FTFC'18 WWII SAM-7 designed by FoamyDM

[FoamyDM]

This Build thread will tackle the Russian Fighter Escort Moskalev SAM-7 "Sigma" in the great effort for Russia to design effective Tailless Craft for the promise of greater maneuverability, speed, fuel efficiency and larger threat zone in combat.

The project is spurred on by the FliteTest Forum Challenge for WWII Concept planes

I choose the SAM-7 because it looks like a fighter version of the Kalinin K-12 (Build Thread here) which I am also taking on. I found the SAM-7 as a familiar styled silhouette on the bottom of the Kalinin K-7 model Kit page. dug around and found the link above. There isn't a whole lot more to say on this yet but stay tuned.

Here are some Concept Drawings:

And a lego version:

History (lifted from HERE)
A.S.Moskalev was an outstanding Soviet aircraft designer who created a lot of unconventional projects, many of which were built and successfully flew. The SAM-7 was an extraordinary tailless all-metal aircraft featuring the delta wing with two fins on its edges and a short fuselage with the separate pilot and gunner cockpits. The plane was powered with the M-34 engine (750 hp) cooled by the vapouring radiator in flight. The retractable conventional radiator housed behind the pilot's cockpit was used on low speeds and on take-off. The wooden propeller had four blades. Airplane's armament consisted of four 7.62mm ShKAS machine guns : two above the engine and two flexible - in the gunner's cockpit. The SAM-7 was built in 1934-1935 and was initially tested on the aircraft plant airfield. Despite good characteristics the whole program was cancelled by the VVS in favour of the same delta wing tailless bomber K-12 which entered small series production on the same plant a year later.

SAM-7 "Sigma" data:
Length .........................7 m (23 ft)
Span........................9.46 m (31 ft)
Wing area...............20 sq.m (215 sf)
Take-off weight.........1480 kg (3262 lbs)
Wing Loading 74 kg/sm (15lbs/sf)

Anticipated Dimensions for - A-Pack 1:20 Scale
Length .........................350 mm (13.75")
Span........................470mm (18.5")
Wing area...............695mm^2 (10.75 in^2)
Take-off weight.........250 g (8.67 oz.)
Wing Loading 0.36 g/smm (0.8 oz./si)

 

[DamoRC]

Cool! - Looks like an FT Arrow with a vintage car body sitting on top!

DamoRC

 

[FoamyDM]

That's what I was thinking! With a mother-in-law suite out back

Rough Plans in an hour or so.

 

[FoamyDM]

Here's the link to the ALPHA Drawing. It's Printing right now, and well, We'll see. 2 hrs 15 mins.

https://drive.google.com/file/d/0BzBs1R9ENrQIZnRGSmltRlVyVXc/view?usp=sharing


Comment as you like.

 

[FoamyDM]

Note to self - spar nubs are too big. Gap in fuselage undercarriage at the flaps. Tip doublers may not help. 5G servos or lighter. Work on back top and cockpit. Wing arc is perfect. Spar notch is too low in fuselage. Front ledge need improvement to be able to round bottom too.

I love how it looks. I'll post pics tomorrow. Pics from phone directly are over 2mb.

 

[FoamyDM]

Here are the Promised Pics. It looks SO tiny.
Plans Mounted and Cut:


Pieces Cut and Punched Out:


Wings beveled curled glued and ready:


Curling the Engine Cover:


Fuselage - The back needs some help:


Bottom View - note panel section added, oops (same width as flaps)


View from the Back - This is ready for Servos and Wing Tip rudders.


Any suggestions on how to get the back looking right?

 

[FoamyDM]

Revisions updated for Drawing R1

https://drive.google.com/open?id=0BzBs1R9ENrQIOW5yNjh6YnhWUTA



Larger Cockpit, improved backend, corrected mistakes. ready for build 2.

 

[Namactual]

That looks good...

...but...

...how do you build these so quick?

Seriously though, it looks good, keep it up.

 

[FoamyDM]

In short, thank you!

In long...
1. I'm an engineer with drafting skills. I have the templates already set. And a great 3-view plan to work from.
2. Note the post time on the note to self message - I start building @ 10:30 ish. I setup a movie/show and get it done. Note electronics are not part of the time.
3. I'm inspired. I work on projects that take months to plan and years to build in my profession, it is REALLY cool to have an idea in my head on Monday and have a tested flying model by Friday. Now if I built the needle foam cutter i'd be like LocalFiend but without the MAD piloting skills. He had the '17 holiday challenge designed printed and flying in maybe 3 hrs of work.

Built Rev1(R1) last night. I really like this version. There were tweaks to the plans to do, bit it turned out much more scale. Pics to follow, so you can be the judge.

 

[FoamyDM]

Rev1 Build Update

Below see the Rev1 Build.
The plans have smaller issues now and it looks much better.

Built - Cockpit (Viggen Style):


Front View:


Back View:


Cock Pit - Packing Tape Laminated:


Changes needed for Rev2 Plan:
* The cockpit was 3/8" thin (pull the inner poly), Widen Cockpit by 3/8"
* Rear Panel was 1" to long now... (how that Happen?)
* Add Rear Gunner Glass
* Rear Bottom sidewalls needs trimming by 1/8"

I'm going to get the Rev1 in the air before I build a "Finalized Rev2 Plan".
Note: I will be using 2.5g servos for this project (ran out of 5g)
Last Detail to build is retractable gear and a cowl.

 

[FoamyDM]

I will be putting together 2 versions;
* Basic: like a small FT Arrow, 1 and 2 Channel Elevons. 3 throttle
* Advanced: 6 Channels. 1 Flapevator, 2 or 2 and 5 Ailerons, 3 Throttle, 4 Wingtip Drag Flaps, 6 Retracts (Optional 5 Camara swivel control (or tied to 4 {rudder})

Last night I got a Wild Hair to build retractable Landing Gear.
I used Flagging Wire (0.6mm), Popsicle Sticks and tongue depressor pant, and a control Arm piece for the linkage. need's a tiny bit of work but here's the progress.







Battery Note: the original Square bay under the Motor is PERFECT for a 2 cell 1100 mAh Battery. So I'm going to modify the Motor Tray to have tabs out the base, and move the tab slots up in order to remove the Motor Tray Shelf in R1, which would make enough room for a 2 cell , and possibly a mid sized 3 (or my homemade 2200 mAh 2 cell made from a busted 3 cell). That should do for that.

Epiphany: I was trying to find a "springy" rod-like piece to return the push-only Drag flap to return to base, per Hai-Lee's Rutan Vari-EZE article here. I was playing with paper clips thinking it could work if mounted right, but I realized I would need to push them back now and again, and I Don't have a range of spring steel control wire gauges. Then I thought, If I have piece of flat wire, like in a wound spring coil it would be easier to attach and be better suit, my eyes rolled across my keys, and I saw the key tag thingies from various stores - EUREKA I have my flaps. I will use strips of gift cards for the spring. I will either glue directly, or mount to an embeded popsicle stick with Servo Mount screws. This definitely be going on both the Kalinin K-12 and this SAM-7 Sigma.

Next up will be the wingtip drag flap push mechanism, Detailed below.


Progress pic thus far:






FPV - Lastly, I mentioned wanting to throw my Micro Camera on a rudder tied camera. I realized I will need a Cockpit for that. I'm thinking print and glue this to the inside area:

I'm hoping to maiden these this weekend. I shall post updates as I can!

 

[FoamyDM]

Here is an updated PlanSet Rev3. Added Cowl panels, back window (trim to size) and adjusted motor tray.

REV 3 plan post (SAM 7 v1.2)



Enjoy the weekend!

 

[FoamyDM]

Update: I have never worked with landing gear... Ever. So what I made wasn't precise enough and had front to back wiggle which made it catch and mess up the servo. I am using 2.5g and am out of 5g. 9g is too big for this.

Cg point seems ok in glide test at the rear edge of the gear at 1.5" from front wing edge.

The Wingtip spring works. But my stick pusher... Didn't. :black_eyed: it sits too low on the Sam and I add a rocker-arm pusher. Works great on one side, but not on the other. Haven't figured out why yet.

The simple version should be ready to test tomorrow. *crosses fingers*

 

[FoamyDM]

If you care, enjoy the vid on my flap test.

Note: marginal movement on the drag flaps.

 

[planebreaker2000]

Good progress.

 

[Namactual]

Still looking good, I am keeping a close eye on on this.

Good luck with the maiden!

 

[FoamyDM]

Maiden attempt: failed like a leaf on the wind.

This failed like a leaf on the wind. The balance point wasn't right. In never did the clalculator in this one. Just went with 1/3 wing chord. I'd love to see your thoughts on what to try.

This is so small and has such small wheels it didn't work on the pavement. Shoulda tried the sidewalk, just didn't register until after.

Any thoughts, I'm all ears.

my 2nd motor was twitchy for some unknown reason, so I will have to get that figured before maidening the K-12.

 

[FoamyDM]

I took weights measurements.
139g without batt.
186g with 500 mAh battery.

 

[Hai-Lee]

Whilst the 25 to 30% cord is OK for conventional aircraft, for a tailless design the percentages Are around 20% as a very rough starting point though even further forward is OK if the model is Very light Just an increase in reflex angle can compensate easily.

As your plane is quite small I would suggest that you fix the gear and the rudders and add some tail steering for taxiing.

Fly it as a yank and bank until it is flying and then reintroduce the rudders and retracts if still required.

Great work so far, Keep it up!

have fun!

 

[Michael9865]

I second the start with the CG at 20% and glide test into tall grass. You can play with the CG and not worry about hurting it. Something as small as your plane will take a few practice throws to figure out how gentle of a toss is correct. Reflex is usually around 2-4 degrees if memory serves me correctly, I have had luck with 2 and 3 degrees before. Keep working on it.