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Old Jun 25, 2010, 11:15 PM
Lamborghini12345 is offline
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What makes a plane Fly Slow??


Well I set up my Fenix with a motor on top, small GWS with about 80g of thrust, AUW of 117g and it flies OK but quite fast. I want to take it down with me to Indoor at Palmerston North in the School Holidays but it will need to be controllable and slow if thats going to happen. I also tried it with a IPS "A" on it and it did fly Slow but would drop out the sky uncontrollably with no throttle.

SO I am wondering what makes a plane fly Slow and how can I make mine fly Slow? I figure its down to Thrust, Weight, Wing Loading?

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Old Jun 25, 2010, 11:53 PM
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Wing loading, which is a factor of weight and lifting surface area, is what determines flight speed... at least that is what I understand.
Old Jun 26, 2010, 12:08 AM
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Would extending the wing area work then?
Old Jun 26, 2010, 12:39 AM
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Wing loading is one factor, more winger area allows more lift at slower speeds, thus slow flight..

Another thing to consider is prop pitch speed.. not as important as wing loading, but can make a difference. A prop with a high pitch speed may generate more plane speed, like 6th gear in a sportscar.. high top end speed.. A lower pitch speed is more like a granny first gear in an old pick up, lots of thrust but it "winds out" and cannot accelerate a plane beyond a certain point unless a dive is invoked..

So a really good slow flier has a combination of both things, a high torque / low pitch speed prop, and large wing area to help lower the wing loading.

Hence on the micro planes, a diet to loose weight can really help things out, and even the Parkzone micro planes can come in under an ounce, some fly extremely slow like the Vapor..

~Kev
Old Jun 26, 2010, 01:26 AM
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So the GWS EDP-50 DD is probably a high pitch speed with the 3020 prop, I guess the IPS was better because it had more thrust and reduction via gearbox for Slow speed plus high thrust. I think I will use my EPPiper then and keep this thing as a Glider....
Old Jun 26, 2010, 09:47 AM
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Which fenix do you have? The smaller ones are naturally going to be zippy.

Kev
Old Jun 26, 2010, 11:17 AM
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I wonder if AOA can come into play. My DH-6 in my blog is a 13" 3ch peanut. In addition to a light wing loading, I added a lot of incidence in the wings (as per the plans + some). The thing crawls along. Could this be due to a mix of induced drag due to the biplane configuration, wing loading, and incidence?

Also, I left the bottom of the wings uncovered to produce a sort of "parchute" effect. Would this be considered parasitic or induced drag? In other words, do you think that it produces lift or just parasitic drag?

Great discussion!

Thanks,
PC49
Old Jun 26, 2010, 12:04 PM
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We had a discussion on this a while back.
What is the name of lift that a foamy generates?
Old Jun 26, 2010, 12:17 PM
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Quote:
Originally Posted by boredom.is.me View Post
We had a discussion on this a while back.
What is the name of lift that a foamy generates?
Will you please explain how dynamic lift relates here? I don't see how it answers my question(s)...
Old Jun 26, 2010, 01:33 PM
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I didn't say it answered any of your questions. I just said we had a discussion on the topic of lift. And the thread I posted talks about purposely induced drag to create lift.

I just realized that you are in it.

Edit: I meant how drag is related to lift.
Last edited by boredom.is.me; Jun 26, 2010 at 01:40 PM.
Old Jun 26, 2010, 01:41 PM
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isnt parasitic drag caused by items not contributing to lift, like a non lifting fuselage or airflow into an open ended fuselage?
i think if you want the biggest reasons for slow flight, its wing loading AND airfoil. many gliders have wing loading very close to planes like the parkzone sukhoi and yet the top speed is MUCH greater than it because they have a higher lift/drag ratio and the slippery airframe to accomplish it. and on the same note, when that glider changes its airfoil by dropping the flaps, it can slow to a crawl for landing (the lift/drag ratio changes dramatically when that happens as well)
so, you can go slower with a better airfoil at the same wing loading if you sacrifice the performance of having less drag.
Last edited by derk; Jun 26, 2010 at 09:11 PM.
Old Jun 26, 2010, 02:20 PM
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Derk and BIM, thank you both. And Derk, you are right about parasitic drag. BIM- sorry for the confusion.
Old Jun 26, 2010, 06:39 PM
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Quote:
Originally Posted by derk View Post
isnt parasitic drag caused by items not contributing to lift, like a non lifting fuselage or airflow into an open ended fuselage?
i think if you want the biggest reasons for slow flight, its wing loading AND airfoil. many gliders have wing loading very close to planes like the parkzone sukhoi and yet the top speed is MUCH greater than it because they have a lower lift/drag ratio and the slippery airframe to accomplish it. and on the same note, when that glider changes its airfoil by dropping the flaps, it can slow to a crawl for landing (the lift/drag ratio changes dramatically when that happens as well)
so, you can go slower with a better airfoil at the same wing loading if you sacrifice performance of less drag.
Probably a slip of the fingers, but a sailplane with a slippery airframe would have a HIGH L/D ratio. Lots of lift divided by not much drag.
Adding camber with flaps adds lift, but also adds drag. So pulling on flaps decreases the L/D ratio, which is why you can use flaps for glidepath control.
Old Jun 26, 2010, 09:02 PM
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Thanks for all the help guys, I decided to revamp my EPPiper and its charging now, Had a test in the backyard and its Slow and floppy. I wasnt wanting to buy new gear(Well wanted but I just bought new receivers=Broke)so its using the original IPS "A" motor which is gutless but it works! Weighs in at 184g so a wing loading of 4.154oz/sq.ft and about 110g of thrust on the 9070, I might try a 1047 or 9075 but I would need to buy one all my 1047's are bent.
Old Jun 26, 2010, 09:10 PM
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Quote:
Originally Posted by TjW View Post
Probably a slip of the fingers, but a sailplane with a slippery airframe would have a HIGH L/D ratio. Lots of lift divided by not much drag.
Adding camber with flaps adds lift, but also adds drag. So pulling on flaps decreases the L/D ratio, which is why you can use flaps for glidepath control.
oh yeah, i had drag stuck in my head so i got it backwards


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