Propeller/Airscrew design data

[douvie]

Hi Chaps,

Does anyone have the cross-sectional data for a 4 or 5 bladed Rotel prop? I'm interested in data/formulae that was used to manufacture the airscrews used on a Spitfire Mk IX XIV. I'm modeling a spit in 3D and I've had a lot of difficulty trying to get the shape and twist/chord right.

Thanks
double 8)

 

[GregP]

This is a great question!

Let's take it one step at a time. Suppose you don't know the prop numbers but you DO know the aircraft performance. Say we have a WWII fighter that is going 300 mph with the engine turning 2,800 rpm and a 2:1 prop gear reduction ratio. It has a 120-inch diameter prop on it which is a radius of 60 inches. You are interested in the prop angle at, say, 45 inches of radius.

1. We need the forward speed in inches per second. 300 mph equates to 440 feet per second or 5,280 inches per second.

2. The engine is turning at 2,800 rpm with a 2 : 1 gear reduction ratio, so the prop is turning at 1,400 rpm, or 23.333 revolutions per second.

3. So, we advance 5,280 inches for every 23.333 prop revolutions, or 226.286 inches per revolution. This is the pitch.

4. The prop is 60 inches in radius and we are interested in the pitch at the 45-inch point, or 75% of the radius. The circumference at 45 inches is 2 * pi * r, or 282.743 inches.

5. The blade angle is the arctangent of the pitch divided by the circumference, or arctangent (226.286 / 282.743), or 38.67° at the 45-inch station.

This is not quite complete due to prop slippage and angle of attack (and a few other things), but will give you a good start and, if you use that as-is, will result in a correct-looking prop. If you want, PM me and I can send you a spreadsheet to make the calculation easy. It is no more difficult in metric units.

I believe the prop you are inquiring about is a Rotol, not a Rotel, and I also do not know the chord progression, but you can at LEAST get the approximate pitch angle for any prop station at some speed. Of course, stopped on the ground the prop is in fine pitch and looks much flatter. But, you CAN figure out the blade angles for, say, 20 stations, and then you know the shape of the prop and you can twist it flatter to represent the stopped state on the ground. All props have a pitch travel limit specification. I don't have it for the 5-blade Rotol, but it can be found.

Cheers.

 

[douvie]

Oops, you're right about it being ROTOL and not ROTEL - My mistake.

I'm going to have to take it slow - you kinda lost me. I've got a listing somewhere of the types on the airscrews. Someone said that a wing cross-section and a prop cross-section are similar, in theory anyway. The total diameter, ie. from tip to tip, 10 ft(or 3.048 metres). The total wingspan, or OD (diameter) on a 5 Bladed prop was increase, due to improved power of the Griffon/Griffin(sorry, I've seen it spelt both way on the same page) and due to this the fuselage had to sit higher off the ground. The landing gear struts were increased in length. But I digress a little.

From what I've been able to gleen from several sources they say NASA 2416 but I wouldn't know. The NASA numbering here indicates a chord length at 70% of blade length is 24 inches (from leading edge of blade to trailing edge of blade) and the effective prop pitch is 16 inches??? I'm not sure on the NASA 4 digit code either.

Thanks
douvie

why is it so difficult to get original prop design data?

 

[GregP]

I don't believe it is diffcult data to find if you know or can find out who has the data. I'm pretty sure we have some people in here who know where most British aerodynamic data can be found ... it only they read this thead and want to help out.

I have a high interest in the planes and much less so in the propellers as long as they are available for use.

 

[Ivan1GFP]

I built a 3D model of the Spitfire Mk.IXc for Combat Flight Simulator a few years ago. There is plenty of data available for the aircraft but some of it is conflicting. As for the propeller, I did that pretty much by eyeball for the visual model though I believe the aerodynamic data was fairly good.

The drawing I used for the Spitfire Mk.IX was actually the Spitfire Mk.V dimensional drawing that can be found in this thread:
http://www.ww2aircraft.net/forum/schematics/spitfire-3d-29997.html

You can also find screenshots of my Spitfire in that thread. It has not been released yet.

For sources of good information:
WarbirdTech 35,
AeroDetail 27,
Mushroom 6111,

There are certainly a lot more books than this, but these come to mind.
I don't think ANY of these books is going to give you contour information on the propeller.

Good Luck.
- Ivan.

 

[Aozora]

Hi Chaps,

Does anyone have the cross-sectional data for a 4 or 5 bladed Rotel prop? I'm interested in data/formulae that was used to manufacture the airscrews used on a Spitfire Mk IX XIV. I'm modeling a spit in 3D and I've had a lot of difficulty trying to get the shape and twist/chord right.

Thanks
double 8)

I take it this is the type of info you're looking for HOWEVER this might not be a Rotol blade profile: (from Propeller "Classic variable pitch prop coordinates. Scale to fit. Thompson Trophy Racers book")

First thing to know is what model of blade or blades are you dealing with - there wasn't one blade, there were several variants of either alloy (duralumin) or wood composite construction , each of which were identified by drawing numbers such as RA10046:

here, for example is a test of a Spitfire IX using a

Rotol R3/4F5/3, having dural blades to Drg.No.RA.10061

Spitfire F Mk IX BF274 Test

Here's another set of test Spitfire IXs fitted with either duralumin or wooden blades http://www.spitfireperformance.com/proptypes.jpg

If you don't know a blade number and what type of material it was made from it won't be easy getting the data you're looking for; one tool which might be able to help is: Airfoil database search

From reading this: Dowty Rotol Archives? most of the information held by Rotol (now Dowty Rotol) was destroyed by floods during the 1960s, in which case the only way to get such information is if various aircraft preservation societies have sets of original blades and have taken measurements from them.

You could contact the likes of the Rolls-Royce Heritage Trust The Rolls-Royce Heritage Trust - Rolls-Royce or the Aircraft Engine Historical Society AEHS Home .

 

[Rufus123]

Another topic that will be over my head.