smcharg

My Feedback: (1)

Out of curiosity, has anyone considered stab placement in relation to thrust line?  If you view pictures of several full-size aircraft that have implemented the CRP, it's interesting that those (including the P-51) that have tried or used it have a stab that is considerably higher than the thrust line.  Where the stab is higher, there is no need for the vertical fins.  Those that have the stab at or below the thrust line seem to implement them.  Most of our planes have the stab at or below also.  I also notice (it seems) that those that do have the vertical fins added to the stab have placed those vertical fins outside of the diameter of the prop.  Of course the extreme examples have V-Tails to X-Tails but oddly, they all seem to be....trying to get out of the wash of the prop.

I don't have an answer but am just trying to make an observation.

shannah

My Feedback: (5)

You mean like this????

slightly_floored

Funny, I saw these and immediately thought "Bear"
Then I thought "Sea Fury"

Doug Cronkhite

My Feedback: (34)

That's just because it's hard to get past how ugly the Gannet is in the 1st place. LOL.

Doug Cronkhite

My Feedback: (34)

I doubt it Brenner. The location of the fences actually places them ahead of the center of pressure reducing yaw stability (and thereby increasing yaw maneuverability).

Hans Meij

Hi Brenner & others

Tried three things

A Fence on front of stab.
- Not to much stability gain. Counteracts rudded effectivenes during roll therefore tail moves more during roll and more difficult to hold a perfect line

B Fence on end of stab.
- Stability gain to such an amount that I would accept it. Still roll controlability not optimal like in A

C 15*15mm balsa triangle.
- Superb directional stability (So problem solved, really !) Rolling perfect as was before.
- Top speed limited, drag affects speed and consumption.
- Lot of clicks downtrim needed. Most part of the draggy strip is above thurstline and was causing a pitch up moment more than I expected

So it is up to experiment with different strips that give good stability without too much increased drag.
Perhaps little strips on elevator would help too.
Anyhow I'm happy that changing the rudder thickness does solve the yawing problem completely

A


B


C

Dsnow

Hi Hans, thanks for the pictures, never tried the SFG's at the end of the stab panels - interesting idea. If you’re up to some more trials you could extend the triangle stock so the transition is not so sharp: have the same projection from the rudder surface but extend the triangle forward say about 40mm. This should help reduce any elevator trim changes and also increase the speed of the plane some. I've mentioned this to Brenner a couple of times that if the transition is very gradual the stability effect is still there but there will be a very minor loss of airspeed. You can see the rudder I installed on the Spark, post #243 page 10, it is about 1" wide at the trailing edge and straight/flat to the hinge line. Another option to the SFG's at the stab tips are fences at mid stab panel, these should help increase the stability but not effect rolling - at least I never really noticed any effects but your plane may react differently. If you look at post #302 page 13 there are several pictures of the fences installed on the Spark. They are only 3/8" tall but seemed to help settle the tail down some, I was still having some instability issues even with the modified rudder.

Great testing and please keep us informed on your trials, this will really help everyone in the future.

Dave Snow

Brenner

Hey Hans,

Thanks very much for posting pictures and reporting on what you've tried. This is very helpful to the community of pilots who are flying the Contra.

I really like your idea about strips on the elevator. I haven't tried anything like this, but I do remember seeing at least one plane at the worlds that was using this. (not a Contra powered plane though ..)

Also, one other thing to mention is that some pilots are reporting good success with just a thickened rudder. (Dave Snow for one ..) Taking this a little further, it could well be that thicker trailing edges on both the rudder and the elevators is the most elegant setup.

I think I saw at least one plane at the worlds with this setup. I don't remember the pilot's name but it was a very highly respected German pilot who was in the finals. (Gerhard Mayer perhaps ..)

In addition, we've had reports that the Carf Valiant works right out of the box, and one unique feature of the Valiant is the ventral fin on the top of the fuselage between the rudder and the canopy. I'm speculating here, but I think it's possible that this might be having a beneficial effect as well.

Brenner ...

Hans Meij

Hi Brenner,
Just a bit of speculation...
Already with single prop setups I have the feeling that when the intersection of the vertical fin looks more like a 'real' profile (e.g Winds PRO) the yaw stability is better than with some designs where the leading edge of the vertical fin is very thick like halve a circle (e.g. Gaudius, Integral). Is it perhaps that these profiles have some kind of dead-band in the angle of attack <-> lift graph. These properties become extra clear with these profiles in combo with the contra.

Brenner

Hey Hans,

Yes, I agree. Your thinking makes a lot of sense. It would be great if reducing drag on the front of the rudder fin had the same effect as increasing drag on the rudder trailing edge.

Brenner ...

Brenner

Check out the rudder and the trailing edges of the ailerons and elevators on this plane.

http://www.rcuniverse.com/forum/m_10818666/tm.htm

This looks like something that might work with a Contra Drive.

Brenner ...

underdw

My Feedback: (2)

Could I please get some advice on ESC settings for Castle Ice2 HV80 with the Contra drive and Nue motor?
Thanks, Dan

underdw

My Feedback: (2)

My Contra/Neu powered Cation is done!
Easily made weight at 4920gm
Who knows when it will fly? This time of year the temperature and windspeed are about equal and it snows on Fridays!

Some advice to Contra owners when selecting an airframe:
1) Weight: Contra will add about 120gm over a Plettenburg with CF prop.
2) Think about prop clearance with the 22" props. I'll be looking at an aftermarket gear.
3) Spinner diameter = 82mm. Some planes with smaller spinners can have their noses cut off and still have a reasonably circular nose ring.
4) Length! Contra spinner will add about 3/4" over a "fai" spinner. This can put you over the 2m limit.

Dan

shannah

My Feedback: (5)

I flew my Contra Drive Visa today, FINALLY. Between rain, out of town guests, WIND, etc, I finally had a nice day to fly. Flies great. I have all the usual comments: Need to dial in thrust, I've got a small amount of right thrust in it still so that needs to go away. Rudder is very touchy, but it is very solid (no need for the triangle strips on the TE of the rudder), no differential, a bit of down elev to throttle mix, small amount of rudder to elev mix.

Overall, I think I will get this dialed in pretty quickly. Very solid feeling.

I have the 9.89:1 gears and 22x20 props. Good speed overall. It was a very calm day so we'll see how it goes in the wind.

I tried a Turnigy 35C pack and it had noticeably better performance than my TP 25C. So, the higher C packs will probably be a good thing, especially towards the end of the flight.

I wish this Visa had the split rudder, I think that would really be beneficial in toning down the touchy rudder. Opening the rudder would also benefit the plane in normal flight. But, this Visa is a fixed rudder version (I bought it for a test bed, couldn't bring myself to slice up my existing Visa). This is CHip's old all white Visa that I picked up from Matt Kimbro.

Brenner

Both plane look absolutely beautiful! The black spinner looks great on the Cation, and the purple spinner on the Visa really stands out against the white fuse.

A quick tip about the props. there is a probably a small amount of mold release still on them from when Mike layed them up, which will dull over time. What I've been doing is buffing them with Brasso metal polish and a paper towel, and it really shines them up. There are very few voids in the surface, so you don't get any spotting where polish fills the surface voids.

Brenner ...

Passport1

My Feedback: (8)

I wish this Visa had the split rudder, I think that would really be beneficial in toning down the touchy rudder. Opening the rudder would also benefit the plane in normal flight. But, this Visa is a fixed rudder version (I bought it for a test bed, couldn't bring myself to slice up my existing Visa). This is CHip's old all white Visa that I picked up from Matt Kimbro.

[/quote]

Its to bad that plane was built with it and I was actually with Matt when he finished it but we didn't get to test fly. I think they tried it a flight or two and then went back to 1975. LOL Just kidding. Anyway its not a problem just cut it down the center. Until I had the laser cut rudders made thats how Marcelo did them all. Believe it or not its about a 10 min. fix. Xacto around the top, te, and bottom four or five times to get a little depth. Then use a zona saw blade no handle. I bet you can even leave it hinged because the rudder has the split hinges.

Open it about a half inch and cut the movement from your original Visa down about 50%. Good luck

Btw. We should have some new props early next year. If I remember we picked 20.4x22 for the front and 20x22.4 for the rear. I should have some mid to late Jan. I will keep you guys posted.

c

shannah

My Feedback: (5)

Hi Chip
I thought about cutting it open but I wasn't sure if it was going to work. I'll fly it a bit more then decide if I want to slice it open. I'd also need to put the rudder servos in. Looks like you had this one set up with rudder servos midship. But the pushrod supports are gone and it's a pull pull now.

Brenner

We've been testing two sets of props. A set of 22x22 front and rear with 10.56:1 gearset and the 10.33:1 gearset, as well as a set of 20x22 front and rear with a 9.89:1 gearset.

Both setups seem to work very well, with horizontal speed close to 100 mph, and less draw from the packs. Very quiet on the ground too. I'm leaning towards flying my Hacker 13XL next year with the 22x22 front and rear and a 10.33:1 gearset.

Brenner...

pattratt

My Feedback: (1)

Hey Brenner
Try the 22x22 rear with a 22x20 front and tell me what you think. I love what the 22x20 rear with the 22x18 front did on the De Ja Vu. I have almost completed the Contra Conversion on Arch"s Wind "S" Pro that he flew at the Nationals. My all up weight will be 10 lbs 11-1/2oz with f3a packs and 3 oz more with a 45C TP 5000 pack! Can't wait to get it in the air.
Dick

Brenner

Hey Dick,

I agree with you. I flew with mixed props for most of the season. They work great. I haven't tried the 22x22 / 22x20 combo yet, but I will. The only problem is that we got our first snow yesterday, so flying might be shut down for a while.

Brenner ...

serious power

Its to bad that plane was built with it and I was actually with Matt when he finished it but we didn't get to test fly. I think they tried it a flight or two and then went back to 1975. LOL Just kidding. Anyway its not a problem just cut it down the center. Until I had the laser cut rudders made thats how Marcelo did them all. Believe it or not its about a 10 min. fix. Xacto around the top, te, and bottom four or five times to get a little depth. Then use a zona saw blade no handle. I bet you can even leave it hinged because the rudder has the split hinges.

Open it about a half inch and cut the movement from your original Visa down about 50%. Good luck

Btw. We should have some new props early next year. If I remember we picked 20.4x22 for the front and 20x22.4 for the rear. I should have some mid to late Jan. I will keep you guys posted.

c
[/quote]

Hi,
Who are the 'we' that are producing the 20.4x22 & 20x22.4 set ?

Brian

OhD

I installed my motor just like Dave except originally I didn't use blind nuts like he did. I found I didn't have enough hands to hold the motor, nuts, washers and get the bolts started and the hands I have were blocking my view of everything. I recommend using the blind nuts. I will add lock nuts after everything is in place.

Jim O

Brenner

We've started to get prototype parts in for our next version. Here are some pictures:

The new gearcase is shown compared to the one I ran with all last summer. We're adding a second bearing and eliminating the set screws that preloaded the single bearing in the old gearcase. We are also adding an o-ring around the pinion gear to try and eliminate the need for the plastic grease plugs that were needed in the previous version.

These changes are going to add 19g for the extra bearing, but we've reduced the weight of each prop by 15g, so we expect to see a net savings of 11g with the complete system. The reason for the second bearing is to improve robustness to prop strikes. With two bearings we expect to be able eliminate prop strikes as a cause for concern as far as the rear gearcase bearings are concerned.

We are also seriously upsizing the planet gear bearings. The new planet gears, new bearings, and new driveshaft are shown. This is so the durability of the planet gear bearings will match the expected durability of the other bearings in the system. We are shooting for three seasons of flying, or 1500 flights. (The target is actually 1500 flights, even if it takes more than three seasons..)

All of these changes are backwards compatible with the current Drive, with only two exceptions. The double bearing gearcase will need new adapter manifolds for both the Hacker C50 motor, and the Neu f3a motor, (not prototyped yet ..) and installations with the Neu motor will need to have the Drive spaced back into the fuselage by 3mm. Installations with the Hacker C50 are a drop-in.

Brenner ...

Dsnow

Looks like the pins on the planet gear carrier are much larger too, that should prevent any wobble of the planet gears. Looks great. Did the planet gears get any thicker from the new bearings?

Dave

Brenner

Hey Dave,

Yes, the pins are 4mm diameter instead of 3mm diameter. The planet gears are the same thickness as before.

Brenner ...