SOME OF THE DIFFERENCES BETWEEN THE MODELS AND MODIFICATIONS OF THE BEECH 18
click here for the latest addition
It has been my experience that no two Twin Beech's are alike, especially these days, as each aircraft will have its own set of modifications. Some of these are shown below.
All of the images on this page are thumbnails. Just click on a picture to see a larger photo.
This is the stock factory round wing tips found on all the C (1945 and earlier) and D (1946 and later) model aircraft.
This is the squared wing tip typical of the E, G and H aircraft. This was a Beech factory tip that helped increase the gross weight as well as improving the low speed and stall characteristics. As can be seen in the photo the Beech squared tip has wash out which reduces the angle of attack of the wing tip thus the tip will stall last giving good aileron authority and control late into the stall. This will reduce the wing break tendencies during the stall and will tend to mush straight ahead instead of going hard over.
Here is a comparison shot showing the basic difference between the round and the big square tip.
This is one of the STC's wing tips that can be found on many Beech's. This particular one is an Aerospace wing tip made out of fiberglass. These tips were typically a part of the gross weight increase kits that many aftermarket companies produced to upgrade the Beech 18.
The tip in the foreground is a Pacific Airmotive or PacAero. It was also part of a gross weight increase mod. This tip was made from a round Beech tip that was squared off to increase the surface area. I have placed the PacAero tip against a Beech manufactured round tip and a square tip for comparison.
As you can see the square tip is a lot longer than the others. You can easily see the difference in the surface area. I wonder how much benefit was gained by the Aerospace and the PacAero tips as they don't seem to have that much more surface area than the conventional tip.
There are several different landing gear that can be found on the Beech. Mostly the landing gear can be identified by the lower fork of the gear leg as this is the part that is most visible.
The early aircraft (pre 1945) had a gear in which the lower fork was made up of welded tubing. This lower fork was angled and is commonly referred to as the dog house gear as the shape resembles a dog house.
This is Ray Plotes beautifully restored AT-11 that is the most stock AT-11 flying today. Although they are running Cleveland wheels and brakes they have kept the original dog house gear. In this shot you can see the angle of the welded gear leg.
There were two types of the dog house gear. One had shorter forks and was used with the real early (pre and early WWII) Goodyear multi disc brakes and the balloon tires or Airwheels. These aircraft also had shorter gear wells which necessitated modifying the aft end of the gear well if you wanted to change it to the 33SC or the 1100-12 wheels.
The dog house gear was designed for the early aircraft that had a 7850 pound gross weight. Incidentally the AT-11 bombardier trainer had a take off weight of 9800 pounds but a landing weight of 7850 since it would typically be dropping 1000 pounds of bombs. When the gross weight started to increase Beech came up with a stronger gear hence the wishbone gear.
This is the most common landing gear found on flying conventional gear Twin Beech's today. This lower gear fork is made up with a rounded one piece leg that is commonly referred to as the wishbone landing gear.
Here is an interesting comparison that shows the gear leg collapsed. Both the dog house and the wishbone gear have the same stroke. The upper cylinders of both types of gear are also very different. Although no individual parts are interchangeable between the dog house and the wishbone gear, the airframe will accept either gear as they are interchangeable by assembly.
From the Beech boneyard comes this shot of the dog house and the wishbone gear next to each other.
Then there are the tricycle gear aircraft. This particular one is a Tradewinds conversion with the single tail. Incidentally the vertical stabilizer is made from a Twin Beech horizontal stabilizer turned on end, cut and fit to form the vertical.
This gear is also known as the Volpar tri gear. The Volpar gear was a modification that eventually was bought by Beech and was incorporated into the last Beech 18's built.
The upper part of the main gear leg on the tricycle aircraft was made from the upper conventional gear cylinder from the wishbone style gear. Both the nose and the main wheels run 8.50-10 wheels and a different model of Cleveland wheels and brakes.
Here is a shot of the gear well of Remy's beautiful tri gear in Argentina. You can see the white painted upper gear leg and strut was made from the conventional wishbone gear.
Here is an H-18 conventional gear Beech belonging to Steve Oxman that has factory 8.50-10 wheels and the single fork gear leg.
This is a close up of the factory stock H model gear leg. There were some strength issues with this kind of gear and many have been replaced with the earlier full wishbone style of landing gear.
WHEELS AND BRAKES
There are five different types of wheels and brakes found on the different Beech's. The earliest system was the Goodyear Airwheel (also referred to as the balloon tires) system that used a multiple disc brake pack assembly. Don't cinfuse the early Goodyear Airwheel with the more common Goodyear 1100-12 wheel with the single brake disc rotor.
These early Airwheels were typically used on pre war (WWII) aircraft and also the early c-45's, F-2's and the AT-7 Navigation trainer. The tires are nearly impossible to find these days and I have yet to see these wheels, tires and brakes on any aircraft presently flying . The only ones that survive are on static display aircraft in museums.
This is the 33 SC Bendix wheel typically installed on all WWII military Beech's and C model aircraft. This was a drum style brake just like the drum brakes in your car...older car that is...
This wheel is easily identified by the teardrop cutouts between the spokes. The 33SC wheels and tires are quite rare these days also because the tires and inner tubes are nearly impossible to find. They sure look good and there are several of us that want to get together to have a run of fresh tires made. The cost is substantial so the more people we have to help fund this the more cost effective it will be for us all. If you have a need for 33SC tires and tubes contact me and I will put ou on the list.
This is the inside, or inboard part of the wheel showing the brake assembly of the Bendix 33SC wheels
This is the 33SC drum brake assembly which is practically identical to those found on automobiles.
This is one of the few Beech's still running the original 33SC wheels and brakes. This beautiful UC-45E was built by the late Keith Cross and is now lovingly cared for by his Son Brian and his grandson Tyler. It is wonderful to know that Keith's efforts are going to live on through Brian and Tyler who are wonderful people. In fact Keith's whole family is great.
I have heard a lot of rumors about people complaining about the drum brakes. I learned to fly Beech's on these wheels and brakes and I think they are great. The tire and tube availability is certainly a big issue but as far as the braking ability they were always there when I needed them. I put on a new set of brakes when I built the aircraft and over 500 hours later they still had 50% pad left. I was operating out of a 2500 foot strip and the only time they ever faded was after I had pressure washed the aircraft and had water in the drums. Dragging the brakes out of the wash rack would cure this problem easily.
Braking capacity has always been an issue with the Beech and continues to this day. With gross weights increasing from 7850 on the C models up to 10,100 plus on the modified D's and later aircraft the braking capacity was increased.
The next series of wheels and brakes was built by Goodyear and it used a single floating rotor or disc and 1100-12 wheels and tires. The disc came in two different types; one that was notched and one that had a gear cut to the outside diameter. The notched type soon fell out of favor to the gear type because of cracking issues. The gear type presented more surface area to distribute the braking energy from the rotor to the wheel.
The Goodyear disc brake system is the most common brake in use on today's flying Beech's. It is easily identified by the web construction of the wheels. Incidentally it is these webs and the bead flange where these wheels will crack. This should be a part of your pre flight as these wheels have seen a lot of cycles over the years.
This view shows the more common gear type of rotor. You can see how the rotor meshes with a matching ring gear mounted in the wheel. Look at the big screws that hold the ring gear into the wheel as I have seen these screws back out in operation. The Goodyear brake has three pistons built into the caliper that pinch the floating rotor between six round brake pads or pucks.
There are two different styles of piston heads found on these calipers. The one above has
pins inside of adjusting nuts that indicate brake lining wear.
This photo and the one below has larger diameter tubes that will indicate brake lining wear.
Here you can see the brake pucks and the gap is where the rotor or disc rides.
The latest wheel and brake is the Cleveland set. This is an STC'd system that does substantially increase the braking capacity. This wheel is identified by the solid type of wheel without any significant flanges or spokes. This wheel can be used with or without an inner tube as long as there is an O ring installed between the wheel halves. I recommend the O ring along with the inner tube for added safety so if you get into a ground loop situation the air will not spill out of the tire should the bead become unset. If the bead of your tire is departing the wheel you will likely have much bigger problems going on at the time and a collapsing tire will certainly not help things!
The Cleveland brake uses a fixed rotor and a floating (on two pins) caliper that has four pistons built into the housing. This brake has a much larger brake pad when compared to the Goodyear disc brake. Some people complain about not being able to keep the aircraft from rolling when doing a run up with the Goodyear brakes. I usually tell my students to try standing on top of the pedals to get the needed braking action. With the increased surface area of the Cleveland's this problem goes away.
I took a set of Goodyear pucks and placed them on a Cleveland brake pad. It is easy to see the difference that exists between the two. This photo represents only one half of the brake pads found on each wheel. In my experience the Cleveland brakes seem to hold up well to the rigors of Twin Beech flight training. I have had many a student that will substitute lead feet for proper aircraft operation and technique. After a season of air shows and heavy footed flight training I was amazed to see how well the Cleveland pads held up. There is something to say for the large increase in brake surface area.
I still like the Goodyear system and I think that it is a very cost effective system. I have easily flown two seasons of flying rides (sometimes over 20 take offs and landings in a day, every weekend from April through October) before I have had to change the pucks. The Goodyear pucks cost around $20 to $50 each and there are six per wheel. This is a lot cheaper that the Cleveland conversion kit that, last time I checked, was over $12,000. I think the Goodyear system is adequate but the Cleveland kit is perfect for certain applications and pilots.
Here is a Set of Cleveland wheels and brakes modified to fit a C model landing gear, the dog house gear. The pins in the axel caps are different and some machining is required to adapt the Cleveland's to the old style gear. There is also a concern on tire clearance with the wing skin. The D model Beech's and latter have an additional fairing for this which is covered by the longer nacelle fairing.
MORE TO COME:
HORIZONTAL STABILIZER ANGLE OF INCIDENCE
Below is a response to a question asked about the horizontal stabilizer angle of incidence on the various models of the Beech 18. The question and responce were posted on a message board on Kyle Larson's beech18.net. web site.
I will post photos of the differences in the future.
There are three different angles of incidences on the horizontal stabs of the various models of the Twin Beech's that I have seen. The lowest angle of incidence can be found on unmodified C model aircraft (1945 and earlier). The second or what I call the middle one is typically found on factory D model and later aircraft. There is a third one or the highest angle of incidence which I believe is from an after market STC (Bob Parmerter or Nick can verify this).
I learned to fly a Twin Beech in an unmodified SNB-1 (1943 Navy AT-11) that had the factory low angle on it. The low speed capabilities were wonderful which was great because I was flying out of a 2500 foot strip with dykes on each end (Palo Alto Airport in California). I would fly 90 knots on down wind, 80 on base and transition to 70 on final. I would roll in full back elevator trim and hit full flaps over the fence and pull the throttles back to idle she would float onto the runway almost hands off in the gentlest three point landing that you could imagine. I had never had such luck three pointing any other kind of tail wheel aircraft like that SNB-1 could. She would also slow down and stop very short without the need of much brake at all. She had the original 33SC tires and drum brakes. I would routinely get off on the first taxi way of that 2500 foot strip. I was delighted with her capabilities. When I installed the gun turret and fairings her stall characteristics were appreciable altered and the three point landing became a thing of the past.
In flight photos showed that, in normal cruise, the elevator of the SNB-1 was not streamlined with the horizontal stabilizer. It turns out that this was one of the problems that Beech wanted to rectify with the angle of incidence change. By raising the leading edge of the horizontal stab you can make the tail more streamlined and will reduce the drag thereby increasing the cruise speed. The angle change will also increase the speed at which the horizontal stab stalls thus increasing your overall stall speed and the touchdown speed/landing run. My impression was that as time went on cruise speed was more important that the short field characteristics which is why the change was adopted.
The next Beech that I flew regularly was an unmodified RC-45J (SNB-5P) which was basically a D model that was heavy with radios and other military gear. This Beech had the factory middle angle of incidence as most all D and later aircraft did. This aircraft was more critical on landing as you would tend to drop out of the sky in the three point attitude. Timing had to be right on the money unless you want to make the spar flex in ways that it wasn't meant to flex! You could still do it but the timing was critical.
I was selling rides in this Beech for a number of years so after a few months into the air show season of doing 15 to 20 flights a day I would start brushing up on the three points. I would usually pre-apologize to my passengers for the upcoming landing but it usually wasn't too bad. Once again the Beech would stop in an amazingly short distance when three pointed on. I would only try this when I was very current in the aircraft.
Most of the time a tail low wheel landing would suffice even for short strips. Speed is the critical thing for a short runway because any extra speed sure shows up in the landing roll. I would almost say that every extra knot will give you 100 more feet of landing roll. People seem to land too fast and then have to make up for it with more brake. As soon as you get the tail down with full flaps the aerodynamic braking is awesome.
The Beech that I have been instructing the most in lately is a C-45H that a forestry department in Oregon modified the heck out of. They put about every G model mod to it including a tall cabin, tall tail wheel, carb scoops and jet stacks and Hamilton tips. This aircraft also has the highest angle of incidence on the horizontal stab. This Beech is even more critical on speed especially in the pattern. If you let her get under 100 MPH anywhere in the pattern you are asking for trouble. I think that this is where some folks get into trouble in the pattern when they let themselves get too slow and then try and tighten up the turn when overshooting the final approach. This Beech will easily come out from under you if you aren't paying attention. Having said that it is still a great Beech and she does extremely well on the 2500 foot strips. She is also a lot faster, and climbs quicker that the C or D.
The short story is that the higher the angle of incidence on the horizontal stabilizer the higher the stall speed but the higher the cruise speed. Raising the leading edge of the horizontal makes the tail more streamlined and more efficient aerodynamically.
You can easily identify the angle of incidence on the tail on C and D model (low cabin) aircraft by the length of the fairing from the top of the fuselage to the top of the horizontal stabilizer. The low angle will have a fairing that is about 20 inches long from the fuselage to the tip of the fairing on the top of the horizontal. The middle angle of incidence will have a fairing approximately 10 inches long. The highest angle of incidence usually has a one piece fiberglass fairing that also wraps around the fuselage. In this configuration the top of the horizontal is almost even with the top of the fuselage, thus the small fairing on top. On many aircraft you can see two or three patterns of nut plates showing the old location of the fairings.
I believe that the low speed landing characteristics and performance of the wartime or C model aircraft are delightful. With the increased "need for speed" the tail was changed to help the top end thus sacrificing the bottom end and the landing and stall speed.
Not much has changed over the years. A friend who owns Top Gun Aviation here at Stockton, CA tells me stories of the thousands, and sometimes tens of thousands, of dollars that his customers spend on their Mooney's just to get a few more knots out of the airframe. Everyone wants to go faster which is why it is so hard to find stock aircraft these days.
I hope this very long winded answer helps.
This is the highest angle of incidence on a C-45H or D-18S. This is readily identifiable by the one piece fiberglass fairing and fillet. The top of the stabilizer is even with the top of the fuselage.
COWLINGS AND NACELLES
The engine nacelles differ between the C and the D and later aircraft. I have not been able to document this but my theory is that the longer nacelle was to cover up the fairing that was put in the upper wing skin because of the larger 1100-12 tires. Below are two shots that show the different length of the nacelles.
This is an AT-11 which is typical of the C model aircraft and all WWII military aircraft.
Notice how far back the fairing extends down the wing. The D's and later aircraft also had the leading edges changed. The leading edge contour in the C (1945 and earlier) aircraft was straight from the tip to the fuselage. In the D and later aircraft the leading edge swept forward from the inside of the nacelle to the fuselage.
This is the common carburetor intake used in the C and D model aircraft. Air entered the induction system through these scoops at the bottom of the cowling and passed through a carb heat box where ram air could be mixed with manifold heat from the muffs around the exhaust stacks.
This Beech has a ram air scoop on the bottom of the cowling. The ram air scoop will give you quite a bit of extra "boost" which shows up later in the take off roll. This aircraft has the modified ram air scoop and fixed cowl flaps but still retains the single exhaust stack.
This is a close up of the fairing over the ram air scoop on the bottom of the cowling.
This is what the manifold heat box for the ram air system looks like under the cowling.
This is the single exhaust stack common to C and D and later aircraft.
This is the short stack or jet stack configuration. This system was a common modification on aircraft that had gross weight STC's installed. Later aircraft had this system from the factory and there are several types of jet stacks. Notice that this one has a late dishpan with a fixed wrapper sheet. This aircraft also has the JPI 12-1 blower STC.
There are several different types of gear doors on the various Twin Beech's. Gear doors presented problems for Beech and their customers. Maintenance was typically the cause of the problems as the early door system requires special maintenance and attention. A mechanic who installed a 1/4 inch jam nut on a clevis, that he mistakenly thought was missing, could easily cause thousands of dollars of sheet metal damage. Beech issued several service letters on this subject to try and educate their customers on proper maintenance and rigging.
This is the early gear door system that operated with simple 1/4 inch rods and collars clamped to the gear legs. These clamps could slip when lubricated with engine oil and vibration. One fix was to tack weld the clamps the the gear legs. The Canadian's made a clamp that was twice as long thus increasing the clamping surface area. Other things can go wrong with this system as well. More to follow...
This is one of the later gear door systems in which the gear doors operated independently of each other.
The early Beech's (prior to1945) would typically use a 12x5x3 Goodyear tail wheel and had a smaller lighter truss. The D's used a 14.5 SC wheel and tire.
This shot shows a comparison between the three basic tail wheel trusses. On the right is the early truss and fork found on the C model or 1945 and earlier aircraft. The one in the middle is the D and later truss and on the left is a "Tall tail wheel" truss and fork.
The early tail wheel truss was set up for the light or 7850 gross weight aircraft. The axel is a 3/8 rod and the 12x5x3 tail wheel was notched to fit the tire to prevent slipping. These tires are hard to find which is why there are very few aircraft still running them. Most early Beech's have modified their tail wheels to a different wheel and tire. Although you can bolt in a later truss it will not retract because the opening to the rear is not big enough to accept the larger 14.5 tire.
The tail wheel is supposed to have a canvas boot up in the well to keep debris out of the airframe. This boot, which cannot be easily removed, makes servicing the tail wheel truss and retract mechanism difficult. The lack of maintenance or improper maintenance can lead to the tail gear jamming. Originally when the tail gear jammed it would stop the main gear as well so they installed an aluminum bolt to shear in case the tail got stuck. It is important to be sure that you have an aluminum shear bolt installed where the retract cable attaches to the trolley on the slide tube. You can tell if the head of the bolt has a double dash on it or if a magnet will not stick to it. Make sure your mechanic knows about this. I had a bolt shear once doing a ground check and when it did it went off with a bang! I can't help but think that I should hear or feel this in flight when the gear is being cycled. So if you hear or feel a bang after the gear starts up or down you might want to suspect that the tail gear might be disconnected from the system.
The US Navy had continual troubles with their tail gear so they issued a directive requiring that all tail wheels on Twin Beech's be fixed in the down position. Beech put out a letter saying that it is a good system when maintained properly and that you should not fix it down but just maintain it properly. It is almost exactly like the letter they put out about the gear doors which to me sums up the maintenance requirements of the Twin Beech. It needs special attention by folks who know what to look for. I have seen it over and over where regular shops do the best they can but a lot of them lack the Twin Beech experience. My advice is to find yourself a mechanic who loves the Beech, and has that thirst for knowledge to learn as much as possible, then hang on to him with all you have.
This is the D tail gear next to the tall tail wheel system. On this model they simply took a regular truss and made an extension. The other model is built without the original truss and is lighter.
This photo and the one below show the other style of tall tail wheel that is lighter than the one above. It does the same thing and weighs less.
This is a comparison shot of the original tail wheels. On the left is the 12x5x3 early wheel and tire. The middle is the 14.50 SC which stands for smooth contour. On the right is the tire available today which is squared off.
These are the same size tire (14.50) but here you can see the difference between the smooth contour, or rounded tire, and the channel type that is more squared off. The extra meat on the edges means that the tire will last longer. Depending on how much you fly the Beech can eat up tail wheel tires. The SC tires are not made any more so if you find one it will probable be over 10 years old. The tail wheel tire on a Beech is subject to side loading and possible skidding especially when the tail wheel is locked on take off and landing. All it takes is one time trying to turn off the runway with the tail wheel still locked and you will eat up the thinner rubber on the side wall eventually exposing the cords. The channel tread tires have a lot more meat on the edges so they do better in turns thus they also last longer. Save your SC tires for the judging competition and run the channel the rest of the year!
We have had a lot of problems with the new production tires with the splits in the side wall. I mostly replace tires because of these splits long before I have to change them due to wear on the treads. Manufacturers say that splits are okay if it doesn't reach the cord. I have seen splits right next to the wheel that run deep.
Many folks have installed other wheels on the tail since the tires are hard to find and are expensive. I have seen Cessna wheels and other surplus wheels used. Cleveland has an STC for their own wheel that uses a common tire.
COCKPIT GLASS AND CABIN WINDOWS
TO ALL OF OUR COUNTRY'S VETERANS, WE HERE AT VINTAGE AIRCRAFT WOULD LIKE TO SAY:
THANK YOU FOR WHAT YOU DID FOR OUR COUNTRY!
HOME PAGE VINTAGE AIRCRAFT ANNOUNCEMENTS JOB OPPORTUNITIES WARBIRD-RIDES AIRCRAFT FOR SALE HOW THIS BEECH 18 MADNESS BEGAN THINKING ABOUT A TWIN BEECH PROJECT? BEECH 18 SPAR CONCERNS BEECH 18 SPAR STRAP KITS BEECH 18 GROUND TRANSPORTATION TWIN BEECH PHOTOS BEECHCRAFT RC-45J BEECH AT-11 KANSAN RESTORATION OF AT-11 41-27603 C-45H N314WN TECHNICAL MANUALS AND PUBLICATIONS STOCKTON FIELD AVIATION MUSEUM WWII WARBIRD GROUP NORDEN BOMB SIGHT WWII RADIO PAGE AIR SHOWS AND EVENTS VOLUNTEERS WAR STORIES B-25 OLD GLORY B-29 IT'S HAWG WILD B-29 42-65401 NOSE SECTION B-29 GUNNERY SYSTEM HUMOR SEARCH THIS WEB SITE CONTACT US
7432 C.E. DIXON STREET
STOCKTON, CALIFORNIA USA 95206
(209) 982 0273
(209) 982 4832 FAX
KEEP 'EM FLYING...FOR HISTORY!