Wind Tunnel Fabrication

If your engine is producing 300 HP at 2400 rpm then that is what you can get out the other end of the gearbox minus the gearbox losses.

When you half the RPMs you will be doubling the torque. Horsepower will be reduced by the efficiency of the speed reducer.

Remember HP = RPM x Torque/550

You should try and find the power curve for your engine, it will have a maximum power rating at a specific rpm and most likely this is going to be the 300HP at 2,400 rpm (computer says it's rated at 270bhp@4000rpm). At any other speed it will be less than that. As mentioned before, any gearing you connect to it will only change the torque output by the ratio of the gearing, the power will be the same whatever you do (- efficiency). The only way is to get a power source (Engine) that delivers a little more than 550 HP (i.e. 600 HP) and run it at approximately rated speed (delivering about 570 HP), then design/get a fixed ratio gearbox that brings the speed down to the required 1100 rpm.

Dutchy

Power is a rate of work:-

from Wikipedia

"One horsepower is equivalent to 33,000 foot-pounds per minute, or the power required to lift 550 pounds by one foot in one second".

So: if you had a 1 horse power engine you could lift 550 pounds 1 foot in 1 second, and, if you had perfect (lossless/100% efficient) gears you could lift 1100 pounds ½ a foot in 1 second, but, you can't increase the work rate.

G'day,

See other replies for conversion of torque to HP.

I would suggest you run the engine at the speed at which it produces max. torque. This usually occurs at max Brake Mean Effective Pressure (BMEP) or max efficiency. If this occurs at say 1800 rpm, set the gearing at 1.164:1.

HP is a unit of energy. Reducing or increasing the RPM via a gear box will not change your engine energy output; the output energy will probably decrease thru losses. At constant energy output, the RPM is inverse proportional to torque. Look up your engine diagram for RPM vs. maximum HP and run your engine at that speed. If your engine has a 300 HP maximum energy output and you need the 550 HP at start-up condition only then you have two options: a) add a fly wheel to the system or b) ramp the speed of the fan slower, such that you overcome the fan+system inertia at a slower rate. If your fan+system requires more than 300 HP (in fact that would be ~240 HP) for steady state operation then you need another source. Electrical motors are a better option and they can be design/produced for the application with better, less expensive output controls.

Good Luck!

G'day,

In this case, H.P. is NOT a unit of energy but that of work. If you have a constant force applied to a lever you have a "moment" or in this case torque. Since H.P. is this moment expressed over time and a constant, if your torque (moment) in constant then reducing the speed will necessarily reduce the rated horsepower. You are more likely to achieve a favourable result by working with the torque output. So if the donk produces say 400 ft lbs of torque at 2000 rpm that is the maximum twisting force at the crankshaft. If the motor is run at higher revs then the torque will reduce and the gearing altered accordingly. The efficiency of the IC engine will reduce as well. Look at torque, not power.

Horse power is a Unit of Work! Energy is expressed in Ergs.

I did not see mentioned the facts concerning the fan & the fan requirements or your rerquirements for wind speed inside the tunnel (what example is "full power"). For example - the manufacture should be able to provide info stating the RPM needs for a particular model fan. Depending on budget & time constraints it might be best to make tunnel adjustments. Or for example you can provide the maximum output specs (HP & torque for your 454 motor) to the fan manufacture & then they could design around that. Perhaps you can locate the specs on a wind tunnel which you can duplicate with what you have available. You don't have to reinvent the entire setup. Good luck. Carlos

the question arises of what do you need this large of a wind tunnel for? Can you scale the model your testing and the scale of the wind tunnel as well? I have a small 12x12 inch tunnel that I use with 7.5 hp and get almost 190 mph through the test section.

If you can scale your test and get accurate enough data, it will decrease the size and cost of the project.

Everybody, thx for your help, I'm trying to attach the fan specs so that everyone gets a better idea of what is needed. I need one this size because the guys at Ames (Moffet Field, National Lab.) suggested a model size no smaller than 2-3 feet across.

Ok the Graphs won't attach, but some of the specs are below. The Airflow max. is 365,000 cfm, at 1080 RPM, requiring 549 hp at that output. Horsepower and torque requirements reduce down to nile the less the CFM the fan puts out, (obviously). so let me reduce this question down to the basics; If my 454 (well used) puts out 200hp at 4,000 rpm and i gear it down to 1080 will it have enough power to turn the fan?

Spacecannon

84/13-13/50°/PAG/9WL DATE: 2009-10-26

COMPANY: ATTN: FROM: Multi-Wing America, Inc.

IMPELLER INFORMATION:

Impeller Diameter:

No of blades:

Pitch:

Blade Material:

Blade Type:

Impeller Rotation:

84 in

13

50 °

PAG

9W

L

Tests are carried out according to methods described in ANSI / AMCA

210-99 (ISO 5801, DIN 24163)

Sound data is calculated and should be used as guideline only

Program: 9/22/2009 2:28:50 PM Version: 5.1.603

APPLICATION:

Speed:

Tip Clearance:

Temperature:

Elevation:

Density:

Solidity factor:

1080 RPM

0.5 %

70 °F

0 ft

0.07489 lb/ft3

0.36 -B/H: 1.2

To attach graphics you click the camara icon on the editor bar, can't paste directly..

thx for the tip on the camera icon, GA. Spacecannon

Hi spacecannon

You may need to add a supercharger to your engine and maybe also nitrious oxygen to get up to 550 horsepower.

Also, because of the horsepower and speed reduction required, I believe you are in the realm of propeller speed reduction units technology. see

http://www.epi-eng.com/propeller_reduction_technology/gearbox_technology_contents.htm

They have alot of great info on Aircraft PSRUs and also they have a lot information on engine technology for racing engines

Also check out http://www.seas.ucla.edu/~osmith/s51/engine%20assembly.zip

They use a 454 in the Steward P-51

Another area you may want check is PSRUs for airboats

thx I'll look into those.

Fascinating info on the propeller shaft reduction unit (PSRU), thx Gannet, the Mfgr of the wind tunnel fan did say that sudden changes in torque would shear the blades off, and they said a "V" belt pulley system was strongly suggested to allow for slipage. In the 2nd part of this discussion I was going to ask about using some kind of torque converter from an auto-tran, any suggestions?

Spacecannon

If you plan on running the wind tunnel near the rated horse power you mentioned, you won't get there with a 454. You can't get continuous horsepower matching cubic inch displacement and keep it together very long, and that still leaves you 100 HP short. If you can't use an electric motor with electronic speed control ( that would solve your blade overtorque problems ), you'll have to consider something like a larger diesel engine to power that fan. I think you'll find that option too expensive to install and maintain. You could consider multiple fans of smaller size and drive each separately. That would allow you to run at lower speed most of the time on only 1 smaller HP motor or engine. It would complicate the duct design a lot, however. As mentioned earlier, I would consider miniaturization if that would be possible in your application.

model size of 2'x1'x3' is as small as the professionals tell me I should go.

I assume that you've already looked into renting time in an existing wind tunnel. This might be a much less expensive route. I know the University of Washington and Wichita State University have wind tunnels that rent time. There are others as well.

The guys at Ames-moffet field want $5k an hr, the smaller ones are expensive too. I can build one for $10k not counting instrumentation. If anyone can think of a cheaper way to test a 2'x3' model let me know. Its a model of a wind turbine, thats why the scale can't go smaller, the full size concept is Aprox. 600' wide.

Call me on 317 291 8600 x1025 to discuss.

We have a 50m/s, 50% scale rolling road tunnel. You may find our prices are competetive when compared to building your own tunnel, instrumentation is often double the cost of the actual tunnel. Plus unless you have experience designing tunnels you may well see unexpected flow quality in the jet section.

thx, but indiana is too far away. The San Diego air and space museum has one thats apx. $1,000/hr, this is still too expensive for the amount of work i need todo. I aquired 2 big block V8s this week for $200.00 with auto tranys, I still hope to build this wind tunnel for under $10k (not counting instrumentation) and the people of CR4 have suggested many solutions to instrumentation (on privious threads); since Im testing a wind turbine instrumentation maybe as simple as measuring the electricity produced by the generator.

spacecannon

Thx to all of you for your help. Spacecannon

Get a 400 turbo transmission and put it in drive then set your throttle at the rpm's you want.

try this thread [part2]