# Crosby CR-4

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#### Magisterol

##### Well-Known Member
Hello. Anybody by any chance has a drawing of the CR-4 wing construction? I have seen some pics and looks like the wing is made out of 3 sections: one central and two outer panels. but the central panel skin should have a kink on the centre line as the whole wing is tapered. I am curious how the main spar is built with that kink in it and how are the skin panels attached on the median line.

#### TFF

##### Well-Known Member
These pictures or do you have better ones?

#### Tiger Tim

##### Well-Known Member
From photos it looks like the underside skins are joined with a strip a couple inches wide, I assume the same on top.

Are you building a CR-4? I have a big file going on Crosby’s racers on an old, dead laptop that I should resurrect. At one time I wanted to build one but changed my mind watching takeoff videos of other similarly loaded single seaters.

Also, is that Russ’ old Mustang II in your avatar pic?

#### Magisterol

##### Well-Known Member
From photos it looks like the underside skins are joined with a strip a couple inches wide, I assume the same on top.

Are you building a CR-4? I have a big file going on Crosby’s racers on an old, dead laptop that I should resurrect. At one time I wanted to build one but changed my mind watching takeoff videos of other similarly loaded single seaters.

Also, is that Russ’ old Mustang II in your avatar pic?
It is Russ’ airplane. I bought it last year, few month before he passed away. I like it, but he didn’t fly it much before I bought it, so a bit of expenses to bring it back “on line”.... I am not building a Cr-4. I am trying to build something else with a tapered wing and I don’t know how to make the past in the middle: put a kink in it or join it there. The simple solution would be like a Midget Mustang, but with a larger rectangular central panel and two tapered side panels....

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#### Victor Bravo

HBA Supporter
There's many folks here who know a lot more than me about this kind of stuff... but the amount of taper and wingtip chord on that Crosby racer looks really unpleasant. I'd be sh****ng myself going around a low altitude pylon turn in that. I'll bet my a$$that they didn't put any washout in that wing either. #### Magisterol ##### Well-Known Member There's many folks here who know a lot more than me about this kind of stuff... but the amount of taper and wingtip chord on that Crosby racer looks really unpleasant. I'd be sh****ng myself going around a low altitude pylon turn in that. I'll bet my a$$ that they didn't put any washout in that wing either.
From what I heard he was a very good pilot. I guess he build the airplane for his own skills. I don’t think it was intended for “safety” or to be easy to fly. Most likely it was intended to fly as fast as possible on a specific power. I guess those were the days of true race pilots. It would be nice to be able to talk to some of those pilots and asked them to fly the newer homebuilt airplanes and compare.

#### TFF

##### Well-Known Member
From the pictures I think this plane has a mix. You can see some big fittings in front of the face of the spar, and the strip is structural. That joint looks like it was lifted off a military plane. I’m sure it was to truck it to races and put together.

If a wing panel has to come off, I would design it with normal fittings and have a similar filler strip but flush. If you are expecting it to fold, it’s probably best to leave the seam and make it as close as possible.

I’m not quite sure what you mean by kink. A joggle or are you calling the joining panel a kink?

#### Magisterol

##### Well-Known Member
From the pictures I think this plane has a mix. You can see some big fittings in front of the face of the spar, and the strip is structural. That joint looks like it was lifted off a military plane. I’m sure it was to truck it to races and put together.

If a wing panel has to come off, I would design it with normal fittings and have a similar filler strip but flush. If you are expecting it to fold, it’s probably best to leave the seam and make it as close as possible.

I’m not quite sure what you mean by kink. A joggle or are you calling the joining panel a kink?
For me a kink is a sharp bent. I was talking about the top and bottom of the wing where they meets in the centre of the airplane. If there is no joint in that spot, then it must be a sharp bent. That is why I was looking for plans. If there is a joint in the middle of the wing, inside the fuselage, it means that the wing is made from 4 parts: two panels that joint in the middle, forming the centre panel, and the two outside panels.

#### Tiger Tim

##### Well-Known Member
The main spar is probably continuous through the centre section and I bet the top spar cap just runs straight across while the bottom is a very, very shallow V.

#### TFF

##### Well-Known Member
It’s 4 pieces. The bottom of the wing you can see the filler strip down the center. and the book end spots that have to be brackets. All the pictures I see head on, the wing has dihedral to the middle.

#### Magisterol

##### Well-Known Member
It’s 4 pieces. The bottom of the wing you can see the filler strip down the center. and the book end spots that have to be brackets. All the pictures I see head on, the wing has dihedral to the middle.
That is whaa I thought too. It is made out of four panels. The middle two are ”more permanently “ attached togheter, while the outer two can be removed with 2 pins on each side (top and bottom)... Wasn’t sure, but I guess it makes sense now. Thanks.

#### jvliet

##### Active Member
The CR-4 was originally built with a one-piece wing and was trucked from California to Cleveland for the 1938 races fully assembled and canted up at an angle on a flatbed truck. After returning to CA and before its next trip to Cleveland for the 1939 races, the wing outer panels were cut off, then reattached at Cleveland using aluminum strips about 4 inches wide. In photos at Cleveland '39 these strips are seen unpainted.

#### User27

##### Well-Known Member
The wing has tip-stall written all over it!

#### Magisterol

##### Well-Known Member
The CR-4 was originally built with a one-piece wing and was trucked from California to Cleveland for the 1938 races fully assembled and canted up at an angle on a flatbed truck. After returning to CA and before its next trip to Cleveland for the 1939 races, the wing outer panels were cut off, then reattached at Cleveland using aluminum strips about 4 inches wide. In photos at Cleveland '39 these strips are seen unpainted.
Well, it could have been built as a one piece, but being made of metal, unless it was poured hot, it had to be assembled at the middle. That is why I was looking for plans. See how the two parts were joint together.

#### plncraze

##### Well-Known Member
HBA Supporter
Do a search for books on the older racers. Sometimes they will have good pictures.

#### jvliet

##### Active Member
Well, it could have been built as a one piece, but being made of metal, unless it was poured hot, it had to be assembled at the middle. That is why I was looking for plans. See how the two parts were joint together.
I have some construction photos and will take a look to see if any of them clearly show the spar center section joint. I expect it will be riveted doubler plates on top and bottom spar caps

#### CRG

##### Member
Is the wing not flat across the upper surface? With dihedral given by the tapering thickness.

The stated 600lb higher weight of the CR-4 over the SK-4 seems high, I wouldn't have thought the aircraft large enough to have an extra 600 pounds in it.

#### Magisterol

##### Well-Known Member
I have some construction photos and will take a look to see if any of them clearly show the spar center section joint. I expect it will be riveted doubler plates on top and bottom spar caps
That is what I was looking in the photos, magnifying them as much as possible, but the become very pixelated.

#### Magisterol

##### Well-Known Member
Is the wing not flat across the upper surface? With dihedral given by the tapering thickness.

The stated 600lb higher weight of the CR-4 over the SK-4 seems high, I wouldn't have thought the aircraft large enough to have an extra 600 pounds in it.
i think you might be right. Looks flat at the top inside the fuselage. Maybe it is only the bottom spar cap that is made of 2 parts. That might be a solution.