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OXAI Pinnacle Downthrust

Old 02-11-2008, 03:25 PM
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Jason Arnold
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Default OXAI Pinnacle Downthrust

Hi All,

I would like to adjust the downthrust on my Pinnacle and would like to know if/how others have done it. I'm using the standard OXAI enging mount on my 1.40Rx. The engine mount is fitted to the firewall with three screws. I suspect the best way to introduce a little down thrust is to put a couple of washers against the firewall on the isolator side. I could also put two washers under the rear engine screws but this would not be my preferred method due to the engine not sitting flat and heat dissipation etc.

Attached is a pic (hope it works) of the Oxai mount and Oxai nose ring I'm using. The rubber isolators are on the same side as the engine.

Any thoughts, ideas or experience is greatly appreciated..

Cheers
Jason.
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Old 02-11-2008, 09:01 PM
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Troy Newman
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Default RE: OXAI Pinnacle Downthrust

Since I have more time in Pinnacle(s) than anyone...I'll tell you what I found.

Two ways....Shim the mount...or move the mount. I used a Hyde mount on my Pinnacle(s)

Pop the ply plates and blind nus out of the firewall...

Elongate the holes to "lower" the mount in the fuse. Remember is upside down...You want to use a round file and just oval the holes a little bit about 1/8"...2mm or so.

Then install the blind nuts into plywood disks and just pinch the firewall between the disks and the motor mount.

Once you have the thrust line where you want it...then use a little CA to capture the ply disks to the back the firewall.

I would recommend this idea first. Put about 1 turn positive in both wing panels this will act like adding down thrust and may solve your problem. I have had 3 Pinnacle models and helped trim out 2-3 others. All of them benefited from the 1 turn on the wing adjusters LE up. (positive)

Another thing is leave the stab so that you are carrying just a touch of up trim....under power. If you have a thro to elev mix for downlines the elevator trim will be close to flying even with the stab tips at idle for downlines. I found that with all the models we have played with a little up elevator trim actually helped the model lock on and made the uplines more solid. Most is not all of my models are this way not just the Pinnacle. Astral XXc's, the bipes, Supreme(s), Smaragd(s), Fashion, Alliance.

Here is a photo of one of the very first Pinnacle's. This is actually the blue one on the Oxai website. I flew the heck out of it. The thrust line was changed about 3 times in its life...at one time it was here with the stock wing setting. Move the wing and it goes back to the stock thrust line for down thrust. Both solutions worked evenly...By the way this was the change to use the 4 blade with the 160DZ. If you are trying to run that prop on the 140RX you are not going to be happy....The engine doesn't have enough power for that prop. In fact the 160DZ is good but not a bunch extra...the 170DZ is a really good match for that prop combo. The spinner was not a 3" it was a 3.25" because that is what I had with the 4 blade cut.

Prop selections will play a huge role in this down thrust. Part of the reason I changed the thrust line in the model was running a different prop. I have run everything from 140DZ's on 16-12's to the 160 and 170 with 17-12 up to the 18.1-10. The bigger props will require a change in thrustline.....Since you are running the 140RX I would suggest you try switching to a 16-12 regular blade prop and a little positive in the wing compared to factory setting. The plane will lock on and groove really well with that prop and it will have good pull and make sound with ease too. Trying to load it up with larger props is going to have you chasing your tail a little bit...Especially with that engine. The torque effects are much more pronounced as you struggle on power. So putting a big ole blade out there is not going to help your chances with that engine combo.

See the photos on how much you can change the down thrust...also I added a little right thrust...I don't like to do the throttle to rudder mix too much. A little 1-2-3% is OK but you don't want too much of that stuff. It will make the model speed sensative...meaning at different speeds even though the power setting it offset by a given rudder trim...the model may be slower airspeed wise or faster airspeed wise like in windy conditions....and your throttle to rudder trim is all screwed up....Plus at the tops of figures like Humpty bumps throttle back through the radius will really screw you up on rudder trim....To me you can't over come all the affects of thrust with rudder trim...you can only fine tune it a little. Changing props will throw this all out of balance. Any of the models were are flying today will be more consistent on thrust line issues with smaller props. Going to the larger props brings in more struggles with thrust line....

This is on of the main reason Quique used the 4 Blade, combined with Noise. I have been flying my Euphoria with the 4blade on it and its different....than running the 2 blade. I have to make minor changes when switching around props.

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Old 02-11-2008, 11:31 PM
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Jason Arnold
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Default RE: OXAI Pinnacle Downthrust

G'day Troy,

Thanks for taking the time to write back to me. It's much appreciated mate.

I was considering adjusting the wing incidence as you suggest but thought adjusting the donk might be better. In all honesty it probably only requires a small adjustment to the wings as you say. It's just a simple screw adjustment which is easily reversible too...
My Pinnacle is not new. It was previously owned by Alfred Pye with very limited flights which must also mean limited trimming. The stab and wing incidence have been left as he had it for now. I did note that one wing was 0.5 degrees different to the other. I did try matching them but then the aileron trim was slightly out. The elevator trim is flush with the stab at the moment but when I accelerate it wants to climb hence my thinking on down thrust adjustments. The model requires a tad more down elevator than I'm comfortable with when inverted too. The CG is set at ~180mm back from the LE at the fuse. The model stalls and spins quite well. I'll throw the incidence meter on the model again and take some readings relative to the canopy line. I assume this is 0 degrees...

The prop I'm running at present is an APC 17 x 12N as recommended by Alfred. I did have a Bolly 16 x 13W on it before the APC which seemed to work fine. The APC is probably a little quieter.

Thanks for the pictures too. If I had to guess, I'd reckon I have a small amount of upthrust in the stock mount position. I will confirm this with the incidence meter as it may be an optical illusion or it could be the beer goggles blurring my vision.. lol

I must say that since starting in pattern late last year I have learnt so much. It's the little things that make the difference.

Thanks for your help mate.

Cheers
Jason.
Old 02-12-2008, 12:18 AM
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Troy Newman
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Default RE: OXAI Pinnacle Downthrust

Your CG is right on the money I flew mine from 178mm to 182mm depending on which model it was. I have a pretty accurate way to setup the CG to compare model to model. I use 3 scales one under each wheel and calculate the moments in a spread sheet. So I can easily flip back and forth between models...I use an Excel spread sheet and just do a new sheet for each model...

If you require too much push on the inverted don't move the CG back just remove some Expo on the down elevator only and maybe increase the down elevator rate by 5-10%...This will allow you to "catch the nose" easier when inverted and you will not even feel like its nose heavy. This is what I do on all my models. More down elevator than up and less expo....

180mm on a Pinnacle is right where I liked mine.

Also you might try putting just a little positive (LE up) in the stab....This will allow the model to fly with a very slight up elevator trim and it will lock in better. It might cause a slight pull to the canopy on down lines but it will lock in better and be more "biased" this means the model will handle turbulence better and will track better.

The Pinnacle is a really good model. I had lots of hours to get to know mine. I only switched when I flew the Oxai Astral XXc as it rolls better than the Pinnacle. But the Pinnacle does some other things very well maybe even better than the astral.

Both excellent models.

Troy Newman
Team Oxai
Old 02-12-2008, 03:51 AM
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Jason Arnold
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Default RE: OXAI Pinnacle Downthrust

G'day Troy,

I've just done some measurements on my Pinnacle.

I set the canopy line on the fuse at 0 degrees for a reference.

Both stabs are at +0.5 degrees.
The RH wing (from the rear of model) is +1 Degree.
The LH wing (from the rear of model) is +0.75 Degrees.
The engine down thrust is -0.5 degrees. It looks like a small amount of up thrust but the meter doesn't lie... lol

I lied before about the elevators being level with the stab. In actual fact there is a small amount of down trim in it.

Do my setting sound somewhere close?

Cheers
Jason.
Old 02-13-2008, 12:49 PM
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Troy Newman
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Default RE: OXAI Pinnacle Downthrust

Canopy line is not zero on the model....

Give the stab some positive (LE up) to get that elevator trim to a up trim rather than down trim and your pull on the upline will go away.

I don't use incidence meters they are not accurate and repeatable. If you swap ends with them they will give various readings. Especially the Robart style meter meter...very prone to measuring errors.

I would suspect your wings are not off from each other that much...if you turned the meter around going from one side to the other this would be the reason.

Try 1/2 then 1, then 1.5 turns on the stab...TE down LE up and I bet your pull goes away.

Likely you will be puttng the stab back to the factory setting.

Troy Newman
Team Oxai
Old 02-13-2008, 01:25 PM
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mwoytassek
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Default RE: OXAI Pinnacle Downthrust

Pinnacle Setup?

What is the factory setting of the wing and stab?
I rebuilt a damaged Pinnacle needed to remove the wing adjusters and stab tubes.
So the model does not have factory settings. Any base line help will help thanks

Mark
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Old 02-13-2008, 03:27 PM
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Jason Arnold
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Default RE: OXAI Pinnacle Downthrust

Hi Troy,

Thanks for your help mate.

I'll try adjusting the stab for this coming Sunday. By the sounds of it I'll get to having the wing and stab at 0 degrees. This will be a good starting point. I'll let you know how I go.

BTW I am using the Robart meter and deliberately didn't turn the meter around when measuring between the RHS and LHS. Fortunately the fin doesn't get in the road of the meter scale... I also try to place the meter in the same position on each side too. At the very least it should provide a reference.

Off the top of your head where is the zero point on the Pinnacle?

Many Thanks
Jason.
Old 02-13-2008, 03:34 PM
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Jason Arnold
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Default RE: OXAI Pinnacle Downthrust

G'day Mark,

That Pinnacle looks rather sick. It will be fun trying to get the thing back together properly. You'll need to have some good balsa doublers and fibreglass around the fuse break. Did the rest of the model survive unscathed?

From what Troy has just said My plane must be close to the factory setting with exception to the stab.

Good luck!

Cheers
Jason.
Old 02-13-2008, 04:21 PM
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mwoytassek
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Default RE: OXAI Pinnacle Downthrust

Howdy

It is all back together. It was lot of fun. 5 lasers running it get it straight and all square.
Carbon fiber 45 X 45 mat in the missing carbon fiber areas. Armid fiber about equal in weight to .75 oz fiber glass back mat in the balsa areas. New honey comb in a number of areas. Worked hard on keeping the weight down should come in at 10 .5 lbs. I bought the plane in a damaged state to see if it could be rebuilt.

Look forward to flying this spring 3 feet of snow in the yard today.

Mark
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Old 02-13-2008, 09:14 PM
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Troy Newman
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Default RE: OXAI Pinnacle Downthrust

I have no idea where zero is....I never had to deal with finding zero.....

From what I see in Aussie's post the canopy frame is about neg 1/4 to 1/2 deg so that is your reference.

It doesn't matter where zero actually is....what matters is how the model flies. Removing adjusters they should bolt back into the same spot...unless of course they were played with or perhaps you didn't mark left and rights.

I would put the rear stab tube about in the middle of the adjustment area and call that zero. Set the main wing positive to that 1/2deg and start trimming....

Aussie on your model I would not zero stuff out....The wing is not going to fly at zero when you are done...I would just dial some positive in the stab and if it stops the pull on the uplines you are done.

I have never had a pattern model that worked right at zero zero...They all needed positive in the main wing relative to the tail....

How much posiitve...well it will always depend but good designs usually are about 1/2 degree. This is normal and to be expected. I don't measure any of them...I use a flat table and set the LE and TE the same distance off the table with the fuse in the "Level" flying position. Then I calculate 1/2 positive and stick that in the main wing with the stab at zero.

Troy
Old 02-14-2008, 08:52 AM
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Default RE: OXAI Pinnacle Downthrust

Troy

Thanks for the data. Not much to do but fiddle with the planes flying weather is a little cool -15 below and a little windy 35 mph in blowing snow.
Will get plane set close and I agree needs to fly.
The Pinnacle is next on the flat table for last of pre flight checks.
Flat table seen in the background, these were built by Greg F’s Dad a number of years ago.

Mark

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Old 02-14-2008, 09:27 AM
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Troy Newman
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Default RE: OXAI Pinnacle Downthrust

Cool,

I saw Greg on Saturday we got to fly together. He has been really busy with work.

He has a new Pinnacle that is flying very well right now.


Good Luck with it, its a very good model.

Troy
Old 02-16-2008, 05:27 PM
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KGSS28
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Default RE: OXAI Pinnacle Downthrust

Hay Troy: What should we be using for an incidence meter ? I have always used a Robart and I know what you mean about not being able to buplicate readings from side to side . I had thought about about getting a second one to avoid the moving but I dont know if it would help ? I guess it depends on weather the Robart has any accuracy to it in the first place Are any of the other ones any better like the Hangar Nine Digital?

Thanks Kirk
Old 02-16-2008, 10:20 PM
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Troy Newman
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Default RE: OXAI Pinnacle Downthrust

I use Trigonometry. I'm a engineer type. I do have a digital level and have used it with the robart ends and bar...This is similar tot he H9 setup and works pretty good.

I try to attach the bar to the wing then just hold the digital level onto the bar...This way the weight of the meter doesn't affect the reading.


The absolute best method is a good eye that can read a good ruler, and a little trigonometry skill.

Plus I trim the model in the air and can tell if it needs an incidence change....so I get it clos eand fly it...the main deal is to get both sides the same then go from there.



Troy Newman
Old 02-17-2008, 04:21 AM
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Jason Arnold
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Default RE: OXAI Pinnacle Downthrust

G'day Troy,

I just got back from flying the Pinnacle again today. I think I'm pretty close now. Every flight I made minor adjustments to the stab and it kept getting better and better.

In the workshop I set both wings to the same incidence and adjusted the stab a little. After flying it I added a further 1/2 a turn positive on the stab. My elevator is now at neutral for level flight. I'll probably try a fraction more positive on the stab and leave it at that.

Thanks for your help mate. The model is flying so much better now!

Cheers
Jason.

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