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Old Dec 07, 2013, 10:59 AM
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Crusader - Build

I've been thinking about my next classic build and I’ve deicide to build Ralph Brooke's world famous Crusader.

I grew up in the Northwest and Ralph was a larger than life character in our RC world and ferocious competitor at whatever he did. I mean really, really determined!!! Ralph belonged to a RC club in the south end of Seattle and my club was in the north, so I knew him, but not like a good friend.

In the early 70s I bought a set of Crusader plans. By then Ralph was flying his retract gear equipped Gladiator design that had a wing and tail that looked like it came from the Crusader. A fiberglass fuselage and foam wing Gladiator was kitted by Fliteglass in Seattle.

I’m probably committing blasphemy, by even considering changes to the Crusader considering it was designed and flown by a world champion, but I’m making some changes.

Some of the things I’m changing:

1. Updating the fat 18% airfoil with something thinner and more modern. I’ll use the airfoil that I used on the Skylark and Sabre 56. It will have a 12” root and an 8” tip that is close to the original wing platform. Need to check the thickness to make sure the Spring Air retracts will fit in the wing.

2. Change the elevator hinge line so it is swept to match the horizontal stabilizer.

3. Side mount the engine to solve the low fuel tank position problem and make room for a retract nose gear and a pipe. I'll be using one of my OS 61SF ABC-P engines.

4. At 3.5” the fuselage is wider than it needs to be for modern servos.

There is a laser cut short kit available, but with the changes I want to make it would not be much help.

Please feel free to make comments about my build as they are welcome, but if you want to add information that is not directly related to my build, I ask that you post it in the Crusader discussion thread here http://www.rcgroups.com/forums/showthread.php?t=2048357

Some of my other builds on RCG are here, the Skylark 56 http://www.rcgroups.com/forums/showthread.php?t=1843803 and the Sabre 56 here http://www.rcgroups.com/forums/showthread.php?t=1894028 and a few on that other forum that seldom works.

To be continued ……

This thread is dedicated to my good friend and longtime RC buddy Tony Howard that passed away January 19, 2015. http://www.rcgroups.com/forums/showthread.php?t=2329009
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Old Dec 07, 2013, 11:02 AM
AKA 8178
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The February 1965 MAN article on the Crusader.

To be continued ……
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Old Dec 07, 2013, 11:16 AM
AKA 8178
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Ralph did a great job of capturing the essence of the Crusader in his design, but the thing that doesn’t seem quite right to me, is the canopy and the top area around the nose.

The canopy should extend further forward so it stops just slightly behind the spinner. On the Chance-Vought Crusader the canopy is wider and the front part of the canopy frame starts right at the nose cone.

I overlaid a Crusader picture on the plans and traced a new canopy and nose section. It is kind of difficult to graft a scale part on to a non-scale plan, but I’m just trying to make the nose look more Crusader like.

To be continued ……
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Old Dec 07, 2013, 11:47 AM
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Test fitting the 8” tip rib. I will not know how the Spring Air retract unit will fit in the wing until I get the root plot from my friend Tony. My MAN plans show a 67 1/4” wingspan with an area of 680 sq in. I think I’ll shorten the wingspan to 65” for 650 sq in.

The ailerons will be integrated into the wing airfoil rather than just attached to the training edge like indicated on the plans.

To be continued ……
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Old Dec 07, 2013, 01:55 PM
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Doing some planning work on the nose gear. I plan on using dual small wheels like I used on my Century design. The dual small wheels provide a good contact patch for steering and can be further enclosed when retracted.

The full scale Crusader uses a single nose wheel, but this is just for fun so we can take liberties.

To be continued ……
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Old Dec 07, 2013, 02:04 PM
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Originally Posted by doxilia View Post
Kewl Mike!

So it's happening.

I'll try to refrain from random comments on your build thread.

The canopy graft seems just perfect to me.

Quick projection: Will you be doing a PET canopy? Glass cowl? SF-P and pipe it is?

David
David, feel free to make comments, they are welcome and add to the build.

Yes, I think I'm close on the nose shape now. Not sure of the details yet, just working on the big picture. For sure it will have one of my OS 61SF ABC-P engines, side mounted with the pipe slug under the wing.

Mike
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Old Dec 07, 2013, 02:53 PM
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Why thanks.

You know, you just gave me a brilliant idea. I like the dual wheel nose gear - well suited to jet like designs.

Say, what size is that DuBro? Something like a 1-1/4"? I suspect they're no longer made like that in that size.

What type of axle system does one use for dual wheels. Can one bore through a DuBro strut/axle coupler for exit on both sides?

David
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Old Dec 07, 2013, 06:16 PM
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Why thanks.

You know, you just gave me a brilliant idea. I like the dual wheel nose gear - well suited to jet like designs.

Say, what size is that DuBro? Something like a 1-1/4"? I suspect they're no longer made like that in that size.

What type of axle system does one use for dual wheels. Can one bore through a DuBro strut/axle coupler for exit on both sides?

David
David I looked at my Century plans and I have 1 3/4” wheel shown and scaling my picture it looks like a 1 3/4” wheel. I believe I used the smallest wheel available at the time and that would be the Dubro http://www3.towerhobbies.com/cgi-bin...?&I=LXD758&P=7 The 1 3/4” wheel still seems to be the smallest size in a fat wheel.

Dubro has this lightweight http://www3.towerhobbies.com/cgi-bin...?&I=LXD775&P=7 but from what I can tell they are 1/2 oz just like the smooth wheels above. As you can see from the Century picture the smooth wheels have flatter contact area and I like that look better

There is the Sullivan Sky-lite http://www3.towerhobbies.com/cgi-bin...?&I=LXD775&P=7 as well.

Building the dual wheel strut takes a little work. The first thing is bending a dogleg in the gear wire slightly below the coil so that the lower part of the strut is in line with the upper part of the strut, e.g. when the strut is rotated to steer the strut part that is in-between the wheels is centered and rotating in line with the upper part.

The lower part of the strut had a short piece of brass tube slid over it and the ends were also wrapped around the axel. The end was then silver soldered together. I’ll show some pictures when I build the strut.

Mike
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Old Dec 07, 2013, 08:09 PM
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Thanks for sharing your Crusader build Mike! I'll be following closely!

R
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Old Dec 07, 2013, 08:26 PM
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Thanks for sharing your Crusader build Mike! I'll be following closely!

R
Thanks R. I'm not sure Ralph would approve of my modifications and one thing for sure if he was still around he would be telling me. He was never very shy about letting you know his thoughts.

Mike
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Old Dec 07, 2013, 08:28 PM
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Test fitting the first airfoil plots that Tony did for me. This airfoil is what I used on the Skylark and the Sabre 56. A 12” airfoil was plotted for the root and the 8” tip is the same as the Sabre.

To be continued ……
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Old Dec 07, 2013, 08:41 PM
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The next item to do was plotting some lines on the wing drawing to see if the wing is thick enough to mount the retract unit. From the plot, it looks like the top of the retract unit will touch the top sheeting on the wing, so Tony is going to add 3/16” thickness to the root plot and the same percentage on the tip.

To be continued ……
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Last edited by Jet_Flyer; Dec 07, 2013 at 09:14 PM.
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Old Dec 07, 2013, 08:50 PM
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Mike,

Food for thought...

An 18% airfoil isn't too bad. The Vertigo is about 17% and the Dirty Birdy is a 16% root and 14% tip but they are really close to NACA airfoils in their shape. Your airfoils will be a rocket on the down lines.

You may build it that way and it might be the best flying pattern plane out there but I'm skeptical. If you need a NACA template I can send you what you need.


Tim
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Old Dec 08, 2013, 12:39 AM
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Mike,

Is this a foil you sketched out and Tony is drafting?

They are very similar to foils Kato used on several ships. Those are in turn very close to Helmut Quabeck (HQ) aerobatic foils. It's the 38-40% back max thickness and sharp entry radius that makes them interesting.

The Deception foil is similar in the max thickness aspect but rather different up front from there.

David
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Old Dec 08, 2013, 01:05 PM
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Originally Posted by Timthetoolman View Post
Mike,

Food for thought...

An 18% airfoil isn't too bad. The Vertigo is about 17% and the Dirty Birdy is a 16% root and 14% tip but they are really close to NACA airfoils in their shape. Your airfoils will be a rocket on the down lines.

You may build it that way and it might be the best flying pattern plane out there but I'm skeptical. If you need a NACA template I can send you what you need.


Tim
Thanks for the thoughts and the offer of help Tim. Are you suggesting that this thing has got to fly when I’m done? Dang, you are really putting the pressure on me now! (just kidding).

Airfoils are often a major point of discussion in the RC world, but at our Reynolds numbers, it is my opinion that you would need to mess up pretty badly to cause problems.

I’m kind of a follower of Dick Hanson and all the experiments and testing he has done with his foamies. His conclusion is that we are overly sensitive about the RC airfoil designs. I don’t remember his quote exactly, but it is something like a “plank will fly just fine”.

As an example of thin airfoils in odd use; some of the 2M pattern air frames have airfoils that are less than 12%. Of course they have huge fat bulbous fuselages to drag around and depending the design the airfoils are blunter than the airfoil I've been using. They want to fly slow and just flip flop around the pattern so you would think they would use really fat airfoils.

Happily, I only fly pattern for myself nowadays, so there is no risk and I enjoy experimenting with stuff that may look far out.

Mike
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