1/10TH SCALE SAUNDERS-ROE PRINCESS (P173)

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Re: 1/10TH SCALE SAUNDERS-ROE PRINCESS (P173)

Postby Kuni » Mon Jan 24, 2011 9:06 pm

Dave:

pictures sent.

Regards,
Rene
Kuni
 
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Re: 1/10TH SCALE SAUNDERS-ROE PRINCESS (P173)

Postby Adventureguy » Fri Jan 28, 2011 3:15 am

Dave (Ho229),

Hi. It looks like you and others have a great enthusiasm for contra-props, so I will give up my attempts to dissuade...

I wasn't able to find Rene's (Kuni's) mentioned extra long post on the contra-prop theory at the rcgroups website, but he seems to be quite right about the size and pitch of the rear props, from what I know about aerodynamics. The flow field or "wash" from the first prop is smaller in diameter than the first prop and faster than the free stream. If the rear prop isn't smaller, then it extends outward beyond the wash from the front prop. So a same-size or larger rear prop is in both the free stream and the wash from the front prop, meaning that it wants to have two different pitches. Using scaled props will mean that the rear prop is probably less efficient, but if you use the best-compromise pitch on the rear prop, it can make the most of a rear prop's motor or engine along a "line" of throttle settings and airspeeds. I have been assuming engines, but with 10 motors, large electrics would seem to be ready to do the job.

For engines, your gear plan looks straightforward, but I am afraid you will need real bearings on the spider gears from the differential to make this work well, not just thrust washers. I suggest angular-contact ball bearings, similar in principle to those found throughout classic bicycles. For this job you can probably just pick the smallest high-speed angular-contact ball bearing that will fit the stub shaft that would then press into the each spider gear. The outer race would then be a tight slip fit into the housing. I suppose, but do not know for sure, that the outward force on each gear would be enough to keep the bearing from turning over (tumbling into or out of the page in your view) from the torque-transferring forces. (Spider gears opposite one another are sometimes on the same long shaft.) One other thought is that you might actually have better results using the spider gears for the driving gear and driven gear (heavy press onto shafts) and the axle gears for the idlers.

Last, there are actually several different types of differential, one of which uses "straight" (actually helical) gears. (I sketched one, but now I can't seem to get it into this post...and there's something here about the attachment quota being reached. I can't seem to find a link to a good picture, either. These creatures are rare.) Basically, your drive and driven gears are then regular gears (not bevel gears), and each of your spider gears is replaced with a pair of small regular-gear pinions meshing with each other. (That's six straight gears total replacing four bevel gears, the increased number of parts being why these are rare.) One of the pinions in each pair meshes with the drive gear and the other pinion in each pair meshes with the driven gear. It's could be classified as part of what ubergearheads call a Ravigneaux gear set, in case anyone's interested.

Anyway, best regards on the propulsion portion and the rest of the Princess project.

Alan

PS When I commented on a larger scale, I was actually daydreaming about something like a 1/6th scale Princess or a 1/8th scale Hughes H-4 to fly under US ultralight and/or EU microlight rules...
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Re: 1/10TH SCALE SAUNDERS-ROE PRINCESS (P173)

Postby HO229 » Fri Jan 28, 2011 4:52 am

Alen (Adventure Guy),
Contained within this RCG post is the excellent data that was put together by several generous people tinkering with counter rotating prop assemblies (very interesting designs and read).
I remember seeing Rene’s data (unknowing who Rene was at the time of read) in the thread.
http://www.rcgroups.com/forums/showthre ... r+rotating
Interesting data…
.”The flow field or "wash" from the first prop is smaller in diameter than the first prop and faster than the free stream. If the rear prop isn't smaller, then it extends outward beyond the wash from the front prop. So a same-size or larger rear prop is in both the free stream and the wash from the front prop, meaning that it wants to have two different pitches.”

Points well noted; I will make it a point to ensure the aft prop is both pitched up and smaller in diameter.

It must be difficult for the second (aft prop) to achieve high efficiencies seeing as the first prop is feeding high velocity air to the 2nd prop face at a vector (in the wrong direction). NASA /NACA did several reports that spoke to the tremendous gains in efficiency when stator vanes are incorporated.
My thoughts concerning the thrust washers were to try to mitigate some of the high losses spoken to in the engineering data, your idea of tapered/angular-contact ball bearings had crossed my mind but being unsure of the design efficiencies I cautioned the expense of using them until the gearbox was tested a bit.
I like the idea of using one motor to drive both props, I also like the idea of independent motors driving each prop. Both ideas seem to have advantages and disadvantages.

The ARC used this differential style design in the tow tank models, when I dig up the correct report I will try and attach the link.
The nostalgia of the counter rotating prop system is what I find exciting.

Someplace within one of the books I read recently it spoke of the problematic issues of bevel cut counter rotating gear sets. I believe the aircraft was the Mitsubishi-Payen Pa.400, Suzukaze 20, Pa. 112 or the Pa.400 If my memory serves me correctly they worked well for a bit and then started having high vibration issues.

On that note the R3Y Tradewind had a prop & gearbox explosion while flying that terrified the aircrew; the aircrafts poor gearbox and prop design scared the Navy so much they chopped up the aircraft to make sure no one could fly them (from the book XP5Y & R3Y Tradewind).

Thank you for the contribution and information, I always enjoy learning and reading
Dave
Last edited by HO229 on Tue Feb 01, 2011 1:22 pm, edited 2 times in total.
Proverbs 27:17
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Re: 1/10TH SCALE SAUNDERS-ROE PRINCESS (P173)

Postby HO229 » Fri Jan 28, 2011 5:06 pm

I am not sure if the following applies to counter rotating propellers but when I was in the service working at the Intermediate Maintenance Activity (IMA) rebuilding Rolls Royce Pegasus F402, 404, 406, and 408 engines we did the following to the compressor section to increase the thrust:
Upon installation of the compressor into the bearing flange we had a tolerance that the compressor had to be fall within (compressor to stator vane distance/clearance) the measurements were obtained with a precision height gage at several locations around the flange. Adjustment was done by the installation of a precision spacer/sleeve
I was taught and I instructed all the young Marines that the closer the leading edge of the compressor blades were to the trailing edge of the stators the more likely the motor would produce high thrust and low Jet pipe temperature (JPT).
The Marines at the Test cell always knew when my crew built a motor as it always came back from cell with high thrust low JPT.
This did many thing… it kept the mean time between failure low and the pilot’s did not have to work the engines as hard to get the performace.


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The chine area being cut with the table saw; this is the method used to make cove molding. Simply adjust fence angle until the arc is the same as the round stock.
Care must be taken… one cannot cut this in one pass; the blade is raised in increments

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The rough out of the Princess model & Princess P173 at some scale. upon completion this scale wooden model will be used to aid in the fairing of the lines in the CAD model
The Princess in the foregound and the P173 behind, notice the delta in length.

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SR-53 templates quick drying method, will cut this to shape next weekend

Dave
Proverbs 27:17
HO229
 
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Re: 1/10TH SCALE SAUNDERS-ROE PRINCESS (P173)

Postby BillG » Mon Jan 31, 2011 3:58 am

Hello Dave,
Progress looks good. I saw the discussion about contra rotating props, and you just got me thinking. I have a brushed Catalina that could easily have a motor reversed, if I can get the props. The timing would have to possibly be reset by repositioning an endbell on the reversed motor, for equal performance.
I've been searching for new build subjects, so I've been going over some unflown planes and performing tweaks to others lately. I finally got around to getting my PBY flyable, or so I hope. I had the 20+A speed 400 twin setup running on a single FMA 20 brushed controller, fuse mounted to boot. Not good. :shock: Well I acquired a second controller and rewired the plane this past weekend. Power seems promising for an old brushed setup, and now I have 4 seaplanes to maiden this spring.
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Re: 1/10TH SCALE SAUNDERS-ROE PRINCESS (P173)

Postby HO229 » Mon Jan 31, 2011 11:54 am

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My tooling was getting a bit dull so a bit of sharpening was in order, I like Japanese water stones... they are self cleaning and provide a surgical edge.
My mix of home made sharpening jigs and such.

Bill
I am sure you will find a hot item to build, I have a small PBY, it flys well with twinn 8X4 props on 30 amp ESC (brushless).

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Well I need to try out one of these counter rotating gadgets :mrgreen: This has always been my favorite test bed
All up weight of 20 oz, Should be a real HOOT! a AXI 2808 really moves this baby!

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Will have the water jet cut out a small aluminum bracket
The spec sheet says 550 watts combined... I will be interested in real world results!
Proverbs 27:17
HO229
 
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Location: Southern Maryland

Re: 1/10TH SCALE SAUNDERS-ROE PRINCESS (P173)

Postby HO229 » Thu Feb 17, 2011 11:11 pm

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The little SR-53 plug being shaped, a few more hours and I will be done with the half model
Proverbs 27:17
HO229
 
Posts: 42
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Location: Southern Maryland

Re: 1/10TH SCALE SAUNDERS-ROE PRINCESS (P173)

Postby HO229 » Sat Feb 19, 2011 5:11 pm

Some pics of the turbine intake…

I have taken the liberty of tweaking it to achieve a higher intake area

It’s a beautiful thing shaping wood, fast and rewarding


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Getting close to completing the half model, putty, primer and a bit of sanding


Cheers,
Dave
Proverbs 27:17
HO229
 
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