possible. So more time to line up with the 6' hoop.
To drop the candy, is all you need is to come across low and arc it vertical so it is under the 2ft circle, you then can drop. If your sharp, use the high end of the rudder to unlock the candy slot and let it slide off the wing as well as doing a hammerhead with the rudder.
Shoot for a spot landing like the vid did.

KISS, it is.

I named mine "The OtherUP". The reason I made it is to land inverted. Not only land, but got to practice take-offs inverted. How many pilots do you know off that have taken off inverted and also can wave to the audience?

 

[Mr NCT]

Thinking outside the box, myself, I would try this one. It is a modified STOL approach simplified. From a video, made mine and would fit the bill.

It consist of an inclined flat plate, powered in front with prop, three servos for positive control of pitch, yaw, and roll and has end plates to increase wing stability.
On finds on takeoff, air flow is trapped underneath which helps shorter liftoffs as well as the inclined wing.
If you keep a balanced high alpha wing angle and prop setting, a slow forward flight is possible. So more time to line up with the 6' hoop.
To drop the candy, is all you need is to come across low and arc it vertical so it is under the 2ft circle, you then can drop. If your sharp, use the high end of the rudder to unlock the candy slot and let it slide off the wing as well as doing a hammerhead with the rudder.
Shoot for a spot landing like the vid did.

KISS, it is.

I named mine "The OtherUP". The reason I made it is to land inverted. Not only land, but got to practice take-offs inverted. How many pilots do you know off that have taken off inverted and also can wave to the audience?

How do we not have those plans here?!? What a hoot‼️

 

[L Edge]

How do we not have those plans here?!? What a hoot‼️

My design was from the video and I used paper to solve my problems. Like the radius of the side boards so the prop turns and clears flipping it upside down. Over time, the paper pattern got lost and the ship got destroyed when I challenged the flying club president to takeoff inverted. I won $25 to add to my $25 for the Christmas toy fund. So, no plans. No video, that was before I had got a hat camera.

2 things I remember were the 20 x 24' size and the 16 degree angle for the flat plate. That was one interesting plane to bring to the field and demo it. It is like a 4 D airplane. Especially the wave. Your welcome to try it.

 

[Tuttle]

Thanks once again for all the input - what an incredible resource it is to have so many experts in one place! (credit to FT for being the reason we are all here!)

For the person who asked, absolutely enjoy flying RC, combined with being a RW pilot, I have no issues with the flying part of this equation. But I have only ever flown off the shelf aircraft, with only minor custom mods - never something built from scratch!

Of all the ideas, I think we're leaning towards a single high wing aircraft, and the push/pull setup that quorneng displayed is a very unique solution that may achieve exactly what is needed! (Power-weight check, centreline thrust check, counter rotating for centreline tracking check).

Also 100% on board with minimal weight, even at the expense of streamlining or aesthetics!

The complexities of a bi or tri just seem unneccesary (hopefully) and again would lead to an increase in weight.

The big question now is, once the wing surface area calcs are done, how does one determine the length vs chord length ratio to achieve it? Ideally the stubbier the wings the better, but even with a flat plate wing, there mist be some ideal scale model ratio that gives best of both worlds?

 

[quorneng]

Tuttle
You will have to decide what the all up weight is likely to be be. Does not have to be exact, a best guess will do at this stage. It determines the likely wing loading (ozs/sqft)
As a general rule 10 oz/sqft will give fairly gentle flight characteristics, at 20oz/sq ft things will start to get fast.
You obviously have a severe span restriction to fly through a 6ft hoop which would suggest a short stubby wing. How short and stubby the wing has to be will depend of your weight guess.
Lets say you select a 4ft span and give it a chord of 1ft that will give you 4 sqft wing area. At a comfortable 10 oz/sqft wing loading it would limit the total weight to 40oz.. You might consider doubling the weight to 80 oz. It would then need twice the power to fly and would do so at a speed that would likely make it really hard to fly though a hoop with just 1ft clearance either side and about the same vertical clearance.

Like most design challenges it is important to identify which specified limitation overrides all the others. In your case it is flying through the hoop. If you can achieve that reliably the other limitations will have less influence on the design so their solution will be easier to achieve.

About the only plane I have that i would be happy to even try to fly though a 6ft hoop is a very light and slow flyer. 40" span, 1.5 sqft wing area however it only weighs 8 oz so giving a wing loading of just 5.3 oz/sqft.

As a by product If you can anywhere near that sort of all up weight you wont need two motors and thus can use a smaller lighter battery.
Just some thoughts.

 

[L Edge]

Hi, apologies if this is in the wrong section, but I'm hoping to source some input and suggestions on my ideas for an upcoming indoor flying challenge in my uni class.

The challenge is to build a foamie that can fly within the constraints of an indoor basketball court, with a takeoff then a racetrack pattern, flying through a single (upright) 6ft hoop, and then drop a payload (candybar) onto a small (2ft diameter) target, and then re-land in the same takeoff/landing area.
Some constraints are that we cannot use off the shelf products for the airfoils and body, must use the supplied 2 motors and props, and it must be fixed wing.

My overriding principle is to KISS, so unless deemed absolutely necessary, I'm ruling out things like twin wings (I've also decided against a flying wing), multi-dihedral staged wings, flaps, V-tail etc.

My ideas at this stage are:
- 2 motors in traditional config, counter-rotating (centre line tracking on takeoff is a marked criteria)
- single high lift wing, which would allow for constant slowest possible flight (there's no time limit and flight time will be under 2mins).
The types I've found in my research are either NACA 4412, 6412, or Clark Y (with flat underside). From my understanding, the airfoil itself won't be the biggest limitation, but rather speed and weight?
Which brings me to the next issue - unknown mass. With the main wing-length limitation being the hoop diameter, I'm thinking a max wingspan of 3ft (total) to allow for margin of error when shooting the hoop.
Chord length wise, I'm unsure, but we are provided the foam blocks (if choosing to use foam), so plan was to maximize that?
Whitch raises another question - foam wing vs foam board? We do get rewarded for creativity and enginuity, so nailing a hot wire cut wing with the template method would be great, but if the weight penalty isn't worth it, then foam board it might have to be?
For stability, I was thinking of a simple 3 of 4 degree dihedral (with wings rubberbanded on to fuselage at a rigging angle of 3-4 degrees upward compared to level/tail plane)?
- The fuselage I was just going to make a simply square cross-section box type, to allow for electronics, a bit of a nose in case CoG needs moving forward.
- Tail section I was going to go with standard setup, with rudder/tailwheel primarily for ground tracking (airlerons in flight for turns due to tightish space), and standard elevator.
- For the drop requirement, again KISS is my guiding principle, so a vertical "box" to hold the candy bar, running through the fuselage as close to CoG as possible (so no major shift when dropped), and just a simple servo activated flap at the bottom for quick release (or even just a pin).
-Motor mounts: ??? Only ever built single pusher or pullers, so not sure on the KISS way to mount the two 1700kv brushless motors.. Just bury them into the wing (another plus with the foam wing)?

Phew! So in saying all that, do any experts have any feedback, tips, suggestions, criticisms etc?
My goal is to achieve maximum accuracy by flying as slow as possible, whilst maintaining control and not being on the edge of a stall (we do get practice flights to learn the ideal speed).

My main concern lie in the wing loading at slow speeds in the racetrack turns, the ideal wing length and chord length to achieve this without knowing the overall weight (micro RC, small 2S battery, standard micro servos, candybar, and aircraft weight itself.)

Thanks for any input and help you can provide! Looking forward to the build!

Edit, just attached a (very) rough sketch of what my initial idea would look like, mainly to highlight where the candy bar perils sit prior to drop.

Here is my entry for your project. The flat plate is at an angle of 13 degrees and can act as a STOL thru the hoop and (I would use a cup to drop the candy) by going +90 degree vertical and then land. See my thread for build:

Challenge and Some additional fun

Taken from another thread where a student wanted some ideas: The Challenge is to build a foamie that can fly within the constraints of an indoor basketball court, with a takeoff then a racetrack pattern, flying through a single (upright) 6ft hoop, and then drop a payload (candybar) onto a small...

forum.flitetest.com

Abrupt ending was my motor burned out but on a good day claim I could accomplish your mission with real ease.

 

[Piotrsko]

Rules of thumb on wingspan: longer aspect ratio is more efficient. Suspect efficiency isn't an issue here due to needing to fly through hoop. Small flying area denotes need for agility. Ease of build promotes a big square wing. Failing that, I had reasonable success with a 20" diameter pizza pan wing on my slow stick. Aero engineers were horrified with the aspect ratio of 1 and no tip plates, no diehederal.

Don't see points awarded for beauty. Except for oddly shaped tips, @L Edges design checks all my boxe s for your task, but also realize that he flies probably 5 times better than me.

Nice to find out you're not a newbie and can reasonably fly this late in the process.

 

[L Edge]

Rules of thumb on wingspan: longer aspect ratio is more efficient. Suspect efficiency isn't an issue here due to needing to fly through hoop. Small flying area denotes need for agility. Ease of build promotes a big square wing. Failing that, I had reasonable success with a 20" diameter pizza pan wing on my slow stick. Aero engineers were horrified with the aspect ratio of 1 and no tip plates, no diehederal.

Don't see points awarded for beauty. Except for oddly shaped tips, @L Edges design checks all my boxe s for your task, but also realize that he flies probably 5 times better than me.

Nice to find out you're not a newbie and can reasonably fly this late in the process.

Welcome to my method of madness. I like different ways to solve the problem. My way was done to get more info and data for other projects.
Besides, now I can shoot for the other goal. That is land inverted and take off inverted. Depends on my reaction time. Not to my pilots have done that. Do you remember this project you commented on? Some good points you mentioned.

Never got it off, dinged it, but gleaned enough info from this project that I now got 3 things(need more thrust, more weight in front to move CG forward,(like pilot of real plane) and know it will be real twitchy on controls. So this project is still alive.

I enjoy designing things that don't exist in the RC world. How about a transport plane that can hover? 6th generation DarkStar? Done!
How about L E Flaps that are also workable elevons. Won't need canards anymore.

Already have a different approach Red Bull Flugtag model that shows great promise(it flies) and evaluating my approach to getting a NGAD fighter. Don't get points awarded for beauty(your statement), but I do have the beauty of a "skunkworks". Anyway, always appreciate your opinions and suggestions. Keep them coming. I have had the passion to do RC since I was 15 and didn't get to it until I was in my 30's. Making up for it .

 

[Piotrsko]

Never did the inverted take off, thumbs too stoopid. Have flown and landed inverted, often by mistake. The FT bronco drags the horizontal stab on low inverted passes, bad juju but doesn't hurt anything. Whole flight inverted? Wow.
Snatch would be a problem on the LE slats idea.
I dunno, you seem to serve a purpose with the way you hammer away at the problem until it works. Kids today don't have that.