DSM Excelsior re-furb

[Bruce Collinson]

Jeff,

Batteries; the uber-electronic guru at my club replaced his fleet, took out MiMhs and installed LiFes, I recall for this exact reason, no cliff edge and the local Jeti retailer told me exactly the same (Jeti use Li-Ion, without balance leads, for both Tx and Rx).  Balance lead extensions are cheap as chips, Component Shop or indeed the local Precious Shop, MS Leeds.

 

4 Max replacement wires; they do not appear to be handed so good luck with those.   I asked George why not and he said not to worry about it, he has a plane which pre-dates 4 Max and the retracts need to be straightened after every flight ... quod erat demonstrandum, as they say in Leeds ... even I can make an adequate 90 deg axle bend in 4 mm wire, use a large engineer's vice and a hammer.   Not sure it solves the symmetry issue though.   I will find out if I ever  get the wires out of the Saphir.

 

Weather looks dire so might be going to look at the Exelsior tomorrow. We might be comparing notes!   Three of us were doing LMA Elvington tomorrow and UKCAAHuddersfield Sunday but tomorrow is Bohemian Rhapsody weather (thunderbolts and lightning .. etc) so might be Elvington sun instead.

 

BTC

[Bruce Collinson]

Think I might have broken something here, the foregoing reply is a week old but stopped me sending a fresh one.

 

Excelsior is a 188, with a YS 120 so I'm saving up for fuel for it whilst I rip out 3003s and 148s and put Savoxs in; await spinner with APS size hub cutouts so I can try to start it.

 

Post facto, UKCAA Huddersfield wast postponed to this Sunday, I'm away and will no longer have to suffer the ignominy of coming third in Pick 5.  Out of 3.   Elvington was gusty and showery but did manage some essential retail therapy including more LiFe Rx batteries.   Some very good LMA flights too but sparsely attended.

 

Is the u/c answer to acquire some proper 10g piano wire (not cheesium) and identify which of your clubmates owns and operates a proper bending jig, then wait?   That's what I'm hoping for, once I find out how to remove the existing wire legs.

 

Pal/tutor Nigel/Darth has at least one 188 and I have asked him for c of g as his is trimmed for UKCAA schedules so it ought to be right; flies on rails (until he intervenes...).   Will post when I hear from him.

 

BTC 

[Jeffrey Cottrell 2]

HI Bruce

Did notice a certain familiarity about your last post. Don't know about you, but if I'm doing a long post I type it out first in Notepad, then when I'm happy with it I copy and paste into the forum.
Could you have done the same thing, but forgotten to delete it afterwards?
Anyway, no matter.
So, what is it about 188's?
Like the buses, you wait ages then three come along at once. Yours even with 3003's in it.
Think you're right to switch them for Savox's. I used JX's because I already had them.
I found a 56mm spinner with alloy backplate, originally bought but never used for an electric project. Thing is the plastic around the blade holes is moulded thinner so the hole can be enlarged with a scalpel.
Mine adapted pretty easily to APC blades.
As regards the u/c, mine are 4mm diameter, which is 8g, so 10g would be a step down in diameter.
Have found some wheels which have thin enough hubs to use the original axles. My only concern is that they are Perkins ones with a plastic hub. Not sure how they will take to one of my less than perfect landings with a 9 1/2 lb model.
If they don't look up to the job, I wonder if I could get a couple of these, then bend the wire straight and re-bend to 90 deg the opposite way. Might need to apply some sort of heat to make bending easier, but if successful, Bondaero do some wheels with alloy hubs, much stronger. Anyway, on the back burner until I'm sure I need them.
Yet to try removing the legs on mine. I'm told it is only a grub screw through the pivot holes, but are things ever that easy?
Tried out Martin's suggestion of using a diode in series to drop the LiFe voltage down to where the servos will tolerate it. So far, working perfectly.
I got a reply from George at 4-Max, saying NOT to use his servos at more than 6v. I have a servo tester that does continuous cycling, so I had a servo running the reduced voltage on this for about 1/2 hour.
No signs of distress, not even getting warm.
Figure if an E-max analog will be ok like that won't have a problem with the other JX's.
All that's left to do now is make up extension leads for the wing servos, then I'm pretty much there.
Oh yes, shorten back the balance lead on the LiFe. I carefully lengthened it so I could charge in situ, then found out I could remove the pack easily enough to charge outside the model.
Don't like lengths of wire flapping around in the fuz, so that has to go. ho hum.
Would like to know what Nigel recommends as a c/g. Peter has already posted saying 35% of root chord is a good start point. Have to say I would like the c/g to be forward of optimum for the first flight, then adjust from there.
Apart from that, running out of excuses to postpone the maiden.
Wish me luck
Jeff

[Peter Jenkins]

Good luck with the maiden Jeff.  The weather's not looking very promising though.

[Jeffrey Cottrell 2]

Hi Guys, just when it was going so well......

Pretty much ready for the maiden. Still got questions in my mind, but probably will have until it's flown a number of times.
Anyway, final check is on c/g, and that's where I hit a big snag.
I'm using a Jerry Hanson balancer, this one.
Peter suggests a c/g at 35% of chord as a good starting point. I measured the chord at the fuz as 415mm, so 35% of that is 145mm or so.
Set the arms of the balancer to that, and the model balanced massively tail heavy. Loosened the arms and slid them forward as far as they would go, some 200+ from the le, and it was still tail heavy.
With the balancer they supply 200g of stick on weights. Even with all of those perched on the prop driver, model was still slightly tail heavy, though probably acceptable.
However, with the c/g at the recommended position model is basically unflyable.
Keep looking for some major mistake I have made, but can't fathom it out.
Can you guys help?
Jeff

btw, this with tank empty

[Peter Jenkins]

Jeff, are you measuring back from the LE or forward from the TE?  The distance I gave was back from the LE i.e. 145 mm back from the LE.  Let us know which way you were measuring it.  I should have specified measure from the LE back.

Peter

[Jeffrey Cottrell 2]

Hi Peter, thanks
First again, as usual.
First of all, I am measuring from the LE. That is standard, I believe. The balancer I am using does not allow the model to slide far enough forward, so I took the arms off and measured the balance the old fashioned way.
As it stands the balance point is some 220mm behind the le. That's just over 50% of the chord.
However, things have got a little more interesting since I posted.
Had a chat with Geoff Hodgson at Foam-Wings.co.uk. He is thinking of re-introducing some DSM kits.
He did not have the figures to hand for the big Excelsior, but he had instructions and a wing for the 60" Saphir, which he quoted for me.
So, the root chord on that one is 340mm, and the instructions say c/g at 176mm. That's just over 50% as well.
Makes me wonder if the sharply tapered le plays some part.
He also pointed me to a website which will calculate the c/g. Need to take some measurements and see.
So, in a quandary as to whether my c/g is correct.
Had a post a while back from Bruce Collinson, who has a friend with an Excelsior 188. Promised to ask him where his c/g is and get back to me.
When did things get so complicated, and why wasn't I looking?
Jeff

[Peter Jenkins]

I'd forgotten the model had a sharply tapered LE.  Take a look at this article to see if it will help.

[Peter Jenkins]

By the way, accuracy in measuring the exactly position for the CG is greatly overrated.  I usually stick some masking tape on the wing where the CG is mark the position using a rule on the masking tape and check balance with my finger tips supporting the wing at that point.  Provided it's roughly balanced go and fly.  The optimum CG position can be found by flying the aircraft and seeing how much down elevator is needed for inverted flight.  Move the CG fore or aft to suit your taste and fly and check.  That's the optimum place for the CG not necessarily what's marked on the plan or measured off another example.

[Jeffrey Cottrell 2]

3 hours ago, Peter Jenkins said:

I'd forgotten the model had a sharply tapered LE.  Take a look at this article to see if it will help.

Hi Peter

I think that's the main issue, that and the taper is all on the LE, the TE is flat.

Anyway, had a look at that article you linked to. Did seem to concentrate on Mean Aerodynamic Chord, but didn't tell you much about how to calculate it.

The article Geoff pointed me towards is much more useful, here. Also the attached c/g calculator, very handy.

Got the tape measure out and plugged the figures into it, and it came out with an optimum c/g at 220mm from LE. that's about 10mm back from where it is in reality.

That's just over 50% of chord, ties in with the figures Geoff gave me for the Saphir, and I imagine Bruce's friend will come up with something similar. At least I'm on the right track.

I can understand that final c/g position is a matter of taste, but imagine if I had made some major mistake, and the c/g was truly some 2" back from where it should be.

Maiden would be short but memorable, that's for sure.

Changing subject slightly, the same calculator gives wing loading, which comes out at 24 oz/sq ft. That seems to me to be quite respectable.

However I read in other threads that CUBIC loading is a better guide to how the model will fly. Confess I don't understand most of it, but the calculator gives the cubic loading as 9.9 oz, cu ft.

Anybody more into this stuff, is this a good number or not?

Jeff

[Peter Jenkins]

That's all good news Jeff.

 

The article I linked to gives a graphical solution to MAC and then how to extract the CG.  However, you've got there!

 

If you stick with 200 mm aft of the LE at the root you can then decide about whether moving it is worth while.  It is always worth spending time on exploring CG position to get to somewhere you like before doing the rest of the trimming otherwise moving the CG means you have to redo all the other tweaks.

 

Peter

[Nigel R]

10 hours ago, Jeffrey Cottrell 2 said:

cubic loading as 9.9 oz, cu ft.

 

Is spot on for sport or aerobatic types. Will fly and land fairly slow.

[Jeffrey Cottrell 2]

Hi Nigel, thanks

Running out of excuses not to maiden this beast. 'dog ate my homework' just doesn't seem to cut it any more! ??

Jeff

[Peter Jenkins]

Now that you have the CG sorted, make sure your control movements at low(est) rates are aileron and elevator 10 deg each way and rudder around 25 deg each way you should be fine.  I've yet to fly an F3A aircraft that caused a problem on maiden.

 

Peter

[Jeffrey Cottrell 2]

Hi Peter

Thinking along the same lines myself. Set the control movements to those recommended in your book. 15 deg on aileron and elevator and 30 deg on rudder.

In the flesh, these movements look high to me, so I will set rates at 70% or so for the first flight.

Take your point about never having an issue with your F3A models, but how many have you flown now, in total, and how many of those were bought second hand from an unknown builder?

You'll have to excuse me having a few qualms.

Jeff

[Peter Jenkins]

Hi Jeff

 

My recommendation in the book is 10 deg each way for ailerons and elevator and 25 deg for rudder.  15 deg will give a slightly too fast roll rate.

 

Almost all my F3A models are 2nd hand but generally the owners have been better pilots than me and the aitframes are rarely more than 3 years old.  Plus, they are all for electric power my preferred power train for F3A especially in competition.

 

 

[Bruce Collinson]

Now heard back from Darth who says 200mm back from l/e at fus; "it looks quite a long way back compared to "normal" models".   I'm pretty sure that this is an optical illusion caused by the swept back l/e and the straight t/e and it seems to fit with what you've written above.   It also appears right compared with my smaller Excelsior and a Saphir although I can't recall the precise dimension of the latter, but it flies right.   200-210 is clearly safe for your maiden, all other things being equal. 

 

If communicating with Geoff Hodgson, we can find homes for new DSM models.   I have a pair of Excelsior wings from Bill Manley, waiting for a fus builder to volunteer ...

 

New alloy spinner still needs Dremel work which is disappointing as the display version didn't but I'm loath to quibble.   Now deciding whether or not to rip out the existing closed loop cables for safety, whilst changing servo and new alloy arm plus clevises.   All postponed whilst on hols, with regular flights out of Brize Norton to distract me.   Not my flights, obviously.

 

BTC

[Jeffrey Cottrell 2]

Hi Bruce, thanks
That's got to be the clincher, hasn't it?
Must admit I was puzzled when I did the first check. Still of the opinion that the model has flown but couldn't be very well with the c/g so far back from where I would expect it.
Having talked to Geoff and got his figures for the Saphir, and also putting the dimensions into that site which calculates c/g, turns out it's pretty much where it should be.
The info from Garth makes three sources that say the c/g is correct. Can't argue with that.
Did ask that Geoff keep me in the loop about DSM kits, but I wouldn't hold your breath. When I spoke to him last week he said he was waiting for some extra long balsa sheets.
Trouble is, when I first spoke to him, couple of months ago, he was waiting then too. Ho hum.
If he ever does produce these kits, I would be in the market too. I know I have the Smart Move lurking at the back of the bench somewhere, but there is still so much work to do, might give that best and start new.
So, on to your Excelsior.
My thinking always is, if something is not to your liking, replace it. On that basis, you've obviously seen something about the current closed loop that's giving you doubts.
My advice, replace it. Bit too late if you find out it's not up to scratch on the first flight.
I replaced the wires on mine because the builder had used some plain, not covered, stranded wire. Over use that will saw its way through the fittings, so it had to go.
By the same token I also replaced the elevator pushrod. Old one might have been quite serviceable, but it was made from a very soft and rough piece of 13mm square balsa, with great gobs of epoxy on each end.
Now a piece of 13mm dowel with the wires epoxied into proper slots, and bound with kevlar thread.
Whatever else fails, it won't be that.
Another question.
Your Excelsior has a YS 120 on the front, mine has a Thunder Tigre Pro 120. Neither of these is a budget piece of kit, so why did both builders choose cheap and cheerful 3003 servos?
Probably just about ok for torque, but not much to spare, and being analogue wouldn't centre too well either.
Why spend so much on a power plant, then go budget on servos? Beats me.
Just my thoughts
Jeff

[Bruce Collinson]

In haste, my instincts would be, these are 25+ yr old planes, that was what people used back in the day.   I'm sure there are loads of them still in regular use; Mk 2 Escorts spring to mind; prefer my BMW but the Ford will get from A to B.

 

BTC

[Peter Jenkins]

Hi Bruce

 

I don't think CG position has changed from back in the day.  If you work out the MAC and then plot the given CG position I bet it will be in the range 35%-40% of MAC.  

 

Peter

[Jeffrey Cottrell 2]

Hi Peter

I think Bruce was referring to my questioning top of the range motors, with distinctly low end servos.

I note his comparison of the Mk2 Escort with his BMW.

Think fairer to say if you took a Mk2 Escort, with its 70's suspension and brakes, and put a BMW motor in it.

Wonder how long it would be before you saw the wrong side of a hedge.

Jeff

[Peter Jenkins]

Ah - wrong end of stick!  Sorry Bruce.

 

Not sure there was much choice of servo back then.  The Top Flite Mustang 60 which shows an OS 120 FS on the plan also shows Futaba S148 servos all round.  I suspect that with digital servos that something with the power of an S148 would be fine but who wants to take a chance with £3000 of model aircraft dependant on the servo power?

[Bruce Collinson]

Peter,

 

was in haste, written re servos not motors.   I’m a returnee with a 25 yr hiatus and the quantum leaps in radios were astonishing, until I re-learnt the oldest lesson in the world, you get what you pay for.   I might be wrong but I subscribe to your point on £3,000+ in the air, not quite in my case but nudging 4 figures, and cannot reconcile the trend to buying knocked off gear from China.   I’ve crashed a few, mostly Wot 4s, but have yet to break a servo so I gravitate to Savox on the basis they will almost certainly survive whatever slings and arrows I throw at them and remain in stock for the next project.

 

BTW I’m re-reading your tome for the third time.

 

the most perplexing thing is that we still connect our choice of digital HV servos to our redundancy Rx batteries and our 2.4 rxs using the same spindly under-engineered Futaba/JR plugs and sockets.   Wrong forum perhaps, but we have what seems to be a Spekky “hole of death” at our site where there are banjos in the background every time something inexplicably piles in, including my late kitbuilt Wotty.   Convinced it was to do with rx aerial arrangement; hypothetical now as am on Jeti, best move I have made in 5 years.

 

Whatever.

 

I’m not sure the Excelsior is as sensitive to C of G as we seem to assume, with its huge moment arm (?) = long fus which would surely allow at least a flight and a landing with it out of the range we have apparently agreed.  I’m not arguing that it would be trimmed.   My smaller one (160? Was well used when I acquired it by selling it to myself in a late modellers auction, only bought it for the NIB Saito it came with, which was marginal) flew really straight to the point where I was slow rolling it, after a fashion, as soon as it was trimmed.  I think we did a rudimentary check on the c of g and left it.

 

N. Leeds had a resurgence of Anderson’s Rocket before lockdown, mainly because its designer is a member, and now a similar thing may be about to happen with the big Excelsior as four of us are occasional UKCAA participants and a Rocket was lost last week.   Bill Manley has made two pairs of wings, just the fus to replicate, then decide on power plant.   An OS 120 pumper is being debated, but £600 ....

 

BTC

 

[Bruce Collinson]

PS am contemplating chopping in a dearly loved M 140i for an M2; how long before a hedge appears in the mirror?

[Jeffrey Cottrell 2]

Hi Bruce, couple of thoughts
Is the Rocket you mention the Terry Anderson design from a while ago? Sometimes I buy plans just for curiosity, and that plan was one of them.
Dug it out for another look.
Very Aerostar'ish which is no bad thing. Looks to me it could be built very light,so ideal for electric.
Might put it on the build list for a possible gap in the schedule.
I assume Bill Manly is 'Billkits' yes? If so, what's the quality like? Talking to Geoff at Foam-Wings, I get the impression he has a computer controlled wing cutting machine, which should ensure accuracy of section if nothing else.
The powerplant you have to decide on, is this for a Rocket or a big Excelsior?
Reason I ask is while I was contemplating the Excelsior, I put some figures into e-Calc and came up with an electric set up which looks pretty close to the Thunder Tiger I now have on mine.
Thing is, on current prices I reckon about £160 for motor, esc and batteries. Sounds a bit better than £600.
Details available if you fancy a look.
Meanwhile agree with you about servo plugs. mentioned this a few times on the forum, but all I seem to get is that they will be fine.
For me, Murphy's law will surely say different. Couldn't do much about the basic layout, but I did run two separate leads from the switch to the receiver, just as insurance.
Time will tell.
Finally, swapping your M140i for an M2, sounds good. Can I assume you couldn't afford a Mk 2 Escort? ??
Jeff