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Trimming Question after Crash :-(

Question on trimming

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christopher Myers10/11/2019 16:45:31
6 forum posts

Have a RCRCM Hornet and was trying to trim and setup correctly. The CofG was set as per the plans and a dive test and inverted was as expected gentle pull out and not to much down elevator when inverted. The throws were set as per the instructions to high setting. Its my first all moving tailplane.

Symptoms and reason for crash. Real reason is poor pilot but putting that aside for the moment.

The role rate was very poor unless i went full length by mixing the flaps to act as ailerons. I was going fast and trying to do a sharp turn by flipping vertical and pulling up but instead of coming round it spun. Loops would also spin out rather than a clean loop.

This is my first moulded plane but i also have a Kunai 1.4 which rolls faster does pylon type turns and I can fling it round the sky. Was expecting this to be faster and more nimble but if i get it moving it it seems to stall and spin.

Apart from pilot which I'm stuck with any ideas what i should be looking at?

Cheers

Chris

Steve Hargreaves - Moderator10/11/2019 17:38:36
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Hi Christopher & welcome to the forum.....thumbs up

I'm not a "glider guider" so my experiences will be of little use but I wonder if you might have simply had too much movement & induced a high speed stall thus making the model flick into a spin. I had a YAK 54 (RIP) which was very prone to this.....too much elevator & Whoa...you'd best be 3 mistakes high or it was curtains (one day it did it & was only one & a half mistakes high & ran out of altitude, airspeed & idea all at the same time hence the RIP).

The flicking out of loops tends to support this theory too IMHO.

It may be that the model is one that prefers smooth high energy aerobatics using smaller control surface deflections rather than being forced through tight turns/loops etc. using a lot of control surface movement....

But as I say I'm not a glider man so hopefully someone who is will be along soon to set us on the right path...wink 2

J D 810/11/2019 18:20:35
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1317 forum posts
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Like Steve I am not a glider man but I agree it may well be to much elevator movement.

I have a Seagull AT6 and I had to reduce the recommended elevator movement a lot. At least at lower speeds it behaves but flat out it can still be provoked into a spin with just the elevator.

christopher Myers10/11/2019 18:34:51
6 forum posts

Many thanks the elevator is the thing that's really been a mental block as its all moving and ive really struggled to know how to set it up. What got me was it was really motoring and i was expecting a pylon like turn with lots of energy retained but your right its like stopped and fell out the sky in a spin managed to recover it had it not been for the tree still at least it caught it for me !

on the plus side i can rebuild her and we shall try again with less throws and a bit more height before i start pushing my limits!

Thanks for the reply much appreciated.

Steve J10/11/2019 19:06:03
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Posted by christopher Myers on 10/11/2019 16:45:31:

Apart from pilot which I'm stuck with any ideas what i should be looking at?

Firstly, you may be better off asking on a more glider oriented forum.

A couple of things to consider trim wise: 1) CoG a bit further forward (the Prodij in my avatar was a bit snap happy until I moved the CoG forward a few mm); and 2) mixing a bit of flap with elevator at the higher rates. A loop with a 2m glider requires a decent amount of energy going so as not to fall off the top. I mix flaps with the ailerons when rolling my 2m.

christopher Myers10/11/2019 19:21:28
6 forum posts

Thanks all,

JD8 that's it, plodding around the sky or fast in straight line it was fine , it was only when i started speeding things up in the turns or loops it sort fo fell out the sky and did funny things. I think the consensus is right there is too much elevator / I'm putting too much elevator in.

Steve J , thanks the flaps with aileron did give a good roll rate and snap flap seemed to work but never really got to try it as was focussing on trying to trim the basics . Will try the C & G but the dive test and inverted seemed good.

On the plus side landing with crow was awesome.

Thank you all.

Frank Skilbeck11/11/2019 13:19:22
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It's all down to angle of attack not speed, the Hornet has a fairly thin wing section for efficiency and speed, the offset is that it will stall at a lower angle of attack than a thicker section. So a large sudden increase in angle of attack would cause the wing to stall.

Steve I had a Graupner Extra many years ago and with the suggested elevator movement it was really sluggish, so I dialed in a bit more elevator, after which it was prone to tip stalling, it was fine with the larger elevator response when flying slow but high speed yank and bank turns and pulling out of loops and it would drop a wing a flick into a spin

christopher Myers11/11/2019 17:28:58
6 forum posts

https://share.icloud.com/photos/0omWuDDlKbmk0VzLF4L4_cC-A

 

Hopefully this pic will work its resting paste 

Edited By christopher Myers on 11/11/2019 17:29:24

Steve Hargreaves - Moderator11/11/2019 22:10:11
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6728 forum posts
191 photos

Frank, was that the red & white Goodrich one....about 60" span...like this

extra5.jpg

extra6.jpg

I had one too & you're right it had a really vicious streak. Lovely looking model but you always felt it had one malevolent eye on you waiting to drop your guard & get a bit careless with the elevator.

Much as I liked mine it was almost a relief when it crashed....dont know

Chris the best way to post pictures is to upload then to your Albums on the site & link to them there.

There's a "How to do it" Tutorial just here & here

Frank Skilbeck11/11/2019 22:32:42
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4515 forum posts
101 photos

Yep, that's the evil beast laugh, in the end it crashed when somebody else was flying it, I told them they'd done me a favour smile p

alex nicol11/11/2019 22:41:26
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305 forum posts
15 photos

I had the same issue with mine, I bought the kit after reading the RCM&E review, right down to the ST 90.

First couple of times it flicked it really scared me, but as above reduced the elevator throws and it behaved not too badly.

 

Edited By Steve Hargreaves - Moderator on 12/11/2019 20:41:37

Dickw12/11/2019 09:44:10
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497 forum posts
76 photos

Hi Chris

I am not familiar with the Hornet, but I fly similar fast 2m electric gliders and am familiar with what happened to your model. Flicking out of a tight turn at low level is a plane killer!

One of the tests I do on my first few flights with a new model of this type is to get it high and fast, quarter roll until wings are vertical, then pull full up elevator. If it goes around a 360 degree turn OK then all is well, but if it flicks out then I am high enough and ready enough to recover and land safely. If it flicked out, reduce elevator throws and try again. Repeat until it doesn’t flick out of the turn.

If you want a tighter turn after that, try adding “snapflap” if your Tx will allow it – ailerons and flaps go down a few mm as the elevator goes up. I use about 5mm down, but I would start with 3mm for initial tests. Ideally you don’t want the snapflap to begin until the elevator is about halfway up, and you don’t need the reverse with down elevator. Changing the wing section (camber) like this increases lift and can delay the stall at the critical time.

I Just had a quick look at the Hornet manual and note this sentence regarding throws:- “These throws are specific to the role of predominantly gliding. If you choose to go fast (DSing) be prepared to modify the suggestions substantially to support higher speeds.”

All controls are more effective at speed, so I use different flight modes for fast and slow flying with less throw at high speeds.

Looks a nice model, so enjoy it.

Dick

christopher Myers12/11/2019 20:01:34
6 forum posts

Thank you Dick that’s amazing and gives me something to work with. I had snap flap setup and full length ailerons but was trimming so hadnt got to that before the tree struck ! I think with hindsight my expectations was it would be faster and then better than my 1.4 and this isn’t necessarily the case and definitely I had too much elevator and was causing the spin. again with hindsight I’ll increase aileron for better roll rate and reduce elevator and start again from 3 times higher using your tips!

ahh well the plus side is apart from pride and a small repair we will fly again! You live and learn

thank you all for all the help , Dick that is some great tips !

cheers

chris


Dickw13/11/2019 16:29:00
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497 forum posts
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Posted by christopher Myers on 12/11/2019 20:01:34:

...................! I think with hindsight my expectations was it would be faster and then better than my 1.4 and this isn’t necessarily the case ......................

Don't forget that it is a bigger plane and bigger planes always seem to look slower than smaller planes, and also the longer heavier wings will require more force to roll. Once you are used to it and have it trimmed out and set up properly you will probably feel differently about it.

Do you have anyone with similar sorts of models that you fly with? If not, where abouts in the country are you?

Dick

christopher Myers14/11/2019 19:29:39
6 forum posts

I’ve got it Dick basically it’s a skill / experience thing your tips of what to do have set me up well so I’ve got a minor repair and I shall be back and trimming it out and having fun. We live and learn and I’ve had fun.

I fly from either Bournemouth or Bristol .

thanks for all the help , support and advice from the forum much appreciated.

regards

chris

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