Prop size?

[cgoffroad]

Hello All,

I am in the process of drafting up a set of plans for a Navy P3 Orion and I have run into a scale problem. Hopefully some of the designers on here can chime in.
At the design scale from the wing root to tip is 46 inches. This is not my intended model scale, I am shooting for approximately 50-60 in wingspan total. Using the numbers I have now, the distance from the root to the inboard nacelle is 10.48 in rounded to 10.5 and between nacelles is 14.65 in rounded to 14.5. If I halve the distances to get close to the intended model scale, the distance between nacelles gets uncomfortably close, leaving just enough room for a 6 inch prop.


I am trying to hold to the Flite test power pack size and this spacing is too close for a power pack C -10 in prop. Does anyone have experience with running 4 smaller props on a larger scale model?

Thanks In advance
Joe

 

[Michael9865]

Welcome to the forums. Not sure of your answer, but I am interested in seeing your P-3. My first trip to Great Britain was aboard a P-3.

 

[Merv]

I had an opportunity to fly the HK B17, it flew great. You might take a look at the specs.

https://hobbyking.com/en_us/b-17-v2-flying-fortress-pnp-wingspan-1875mm-silver.html

 

[BATTLEAXE]

Welcome to the forums. Cool build!

You can sometimes cheat the prop clearance issues by going to a 3 or 4 blade prop. Like a 1045 prop can be traded for a 8x6x3 on the C pack radials.

 

[cgoffroad]

Welcome to the forums. Not sure of your answer, but I am interested in seeing your P-3. My first trip to Great Britain was aboard a P-3.

Its not much right now. I have most of the structure modeled in Solidworks and flat patterns in Illustrator. I have to figure a clean way to skin the fuselage. At the design scale its big enough to go crazy with extras like flaps and bay doors and retracts. I am a designer not a pilot and I get more excitement from building than flying. My plans are to build a prototype then release the plans here for anyone interested in taking it to the next step.

 

[jfaleo1]

Welcome to the forums. Cool build!

You can sometimes cheat the prop clearance issues by going to a 3 or 4 blade prop. Like a 1045 prop can be traded for a 8x6x3 on the C pack radials.

I usually go down one inch per blade you add, but I agree since you are increasing pitch that should work. Plus the 3 of 4 blade props will look better.

 

[varg]

Its not much right now. I have most of the structure modeled in Solidworks and flat patterns in Illustrator. I have to figure a clean way to skin the fuselage. At the design scale its big enough to go crazy with extras like flaps and bay doors and retracts. I am a designer not a pilot and I get more excitement from building than flying. My plans are to build a prototype then release the plans here for anyone interested in taking it to the next step.

The skinning is the hard part, that and replicating compound curves using paths and sweeps/revolves in solidworks. It's not much for scale sound, but a set of powerful quadcopter motors spinning 6" props fast is the quickest way to attack the problem. You can get a lot of thrust out of a ~2300kv 2207 and a 6" prop on 4S, just not as efficiently as with a setup like power pack C.

 

[cgoffroad]

The skinning is the hard part, that and replicating compound curves using paths and sweeps/revolves in solidworks. It's not much for scale sound, but a set of powerful quadcopter motors spinning 6" props fast is the quickest way to attack the problem. You can get a lot of thrust out of a ~2300kv 2207 and a 6" prop on 4S, just not as efficiently as with a setup like power pack C.

For skinning in solidworks I created the surface geometry with boundary and lofted surfaces and a whole lot of guide curves, making sure I leave a common reference line. Then using the flatten surface command on the common reference line, I can stitch the flattened surfaces together to create larger sections. Using the flatten command makes it easier to pull the geometry into illustrator. I haven't cut anything yet so it remains to be seen if this method is effective or not.

Tinkering with the scale I've come up with these numbers, all dimensions are in inches

Scale​	Wing span​	chord to tip length​	chord to inner nacelle​	between nacelle​	prop size​
40%​	41.2​	18.26​	4.2​	5.86​	5.00​
50%​	51.5​	22.83​	5.25​	7.325​	6.75​
60%​	61.8​	27.4​	6.3​	8.79​	8.00​
75%​	77.25​	32.25​	7.875​	11.0​	10.0​

I watched a few of the Flite test build videos and they seem to do a lot of "monster Builds". Realistically though how many people build and fly larger planes? 77" wing span seems large for a casual flyer.