Going high tech

Watch out you SARL types, Bob, Bob, and Mark, ect! I am going high tech!

I raided my retirement account for $35 and bought a used wind tunnel from my local school district. Cleaned up the dust, replaced the on/off switch, and it runs and looks as good as new.

Pretty cool Wade!

Lemme see, if we get busy, Bob can send you wingtip mock-ups, Mark can send you EVO-2 wing mockups, and I can send you ram air inlet mockups...really itty-bitty mockups! Better get those tweezers and magnifying glasses ready!

How much will tunnel time cost us?!?

The SARL boys be warned...there's a new scientist in town!

Have fun with it, and show us what ya test in it!

Cheers,
Bob

Seriously

rvmills said:

Pretty cool Wade!

Lemme see, if we get busy, Bob can send you wingtip mock-ups, Mark can send you EVO-2 wing mockups, and I can send you ram air inlet mockups...really itty-bitty mockups! Better get those tweezers and magnifying glasses ready!

How much will tunnel time cost us?!?

The SARL boys be warned...there's a new scientist in town!

Have fun with it, and show us what ya test in it!

Cheers,
Bob

Click to expand...

Seriously, what he said! If you get any test photos I would like to see them Posted.

Bob Axsom

Bob Axsom

Very cool!

I love it!

The fun you could have with that! Can't wait to here about some of your experiments!

Yep

I can see testing "roll your own" NACA ducts, hockey puck GPS antennas...pop rivets vs flush rivets on a -12, filled-in elevator tips and so on....airfoil shaped latches on sliders and tipups vs unmodified.

Best,

Very neat Wade! We have a wind tunnel in a hangar on our field that belongs to an Aero PhD friend - but it hasn't run since he moved in (neither has his Vagabond....), and would require some "work". I suspect that yours will provide hours of enterntainemnt!!

paul

Glad you all got a laugh. I am looking forward to hanging out with you guys at my first SARL race.

Being serious for a moment, I am currently trying to rig up an experiment to compare 2 different designs for my flush fuel vents with the stock set-up. I just need to scrounge up or build a high resolution manometer. I will post pictures and data when done.

If I can come up with a low cost smoke generator, I was thinking I might get some good visual data of the wing leading edge/gear intersection flow.

Scale will be difficult for large structure experiments

1 - A possible experiment would be interlocking airfoil shapes like a landing gear strut and the interface fairing with the fuselage. Comparative test with the joint naked vs. taped.

2 - The chord of the RV-6 airfoil is just under 5 feet (approximately 4 ft 10 in). It looks like you could produce a 1" to 1' scale outer wing section and test various tip designs on it. I think I can still dig back through my records and validate your experiments with respect to stock, flat, semi-flat and streamlined tips.

3 - Same method as "2" but change the length of the exposed wing and record differences in lift and drag.

Smoke would be good, strain and maybe thread tufts could be tried as means of comparisson. It will require careful work.

Bob Axsom

first experiment

Ran my first experiment today. I compared my mark 2 flush fuel vent to the std plans 45 cut aluminum tubing using a manometer to record the readings. It took some "creative rigging" as the wind tunnel is meant for flow and drag measurements and the design creates low pressure. I found that if I pumped the inlet with my leaf blower I could get positive dynamic pressure. Since I am directly comparing with the same set up, it shouldn't matter about the flow errors induced.

The results are the flush vent is equal to or actually slightly better than the std vent in total pressure. Pressure recorded with a Dwyer magnahelic gauge 0 - 2 inches of WC. The maximum recorded avg readings for pressure were;
Std tube = 1.9 inches of WC
Flush vent = 1.9 + inches of WC. Gauge increments 0.2" so needle position is subjective.

Vent in place on the wind tunnel wall.


Vent mold.


Vent itself.

Slowdown?

Paul Lipps has a posthumous article in Contact magazine that denies slowdown. Jack Norris and many others believe in it. I am a doubter because I have not been able to observe it in open blower tests. This would be a good experiment. However, we need to measure velocity, not pressure.

Fuel Vent

hevansrv7a said:

However, we need to measure velocity, not pressure.

Click to expand...

A fuel vent only has to have positive pressure, there is no flow velocity to speak of (unless your engine is a Pratt and Whitney R-4360 Wasp Major at full throttle).

Glad to see this experiment. I have made a set of machined NACA fuel vents that I'm going to use as supplementary vents tee'd to the standard vents. Lacking a wind tunnel, I located them ahead of the spar just inboard of the gear legs. Will post some pictures when I have a chance.

hevansrv7a said:

Paul Lipps has a posthumous article in Contact magazine that denies slowdown. Jack Norris and many others believe in it. I am a doubter because I have not been able to observe it in open blower tests. This would be a good experiment. However, we need to measure velocity, not pressure.

Click to expand...

I just got the issue and haven't read it yet. But, as it is now I am not sure how I would do that experiment.

----------------------

Terry

I remember your posts on the fuel vent thread. Why are you doing both with a Tee? I could see doing both and measuring the pressure and then picking one.

I ended up tweaking the design a bit based on the latest Airbus retrofit for lower drag vents. That is why it is not a pure NACA shape, I made the rear edge curved. I am thinking they went with that shape (though much more dramatic) to minimize flow disturbance.

Ice protection?

Wade,

Any chance that this method of venting the fuel lines would provide additional ice protection as well as less drag. I'm curious why Airbus and the like would use NACA type ducts on their fuel vents as opposed to the tried and true "tube in the wind" method... other than "ugliness."

ppilotmike said:

Wade,

Any chance that this method of venting the fuel lines would provide additional ice protection as well as less drag. I'm curious why Airbus and the like would use NACA type ducts on their fuel vents as opposed to the tried and true "tube in the wind" method... other than "ugliness."

Click to expand...

Mike

Actually, all the big iron makers use NACA type fuel vents. These type of vents are the least susceptible to icing. Search the archives for fuel vent and you will find posts with the links to NACA icing studies. The Airbus retrofit (it is installed inside the original) basically makes the original factory NACA vents smaller and curves the back wall.

Here is their description. http://www.airbus.com/fileadmin/med...ications/FAST_magazine/FAST47_7-naca-duct.pdf

Test results, location and size..

Wade,

Thanks. I am excited to know how your testing/optimization goes. I am now considering this mod for my fuel vents as well.

Terry,

Why did you mount your vents close to the fuse? Is there a particular reason for that location. I read about others having issues with fumes building inside the wing root fairings and getting sucked into the fuse. Someone suggested moving the location of the fuel vents outboard to prevent this. Wade's PDF article from Airbus suggests that their fuel vents are at the wing tips. Any thoughts on best location for the vent on a Vans?

Mike

NACA Fuel Vents

Wade and Mike,
After reading of several engine stoppages due to clogged fuel vents (not all RVs) I did a typical engineer's investigation of the "state of the art". This resulted in my Kitplanes article in the July 2011 issue. The one airplane that I studied that I really liked was the Beech King Air (I know, I know, IFR certified for known ice, turbine powered, etc. etc.). The fuel vents have an external 45 degree cut tube with a wound wire heater on the OD plus a rectangular submerged vent tee'd together and are located on the lower wing surface outboard of the nacelles at about half chord.

Since the Van's fuel vents are already located in the fuselage forward floor, I decided for ease of plumbing, to locate the NACA vents also in the forward floor. In this case I picked a spot forward of the spar inboard of the gear legs. The vents themselves are machined from the solid (very aerospace, the chips weigh more than the part) with a riveting flange inset from the bottom. After I cut a suitable hole in the fuselage floor, prosealed and riveted them in, the bottom surface was flush with the outside skin. The vents themselves have a debris screen and are sealed on the inside with an AN fitting adapter which connects to the existing vent tubing with a tee.

The LH and RH tank vents now have full redundancy with an external and a submerged vent. When I get it flying, I'll fly first with the standard vents, then measure the pressure with and without the NACA vent before connecting them.

The following NACA reports show the results of the tests on vents with straight and curved sides and curved floors.
RM E8A27b (Mar 1948), RM E8B05a (Mar 1948) and RM E8C05 (April 1948)