Crawford Bros. Aeroplanes

Legendary member
Got the center section cut out, I'll start gluing everything up a bit later. I also enlarged the intakes to better match the R model, should also help it breathe better. I'm thinking I might cut a full length wooden spar just to be safe. Banana for scale.

IMG_20201201_171330.jpg
 

Grifflyer

WWII fanatic
Got the center section cut out, I'll start gluing everything up a bit later. I also enlarged the intakes to better match the R model, should also help it breathe better. I'm thinking I might cut a full length wooden spar just to be safe. Banana for scale.

View attachment 184996
That looks like enough spar to me, it's not like you'll be doing full throttle dives at the ground and yanking back as hard as you can........right?
 

Crawford Bros. Aeroplanes

Legendary member
That looks like enough spar to me, it's not like you'll be doing full throttle dives at the ground and yanking back as hard as you can........right?
Just slow, scale soaring around the field. Probably won't be doing realistic altitude either.

In all honesty that's scale, the real plane has like 10 degrees of dihedral on take off :LOL:
What I like about wooden spars is that they have a bit of spring to them, foamboard spars tend to crease and create permanent weak spots. I did some stress tests and it has quite a bit of give before it gets to breaking point, I'm just concerned about nasty foam creases showing up in the top surface.
 
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Crawford Bros. Aeroplanes

Legendary member
I'm also thinking about putting a downward facing fpv spy cam in the belly for spectators to use. Just depends on space and weight.

I could put it in one of the superpods on the wing...
 
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Crawford Bros. Aeroplanes

Legendary member
This looks beautiful. I'm hoping you might make plans?
Thanks!

Plans aren't something I've typically had good success with, if I can get some made I'll publish them but I can't guarantee anything. This is my first truly master series design too and I don't know if I'll be able to map out some of the curves but I can certainly try.

All this assumes that the thing flies in the first place.

If worse comes to worse I like to find papercraft models and use those as a reference in the design process. It makes designing the skins so much easier, you just have to be a bit creative with the frame to adjust for the thicker board. I didn't do that for this model but I've attached one I just found if you want to take a look at it. The nose goes together a bit different than mine though, especially around the intakes.


EDIT: Definitely gonna try to make plans, we'll see how it goes.
 

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Crawford Bros. Aeroplanes

Legendary member
Started putting the rest of the fuse together tonight. Due to the size of this plane it is impossible for me to either store or transport it in one piece. One of the biggest challenges for this build was designing a removable wing for an EDF fuselage that's pretty much just a molded tube with no internal structure. My original plan was to have either wing slide off like many store bought models, but I decided that torsion (wing twist) would become a huge issue without excess reinforcement, i.e. added weight. This technique works better with hot wire models.

I should've taken better pics of the system I've come up with, I'll post some later. Without pics the system is a bit tough to explain but I'll try. Basically a large section of the bottom half of the fuselage is removable along with the wing, the entire module is held in by rubber bands. The top half of the fuse offers structural support and joins the nose to the tail, tension from the rubber bands prevents this piece from flexing in flight.
The wing runs through the center of the fuse, forming two ducts above and below for air to travel to the EDF. It's not ideal and I think there may be some breathing issues so I've marked out some cheater holes under the wing that I'll cut out if needed.


Here you can kinda see how the wing is separate from the upper fuse as it pulls away a bit in the rear. The lighting makes the top look a bit flattened in this pic, it is round:

IMG_20201203_201710.jpg


IMG_20201203_193200.jpg


Now just to add the rear fuse and EDF housing and start wiring everything up.
 
Wow man you stress as much as I do. It's looking fantastic, and at that size and proportioned a lot like a sailplane, it should be fine.
I stressed so much over my RB-57D. It was a lot of unknowns all put together in one plane. In the end the only real problem was it has more power than I'm ready for!
With the elevator that close to the wing, one big mistake I made was my elevator throws were much too great. Reducing ALL throws made it much more manageable.
 

Hutch Bunch Rc

Well-known member
Looks really good
Now that I'm back early from Basic (medical issue) I decided to revisit this project. I scrapped most of the fuse before I left but I still have the nose so the hardest part is already done. I got a better edf that fits the fuse better too. Started on the wings tonight but ran out of foam board. The wingspan is 72" since the R model has a longer wingspan than the originally intended B model.

I haven't started the center section yet but the outer panels are positioned properly.

View attachment 184890
looks really good! Check out my huge Guinea pig!
 

Crawford Bros. Aeroplanes

Legendary member
Wow man you stress as much as I do. It's looking fantastic, and at that size and proportioned a lot like a sailplane, it should be fine.
I stressed so much over my RB-57D. It was a lot of unknowns all put together in one plane. In the end the only real problem was it has more power than I'm ready for!
With the elevator that close to the wing, one big mistake I made was my elevator throws were much too great. Reducing ALL throws made it much more manageable.
I think glide testing is hugely underrated, it's a great way to get the feel for a plane to dial in the controls without much risk. Definitely gonna be gliding this one first for sure, then by the time I'm ready to maiden I'll fell like I've already flown it a bunch and won't be as stressed out. Part of the issue is that I really haven't flown much to begin with and I haven't flown at all in three months...

Looks really good

looks really good! Check out my huge Guinea pig!
I did see it the other day, really nice build. It was part of my decision that my long springy wing wasn't much of a problem.


I'm starting to notice that you can really get a feel for some of my other hobbies based on what shows up in the background of some of my pics...
 

the rc project

Well-known member
How big would I have to scale up to fit a 90mm, I think it would be sweet to put some cameras and maybe set a edf endurance record...? Any idea how long an edf powered aircraft has flown?
 

Crawford Bros. Aeroplanes

Legendary member
How big would I have to scale up to fit a 90mm, I think it would be sweet to put some cameras and maybe set a edf endurance record...? Any idea how long an edf powered aircraft has flown?
Probably around a 100" wingspan or so. I'm not sure what the endurance record for an EDF is, EDFs aren't all that efficient so you might be better off with a prop-driven plane. Proper ventilation would be key and on this model there's a lot between the fan and the intakes messing up proper airflow.
 

Crawford Bros. Aeroplanes

Legendary member
General formula for how to scale plans:
View attachment 185300
You can use that scaling factor for any dimension. For example, wingspan:
128.6% x 60 in = 77.1" wingspan.
I just guessed haha
Although the wingspan is ~72," probably closer to 70" which gives an upscaled wingspan of 90." I think a 90mm should handle that fine, there's another guy here who built a 100" U2 but ran it on a 70mm. It worked fine at first but it got too heavy when he painted it.
 
How big would I have to scale up to fit a 90mm, I think it would be sweet to put some cameras and maybe set a edf endurance record...? Any idea how long an edf powered aircraft has flown?
But joking aside, scaling your plan to fit the size of your 90mm EDF is simple algebra. I've never dealt with EDFs but I believe its just about the outside diameter of the fan housing, to scale the plane enough to fit that unit into the engine nacelle, or into the fuselage.

Comparing the thrust of a larger motor/EDF to the larger size & weight of the plane is another story. It may be that the thrust of the 90mm EDF compared against the smaller EDF scales to your advantage - giving you a large plane with even more power than it needs. I dunno. Like if the larger EDF gives you 50% more thrust, and you're fitting it to a plane only 15% bigger.