Hangar 9 P47 repair

[Geoff S]

About 4 years ago an engine cut after trying to apply power as I climbed out from a low pass forced me to attempt a 180 degree turn back to the patch (or somewhere near). The inevitable result was a tip stall and crash. The fuselage was seriously damaged as far back as the wing and the wing is less seriously damaged.

I bought replacement fibreglass parts (cowl and wing belly-pan) very soon afterwards but the actual repair has been delayed. However I determined to repair it over winter once my Ryan ST is finished, hopefully early in the New Year. I've had to clear the 'garage' (ie bike shed, wife's garden shed, large mode storage hangar and general junk store) this week because we're having the asbestos roof replaced so the P47 wing has ended up in my workshop a bit earlier than I'd intended.

Here's the damage: Not too serious but I need to remove the retracts to do a proper job:

As you can see, I've managed to remove one but there are still 2 screws I cannot shift in the second.

All the screws were very tight but by spraying some lubricant on them and leaving overnight I succeeded in unscrewing 6 of the 8. I just cannot apply enough torque to turn either of these even with a long, well-fitting screwdriver; the screwdriver simply rides out of the slot. The screws I've removed are slightly corroded and I think that's what's holding these final two.

I've tried drilling but the heads must be hardened because even a decent bit won't touch them. Any ideas for getting them out? If they won't come I have a plan B which involves cutting round the holes (the retract flange is plastic) and exposing the screw shank and using a Mole grip to unscrew. I'm sure I can think of a way to refit (ie bodge) the retract afterwards.

Geoff

[Kim Taylor]

Without teaching granny to suck eggs, are you sure you had the right type of screwdriver?

Are they Philips, Posidriv or JIS? I don't know what the difference is, but I know it can make a screw difficult (impossible) to remove if it's a tight'n.

Beyond that, as you have suggested, brute force and ignorance will win the day!!

Kim

Edited By Kim Taylor on 10/12/2018 16:30:36

[Denis Watkins]

You can run a single slot deeper, and straight across Geoff, with a Dremel

Do one at a time, and slot enough to fit a hefty straight blade screwdriver

Edited By Denis Watkins on 10/12/2018 16:21:18

[J D 8]

One of those T handle drivers can be helpful. Or if you have a battery drill with variable torque put it on a low setting and see if the vibration will shock the screw free.

[alex nicol]

As above, Dremel a good sized slot and try a flat blade. worst case if you damage the retract lug a washer can always fix that out for you.......good luck.......would be good to know how you get on

[Geoff S]

Thanks for the suggestions, gents. I'll give them some thought. I'm pretty sure I'm using the right screwdriver because it worked OK on the other screws but the differences between the different cross head screwhead types isn't easy to check other than actually trying them. I might have a go cutting a slot with my trusty Dremel before butchering the retract fitting flange.

The model is certainly worth repairing because it flew well before the 'incident'. I'm sorry to inform the glow engine enthusiasts out there that the rebuild will involve a conversion to ... electric power - 6S probably

Geoff

Edited By Geoff Sleath on 10/12/2018 16:59:14

[Jon H]

Posted by Geoff Sleath on 10/12/2018 16:58:48:

The model is certainly worth repairing because it flew well before the 'incident'. I'm sorry to inform the glow engine enthusiasts out there that the rebuild will involve a conversion to ... electric power - 6S probably

Geoff

boooo

[Geoff S]

Success! The Dremel slotting method worked very well. As I thought, both those screws were corroded rather more than the others I removed.

You can see why I needed to get the retracts out but a reasonable repair is certainly easily feasible.

I certainly congratulate Hangar 9 for the sound mounting of the retracts. It looks very solid. Obviously they were retracted at the time of the crash and weren't stressed particularly.

These retracts are mechanical. I'm thinking of fitting servoless electric ones. Any recommendations for a model which weighs around 4kg?

Jon: The engine was a new SC 90 four-stroke (the specified engine is for a 60 2 stroke) and didn't properly recover from the closed throttle run in for my low pass and didn't pick up properly when I opened it up for the climb out. Unfortunately it was heading away from the airfield so a straight descent wasn't safe and my attempt to recover failed. I know you'll say it was because I hadn't set the engine up correctly and I suppose you'd be right but it is a common glow engine problem. I just have a lot more confidence that an electric motor is unlikely to exhibit similar issues and be more reliable.

I assume a Laser wouldn't have been a problem

Geoff

[Bob Cotsford]

I've found the JP Retracts to be reliable and sturdy so far Geoff. Similar to E-Flite but in my experience more reliable, and a drop in for most 60 size models.

Best to check the price with Webbs as it's is marked as 'each'  whereas the last pair I bought were about £99 a pair.

Edited By Bob Cotsford on 10/12/2018 19:06:16

[Geoff S]

Thanks, Bob. I think that is the price for a pair. It's probably like shoes BOGOF (Though my Dad only ever needed one). I'll probably leave it until I've done the repair. I had a separate battery for the retracts when I last flew this in case a jam drained the battery. Is that also a good idea with servoless?

I'll update this thread when I start the repair proper. It was just that I thought I'd remove the gear so I could see how bad the damage is. Then it's rather like intending to drain the swamp and get distracted because you're up to the nether regions in alligators. At least these particular alligators are slain now the screws have been extracted successfully.

Geoff

[Bob Cotsford]

The electric units that I've used have all had overcurrent and stall protection so I've not bothered with a separate battery but I don't rely on the ESC's BEC. Instead I use a large capacity 2S LiFe pack (A123 or at least 2AHr) for the radio and retracts.

[Jon H]

Jon: The engine was a new SC 90 four-stroke (the specified engine is for a 60 2 stroke) and didn't properly recover from the closed throttle run in for my low pass and didn't pick up properly when I opened it up for the climb out. Unfortunately it was heading away from the airfield so a straight descent wasn't safe and my attempt to recover failed. I know you'll say it was because I hadn't set the engine up correctly and I suppose you'd be right but it is a common glow engine problem. I just have a lot more confidence that an electric motor is unlikely to exhibit similar issues and be more reliable.

I assume a Laser wouldn't have been a problem

Geoff

If you would rather use a leccy motor then by all means go ahead Geoff. Its your model at the end of the day.

You are right though. The issue was probably a combination of setup, lack of engine run time, and perhaps an issue with the carb, maybe the wrong plug? The thing that interests me is that even given that you accept a likely setup problem, you go on to say 'its a common glow problem'. I actually agree with the statement, but only so far as i agree that it is a common problem for engines to be set up such that they are prone to failure. I suspect however your intended meaning was more that the underlying principals of glow engines makes them prone to this sort of failure and that is something i would disagree with.

Your point about reliability of electric is interesting too as i have not suffered a random engine failure in over 10 years. And sure i fly a lot of lasers but i fly other brands too without issue. Its easy to set up a laser to be as awful and unreliable as you like, you can with any engine, its not about the brand in many respects. If its set wrong, its wrong and even a good brand will still fall over. It would be like saying electric is unreliable as an ESC caught fire after you constantly ran it 10% over its max current rating with poor cooling. Its the setup that killed it, not the brand or technology itself.

This is not an i/c vs electric, good vs evil post and is not a criticism of you Geoff, and its entirely possible i misunderstood you. I just found your post very interesting the way you worded it.

For your repairs, electric retracts are hit and miss in my experience but the ones bob suggests look good. I would not recommend trying to use anything with too many plastic parts. I would personally use another battery for my retracts. Some of my large sets draw nearly 5 amps so it would be worth checking the ones you use and then making the choice. Im sure Bob is on the ball, but i would not risk it on one of my models given that an extra battery is not very heavy.

One final thing, if you do rebuild it as i/c, perhaps try your laser 80 if you dont have faith in the ASP. If you do, just remember to lower the fuel tank

[Rich too]

you need a nice 20 petrol motor

Seriously though, I have eflight retracts in mine, and they work well. Did you fit the flaps?

Following your repairs with interest, good luck, it is a nice flying plane. 👍

[Bob Cotsford]

Jon, the 60-120 size units listed stall at about 1A, I've tried stalling a leg while monitoring pack voltage and saw only in the region of 0.2v drop before the stall protection kicks in. There's a bit of a surge as the legs first start moving, too quick for me to record, so for scale models where larger wheels need to be lifted I put the legs on separate channels with a delay on one leg.

My Curare uses three units for it's trike u/c and has given zero issues running a single 1700mAH 2S LiFe pack even with all three legs moving together. That uses 'Jetcraft' branded units which appear identical to the JP units.

Oddly the highly acclaimed and highly priced E-Flite units have been temperamental.

For the ultimate in build quality and reliability then you can't beat Lado units, but what a price! €220 EACH, for some reason they all show as 'out of stock' these days.

HK units have proved quite reliable for me, certainly better than E-Flite, only the plastic trunnion versions ever giving me a problem other than where I've had to excavate them from an unplanned arrival site.

[Geoff S]

Rich too: I bought the model on eBay as an unflown project. IIRC I paid about £100 when the price new was about double that. A club mate had a similar model and he'd modified the wing for flaps and I did the same. P47s have flaps that move the whole t/e rather than the more common split flaps so it was relatively easy to do a scalish mod.

As to fitting a 20cc petrol engine, the guy I bought it from had bought one to fit and offered it to me but I decided against it. Can't recall which it was. I have a couple of models with petrol engines. One is a 26cc Zenoah and the other a 30cc Mackay. The Zenoah is quite noisy but the Mackay has a Krumscheid silencer that cost me an arm and a leg (almost!) and is acceptably quiet. It's a pity so few (any?) small petrol engines don't come supplied with decent silencers as glow engines often are.

Jon: Thanks or your comments. I used to run glow engines a lot and reasonably successfully but they do seem to be a touch sensitive. I've seen numerous times in others' models as well as my own when an engine is left ticking over for some time (eg when waiting for the opportunity to take off) they 'choke up' and hesitate or even stop when powered up for take off. I assume that's what happened to me with this model.

I'll probably keep the mechanical retracts at first and retrofit reasonable quality servoless ones once I'm satisfied with its performance.

As for fitting my Laser 80, I think it would go in upright as the cowl is massive, so I guess fuel tank position might not be a problem.

Geoff

[Denis Watkins]

Posted by Geoff Sleath on 11/12/2018 11:37:01:

Jon: Thanks or your comments. I used to run glow engines a lot and reasonably successfully but they do seem to be a touch sensitive. I've seen numerous times in others' models as well as my own when an engine is left ticking over for some time (eg when waiting for the opportunity to take off) they 'choke up' and hesitate or even stop when powered up for take off. I assume that's what happened to me with this model.

This comment is only my belief Geoff, with no science attached, just years and years of sitting at too long an idle

Then throttle up, to Stop

I believe, or IMAGINE, the glow crankcase gradually filling, drip drip with a puddle of fuel

That then interrupts the slow moving conrod in its cycle.

As I say, no proof, but a tuned motor, waiting at idle a long time, just move the stick regularly giving a blast to move that fuel

Pure speculation, but advice given after many many times waiting, then success at idle up to take off

[Jon H]

Bob - 1A isnt too bad to be fair so i can see your thinking. I will always use 2nd batteries though just because its what i will always do. Its not worth the risk to me.

Geoff - yea i know the type of cut you mean. It comes from fuel building up in the intake and then being sucked through in a blob as soon as you open the throttle enough to pick it up. The fuel 'condenses' out in the intake due mostly to excessively rich mixture on the low end (ASP engines are shipped very rich) but also due to the nature of the design. The rich mixture at idle gradually cools the glowplug and produces that gradual coughing run down we have all seen. The excess the fuel in the charge is 'thrown' out of the air as it goes round the corners in the intake causing an accumulation near the valve. Running the slow run needle as lean as you can will solve this problem but ASP carbs are not super accurate so its not always possible to get it 100% on those engines.

In a 2 stroke the effect is similar but the fuel accumulates in the crankcase as Denis suggests above. The only difference is the fuel does not impede to rod but is instead thrown up the transfer passages once rpm rises enough to pick it up. Again, we see it as coughing and stuttering pickup. Its more difficult to get around the problem in a 2 stroke than a 4 stroke, but again running the slow run as lean as you can will solve the problem almost completely.

[Tim Flyer]

Hi Geoff I’m replying here as I have a “soft spot” for P47s . Plus I also think it’s a shame on this particular plane to convert to electric just for reliability. A nice four stroke in it sounds so good😊 The problem with idling for many people on glow engines I have found over the years is that nearly everyone either only sets the mix once or never . Most engines nead an initial adjustment but even so will still run on factory settings. One run in they need another tune on idle . Depending on carb design some slow needles can also loosen with vibration. When we quickly throttle up the engine rpm have to “ catch up” with the amount of mixture being offered by the carb . During long periods if idle the glow plug slightly cools so when presented with a sudden burst increase in mixture it can overcome and stall the engine. The solution is to properly lean the idle mixture which will reduce plug cooling. Some carburettors and engine designs are better than others but if you adjust your laser correctly you should find it very difficult to stall . On one of my club mates laser 70s he had his idle about half a turn too rich... but it still ran . If tuned nicely all decent “sport”engines should have a nice idle and pick up whether 2 or 4 stroke.

[Geoff S]

Thanks for all the comments. I've stored the wing up in the indoors 'hangar' for now until the Ryan is finished. Most of it is framed up (as the Americans say) and I've worked out how to blend from the almost cylindrical fuselage to the wing and all the control surfaces are hinged and pinned ready to be installed. So it will get done and then it will be on to the repair.

I had a quick look at the fuselage and, whilst it looks a bit of a mess at the front, I'm looking forward to some creative bodging. It probably won't be as hard as building the Ryan

Geoff

[Jon H]

However it ends up Geoff im sure it will fly well after its surgery. Apologies if i went too far down the rabbit hole on the engines front

[PatMc]

No doubt Geoff will wear a suitably soulful expression as he carries out the electric power conversion.

[Geoff S]

Posted by Jon - Laser Engines on 11/12/2018 22:55:43:

However it ends up Geoff im sure it will fly well after its surgery. Apologies if i went too far down the rabbit hole on the engines front

No apology needed, Jon. I'm not particularly sensitive about arguments on the pros and cons of model aeroplane propulsion methods. It's merely a personal choice and there are viable reasons to choose either ic or electric (but none for 'leccy or 'gas' - unless it's CO2'!).

The surgery is extensive whatever route I take and a period of convalescence will be required (for me, not the model )

Geoff