Northrop's N-191 Proposal and Its Design Evolution

One of the drawbacks of writing a monthly column on the side while working full-time (or more) at a my real job at Northrop Grumman was the eternal deadline pressure. 

Initially these articles were to be no more than 500 words long, but as I got more into the history of the various projects that interested me, 500 words soon became inadequate for much of what I was doing. Working on multiple long stories at once became the norm, which led to multiple research tracks as I tried to find accurate information and learn it well enough to write about the subject at hand, all while feeding the deadline beast.

My ever-present fear was of getting something substantively wrong beyond the usual spelling errors that always seem to slip by and other minor irritations.This article was one of those times when I did get something wrong. Fortunately I was able to correct that mistake in the next month's column.

I am presenting this as it was published without corrections because it was the article that was cleared by PROCS, Northrop Grumman's public release process. By the rules, if I change a sentence or even a couple of words, I need to resubmit the whole article for approval. 

Having had more than my fill of the process I am loath to enter any more articles to PROCS than necessary. Since I have the follow-on article approved, too, I will post that in a couple of days. Hopefully this issue will be moot in the future when I retire in a few months.

As I mentioned in the article models and drawings out of context can confuse researchers, especially ones with deadlines. The silver model with the dorsal inlet was the one that tripped me up as it was wrapped together with the other two models when they were rediscovered in 2000. They were originally part of the old Northrop Heritage Hall which was closed in 1989 and had lost their labels.

As a result, the cursory examination of Jerry Huben's drawing led me to believe I had examples of all three versions. I did note a discrepancy, but did not think it was because the model was of an entirely different program, which it turned out to be, but of a variant that wasn't recorded in Jerry's drawing. Knowing Jerry I should've known better. Alas, I went with my first impression and was proven wrong.

The model turned out to be of the Northrop N-196, the company's proposal on what turned into the Hound Dog missile program. As I mentioned, I will post that in a couple of days.

One final note, since this was published in August 2012 I've had the opportunity to visit Jerry in his retirement. About six months ago he asked if I'd be interested in a couple of Northrop related items that he had. Of course I said yes. One of the items turned out to be the original vellum of the N-191 drawings. It felt like the passing of the torch and I was honored and humbled.

I would love to frame and hang the vellum, but I'm afraid it will fade if exposed. Anyone have any suggestions?

This article originally appeared in the Northrop Grumman Engineering Department's in-house, on-line magazine Airspace, Vol. 3, no. 21, August 2012. It is posted here with permission and has approved for public release number 12-1630.
 

Northrop’s N-191 Proposal and Its Design Evolution

By Tony Chong

One of the more interesting aspects of aviation history, especially on the technological side, is the tracing of aircraft designs from their initial concept to final proposal. Then, if the program succeeds, it’s on through the prototype and into the production phase with all of its potential variants. The changes are fascinating and help illustrate a company’s engineering philosophy during that particular timeframe as they developed solutions to specific mission requirements.

Unsuccessful proposals are, by their nature, more difficult to study: They are ephemeral projects that may produce many versions but no hardware results. They are quickly forgotten and easily misinterpreted decades after the fact as data is lost or destroyed.

The heritage Northrop N-191 is one such example. The project spawned three distinct variants with scale models being built to showcase each of the designs. Over the passing decades, the models acquired different labels so the relationship between them was lost and the impression was fostered that they were unrelated proposals.

Fortunately, Jerry Huben, a retired heritage Northrop engineer with over 68 years of service in the company, saved a series of line drawings that he made in 1958 on the N-191 which cleared the confusion that surrounded the models.¹

The N-191 was to be a turbojet-powered Mach 3 intercontinental cruise missile. According to Huben’s notes the start date on the new project was March 7, 1957. This was six years after the cancellation of Northrop’s earlier Mach 2 cruise missile proposal, the MX-775B Boojum .²

Design requirements included a desired range of 4,250 nautical miles. The vehicle would use a zero-launch system incorporating solid propellant boosters like those utilized on the company’s N-69/SM-62 Snark. Take-off weight was to be 100,000 lbs.

The missile was to carry a 6,450 lb. warhead located at the vehicle’s center of gravity (C.G.). Alternative warheads ranging from 1,500 lbs. to 9,000 lbs. were possible, also carried at the C.G.  Extra fuel tanks or a reconnaissance payload could be carried in the bomb bay if required.

Additionally the entire system was to be transportable by air via a U.S. Air Force/Douglas C-133 Cargomaster, with initial operational capability targeted for mid-1962.

The first design featured in Huben’s drawing was dated April 17, 1957. The proposal must have been promising enough that the company created a brochure around the concept (NAI-57-543). It was to be powered by two Allison 640-G2 (J89) turbojets mounted near the tips of the wings similar to the Boojum.

The vehicle would have been 98 feet long with a span of 61 feet. Instead of the delta wing of Boojum the N-191 featured a large trapezoidal wing with a cruciform tail structure. The drawing was given Preliminary Design number PD-0773.

Alternative engine studies followed using the same twin-engine layout, but on September 11, 1957 the first single-engine study appeared with a raised dorsal inlet (PD-0806). This sleek-looking design was to be powered by a Pratt & Whitney J91. The fuselage was lengthened to 112 feet while the trapezoidal wing shrank to a span of 50 feet. The cruciform tail remained as a feature of the vehicle.

Again more alternative engine studies commenced, but on March 6, 1958, the cruise speed design requirement was upped to Mach 3.5. Engine selection was narrowed to the Pratt & Whitney J58 and the General Electric J93. Operational introduction was pushed to 1963.

March 22, 1958 saw the first annular nose inlet design for the N-191 (PD-0842). As Huben remarked in his drawing notes, this inlet was, “chosen for greater reliability & efficiency.” The length was now 101 feet and the trapezoidal wing was reduced further to 47 feet. The cruciform tail was retained.

The final design was PD-0844 and was a variant of the annular nose inlet type. Length was now 97 feet and span 45 feet. The trapezoidal wing now featured ailerons due to the fact that the cruciform tail was eliminated and replaced by a larger dorsal vertical with rudder and two smaller anhedral horizontals. Speed of the J58-powered vehicle was projected at Mach 3.5 with a take-off weight of 81,000 lbs.

Finished on April 10, 1958, PD-0844 “Super Snark” was submitted to the Air Force’s Wright Field Labs for review. Unfortunately the results of that review are not currently known. What is known is that the successful first flight of the Atlas intercontinental ballistic missile in June 1957 negated the need for an intercontinental cruise missile system. The N-191 essentially ended in April 1958. The subsonic Snark followed shortly, being withdrawn from operational service in June 1961, a scant four months after unit activation.

As has been mentioned before, the 1950s were an incredible period of emerging technologies and design advances. In that environment the value of a project like the N-191, even in failure, was immense, for it helped hone the company’s engineering talent and sharpen their problem solving skills, which were critical for effective competition in future programs.  

That holds true for today. What could be more critical than the preservation of project documentation for the edification of current and future engineers, allowing them to understand the lessons and context of the programs that did or did not win?

Footnotes

1.  The series of drawings were actually part of a larger overall drawing designated PD-0845 and completed on April 10, 1958, along with the final design variant PD-0844.

2.   For further details of this vehicle, read “For the Snark was a Boojum, you see” by Tony Chong, Airspace, volume 2 number 11, September 2011.

Tony Chong is a historian, photographer and a contributing editor to Airspace. He leads activities in the Aerospace Systems Display Model Shop and works in El Segundo.

References and Notes

A useful book for understanding the history of the cruise missile and the developmental hurdles faced by the various contractors in the turbulent 1950s is: The Evolution of the Cruise Missile, by Kenneth P. Werrell, Air University Press, Maxwell AFB, 1985. It can be found in pdf. format here:

http://aupress.au.af.mil/digital/pdf/book/b_0006_werrell_evolution_cruise_missile.pdf

A brief description in French on one of the N-191 twin-engine variants, including a silhouette 3-view, can be found in this interesting book: Les Avions et Engins Northrop, by Alain Pelletier, MiniDocavia #21, Guides Larivière, Editions Larivière, 2006, France, 98-99.

If anyone has the N-191 brochure NAI-57-543 in their possession, or the Engineering Report NAI-57-800, the author would like to borrow and scan them for future reference.

The author is indebted to Jerry Huben for providing him with a copy of Huben’s PD-0845 drawing back in 2002. It drove home the point that not everything we see is what we think it is – especially when it is out of context.

Photo Captions

1.  

  

Placed here as a refresher for the reader is this three-view of the MX-775B Boojum, the earlier Northrop proposal for a supersonic intercontinental cruise missile. Despite being cancelled in 1951 the Boojum undoubtedly provided its generalized configuration as a starting point for the N-191. Since Boojum’s earlier N-25B designation was now assigned to a Snark decoy variant, it is possible the old design was given the new N-217 allocation as a means of keeping track of the correct vehicle in the system. Picture Credit: Tony Chong collection.

2.

 

The basic layout of Boojum has been refined in the initial N-191 design to incorporate a large trapezoidal wing and cruciform tail. It has also grown in size. The Allison 640-G2 afterburning turbojet was that company’s internal designation for the military J89. Picture credit: Tony Chong collection

3.  

An alternative engine layout using the General Electric X279F, an advanced version of their J79 engine that eventually evolved into the J93, was considered along with the Pratt & Whitney J58 and J91 turbojets. Overall dimensions remain the same on the vehicle. Picture credit: Tony Chong collection.

4. 

PD-0806 marks the first appearance of a single-engine variant five months after proposal start. In this configuration the vehicle was only capable of Mach 2.5 speed while take-off weight soared to 118,000 lbs. Huben’s note indicates the J91 proved too large for this mission. Picture credit: Tony Chong collection.

5. 

A version with dry (non-afterburning) P&W J58s was also considered as a R&D schedule and cost reduction proposal. The afterburning J58 would gain fame as the engine for the Lockheed A-12/YF-12/SR-71 Blackbird series of Mach 3 aircraft. Note the addition of landing gear for training purposes. Picture credit: Tony Chong collection.

6. 

PD-0813 marks the first growth variant of the twin-engine design. Length is now 104 feet. Note that initial engines are P&W J58s dry with a Mach 2.5 speed, but the vehicle could be updated to Mach 3.5. This is likely the version shown in Pelletier’s book. Landing gear is now a permanent feature for all missions.  Picture credit: Tony Chong collection.

7. 

 

PD-0815 marks the last twin-engine variant in Huben’s series of drawings. No engines are defined but the Mach 2.5 speed suggests P&W J58 dry turbojets were the option considered. Picture credit: Tony Chong collection.

8. 

PD-0838 marked a return to the single-engine proposal. As noted by Huben, inlet improvements made the design more feasible. Note the shock cone in the inlet, a feature absent in the first single-engine iteration. Length and span are reduced as well. Mach 2.5 is still the top speed of this version, powered by a wet P&W J58. Picture credit: Tony Chong collection.

9. 

 

Oddly this version, with a date two days later than the previous image, also carries a PD-0838 number. Whether it was a transcription error or they actually carried the same PD number is not known at this point. Note that the vehicle is larger in length but shorter in span. It is also the last version to have the P&W J91 as an option as the engine was cancelled. Also note that all subsequent drawings will be without gaps in the sequence. Picture credit: Tony Chong collection.

10. 

 

PD-0839 featured a decrease in length and an increase in span. Speed is holding steady at Mach 2.5 with a G.E. X279J turbojet in this instance. Picture credit: Tony Chong collection.

11. 

PD-0840 was the last version before the decision was made on March 6, 1958 to set Mach 3.5 as the speed requirement. Note Huben’s comments about performance compromises with the P&W J58 dry option. Also note the reduction in span to 35 feet. Picture credit: Tony Chong collection.

12.

The last single-engine dorsal inlet version considered was PD-0841. Speed is now Mach 3.5 with a P&W J58 wet turbojet. Span is back to 47 feet while length is now 104 feet. Picture credit: Tony Chong collection.

13. 

One year after proposal start PD-0842 would mark the introduction of the last significant configuration change, namely the annular nose inlet. All remaining PD numbers will feature this style of inlet. Although it is difficult to see, the fuselage transitions into an oval cross-section past the nose. Note Huben’s remarks about greater reliability and efficiency with the nose inlet, suggesting the dorsal inlet would suffer impeded airflow at its cruising angle of attack. Picture credit: Tony Chong collection.  

14. 

  

The beginning of April saw the basic dimensions being set at 97 feet long with a 45 foot span. Fuselage cross-section is still oval. The P&W wet J58 became the engine of choice in PD-0843. Picture credit: Tony Chong collection.

15.

 

PD-0844 became the final configuration for the N-191 and the version submitted to Wright Field Labs in April 1958, 13 months after proposal start. Dimensions are the same as PD-0843, but the fuselage is now circular throughout its length. According to Huben’s notes the change was made to optimize volume/surface ratio and to facilitate production. The other major change was the elimination of the cruciform tail in favor of an enlarge vertical with rudder and anhedral horizontals like on the F4H-1 (Northrop was a subcontractor to McDonnell on the Phantom II, project number N-154). Ailerons were added to the wings as well. Also note the G.E. J93 was offered as an alternative engine.  Picture credit: Tony Chong collection.

16. 

The twin-engine variant was the only model to visibly carry the N-191 designation (see base of dorsal vertical fin). The discoloration on the nose is where the representation of a Pitot tube or probe broke off the model. Based on the shape this is likely the initial PD-0773 proposal, which also formed the baseline design for the brochure. The model is currently on display in the ASDC Lobby 10, Building 202 in El Segundo. Photo credit: Tony Chong.

17. 

 

The dorsal inlet version did not come with any N-191 identifiers. Based on the lack of shock cone this is likely the initial version of this variant, PD-0806. While it looks like there are no vertical fins to the tail, there was a ventral fin which was broken off the model. Curiously the model does not appear at first glance to have had a dorsal fin as the area is smooth and painted. Either it was repaired at a later date or there is a variant not noted in Huben’s drawings. The model is currently on display in the ASDC Lobby 10, Building 202 in El Segundo. Photo credit: Tony Chong.

18. 

 

This model of the annular nose inlet version likely follows the practice of the previous two models and is of the initial design for that configuration (PD-0842). Note the distinct slab-sided look to the fuselage indicating the oval cross-section. Photo credit: Tony Chong.

19.

A side view of the annular nose inlet model showing the ventral fin of the cruciform tail. “Super Snark” is emblazoned on the forward fuselage as well. Ironically, the N-69/SM-62 Snark was originally named “Super Snark” to differentiate it from the earlier N-25 Snark (Also known as N-25A). Photo credit: Tony Chong.

 Northrop Grumman approved for public release case number 12-1630