Author Topic: P-40 Shoestring (Read 5854 times)

Bob Reeves · « **on:** March 09, 2009, 07:10:41 AM »

Put the first trim flights on the Shoestring yesterday and have to say this is the best flying Profile I have ever flown. Joe Gilbert flew it and agreed, it turns flat with a killer corner and just doesn't do anything funny or not expected.

This thing was created from a whim.. Had a scratch and dent Brodak P-40 ARC and was talking to one of our club members (Tom Martin) about what to do with the wing and stab.. He said it looks like a Shoestring to me so I went to work throwing this together. Geoff Goodworth sent me a CAD file of the Midwest Shoestring, I pulled the fuselage and blew it up to match Pat's P-40 numbers.. Pat sent me the wing cut-out for the P-40 so I ended up with a CAD drawing of the fuselage.

Built like any conventional profile, 1/2 inch balsa slab fuselage, 1/8 light-ply doublers nothing fancy or trick. Covered with Ultracote except for the white on the fuselage which is Rustoleum over carbon. RTF weight came out at 46 ounces, Saito 40 Golden Knight with my normal Saito set-up.

As I said it was pretty much thrown together no frills like wheel pants or even the Shoestring air scoop and oil cooler. Wasn't really expecting much above an average profile that looks kinda cool but as it turns out it will be my #1 P40 competition airplane.

Trimming issues are simple normal stuff.. Had to tweak the outboard trim tab up a bit, thinking about adding a little nose weight and longer lines. The trim tab tweak is because I put the wing a tad high in the fuselage, when I build another one I'll move the wing down 1/4 inch. Joe can make it turn without a bobble but I can't hence the nose weight.

Was flying it on 58 foot lines and it was a little fast at 4.7 sec laps, we re-tuned the Saito intake and lowered the RPM down to 7900 but the Saito just didn't seem happy.. Even at that it flew the airplane just fine, just wasn't as solid and consistant as it is when it's real happy at 81-8200. This is with a Rev-Up 11-7 and even at the lower speed, line tension was solid everywhere. Longer lines and getting the Saito at an RPM it's happy at should settle things down plus give me more room.

Isn't it funny, you spend months building a stunt ship only to have it have some weird trim issue that may or may not be fixed then you throw together a silly old profile for fun and it turns out to be a killer. Thanks Pat for a great design, now I understand why everyone is raving about your P-40.

Mark Scarborough · « **Reply #1 on:** March 09, 2009, 09:03:42 AM »

Not only that, but it looks SWEET!!!!
Have to agree, that wing and setup is just a great universal stunt wing. Pat and I are trying to generate some interest for a design fly contest using the P-40 wing as a basis for design,,,

Clint Ormosen · « **Reply #2 on:** March 09, 2009, 09:04:01 AM »

Looks great, Bob. I just love it when you can take spare parts and make a great flying plane.

Allan Perret · « **Reply #3 on:** March 09, 2009, 10:29:31 AM »

Way cool Bob. I like the trim scheme.

jim gilmore · « **Reply #4 on:** March 09, 2009, 10:46:49 AM »

For those of us whom aren't in the know. when You say p-40 wing you're not talking about the wwII fighter corrrect ?

Bradley Walker · « **Reply #5 on:** March 09, 2009, 10:48:01 AM »

I love that!!! Love it.

The P-40 is the best profile on the market... in my opinion.

Mark Scarborough · « **Reply #6 on:** March 09, 2009, 11:05:27 AM »

Jim,
I will jump in here for him. It IS the wing from the Brodak P-40 Profile. Yes thats the P-40 warhawk profile warbird that they offer as an ARF , ARC , and kit.

Bob Reeves · « **Reply #7 on:** March 09, 2009, 11:49:26 AM »

Quote from: Mark Scarborough on March 09, 2009, 11:05:27 AM

Jim,
I will jump in here for him. It IS the wing from the Brodak P-40 Profile. Yes thats the P-40 warhawk profile warbird that they offer as an ARF , ARC , and kit.

Mark is right, not sure as I haven't asked or looked but Brodak might sell just the rib set for the wing.

Bob Reeves · « **Reply #8 on:** March 09, 2009, 12:46:15 PM »

Quote from: Allan Perret on March 09, 2009, 10:29:31 AM

Way cool Bob. I like the trim scheme.

Thanks Allan,

Kinda a funny story.. See the checkerboard at the front of the elevators.. This is the stab and elevators from the ARC and without thinking or checking the radius at the front of the elevators I cut my normal hinge recesses, covered the stab and elevators and didn't think any more about it. After it was built I epoxied the flaps and elevators on as I normally do with almost zero gap. After the epoxy was set I discovered I only had about 10 degrees of elevator throw because it didn't have enough clearance in the radius on the leading edge of the elevators.

Oh crap what do I do now, it's finished and the epoxy has cured, no way are the hinges coming out. Well I fretted over it for a couple days trying to crush the leading edge balsa with the round end of an xacto without messing up the covering. Finally I just turned the xacto around and cut, covering went away along with enough balsa to give me 30 or so degrees of throw. One of our club members had left me a roll of checkerboard Ultracoat in case I thought I might use it for something on this airplane. Heck why not use it to fix my screw up..

Cut two strips 3 checkers wide which was enough to put one row on top, one row in the hinge line and one row on the bottom. I cut slots for the hinges and a slit out the bottom for each hinge. Wiggled it down into the hinge slot working the slits around the hinges and lining up the precut slots with the hinges. Once it was in place a trim iron sealed it down. On the good side, I now know how to cover a hinge slot on a built airplane

Randy Powell · « **Reply #9 on:** March 09, 2009, 01:20:13 PM »

Bob,

I think we have all, uh, altered the trim scheme or inklines of a plane to camouflage a boo-boo.

Neville Legg · « **Reply #10 on:** March 09, 2009, 02:00:49 PM »

Thats a superbly finished model, but how did you teach that tree to fly so well?

Cheers Neville

Paul Taylor · « **Reply #11 on:** March 09, 2009, 02:07:39 PM »

That is just too Cool Bob!!!!

catdaddy · « **Reply #12 on:** March 09, 2009, 02:14:56 PM »

Quote from: rootbeard on March 09, 2009, 02:07:39 PM

That is just too Cool Bob!!!!

Yep it really is. I think I can speak for the whole club when I say that we have a bunch of good flyers and a few good builders, but Bob is the whole enchilada, I kid you not! He strives for perfection and is an inspiration to every Gluedobber. Bob we're proud to have you

john e. holliday · « **Reply #13 on:** March 09, 2009, 03:55:59 PM »

Bob, the Shoestring P-40 is awesome. I love the color scheme and if you hadn't said anything I would have thought the checks were part of the scheme. Now keep it away from Joe. DOC Holliday

Allan Perret · « **Reply #14 on:** March 09, 2009, 04:08:23 PM »

Quote from: Bob Reeves on March 09, 2009, 12:46:15 PM

Cut two strips 3 checkers wide which was enough to put one row on top, one row in the hinge line and one row on the bottom. I cut slots for the hinges and a slit out the bottom for each hinge. Wiggled it down into the hinge slot working the slits around the hinges and lining up the precut slots with the hinges. Once it was in place a trim iron sealed it down. On the good side, I now know how to cover a hinge slot on a built airplane

OK, you let the cat out the bag. Now you gotta put a row of checks on the flap line.

Randy Ryan · « **Reply #15 on:** March 09, 2009, 04:57:37 PM »

WOW Bob!! That's simple gorgeous!!! I love Shoestrings and your's really reinforces that feeling!

Bob Reeves · « **Reply #16 on:** March 10, 2009, 07:38:17 AM »

Oh! As if most of you didn't already guess... All photos were shot by Elwyn, another great Gluedobber. Our club is blessed to have so many that add so much and our rock, De Hill who kept it alive all these years.

Geoff Goodworth · « **Reply #17 on:** March 10, 2009, 10:45:24 PM »

Guys

A great model but the fuselage is actually an enlargement of my drawing of the Goldberg Shoestring.

When Bob and I first started talking about the feasibility of this project, I superimposed the P40 wing and tail on scale outlines of the Shoestring and was amazed at how close they were.

However, there is one thing I would have done differently.

On the full-size aircraft, the top of the cheek cowl is almost parallel to the engine thrust line but tapers down very slightly toward the wing. Had it been my model, I would have fitted the cheek cowl with the front centred on the engine thrust line and the the top parallel to the thrust line. I would have then located the wing so the high point was tangent to the cheek cowl. This would have lowered the centreline of the wing a little giving a slightly more scale-like appearance.

Would having the wing maybe 1/2" lower have any negative effect on the flight characteristics?

Cheers, Geoff

Mark Scarborough · « **Reply #18 on:** March 10, 2009, 11:21:31 PM »

short answer, yes it would have an effect. It would throw the vertical CG off potentially causing the plane to fly not straight on the lines.. Now if you added a 1/2" of dihedral to get the leadouts in the same place it would be fine.

Glenn (Gravitywell) Reach · « **Reply #19 on:** March 10, 2009, 11:54:45 PM »

Ditto....what Mark said.

Bob Reeves · « **Reply #20 on:** March 11, 2009, 10:29:05 AM »

Quote from: Geoff Goodworth on March 10, 2009, 10:45:24 PM

Guys

A great model but the fuselage is actually an enlargement of my drawing of the Goldberg Shoestring.

When Bob and I first started talking about the feasibility of this project, I superimposed the P40 wing and tail on scale outlines of the Shoestring and was amazed at how close they were.

However, there is one thing I would have done differently.

On the full-size aircraft, the top of the cheek cowl is almost parallel to the engine thrust line but tapers down very slightly toward the wing. Had it been my model, I would have fitted the cheek cowl with the front centred on the engine thrust line and the the top parallel to the thrust line. I would have then located the wing so the high point was tangent to the cheek cowl. This would have lowered the centreline of the wing a little giving a slightly more scale-like appearance.

Would having the wing maybe 1/2" lower have any negative effect on the flight characteristics?

Cheers, Geoff

Hi Geoff, glad you chimed in.. Actually the wing does need to be moved down but only about 1/4 inch.. Might be enough to do what you are thinking. This could be a very nice semi scale if someone wanted to take the extra steps, I short-cutted by not doing the lower air intake, wheel pants etc. Actually I was planning on doing the air intake and oil cooler but screwed up and rounded off the fuselage before thinking.. Rather than trying to come up with a fix I just left it off. For me it was just something to throw together using the ARC wing and stab. Now wished I had taken a little more time.. Could still add wheel pants but the wing is already too high and wheel pants would just add more weight below the cg.

Zuriel Armstrong · « **Reply #21 on:** March 11, 2009, 12:06:19 PM »

Bob,

Cool plane...Love the "PURPLE"

Stooge is on the way.

Geoff Goodworth · « **Reply #22 on:** March 11, 2009, 10:51:54 PM »

For those who are interested, I have just had a play with the drawings. 1/4" lower gives the result I was looking for.

Bob and I might see what we can do with the new information.

Cheers

Geoff

Bob Reeves · « **Reply #23 on:** August 22, 2009, 06:50:06 AM »

Bringing up this old thread just to add a few pieces of information I've discovered along the way.

Geoff, 1/4 inch lower would be great, as I said in the first post I have it a little too high and the vert CG isn't where it needs to be. One reason it doesn't have wheel pants, can't afford the added weight below the vert CG.

If anyone wants to follow the engine setup I ended up with the details are posted in the 4 stroke section.

http://stunthanger.com/smf/index.php?topic=13100.0

http://stunthanger.com/smf/index.php?topic=13536.0

W.D. Roland · « **Reply #24 on:** August 23, 2009, 09:45:02 AM »

Hi Bob

Your Shoestring just looks like it would fly good!
I love Shoestrings-the just look right.

Would like to ask if that is the old Midwest P-40 based on the Magician ?(basically)
48in span if memory is remembering.
Someone told me it is not.

I have a P-40 topflight (sureform?)converted to a Shoestring!
Flies fantastic other than an OS .35S is way much power. a .19 would have been better.
Looks like P-4os might be better off as Shoestrings!

Check out the yellow and white P-40/Shoestring in this thread.Nose is to big.
Built in 79 and still going!
http://stunthanger.com/smf/index.php?topic=13641.0

David
51336

Ward Van Duzer · « **Reply #25 on:** August 23, 2009, 12:42:44 PM »

Kooool! Kit Bashing has just been promoted to ARF Bashing. Yipeee!

W.

Matt Colan · « **Reply #26 on:** August 26, 2009, 02:36:22 PM »

And now I have a P-40, that I'll name the Stunthangar P-40, sine I won it here. I'm looking foward to a nice layed back kind of build I'm expecting for the P-40 and i'm also expecting a good flying airplane. that look's like a shoestring there Bob and I'm glad you're happy with it

Geoff Goodworth · « **Reply #27 on:** August 27, 2009, 04:31:18 AM »

Matt

Just remember that Pat designed the profile P40 with 1/2" dihedral in the wing to get the vertical GC right. Don't leave home without it.

Cheers, Geoff