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Pumpkin drop event

Fire Fighting Plane "Challenge

#21
Here are some pictures of the build. The first picture is of the plane with wings sitting on top of fuselage. Note that the wings are not connected (as i am still trying to figure out how i want to connect them) IMG_6019.JPG The second and third pictures include the electronics IMG_6018.JPG IMG_6016.JPG The fourth picture is just the wing and fuselage.
 
#22
Whilst your chosen props, motors and battery will work it will be an inefficient high revving small prop layout and 4 motors will work your chosen battery pretty hard giving about 3 minutes at full power. Not ideal for a 'do anything' plane.
Small props are not particularly efficient and 4 blades even less so. You need a positive reason to adopt such a layout (scale?) and accept its drawbacks
Just one bigger motor driving a single larger 2 blade prop could easily generate the same thrust level and likely only need about half the amps to do it.
Less amps = longer flight!

Ok, thank you for the input, would some 6.5x6 props be better? I am trying to keep the same motors because someone gave them to me and i would much rather use them than buy a new motor. As for the props and battery i would be fine with getting a different prop\battery setup. are their any four blade props that are bigger and would be better? Also, what battery would you use. I am hoping to stay with a four blade prop as i think it would look very nice. Thank you
 

Attachments

Tjhochha

Active member
#23
Here are some pictures of the build. The first picture is of the plane with wings sitting on top of fuselage. Note that the wings are not connected (as i am still trying to figure out how i want to connect them)
You could go with the old pin and rubber band over the top method, but since you plan on carrying weight, the wing might tend to move around on you a bit. I stupidly didn't take any pictures of my wing attachment on my P2V build, but I attached some birch ply to the inside of the wing surfaces. I have a sleeve in the fuse that snugly fits around the wing. I added birch ply to the outside of the sleeve, then drilled through the fuse and the wings and used BBQ skewers to pin them in place, I'm not sure how structural it all is but that's half the fun of building. Breaking stuff and seeing what I can do different the next time to make it better.

Here is the best pic I have of the sleeve.
IMG_6970.JPG

Here is the best pic I have of the fuse with the 6 pins through the top of the fuse pinning the wings in place.
IMG_7005.JPG

I also have one paint stick attached to each wing on opposite sides of the center spar. they fit tightly into the wing and should add a decent amount of strength. Hopefully enough
 

FoamyDM

Building Fool-Flying Noob
#25
In my spruce goose, as a bouyancy measure I built in a lower section that I make airtight. It also gives me a flat space on top for things like batteries. Or a cargo bay.

Waterproof the space below and it can easily be used as a water/ baking powder bay. I would use a bifold bay door opening up. build a track for rollers to support the door. Power it with a tubed wire from a servo in the upper bay. Like a bike brake.

If you decide to use water the vent is important. Look at rc subs for ideas. Mr. Martin of Nautilus dry docks. And his you tube channel rcsubguy. As far as channels. The filling and dumping is just a bay door. Use the gear channel. (The plane won't have gear.

My last idea would be put in a Keurig pump. And have it pump in and out. It would be slow.
 

b-29er

Active member
#26
Alrighty, so here's what i'm seein.

To start with your motors, you're strapping a v8 to a golf cart tire. What do i mean? Your motor doesn't have a spec sheet, but heres one for a motor with the same size and 100kv reduction.
1543443121576.png
Basically you are trying to build a WACO Glider, and speed isnt as much a concern as power, so you can perform short takeoffs. My strong suggestion would be to get an APC E 7x5, because that prop will still be fairly small and potent on a 4s, or follow the guide above to figure out what to run on a 3s.

For your aircraft design, i would suggest redoing the wings for a few reasons. For an aircraft that is designed for payload:
1. Your wing doesn't have much thickness to it, so you won't generate much lift with the bernouli principle
2. Your wing is thin, which would be good for a glider, but doesn't leave much room for cargo
3. Your chord (aside from the tips) is pretty narrow, so you're reducing wing area.

My suggestion would be look at something like a trainer's wing. Take a look at this avistar for example:
1543444180769.png
Notice how the airfoil is fairly thick, but semisymmetric, and the chord is low? When the nose is pitched up, not only is the engine using some of its thrust to help lift the aircraft, but you also wind up with a very thick and clean airfoil section that generates a lot of lift. Sure, its not a great glider, but the extra surface area provides more lift and slower takeoffs and landings. The extra thickness also gives you area for extra structure, like spars, which you will need. Also notice the techniques they pointed out in the STOL website, like the hoerner wingtips and flaps?

My suggestion would be to re-do your wing. Use a much more aggressive airfoil. You could use something like the Armin wing, and up-size it to a 12-14" chord, and run a Home Depot ruler or two through each wing as a spar and mounting point for engines, which could also be attached with more home depot rulers. This would also give you a channel to mount wiring for motors/servos. If you're looking to mount it, rubber bands would probably work if you reinforce the fuselage with a couple of wooden formers glued to the inside with dowels running through them. When you do get ready to mount your wing, try to create a slight ramp to mount your wing with a bit of an up angle (like maybe an extra 2-3 degrees). That way you get a good angle of attack for slow takeoffs/landings, and you are mounting your engines at an angle. Also definitely have a set of flaps behind each engine. I would also upsize the elevator and rudder, so you have good authority at low airspeeds, or use a triple rudder like the Super Constellation.
 
#27
Alrighty, so here's what i'm seein.

To start with your motors, you're strapping a v8 to a golf cart tire. What do i mean? Your motor doesn't have a spec sheet, but heres one for a motor with the same size and 100kv reduction.
View attachment 119363
Basically you are trying to build a WACO Glider, and speed isnt as much a concern as power, so you can perform short takeoffs. My strong suggestion would be to get an APC E 7x5, because that prop will still be fairly small and potent on a 4s, or follow the guide above to figure out what to run on a 3s.

For your aircraft design, i would suggest redoing the wings for a few reasons. For an aircraft that is designed for payload:
1. Your wing doesn't have much thickness to it, so you won't generate much lift with the bernouli principle
2. Your wing is thin, which would be good for a glider, but doesn't leave much room for cargo
3. Your chord (aside from the tips) is pretty narrow, so you're reducing wing area.

My suggestion would be look at something like a trainer's wing. Take a look at this avistar for example:
View attachment 119364
Notice how the airfoil is fairly thick, but semisymmetric, and the chord is low? When the nose is pitched up, not only is the engine using some of its thrust to help lift the aircraft, but you also wind up with a very thick and clean airfoil section that generates a lot of lift. Sure, its not a great glider, but the extra surface area provides more lift and slower takeoffs and landings. The extra thickness also gives you area for extra structure, like spars, which you will need. Also notice the techniques they pointed out in the STOL website, like the hoerner wingtips and flaps?

My suggestion would be to re-do your wing. Use a much more aggressive airfoil. You could use something like the Armin wing, and up-size it to a 12-14" chord, and run a Home Depot ruler or two through each wing as a spar and mounting point for engines, which could also be attached with more home depot rulers. This would also give you a channel to mount wiring for motors/servos. If you're looking to mount it, rubber bands would probably work if you reinforce the fuselage with a couple of wooden formers glued to the inside with dowels running through them. When you do get ready to mount your wing, try to create a slight ramp to mount your wing with a bit of an up angle (like maybe an extra 2-3 degrees). That way you get a good angle of attack for slow takeoffs/landings, and you are mounting your engines at an angle. Also definitely have a set of flaps behind each engine. I would also upsize the elevator and rudder, so you have good authority at low airspeeds, or use a triple rudder like the Super Constellation.

Wow that was a ton of information! i really appreciate this as i am not a beginner in RC planes but am a beginner in scratch building. So what your saying is that the motors are fun but i should switch propellers? I didn't know there were different types of propellers and i also didn't know that they made a difference. Do you know someone who has a good definition of the different types of propellers and there different performances? So would something like this work for the prop? Which do you think would work better? https://www.motionrc.com/products/apc-7x5-thin-electric-propeller-black
or
https://www.motionrc.com/products/apc-7x5-slow-flyer-electric-propeller

Would you run this on something like a 3200 3s, a 2200 3s, or a 3000 4s?

So for the wing could i do something like this just with a 12 inch chord? Would that work with the fuselage i built (It seems like a huge wing)? So are you saying i should keep a 60inch wingspan but increase chord to 12 inches? Would this work? (just with thicker chord) .


Do you think the rudder/elevator i have on the fuselage would work? You don't know how much i appreciate this your help, thank you so much!
 
#29
I planned to use the four motors on the plane have differential thrust so i won't need a rudder servo, I also planned to have elevons instead of ailerons and an elevator just to make it more simple, i was hoping to just have three servos on the plane, left aileron, right aileron, and cargo door. Do you think this would work? Sorry for the ignorance, i know next to nothing in the world of scratch building. Also, do you know how dropping whatever it is that i drop would effect the flight characteristics? I plan to have the weight right on the CG so it wouldn't do to much, right? I figured i could just do a ramp style door on the center of Gravity.
 

b-29er

Active member
#30
Wow that was a ton of information! i really appreciate this as i am not a beginner in RC planes but am a beginner in scratch building. So what your saying is that the motors are fun but i should switch propellers? I didn't know there were different types of propellers and i also didn't know that they made a difference. Do you know someone who has a good definition of the different types of propellers and there different performances? So would something like this work for the prop? Which do you think would work better? https://www.motionrc.com/products/apc-7x5-thin-electric-propeller-black
or
https://www.motionrc.com/products/apc-7x5-slow-flyer-electric-propeller

Would you run this on something like a 3200 3s, a 2200 3s, or a 3000 4s?

So for the wing could i do something like this just with a 12 inch chord? Would that work with the fuselage i built (It seems like a huge wing)? So are you saying i should keep a 60inch wingspan but increase chord to 12 inches? Would this work? (just with thicker chord) .


Do you think the rudder/elevator i have on the fuselage would work? You don't know how much i appreciate this your help, thank you so much!

Well, that all depends. I would expect similar results if you go with those APC 7x5's on 4s as i would the XOAR 10x5 on 3s, which is to say between all your props, you should be at around 6.5lbs of thrust, full power (note, the testing took place at around 4500 feet, so you may wind up with more thrust, power draw). so keep it under...oh 12,13lbs, you should be good.

Yes, there are different propellers and different motors for different jobs. KV is a critical factor, as is size. KV is basically how many RPMs the motor will spin max with no load. The lower the KV, the higher the torque tends to be. Ex, those huge pancake motors they use on high lift quads tend do be super low KV, like 270. This means you can spin a massive propeller, but not very fast, or with a LOT of extra voltage. On the other side of this, you have racing quad motors, like the 2204/6/8 2300kv motors that spin a tiny prop but generate a very good amount of thrust at REALLY FAST SPEEDS. Now if you remember your physics class (i think) the formula for kinetic energy is 2*m*v^2. This is important because your propeller/motor is a way of moving air around. So its easier to move a large mass of air slowly than it is a smaller mass of air quickly. Its also easier to move a larger propeller through the air at a slower RPM than it is to move a smaller propeller through the air at insane speeds.

When you're picking stuff out like propellers and powerplants, you need to have a few things in mind in terms of your end goal, specifically:
1. How big is this thing going to be/ how much is it going to weigh
2. How do i want it to fly?
If you are going light and fast, for example like a pylon racer or you are trying to go over 100mph on a punjet, a racing quad outrunner or a high RPM inrunner is a good choice, because you get high RPMs and enough torque for your thrust. In your case, you are going average to slow speeds, probably in the mid 30s, and you want payload, so you want a motor that can at least hit a static pitch speed (how fast the air is leaving the prop) in your 40mph range, if not a bit more for cruise. I like to go for the kind of powerplants the RMRC anaconda uses, 5050 or so at 500kv or so, and a pretty pitchy 14" prop. This means takeoffs are inefficient, but i can hit a pretty good cruise with low amp draw because i don't necessarily have to keep my propeller spinning fast to keep it pushing air faster than the plane.

On your battery, here's how it works. Figure out how much amperage you are using at full power, in your case its like 80-90 amps. Now on your battery there should be an average C rating (dont go with the max C rating), and multiply this by the capacity of the battery. So a battery with 20c and 4a capacity is capable of safely discharging 80a constantly. If your battery is capable of an 80-90a discharge by that calculation, you should be fine.

Next off, the airfoil. The big question you wanna ask is, again "what do i wanna do with this plane?" If your answer is to go fast, you want a thinner, sleeker airfoil that is just barely bigger than the carbon fiber you're using for the spars, and you want a symmetric foil (same on top and bottom), which tends to be better for not creating lift-based drag and for flying inverted. In your case, you're looking for lift, so an airfoil with a higher thickness to chord and a flat bottom, like the armin or a clark Y, are great choices. Thicker airfoils have two advantages, they allow you to use a lighter spar, because you are putting the forces on your spar (tension and compression) farther from the center of the spar. The b-36 is a great example of this. It uses a 20% thickness NACA 63-420 airfoil, meaning the thickest part of the airfoil is 20% of the length of the airfoil. This makes the wing about half as thick as the body in places, but allows for an airfoil thats very clean, provides a LOT of lift, and plenty of area for the wing spars to support the wing, which is why you could see a plane with a wing 30 feet longer than a 747 being flown 20 years prior. In your case, the armin wing should be fine, though i might suggest gluing some wooden rods to the top/bottom of the foam spar to add some strength, or just use a home depot ruler.

So TL;DR, and to actually answer your question: Yes, a 12" chord, 60" wing should be good, you could almost go 14" if you want. Your motors should be plenty punchy for that if your all up weight is less than 12lbs. Multiply the C rating of your battery by the number of amps it holds, if it goes up to 90 in your case, you should be good.

On your rudder/elevator situation, the point is to give you authority on your pitch/yaw (up/down, left/right) axes. These need to be larger to be able to keep up with your aircraft at lower speeds where your control surfaces have less authority. So my thought would be go larger on both, and you can always downsize later if you feel like they are too big/too draggy. But look at the Guinea Pig, it has a triple rudder setup and a pretty sizeable elevator. Given what your plane is doing, i would look at that for inspiration.

Oh, and for those videos...
1543452057873.png
they're from the same guy on the same airfoil, one is just a little more complete (The colored wing one) so watch both if you like, i would recommend the one with the colored tape, because i like colored tape.
 
#31
You know I was thinking to build a plane just like this. I think for your wings you should probably put some reinforcement especially if you decide to put water in the plane as the weight could snap the wings in a high-g scenario. Maybe some popsicle sticks or a paint stick is what I would use.
 

quorneng

Well-known member
#32
The first rule of scratch building is "copy what others have done" and the second rule is to check from others what they did really works.

As b-29er suggests a commercially successful trainer plane is a good starting point to give you workable dimensions. It will not be the most efficient in aerodynamics but it will fly well and have reasonable manners. It would not be much use as a trainer plane if it didn't!
Any plane is a compromise of conflicting requirements. If you stray too far from the basic layout you might get a benefit in some ways but with a penalty in others.
For example a high performance glider layout, big span narrow chord wings and tiny everything else, is aerodynamically efficient, it can glide a long way relatively fast yet only slowly looses height, but it is not a good load carrier. The wings simply cannot be made strong enough.
A plane with a shorter broader wing of the same area will be better able to carry a load but it will need at bit more power to maintain level flight.
Bigger slower tuning propellers are significantly more efficient than small high revving ones but at some point the size of a single prop compared to the wing span can bring its own problems.
The conventional ailerons, elevator, rudder combination is a very common layout for a reason - it works! You can do without ailerons or rudder but not both but you have to compromise on other things to do it. A delta can be flown perfectly well using just two servos but it does require significantly more power than a convention layout.
You can use differential thrust to steer and do away with a rudder servo but the complexities and penalties from using two or more motors will likely outweigh any weigh penalty of a correctly sized rudder servo.

So copying is much easier to start with until you have acquired the necessary design experience which for most modellers comes from much trial and error. ;)
 

b-29er

Active member
#33
You know I was thinking to build a plane just like this. I think for your wings you should probably put some reinforcement especially if you decide to put water in the plane as the weight could snap the wings in a high-g scenario. Maybe some popsicle sticks or a paint stick is what I would use.
You remind me of a friend of mine, would use hot glue and popsicle sticks for everything. Given the size, i'd recommend Home Depot rulers, since they'll go from root to tip easily on each half of the wing, and are plenty thick and strong, and you really can't beat $4 for a pair of wing spars
 

Tjhochha

Active member
#34
As for your control plans, I may be completely off base, I have never flown a plane with elevons and am fairly inexperienced with RC flight. In my basic understanding, the differential thrust should work ok for turning with the relatively small vertical stabilizer, but keeping the small stabilizer can lead to stability issues. Also as quorneng said, the quad motors will reduce the effectiveness of the differential thrust. I believe planes rotate around the center of mass. With two motors on one side of the plane, even though the thrust will only be coming from one side of the plane, the two motors will attempt to continue at the same speed relative to each other as opposed to a single outside motor forcing the plane to rotate around the center of mass.
IMG_7064.JPG
I believe you may also have issues with your elevon control plan. With a flying wing, the elevons are very large compared to the aircraft size, they have a huge control area, they are also the farthest back portion of the plane. I think with the elevon plan you have with a tail, the tail will have more authority than an the elevons and will prevent your plane from changing the pitch of the plane. If I'm thinking about it correctly, a plane uses the air traveling over the horizontal stabilizer and control surface as a force acting on a lever. With the tail a long ways back, a small force will rotate the plane around the CG causing the plane to pitch up or down. when using elevons on a plane with a tail will require more force from the elevons to overcome the stabilization provided by the tail in order to cause the plane to rotate and pitch up or down.
IMG_7067.JPG
I think what you have planned will act more like flaps, increasing and decreasing lift on the main wing vs. a more conventional rotating the plane around the CG.
I agree with quorneng, a more conventional control plan at least with elevator control would greatly increase the ease of flying when you get it finished up.

Well there's my 10¢, that was way more than 2¢, and probably unclear and mostly wrong.
 

Tjhochha

Active member
#35
For my wing profile, I copied the wing design of the Guinea pig and modified it for the wing dihedral and for the taper of the wing from the dihedral point. It may end up not having the lift I am looking for but I thought it was a good starting point. I also copied the rest of the plane design from an old control line plan set I found for the P2V I was building. I need to go out and take some pics of the P2V they set at our airport entrance after they retired it. after looking at my plane and driving by the airport the other day, the real plane seems much more "stocky." shorter and thicker fuselage, thicker wings, larger tail surfaces.
 

b-29er

Active member
#36
As for your control plans, I may be completely off base, I have never flown a plane with elevons and am fairly inexperienced with RC flight. In my basic understanding, the differential thrust should work ok for turning with the relatively small vertical stabilizer, but keeping the small stabilizer can lead to stability issues. Also as quorneng said, the quad motors will reduce the effectiveness of the differential thrust. I believe planes rotate around the center of mass. With two motors on one side of the plane, even though the thrust will only be coming from one side of the plane, the two motors will attempt to continue at the same speed relative to each other as opposed to a single outside motor forcing the plane to rotate around the center of mass.
View attachment 119374
I believe you may also have issues with your elevon control plan. With a flying wing, the elevons are very large compared to the aircraft size, they have a huge control area, they are also the farthest back portion of the plane. I think with the elevon plan you have with a tail, the tail will have more authority than an the elevons and will prevent your plane from changing the pitch of the plane. If I'm thinking about it correctly, a plane uses the air traveling over the horizontal stabilizer and control surface as a force acting on a lever. With the tail a long ways back, a small force will rotate the plane around the CG causing the plane to pitch up or down. when using elevons on a plane with a tail will require more force from the elevons to overcome the stabilization provided by the tail in order to cause the plane to rotate and pitch up or down.
View attachment 119375
I think what you have planned will act more like flaps, increasing and decreasing lift on the main wing vs. a more conventional rotating the plane around the CG.
I agree with quorneng, a more conventional control plan at least with elevator control would greatly increase the ease of flying when you get it finished up.

Well there's my 10¢, that was way more than 2¢, and probably unclear and mostly wrong.
Wow, i didnt see the elevon mixing part. Yeah elevons dont work on conventional aircraft. You need an elevator, unless you're doing a canard or a delta. Which...Canard may not be a horrid idea, if you're willing to do the math to figure out the CG. You could use a larger elevator and give yourself even more lift.
 
#37
You remind me of a friend of mine, would use hot glue and popsicle sticks for everything. Given the size, i'd recommend Home Depot rulers, since they'll go from root to tip easily on each half of the wing, and are plenty thick and strong, and you really can't beat $4 for a pair of wing spars
Yeah, and those rulers provide great strength while not adding too much weight either!

On a separate point, however, I see that the title of this post has "challenge" in it. Does this mean that someone else could partake in the fun? I personally would be interested in another project to chew on.
 
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b-29er

Active member
#38
Yeah, and those rulers provide great strength while not adding too much weight either!

On a separate point, however, I see that the title of this post has "challenge" in it. Does this mean that someone else could partake in the fun? I personally would be interested in another project to chew on.
i mean, i don't think IcedStorm is putting a patent on an RC plane that fights fires, go for it.
 
#39
Wow thank ya'll for everything, As for my battery it is a 30C 3S so i am good there. I will be making the armin wing from the video, with a 13 inch chord and two 30 inch segments. Which propeller do you think i should run using a 30c 3s? Does it matter?
https://www.motionrc.com/products/apc-7x5-slow-flyer-electric-propeller
https://www.motionrc.com/products/apc-7x5-thin-electric-propeller-black

Do you think i need counter rotating props? I would rather not do them if i don't need them because its just more complex but if i need them.
I will be using home depot sticks as spars. I guess i will upscale the rudder/elevator situation. Because of your input, i will be doing one elevator per wing with a elevator on the tail (per usual), my rudder control will be through differential thrust. I would love if you joined me on this journey jaxie6 as i made this thread because i thought it was something cool and i wanted to do it in the hopes that other people would follow (although as it happened i am glad that i am the follower). So go ahead! i would love to see what you come up with! 12-13 pounds wow! I didn't plan for this plane to carry that much weight! I was planning for it to have a small cargo hold maybe half the size of a water bottle! I guess i will have a lot more carrying capacity then i thought! I did the math and those propellers which are very similair to the APC E 7x5 should be giving me in total about 4.15 pounds of thrust on 3S so that should work as even if the plane is 6 pounds it should still produce a good thrust ratio. Thanks for all the help as with you i would never be this far!
 

Tjhochha

Active member
#40
From watching FT videos, It doesn't sound like counter rotating is essential, but does help.

Sorry, I didn't mean to sound so critical in my post, I just wanted to help out a bit to give our planes the best chance of flying.

Initially I only intended to have just a set of bomb bay doors on the bottom of my plane so I could drop stuff, but I do like your idea of trying to hold water to dump. I think initially, I may just drop small water balloons. I also haven't figured out where I want to fit my electronics.
 
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