Jump to content

DSM Excelsior re-furb


Recommended Posts

Hi Bruce

 

I am flying JR XG series equipment - i.e. JR's own 2.4 radio and protocols not the Spektrum radio as in the JR DSM series of radios.  

 

The radio uses the under specced plugs and sockets you mention.  I've never had a radio problem with these plugs and sockets and I've never heard of anyone else having a problem unless the plug has been damaged.  These days, I tend to use the Maxlock connectors that are self locking and so eliminate the need to fit a servo lead lock.  They are also pretty much the same as the other JR/Futaba plugs and sockets.  So, why do you think they are under specced?

 

Good to hear you are giving my book a good reading!  Did you pick up the list of errata that I published on the thread?

 

Peter 

Link to comment
Share on other sites

Hi Peter

Me too, mine are pretty good. Wonder if you can get the holders with safety clip as separate items? Best of both worlds.

Might try one of those Maxlock ones in 9 way type, but only if I can get round George wanting £4.75 shipping.

Need three way for both ailerons and retracts.

Brings me neatly round to the next question.

Currently running the retracts from the main power pack. Probably won't be using them for the first few flights, but when I do, like the idea of running from a separate pack.

So, how to wire it?

My guess would be that the negatives (Black)  from the main and the retract pack are joined at the receiver. Then the signal wire (White) comes from the receiver, and the power (Red) wire from the retract pack.

How does that sound, any better ideas?

Jeff

Link to comment
Share on other sites

Hi Peter

Thanks for that, good to know.

Now, I can't fit the model in my car in one piece, so I have to unplug the wings to get it home.

Would I be correct that unplugging the servo lead would be the same as having a switch in the circuit? Also since the retract lead would have both positive and negative going into it, if I made up an extension lead with only red and black leads, could I use that for charging?

That's two possible sources of unreliability done away with.

Your thoughts?

Jeff

Link to comment
Share on other sites

Hi Guys
With the Excelsior pretty much done except for the noisy bit, could I express my thanks to all who contributed, with special mention for Peter Jenkins and Nigel R.
Unused to having a clear bench I have decided to wake the Smart Move from its hibernation and do some more on that.
Don't want to clutter up this thread, so I have started a new one, here.
All welcome.
Jeff

Link to comment
Share on other sites

Jeff,

 

No maiden yet?   Do tell all as and when, as it seems that the (not so) Smartmove may be a little way away.   Incidentally the link you posted re foamwings.co.uk doesn't seem to be active, did I see new ownership, website under construction?   Have you found out how to remove the wires from the retracts and beef them up?   Apologies if I missed that, I'm away from home and only intermittently surfing.

 

Peter, 

 

Candidly, my misgivings about spindly servo leads and JR plugs are twofold; firstly I have had to splice a couple of rx packs which are on the bench for servo tester use but mainly, my attempts at crimping were less than satisfactory so it's sour grapes.

 

BTC

 

 

 

Link to comment
Share on other sites

Hi Bruce

That link should take you to a page that does say 'under new management' but it should also include a mobile number for Geoff Hodgson.

If it doesn't, here you go  07966 084294. I have contacted him a few times now on this number.

Haven't taken the legs off mine yet.

I did find some wheels with a thin enough hub to use the existing axles. Trouble is they are plastic wheels and I would question their strength on a 9 1/2 lb model. Can't really beef up the legs, but if the wheels do fail, I can get new legs modified with a longer axle, so I can use some alloy hub ones Bondaero sells.

That's the plan anyway.

I've been crimping my own leads for quite a while now, and generally produce a satisfactory job. My question would be that I understand servo plugs are only good up to about 3a. Won't get anywhere near that on one servo, but running 4 x digitals and 1 x analogue the lead from the battery to the receiver is suspect.

I got round that by fitting two leads from the switch to the receiver. Ideally I should have plugged them into sockets at  opposite ends of the receiver but didn't have enough spare sockets, so they had to go in side by side. Near enough.

Sadly, no maiden yet. Waiting for wind and rain to die down, but also trying to persuade a clubmate to join me. Need to do a 'motor running' range check, which is only safely done with two people.

Don't worry, it's not going anywhere.

If you're intermittently surfing, does that mean you're in Cornwall?  ??

Jeff

P.S. pm sent

 

Link to comment
Share on other sites

Bruce,

 

the trick with crimping for me was getting the right pair of crimping pliers and a pair of needle nose pliers.  I use the pliers to press the two end flaps together to hold the plastic outer in place on the pin/socket and that stops the wire dropping out as you crimp!  The second set of pliers I got have a spring loaded action to give the correct pressure to the crimp.  I can now usually hit a 90% success rate - still have the odd cockup so best to have some spare pins and sockets handy!

 

Jeff

 

Interestingly, there was a similar issue with the apparent rating of the Powerbox Digiswitch.  However, on closer examination, it turned out the switch would take 10A and not the 6A quoted.  I have never run more than 7 servos in a model.  However, these were all Futaba digitals and only had a single wire to from the battery to the Rx.  Never had a problem.  With more than 7 servos, especially digitals I think there are different power lead arrangements now offered which are much thicker wire with heavier gauge connectors.  I guess if I were to stall all 7 servos simultaneously there might be a problem but so far, I've not managed to do that with the 4 aileron, 2 elevator and 1 rudder servo that make up the 7 in my Citrin Biplane.

 

Peter

Link to comment
Share on other sites

Hi Guys
Just in case you hear a strange rattling noise in the background, don't worry, it's only my knees knocking.
As you may have guessed, I finally got to maiden the Excelsior.
Just a quick 5 min shakedown, so no conclusions, just a few things to think about.
However, took off, flew around a bit and landed pretty much on one piece, so that's a win in my book.
First time starting right side up, on its wheels. Seemed reluctant to hand start, but came to life readily enough on the starter.
With the short u/c legs the model sits pretty flat to the ground, so didn't want to unstick. Had to haul it off with the rough approaching at speed. Might have to feed in up elevator a little earlier in the take off run.
More practice needed.
Also wondering whether lower pitch prop might give me better acceleration.
Noticed too it wanted to climb steeply under power. Could be c/g, incidence issue or needing some down thrust.
Kept it high this first flight, so couldn't really tell how it was under partial power. Next time I'll try some lower passes at different throttle settings, get a better clue what it needs.
Did try a couple of rolls, just for fun. Seemed pretty axial, but a little slow to my taste. Might need to wind up the movement a little.
Landings too require a change of system. Coming in with the nose a little high, model just floats the length of the field. First approach with the end of the field rapidly approaching, needed to open up for a go-round.
Motor took a couple of seconds to pick up (how I missed the instant response of electric).
Second approach was a little better, but I let the nose drop a bit on finals, and the model came down with a bit of a thump.
No damage done, just one of the legs bent a little so have to sort that out. Pleased to see those spindly plastic wheels survived intact.
Probably need to refine the needle settings a little.
One question:
With a pumped motor, does it really need tanks pressure? Reason I ask is once it was down, I noticed the pressure pipe had come adrift from the manifold. Not sure when this happened, could have been any time.
Did notice at one stage the tickover sounded a little rough, sort of like a 4 cylinder car on three cylinders.
In general the sound on the pipe was not obtrusive at all. In fact at height and a particular angle couldn't hear it at all.
Wondered if I would be practising my dead stick landing early.
Anyway, all in all nothing really serious. Successful maiden in my book.
Onward and upward
Jeff

Link to comment
Share on other sites

Congratulations Jeff!

 

No, you do not need tank pressure with a pumped engine.  On my Gangster 75, the tank is on the CG and the pump feeding the ST90 does so without any exhaust pressure.  All works very well.  Remember to plug the exhaust outlet to avoid altering the pipe operation with a leak!

 

The slow pickup on opening the throttle indicates the slow running mixture is too rich.  If you can tweak the slow running jet while the engine is running close it 1/8 turn at a time and check the pick up from idle otherwise you have to stop the engine to adjust the idle screw.  Another way of checking for too rich an idle mixture is to measure engine speed as you remove the glow plug.  If too rich, revs will drop as the plug gets cooled by the excess fuel.  If there is virtually no change in rpm then the idle mixture is spot on.  You'll know when you've gone too far as the engine will die when you open the throttle.  The slow running jet is in charge up to 1/2 throttle by the way.

 

Sounds like the main wheels are too far behind the CG if you are having difficulty rotating for take off.

 

Have you checked the wing and tail plane incidence as well as the engine thrust line?  Models of that era were generally zero degrees for all those measurements.  If wing and TP incidence is zero ref the datum then you will need some down thrust.  What you are looking for is no disturbance in attitude as you rapidly open or close the throttle.  The aircraft will climb eventually under full power as the lift will increase with greater speed and vice versa.

 

Hope that helps.

 

Peter

Link to comment
Share on other sites

Hi Peter

Thanks, that helps a lot.

Ok, I'll try without tank pressure. Easy enough to block off the pipe connection, but I assume the vent pipe to the tank has to be left open to allow air in.

Even with ground running the pick up seemed a little hesitant. My clubmate who got it going for me, and found approximate main needle settings didn't play with the slow running.

Weather permitting, might spend some time at the field just optimising needle settings. Worth doing now I know it flies.

Not sure about the wheel position. Bear in mind it's a tail dragger, so having established that the given c/g is pretty close, the wheels are well in front of it. My thinking is that, with the u/c legs so short the wing is pretty flat in relation to the ground. Most of my other models have this at quite a positive angle and basically fly themselves off the ground once unstick speed is reached

Haven't checked incidences yet, so that may well provide a clue. Did notice that the builder had glued some thin ply strips to the fuz wing cut out. There is one layer at the front but two at the rear, so should give the wing some positive incidence. Whether that's as it should be, I can't say.

I believe the datum for these measurements is the top edge of the fuz. That could be an issue, because it has been sanded to a curve and then covered. Any other ways of doing it?

One thing puzzling me is that the pipe tunnel on the wing doesn't match the fuz. Looks like that was fitted before the builder decided to add those ply strips.

 

709063246_DSCN00011.thumb.JPG.9e894897937b25a3624869e2ffa2107c.JPG

 

Either way, some figuring out to be done.

Jeff

 

Link to comment
Share on other sites

Hi Jeff

 

Yes, the tank vent needs to be open to atmospheric pressure or the fuel will gradually stop flowing and or the tank will collapse!

 

For some reason, I thought it was a trike u/c!  Did you get the tail up on the take off run or was the tailwheel on the ground all the time?  It sometimes helps to get the tail up to allow the aircraft to accelerate faster and then rotate the tail down to unstick.  Normally, aerobatic aircraft have so much power they just get off the ground in a very short distance.  If the wheels are a long way in front of the CG then, as they are retracts, you are a bit stuck on getting them further back!

 

Doesn't matter what you pick as your datum so long as you always use it.  Alternatively, set the wing to 0 deg and then check the others against it.  The shimming strips you can see may have been used to zero the wing incidence against datum - can't think of why they would be there otherwise.  Obviously only found this late on so the pipe tunnel is not flush with the rear fuselage presumably.

Link to comment
Share on other sites

Hi Guys

Couple of people have asked about removing the legs from the retracts. My first landing on the maiden was not perfect, and slightly bent both of the legs. Not by much but they wouldn't slot back into the wing recesses, so I had to pull the legs to straighten them.

Operation proved to be easy. Just as well, I might need to do this often.

Anyway, disconnect the operating rods from the units then pull them out. The builder of mine used some ordinary wood screws to hold the units in, which seemed , at first, to be an odd choice. However I have had the units in and out a few times now, and the screws still do up tight, so I'm sticking with them.

So, once the units are out you can see the brass barrel they pivot on. In the middle of this barrel is a grubscrew. Just loosen that and the legs slide out.

Easy as.

I was dubious about the strength of the plastic wheels. They survived a heavy landing ok, but just in case I bought myself a couple of spare legs from 4-Max.

Overall length from coil to end is 120mm, but the bend is in the wrong place. I figure if I can beg, borrow or steal the gear to bend the leg straight, then make another bend further down, this would give me about 25mm axle length, enough to use alloy wheels from Bondaero.

There if I need them

Jeff

Link to comment
Share on other sites

Hi Peter, couple of things

Should have mentioned earlier, but I read the review of your book in the current RCME.

Spoke very highly of it, which we already know is correct, but I wonder if it might introduce your book to a wider audience. Let us know if you see a surge in sales.

Having done a fair amount of bench testing and then the maiden, charged up the LiFe and it only took 137Ma. Sounds pretty good to me.

I had heard that LiPo's don't like to be 'topped up', that is frequent charging by small amounts. Not sure whether that's true, and whether it applies to LiFe.

My thinking is to charge after each session, so I know the battery is fully charged before the next session, but is this wise?

Finally, I was looking at the Thunder Tiger website, and it recommends a 16 x 8 prop rather than the 16 x 12 fitted. Wonder if this might be a better bet. My field is pretty good, but the runway is rather short. On the maiden I found myself having to haul the model off the deck to avoid running into the long grass.

Thinking the lower pitch prop might accelerate faster, sort of like starting a car in a lower gear.

What do you think?

Jeff

Link to comment
Share on other sites

Worth trying the 16x8.  You will get more power at take off and so acceleration will be better.  See how you get on with that.  

 

The best engines for aerobatics today are the YS range which are significantly more powerful than most other engines.  2 strokes ended up being very high revving and noisy so were replaced by bigger 4 strokes.

 

You generally don't top up the LiPos in flight packs.  However, the smaller LiPos I use in my 2 mtr birds are 850 mAh capacity.  They are good for 5 flights.  Each flight takes about 80 mAh so I rarely go below 50% capacity.   I would recommend you start with a fully charged pack, fly 3 flights and then recharge to arrive at average consumption per flight.  Remember though that I tend to fly the same schedule which takes between 7.5 and 8 mins.  

 

I don't know if there is a technical reason for not topping up LiPos - they don't lose charge like NiMHs do though.  I only top up my flight pack LiPos if they drop below 90% indicated capacity - a very rare occurrence.  My radio packs get charged every time I've used them but only when I expect to fly the next day.

Link to comment
Share on other sites

  • 2 weeks later...

Hi Guys
So, second outing for the Excelsior, and a disappointing end to it.
Suffered my first dead stick for many years. Had a lot of height in hand so coped with that ok. Second flight not so good.
Lining up for a landing approach, and the model just did not want to come down. In hindsight, many things I should have done, but eventually it overran the landing strip and dumped in the long grass beyond.
Wing was undamaged, apart from bent u/c legs, but the fuz not so lucky.
Ripped out one of the wing bolt brackets and took a large piece of the doubler with it, and also broke the front former that holds the wing dowel, and the flat base under the pipe mount just fell out.
All should be repairable, but I'm disappointed that a relatively soft crash should cause to much damage.
Also, since this area has the motor on the front and the wing mounting on the rear, will have to be careful to build enough strength back in.
Anyway, this model back on the repair list, and a good dose of head scratching.
Couple of oddities.
Trying out the 16 x 8 prop in the hopes of getting better take off performance. Didn't get that, still had to haul it off before I ran out of runway, but I did notice a lot more noise, due to higher revs.
Have to say with the lower pitch, seemed to have a good vertical, but then was adequate with the 16 x 12, and a lot quieter.
Second, the nose structure is a bit odd.
Looks like the builder used veneer as doubler rather than thin ply. Nothing wrong with that, except he fitted it with the grain lengthwise, where I would have thought grain vertical would have been better.
Anyway, lots to ponder.
Jeff

Link to comment
Share on other sites

Jeff

Sorry to hear all is not going well.

One of the other reasons for having to "pull" the aircraft off the ground could be that the wing sits at a negative AOA when on the ground.  Lengthening the nose leg is one way to solve this or shortening the main legs.  Neither of these solutions might be feasible for your installation though.  

The other thing to consider is that the more you repair the airframe the more the weight will tend to increase.  More weight equals a reduction in performance as the wing has to generate much more lift particularly when the additional weight is multiplied by 10 to 15 times to replicate the G you might be pulling in manoeuvres.

Peter

Link to comment
Share on other sites

Hi Peter, thanks for the quick reply.
First of all, believe I mentioned that this model is a tail dragger, so no nose leg to extend.
On the ground the wing does have a positive AoA, although not much.

 

DSCN0002.thumb.JPG.cafb1149da9d7413a80ca75babebf6b5.JPG

 

Note also minimal prop clearance

 

DSCN0004.thumb.JPG.99ec6fbac3e09214d0d720841667331c.JPG

 

Have to say once up to speed on the ground, unstick is fuss free. I'm not dragging it off on the verge of a stall. In fact, with the 16 x 8 prop, it went into a respectable vertical climb.
Just looks inelegant.
My main concern is how fragile the front section is, and the amount of repair work needed.
This is the section that connects the motor bulkhead to the wing mounting, but a relatively innocuous hard landing has broken it into pieces.

 

464434386_DSCN0001-0011.thumb.JPG.37ef6e561bef1d56f4850526968102dc.JPG

 

1054335855_DSCN0002-0011.thumb.JPG.71c88b63ecb491a476cd4db6f598b966.JPGAppreciate

 

Appreciate your thoughts on adding extra weight, but I need to make this area stronger.
Back on the bench and more head scratching needed.
Given the Smart Move keeps on throwing up issues as well, wonder if I will ever meet you in competition.
Time will tell
Jeff

Link to comment
Share on other sites

19 hours ago, Jeffrey Cottrell 2 said:

Looks like the builder used veneer as doubler rather than thin ply. Nothing wrong with that, except he fitted it with the grain lengthwise, where I would have thought grain vertical would have been better.

Some years ago Marvic Models churned out a number of designs (including iirc some DSM ones) with pre-built fuselages.  I had their Wolfgang Matt Joker and found that too used veneer as a doubler from the wing seat to the engine bulkhead so I don't think it was the builder of your model's idea but the kit supplier.

Link to comment
Share on other sites

Hi guys, thanks

Bob

Agreed, veneer does make good doubler material. in fact I have used it myself on some smaller models. What I would question is using it with the grain in the same direction as the balsa sides.

To my way of thinking, it contributes nothing to the strength. A close look at the damage on mine shows the impact has split the material along the grain, balsa and veneer both.

In my opinion it should be across the balsa grain, or at least on a diagonal if the veneer sheet is not wide enough.

I understand that DSM supplied their fuselages jig built, same as Marvic. Can only imagine if they did it this way, would have been for economy of material.

John

Agreed that would be one way to go, but there is a problem.

Where the wing mounting bolt tore away, it took a big chunk of the doubler with it. Came away clean, couldn't see any traces of glue. On the same basis, I have no idea if the doubler in the front section was glued in properly.

If not, then the glass would be adhering to a surface not necessarily secured to the fuz side.

Long winded operation would be to strip and replace all the veneer from the engine bulkhead to behind the wing seat. Then, possibly to glass the bay behind the motor bulkhead for extra strength and fuel proofing.

Would mean stripping out all the fuz fittings. I had to do that with the Smart Move, and not sure if I want to get into that again.

Going to put the whole plot to one side for the moment, give it a good dose of thinking about.

Only good thing to come out of this, if it does come down to serious surgery, means I have an excuse to pull the motor out and give it a good clean. Been wanting to do that for a while.

Watch this space

Jeff

  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...