HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Oct 30, 2012, 08:34 PM
Flying Hazard
SU-4ever's Avatar
Spain
Joined May 2006
2,624 Posts
For the records: I don't know the exact altitude I fly at but I'm very, very, close to sea level, just 3 or 4 km from the beach, so you can guess.

About the Take-off jump issue...
I guess the trick is to get to the right speed and then just pull the minimum necessary for roll and neutralize immediately after, even pitching a bit down after rotation.

Since the Su's tailerons are BIG surfaces their momentum response on ground is not linear because if you fully deflect them suddenly, the surface stalls and generates a lot of drag but not necessarily the enough negative lift for tail lowering. At least when I have the speed limited by grass. In fact the idea of such great surfaces is that they can create great lift forces with very little deflection and thus reduced drag, which is very nice for endurance in closed quarters dogfights. Now someone will say: HEY! then limit the throws so that the tailerons never stall! But the even nicest thing about those awesome huge surfaces is that when you are turining very sharply (As in a cobra, or just flying High Alpha) the plane does not fly forward but rather drift the air, and the "neutral" position for tailerons change, so you are going to WANT that extra travel for radical flight. Because on a high alpha you can use full deflection without taileron surface stalling.

Then, my theory is, on the ground we are impatient and pull hardest because nose doesn't go up, but by doing so, we are not really helping rotation in terms of taileron effectiveness but the TV DOES. So we finally get to rotate thanks to thrust vector and THEN the flow attaches again to the taileron surface, which boosts its aerodynamic efficiency, making it couple with the already hard working TV and subsequently shaping our most beloved violent rotation.

I think we should improve take-off performance by setting a special mix just for takeoff that enables full TV deflection but limits taileron pitch.

I will try myself when I get my su flying right again and share the results.

Cheers!
Jandro.
SU-4ever is online now Find More Posts by SU-4ever
Reply With Quote
Sign up now
to remove ads between posts
Old Oct 30, 2012, 08:38 PM
Should've, Would've, Could've
v8truckin's Avatar
United States, CA
Joined Dec 2010
6,539 Posts
Quote:
Originally Posted by SU-4ever View Post

About the Take-off jump issue...
I guess the trick is to get to the right speed and then just pull the minimum necessary for roll and neutralize immediately after, even pitching a bit down after rotation.

Cheers!
Jandro.
Thats exaclty!!! what i do. Too much she pulls hard up, so just gotta pull back slowly when the time is right. Ive been flying her from the get go so ive got it down others will have to get used to her.
v8truckin is offline Find More Posts by v8truckin
Reply With Quote
Old Oct 30, 2012, 08:46 PM
Flying Hazard
SU-4ever's Avatar
Spain
Joined May 2006
2,624 Posts
Quote:
Originally Posted by v8truckin View Post
... others will have to get used to her.
Rough girl, ain't she?
SU-4ever is online now Find More Posts by SU-4ever
Reply With Quote
Old Oct 30, 2012, 10:03 PM
Should've, Would've, Could've
v8truckin's Avatar
United States, CA
Joined Dec 2010
6,539 Posts
Quote:
Originally Posted by SU-4ever View Post
Rough girl, ain't she?
lol! Yup sometime plays hard to get.
v8truckin is offline Find More Posts by v8truckin
Reply With Quote
Old Oct 30, 2012, 10:53 PM
Registered User
United States, CA, Woodland
Joined Dec 2008
163 Posts
If I remove the red wire for the plug going into the throttle channel of receiver and supply receiver with another battery will everything work if the bec on esc are defective.
R. Mike Neely is offline Find More Posts by R. Mike Neely
Reply With Quote
Old Oct 30, 2012, 11:02 PM
Life begins at transition
Australia, VIC, Sale
Joined May 2007
3,593 Posts
Yes - that's what I've done, but with a BEC instead of an Rx battery.
Odysis is offline Find More Posts by Odysis
Reply With Quote
Old Oct 30, 2012, 11:26 PM
Registered User
United States, CA, Woodland
Joined Dec 2008
163 Posts
Thank you very much for staying with me on this problem. Finally realize red wire was power from esc and removing it to add another battery would see if esc was alright.
ALL IS RIGHT WITH THE WORLD he! he!
R. Mike Neely is offline Find More Posts by R. Mike Neely
Reply With Quote
Old Oct 30, 2012, 11:28 PM
Registered User
United States, CA, Woodland
Joined Dec 2008
163 Posts
and thank you too fredmdbud
R. Mike Neely is offline Find More Posts by R. Mike Neely
Reply With Quote
Old Oct 31, 2012, 01:13 AM
You are a "go" for reentry
Maxthrottle's Avatar
High Orbit.....
Joined Jun 2009
6,261 Posts
Pete?.... Flight speed is flight speed. Once you reach it short rollout or not you know it will fly once off the ground; quicker if you have a head wind.

Not sure if this is the old debate over US vs UK way of lift off. US is get air born once you reach flight speed which is why unless carrying heavy ordnance they pull hard without the long roll outs. The UK is use all of your runway as long as you remain below the wheels spin safety margin.
There are reasons for doing either in the real world but we are not in the model. We can only use VFR. Waiting till the nose lifts on its own can mean its a dot where you see nothing.

Too with grass you also kind of reach a terminal velocity. There is enough friction that you don't go any faster unless you break from of the grass. So as long as you are at flight speed, getting out of the grass sooner can be a better VFR and better for the gear.

The rest SU4Ever covered but the sell point for TV is they vector with little drag regardless of speed. Good for attitude approach, they bleed speed less in turns and help LO.
Mind you SU stab stall angles changes with speed. They can be very effective, needing more angle as it nears zero forward V though such extreme isn't desired for takeoff.

Regarding throw though, in changing winds a gust and then sudden nothing can need more input to correct. You see this on real ones in a stalled profile. And at slow speed landing and takeoff, the aircraft is most vulnerable to this change. Jason Cole was quoted in a model mag saying exactly this; that most have it a little backward. You need more throw when slow but you need to learn how to not over steer it. If you ever do a harrier you know why.

Quote:
Originally Posted by SU-4ever View Post
.....I think we should improve take-off performance by setting a special mix just for takeoff that enables full TV deflection but limits taileron pitch.

I will try myself when I get my su flying right again and share the results.

Cheers!
Jandro.
Quote:
Originally Posted by v8truckin View Post
Thats exaclty!!! what i do. Too much she pulls hard up, so just gotta pull back slowly when the time is right. Ive been flying her from the get go so ive got it down others will have to get used to her.
Maxthrottle is online now Find More Posts by Maxthrottle
RCG Plus Member
Old Oct 31, 2012, 02:07 AM
Registered User
Australia, VIC, Melbourne
Joined Nov 2006
10,442 Posts
Flight speed is not flight speed......
I am not sure where that comes into the take-off issue... but if anything, my take-offs (any aircraft) are more based on that sort of correct 'flight speed' point.

You can force a plane to leave the ground too soon. In a real plane you will be in trouble most likely... but in models, which all in stock form come with that ridulously low wing loading, you have a HUGE range of speed that you can take off at long before any truly decent airspeed is reached. And this is what MOST people do.... by a LONG way. eg P-51's taking off in 5 metres. EDF's a bit longer. Like there is some sort of rush to get into the air.
And it is even hard to force it to take longer.

Even at airshows, where they often 'show off' the minimum take-off distance via after-burner into extreme climbs, it is still a LONG roll-out. Relatively. It would still be 100m (probaby even a lot more) at 1/6th scale. (forget catapulted special cases, LOL)

Many EDF's (certainly not all aircraft types) get 'stuck' to the ground X amount and might need more speed before you have control authority to break them free of the ground, whether that still ends up being lower or higher than a 'proper' flight speed.
(I would say my maiden's "2/3 of a football oval, on grass" was a bit long for scale! hehe)

So flight speed is not flight speed... in models.
1) Due to excessively low wing loadings
2) EDF ground sucking issues
Both case take-offs can be 'forced' to occur at different points of airspeed. eg TV use, elevator use.... or the opposite to prolong take-off.

There could be a reason (reasons) why some people do need to take off sooner than later, and anyone can do as they please anyway. But why have a scale aircraft if you fly it unrealistically... you may as well have bought a UFO shaped plane! LOL.
Half the appreciation of realism is the scale look, the other half is scale actions. Mess with either of those and it becomes more just a 'model aircraft'. Which again, anyone can choose to do as they wish.....

But if you want it to look and fly scale... you let it roll out a LONG way. And you will also need that extra total weight to make its mass/inertias correct to scale too, so it behaves realistically in the air - not via TRYING to control it to reflect that, but by actually doing it naturally itself. Which also happens to enforce more realistic take-offs and landings, and their required processes.
You don't really have to get scale speeds and distances dead to scale, but just get the 'big picture' to match what a real one LOOKS and acts like when viewed. And that is a LOT longer roll-out than almost ever seen in models being flown. You have to search far and wide to find videos of a particular model taking off anywhere near a scale distance and speed. 98% are too fast, too soon, and a leap into the air.

Fly from "impeding grass" and you are going to have trouble achieving a scale take-off process. Or from a "runway" that limits distance you can roll-out to. But that is all you can do in that case. At least that is a 'valid' excuse.
(It is still all personal preference in the end..... but if you want "scale", there are certain things you have to do).
PeterVRC is offline Find More Posts by PeterVRC
RCG Plus Member
Old Oct 31, 2012, 02:57 AM
Life begins at transition
Australia, VIC, Sale
Joined May 2007
3,593 Posts
From freely available data, the Su27 family need ~20 aircraft lengths to take off, and ~30 to land.
For our model, that means 32m (100') to take off, and 50m (150') to land.

I had to pull mine off the deck, even with 250' of concrete!
Odysis is offline Find More Posts by Odysis
Reply With Quote
Old Oct 31, 2012, 08:19 AM
Registered User
Australia, VIC, Melbourne
Joined Nov 2006
10,442 Posts
That will be 'airshow' afterburner take-offs... not more 'normal'.
PeterVRC is offline Find More Posts by PeterVRC
RCG Plus Member
Old Oct 31, 2012, 08:39 AM
Life begins at transition
Australia, VIC, Sale
Joined May 2007
3,593 Posts
Nope, that's at MTOW.
sub 50m (150') is the "airshow" record.

Pride Aircraft list their Su27's takeoff run as ~2400' - the 35 has slightly more thrust, so I'd expect similar performance.

Not to be argumentative, it's just the distance required isn't really the issue here, it's the behavior during the rotation that is tough to replicate.
Odysis is offline Find More Posts by Odysis
Reply With Quote
Old Oct 31, 2012, 09:09 AM
You are a "go" for reentry
Maxthrottle's Avatar
High Orbit.....
Joined Jun 2009
6,261 Posts
Pete you never cease to amaze

I make clear points and conditions and you move them to where it doesn't apply.

Flight speed, where the aircraft is moving fast enough to maintain flight.
You can reach that in grass but the grass pulling the nose down can prevent it from ROG. Simple point then just break free of this ground effect and fly.

To fly scale as you indicated is a much longer roll out which for a model starts losing proper VFR and requires specific kinds of fields where the pilots box is further from the run way etc. But the problem as mentioned is we fly from where ever we can which isn't ideal. So you give up scale right there.
And as I said this flies off carrriers so not sure why that's not scale enough for you. So if its fliable in short distances and a pilot favours maintaining VFR over scale, what would your point be?

Not sure how any of your comments helps the pilot who described limits of his field and can't get the model off the ground using up said field. My comment was not to recommend short take offs. It was a contrast, if he's using the entire field and can't lift off where, here's where my comment comes in, I can get up out of grass in some fairly short conditions. It makes me wonder if there is a different reason why even on a long roll out he can't ROG.
Maxthrottle is online now Find More Posts by Maxthrottle
RCG Plus Member
Last edited by Maxthrottle; Oct 31, 2012 at 09:19 AM.
Reply With Quote
Old Oct 31, 2012, 01:46 PM
Flying Hazard
SU-4ever's Avatar
Spain
Joined May 2006
2,624 Posts
I just want to contribute that Su-33 DOES NOT use a catapult to take off from Admiral Kuznetsov. And I'd like to remind that the sky ramp only maximizes MTOW, nothing more, so that makes a 90m run...
I can easily make those 90m in order to ROG my model Su-35, so kinda seems my take offs are unrealistic THE OTHER WAY.
SU-4ever is online now Find More Posts by SU-4ever
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion LX F-35 Vs Freewing F-35 Mmarshall Foamy EDFs 17 Jul 09, 2014 06:49 AM
Found SU-34 Freewing lw777pilot Aircraft - Electric - Jets (FS/W) 1 Dec 15, 2013 01:25 PM
New Product Brand New SU-35! 70x2,TV and made by Freewing!Update:Worldwide Availability neversommer Foamy EDFs 593 Jan 09, 2012 09:02 PM
For Sale Freewing SU-34 stock battery - Brand New JGuilty13 Aircraft - Electric - Batteries & Chargers (FS/W) 0 Nov 29, 2011 02:01 PM
For Sale Freewing SU-34 stock battery JGuilty13 Aircraft - Electric - Jets (FS/W) 0 Nov 29, 2011 10:29 AM