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Jan 01, 2014, 11:35 AM
Oh no, not again!
jhspring's Avatar
Contest

Scale Build-Off 3 - 1/12 scale Blohm & Voss P.170 Schnellbomber - Video of Maiden


First off, I build kits or ARFs. I enjoy modifying someone else's design, but have never started one from scratch. I have several planes on my "one-of-these-days" list, but most are too complex for a 6-month build-off. On the other hand this one seems just right. Constant cord wings, circular (mostly) fuse, simple landing gear. There is one with brushed motors and fixed gear on youtube:
Blohm & Voss BV P.170 (3 min 15 sec)
so apparently if you keep it light it will fly. THe builder said he thought it would perform better if it used counter-rotating props as in the original design.


I have also been inspired by Roy and Daz's depron works of art and thought that this might be my excuse to try building with that, see if I can keep things light. The one thing I have noticed is that the landing gear mounts seem to be the weak points in their builds, so I will have to pay special attention there. The landing gear will have a couple of kinks in any event. Since I am a complete newbie at design and depron both, all suggestions will be appreciated.

I am looking to go 1/12 scale, so 52" span or thereabouts. Particulars to follow.

Regards,
Jeff
Last edited by jhspring; Mar 23, 2017 at 08:46 PM.
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Jan 01, 2014, 02:04 PM
Oh no, not again!
jhspring's Avatar
Okay, so I need another project like I need another hole in my head, but here goes anyway.

Full Scale Design Concerns:

The original was designed to have minimal fuse cross sections to enable high speed. It was envisioned to have a role like the Mosquito - streak in, deliver the bombs from low altitude and clean, it was faster than any allied operation fighter by a considerable margin.

There is an awful lot of mass out at the end of the wing tips, which is going to adversely affect roll and put a lot of stress on the main wing. Apparently the wing skins were to be 1 mm steel, but that seems a bit heavy for a model. There was no vertical fin on the fuse, so it may "hunt" in yaw. The one on youtube had a vertical stab added to the fuse. Based on my experience with Zagis, I think it will be okay if I use C/R props, although I don't expect the nacelle rudders to be very effective.

The only real compromise will have to be the ailerons. As designed, the P.170 appears to have had full-span flaps into which the ailerons were inset. I don't have clue one on how to rig linkages that will work for that, so I expect I will use the flaps as ailerons and have no flaps. As stated above, the ailerons will have their work cut out for them.

Model Design Concerns and Compromises.

I think I can be fairly true to the original. In the interests of maintaining c/g, I will forgo the retracting tailwheel and have a painted cockpit. Probably take some fiddling with struts, but electric retracts are easy. No info on gear doors, so I will do something traditional. At 1/12 scale, the fuse/nacelle diameter should be about 4.375". Keith Sparks makes a really nice Corsair cowl that would sub in for the tightly cowled BMW 801Ds. The cowls are 5" diameter, so the fuse and nacelles would be slightly oversize. I could increase the wingspan to 60" to compensate, but this is about as big as I want to build. The alternative is to use the 4.375" cowl Keith makes and fit dummy engines in, which might be the better choice.

Fuse volume is going to be problematic. Where to put the battery or batteries? The fuse will be crowded, but if I stick lipos way out in the nacelles I make the roll control problems worse. That one will take some noodling. I''ll use as much recycled gear as I can.

I have the 3-views blown up, need to get them printed out and order some depron. Maybe have something to show in a week or so.

Regards,
Jeff
Last edited by jhspring; Jan 01, 2014 at 02:55 PM.
Jan 01, 2014, 02:35 PM
Isaiah 40:31
rc capo's Avatar
Looks like Lucas got his inspiration for his desert racers by the 3rd Reich's X-planes.
Very cool.
rc
Jan 01, 2014, 02:59 PM
Senile Member
Lnagel's Avatar
Are you sure that diagram of proposed cockpit layouts is not an illustration from the Kamasutra?

Larry
Jan 01, 2014, 03:15 PM
71% of the world is runway . .
Bart83's Avatar
Very unusual design. That B&V factory in Hamburg made some very cool designs. It will be very intresting to see this bird being build.

Good luck and have fun ,

Bart
Jan 01, 2014, 11:55 PM
Registered User
D-Rock's Avatar
Jeff, this is one cool subject and will be a fun challenge. How thick is the airfoil you are planning? You may be able to mount the batteries just outside the main fuse like internal wing tanks.

D-Rock
Jan 02, 2014, 06:58 AM
Oh no, not again!
jhspring's Avatar
Quote:
Originally Posted by D-Rock
Jeff, this is one cool subject and will be a fun challenge. How thick is the airfoil you are planning? You may be able to mount the batteries just outside the main fuse like internal wing tanks.

D-Rock
No clue how thick the airfoil should be D-Rock, no info on the 3-views. There is a paper card model that has a VERY thick section, but I don't think it can be trusted, it was designed for stiffness, not flight. Cord is 9" so even a 12-15% thickness gives me less than an inch. The 1/1 had 3 independent power pods, separate oil and fuel tanks, no interconnects or cross-feeds. It's further complicated b/c if I build in dihedral like the 1/1, the fuse is mid-wing while the nacelles are shoulder mounts (more useful room). I am still considering sticking a 3S 2200 in each nacelle, but obviously concerned about the adverse effects on handling.

I hope I can get a better feel once I have the full size drawings so I can lay things out and see how to shoehorn them in.

Regards,
Jeff
Jan 02, 2014, 09:30 AM
Übung macht den Meister..
Deuce's Avatar
Years ago, I haunted the Nasty Toes Aviation site (sadly, now defunct ), and they had whipped upp a BV 170 using their foam components. Looked cool and flew rather well.

Even as I flirt with entering this contest (spare time available is limited...), I had considered this subject! Yes, the general shape is simple, but it would have been an introduction to multi-engine stuff. Without a deadline, I'd tackle the sort, but not this time!

Watching!

James
Jan 02, 2014, 09:48 AM
Fly, dangit!!!
Led Zepplin's Avatar
Jeff - Holy cow this one is just too weird not to follow! I've never seen this one before, looks like a WWII Star Wars pod racer.

It does look like it's going to be really hard to control, especially in roll and yaw as noted. What about mixing in some differential thrust on the outer two engines to help in yaw? It does seem like you'd want to avoid putting the batteries out in the nacelles...

Good luck!

J. B.
Last edited by Led Zepplin; Jan 02, 2014 at 01:26 PM. Reason: Spelling error
Jan 02, 2014, 10:43 AM
Oh no, not again!
jhspring's Avatar
James, like you I haunted the Nasty Toes site, but I guess none of us actually bought anything which led to their demise. I liked their take on the P 170 as well, but I don't have a foam cutter to do the fuse sections. I toyed with (and still might) order foam wing cores to simplify things.

J.B., you are the second person to note the resemblance to pod racers. Yah, I am worried about wingtip mass, so I will have to get creative with lipo placement. Should be interesting.

Regards,
Jeff
Jan 02, 2014, 11:24 AM
North East England
That video was one of the best I've seen - both from the flying and camerawork angle. It's certainly a very flyable model subject. no doubt of that.

Anyone else have the impression that, if you reversed the motor locations, it would fly equally well as a canard?

Look forward to this build.

Steve
Jan 04, 2014, 03:41 PM
CH Spring
Definitely not the prettiest design I have ever seen.

I'd never heard of the BV170 before.

This ought to be an interesting build.

Cheers!
Jan 04, 2014, 05:31 PM
Oh no, not again!
jhspring's Avatar
Cool though, right? Cowls arrived from Parkflyer today and 4.4" is larger than I imagined. I have some slim 3S 3A lipos that I should be able to use in pairs and slide right up next to the motor. I think. Need to get my enlarged 3-views printed so I can start scheming. J
Jan 04, 2014, 08:06 PM
Registered User
TripleW's Avatar
Quite a challenge you got there Jeff! I like the Western Front Camo.
What are you building it out of Foam or Balsa?


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