Exit air flight test videos

[AX-O]

All,
Below are a few videos of the test I did this weekend. I have not fully analyzed the videos yet but there is plenty to fix based on what I am observing. The one that caught me by surprised was the reversed airflow in front on the cowl flap when opening over 1.5 inches. I expected the turbulent flow below and aft of the exhaust pipes. I will be making a fairing in the future and repeating the test. I will also be modifying the cowl flap.

Hope we can all learn something, this is just cool stuff.

Take off
https://youtu.be/PYoPUOCfQ8g

Cruise - cowl flap open to closed
https://youtu.be/Qb7ypnvV9vw

Cruised - cowl flap open
https://youtu.be/CdGLPGgpyQA

[Tom Martin]

good videos; I expect the reversed flow when the cowl flap is open is a function of angle of attack, that the air has stalled at that point.

A couple of things noticed.

The air along the sides of the tunnels, just outside the exhaust pipes, seems more turbulent then other air. Perhaps an internal duct issue?

I am curious as to why the cowl flap is cut shorter then the rest of the cowling? My work from a few years ago had increased cooling and lower drag when the cowl flap, and or cowling bottom, extended aft of the firewall by at least 2 to 3 inches. Again internal exit ducting will have an impact on how smoothly the air exits the cowling.

[AX-O]

Tom, when the cowl was flush at the back, oil temps and CHTs were through the roof. The ramp angles up making the area smaller based on the edge of the cowl so exit area was about 26 inch square if i remember right. With the area cut i now have 33 inches squared and the temps are down. They still run hoter than i want.

The pipes dont have much air circulating at the top. There is only about 1/2 inch of clearence between the tube/firewall and the pipes. There is less clearence than that between the cowl and the pipes.

I can extend the area back and tuft it. That can give us good data too. What i need to do is get all the preassure testing done like Dan and others.

Thanks for the feedback.

[rv6ejguy]

Thanks for posting these videos. Will be interesting to see if you can clean up the flow at the edges or not. I suspect the momentum losses present in the air cooled layout may mean that the exit and freestream velocities always have a fair mismatch while being able to cool the engine properly.

Collecting the pressure data will be very useful for sure.

Keep up the good work!

[DanH]

Ax, I think Tom is right. Might be worth the time to extend the movable panel rearward to a point even with the cowl edges at the pipes, and tuft it. I suspect it may increase velocity behind the pipes.

All builders should see these kinds of videos just to understand how much the pipes move around!

I note that when the door is fully open, it gets beat around a lot. Mine broke a phenolic insert out of one pivot after a few hundred hours, so the prop beats it pretty good too. Keep an eye on things for cracks.

Does it really need to open that far? The "reverse flow" on the door surface just aft of the forward slot is probably local circulation, not flow into the cowl, and even if it was, less door angle would stop it and improve flow. Watch the tufts there around 34 seconds, when the slot is closed to about an inch.

Re area measured at the firewall, note that the system I use makes no attempt to vary it...it's a solid, non-movable panel where it overlaps the fuselage. Old video here: https://youtu.be/nA5PY7PYBsU

Door isn't fully closing on this early version, later fixed, but the tufts are instructive.

[nickj02]

Looks like we were doing the same thing last weekend. Cht issues here as well. I have to run around 50f lean of peak to keep the temps down in cruise (less rpm less horsepower less heat). Rv-9a , eci io320, catto prop, dual pmags, James cowl and plenum. Around 2550 rpm I get temps stabilized around 385. Any more RPM and temps shoot through 400.

https://youtu.be/phlPS1gQ-EA

[crabandy]

Thanks for posting, I'm looking forward to the next round of videos.

I shrunk my stock lower exit to approximately 35 sq inches and at the same time I extended it back and curved all the corners. Pics in this thread:

http://www.vansairforce.com/communit...=94648&page=51

I tried to pattern size and shapes from what others have so generously posted on VAF. I was happily surprised to find my CHT's and Oil temps remained the same as before with a 2ish knot gain, guessing the improved shape of the exit flows the same volume of air through the smaller exit by increasing velocity. Tuft testing videos are on my radar as I slowly finish other projects, hopefully within a year or so.

[rmartingt]

So I have a question... on both Dan's door and now yours, you have the door pivoting at about the midpoint or so and opening both in and out. Why?

[Hwood]

Great videos! .....but no music?

[rv8ch]

Originally Posted by Hwood

Great videos! .....but no music?

Thankfully!