Prop choice and thrust vs top speed vs acceleration

[Andy.T.]

My motor mounts on foamboard planes have evolved. Because all my FT planes are belly landers I've moved to reinforcing the front of the sides of the fuse with balsa wood. Peel the paper off the front of the fuse back to the wing and glue/laminate some 1/16 balsa to the fuse. Glue the firewall to the balsa. Go ahead and use filament tape too.

Great thread...thanks for bringing up the topic.

The reinforcement with 1/16" balsa seems like a good idea. I haven't done that with a significant area of a fuse yet; so far just added some 1/16" plywood around where landing gear meet the fuse.
Would you mind sharing a pic of how your motor mounts are? I've thought about doing away w/ the concept of a power pod but haven't worked out how to have the motor mounting accessible enough to be permanently mounted. I've thought about making something out of balsa or other wood that is similar in concept to the swappable power pod - maybe a bunch shorter since weight. But that's still not really a permanent mount. This FT3D build seemed like a good time to try something tho as I don't expect the plane to remain fully intact indefinitely, and I figure I'll end up having to put a larger motor on it requiring not using the metal X mounts anyways.

 

[Merv]

...So I was curious how long your landing gear wire is and how much prop clearance you have...

My landing gear is about 4 inches tall, I'm using 2.5 inch wheels & have about 2.5-3 inches of ground clearance. My wheels are slightly forward of the wing when the plane is level.

...You don't have issues w/ the motor being bolted directly to the firewall...

No, I run screws through the firewall directly into the motor. The firewall is hot glued & fiber reinforced taped to the power pod. I have upgraded the power pod, I use coroplast instead of foam. I cut a slot in the PP to allow it to be driven into the fuse whenever it lands motor first.

The firewall connection to the power pod is definitely the weak link. I have to reattach it every 10-20 flights.

I learned to design a weak spot that will give way first. Something that is easily repaired. I'd rather reattach a firewall than replace a bent motor shaft.

 

[danskis]

@Andy.T.

Sorry no pics as everything is buried. And yes, I have traded off accessibility for durability. Perhaps Merv's reinforced power pod is the solution you're looking for. It sounds like a good idea to me.

I use the X mount with small sheet metal screws put in from the front to hold it on. I'll use at least a 1/8 inch thick plywood firewall glued to the balsa with some fillets in the corners. On some planes I have attempted a removable cowl to improve access which adds a level of complexity to the build.

 

[Andy.T.]

My landing gear is about...
...
I learned to design a weak spot that will give way first. Something that is easily repaired. I'd rather reattach a firewall than replace a bent motor shaft.

Love it, all good stuff. Appreciate the info as always. I must have put my landing gear a smidge further back; I think mine are about level with the leading edge. The slot and insert method like in the Simple Cub was easy and convenient, but I don't think I could have moved it much more forward and still had room for the battery.

I really like your comment about designing in a weak point. I've, sort of unfortunately?, had the opportunity to see how well those weak points absorb the force of a...steeper angle of impact or harder impact than intended
One of the firewalls on my Cub that I replaced after my first signal loss crash just absolutely exploded; the tape mostly held it together, but it was in crumbly half a dozen pieces.
Where/how do you cut this slot into the PP though? I'm having troubles envisioning a slot that would help the power pod slide further into the fuse. Something akin to an intended crumple zone sorta makes sense to me to absorb energy.

 

[Merv]

...Where/how do you cut this slot into the PP though...

Install the PP where you want it, then poke the bbq squire through. Shove the PP into the fuse about 1.5 inches or so and poke a 2nd hole. Then remove the PP and connect the holes with your razor blade making the slot.

I should also add, I don't make the firewall taller than the PP, this allows the PP to slide inward more freely. I now have to support the PP from the bottom with something else.

I discovered this when one of my planes nose planted & shoved the PP into the fuse. The squire made a "slot" in the side of my fuse. This has probably never happened to anyone else. I thought, this looks kinda ugly in the side of fuse but if the slot were in the PP nobody would know. Now I reinforce the hole in the fuse with a gift card or other material & cut the slot in the PP.

You are right, it is a designed crumple zone to absorb the energy.

 

[L Edge]

I got to fly my FT-3D a couple times over the holiday weekend. Before I got it trimmed, holy cow was is squirrely!!! Surprised me a bit how much left aileron trim it needed, but it's fine. I probably just need some stick time, maybe even when I'm not shivering in 10 degree weather, but even the 50% expo felt pretty twitchy at times to me.
As usual, I had a question though. With only trying on an 11x5 so far, I think I can see your point about a 12" being even better. But with the 11", I only have 2" of clearance between prop and flat surface of workbench. That already seems to be more than eaten up when transitioning between uneven patches of grass, as the prop seemed to dig in on all the landings. Granted, landings were first 2 out of 3 rather dicey. So I was curious how long your landing gear wire is and how much prop clearance you have. I used the same gear as I built for my FT Simple Cub with 2.75" wheels. That leaves the "height" part of the landing gear wire at about 4.25".
Also related to prop clearance, the aluminum motor mount kept getting bent when prop dug in, significantly altering line of thrust. You don't have issues w/ the motor being bolted directly to the firewall, and it always ripping the firewall off the powerpod if the prop ever hits the ground or something? The heavy duty packing tape and hot glue for motor mount seems like maybe a 3536 is getting a big for that. And I'm still only running on a 2836

See you got it in the air. Like you said, it's twitchy until you get some stick time and later on reduce the expo. Are you shooting for a particular maneuver or take it as it comes?

I just built my design out of Adam's Redi-board and it does rather well. Used only 3 servos and built the top and bottom fuse area the same which makes it do a knife edge much easier being balanced. To handle damage, I just hot glue the motor mount right to the foam. So if the prop strikes the ground, it rips off the motor mount with some foam and glue. What I do is make the nose about an 1/2" longer and just cut away the damage fuse, and re-glue the motor mount to the fuse and move the battery to get the same CG.
I have never bent a motor shaft and even times, saves the prop.

 

[Andy.T.]

Install the PP where you want it, then poke the bbq squire through. Shove the PP into the fuse about 1.5 inches or so and poke a 2nd hole. Then remove the PP and connect the holes with your razor blade making the slot.

I should also add, I don't make the firewall taller than the PP, this allows the PP to slide inward more freely. I now have to support the PP from the bottom with something else.

I discovered this when one of my planes nose planted & shoved the PP into the fuse. The squire made a "slot" in the side of my fuse. This has probably never happened to anyone else. I thought, this looks kinda ugly in the side of fuse but if the slot were in the PP nobody would know. Now I reinforce the hole in the fuse with a gift card or other material & cut the slot in the PP.

You are right, it is a designed crumple zone to absorb the energy.

ohhh, brilliant, makes sense. I've been reinforcing both power pod and fuse w/ giftcards. I will rethink that! I hadn't thought about modifying how the front secures, that's cool!

 

[Andy.T.]

See you got it in the air. Like you said, it's twitchy until you get some stick time and later on reduce the expo. Are you shooting for a particular maneuver or take it as it comes?

I just built my design out of Adam's Redi-board and it does rather well. Used only 3 servos and built the top and bottom fuse area the same which makes it do a knife edge much easier being balanced. To handle damage, I just hot glue the motor mount right to the foam. So if the prop strikes the ground, it rips off the motor mount with some foam and glue. What I do is make the nose about an 1/2" longer and just cut away the damage fuse, and re-glue the motor mount to the fuse and move the battery to get the same CG.
I have never bent a motor shaft and even times, saves the prop.

Neat! that's clever, just building in some throw-away length! I hadn't ever really seriously wanted a flat plane like that, but I've been thinking more and more about it. I bet it's REAL light, huh? That could be fun, probably pretty quick build too. Not that the FT3D was that long of a build either, honestly.
Torque roll and harrier I suppose are what I want to be able to do the most. These particularly have made me think about the simple flat ones in the last week. Followed up by elevator and flat spins. I'm super excited to get some more stick time. I tried to hover it a little the first time I had it out for a few batteries. Went ok, actually. Probably better than a couple elevator attempts; these ended up having more forward movement as the plane fell. When I tried to do this one slower, I kept dropping a tip. The harriers I got it into were a little faster and lower AOA than I was hoping for. More stick time, and maybe a 12x4, can't wait to do more.
I was thinking about putting wingtip fences on; hadn't gotten to that yet.

 

[Andy.T.]

See you got it in the air. Like you said, it's twitchy until you get some stick time and later on reduce the expo. Are you shooting for a particular maneuver or take it as it comes?

I just built my design out of Adam's Redi-board and it does rather well. Used only 3 servos and built the top and bottom fuse area the same which makes it do a knife edge much easier being balanced. To handle damage, I just hot glue the motor mount right to the foam. So if the prop strikes the ground, it rips off the motor mount with some foam and glue. What I do is make the nose about an 1/2" longer and just cut away the damage fuse, and re-glue the motor mount to the fuse and move the battery to get the same CG.
I have never bent a motor shaft and even times, saves the prop.

Yeah the more I think about it, the more sure I am that a (flat foamy? I think thats what they're called....) will wind up in my hanger. I don't know that the FT3D feels like it flies quite as light as I wanted. Maybe the 12" prop will help that, idk...
How did you get away with only 3 servos? does one servo operate both ailerons ? Do you need to do anything to make the ailerons more rigid so the don't deflect more at the wing root, closer to the servo, then they do at the tips?

 

[L Edge]

Yeah the more I think about it, the more sure I am that a (flat foamy? I think thats what they're called....) will wind up in my hanger. I don't know that the FT3D feels like it flies quite as light as I wanted. Maybe the 12" prop will help that, idk...
How did you get away with only 3 servos? does one servo operate both ailerons ? Do you need to do anything to make the ailerons more rigid so the don't deflect more at the wing root, closer to the servo, then they do at the tips?

If you look close to mine, you will notice that the servo is mounted within the fuselage with a long servo arm that is connected to both ailerons. Tx and rx powered up, servo subtrim is set to arm(90 degrees) and both ailerons are trimmed. You then hot glue the servo to fuse and you are all set.
A 3D plane is designed to be lightweight, so if you tape top and bottom of the aileron, should be no warping problem. A good 3D pilot is not going to pull very HG loading.

If your Ft 3D plane is keep at 2-3 crash heights, it will last you a long time, so if you practice and follow the rules, no need for another model. What you need to do is to set a goal(say fly inverted and do figure 8"s) and go out and practice it until it becomes natural. Then move on to another and do the same. Take video and evaluate it at .25 speed to see where you need to fix your mistakes. After watching a FT person perform some 3D in the video, if you duplicate the build, it will perform well.

Practice, practice, and I would explore the prop 11 and 12 size with different low pitches including perhaps a 12 wide one.

 

[Merv]

...A good 3D pilot is not going to pull very HG loading...

I agree with most of your advice. But high G maneuvers are some of my favorites. I love doing square loops.

...follow the rules...

I guess this is my problem, I'm not a good rule follower. I learned 3D by throwing the sticks to the corners and seeing what happens. Pretty soon I was doing all kinds of tricks, mostly for my own enjoyment. Every once in a while I would impress someone else, which was a bonus, not the main goal.

My theory, if you don't crash every once in a while, you are not pushing yourself hard enough to grow as a pilot.

 

[Andy.T.]

Good tips, thanks! Sounds like a plan about just get out and practice with specific goals. I'll try to maintain focus on a goal when I fly
I like when I get video, but usually am not able to get anyone to come with that CAN video. Might be even harder to convince any of my girls to come w/ now that it's cold.
And also hear you about just making the FT3D last a while; I kinda just want to build and fly, everything.

Merv, I suck at following rules too. I also totally understand about for your own enjoyment. I usually fly alone. I don't mind, less nervous. Less hecklers. And the learning on your own. Up until these forums, the only things I knew were what I figured out myself. Probably why I have so many questions

 

[Merv]

...I usually fly alone. I don't mind, less nervous. Less hecklers...

Flying alone is good but fly with friends is better. I've had some incredible crashes and I'm glad I could share them with people i consider friends.

 

[Andy.T.]

Flying alone is good but fly with friends is better. I've had some incredible crashes and I'm glad I could share them with people i consider friends.

that's cool, I'm a little jealous. My dad usually comes to watch, but less so in the winter. And, he's a little too old for much video'ing; doesn't seem to have the knack for it.
I just don't have anyone else to fly with. All my RC friends I guess are from model warship combat. The ones that also fly are mostly across the country.

 

[L Edge]

I agree with most of your advice. But high G maneuvers are some of my favorites. I love doing square loops.

I guess this is my problem, I'm not a good rule follower. I learned 3D by throwing the sticks to the corners and seeing what happens. Pretty soon I was doing all kinds of tricks, mostly for my own enjoyment. Every once in a while I would impress someone else, which was a bonus, not the main goal.

My theory, if you don't crash every once in a while, you are not pushing yourself hard enough to grow as a pilot.

that's cool, I'm a little jealous. My dad usually comes to watch, but less so in the winter. And, he's a little too old for much video'ing; doesn't seem to have the knack for it.
I just don't have anyone else to fly with. All my RC friends I guess are from model warship combat. The ones that also fly are mostly across the country.

Why don't you make a camera hat? I design a lot of experimental aircraft and my camera hat really helps me analyze and solve my design issues. I even solved the Warthog's problem with 64 EDF's by catching a frame that gave me the answer.

Use an old hat's brim, velcro, foam, and hot glue and track it following the plane.

 

[Merv]

+1 on the hat cam.
I bent some coat hanger wire into a holder for my camera. It just slips onto my hat & has an adjustable angle. I use the bill of my cap as a sight of sorts, when I look the plane & have it centered in the bill of cap, the plane is centered when in the video frame.

 

[Andy.T.]

Wow, you guys are pro's! The aiming it seems like there's some trial and error involved in figuring out how to center it. Someday I'll get around to the hat cam, that's a great idea.

 

[Andy.T.]

I know this is getting long and old, but just in case, I'll keep firing away with FT-3D, experiences

I got to fly a little more the other day. I made longer landing gear wire to give a little more clearance even with a 12" prop. The plane flew very well again. After the scary out of trim maiden, I think I am working thru a little PTSD with the plane, so I was surprised at how well it flew. Sidenote, I think I figured out why I had to use so much left aileron trim to get it straight and level. I think the top airfoil of the right wing didn't fully take the nice airfoil shape over the spar; it looked just a little flatter from the spar back than the other 3 wing surfaces. I think this made the right wing make more lift on the bottom than than the top, which in upside-right flight, I think would have caused a fair bit of right-roll needing to be corrected w/ the left aileron trim. Anyways, I digress.
I liked the 12" prop. BUT the only non-slow-fly or multi-rotor 12x4 I could find was this E-Flite prop. Same price on Amazon as at the closest hobby shop. Well, I still managed to break it when I landed. I'm not sure if I came down with more of a nose down attitude than I thought, or if the sidewalk I was landing on is too uneven. The new gear wire is 1/8", a little thicker and way harder to bend than the 3/32 I've used previously. I don't think I came down hard enough to flex the gear wire, as there was no new stress marks on the fuse where the gear inserts.
Thoughts on the prop...any other options that I might have missed or other places to look other than the jungle website? 6$ per flight is going to add up to a point the wife notices. I found some of the slightly cheaper grey props in a 12x4.5 MR, but from what I've tested with some 10" MR props, while they make gobs more thrust, they also crank up current draw pretty hard. I was still temped to try them...