raron455

My Feedback: (38)

I have been doing alot of reading about props,pitches, and composition matierial, and such one term that keeps popping up is downline braking,, WHAT exactly does that mean?? I have not been able to find a definition or visual example to help me understand what downline braking is... Sorry if its a simple question I just dont know,,and I know plenty of you do and can help me figure it out,,,thanks in advance

1320Fastback

As I understand in pattern you want the plane to keep the same speed thru maneuvers.
On your vertical Down Lines (diving towards the ground) you do not want the plane to speed up and this is where the Braking effect of the prop comes into play. Either at idle or part throttle.

I could be totally wrong but am sure other will chime in.

BMatthews

Nope, you hit the nail on the head soundly and truly. Downline braking is about using the prop disc running at idle or a low power setting as a brake to hold the plane from speeding up to excess in a vertical or near vertical dive in maneuvers.

da Rock

BTW, it's something pattern pilots have messed around with for quite some time.

About the only thing you can predict about it is the more diameter or more blade area, the more braking you'll get.

rmh

If you realluy want downline braking -you have to run an electric motor - these WILL provide a low spinning prop speed - like hitting a brick wall.
On glo/gas - the engines spool up on the downlines so you have to run a flat pitch to attempt to get some braking action .

combatpigg

My Feedback: (3)

Really light planes...like your control line stunt planes will show off the down line braking effect..but you only get to enjoy it for 1.5 seconds before the pilot has to do his pull out.
The really high compression Super Tigre stunt .35 also seemed to resist "spooling up" better than other engines. These engines are set to run "wide open"..but their venturis are generally sized for what would be part throttle on a RC engine.
If there is ANYTHING diesels do better than glow, [besides being repulsive to females] it is also maintaining nice, slow down lines.

Lnewqban

Considering that a propeller works as a wing, imagine an airplane, falling in the inverted position and in a horizontal attitude.

The braking affect comes from the drag generated by the wings moving in a perpendicular direction respect to the airstream.

rmh

simply put - the prop stops turning-or slows drastically- an electric setup is the only way this can be done with noticable result
Why?
the electric motor can be asked to put it's output (caused by the airstream turning the prop) to esentially a controlled short circuit which makes the blades resist turning
In the new electric cars they call this regenerative braking. It has been used in various setups for years- on commercial sewing machines to instantly stop the needle - on other machinery to stop even heavy masses from spinning freely.

speedracerntrixie

My Feedback: (29)

I agree with most of this. On the electric setups you are limited to how much brake you can program in. Too much and the motor will let you know by letting out a loud screetch when power is applied. Not sure of why but it happens and it is not good for the power system. The electric also run alot more pitch so tend to spool up more then a gasser will. Much less noticable because the current crop of electric pattern jobs are drag buckets.


On IMAC type airplanes, I would set mine up to fly as slowly as I could and still had the airplane track well. Entering a downline a slow speed is probibly the best way to control downline speed. The other is to use a heavier prop and use as little pitch as you can get away with. tuning your engine so you can get a nice reliable idle without it stalling during a spin or downline snap helps too. Nowadays building super light, high drag airplanes IMO is the key. The engines now available can easily overcome airplane drag for verticals.

rmh

We use soft brake and a little bit of idle up - that's it - works well -
props being 20x14 -thereabouts. no screetchin. Hacker motor - and a Hobby wing ESC.
Tho the flight times are low - about seven minutes - the power on tap exceeds any of the glo stuff.
The best new pattern stuff is not draggy - very small thin wings - and a large but well streamlined fuselage tho the fuselag sq in area equals wing area .
When we did our last IMAC models we clipped the wings and took all possible weight out .
Power to weight was excellent - but not as good as the new electric stuff.
The prop I ran on my 160 ZDZ was a 30x14 -which some thot was too much pitch- but it worked extremely well on the 40 pounder.
the pattern was so large that speed appeared pretty constant-

speedracerntrixie

My Feedback: (29)

Rich, I am aware of your accomplishments and have a great deal of respect but it seems we are going to dis-agree some. Today's pattern airplanes are quite draggy, yes they have small, thin wings but thin dosen't nesessarily mean clean. The large fuselages with the occasional canalizer and some models even have rudder trailing edges close to an inch thick produce lots of drag. Worlds apart from the Rossi .60 powered Dalotel Chip flew in the Reno Nats. LOL A little trip down memory lane.

30X14 is not too unreasonable depending on the airplane.If it was in something like a Radiowave 330 it would have been fine but the same setup on a 38# Fiberclassics or Comp ARF 330 would be a bit fast. My current GS aerobatic airplane is based on the old Godrey Laser 200 but with an airfoiled tail group and my own draggy airfoils. Its 93" span, 16 lbs and powered by a DLE 55. It flys slow enough to do the IMAC unlimited sequence about 150' deep in the box and still saty in the Pattern 60 degree box. Prop is a 23X8. I have tried a 22X10 and it was just a bit rushed. Then again, it's all about perspective, what's fast to me may not be so to you.

rmh

The pattern guys ar e slowly learning that drag at the readr is good and drag up front bad - the braking prop being the exception
Cantalizers?
phooey
My son has one of th laetst fuselage designs coming onto the market ( It's a Jesky design)- actually pretty darn clean.
No bulbous "simulated cowl"and the canopy is slimmer .
Thewe things fly on about 900 squares at a fairly high constant speed - but all up weight is only - 10.25 lbs.
The pattern is flown way too far out for my taste- but the maneuvers are just too involved to permit smaller spaces.
That early Dalotel design Chip flew was a compromised early pattern /scale setup.
later on we did the Dalotel for IMAC - scale except for 10% tip clip- better flyer

speedracerntrixie

My Feedback: (29)

That Dalotel is sweet! I would love to build one. I had a Bridi kit once and got it all framed up with a wing tube and clipped the wings down to 2M. Had an MVVS 1.4 twin for it too. Ended up selling it to finish off a 40% Extra. New rule, NEVER sell airplanes or cars that arent available anymore LOL

rmh

Thanks - I did a goof and sold my larger versions and this one is from late 1990s - a friend returned it to me when he passed on.
I still have a 1990 TOC Bucker tho The electric setup on the Dalotel is incredible - -prop went from 18x8 to 20x14 and INSTANT full power . Still waiting for longer flight times - if some new batts made from unobtainium are ever developed.