osxuser

osxuser

Well Known Member
Two questions:

Does anyone fly without flaps regularly on their -4's?

Has anyone built a fowler flap setup for one?

I'm in between eliminating them altogether, or making them... better. Leaning towards eliminating them. Downsides? Other than increase stall/landing speeds. Any "problems" with this approach... pun intended.
 
I'll jump in on this.

You could probably eliminate the flaps without any major problems. Why do you want to?

My experiences with my RV-4 (Everett Hatch-built O-360A1A, 200 hp, Hartzell prop with F-7666 blades, 1070 lbs, CG in a forward location):
The stock plain flaps decrease stall speed from 55 KIAS clean to 50 KIAS with full flaps. Extending flaps decreases the landing roll, but with the RV-4 that really is not significant. I can get the plane stopped in 500 ft with moderate braking. With flaps up that increases a few hundred feet. You could still operate comfortably from 1000-ft runways with a constant-speed prop.

The two major advantages to extending flaps for landing is a steeper approach, and a landing attitude closer to the stalling angle of attack. All RV-4s, even with the newer long gear legs, are still flying in the 3-point attitude, even with full flaps. Landing with flaps up means you are touching down well below the stalling angle of attack. If you plan a fixed-pitch prop, you will find speed control more difficult on final approach without flaps, necessitating a shallower approach.

I practice no-flap landings periodically. No problem, just a moderately shallower approach and moderately increased landing roll.

With a constant-speed prop I take off with flaps up anyway, so there would be no difference there.

You could design and build fowler flaps if you like, but again why do you want to? The RV-4 has such ridiculously good short-field performance anyway that the expense and effort probably wouldn't be worth the slight improvement. With my RV-4, light weight, solo, cold day, max performance gives a takeoff roll of 150 ft. Max effort landing roll, same conditions, max braking, can be as short as 200 ft. Fowler flaps really wouldn't decrease your distances much below that.
 
The reason I ask is because plain flaps don't typically do a whole lot (As noted above...)

I figured either do it right (fowler) or not at all. Made sense to me. As for mods... not really intimidated by straying from the plans myself. Planning on clipping the wings a little, so trying to figure out final layout before I build my jig again.
 
osxuser said:
The reason I ask is because plain flaps don't typically do a whole lot (As noted above...)
Click to expand...
One big thing the flaps do is pitch the nose down for much better visibility at the same airspeed. On downwind, I am always relieved to get down to flap speed so I can put them half down and see a lot better.
 
Stephen,

I've always wondered what change in stall speed an RV-7 or -8 would get by fitting a modified the -9's fowler flaps. The only downside that I can see is the hinges would hang out in the wind. Really not a big deal, IMHO.

As for not including flaps, one thing I have noticed in doing no-flap landings in my -9, this may not apply to the -4, is that it has to come in really flat and low. If your runway is short and has trees, as mine does, this isn't such a good option.

My $.02.
 
IIRC Bruce Bohannon did this (deleted flaps) on the RV-4/-8/Rocket hybrid Flying Tiger. He said in an interview that he missed the drag on landing and would put the flaps in if he were doing it again
 
Ive taught a lot of guys no flap landings...

...in my -6A and they all come away with a much greater appreciation for the flaps after a no-flap landing, as I do. Van's got it right. I think you discount their value more than is justified. I also fly my buddy's -4 often..always full flap landings.

Regards,
 
pierre smith said:
...in my -6A and they all come away with a much greater appreciation for the flaps after a no-flap landing, as I do. Van's got it right. I think you discount their value more than is justified. I also fly my buddy's -4 often..always full flap landings.
Click to expand...

With my 6A and C/S prop, I'll do lot's of half flap landings..........as it still comes down like a rock with the added effect of constant speed braking.
But I agree, the 6's flaps are very effective. You feel it as soon as the flap motor starts whirring. I'd have to assume that the 4 is much the same.

L.Adamson
 
Think OSH

n5lp said:
One big thing the flaps do is pitch the nose down for much better visibility at the same airspeed. On downwind, I am always relieved to get down to flap speed so I can put them half down and see a lot better.
Click to expand...

This is an important point. When I practiced slow flight in preparation for flying the Fisk approach to Oshkosh, were you may be behind a 70 kts cub, the flaps are needed to get the nose down. Slow flight at even 90 kts was at a better attitude with 10 degrees of flap. With out flaps at 80, 70 and 65 kts the nose high attitude and subsequent forward visibility was very poor/uncomfortable (level flight). At these speeds 30 degrees worked best to get the nose down to a level attitude.
 
Slipping it

I have a friend with an RV4. He has flaps but never uses them. He slips every landing and has a great view of the runway. Not my thing but it works well for him. He is also ten times the pilot I am as far as time and aerobatic proficiency.
 
I've been pondering fowler flaps on my rocket for quite some time now. If you study the fowler flaps on a Helio Courier, they have the best flap track design. The Helio uses the NACA 23000 series airfoil, same as the RV's. I think if you build the flaps just like the ailerons on the RV with slotted tracks you would come very close to the Helio design.
 
rocketbob said:
I've been pondering fowler flaps on my rocket for quite some time now. If you study the fowler flaps on a Helio Courier, they have the best flap track design. The Helio uses the NACA 23000 series airfoil, same as the RV's. I think if you build the flaps just like the ailerons on the RV with slotted tracks you would come very close to the Helio design.
Click to expand...

Bob,

While using a slotted track is optimal, Van elected to go with a fixed position for his flaps. In the fully down position they are supposed to be in the "right" position. This reduces construction and complexity as you only need one pivot point. Besides, you could just by the RV-9 flap hangers and brackets to incorporate into your flaps.

Just my thoughts on this, which I have spent a lot of time thinking about it.
 
If you have fixed pitch prop, I wouldn't consider doing w/o...flew a -4 for 12 yrs. & had to slip it even w/ flaps down. My 4 loved to float. Had to use shallow approach w/o flaps because the bird wouldn't slow down. Have had an 8 last 3 yrs. and its totally different. Steep approaches always best for safety. If you have CS prop I'm sure its much better w/ that big speed brake like on my 8.:)
 
Stephen,

I don?t have much RV time, but I do have lots of Super Cub time. As you know Super Cubs come in several flavours, but the bulk of them were built as 90 hp without flaps and 150 hp with flaps. The two are like night and day and in my opinion the flaps make as much difference as the increase in power. To summarise the reasons you want to stay with the flaps:
1. The obvious is the lower stall speed. As quoted above it does make a difference.
2. Lower nose attitude with flap out.
3. Greater drag. This means steeper approaches and greater aerodynamic drag which does shorten your landing roll. However in my opinion the most important benefit here is how it helps in the approach and touch down phase of your landing. If you can hang out loads of drag when you need to, and then add loads of power to counteract this, flying the approach accurately is dead easy as you only need to alter that power a bit to correct your desired approach path. If you have enough of both you can still fly a steepish approach with plenty of power and therefore control it. If you don?t have the ability to add all this drag, you are often faced with a power off or low power approach with little scope to vary the approach path with the throttle. Secondly if you are able to carry a lot of power up to your touch down point closing the throttle brings about a fairly immediate landing instead of floating up the field. This means you land where you want to and can then get on the brakes which are far better braking than aerodynamic drag ever will be. The previous posters have covered all this, but I'm trying to wrap it up into one paragraph.

We won?t get into the possible benefits of dumping flap on landing or use of flap on take off, but the benefits of flaps are pretty clear.

I agree that these sort of mods need not be shied away from. This is what homebuilts are all about, after all a variation on a well proven design (the Stitts Plyboy) is what got Vans started in the first place! I?m a time away from having to worry about this, but I am building an RV6 and have already given some thought to building and installing RV9 slotted flaps on my RV6. I have the RV9 pre-view plans and considering the parts are already thought about designed and made, figure that this would be a good compromise between going exactly per the drawings and developing something completely new like fowler flaps.

I wonder if anyone has done this? Seems pretty mild compared with some of the changes around???..

Please post what you do!

Cheers,
Andrew.
 
The hard points are not there...

...for flap attach brackets like they are on the -9. The loads are transmitted from the flaps to the wing along the entire hinge, whereas on the -9 you have how many, three attach points. I'd definitely have an aero engineer look at this mod...you know what Van would say.

Regards,
 
Hard points

The -7 & -9 wing structure are the same, the difference being the shape of the ribs and the length.

The flap hangers are simply riveted to the side of each rib with two small brackets made out of AA added to spread the loads.

One bracket is installed vertically and ties the aft spar to the side of the flap hanger and the other is installed horizontally and is riveted the flap hanger and the bottom skin.
 
Yes Pierre, I got to exactly that point with respect to the difference between piano hinge and individual brackets and how the loads will be transmitted back into the wing. Similarly, the effect of the different flaps on the centre of pressure and the coefficient of lift may stress the wing structure differently. As you know its not something I have to make a decision on just now so after I figured it was mechanically possible, I closed up my RV9 drawings and went back to drilling holes! Its still good to toss these things around.

Cheers,
Andrew.
 
Fowler flaps

Fowler flaps make a big difference to the stall speed of a jet aircraft. One major consideration is the nose down trim change on extension. Most modern transport aircraft have large leading edge devices which tend to reduce the pitch and trim change. Older machines with less powerful LEDs, like the 727, have a trim change that would shock most small aircraft drivers.
Just about every commercial jet has an all moving horizontal stab. They really need that kind of trim authority to cover the trim changes associated with a large speed range and the pitching moment that comes with flap extension.
I think the need for greater trim authority would be the biggest obstacle.

Hey, wait a minute! How about an RV with Fowler flaps, leading edge devices and a moving horizontal stab! I'd like to take that one to Oshkosh.
 
I have been flying my RV-4 for 3 years. I am a CFI CFII, MEI and fly much more than I drive.

I find that the RV's are difficult to slow down and get down. You have to plan your descent way ahead of time ( as in Mooney). Almost every approach to an airport involves the challenge of getting her slowed down. What runs through my head is get it down and get it slowed down. The huge flaps of the RV WORK. I is interesting though. You roll in the flaps and their appears to be no effect for about 10 seconds and then all of a sudden whoa, your dropping like a rock. The effective flaps of the RV are great for keeping it slowed down and dumping altitude.
 
bill price said:
I have been flying my RV-4 for 3 years. I am a CFI CFII, MEI and fly much more than I drive.

I find that the RV's are difficult to slow down and get down. You have to plan your descent way ahead of time ( as in Mooney). Almost every approach to an airport involves the challenge of getting her slowed down. What runs through my head is get it down and get it slowed down. The huge flaps of the RV WORK. I is interesting though. You roll in the flaps and their appears to be no effect for about 10 seconds and then all of a sudden whoa, your dropping like a rock. The effective flaps of the RV are great for keeping it slowed down and dumping altitude.
Click to expand...

On the other hand, a C/S prop on the front of an RV allows for immediate slowdown. Between the C/S and flaps, I can do just about anything that's required to adjust to changing pattern conditions. While a C/S isn't for everybody, it really is a great tool for dealing with different situations regarding speed adjustments.....immediately!

L.Adamson --- RV6A
 
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