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Author Topic: Trimming the Power Phase  (Read 322 times)
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Sailaway
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« on: May 03, 2021, 12:22:42 PM »

Hi, I am new to powered flights.

My model climbs straight, with no major turns when climbing. As soon as the power cuts off, it dips and looses height. However, once it recovers, the glide is nice and slow with a big enough right turn.

This pylon model is supposed to fly Right-Right, So have given a small (1/32) right rudder at the base and a bit of left and down on the motor.

So basically the question is : how would I go about eliminating the big dip as soon as the power cuts off?

Thanks in advance to help me think through this.


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billdennis747
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« Reply #1 on: May 03, 2021, 01:32:04 PM »

Are you using wing warps? I assume there is no autorudder or VIT
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Sailaway
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« Reply #2 on: May 03, 2021, 02:45:00 PM »

No Sir. No washin or washout. No auto rudder or VIT. Just a basic high wing pylon model .
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billdennis747
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« Reply #3 on: May 03, 2021, 03:08:48 PM »

In the UK this would be in the Slow Open Power class. Typically they have washin on the right inner panel and a rearward cg. They are trimmed so that the washin rolls the model to the left to control the loop and it goes up in a right spiral. This then gives a good pullout into the right glide. There have been many articles in Aeromodeller over the years on this trim
An expert will be along soon - Glidermaster? Meanwhile, this is the one to look at
https://outerzone.co.uk/search/results.asp?keyword=dixielander

and maybe this
http://www.supercoolprops.com/articles/dixielander.php

and this
file:///C:/Users/bill/Downloads/Slow_400_DBHL_oz9294_article.pdf
« Last Edit: May 03, 2021, 03:53:44 PM by billdennis747 » Logged
USch
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« Reply #4 on: May 03, 2021, 03:49:43 PM »

This type of power model is first trimmed for the climb and only later for glide!
Of course a few hand-launch to start with to find a decent glide is OK.

The climb trim can be modified trough:
motor down and side thrust, this adjustment is strongly felt at low speed (launch)
wash-in as Bill said, normally on the right-hand inner panel
Trim tab on the rudder or alternatively a piece of trailing edge as Gurney flap for the right turn under power
Remember, during acceleration the aerodynamic forces overcome other asymmetries as motor offset. That means that the rudder tab or the wash-in are more effective at high speed.

Transition from climb to glide you get by the right turn during the power phase which will put the model into the glide circle.

Once sorted out the climb you adjust the glide with the CG, don't touch the incidence but move the CG back if the glide is to fast. Move it back until you got a floating glide. The glide turn you adjust not with the rudder tab but with tail tilt. Tail tilt is not felt in the climb pattern.

Now this is a fast and furious intro to trim locked down power models. But I think to have covered the most important points  Grin

One last thing, CG does not have to be on the trailing edge, I normally start with 70%, but that's largely dependent on the architecture of the model (Tail size, moment arm etc.)

Urs
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glidermaster
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« Reply #5 on: May 03, 2021, 07:08:49 PM »

I don't think I can add much to what USch has said, it seems pretty much bang on.

Out here on the West Coast there are different ways of doing things, but I can't say I have (or want) any experience of it.

Perhaps you could post a picture Sailaway. So we know what we're discussing.

John
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danberry
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« Reply #6 on: May 03, 2021, 11:02:17 PM »

You cannot fly straight.
There are available articles that explain things.
I will guess that you don't have enough decalage and you don't have any roll.
You need to be flying a LARGE loop with right turn and left roll.
You need washin on the right main along with some decalage. How much and which direction rudder tab cannot be determined until after you get the roll.
You can use an adjustable tab which has it's own quirks and detrimental possibilities or you can just use TE stock glued on appropriately.
Is this a proven design?
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Sailaway
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« Reply #7 on: May 04, 2021, 03:23:09 PM »

Thank you all so much for your quick responses. Sorry for delay in reply . I read through and tried to understand all of your valuable inputs.

So as a newcomer I now realized that "You cannot fly straight." even though it was a very nice steep climb with wings level. But as soon as the prop stops, it had to fall till it regained speed to glide again. Thank God for the height it had obtained , else I would have re kitted the model.

So today, it was cloudy but very calm, just a gentle breeze. Based on so far what I have understood, put a tiny bit of left and down on the motor and a sliver of right rudder gurney to the base.. That called for a washin on my wing as it started to climb left, wings no longer level. Once I got the stab incident increased just a bit more, put a tiny clay on the nose, whoa it climbed to the left circles. It transitioned flat to the right glide. I was happy with the stab tilt as the glide circle was a good looked like 30 feet or so in diameter. Smooth glide.

Flew two more successive flight, to confirm that this was not a fluke, it got scary high and had it not been for the DT I would have lost it. The model now flies left-right with no nose drop during transition, even though the original model should be flying right-right. I am going to leave it as this works. 

One observation: As soon as I launch, in the left climb it looks like it is chasing its tail. As the full power comes on, the circles get larger and looks less scary. Is this normal, or what should I do about it? The left and down on the motor on this model is very finicky, slight adjustment and it is way off. 

Thank you all to help me understand, or at least I think I got this concept clear? "Fly straight, there is no chance of transition and you drop like a rock".

Thanks !
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flydean1
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« Reply #8 on: May 04, 2021, 05:25:40 PM »

A picture of the model would sure help.  If it is a conventional pylon model, you are about to re-kit it.  They MUST climb to the right.  The left thrust is probably OK, you don't have enough right rudder.  You should make ONE change at a time.
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USch
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« Reply #9 on: May 04, 2021, 05:38:56 PM »

So you climb to the left  Huh

Wonder happen.....but not on request and not always  Roll Eyes

Now you know what means "knife edge trim", don't trust that next time it flies exactly the same way. You are right on the verge of stability, a bit less, a bit of wind and you have again the kit you started with  Wink

Personally I would take out that left on the motor and give it slightly to the right.

As the full power comes on, the circles get larger
Question: do you have an IC engine or an electric motor?

Urs
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danberry
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« Reply #10 on: May 04, 2021, 08:16:18 PM »

You probably still don't have enough decalage.
Your wing is probably set with the starboard tip skewed forward which is probably why it's going left.
Your initial flight mentions it fell a long way before gliding indicates the aforementioned lack of decalage.
If you continue to go left under power you won't need to worry about long-term storage for the plane.
30 ft diameter glide is way too tight. By a factor of 3 or 4.
You mentioned it's chasing it's tail going left. It's just a matter of time until it plants itself going left. Windy conditions will help the planting.

What is the design?
Are you electric or gas?
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Sailaway
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« Reply #11 on: May 04, 2021, 09:16:49 PM »

Thank you Urs, Flydean1 and danberry for that eye opener and here I was rejoicing in a false belief that the problem is solved, as the transition to right glide was flat all 3 times with very high climbs. DT took around 20 seconds to land on ground. Thank you for that strict warning of a disaster awaiting after some lucky flights.

Correct,  there was no wind at all, just a very mild breeze under a cloudy sky. Understand that I just  got lucky as to there were no wind gusts to a re kit disaster. Just got lucky.

 I have about 1/32 right tab at the rudder base. I have about 1/16 washin tab at the edge of the wing tip break on the right wing as it used to dip the right wing in the left climb a lot and this took care of it. The only reason I picked these wood sizes was that I wanted start small. I have 1/32 decalage TE upon the stab to get a floaty guide in the glide test. Confirmed that the wing center line is not skewed.

This is an electric motor.  Just like in 1/2A pylon gas model, my timer runs the motor full speed to the end and stops. There is no fancy deceleration at the end like many timers have that option.

The model is proven and a wonderful  kit. With E20 it helps me to fly closer anytime (silent flight) to home versus a 2 hour drive each way to the free flight field. The model is GTS E20. Love the way the kit is designed, a pleasure to build. You can see the plan here:

https://docs.google.com/document/d/1RG-fci7HZh_tu7NsceQMMk43_Nh083SHHU119ZRnVk8/edit?fbclid=IwAR11hv71Wba8d2Uv3HG-Mi_ZeIjDYZQleib2upVW-Jj_VVNdZsAwzyJzs_0
 
After gaining some experience ,my ultimate goal is to enjoy flying a 1/2A  pylon model and E36. For now this pylon E20 will serve me as a training ground.

Next Step: What would the recommendation be as a next step for me to Safely achieve :
"You need to be flying a LARGE loop with right turn and left roll.
You need washin on the right main along with some decalage. How much and which direction rudder tab cannot be determined until after you get the roll."


 Sorry for such newbie questions considering that I am surrounded by experts in HPA. But Thank you so much for your support.

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flydean1
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« Reply #12 on: May 04, 2021, 10:11:52 PM »

I would start with about 2 degrees of decalage.  That means 2 degrees difference in the wing and stab angles.  Stab negative relative to the wing.  It helps to have some means of measurement.  A simple method is to use a protractor of about 6 inches diameter with a string through the center or zero hole and a plumb bob of some kind on the end of the string.  Block the wing at zero and measure the stab.  Don't worry about the glide.  Read Danberry's information.  Get the power pattern right, then trim the glide by shifting the CG.  It may be possible to do this as simply as shifting the wing forward or aft.

I looked at your model in the link.  Should be a great flier and good trainer for later power models.
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che
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« Reply #13 on: May 05, 2021, 04:57:21 AM »

Sailaway,

I've built two versions of this kit and did a detailed review in AeroModeller; the kit and model are simply superb. If you've built it with a flat wing according to the instructions then you're in a good place to start trimming.

I did have my model go left at one point and it is sort of stable as the thrust is not too great, but it MUST fly to the right under power as everyone has said.

The decalage is set by the 2.5mm tail TE packing - no need to change this. I set a 50% CG and found it test glided OK, using some small (1mm) wedges of balsa on the fin TE to set the glide turn.

The trustline is easy to adjust using the very clever motor mount. Use the 5deg front part and set for equal side and down-thrust to start with. Use a fully charged battery every flight and a short run - better if you have a RCDT fitted. Adjust the motor mount to give a positive right spiral climb.

I found the model trimmed with no vices. I always got a climbing turn to the right (other than noted above, a trimming error on my part) to a good height. The transition can be improved if the right spiral climb is a bit tighter, but I never had a long time for the glide to stabilise so I wonder if your CG is too far forward - can you measure and report back please ? I'd set it at 50% to start with.

Sevak has said the model will fly with no wing warps. I have one with warps and one without and both fly very similarly, but I added a 15mm long wedge of 1mm balsa at the DH break to stop any hint of spinning in if I contacted one of the humongous Scottish thermals that appear once a decade.

Be careful, methodical and make small changes and you'll be rewarded with an excellent flying model. Like you I built mine to be able to fly in a local filed and I've hand maybe 200 flights with mine since I bought the kit at the end of last year.

Feel free to send a private message if you prefer.

CHE
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danberry
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« Reply #14 on: May 05, 2021, 09:01:12 AM »

Didn't know it was an E20.
Everything regarding trimming is off the board.
Going left under power is not such a big problem with the small prop and lack of power.
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USch
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« Reply #15 on: May 05, 2021, 09:56:33 AM »

Wise choice to start with a E-20.
So everything is less dramatic. E-20 have lower power to weight ratio and climb therefore slower. Errors do not necessarily have deadly results  Grin

But what has been said about trimming is true nonetheless.
It may point out that who askes for help should state in the first place about what we are talking.

Urs
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Sailaway
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« Reply #16 on: May 05, 2021, 12:02:54 PM »

Let me take this opportunity to learn what it takes to climb right correctly with your help. Nice to know that in the E20 it will not matter for a left climb. But this one is my training model, so will make use of that to learn correctly.

I have re measured everything: The wing sits square, no warp in the wing or tail, no warp produced in the wing by tight rubber band hold-on on the pylon, both halves of the wings are of equal weight, fin is straight up and down, no tilt. The wing LE and TE are on the same height of the pylon, no incidence. The stab has the incidence at 2.5 mm TE up as advised. The motor has an equal amount of left and down about 5 degrees.

The only thing is that at the rudder TE base , I do not have 1/32 to the right tab. I measured and the rudder tab thickness is about 1/64 or less. Will just make this one change to a 1/32 thick tab and try it on Friday when once again they predict very mild breeze through noon. Any other suggestions to make it climb right with a good flat transition is appreciated.

Thanks again to all of you, will provide feedback after Friday trials.
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