HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Oct 09, 2005, 08:45 PM
a.k.a Maltone
Pat Lynch's Avatar
Australia, NSW, Goulburn
Joined Jan 2005
6,966 Posts
Stinson SM-1 Detroiter

In my eternal search for something different but not-too-difficult, I found this excellent 3-view in a local magazine of the Stinson SM-1. A search of RCgroups found only one mention of the Detroiter Jr. so can I conclude that it is not often modelled?
The 3 view shows the basic box frame but the cross section shows rounded top and bottom to fuselage. I can not find any web pictures of the SM-1 frame but quite a few of the Reliant - is it safe to assume that the contruction would be similar, i.e. steel box frame with rounded formers on the top and bottom and lightweight stringers all over (a couple on the sides and a few top and bottom.
Any comments on this as a large-ish slow electric - 60", geared 480 or eqiv, 1kg?
Cheers
Pat
Pat Lynch is online now Find More Posts by Pat Lynch
RCG Plus Member
Last edited by Pat Lynch; Oct 09, 2005 at 09:33 PM.
Reply With Quote
Sign up now
to remove ads between posts
Old Oct 10, 2005, 03:16 AM
Light and floaty does it
Work in Progress's Avatar
Cambridge, Great Britain (UK)
Joined Sep 2004
2,859 Posts
Hi, Pat,
It looks like an ideal RC subject in many ways, only a couple of points that might be worth a thought. The tailplane is towards the bottom of the size range, though it will be OK if you keep the CG well forward. For a non competition model I think I would add 10 per cent to the tailplane all round in linear dimensions, that will increase its area by 21 per cent and give you a wider CG envelope to play with. Not enough to make a visual difference but it will help the flying quite a bit.

The build is going to be easy. The wing looks dead flat and rectangular so no need for washout, and the airfoil is as close to Clark Y as makes no different, so use that arnd you are sure to end up with a good wing. From the drawing it looks rather as if the inner panels are see-through. If that's the case, cover the whole thing in Doculam and then you can tissue, So-Lite or paint the opaque areas over the top. I'm not sure if the centre-section itself is glazed. If so, you will need to think about where to put the aileron servo. And I wouldn't expect too much action from those ailerons, even with zero dihedral. Go with plenty of differential, and I think I'd be tempted to extend them inboard by a couple of rib bays. Actually, adding just one degree of dihedral may give you a wing that looks flat, whereas a truly flat wing generally looks droopy, it's an optical illusion but very powerful. The struts should of course be functional.

There may be some stringers to give a bit of curve into the fuselage cross-sections, but I can't see any on the photo or drawing you posted. If you have them at higher resolution you may be able to see more than I can. I must say, the whole aeroplane seems to have been designed with a rule and set-square, so maybe it had just flat sides. It would almost certainly be welded steel tube on the full size. I like lightweight structures so I'd probably go with a combination of 3/16x1/8 strip for the main members and 1/8 square for the diagonals and the verticals towards the back. Laminated curves for the tail.

Scale size prop should be easy, and if you work out what size it is we can have a think about gearing. I guess it's not going to be too far from what you had on the Lizzie.
Work in Progress is offline Find More Posts by Work in Progress
Last edited by Work in Progress; Oct 10, 2005 at 03:22 AM.
Reply With Quote
Old Oct 10, 2005, 04:06 AM
a.k.a Maltone
Pat Lynch's Avatar
Australia, NSW, Goulburn
Joined Jan 2005
6,966 Posts
Thanks WIP - I'm not sure about those inner wing panels - the drawing shows similar hatching to the windows but I had assumed they were fuel tanks! Maybe someone can enlighten me. There is a large cylindrical tank going right through the fuselage just in front of the dashboard - it shows on external pics - maybe it had lots of fuel tanks? The big wheels are a bonus on our club field - very rough at the moment. Even at 1:10 scale, they are over 3" diameter and the prop 10" - gives span of 55" - the "hot" 480 I have might be a bit much?.
I'm drawing up the plans in Autocad so will scale thimgs to suit the circumstances. I've not found any colour schemes yet - I guess colour photography was a way off in 1926
At 1/10 scale, the wing is about 3.2 sq feet (55x8.4") and if I could manage 32 oz - 10oz/sq ft - maybe a bit light?
Thanks for the tips on the tailplane and ailerons etc - a little dihedral would hardly be noticed I agree.
Still thinking
Pat
Pat Lynch is online now Find More Posts by Pat Lynch
RCG Plus Member
Latest blog entry: A Small Diversion From Annie
Reply With Quote
Old Oct 10, 2005, 05:46 AM
Light and floaty does it
Work in Progress's Avatar
Cambridge, Great Britain (UK)
Joined Sep 2004
2,859 Posts
Ah, yes, I think you're right about them being fuel tanks. That makes more sense, it would have been very unusual to have that part of the wings glazed.
32 oz and 10 oz / ft2 sounds perfect to me, the low wing loading and high-lift wing will give you a sedate cruising speed and you won't need a hige amount of pitch speed. I know when you were building the Lizzie you were thinking of getting a deeper gearbox than your existing 3.3:1 and I think this would be a good home for it.With a 3s LiPo in the range of 1500 mA/h I'd have thought 10x7 prop and 4:1 gearing would be ideal with a bog standard 7.2v Speed 480. That said, if you stick with 3.3:1 then I reckon a 9x6 prop would give you a good run for this model on 3s. Either setup should give good duration and spirited full-throttle climb, combined with a gentle extended cruise around on part throttle.
Exactly what kind of hotted up 480 have you acquired? It might well be more of a Spitfire motor than a Detroiter one... Perhaps Vintage 1 will provide some more finely-tuned thoughts, his power system assessments are far more scientific than mine.
Work in Progress is offline Find More Posts by Work in Progress
Reply With Quote
Old Oct 10, 2005, 06:04 AM
a.k.a Maltone
Pat Lynch's Avatar
Australia, NSW, Goulburn
Joined Jan 2005
6,966 Posts
WIP - the motor/gearbox I have was bought to update the Lizzie but decided to give it a new home: Graupner 7.2V speed 480 race (#6330) and an MPJ 3.8:gb. On a 3s LIPO it calculates at around 24oz in-flight thrust (34 static) with an 11X6 prop. Max current at full throttle is a bit steep at about 17A but would seldom be used. A smaller prop or lower pitch might be possible. I drew an alternate plan for 60" span - to suit an 11" scale prop and the wing area is around 3.8 sq ft. Scale is about 9.2:1. Now I understand how many of the "top guns" get their strange scales - from scaling to suit available hardware! at this scale the wheels are 3.5". They are wire spoked so there is another skill I need to acquire!
Pat
Pat Lynch is online now Find More Posts by Pat Lynch
RCG Plus Member
Last edited by Pat Lynch; Oct 10, 2005 at 06:13 AM.
Reply With Quote
Old Oct 10, 2005, 12:38 PM
Registered User
Mid-Michigan
Joined Aug 2002
2,178 Posts
Great subject. The Detroiter(s) were popular planes for a few years in the mid '20s, but were quickly eclipsed by better planes. But they launched Stinson into the airliner and business-flier market. Stinson got into aluminum sheet construction much too late, so the companies that dominated that market by 1940 were Douglas and Lockheed, however. The Detroiters were indeed a welded steel-tube frame with wood formers, wooden wings, etc. I'm working more on Fairchilds, and the Fairchild FC-2 and it's siblings all had metal tanks in the wing center section, their tops exposed to the weather. If you PM me I'll copy some of my source material, (old magazines), on the Detroiters and email it to you.
uscra112 is offline Find More Posts by uscra112
Reply With Quote
Old Oct 10, 2005, 12:49 PM
Registered User
E-Challenged's Avatar
United States, CA, Garden Grove
Joined Oct 2000
12,229 Posts
I am bogged down on my 42" Berkeley Stinson SR-7 gull-wing project. Couple of "heads up" things that I have learned:

Short nosed scale models usually wind up tail-heavy. I had to mount 8 KAN 1050 2/3 A cells in front of the Stinson's firewall mounted on a plywood ring around the AXI 2212/20 motor. No room for an equivalent lipo pack.

If you want to use lipo packs, they don't weigh much and are somewhat bulkier than round cells. You will need to move everything as far forward as possible and may still need to carry ballast. Lipos need good cooling air flow and need to be removed for safe charging and change-out so good planning of the battery compartment is needed . I am finishing a GWS foam Zero where I had to open the battery cavity so that small 3S lipo pack protrudes to front of cowl through the firewall. Also added a lot of modeling clay to inside front of cowl ring.

Keeping the fuselage and tail as light as possible is mandatory to reduce tail heaviness. Consider using pull-pull linkage for elevator and rudder servos to replace push rods going aft and avoid any beefing up of the tail feathers. Enlarging the scale Stinson stab may help stability. Rudder is plenty big.

Your motor/gear drive/prop combo must have enough thrust for ROG takeoffs with authority. Some wing washout is a good thing for stability/prevention of tip stalls. If you are not using ailerons, build in "noticeable" dihedral. Make sure to incorporate enough down and right thrust into the motor/gear-drive mounting. It's nice to have motor mounting where you can change to different/upgrade motor/gear drives if needed.

I went the painted Doculam route but be aware that getting the paint scale-like and opaque will add weight. Prime it by wiping with vinegar and then alcohol before painting with acrylics. Accepting semi-transparency will allow you to use a number of light iron-on covering materials. BTW, there is a website called the Plan Page that has a picture of an SR-5 Reliant with straight wings. Hope this wordiness helps!
E-Challenged is offline Find More Posts by E-Challenged
Reply With Quote
Old Oct 10, 2005, 05:38 PM
a.k.a Maltone
Pat Lynch's Avatar
Australia, NSW, Goulburn
Joined Jan 2005
6,966 Posts
Thanks folks - Engine mounting is always a bit tricky when there is no cowl to hide things! so I'm spending a bit of time there. Tail-end construction - my Lysander turned out nose heavy so I've learnt some lessons from that. Those massive wheels/struts/bracing will need to be addressed also. I'm hoping for an AUW of around 32 oz so power for T/O should be ok with the 480 race.
E-challenged - a thousand wise words is better than a fuzzy picture!

Pat
Pat Lynch is online now Find More Posts by Pat Lynch
RCG Plus Member
Last edited by Pat Lynch; Oct 10, 2005 at 07:00 PM.
Reply With Quote
Old Oct 11, 2005, 06:18 AM
a.k.a Maltone
Pat Lynch's Avatar
Australia, NSW, Goulburn
Joined Jan 2005
6,966 Posts
Could some kind person please clarify the Whitehead formula dimension "Tail Moment"? Is it Wing LE to Tail LE or some other reference. For the Stinson I get about 35% MAC for the CG - this is with a 10% enlarged tailplane area.
The 10% scale model works out at:
Main wing area - 462 sq" (55 x 8.4)
Tailplane area - 84 sq"
wing chord (MAC) - 8.4"
Wing LE to Tail LE - 23".
Perhaps not unusual in an older plane, this CG does not fall on a main spar.
With these dimensions, scale prop is 10" (handy) and should be easy to build 32oz AUW.
I'm still CADding on..............
Pat
Pat Lynch is online now Find More Posts by Pat Lynch
RCG Plus Member
Latest blog entry: A Small Diversion From Annie
Reply With Quote
Old Oct 11, 2005, 07:59 AM
Light and floaty does it
Work in Progress's Avatar
Cambridge, Great Britain (UK)
Joined Sep 2004
2,859 Posts
I've always worked out the moment arm using points at 25% of mean chord for the wing and tail.

A CG at 35% MAC sounds a fair way back to me, for a model of that configuration. Left to my own devices I think I would start trials at 30%.
Work in Progress is offline Find More Posts by Work in Progress
Reply With Quote
Old Oct 13, 2005, 09:18 AM
Registered User
Zephyr41's Avatar
Malanda, QLD Australia
Joined Jul 2004
975 Posts
Yes, 'tail moment' in the Whitehead formula means the distance between 25% MAC of wing and tail.
Zephyr41 is offline Find More Posts by Zephyr41
Reply With Quote
Old Oct 13, 2005, 04:14 PM
a.k.a Maltone
Pat Lynch's Avatar
Australia, NSW, Goulburn
Joined Jan 2005
6,966 Posts
Thanks folks.
Pat
Pat Lynch is online now Find More Posts by Pat Lynch
RCG Plus Member
Latest blog entry: A Small Diversion From Annie
Reply With Quote
Old Oct 13, 2005, 04:54 PM
Registered User
P_J_Glor's Avatar
Valencia, CA
Joined Oct 2002
3,728 Posts
If you run across one of the "Best of Wylam" books in a hobby shop, on e-bay, or Amazon, it has a series of drawings on the Stinson Detroiter through Gull Winged Reliants that show complete structural and cross-section details. You would probably find it very useful. The series was also in "Model Airplane News" in the 50's or 60's, but I am not sure which specific issue. You might be able to find it in one of the e-bay stores that specializes in old model magazines and searching on "Stinson."

Pete G.
P_J_Glor is offline Find More Posts by P_J_Glor
Reply With Quote
Old Oct 13, 2005, 05:35 PM
Registered User
Mid-Michigan
Joined Aug 2002
2,178 Posts
Short noses are where the old Astro Cobalts really shine. They are heavy, but it doesn't matter because you need the weight anyway. They are powerful, have 80%+ efficiencies, used cheaper ESCs, and they run forever.

Got your PM Maltone, and I'll see what I can dig up over the weekend.
uscra112 is offline Find More Posts by uscra112
Reply With Quote
Old Oct 13, 2005, 09:23 PM
a.k.a Maltone
Pat Lynch's Avatar
Australia, NSW, Goulburn
Joined Jan 2005
6,966 Posts
Thankyou - I'll look up that book. uscra - agreed, no point in an expensive lightweight motor if ballast has to be added to get the CG right!
Cheers
Pat
Pat Lynch is online now Find More Posts by Pat Lynch
RCG Plus Member
Latest blog entry: A Small Diversion From Annie
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Stinson Voyager 1/4 Scale J-5 Enterprises hopkimf Scale Fuel Planes 2 May 24, 2009 08:09 PM