Flap Speed

P

peterdeon

New member
The 86 mph flap speed on my plane is a real pain. It occurs to me that if that holds for full flap, then at less than full flap perhaps we can use more speed. I did some calculations. Bear with me if you don't recall your high school trig. I also make some assumptions that may need correcting, so please get back to me if I've made mistakes. My major assumption is that force applied to a plate moving through the air varies by the square of the speed. (I couldn't recall if it was the square or the cube-if it's the cube, I will have to recalculate everything) Anyhow, I drew a right triangle where the hypoteneuse is the flap and the side opposite is the "plate" (the area as seen by the air striking the flap) and the angle is the flap angle. (I'm assuming full flap is 40 degrees-correct me if I'm off) Any how the Force at full flaps is the plate times the speed squared. That is sine 40 degrees times flap(trig function-sine equals so/hy) times 86 squared is the force. Then I made calculations for varying degrees of flap and I came up with ten degrees-165 mph 20 degrees-117 mph and 30 degrees-97 mph. If anyone is dying to see my diagrams (can't figure out how to draw them online, but perhaps I can Fax my drawings to you) please contact me. If my assumptions (such as square instead of cube or that full flap is 40 degrees) are wrong, let me know and I will recalculate. Anyhow, it would seem that we can use partial flaps at considerably higher speeds to help slow the plane to full flap speed. Thoughts??
 
I've already discovered one error I made-the full flap down is 46 degrees-not 40. I will recalculate after other errors have been pointed out.
 
I won't pretend to be able to follow your calculations, but when i learned to fly thirty five years ago, I was taught to pull one notch of flaps at XX speed and then the second notch when the aircraft slowed to XX speed and the third notch (if there is one) at an even lower speed. In my head, the question would be what is the maximum speed one can pull that first notch of flaps? And it should be in the aircraft book. :?
Gary
 
In my humble opinion there are two reasons to be very careful about overloading the flap system
1. These airplane structures are very old and brittle and the area of the wing that carries the stress of the actuating cable is in an area subject to rot from moisture getting under the wing walk.

2. If one of the wood blocks that carries the final pulley where the cable turns down to attach to the flap actuator horn were to fail...you have an instant ascemetric flap situation.

As I rebuild my wings I am beefing up that area and replacing all the wood....if your root area is marginal.......keep the flap speed low. ..Ken McCune A&P/IA
 
Logically, given that the Vfe for 46 degrees of flaps is 86, and that speed was intended for a new aircraft or one in good repair, then following the book numbers is unsafe. Peter's question is an issue wholly different from the one you raise, Ken....which is a good point nonetheless.

The chief weakness of the flap system is that it has two attach points for a HUGE flap. Later Vikings have a third attachment point in the middle, raising Vfe and making the whole set-up far more mechanically sound. It would be nice to be able to retrofit the later design, but despite the similarities of the wings, just imagine what it would take to gain approval. The low Vfe is really no big deal, unless you fly IFR and get slam-dunked.

Peter's argument is purely a matter of physics and is scientifically sound. Cruiseairs have a partial flaps setting for take-off, but I have no idea if they have such settings for landing.

There are two reasons why partial flaps were never part of the Cruisemaster POH for take-off:

1. No detents - the Cruisemaster has hydraulics, with a crude flap gage on the panel and no markings on the flap root to tell you the percentage of flaps deployed.

2. Vy for the 'Master is higher than Vfe....much higher (102mph).

Pilots who fly 'Masters out of short strips developed their own short field take-off procedure long ago. Using a Vx of 80-81mph (some use a much lower figure), using 20 degrees of flaps was fine - you just have to remember to retract them before proceeding to Vy. For really short strips, some pilots "pop" the partial flaps mid way during the take-off roll. This eliminates flap drag during early acceleration.

Technically, as I'm sure we've all heard or said for years, any time you deviate from the POH you become a test pilot. Your argument is perfectly sound, Peter apart from the aforementioned difficulty of precisely gauging how many degrees of flaps you're hanging. Had our POHs been written in later eras perhaps this would have been tested. Regardless, I just feel safer using the method of chopping throttle on the downwind, hauling back on the yoke, deploying all the flaps at 80mph (I share Ken's concern), and employing whatever power you need, base to final.

Perhaps it's best to consider our flaps as exceptional glide slope control tools that also deliver an outstanding, low stall speed, than to think of them as speed brakes.

In short, physics is fine, but bold and old involves variables beyond straight calculation.

Jonathan
 
Keeping in mind the age of our wings, perhaps full flaps should not be used until somewhere under 86-maybe 75. I think with the numbers I came up with (which will need some tinkering, it would indicate that the stress of popping 10 degrees of flap at 110 (after dropping the gear) and maybe 20 at 90mph and then at 75 full flaps would be less stressful than waiting until 86 and then punching in full flaps. My strip is in the mountains and I am limited to how wide and long my pattern can be and it seems like it takes forever to get from 125 mph to 86mph) I usually drop the gear abeam the numbers. Curiously, the 14-19 has a 90 flap speed and the -2 reports 86. Are there differences between the two systems? (or did a lot break over the years so they came up with a lower number for the later models)
 
Peter:

The copy of the TC I have gives the same speed for both aircraft.

I didn't know the special challenges your home plate presents. Now I understand your keen interest in the subject. As I said, I deploy the flaps during the slow-down-haul-back as the needle passes 85 heading toward 80. But, due to many misfortunes I've mentioned in excruciating detail too many times in this forum, I don't have a lot of time in my 'Master between mechanical snafus. So I read a lot of stories written by people who have flown them a lot :) There was one fellow, Jan Gerster, who flew his 14-19 in the Idaho back country for 29 years, and told me a bunch of flaps stories :!:

If you ever have your flaps off (mine have been tinkered with many times, and have been removed at least twice while I've owned it) and see their attachments, as I'm sure Ken has, it will make you gulp at least once. Those fittings holding on a flap the size of a Sloop's mainsail are...interesting <cough>.

Jonathan
 
I had my left flap pull off of the wing on landing back in 2000. The flap plastered itself up against the fusaloge. I don't know If the plane did anything out of the ordinary . I did not relaize what had happened at first and I applied power and went around untill I found out what made that very loud slapping noise. I landed with the right flap up and when I came to a stop the left flap hit the ground. That started a ground up restoration which took 22 months. They are right about what holds the flaps on to the wing. I basicly doubled all wood in those areas so this would not happen again. I have pulled full flaps at 100 mph a time or to at night trying to make a runway in bad weather and have not had a problem. I would not do it with the origanal setup it is to weak.

On another note Jonathan I just went downstairs and looked at my flaps on my 74 Viking and they are set up just like the 47 cruiseair seting next to it. There is not a 3rd hinge .

I have a sign in front of my hanger that say's Bellanca Parking Only all others will be towed. I tell everyone else to park in the grass out front . I really like the Bellanca line and when we travel people always come out and look at the Bellanca . I do not like having the same thing every body else has like Cesnas and RV. :lol: :lol: :lol:
 
My two cents....When I need to dump speed above Vfe, I just pull the power back and throw it into a mild slip. That slab-side is a great speed brake and no worries about flap damage. May not be a graceful manuever but it does slow you down in a hurry...

My last airplane (Ercoupe with rudders) and a J-3 Cub I flew didn't have any flaps so slips were my "flaps" for steep approaches.
 
Randy:

The third hinge was something Dan Torrey told me years ago...at least I think he did. Got back this morning after taking the red-eye from Vegas...feeling a mite dizzy.

So the real question is, if there is not a third hinge, how did they engineer the Viking flap system to withstand a highter Vfe?

Russell Williams just sent me some photos of the major hydraulic parts he's refinished in preparation for installing them...along with undoing all the terrible work done by others over the years. I'm not saying I'm looking forward to testing the partial flaps theories...I'm no test pilot, I'll just be happy - delighted - to have a flying Cruisemaster once again :)

Jonathan
 
OK. This should be the last word on flap speed restrictions on Bellancas. Abide by them!!!! As a Bellanca owner since '70 and an AP mech, I know the weakest spot in the whole Cruisair (-9,-12, and-13 system) is the 1/16" cable operating system and the hinges that mount the flap to the wing. The wood is not normally a factor unless you have deteriorization. Here's was I use: Downwind-100IAS,gear down. Watch for traffic. Don't mimmic the Bonanzas and Lancairs with a warp speed downwind. Slow to 85, just prior to base-first notch, touch of power, Base-80 mph -second notch. final 70mph, third notch a touch more power. The Cruisair will fly just fine at 60 IAS-but it does take some power to arrest the sink rate. The Cruisemasters should follow closely. Dan Cullman
 
Yes, that is about what works for me, though I try not to have to bump power, by holding a just a bit more airspeed and keeping it in close. Traffic obviously may require changes. I also "seem" to have four notches of flap...another (?!)mod! Kind of nice though.
 
If you use a powered approach, full flaps, 60-65 IAS crossing the fence-then reduce power to idle- there's enough left to flare-and no float. That's how you can operate out of a 1000' strip.
 
My experience is like Dan's: 60mph or even a bit less on short final, carrying power. (My airplane is very light and who knows how accurate my ASI is?) Like Larry, I have 4 notches to the flaps in my Cruisair, though the first two are pretty small. For short or rough field takeoffs, I always carried two small notches, but maybe I should be carrying three, which is about half flaps. I love short field ops. I wish I could put vortex gens on my bird. Has anybody out there done this?
 
86881 actually has four notches. I think the 2d notch is the one added by ???????????? to a lot of Cruisairs. The T14-14 has five notches. The third of which corresponds to the 46 degree position on the 14-12 and 14-13 series.
 
I think that the point of my original post was that the force due to the air hitting the flap at 150 mph is less than the force of the air hitting full flaps at 86. I think a good plan might be to drop gear at 125 mph or less, and to help get the speed down below 86 mph without putting the engine at idle or going uphill, drop 10 or 20 degrees of flap as you head down to "flap speed" which is really full flap speed. Keep in mind that the flaps are not sturdy, perhaps using full flaps should be reserved for 75 mph or less. My home field is Truckee (TRK) and when making approaches to 28 (the preferred runway) the placement of base leg is not determined by what a standard pattern looks like but is instead determined by rapidly rising terain on that side of the field. We are just a few miles from the crest of the Sierras and can get very squirrelly winds and in the summer the 90 degree temperatures make the field elevation (5900 at standard temp) quite interesting. Despite all this, we do get some jet traffic. Our airport board has been taken over by non-pilots who want to stop the flow of traffic into the airport and they want to shorten the main runway. I don't think that will stop any traffic, but it will kill someone. I wonder what a bunch of soft hearted California Jurors will say when they hear that the airport spent good money to dig up part of a perfectly good runway thereby causing the death of a lovely family.
 
Although I'm often wrong, when I asserted that there was a third hinge on Viking flaps that gave them a higher Vfe than our Triple Tails, I got a bit of...well...jockular ribbing because some folks said it didn't exist. Oh, Randy...you still here? :) I asserted this based on what somebody told me, and felt properly chastised because I'd not actually witnessed one first hand. Oh Randy...

The other day a Viking landed at an airfield I frequent. No big deal. I've never poured over one the way I would a Triple Tail or an unusual old airplane. This one I did, and there it was, by golly: a flap hinge in the middle of the flap. I beheld the mythological third hinge. No, I didn't take a photo, though I considered taking several, from different angles, and posting every damned one of them here, but make them real grainy like those photos of the Loch Ness monster. But the whole affair was much too silly to waste whatever storage space this forum has at its command, and this goofy bit of business took place awhile back.

So maybe it's not called a hinge. This could be like the time I went into an auto parts store asking for a signal light and faced blank stares until someone said, "I think he wants a directional bulb."

But it's there I tell ya :!:

So where did Randy go?

Jonathan
 
When I recovered my flaps and ailerons on the Cruisemaster this last year I bought the "3rd" hinge and the parts to go in the wing. I put the part in the ailerons and I will install the parts in the wing when I possibly do the recover on the wings next year. The guys in Alexandria got them right out to me--don't remember the part number but it is in the Viking parts manual. I also acquired and extra set of flaps off a wrecked Viking--they are the same as the ones on the Cruisemaster I have--and they have the third hinge. Maybe the Vikings were built with only 2 hinges but I never seen one.
 
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