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elippse

Well Known Member
Has any one of you ever flown an RV with the upper and lower fairings that go from the wing to the fuselage not installed? If so, or if you know of someone who has, would you please tell about it! Thanks!
 
elippse said:
Has any one of you ever flown an RV with the upper and lower fairings that go from the wing to the fuselage not installed? If so, or if you know of someone who has, would you please tell about it! Thanks!
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I haven't myself but I know someone who claimed to have done it.
From his description, it was a rather frightening experience.
Not recommended.
 
rvbuilder2002 said:
I haven't myself but I know someone who claimed to have done it.
From his description, it was a rather frightening experience.
Not recommended.
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I heard about the same. Apparently they were not installed after a paint job, and had a dramatic effect on the landing flare.

L.Adamson
 
I know a guy who flew his -4 for the first 100 hours without the wing root fairings. He flew the aircraft half way across the country and over the Rockies with the fuel lines exposed to the breeze. I rode in the back of the airplane before they were installed. The aircraft would buffet a bit in flight and the buffeting would increase as the AOA increased as the aircraft slowed or when pulling more than 1 G. It buffeted around the final turn for landing just like the T-38.
 
One of our local pilots, who sometimes posts here, flew with wing fairings but without the rubber seal. I'm told the -8 had a severe tail buffet at slow speeds and high AOA. The plane was grounded and the pilot borrowed my gap seals until his Van's order came in. The plane flew normally with the rubber seals in place.

I don't recommend flying without the fairings or the rubber seals. If your that close, just take a little extra time and install everything right.

Karl

Now in Sandpoint, ID. :)
 
I'm Watching

Paul, I just know you have something up your sleeve and I'm watching to see what your mind is working on. I noted Scott's careful response so I don't think I'm alone.

Bob Axsom
 
Bob Axsom said:
Paul, I just know you have something up your sleeve and I'm watching to see what your mind is working on. I noted Scott's careful response so I don't think I'm alone.

Bob Axsom
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Am I that transparent, Bob? Actually, yes, I do have something up my sleeve! The low pressure region above the wing extends in a somewhat elliptical manner from tip-to-tip; it actually goes up over the fuselage and canopy. That's why a canopy will try to open, regardless of the airplane's flight speed. Part of the lift of the aircraft's weight is on the canopy. And you cannot have lift at the wingtip since there can be no pressure differential there.
But if you have a gap at the inboard end of the wing between the wing and fuselage, guess what? You have now put two tips on each wing panel. The lift will go to zero at the inboard end and form an additional tip vortex there. You've considerably cut into the wing's lift capability, to say nothing of the increased drag as air tries to flow past the exposed spars and lines. I had heard that this was a potential problem, and wing lift theory supports it.
But my real reason for getting confirmation of this is to point out that the same situation exists in the propeller realm. If the prop is not sealed against the spinner so that lower surface to upper surface flow can exist, the lift/thrust of the prop will go to zero in the root region and produce a vortex which affects the flow into the induction and cooling inlets, as well as creating rotational and axial drag. Sealing of a fixed-pitch prop to the spinner is very easy, since you don't have a blade swiveling on its pitch axis as you do with a CS. But take heart! It is possible to create a rotational seal at the root end of a CS prop, and I'm sure a lot of you wizards out there can figure out how to do it and increase the efficiency of your propulsion! For those of you with klunky-shaped root sections, a streamlined cuff is necessary to form the blade portion of the sealing surface. They use a cuff on some of the P-51 blades, and prop shops know how to affix them to the blades to keep them attached in flight. Let's see if some of you can figure out how make a cuff for your blades and use them to make a rotating seal! I think this should be an especially interesting challenge for those of you who want the most performance from your planes, such as those of you who race, or just want more mpg!
 
My recent experience in RV-8

I recently experienced flying my RV-8 with the rubber moulding strip missing on one side. Flight characteristics and control were altered in an unpleasant way--I don't recommend it.

While returning home from a cross country flight, I noticed a thumping sound on one side of the fuselage. With my hand I located the site of the thumping on the left inside of the fuselage near the wing root. I landed at a nearby airport and found about 5 inches of the rubber strip loose near the trailing edge of the wing root. Being only 20 miles from home, I decided to remove the complete rubber strip and fly home to re-install it. Take off and cruise seemed normal but at high-angles-of-attack, there was a very strong asymetrical tail shake and turbulence. There also was a disconcerting tendency to roll toward the side missing the rubber moulding. I noticed this behavior when I started a loop and aborted before reaching vertical. I landed slightly faster than normal due to concerns about asymetrical stall characteristics. After re-installing the rubber strip, flight characteristics returned to normal.

I would not recommend flying RV's without the wing-root fairings and the rubber seals.

Cheers,

Dan Miller
RV-8 450 hours
 
elippse said:
But my real reason for getting confirmation of this is to point out that the same situation exists in the propeller realm. If the prop is not sealed against the spinner so that lower surface to upper surface flow can exist, the lift/thrust of the prop will go to zero in the root region and produce a vortex which affects the flow into the induction and cooling inlets, as well as creating rotational and axial drag. Sealing of a fixed-pitch prop to the spinner is very easy, since you don't have a blade swiveling on its pitch axis as you do with a CS. But take heart! It is possible to create a rotational seal at the root end of a CS prop, and I'm sure a lot of you wizards out there can figure out how to do it and increase the efficiency of your propulsion! For those of you with klunky-shaped root sections, a streamlined cuff is necessary to form the blade portion of the sealing surface. They use a cuff on some of the P-51 blades, and prop shops know how to affix them to the blades to keep them attached in flight. Let's see if some of you can figure out how make a cuff for your blades and use them to make a rotating seal! I think this should be an especially interesting challenge for those of you who want the most performance from your planes, such as those of you who race, or just want more mpg!
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I understand the reasoning behind the theory, but I don't think it is valid. The blade shank of a prop near the spinner is so far away from being an airfoil that is producing any amount of thrust, that I think sealing would make no difference. It may clean up the flow around the spinner some for better flow into the cowl but I don't think it would be related to improving the low pressure area on the fwd face of the prop. I would be interesting to see some test data though...
 
rvbuilder2002 said:
I understand the reasoning behind the theory, but I don't think it is valid. The blade shank of a prop near the spinner is so far away from being an airfoil that is producing any amount of thrust, that I think sealing would make no difference. It may clean up the flow around the spinner some for better flow into the cowl but I don't think it would be related to improving the low pressure area on the fwd face of the prop. I would be interesting to see some test data though...
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All of my prop designs produce thrust all the way to the spinner! In fact, the thrust/torque ratio is almost the same from the root to the tip, falling off somewhat at the tip due to the higher parasitic drag at the tip at its high Mach values. I suggested that with the klunky, no-thrust root section you speak of that by putting a streamlined cuff at the root you can not only decrease the drag but actually get some thrust. I don't know why the thought has taken hold that there can be no thrust in a prop blade root region. That root section is following a helical path through the air just as all of the rest of the blade is, and its velocity, due to rotation, is even greater than the plane's forward velocity! Given the proper design, it will produce thrust at a very good L/D. Better that than only producing drag!
 
elippse said:
I don't know why the thought has taken hold that there can be no thrust in a prop blade root region. That root section is following a helical path through the air just as all of the rest of the blade is, and its velocity, due to rotation, is even greater than the plane's forward velocity! Given the proper design, it will produce thrust at a very good L/D. Better that than only producing drag!
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Sorry Paul, I didn't mean to imply they couldn't. I was speaking in the context of the popular propellers that are being flown on most RV's.
If it was easy to execute, I have to wonder why Hartzel hasn't done any work on this.
Many propellers on turboprop applications have blade designs more along the lines of what you describe but I imagine that each one is more of a specific application propeller. This type of thing would be very expensive for RV's
 
rvbuilder2002 said:
Sorry Paul, I didn't mean to imply they couldn't. I was speaking in the context of the popular propellers that are being flown on most RV's.
If it was easy to execute, I have to wonder why Hartzel hasn't done any work on this.
Many propellers on turboprop applications have blade designs more along the lines of what you describe but I imagine that each one is more of a specific application propeller. This type of thing would be very expensive for RV's
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OK, just think about this. You make some nice little streamlined cuffs out of carbon fiber, about 5" to 6" long, that fit over the root of the blade. You shape the bottom of the cuff so it just comes down to the spinner with the prop in its most forward position. Now you put some epoxy-micro on the spinner and rotate the blade to the low pitch position so that the blade forms the filler to just meet the bottom of the cuff. You've just formed a rotating seal! It appears it will be really quite simple and not at all expensive. I have a CS that we are making a rotating seal for and if it works as I think it will, improving the blade's efficiency, it will be making news!
 
Dont do it

I flew mine for the first flight without the fairings. Everything felt okay on take off. But I had a lot of elevator flutter, I landed and never flew untill I installed the fairings.

Jim Knight
Burlington Iowa
300 hour RV-6
 
Hi Paul, A freind just sealed the area around a Cap-220 prop and gained 100-150 static rpm's. It was real dirty. Good idea! Steve
 
rv6srb said:
Hi Paul, A freind just sealed the area around a Cap-220 prop and gained 100-150 static rpm's. It was real dirty. Good idea! Steve
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Hi, Steve! Could you elaborate a little about the type of prop, CS or fixed, and how he did it? Pix, too, if available! Also, whether he saw any cruise or top speed improvement.
This is an area, neglected 'til now, for homebuilders to improve their performance with little effort. It was OK to ignore this klunky region on our Cubs and Champs, this wouldn't have done a whole lot for them! But at 200 mph, klunky's no good! Thanks for the info! Paul
 
HI Paul,
The prop is a MPS CAP 220. The revised version of the older NSI cap 200. They are electric props. I will check with James on pictures of what he did. The spinner needs to be bigger on these props as the blade cuff sticks out of the spinner. I have a Cap 200 on my rv-6 and plan on cleaning it up. I hadn't thought of it before, but it just makes sense. I don't know about cruise improvement, but will ask. Steve
 
I was once a part owner of a Corbin Baby Ace. This aircraft is a single seat aircraft with a parasol wing with fairings(upper and lower) covering the gap between the two wings. I was a pretty big guy and found the top of my head would bump up on the lower fairing, and was uncomfortable at times.

I had the bright idea one day ( circa 1973 ) to remove the fairings and go flying... dumb idea. On a 5000' grass strip, I could NOT get that little 60mph airplane to lift off the ground to save my life!!:eek:

So, I put the upper fairing on and left the lower one off for my head clearance, and she flew just fine...go figure!

I'm no engineer (obviously!), but I wouldn't suggest flying without them, especially after what I just read above!:confused:
 
rv6srb said:
HI Paul,
The prop is a MPS CAP 220. The revised version of the older NSI cap 200. They are electric props. I will check with James on pictures of what he did. The spinner needs to be bigger on these props as the blade cuff sticks out of the spinner. I have a Cap 200 on my rv-6 and plan on cleaning it up. I hadn't thought of it before, but it just makes sense. I don't know about cruise improvement, but will ask. Steve
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Here's another thought for you those of who are interested in getting the best performance out of what you have. Just as with a wing, a propeller blade produces a deflected flow i.e. "downwash" off the trailing edge. You can do a simple test of your propeller's aerodynamics by putting a yarn string on the top of the cowling fastened at the front center. If the yarn deflects back toward the pilot, the prop is making thrust in the root region. If the yarn flows straight back or is bouncing around, then it is producing no thrust but only parasite drag. If it deflects back toward the passenger side, your prop is producing negative thrust! If that's the case, and your prop is fixed-pitch, it doesn't have enough pitch in the root region. If it's a constant speed, you need to get the prop re-twisted.
 
Oh the temptation

I have a 72" Hartzell with 7666 blades and the AirVenture Cup Race is coming up in less than three weeks. I find in my modification program that I have to be very methodical and not rush in a major change without taking a LOT of time and thinking the change to death before committing to an implementation approach. I'm consistently over 200 mph in the races now (205.56 mph in the Colorado 150 a little over a week ago) but there is a vast gap between me and John Huft so I am always looking for more speed. I will give this a shot but it will probably be next year. I do have a filler plate ubder the blade now but there is a gap for full pitch travel. The seal would not have to be very large actually since the pitck angle doesn't change a great deal. My thinking right now is a movable plate that is part of the spinner and gets pushed into the required position by the prop rather than locking it to the prop. Like I said, I have to think about it.

Bob Axsom
 
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