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Author Topic: Flap Question  (Read 538 times)

Offline Gary Dowler

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Flap Question
« on: June 21, 2018, 01:03:31 PM »
For the PT-19 Im about to begin for a scale project it has been brought to my attention that its a good candidate for brakes and flaps.  Specifically it was mentioned that "centrifugal" flaps would be easy to work in.   Im unfamiliar with this design.  Anyone know what Im referring to?  Apparently the concept I envisioned when this was brought up isn't close to how they work.  Anyone have any photos or drawings that show how this works?

Gary
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Offline Avaiojet

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Re: Flap Question
« Reply #1 on: June 21, 2018, 01:27:57 PM »
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Offline chuck snyder

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Re: Flap Question
« Reply #2 on: June 22, 2018, 06:51:45 AM »
Gary, I have never heard the term "centrifugal flaps" either. The drawings show the linkages for split flaps.

I would also suggest you carefully consider whether you really want to add brakes. With flaps you will have plenty of opportunity to fill out a complete competition flight. The brakes option is not often seen (never in my experience). It is common for R/C models, but I don't think it is used as an option. I suspect you will run the risk of judges making impromptu decisions about how you must use the option in your flight. Right off the top of my head I would require you to use them for an engine run up and to significantly shorten your landing roll out. Consider the risk of a nose over! They are going to add measurable weight and complexity to your model.

Chuck

Offline Gary Dowler

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Re: Flap Question
« Reply #3 on: June 22, 2018, 10:49:37 AM »
Gary, I have never heard the term "centrifugal flaps" either. The drawings show the linkages for split flaps.

I would also suggest you carefully consider whether you really want to add brakes. With flaps you will have plenty of opportunity to fill out a complete competition flight. The brakes option is not often seen (never in my experience). It is common for R/C models, but I don't think it is used as an option. I suspect you will run the risk of judges making impromptu decisions about how you must use the option in your flight. Right off the top of my head I would require you to use them for an engine run up and to significantly shorten your landing roll out. Consider the risk of a nose over! They are going to add measurable weight and complexity to your model.

Chuck

The brakes are fairly straightforward. It's simply a small coil spring that constricts on the hub.   The advantage of them is allowing a landing and stop at a predetermined point, then taxi around a lap and according to the rules a second stop with a foot of that original point.   The brakes are tied to the down elevator, so as down elevator is applied the brakes are also. A close friend has this setup on all of his scale ships.  Makes for a very realistic flight.

Gary
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Online Bob Heywood

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Re: Flap Question
« Reply #4 on: June 22, 2018, 07:48:44 PM »
Gary,

You didn't say if your friend uses the down elevator for brakes on taildraggers and /or tricycle gear planes. However, if you research tailwheel basics you will find that down elevator (stick forward) is ill advised. For your model there are a couple of issues. One, you run the risk of putting the plane on its nose. Two, a keen eyed judge will down grade your score because taildragger pilots know to keep the stick back except in certain very specific cases, namely when having taxi in a down wind situation. Even then the elevator is held close to neutral. For tailwheel airplanes keeping the tail stuck to the ground is paramount.
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Offline Fred Cronenwett

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Re: Flap Question
« Reply #5 on: June 22, 2018, 08:00:30 PM »
I tried brakes one time and they worked but I have noticed that I can trim out a model to come to a stop even without brakes. Bob is right with a tail dragger the pilot would typically hold up elevator during taxi and other operations. You get use to how much rollout distance you need to come to a stop.

If you use 2.4 Ghz you can put brakes on it's own channel but I would hate to have the brakes on when I came in for a landing! The chance of having the brakes ON could easily happen.

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Offline Gary Dowler

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Re: Flap Question
« Reply #6 on: June 22, 2018, 10:39:12 PM »
You guys make interesting points. The one scale plane he has that I am recently familiar with from the regionals is tricycle gear.   
I can see how one could easily add a simply friction brake to the tail wheel that is just a source of constant light resistance and could be enough to stop it reliably at bottom throttle setting.    I'll delve into this further. Got a long ways to go before it's a concern anyway.

Gary
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Online Tim Wescott

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Re: Flap Question
« Reply #7 on: June 23, 2018, 10:32:02 AM »
Did we "brake" the subject line?

I seem to recall someone advising a light, controlled amount of friction on the outboard wheel, to help with stopping while keeping the airplane out on the lines.  Am I cracked?  My first trial at scale is still on the building board, so I have no practical knowledge.
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Offline Trostle

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Re: Flap Question
« Reply #8 on: June 23, 2018, 11:39:18 AM »
My experience with several scale models over a number of years, including single engine scale from 1/2A to 60 size models to the multi-engine 1/2A scale models for the Tucson/Phoenix contests is that an active brake system is not necessary.  If the engine or engines haves a good reliable low idle, you can stop the model at any part of the circle and get the full points for a taxi by stopping it in that same place one lap later.  I once put a plate on the nose wheel of a 4-engine ship activated by down control to stop the nose wheel from turning.  The non-turning nose wheel would just skid across the pavement.  I think the same thing would happen with a some sort of a drag on a tail wheel.  The brake on the nose wheel was not necessary because I cold still stop forward movement at low throttle, even with all 4 engines running.

Keith

Online Bob Heywood

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Re: Flap Question
« Reply #9 on: June 23, 2018, 02:46:43 PM »
Since I don't know anything of your knowledge or involvement with full scale aviation please do not take the following wrong. It might be worth your while to find a local airport that has Citabrias. You should be able to buy an hour of dual time and have the instructor run you through the basics of handling a tailwheel airplane. They often give an introductory rides. Plus, it shoud be fun.

As for the PT-19, Fairchild could not have designed a better model subject if they had tried. Good luck with your project!
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Offline chuck snyder

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Re: Flap Question
« Reply #10 on: June 23, 2018, 04:49:59 PM »
I used to have a full-size Cessna 170, a tail dragger. The brakes are the best way to nose one over. Supposedly it is not possible nose over using only the elevator, but I was never about to test that theory! (I have seen a photo supporting this claim) I was careful to put my feet at the bottom of the rudder pedals so I could not possibly use the brakes when taking off, and used full up elevator when I did apply them. As mentioned above, full up when taxiing anything but downwind. Downwind?? lots of full scale debates about where to hold the elevator.
Chuck

Offline Trostle

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Re: Flap Question
« Reply #11 on: June 23, 2018, 05:16:22 PM »
One more thought about putting a brake on a tail wheel.  If one would do this, it will do nothing more than transform the tail wheel into a tail skid and do little to nothing to impede the forward motion of your model assuming the main gear is located reasonably well with respect to the CG.

Keith


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