Douglas DC-9 in 1/72 scale

[MacSongLi]

Very nice Isaac. I love your idea of the dowel with the hole drilled in.


Gary

[Erik Zwaan]

Looking good Isaac. The upcoming wing-fuselage fillets require quite a bit of patience and I used construction kit with a similar color to fill up the small gaps I remember. Think that was the hardest part of the build .

Erik

[Isaac]

Originally Posted by Erik Zwaan

Looking good Isaac. The upcoming wing-fuselage fillets require quite a bit of patience and I used construction kit with a similar color to fill up the small gaps I remember. Think that was the hardest part of the build .

Erik

Erik


Yes, Those wing fillets do not fit properly and I had a super hard time with them. Still not happy. That is my one major issue with this model.

Pictures soon.


Isaac

[Isaac]

The DC-9 wing to fuselage has a fillet consisting of four parts. Forward, aft, center bottom and center top.

I knew fitting this will not yield good results.



here are the forward and aft sections glued. Notice I used a wood piece in the center instead of the card ribs which I could not fit well here.


bottom is shown here. The fit is bad for me and the color is different than the metallic belly. I don't have the reference color on the bottom for the Eastern plane , so I do not know if the light yellow color is correct.



Here is the top fillet which is a thin flat part. I did the best I could here and I may need to revisit this section




I am not happy here and if I build another DC-9, I will look into a different joining technique.



Isaac

[Isaac]

Here it is so far



Isaac

[MacSongLi]

Isaac,


You still finished the fillets with a pretty good result. I believe that colour is supposed to be corroguard.


Gary

[Isaac]

Originally Posted by MacSongLi

Isaac,


You still finished the fillets with a pretty good result. I believe that colour is supposed to be corroguard.


Gary

I wonder if I pre assembled the lower front, center and aft fillets first and then attach to the fuselage/wing if it would be better.

One issue is that the blank coloration on the fuselage where the fillets goes is exact fit in perfect condition. Maybe it should have been colored the same as the lower fuselage with a thin outline.


Anyhow, another lesson learned.


Isaac

[Isaac]

The DC-9 series as well as the Boeing 727 and early 737 used the first generation Pratt and Whitney JT-8D engines. These were low bypass fan jets.

They had a primary core and also a secondary flow path ducted around the core and remixed at the exhaust. One advantage these ducted engines had is they were relatively quieter than a turbojet since the fan air was cooler and mixed at the exhaust to "quiet" the engines. Thus the name Whisper Jet.

Pratt & Whitney JT8D - Wikipedia

Later generations of the MD-80 were powered by a larger growth versions called the JT-8D 200 series. While more efficient, the low bypass jet engines on commercial passenger and cargo planes came to an end in favor of the High Bypass fan jets like the CFM-56. However, small business jets have continued with the low bypass for a bit longer because speed was more important than efficiency.


The nacelles are smooth full length and unless you knew the details, you could not see the fan bypass duct inside.


Also, the nacelles had a clam shell type of thrust reversers that were flush when not active and then slide aft while blocking the exhaust and diverting a portion down and slight forward. This action was used not only to slow the aircraft on landing, but also push back from the gate at the airport terminal without the use of a tow vehicle common today. The reality is that it is a bad practice to use thrust reversers when the aircraft is static or even below 60 kts or so because the exhaust gasses will mix with clean air at the inlet that may cause a stall condition. Secondly, there is all sort of sand and debris on the tarmac and you don't want to ingest those in. lastly, you burn up engine parts by going to high power on the ground un necessarily.


TR in deployed position ( during maintenance )



TR airflow figures





backing up




Isaac

[Isaac]

Now that you know about the engines on the DC-9, here is the model build.

The design is relatively simple and consist of circular sections mostly

Here is the location for the engine pylon on the rear fuselage. I decided to glue the rib to the fuselage first.



here are the nacelle parts



sub assemblies



engines completed



here are the pylons along with the nacelles


pylons glued to nacelles



ready to install



I added a small wood dowel to support the overhanging nacelle better



dry fit first




engine nacelle is now glued


underside view
Note : It would have been a better practice to design the nacelle axial glue seams to be under the long pylon. This way they would look smoother on the bottom.



both nacelles are on now.



Isaac

[MacSongLi]

Very nice work, once again Isaac. I'm wondering if it would be better to put the seam on the same side as the pylon?


Gary