Are Flaps Over Rated?

[mvivion]

375handh,

Sorry, you apparently missed the basic point of the discussion. I stand by my assertion that the "best angle of climb" by aircraft definitions in a helicopter, would, indeed, be straight up. I didn't suggest that it was particularly safe however.

You are correct about the height/velocity curve of course, but helicopter pilots violate that somewhat regularly, for (hopefully) good reasons, such as long line operations or animal capture work, for example.

The definition of best angle of climb (or Vx) is: "The speed for Vx is that which will result in the greatest gain in altitude for a given distance over the ground" (Airplane Flying Handbook, US DOT, Federal Aviation Administration, FAA-H-8083).

My reference to a helicopter climb was somewhat joking, but by this definition, the best angle (not the best rate, which would, as you note, be achieved post translational lift) of climb in a helicopter would obviously be straight up. Watch a Llama (AS 315) go straight up sometime with a long line operation and you'll be a believer. Granted, if that big engine quits......

While the definitions for helicopter operations may be different, the risks aren't so very different. If your engine checks out going straight up in a helicopter, it isn't going to be pretty. If your engine checks out at best angle of climb in a Cub close to the ground, you are probably almost equally likely to land hard. My guess is you'd still be way better off in the Cub, from a purely personal standpoint, but both aircraft are going to be worse for the experience.

MTV

 

[375handh]

Mike:

Just one helicopter correction: best angle of climb, i.e. Vx, in a helicopter is still above ETL. You can go straight up (usually), but that is still not Vx.

375handh

 

[ground loop]

Can someone explain to me the differences between cub flaps and husky flaps (and how they work)? Why didn't the top cub or dakota wings get redisgned with husky flaps or any other type of flaps?

 

[mvivion]

375handh,

Yeah, I was applying fixed wing terminology to a helicopter example, but just trying to illustrate the ultimate in obstacle clearance climbs.

Ground Loop,

The Husky flap is HUGE for one thing, probably twice the physical size of the Super Cub flap. Take a good look at one each, side by side some time. I don't have measurements, but the difference is large.

Secondly, the Husky flap is a semi Fowler design, compared to the Cub's simple flap design. The Fowler flaps develop much more lift for a given deflection. Simple flaps are pretty good drag devices, and produce a little additional lift.

The reasons someone didn't design in Husky type (and note that most high wing Cessnas have semi Fowler flaps also) are likely the cost to redesign the wing, completely different parts, as in ribs, spars, fittings, etc., and a big difference in the aft spar, and I assume the rear spar attach point to take the stresses of the bigger, more effective flaps. Not to mention a whole lot of testing, etc. I'm just guessing, mind you.

Semi Fowler flaps do work very well, though, as anyone who's flown a Cessna 170 A and a 170B will tell you.

MTV

 

[ground loop]

Mvivion,
Are there any advantages to the simple flap design over the semi-Fowler beside construction simplicity? I know in theory that the cub flap doesn't create as much lift, but I do feel some lift (they must since they decrease stall speed?). How do they work differently? Doesn't the mountain goat us a fowler design also?

 

[bob turner]

Nope - on a helicopter, best angle is straight up. Same in a Cub, if you are light enough with a big enough engine. Best rate is a different story, and is always always always flaps up. Unless that Beaver story is really true. I have heard from several Beaver pilots that there are some speeds where it won't climb at all without flaps, but that sure doesn't square with aerodynamic theory.

Edited Monday AM - I posted this on page one, then found the subject of max rate for helicopters well treated before this post. I really didn't spend the time to understand the difference between best angle for fixed-wing and that for helicopters, but you simply cannot do better than straight up. Also, glad to hear that someone else has qualms about Vxfe in a Super Cub. It's almost as bad in the 180, but not quite.

 

[RON NORMARK]

One aspect of flaps that has been hinted at by the mention of stabillty in turns with flaps deployed, is that they increase the angle of attack of the flapped portion of the wing. This has the same effect as increasing washout. The inboard section will stall sooner, while leaving the outboard portion of the wing flying. The result is a more docile stall characteristic with flaps deployed. I routinely do steep 180 degree turns with full flaps at 45mph. The manuver saved my neck when the engine quit one day. Be careful about your CG if you try it, however.

Ron

 

[Steve Pierce]

Husky wing design is pretty close to the SC including spars and compression struts. The flap hinges are a lot different. I shipped a guy on this site a set of flaps and inboard section of spar to modify a SC wing. I bet he is getting close to finishing it up.

 

[mvivion]

Ground Loop,

To the best of my knowledge (and aerodynamics 101 was not my strong course), the primary advantage of a simple flap is ease and simplicity of design and installation.

Semi Fowler flaps are found on LOTS of aircraft, of all sorts of designs. And they offer some very significant design advantages. Some or most of the go fast turbine singles use them to get stall speeds below the magic certification goal of 61 knots, for example.

The other difference in the Husky B model wing is that the rear spar is made from a different material, much stronger. This is what permitted the higher gross weight and the higher flap speed.

In other words, I don't think you could just hang a set of Husky flaps on a Cub wing.

MTV

 

[Steve Pierce]

No, but this guy is an aeronautical engineer and it will be his butt hanging out there so I am sure he has researched the subject. These flaps and spars were off one of the early border patrol Huskies. Lots of pop rivets and Univair PA18 parts in those wings.

 

[Anne]

The first notch of flaps has more lift than drag.
The second notch of flaps has about the same lift and drag.
The third notch of flaps has more drag than lift.

Whichever type of flaps you are using, you are changing the basic shape of the wing when you use them. Air flows differently over different shapes. So, when you say you're using flaps, be aware that the different deployments yield different results.

Anne.

 

[ground loop]

annestoy,
But, third notch has more lift than first notch.

 

[heege-brigmann]

4 weeks ago at 4000´ on a plateau in the North-West-Territories I was happy that I had 8´ 50° flaps to pump me up in groundeffect after 1000´pretty rough groundroll and I have a 180HP engine in front. For sure emideately after airborne I had milked the flaps down to first notch.

 

[mvivion]

Steve,

Aeronautical engineer or not, the early wings weren't nearly as strong as the later wings. The A model added spar cap strips, which somewhat strengthened the wing, but still didn't increase the flap speed, which was very low on the early airplanes.

The increase in gross weight and flap speed increase came about largely from the change in the alloy used in the aft spar, and beefing up the rear spar attach point.

As you say, hopefully, he's doing load projections, etc. and has figured out the issues. There is a lot of stress in that area, though, due to the size and configuration of the flaps.

MTV

 

[Steve Pierce]

These wings had spar reinforcements over the attach fittings like the Wipair STC. It was a Christian Husky. I am sure he did some calculations. Be interesting to see how the Cub wing does with a lift producing flap.

 

[bob turner]

We did this in another thread, but the Husky and recent Cessnas apparently have restricted flap extensions because of certification requirements. Thus, the Cub flaps slow you down a lot quicker in the flare, because they hang out about twice as far as the Husky, and actually a lot further than that wimpy 30 degrees that Cessna has been stuck with.

Husky flaps are a better design, but they do not produce enough drag at their restricted extension. That's why you have to be so careful to not get above 55 on the approach.

Lift is a funny thing - you only need enough to counteract weight at a given speed. Lift doesn't make you go up; excess power does. Anything that adds drag subtracts excess power. Even high-lift flaps!

 

[jon s. blocker]

flaps

Bob, my Cessna 170B has a STOCK 50 whimpy degrees of flaps, not 30. Jon

 

[PhilP]

I don't have flaps on my 2+2, I have spoilers. There are places around here I know I could get in, and I want to, but I'd have to take the wings off and truck it out. Flaps are not over rated. On our type airplane I think It makes a 100ft difference on ground roll.

I'm with you! And I wish I had an O-320 sittin' around with a spare set of PA-18 tail feathers as well. Ya know what I mean?? :lol:

Speaking of landing and not getting out. Seems our friend with the C-120 out of Deland has given up on the Island. I've got access to an old Lobster Boat up here in Jax that could haul enough equipment to get that place usable again. All I need is a little motivation, or a helicopter.

Whacha think, and are you coming down here soon?

 

[Tim]

I'll be down the middle of Oct. get the lobster boat ready. I'll call C-120 Jim and see whats up, hate to lose a good strip.

Tim

 

[mvivion]

Steve,

The reinforcements you mention are the cap strips. They just strengthen the wing at the lift strut attach point. The factory changed the rear spar alloy to increase the GW further, plus this allowed them to increase flap speed. In other words, they considered that a vulnerable spot, load wise, with those big flaps. Course, it depends on what weight he intends to operate at, as well.

I'm with you. There's a local guy who's been building a four seat Arctic Tern fuselage, with Husky wings and an IO-360 200 hp engine. Should be a really interesting airplane when done.

Take a look at Dream Aircraft Works Tundra airplane kit. That looks like a REALLY nice piece of work to me. Unfortunately, I'd have to build it. Which, of course would mean I'd then have to fly something I built .

MTV

 

[ground loop]

bob turner,
Your last post in this section was very good!

 

[bob turner]

Thanks - but I think I have gotten a bit obsessed with flaps. I guess I never really thought about it until one of my students started climbing with 20 deg. flaps out at an indicated 90 mph. He says that's the way the real 180 drivers do it!

You have to ask: if flaps are such good things for climbing, why is it that we train to clean the darn thing up before doing the engine fire/ failure checklist?

 

[mvivion]

Bob,

I would suggest that the restriction in flap extension on the Cessnas and Husky may or may not be a "certification thing", based on the fact that Cub Crafters got essentially the original Super Cub flap system, including full deflection, approved under FAR 23.

MTV

 

[StewartB]

I thought the 30* limitation on Cessnas had to do with the ability to go around with full flaps at gross weight. Some models weren't capable, especially as gross weights increased and/or floats were added.

Here's an interesting article about flaps.

http://whitts.alioth.net/Pagec81Use of Flaps.htm

SB

 

[ground loop]

SB,
Is it safe to assume that a lot of that info is mostly applicable to planes with Fowler flaps and not to cubs?

 

[StewartB]

You'll have to ask someone smarter than me. I just flies 'em.

SB

 

[mvivion]

If you look at the Cessna flap restrictions, they occured not necessarily when the airplanes were recertified under FAR 23. A Cessna 182 can climb with 40 flaps down, but not enthusiastically, and it does require some skill on the part of the pilot.

I believe most of what drives the restriction of flaps on Cessnas is related to liability issues, as opposed to actual certification requirements. But that is purely speculation on my part.

Take a look, for example at the 150 vs the 152. The later airplane actually had MORE power, but they restricted the flap setting. That doesn't sound like a certification issue to me, but.......

MTV

 

[S2D]

The first notch of flaps has more lift than drag.
The second notch of flaps has about the same lift and drag.
The third notch of flaps has more drag than lift.

Whichever type of flaps you are using, you are changing the basic shape of the wing when you use them. Air flows differently over different shapes. So, when you say you're using flaps, be aware that the different deployments yield different results.

Anne.

Just watched a show on Doolittles Raiders last night. They took off fully loaded with Full Flaps in the B-25. 500 feet in a Loaded B25 must have been pretty impressive.

 

[ground loop]

Just saw a picture of the new Husky. Those flaps are HUGE.

 

[bob turner]

Actually, in another thread I thought it was Mike that responded to my query about why the Husky flaps were restricted by saying that it was a certification problem. I think the Husky might beat the Cub if it had a flaps 50 setting, like the Cub.

The thing that makes a C-180 is the flaps. And I understand that the L-19 goes to 60 degrees! I am dying to try that! Cessna will probably never go into 180/185 production again, but if they did, you can bet they wouldn't sell many with flaps restricted to 30.

And I am the guy who consistently says that flaps are over-used!