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Warbirds Replicas P51 Mustang


RICHARD WILLS

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On 22/02/2021 at 06:49, Paul Johnson 4 said:

David

The NTM 4248 650kv with the Dynam 13x7.5x3 is a great match. On a 4 cell 3300mah you'll get 4 to 5 mins exciting flight times.

The NTM 5050 580Kv on the standard FMS 4 blade 14x8x4 is an approximate equivalent. With about the same performance.

The FMS Mustang uses a 540kv standard motor so the 580kv is a 'hot replacement. A little bit like replacing the Alison engine with the Merlin.?

 

Gents, having received the NTM Propdrive v2 5050 580kv (2 of them) from HobbyKing, I was impressed by the heft of the unit, but noticed very quickly that the bolt on adapter has a different thread than the clamp on one. Both M8 width, but the bolt on has a narrower pitch thread and as such will not work with what I call "standard M8". Lo and behold, the beautiful alu spinnner shaft extension doesn't fit! Arrrggghhh! 

 

I have a query in with HK product support asking if they can explain exactly why on earth they chose to use a "non standard" M8 thread for the bolt on adapter, but not had a meaningful response from them yet. I was hoping to use this motor for the P51 when I get around to building it and am now a bit stumped as to what to do.

 

I had planned to put my 4248 650kv in the spit, which itself isn't devoid of issues: The bolt on adapter is so short I need to use a counter sunk nut if I plan to use the deep hubbed dynam. This also eliminates the possibility of using the shaft extension from the other Alu spinner I received for the Spitfire! Thoroughly regretting not getting hold of FMS units right at the moment!

 

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Spinner adapter nuts are a frequent issue. Usually the problem is the other way round - trying to fit a spinner aimed at i.c. Engines (which usually have imperial threads) onto a metric prop adapter. Once you know what thread you’ve got (sounds like it may be 5/16 unf ?) have a look on eBay. It’s come to my rescue several times.

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17 minutes ago, Trevor said:

Spinner adapter nuts are a frequent issue. Usually the problem is the other way round - trying to fit a spinner aimed at i.c. Engines (which usually have imperial threads) onto a metric prop adapter. Once you know what thread you’ve got (sounds like it may be 5/16 unf ?) have a look on eBay. It’s come to my rescue several times.

 

Thanks Trevor. I've ordered a silverline thread identification tool off of amazon for 70p (plus £3.89 shipping!!) - hopefully I'll be able to identify the thread using that tool. Beggars belief as to why HobbyKing chose in their wisdom to provide a motor which has different threaded prop adapters for bolt on vs clamp on, but hey ho...

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2 hours ago, David Hazell 1 said:

Oooh, searching for adapter: 

 

https://hobbyking.com/en_us/brass-nut-for-spinners-m8x1-m4-1pc.html

 

Ordered this. I can't find an equivalent to what Richard provided with his spinners, unfortunately. 

 

These were made for him specifically and based upon his original suggestion of using the predator. I must admit I had the same issue with the 5050 and had to make one specially for the plane I got it for. Have you noticed that our hobby is a series of 'problems' to overcome.

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Just engines do a large range of adapters for spinner attachment plus ones where there isn't enough shaft thread sticking out beyond the prop hub, common issue when using Dynam props.

 

This is the one that I made to get over that problem (spinner is not shaft mounted).

95CEF369-EBB3-4E36-81D8-43D1F6E89AD2.jpeg

3995C46A-9E93-489F-BEA4-226959F5E4C8.jpeg

Edited by Ron Gray
Forgot photos
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1 hour ago, Ron Gray said:

Just engines do a large range of adapters for spinner attachment plus ones where there isn't enough shaft thread sticking out beyond the prop hub, common issue when using Dynam props.

 

This is the one that I made to get over that problem (spinner is not shaft mounted).

95CEF369-EBB3-4E36-81D8-43D1F6E89AD2.jpeg

3995C46A-9E93-489F-BEA4-226959F5E4C8.jpeg

 

Beautiful job there Ron. I think Richard posted something very similar to this a few pages back on this thread. I found these on eBay and ordered some which arrived from china - I ended up with 25 of them, but I may find another use for them. I don't know if I will have to do something to get them to balance or not:

 

https://www.ebay.co.uk/itm/M4-M10-Square-Tee-Type-Carbon-Steel-Weld-Nuts-Machine-Screw-w-Projections/362632985898?ssPageName=STRK%3AMEBIDX%3AIT&var=631773939121&_trksid=p2060353.m2749.l2649

 

on the 4248, I do have the M3 female threaded centre on the  bolt on adapter I can use to attach the spinner - don't know if it will be man enough though...

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I am working on completing the nose section and considering how to instal the sound system. I am planning to mount the transducer (speaker) on a 2mm depron
 sheet. This will be screwed or bonded onto the lower side members which attach the bottom skin on the forward fuselage, just after the cowling. I am wondering what diameter of hole to cut in the bottom skin to allow the sound to exit. Does it need to be the same diameter as the transducer or larger. Will it work if the hole is covered in some sort of material similar to hi-fi speaker?

Any advice very welcome.

 

 

IMG_8738.jpg

IMG_8743.jpg

IMG_8741.jpg

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Gordon before you decide where to install the speaker check your C of G, I have not fitted mine yet as have been looking into other issues with a previous partially finished build. Eric mentioned that with the 4000mAh battery she is nose heavy I would visit this install towards the very end before committing to it. When i get the chance I will have a look. As I have put an open radiator in the mid section this might be the place for it but cannot confirm this yet. Obviously this is dependent on what battery you use to where you could/can fit it. If you look at how I left myself the option to remove the battery tray to access the lower nose for a retrofit it gives more options to any balance issues in putting unnecessary weight onboard.

 

 

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43 minutes ago, Paul Johnson 4 said:

Gordon before you decide where to install the speaker check your C of G, I have not fitted mine yet as have been looking into other issues with a previous partially finished build. Eric mentioned that with the 4000mAh battery she is nose heavy I would visit this install towards the very end before committing to it. When i get the chance I will have a look. As I have put an open radiator in the mid section this might be the place for it but cannot confirm this yet. Obviously this is dependent on what battery you use to where you could/can fit it. If you look at how I left myself the option to remove the battery tray to access the lower nose for a retrofit it gives more options to any balance issues in putting unnecessary weight onboard.

 

 

Paul, very sensible advice, thank you. The transducer is quite heavy (I must weigh it) and will certainly move the CG forward if I instal it in the front fuselage. I will follow your advice and make provision for the sound system in the front and rear fuselage as retro-fit possibilities. Better to keep the options open until I find the likely CG location! 

 

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