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FF2017 Int. Racers: Crosby CR-4

HilldaFlyer

Well-known member
#1
Well, I finally made a decision for a racer

Crosby CR-4



The plan is to build close to 1/3 scale which puts the wingspan just over 60". Construction will be made primarily with foam core skinned with fiberglass. The rest will be figured out as I go.

 
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PsyBorg

Wake up! Time to fly!
Mentor
#3
hehe What's wrong with the one in the picture. That looks beautiful. Those type planes had to be wild to fly sitting so far back looking out over them long noses.

Are you planning to set it up with FPV? If not could you at least put a flight cam in the cockpit to give us that experience of what real pilots see when flying something like that maybe? I sort of have an idea after all these years looking out over my own beak when walking around but an aerial perspective would be way cool.
 

HilldaFlyer

Well-known member
#4
Are you planning to set it up with FPV? If not could you at least put a flight cam in the cockpit to give us that experience of what real pilots see when flying something like that maybe? I sort of have an idea after all these years looking out over my own beak when walking around but an aerial perspective would be way cool.
I bet these kind of planes were a handful to fly, if you could call it flying. More like slicing the air and putting the nose in the direction you want to go.

Well, I had no intentions of flying this rig FPV, but, that is a great idea to put a camera in the cockpit. I was planning on having a clear canopy... so why not? Just dress up the Mobius with some goggles and a scarf.
 

PsyBorg

Wake up! Time to fly!
Mentor
#5
hehe right. Get a set of Barbie size aviators mirrored glasses and mount the Mobius in a snoopy head with the scarf n glasses.

I always thought that those guys were just letting a motor drag them thru the air and the rest of the craft was nothing more then a nice place to sit.
 

HilldaFlyer

Well-known member
#8
That plane just looks fast. Are you thinking of using it for both the air race and duration? I haven't decided on a model yet.
This plane is just the air race... however... I think it would be a pretty interesting competition to mix the two categories together because fast fliers tend not to have low energy costs.

I'm hoping that I'm talented enough to get it to fly/land because I bet it doesn't glide that well. I'll call it a success if I get it past the maiden.

My endurance plane/aircraft will be probably be a wing but its final design will depend largely on the specifications that are pronounced by the master(s) of ceremony - Willsonman/CraftyDan. I would like to utilize a 3500 mAh battery pack so I can use some NCR18650B cells which have a higher energy density per weight than the LiPo batteries.
 

HilldaFlyer

Well-known member
#9
I did a little digging about the internet over the weekend and I have to say that I didn't find many plans or pictures that could be used for plans. I think the drawing above is sufficient to get the job done, I guess it will have to do.

I set a few goals so that the project scope would not expand beyond my ability to deliver.
I would like to use FT techniques as much as possible on the build so others can repeat if they desire. Getting the plane more to scale will require a bit of foam molding to produce the sleek curves of the fuselage, something that is new to me.

I created plans in Illustrator and did some measuring. Turns out that my original plan for a 1/3 scale (wingspan would have been 5' 4") build will be a tad bit big (for me). I wanted a wing to fit on a single sheet of foam and it did, however, the root is wider than the foam's 20". So, using the root as the basis for measuring, if I make the root 20" wide, the scale is right on 1/4. So, that is going to be the size - 1/4 scale 48" wingspan.

To make this available to other FT builders, the prototype will use a mixture of Ross and DTFB. I will leave the fiberglass skin for a later and possibly the competition build. I have even toyed with the idea of retracts, but we'll have to see how the prototype goes.

The fuselage will be a square tube from the nose to behind the cockpit and then will be reduced to a point at the tail. I will then make round formers with a square hole that fit the fuselage tube to make the sleek fuselage body. I have not yet experimented with molding foam, but the fuselage will likely be skinned with paperless foam using the square tube as the structural component. The motor will be mounted permanently to the front of the fuselage tube, and if a power pod is required for the competition, there is room for that to be incorporated. Depending on where the battery ends up, I will make a hatch in the top or bottom of the fuselage.

Propulsion: Specs may change but right now I'm looking at either 3S 2200 mAh or 4S 3300 mAh, NTM 35-36 1800 kv or NTM 35-30 1100 kv (which is what I believe is in nnChipmonk v2). Any recommendations from experience is welcome.

I think the plane will come in between 2 lb and 2.5 lb, but that is a total guess.

Servos - I'll ask what is recommended. I noticed nnChipmonk v2 used 12 g servos. If that is needed for this, I'll have to get some because so far I've only used 9 g servos.
 

HilldaFlyer

Well-known member
#11
Sounds like a good plan of attack! Any thoughts on putting in flaps to help with landing speed?
Sure thing... The plane has flaps in the design, and I will be installing. They run from the center line to the ailerons. Probably don't need a 12 g servo for those since they'll only be deployed at lower speeds.

Check out this document on the rebuild - LINK





 

rockyboy

Skill Collector
Mentor
#13
Excellent! The side profile really shows off the graceful lines.

I see you're heading straight into the round body formers - I'm chickening out and saving those for v2. :)

What software are you using for the initial sketches?
 

HilldaFlyer

Well-known member
#14
I see you're heading straight into the round body formers - I'm chickening out and saving those for v2. :)
Nice thought... Yes I am drawing the roundish formers now, but v1 will be foam board designed with "as close to curves" as I can get using FT techniques (lots of fold lines with lots of relief cuts and messaging).

If v1 looks too boxy for me, then v2, will probably use non-FT techniques to capture the curves, you know techniques that I haven't used before. Right now the v2 is planned to be made by sliding the round formers over a square tube structural fuselage. The thick lines on the fuselage will mark the placement of the square tube so I'll have to cut square holes in the middle of the formers and slide into place. I would like to capture the smooth curves if possible, but I'm not entirely sure How I want do it. I am intrigued with the solid foam method demonstrated by Wilmracer Pitts, but I am trying to stick on being very light since the wings are so stubby. I have considered using 0.5 to 1 mm foam sheets skinned in fiberglass, but that method doesn't do well with compound curves without relief cuts - which makes the skin not so smooth and sleek. Another way that I am familiar with and is more likely to be done is to use tissue paper. There might be a little dip between the formers like in cloth covered planes, but it will be curvy. Other thoughts are welcome.

What software are you using for the initial sketches?
I use Illustrator CS6. Played with sketchup a bit, but since I know Illustrator basic functions... it is still pretty easy to get cut out plans this way.
 

HilldaFlyer

Well-known member
#15
Spent a few hours building a prototype wing. The prototype was needed to measure spacing of the spars and servo placement.


There will be 3 spars and a spacer plate along the trailing edge.


The flaps will be flush with top wing panel and drop down. All trailing edges are sanded on the inside and joined so that the trailing edge is a real a point.


The ailerons will be hinged with carbon fiber and polyester cloth X hinges for full non-friction travel.
 

PsyBorg

Wake up! Time to fly!
Mentor
#16
How would using card stock like was done for some of the turtle decks on so of the FT builds then glass that on V2? It would be easy enough to roll into a tube and not have lines fold into it I would think. Same thing for the curvy parts around the wings. Nerdnic had a nice method for one of his fancier builds that did that. 9dont ask my broken brain to specify which at this point though) Maybe poke him with a stick for some tutelage.

EDIT: Its the Chipmunk build. Watch the last 15 mins. or so.

[video]http://forum.flitetest.com/showthread.php?27973-nnChipmunk-v2[/video]
 
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HilldaFlyer

Well-known member
#17
How would using card stock like was done for some of the turtle decks on so of the FT builds then glass that on V2? It would be easy enough to roll into a tube and not have lines fold into it I would think. Same thing for the curvy parts around the wings.
The final build will have the curves done someway and nn has some great ways of doing that. Right now I'm leaning on doing the turtle deck with foam, but that method has the challenge of smoothing the abutting pieces. Poster board is another great option. We'll see how it goes.
 

HilldaFlyer

Well-known member
#18
I thought I update this tread since I've made some progress, but it feels like 4 steps forward 5 steps back. I started planning and building before the final size requirements were announced, so this thread starts with a 1/4 scale plan. I've decided to complete it since I've got most of the parts cut... so here is where I am.


The tail is two sheets thick, the leading and trailing edges were tapered by sanding.

They were then skinned with 0.73 oz fiberglass.

The fuselage turned out to be two sheets long..

Here are the two panels that will be joined. The vertical fuselage panel (top) will be cut in half and glued to the horizontal panel (bottom) to make a profile "+".

 

HilldaFlyer

Well-known member
#19
The elevator is split, so I had to figure out a way to get them connected. I settled on installing a torque rod underneath the hinge.





And here is the final horizontal stabilizer and elevator with control rod installed to the torque rod.


 

HilldaFlyer

Well-known member
#20
I decided to make the same configuration for the vertical stabilizer so the control rod will be hidden in the fuselage.

Here are the parts.



Here is a test fit on the fuselage before I glued it together... looks like it fits so glued it


And here is what the final product looks like with the servo installed below the fuselage turtle deck.