Sopwith Baby Project - Page 40

Joe Perkel · 21 August 2008, 08:47 PM

Hi WF2,

Petr Svoboda’s Strutter, I’m familiar with it and it’s a beauty! Equally beautiful is that lovely Rotec, if I recall, his is the 2800.

I haven’t looked at the original specifications for the Strutter and I don’t know what he figures he needs but, to drag my big feet out of the water and establish a decent climb rate, I need a lot more torque and a bigger prop than the larger 3600 can give me.

You may have missed some fairly recent musings over the engine issues on my Specifications Page. Original Specifications

If I have this correct, the original Clerget delivered those specifications with a T.O. torque of 546 ft lbs with a weight of 381 lbs. The larger Rotec then gives me 150 HP @ 3600, reduced to 2,400 gives me 326.25 ft lbs, that’s just about 40% short. If my assumptions are incorrect, someone please point it out, this choice (power) makes or breaks the machine.

I am truly hoping that Rotec (or someone) responds to a market demand for a BIG & SLOW prop engine, if that demand is strong enough. If not, I’ll hide a modern flat in that pinched Schneider cowl and move the firewall as appropriate. I would much rather have this thing perform, than look pretty.

Thanks for the picture, looks like he’s probably flown by now!

David Paule,

Here’s what my source says about the Kinner

Quote:

The Warners, Kinners, Leblonds, and so forth are not only early technology and not overly reliable, the parts situation has gotten to the place that the engines are very difficult to support.

Out of deference to my source, as his candor to me is not conducive to sales, I will not identify him. Suffice to say I consider his opinion authoritative.

Albatros Ace,

Thanks for the kind words!

brinesharks · 22 August 2008, 02:02 AM

The whole engine issue is a problem. I too would like to use a Rotec - they certainly look and sound great.The Nieuport 17/24 needs a 110hp+ LeRhone or Clerget. I will have to go to a 225hp M14 to swing the big prop and as you say get the torque needed at the low RPM. This poses some construction problems around the forward fuselage! Not the least is where do I hide the starting air tank?

Joe - I sent you a couple of emails on this topic today. Just throwing some ideas around.

Joe Perkel · 27 August 2008, 06:29 AM

I've found a number of online calculators for various propeller and thrust calculations, mostly marine and, or hovercraft.

Is there something that exists, calculator or formula, to estimate static thrust of any particular prop, pitch, hp, rpm, @ standard conditions?

Thanks!

womenfly2 · 27 August 2008, 06:52 AM

" Removed, I should have ask for permission to re-post this "

I will let Paul Chernikeeff from Rotec reply himself to this.

WF2

Joe Perkel · 27 August 2008, 07:23 AM

Quote:

Originally Posted by womenfly2

Hi,

Here is a brief contact I had with Paul Chernikeeff design engineer at Rotec. Maybe someone would like to carry this further with them. Seems like a great engine to sub as a LeRhone if the Torque and RPM can be meet.

Read from bottom up.

Cheers,
WF2

WF2,

Thank you for that interesting exchange! I think Rotec was a bit harsh there but, perhaps justified at some time or another.

I want to be successful in this very expensive and potentially dangerous project, which is the singular reason for the existence of my web-site.

My comments on the R3600, were simply based on mathematical calculations which I have posted on my Original Specifications Page, ...calculations, which if in error, I fully wish to be corrected. Otherwise, I find the Rotec beautiful and I want one that can do the job.

I posted some static thrust numbers given to me by Steve Culp a while back. Even though I am out of the business now, I cannot ignore the fact that thrust moves airplanes.

Thanks again WF2.

Joe Perkel · 27 August 2008, 09:24 AM

Quote:

Originally Posted by Joe Perkel

I've found a number of online calculators for various propeller and thrust calculations, mostly marine and, or hovercraft.

Is there something that exists, calculator or formula, to estimate static thrust of any particular prop, pitch, hp, rpm, @ standard conditions?

Thanks!

Unless something as per above already exists, perhaps we can make one for the use of builders on this forum.

It seems to me that one could likely create a calculator in Excel where you plug in certain unknowns. As far as I can see if you use standard atmosphere conditions, then the parameters involved would be prop pitch, disk area, RPM, torque, HP, velocity of air moved, measure of pressure against a fixed point in space = estimated static thrust???

I am not an Excel expert, and if I am missing something obvious, please do let me know, and I could use some help on this if it's doable.

Thanks!

Joe Perkel · 27 August 2008, 11:02 AM

Quote:

Originally Posted by womenfly2

" Removed, I should have ask for permission to re-post this "

I will let Paul Chernikeeff from Rotec reply himself to this.

WF2

WF2,

Don't sweat it, I can understand the man's frustration, the numbers may not add up for all applications but, he still has a very fine and useful product.

Aviation moved on from these "Kites" with a man in it, to the higher speeds we see today. So naturally, engine and prop manufacturers moved on as well, leaving behind the technologies that would have provided us with highly efficient propulsion at our speeds,... it's that simple.

I don't really think there is ever going to be enough of a "rotary" liking market for these manufacturers to ever respond appropriately. I hope I'm wrong,...let's see!

The best flat opposed I can find so far, is 360 ci, 210 HP @ 2575, and weighing in at 379 lbs to give me 428 ft lbs. The W670 radial gives me the best numbers but, a bit heavy @ 415 lbs and old as the hills!

Clearly, I am going to take a wait and see approach!

RobW · 27 August 2008, 11:33 AM

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

womenfly2 · 27 August 2008, 11:41 AM

Hey RobW, I tried your cal site for the prop I used on my Pietenpol.

Seems only model airplane blade configurations are shown. How would one do a comparison on blade shapes? Does it matter?

Nice web site! BTW.

Cheers,
WF2

RobW · 27 August 2008, 12:08 PM

Rats... you are right. It'll work for larger props.. but it does not take pitch into account and uses a factor that accounts for the airfoil shape that I haven't been able to define... CF... hmmm

I compared the output from the model with some recorded thrust from another website... and the model is overly optimistic... darn.

oh well...