Forward Sloping Windshield Mod RV-6,7-9

rv969wf · #1 11-19-2006, 04:18 PM

If anyone has thought of it don't waste your time. Forward sloping windshield on my RV-6. I tested and tested a couple of years ago!!!!! It made no improvement, no speed gain, nothing. This was a temporary .125" lexan wrap taped in front of the OEM windshield. It extended forward just about to the firewall. Waste of time if anyone is thinking about it. Only positive was a 2 db noise reduction and maybe a less chance of a bird coming in the cockpit if made 1/4" -3/8" +++

Bob Axsom · #2 11-19-2006, 04:30 PM

Alan that is another good piece of info. This aero stuff is fastenating isn't it? That is one experiment that I won't try.

Bob Axsom

szicree · #3 11-19-2006, 05:18 PM

Dang, you're quite the tinkerer. I looked at your cowl mods and I gotta say that it's real impressive. Looking at the photos of the windscreen I have a couple of thoughts. In profile it looks that the modded version should be faster, but in the more frontal view it looks as if the new version is very flat side-to-side. Seems like you're letting the air get up and over easier, but making it harder to go around the sides. Just a thought and worth even less than you paid.

P.S. Nice checkers on that bird!!

rv969wf · #4 11-19-2006, 05:39 PM

Quote:

Originally Posted by szicree

Dang, you're quite the tinkerer. I looked at your cowl mods and I gotta say that it's real impressive. Looking at the photos of the windscreen I have a couple of thoughts. In profile it looks that the modded version should be faster, but in the more frontal view it looks as if the new version is very flat side-to-side. Seems like you're letting the air get up and over easier, but making it harder to go around the sides. Just a thought and worth even less than you paid.

P.S. Nice checkers on that bird!!

Your probably 100% correct. You can't see the tuft work on the top of the canopy in the pictures but I could see them looking thru the top of the canopy and the tufts stayed attached very well. I agree if the windshield had a nice gentle curve and not a flat wrap, the air flow might be different. I do have other pictures with tufts on the sides and other areas but I didn't post them. There were a few tufts that wiggled around the sides, but without the added windshield extension the tufts looked the same as the stock VANs.

Anyway I tossed this idea in the trashcan.

pierre smith · #5 11-20-2006, 06:03 AM

Hi Alan,
Neat tuft tests, buuuutt wait! I spoke with an aerodynamic engineer/RV builder about a retrofit tapered wing for the RV series. He said that it was easily workable to make a bolt-in replacement wing. He also went on to say that the landing config stall speed vs. the flaps-up stall speeds are too close and can be further optimized by having less wing area, larger fowler type flaps and smaller ailerons. Yield could be 25 MPH added cruise speed and 10 MPH higher stall.

He asked if I'd be willing to give up 10 MPH in landing speed (faster by 10) to gain maybe 20 in cruise. At first I said definitely and a day or so later, started questioning that choice. In a forced landing situation, the added 10 MPH would have a huge impact on landing forces generated so I decided that I'll just be content with the 200 cruise and the slower landing speeds. There's a definite compromise and when built straight, light and clean, 200 MPH ain't so bad after all.

You are on the right track with the aeromods, leaving the wing area alone.
Regards,

gmcjetpilot · #6 11-20-2006, 03:15 PM

Quote:

Originally Posted by pierre smith

Hi Alan,
Neat tuft tests, buuuutt wait! I spoke with an aerodynamic engineer/RV builder about a retrofit tapered wing for the RV series. He said that it was easily workable to make a bolt-in replacement wing. He also went on to say that the landing config stall speed vs. the flaps-up stall speeds are too close and can be further optimized by having less wing area, larger fowler type flaps and smaller ailerons. Yield could be 25 MPH added cruise speed and 10 MPH higher stall.

Huaaaa? "He also went on to say that the landing config stall speed vs. the flaps-up stall speeds are too close"

That is true but its also intentional. Van designed the wing, flaps and ailerons intentionally as they are. There are always better ideas but rarely do you strike such a beautiful balance of compramises that makes the RV such a joy to build, fly and own.

Your friend is right, the RV's stall speed flap down v. up is small, about 3 mph but so what, the stall speed is already low. Fowler flaps are going to be complex, heavier, harder to build and more costly than the light simple hinge flaps we have.

Van's RV cruises and tops well over 200 MPH but has a stall speed in the high 40's or low 50's of MPH, basically C152 stall speed but twice the top speed. That is a ratio of 4 to 1, max to min speed. How slow do you want to go, and VERY FEW planes have this ratio.

The NACA 23013.5 airfoil with constant chorde/thickness is a great airfoil. Have you built a tapered wing? Again more complex, expensive and harder to build.

This IDEA has been done and is being done> Teamrocketaircraft.com sells QB Rocket kits, similar to the Harmon Rocket. They offer a new Evo Wing as your friend describes. The standard Rocket uses a RV-4 wing but is cliped about 14" (104 verses 110 sq-ft area).

The standard "Rocket": top speed: 250 mph, cruise speed (75%@8k): 230 mph, stall: 54 mph, wing area: 104 sq-ft.

The Evo wing: top speed: 265 mph, cruise speed (75%@8k): 240 mph, stall: 50 mph, wing area: 102 sq-ft. The Evo wing is about $5,000 more.

The bottom line is +15 mph top, +10 mph cruise -4 mph stall, which is nice but is it worth it. Takeoff/Landing are listed as the same. Handling? There is some info on their teamrocketaircraft.com web site. The negatives are slower roll rate and smaller CG range, but it sounds like it handles nice overall.

Smaller ailerons? No thanks.

Many planes, Boeing jets have fowler flaps, double and triple slotted fowler plus leading edge "high lift devices". Its all good but it adds weight and complexity.

The overall performance, handling and joy of a RV is a delicate balance of many factors, not the least is kit cost and build difficulty. A constant chord / thickness wing is a joy to build. A new wing will make it a different handling plane, and probably not a "RV" feel. Speed is great but if you have to live with it as a "sport plane" there are other qualities that are as important or more important.

pierre smith · #7 11-20-2006, 03:32 PM

George,
You're correct on all counts.......the RV has an incredibly good balance and any bigtime mods like shorter or tapered wings will yield something other than an RV for a small speed increase.

It's such an easy airplane to transition to as my trainees have discovered and I thoroughly enjoy just flying mine.

A little cleanup here and there plus a few fairings on drains and aileron brackets will all help some but that's for later. The little added speed is probably Chump change.

If the guys just rig very carefully, build it light and straight with close control system gaps and smooth the ends of the flaps/ailerons/stabilizer and rudder, the speed will be there.

Regards,

cawmd82 · #8 11-20-2006, 03:39 PM

Who did your paint job?

rv969wf · #9 11-20-2006, 04:44 PM

Quote:

Originally Posted by cawmd82

Who did your paint job?

The painter? A hippie from Kansas City, MO. He's one of those guys you see coming out of a hippie van with hair down to his back with tatoos and smoking something other than a cigar. No sh#^&t!!! He had never airbrushed graphics on an airplane before and refused to do another one. When he went to sleep at night, if he did, all he saw was black and white squares!

He had mostly done show cars and motorcycle graphics. 3 months of solid work, 10 cases??? of masking paint and $9K later, in 1998. The checkers actually wrap around under the tail and fuselage, major pain in the rear. Paint is all PPG 2 stage Dodge Vipor Red. These pictures are a couple of yrs old and all the mods, rear canopy, lower cowl on the -6 are painted now btw.