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DSM Smart Move re-build


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Not doom and gloom here.

 

Facts as we have them give a better picture of where things end up, is all.

 

My take home is that you might be better off propping for a speedier flyer than the low rpm low pitch setup. 

 

 

Fx ax sf all much of a muchness performance terms. Quite a few ax flying at my club, all run nice. Decent silencer too. 

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I'd agree with Nigel's post above.  Once you lose wing area you have to fly faster to generate the same lift.  Because you are flying faster turning radius increases.  Stalling speed increases as well.  With aerobatics, light is good.  My question Jeff is are you expecting good aerobatic performance as a result of your efforts or will you be satisfied with a below par performance?  If the latter, press on.  If the former, stop now and don't spend any more money or effort on the Smart Move you have.  Build a new wing and then things look different.

 

BTW, I get 272 watts per pound out of my 2 mtr electric motors in the 5 Kg (11 lb) airframe and 3,000 watts power - photo attached.  In one airframe, I use a 3 blade prop of 21x13 in while on the contra the front prop is 22x18 and the rear 22x20 in.  They do something like 2,800 rpm but it's difficult to measure!  I use motor speed divided by the gear ratio and then halve the number.  The contra has a stalky undercarriage!

 

On my 70 size electric model, with a 420 kv motor and around 1200 watts available, I had to use a 17x12 APC E prop to get the watts in the air (using telemetry) with a 5S pack - note this kv is really for a 6S.  On the ground, the motor generated almost 1800 watts momentarily before I cut the throttle!  It was fine in the air!  Ground clearance was minimal btw.  I changed to a 585 kv motor (geared for a 5S so to speak, kc's point) and was able to use a 16x10 APC to generate the 1200 watts I was looking for.  This gives unlimited vertical performance as well as allowing taxying without clipping the prop!  But again, overstresses the motor/ESC if full power is used on the ground with the model restrained.  That's the nature of the electric motor by the way unlike an IC which will not self destruct with a larger prop than recommended - just won't generate the power.  

20210718_191812.png

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Actually I think we are all trying to be realistic and not suggesting gloom and doom!

I was not actually suggesting putting the OS in as it seems to be an electric plane and hopefully uncontaminated with oil.   But if I were suggesting putting in a glow I would suggest looking for an Enya 40SS plain bearing - loads of power and reliable with no bearings to rust.  These often sell for very low prices as nobody knows about them!    I won't part with my 2 Enya 40's as they will outlive me!   Especially as I fly with an all electric club.........

If the model weighs only 3 pounds without power unit then look for an electric setup that weighs about a pound and will balance nicely.   Even 500 watts will probably give a decent flight with a 4 pound all up weight even with clipped wings.  More watts without much more weight will be even better.  With electric you often have to sacrifice flight time for good performance.    But 6 minutes of great flight is much better than 12 minutes with an overweight missile surely!   It all depends on what type of flying you desire- for me an everyday practice aerobatic model  with low weight and low cost would be fine.  

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3" off the span shouldn't be the end of the world.  It will fly a little faster, and as Peter points out, stall at a slightly higher speed.  Me, I'd look on it as a typical classic aerobatic model from the 70s and fly it as such - ballistic!  I'd look for 150W/lb so 750-800W though more would be ok.  600-700kv motor on 6S or 700-800kv on 4S at a guess, 11*7 for 6S or 13*8 for 4S prop?  It might be worth looking for the Crescent/PBM Bullet builds to see what was used on those.

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Hi Guys
First of all, in hindsight, perhaps doom and gloom was not the right wording. Just seemed to me that all the plans I had for this model would have made it worse, rather than better.
However it was never intended to make little of all the help and advice you guys are giving.
If that's how it came across, I apologise, that was never my meaning.
So, to horse:
Seems a broad choice of what to do now.
Appreciate the idea of getting a new pair of right size wings, but then I would be wondering about the fuz.
Managed to get most of the junk out that I could see, but there's always the chance that that could be lighter too.
Before long, my Wings & Wheels buy has become nothing but a template for making new bits.
Also, Bob's post seems to say that ballistic flight was in fact the style for models of that era.
On that basis, I'm going to carry on with the model as is. I'm going to switch to the lighter power train, and hope it doesn't cause too much balance issues.
If I can get it down to around the 5lb mark, should be ok.
We'll see
Jeff

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On 21/08/2021 at 10:26, Peter Jenkins said:

 My question Jeff is are you expecting good aerobatic performance as a result of your efforts or will you be satisfied with a below par performance?  If the latter, press on. 

Hi Peter

Interesting question, but very subjective.

Looking at the standard of models you fly, mine could be below par but still pretty good.

Bearing in mind I am resurrecting a poorly built model, and of a dated design to start off with, I would be happy with a model that is a little smoother and more precise than the one's I am flying at the moment.

An average club sport/ aerobat would do me. If it turns out to have good vertical, that's a bonus, but depends on how light I can make it.

I am carrying on with the model as is, but if I find it does need a new wing, then that could be retrofitted later. In fact, I could do a built up wing and make it even lighter.

First things first is to get in flying then see what I need to improve.

Work in progress

Jeff

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