Sopwith Baby Project

[Joe Perkel]

Originally Posted by RobW

Joe,
Maybe this will work for you:

Thrust Calc


oh, and I now have a webpage for Great War Aerodrome:
Great War Aerodrome - Home


(ok, shameless plug..)

Rob

Rob,

Wow, your web-site is looking very, very "purdy!" Great job and congratulations! I will link to it next time I update.

Thanks for the calculator, when I get a minute, I will contact the webmaster and see what I can learn from this to make one applicable to us if possible. It would be nice to plug in original numbers, see what you get, then see what combinations theoretically do the best job. Testing of course, is the only way to confirm but, by then decisions are made and checks have been written.

[drrivah]

Hi Joe:
I rescued a discard from our technical library "A treatise on Airscrews",
Whyrill E. Park (Lang Propellor Ltd), 1921, EP Dutton & Co, NewYork, that goes into significant detail on period thrust calculations and how, starting with engine power curves and airframe, a prop is designed, carved and tested.

I would be happy to send the formulas or some xeroxes if someone wants to automate it for the web.

To avoid looking like an idle scholar, attached are photos of a first shot at carving project, a scimitar I designed for my C85 engine specs (W72 GK 44). The curved face is in progress, and it is made for display, not airworthy (pine), but has been an interesting first experiment.

-pete

[RobW]

Originally Posted by Joe Perkel

Rob,

Wow, your web-site is looking very, very "purdy!" Great job and congratulations! I will link to it next time I update.

Thanks for the calculator, when I get a minute, I will contact the webmaster and see what I can learn from this to make one applicable to us if possible. It would be nice to plug in original numbers, see what you get, then see what combinations theoretically do the best job. Testing of course, is the only way to confirm but, by then decisions are made and checks have been written.

Thanks Joe,
We appreciate the compliment. We are looking forward to the fly-in in a couple of weeks. I hope the calculator is useful... didn't look at it close enough before I posted it.

rob

[Joe Perkel]

I would be happy to send the formulas or some xeroxes if someone wants to automate it for the web.

Hi Pete,

I looked this reference up for purchase,... the cheap one was $100.00! Neat book though, perhaps somewhere down the line I'll pick one up.

Hold this thought above for now. I'm not going to ask you to send me these formulas and then have them sit idle. This will take someone who knows Excel to do this calculator. The language Excel uses for those spreadsheets looks like alien writing to me, and I've got too much on my plate at the moment to learn it.

Still, anyone reading this thread with the necessary spreadsheet skills should consider taking this on. Not just for me, but it would be truly useful as a tool for everyone.

Your prop experiment is really neat! I think that's a worthwhile project in it's own right as a display, really very nice and I've got just the spot for it! I'll file this in my mind for future reference, it never occurred to me to carve a pine display prop for practice!

Thanks Pete!

[RobW]

Pete, I can do the excel stuff... but not till after the fly-in...

Joe, carving a prop is surprisingly easy...(at least a non-airworthy prop). If you look at my web page under the tab that says "You'll Know"... you will see the prop that we carved... that was actually the second one we did... the first was out of balsa wood just to get a feel for how to do it (that one was really easy, and suprisingly durable...). The second we did out of poplar. For reference I used Achim Engel's "The easy way to carve a prop" guide. As I get a little more time I will post more detailed pics of the prop and gate.

Rob

[knapper]

Originally Posted by drrivah

Hi Joe:
I would be happy to send the formulas or some xeroxes if someone wants to automate it for the web.

-pete

Hi Pete,

If you'd like to send the info through to me I should be able to knock something up in excel and/or make it web based. Send the info through in which ever form you think best. My email is:

richard at entwinesolutions dot co dot uk.

and I'll see what I can do.

[Joe Perkel]

Originally Posted by knapper

Hi Pete,

If you'd like to send the info through to me I should be able to knock something up in excel and/or make it web based. Send the info through in which ever form you think best. My email is:

richard at entwinesolutions dot co dot uk.

and I'll see what I can do.

Welcome Richard!

Pete, if you can scan and email the info to Richard and when he is done, I'll give the calculator a dedicated page on my site. Likely Rob would do the same, and that is how you start to build a toolbox!

[lake flyer]

I have just completed reading through your thread .

It was great reading and I think I will do a repeat run through , as there is too much to grasp in one go .

Do you know if the airfoil used on the Baby is the same as was used on the Tabloid ( Schneider Trophy version )

[Joe Perkel]

Originally Posted by lake flyer

I have just completed reading through your thread .

It was great reading and I think I will do a repeat run through , as there is too much to grasp in one go .

Do you know if the airfoil used on the Baby is the same as was used on the Tabloid ( Schneider Trophy version )

Fairey Hamble Babies (a subcontractor), experimented with an increased camber airfoil as well as some other changes. Otherwise, the Sopwith and Blackburn Babies were direct lineage from the Monaco Schneider.

Sopwith Aviation Company's first mass production aircraft was in fact the Schneider, and the first 100 or so were actually wing warping versions, even though they had already flown with ailerons after Monaco, the Admiralty wanted the Monaco bird.

My airfoil drawing is dated 1915. In fact, I have an interesting mixture of Tabloid, Schneider, and Baby drawings which is causing me a bit of confusion but, nothing that I shouldn't be able to work through.

Thanks for the comments. You will note some hesitancy on my part in the beginning of the thread as to what level of authenticity to pursue. Power choices, continue to plague me as you can see in the last few pages.

[drrivah]

Joe:
Waiver: don't try this at home, folks (educational/entertainment use only). If you need an airworthy prop, find a certified professional.

I agree with Rob: carving is straightforward. Problem is, for most of the original engines, the engineering dwgs (plan and elevation) are scattered and/or unavailable.

If you go with a modern engine, there are recommendations for most certified a/c in the catalogs, based on design modified by experience. Have to choose whether the prop is optimized for climb, cruise or a compromise. There are jigs to duplicate carve existing prop shapes.

If you are doing a "classic" airframe with a previously untried engine (Sop Baby with a Rotec, for example), you are on your own and have to hire an engineer, or learn design. Might be good to walk through the numbers for
the Rotec/Baby, if of interest later.

For an overview of period construction methods, Achim (Engels) sells a super CD/DVD showing the original process of shaping boards for an Axial, glue up, spokeshaving and finishing, complete with faux movie film effects and original period music. Good inspirational value.

Again, as pointed out by Jeff, Achim's approach of doing a decent dwg first is the way to go, if you can find the original specs.

The process of design that precedes dwg and carving is also of interest. Good to know why certain woods and glues are preferred, their properties and strengths.

I am dubious that an automated algorithm can really spit out prop dimensions given desired thrust, or that dimensions plugged in, will give an exact thrust. However, some first guesstimates seem within the spreadsheet approach and we should give it a shot. Again, educational use only here.

Can't do a prop design without knowing about the engine and the intended airframe.

Factors needed for first shot at prop design (from Park 1921) are:

1. Power curve of the engine
2. Gear ratio (if PRSU is used, need efficiency)
3. Variation of engine power vs altitude
4. Curve of total resistance of a/c at various speeds (at desired altitudes)
5. Weight of a/c in flight
6. Antipated max flying speed/level flight; max speed; max climb rate
7. Details/dimensions of engine prop hub
8. Specifics of a/c (pusher vs tractor; distance from crankshaft to ground
etc)
9. Engine vibration/non-uniformity of torque

Usually, all these factors are not available for a new design (airframe + engine), so he recommends design to the best available engine specs, then experiment.

Stages of design are: airscrew analysis at top speed (number crunching), prop rotating on ground (more numbers), bending moments (numbers ...),
stress analysis (right: more numbers). Then, some fudge factors, weight (of prop) calculation and rule of thumb adjustments.

After balancing, you try the prop on the engine (and airframe if possible), check the indicated static speeds and hp absorbed, assuming the thing doesn't vibrate, whip, twist or disintegrate, and go back to the drawing board to fine tune. More than just plugging into an algorithm, it looks like.

Personally, I wouldn't believe thrust or design calculations until experimentally verified from actual data taken from an experimental prop. Testing a homebuilt carved prop on an engine and taking it into the air are best left to professionals.

Attached is a period example of what might go into a "top speed" spreadsheet, in this case analysis of an 11' diameter two-bladed prop with mean face pitch of 11.5' run at top speed (in this case 1080 rpm) when the a/c is doing 176 ft/sec (x 3600 sec per hr/ 5280 ft per mile~120mph). OK, more on parameter definitions, formulas, bending moments and stress analysis later, or offline.

Final waiver: I have just started my first carving trial, and so time will tell if
any of this is on target. Comments welcome from the "pros" if any of this is wildly off.

I will email details to knapper soon as I get a free moment.

(to be continued...)