DSM Smart Move re-build

[Jeffrey Cottrell 2]

Hi Guys
With the successful conclusion of the Excelsior re-furb, turning my hand to the Smart Move. This is going to be more than a re-furb, read total rebuild.
So, bit of background.
I bought the Smart Move and the Excelsior both at the Wings & Wheels show a few weeks ago. The Smart Move was on the B&B stand and looked fine from the outside.
However the wing was held on with masking tape, and I couldn't get a look inside. The stallholder said the seller had 'forgotten' the wing bolts, and my spidey sense was absent that day, so I bought it.
Ok, price was reasonable but still.......
When I got it home and pulled the wing off, a horror story was revealed. The fuz was literally held together with great gobs of epoxy, and the radio install was not the best (that's being kind).
However the wing was even worse. The retract servo was in a hole that looked like it had been cut with a chainsaw, and the retracts and wing servos had been GLUED in.
I though about it for a while, even posted a question on GBRCAA, and the general conclusion was that the wing was not safe to fly without modifications.
In the end I went drastic, and cut the wings in half just outboard of the fuz joint.
Lined the roots with some 1/8 balsa to form the root joint.
Now, according to my info, the original Smart Move was 60" span. Mine when I got it was 55" and after my mods it was down to 52".
Definitely not right somewhere.
However a trial assembly looked in proportion, so not too bad there.
I had to cut the retracts to get them out, so threw them away. Removing the wing servos took quite a bit of the foam core with it, so I used SLEC side mount brackets, mostly to hide the damage.
Currently in the process of filling in all the holes in the wing, and after that will re-join them with proper glass re-inforcement at the centre.
So, first question.
When I cut the wing panels I managed to get them quite accurate (luck) but temporary join showed a small amount of dihedral. Propping the wings up at the join angle, a ruler across the wingtips showed a gap of about 3/4" at the centre. Not much but will it effect the flying?
Inclined to think it won't but your thoughts?
Should be some pictures around here, to show what I am facing.
Any suggestions, ideas would be most welcome.

Jeff

 

Wing centre as received

 

 

 

And now

 

 

One wing holes filled in

 

 

 

other to be done

 

 

 

 

Fuz as received

 

 

 

And now

 

 

 

Control snake layout, fuz

 

 

 

Control layout, tail

 

 

 

[Jeffrey Cottrell 2]

Hi Guys

Sorry forgot to add a couple of pictures.

This is a quick look at the model with the shortened wings. Doesn't look too out of proportion, does it.

 

 

 

This is a shot next to Excelsior for size comparison

 

 

 

Jeff

[kc]

Jeffrey, there was a Smart Move 40 as well as a 60 engine size so perhaps you have the 40 as its less span.

 

I still have a Smart Move 40 kit unstarted in the garage, so I could get some info from that if you need it.

[Jeffrey Cottrell 2]

Hi KC, thanks

Been researching what there is on the net about DSM. Never seen mention of two sizes of Smart Move.

No rush, but when you have a minute could you measure the span of the one in your garage? Might answer the question.

Cheers

Jeff

[Denis Watkins]

59" from eBay ad

 

[kc]

The Smart Move 40 foam cores measure to 56inch span ( approx -inc wingtips which are separate) with fuselage ( fus supplied ready built in kit ) at about 48 inch firewall to rudder hinge. 

The instructions state

span 143cm

length 148cm

weight 1900-2700 gms

power 40 twostroke to 60 four stroke

 

ailerons 11mm up 10mm down

elevator 11mm up 12mm down

rudder 35 degree Left 30 deg Right

CG 195mm from rear F2

dihedral 36mm under each tip ( diagram shows centre on level with 36mm on each side )

 

All I have to do now is try to fit all the bits back into the box!

Edited August 19, 2021 by kc

[kc]

Adverts at the time showed both Smart Move 40 and 60 - so there are definitely two sizes.  Very few adverts mentioned the 40 when I looked for it some time ago but most certainly a different model to the 60.  DSM is of course Dave Smith Models.  

[Jeffrey Cottrell 2]

Hi KC

Thanks for doing that so quick, much appreciated.

That's certainly the model I have. All my measurements are pretty close to yours. Only discrepancy is the instructions show the fuz length at 148cmm, which is 58" or so.

However, this might have been measured including the rudder, or possibly from the prop driver.

Either way, no biggy.

The extract from the instructions will be useful too, when I come to set it up. Already produced a couple of encouraging results.

First of all, the root chord on mine is now 335mm. Allowing for the chunk of the centre section I cut away, it probably started at 355mm.

Th c/g is shown as 195mm from F2, which comes out well over half chord.

This is a question that came up with the Excelsior as well, c/g being further back that expected. Turns out on checking that that's right and due to the sharp sweep back on the le.

All confirmation I'm on the right track.

Most surprising of all is the dihedral.

When I cut the panels away I didn't measure to any accuracy. Figured I could sand the roots true afterwards.

Your instructions show 36mm under each tip. With one panel flat, that would mean the other tip propped up 72mm. Without any information to go by, with mine on the bench I have to prop up one tip by 60mm to get the centre join ok.

So, 60mm as opposed to 72mm. Good enough for me, by pure luck.

Not sure what size prop a 60 2-strike or a 90 4-stroke would turn. Mine's going to be electric, and the figures for my set up are 7900 rpm on a 14 x 8 prop.

Anyone suggest how this might compare with the ic engines above?

So far, looking good. Work in progress

Jeff

[kc]

Of course if it's the Smart Move 40 it takes a.40 two stroke or .60 four stroke, so need the electric equivalent.  

My view as i have mentioned in other threads is that it's very important to get the Lipo well forward to avoid masses of lead to get CG right.  In this case perhaps even more important as the tail is very long and it's likely heavy anyway if the original builder used lots of epoxy.   I suggest a 'lash up' at an early stage to see where the Lipo should sit.   On one model I used a length of ply on the nose and taped all the parts to that to see where the balance lies.   The result was that replacing the OS46 two stroke needed the firewall moving forward 5.25 inches to keep the CG without lead.   ( prop driver came out only 2inches in front of firewall as the electric motor is so much shorter than the OS )  Completely different model of course but the principle is the same.   That model used just a 4S3000 and the Lipo was hard up against the firewall.   Lighter models fly better and crash less!

 

Fus length I measured was the bare fuselage without glass fibre cowl or rudder so that would come to 148cm I expect when those are fitted.

Edited August 19, 2021 by kc

[Jeffrey Cottrell 2]

Hi KC
Yes, that will be a consideration.
The fuz already has a ply box mounted on the firewall, some 40mm deep. The motor I am using has both bolt on and collet type prop drivers. Using the collett type, that puts the prop driver some 75mm from the motor base. Add that to the ply box and that means the driver is some 115mm (4 1/2") from the firewall.
The motor is also relatively heavy, so I'm hoping that will be close enough.
We'll see.
Out of interest, if you look at the picture of the fuz before I modified it, that large ply plate with the wing bolt fixings in it was also the battery mounting plate, at the REAR of the wing opening. What that did to the balance I do not know.
Oddly enough, that plate had written on it '4-Max 4s 3700'. Mentioned it to George and he remembered the customer insisting he was going to use 4s, despite George's advice to go 6s.
My set up is based on a 4000 Ma LiPo and, in theory, should give me about 11 mins of mixed flying.
Haven't yet decided that for sure, but if a 4000 will fit, that would be the minimum size I would use.
After all, if I need extra weight up the front, might as well make it do some work.
I suppose, if the worst comes to the worst, I could re-make the motor box bigger, and cut a hole in the firewall to allow the battery to slide forward as far as possible.
I'm also converting to closed loop for the rudder and a single snake for the elevator, which should minimise weight at the tail.
For the moment, concentrating on getting the wing done. Once I finalise its mounting, might be able to mount the servos further forward as well. Every little helps.
Clearing out the  junk from the fuz has lost a lot of the epoxy as well. Maybe not as light as it would be if I started from scratch, but shouldn't be too bad.
Work in progress
Jeff

[Jeffrey Cottrell 2]

Hi Guys

Been looking at prop sizes for the Smart Move. KC kindly posted the instructions which recommend 40 2-stroke or 60 4-stroke. Obviously the 2-stroke would use a relatively small, high revving prop, but the recommendation for the 60 4-stroke is 12 x 6 to 13 x 6.

Anybody running those sizes on a 60 4-stroke, could give me the rpm achieved?

My electric set up suggests 7900 rpm on a 14 x 8 prop. Feeling is this will be plenty, but would like to have a closer idea.

Thanks

Jeff

[David Davis]

I used to have one of these. Somebody gave it to me. It flew beautifully but I was not an experienced pilot at the time and I made a horlicks of the landing on the third flight and completely fubered the fuselage. Picture below. OS 61 SF up.

 

A couple of years back I bought a scuffy but sound example with two sets of wings off eBay which I've never got round to restoring. The canopy was just a bit of black plastic inexpertly stuck to the fuselage. I sent the dimensions to Carbon Copy and they provided a replacement even though it was intended for a different model. When I removed the old canopy I discovered that the builder had installed a chicken hopper tank system.

[David Davis]

Sorry gentlemen, I believe that my second "Smart Move" is really an "Aerostar 62" but you can look at the pictures anyway!

 

I'll start a build blog when I get round to it.

 

 

[Nigel R]

Jeff, you like a challenge, that's for sure.

 

Myself I would be treating it as a template to measure from...

 

As a baseline, I have a Chilli Wind, a 40 size similar era similar style mode, weight 4-3/4lb with lipo, flies very nicely on a 750W electric setup, mine uses an 11x8 prop so spins a bit quicker than most electric setups.

 

That aside. Some IC prop numbers for you, 40 and 60 sizes. The Watt number comes from an online calculator I fed the prop figures into - pinch of salt, bit approximate, etc.

 

fours

OS70 FS, 13x6 APC, 10000rpm, 900W

OS81 FS-a, 14x6 APC, 9400rpm, 1000W

OS91 FS, 14x6 APC, 9600rpm, 1050W

OS120 FS, 15x7 APC, 9100rpm, 1250W

 

twos

OS46 SF, 11x6 APC, 11x6 APC, 11500rpm, 700W

OS46 SF on (badly adjusted) pipe, 11x9 APC, 10500rpm, 800W

OS46 SF on pipe, 11x8 APC, 11200rpm, 850W

OS61 SF, 12x6 APC, 11750rpm, 1050W

OS61 SF on pipe, 12x8 APC, 11200rpm, 1200W

OS61 SF on pipe, 12x10 APC, 10400rpm, 1200W

[Jeffrey Cottrell 2]

Hi Nigel and welcome

Did wonder a couple of times whether I had bitten off more than I could chew.

Couple of thoughts kept me going.

First of all, do you recall someone started a thread about lockdown projects, all those repair jobs at the back of the garage? Looking at some of those, which were literally basket cases, being restored to fly again, what have I got to lose?

Second, there's something satisfying about making a silk purse out of a sow's ear. Of course it may not turn out to be a silk purse, more like another part of a sow's anatomy but here's hoping.

Finally the mercenary aspect. The Smart Move actually cost more than the Excelsior. Although neither was very expensive not going to give up without a damn good try.

Thanks also for the prop details.

My electric set up will be turning a big prop relatively slowly, so comparisons with a 2-stroke are not really valid. However some of the 4-stroke figures make interesting reading.

My prop calculator, again theoretical, says turning a 14 x 8 prop at 7900 rpm gives average 893w and max 968w. Looking at the figures for the OS 81 and 91, I'm losing a bit on rpm, but with a higher pitch prop.

Either way the model is listed for 60 4-strokes, so if I can even approach the performance of an 81 or 91, should be good enough for me.

As always the proof of the pudding is in the flying, but everything I've learned so far is encouraging.

Work in progress

Jeff

[Nigel R]

Much is often made of the two stroke four stroke rpm difference. I find there is, end of day, little difference in the air.

 

Yes, larger props are more efficient. But I think the RPM numbers for two and four strokes are close enough that it doesn't matter very much.

 

The main issue (beyond "has the original builder managed to make it straight and true") I can see with this particular rebuild is that you've chucked away a big lump of wing area, possibly 10% or thereabouts. Why not make a new pair of wings the right size?

[kc]

The kv of the motor proposed does not seem to have been mentioned and it doesn't seem clear whether Jeff is using a 4S or6S Lipo.    Matching the Lipo number of cells  to the kv of the motor is the key thing and then choosing the prop to suit.

Watts per pound is the thing  -my setup ( for a completely different model as below) is about 125 watts per pound while Nigel quotes about 157 watts/pound for a Chilli Wind.   That would be the practical range of watts/pound to aim for an aerobatic model in my view. 

 

When I  replaced an OS46SF ( Nigels data says 700 watts approx) with an electric motor I found that a 3536/9  910kv motor gave 500 watts on an 11 by 5.5 using a 4S 3000.    perfectly satisfactory flying on a 4 pound model for around 6 minutes at full throttle, a little more on mixed throttle settings.  

   The weight of the OS46FX plus tank etc came to just about the same as the 3536 and 4S3000 but the really big difference was all the heavy parts of the OS46SF are right at the very front -crankshaft+bearings etc- while the electric setup has the Lipo as the heavy part and thats always much further back.   Thats what requires the extra planning to get the CG right when swopping glow for electric.

Edited August 20, 2021 by kc

[kc]

I hope Jeff didn't throw away the offcut of wing root - that would be a good way to make a root template to cut any replacement wing!    But you still need to get the tip template and in any case you don't know if DSM put any washout in when they cut the wing.  

I think the reduced span might well be OK as long as the total weight is not too high.

[Jeffrey Cottrell 2]

Hi Guys
Interesting thoughts.
Nigel
Rule of thumb for me is that a smaller diameter prop turning high rpm, will fly the model faster than a larger prop of the same pitch but turning slower. However the larger prop will produce more thrust, so improving vertical performance.
Given the current F3A trend is towards slower, but constant speed flight, seems to me that slower but higher thrust is the area I want to be in.
Anyway, all conjecture at the moment. Final proof will be how (if) it flies.
Can't say for sure if the build is straight and true. Not up to me, but hoping so. New set of wings is still an option, if the current plan fails. Worth going with what I have, see what happens.
Rough and ready calculation says I have lost 7% of the wing area. Don't think that will make too much difference.
Could start out with a new set of wings, but that would be admitting defeat before battle had even been joined, plus wasting all the effort to make the current wings safe to fly.
KC
Sorry I thought I had mentioned my proposed power train.
Anyway:
Motor    HK SK3 - 5045 - 450Kv
Lipo    4000Ma 6s
Esc    Plush 32    80a    Has 5a bec, but might use separate ubec.
Prop    14 x 6-8
btw, I did throw away the wing root section. However Geoff at Foam-Wings does have Saphir wings to hand, which I believe are the same. Can't imagine any washout on an F3A wing, which is designed to operate upright or inverted.
Please everyone keep your thoughts coming. Finding them very useful.
Jeff

[Nigel R]

2 minutes ago, Jeffrey Cottrell 2 said:

Rule of thumb for me is that a smaller diameter prop turning high rpm, will fly the model faster than a larger prop of the same pitch but turning slower. However the larger prop will produce more thrust, so improving vertical performance.

 

Not the whole truth? pitch speed (pitch x rpm) is important, a better indicator than the pitch in isolation, thrust is different at different airspeeds and needs matching to airframe and performance

 

airbrake effect of large props is potentially important

 

 

[Nigel R]

18 minutes ago, Jeffrey Cottrell 2 said:

Rough and ready calculation says I have lost 7% of the wing area. Don't think that will make too much difference.

 

Rough calcs, assuming (WAG) a 5lb 575sq in airframe.

 

regular-> 5lb 575sq in, wing loading 18-1/2oz/sqft, WCL 10

7% chop -> 5lb 530sq in, wing loading 22oz/sqft, WCL 11.5

 

10 is typical sport model turnaround pattern (i.e. this one)

11.5 is starting to feel more like the old fast ballistic pattern types (curare)

 

Gut feel is your rescue project may be heavier than 5lb?

I'm not sure on your exact wing area either before or after.

 

Peter J may have some good views on electric props, I have little data to back up anything for this style of model.

 

[kc]

For my type of flying an OS46SF at 522grams would have provided  a nice amount of power in a Smart Move 40 ( or a Graphik 40 or whatever in that era) for glow power..   So to fit 1000grams weight  of electric motor and Lipo  would ( for me ) turn it into an overweight model that would not fly the way I would want.   Especially if the wings were clipped by 4 inches.  Too easy to stall and take home in bits.   But it's your model!

As you have removed the retracts then ground clearance for the prop becomes easier to achieve but it's still a consideration.

[Jeffrey Cottrell 2]

Gentlemen
Not sure how we got here, but we seem to have gone from encouraging to doom and gloom in the space of a few posts.
If I accept what's been posted, I can either carry on with the plan, and end up with an overweight, overfast guided missile, or I can put my foot through it and send it to recycling.
Neither of those is particularly attractive.
Not sure whether KC is suggesting I put an OS on the front. Maybe not as far fetched as it sounds, given that I have had to get glow support gear for the Excelsior.
Two issues. First it goes against my intention to go electric, second, have you seen the price of OS engines these days?
Anyway, need a middle course.
Done a more accurate measure of wing area. Still not spot on because of the double tapered wing tips, but near enough.
I make the total wing area 3.84 sq ft.Assuming final weight of 5 lb, that makes wing loading of 20.83 oz/sq ft, and cubic loading of 10.68.
Nigel tells us that a CWL of 10 is ok, that of 11.5 is starting to get ballistic. Note, not is, but starting to.
I'm guessing that 10.68 would be acceptable, provided I can build down to 5 lb.
So, done a quick weigh of components so far. I have fuz at 23.7 oz, wing at 17 oz and 4 servos at 6.9 oz.
Total of 47.6, or just under 3 lb. Obviously more to add for covering, control connections and a myriad other things impossible to take account of, so it will have to do as a first approximation.
Now, I do have a lighter power train I could use. Motor, LiPo and esc come to 524g or 18.5 oz in old money.
We're up to 4 1/4 lb or so.
Might have an issue with balance with lighter motor and LiPo but that will have to be dealt with.
So, question is:
Much as I hate being beaten, am I just wasting my time carrying on?
Your thoughts?
Jeff
P.S.
Not sure if I'm taking seriously going glow but.....
Couldn't find any SF's apart from new ones at a silly price. However I do see FX, AX and the like. I assume these are lower performance engines, but would one of those fly my Smart Move ok?
Other than that, I do see a lot of shops selling Force engines.
Don't know anything about them except made in Taiwan, not China, and the one I am looking at has a rear mounted needle, which I like.
So, anybody used them, thoughts, opinions?

J

[john stones 1 - Moderator]

The AX and FX engines I've owned have been superb, I'm sure one would fly the SM just fine.

[David Davis]

Lots of people are getting out of two-strokes Jeffrey so it sould be possible to pick up a sound engine second hand. Reliable makes include OS, Irvine, Super Tigre and Thunder Tiger. Later engines from SC and ASP should not be dismissed either.

 

Of course there are also a few dogs out there.