Balsa USA Bristol M-1 - RC Groups
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Dec 09, 2015, 09:38 AM
Bret Martin
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Build Log

Balsa USA Bristol M-1


My son and I built one about 12 years ago and I am going to make some changes to the new one. I am sure it would be fine to build one exactly as the plans/instructions say. This build log is not step by step instructions but more of tips and my changes.

I built the fuselage (basic box) as per the instructions. I stopped at step 30 leaving the curved pieces for the stringers off. I will ad servos, receiver, gyro, battery, motor, tank, etc. It is easier to handle with it square and not risk breaking off the curved pieces. I will add them just before step 3 “Back to the Fuselage” on page 20 that has you install the stringers.
Last edited by SlickZERO; Jan 19, 2016 at 04:36 PM.
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Dec 09, 2015, 09:41 AM
Bret Martin
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Wings


If you have room I would suggest building both wings at the same time as recommended in the instructions. Even though the wings are the same there is different information on the plans from one side to the other. My original Bristol came with wing spars that were very light contest type balsa. The solartex covering ads little rigidity so the wing had a lot of flex and twist. It is usually "breezy" here in Florida so with narrow gear many times the wing would catch the grass on take off or landing resulting in a compressed or cracked spar. The ailerons had little effect as the wing would twist in the opposite direction canceling out the aileron. I installed working flying wires and it helped a lot and made the ailerons effective.

The new kit has much stronger harder balsa spars. Also a revisions page in the manual says in order to strengthen the wings there are included shear webs to be installed on the back side of the spars. They are not shown on the plan.

Maybe my original one just had to light/weak balsa spars so this one may be OK but I substituted Basswood for the bottom spars. The top spar has to be bent down at the end so I used the strongest balsa one in the kit.
When pining down the spars it is not practical to try and push pins though the hardwood so I used T pins and held them with the top ears. Use a block or pin at the ends so they don't slide out of position while installing the ribs.
Last edited by SlickZERO; Dec 09, 2015 at 10:56 AM.
Dec 09, 2015, 10:54 AM
Bret Martin
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Shear webs


Even with the wing flat on the board, after bending the top spars down in place and glued, when pressure is released they tend to bow the wing up slightly. Before installing the shear webs, if necessary, weigh the wing down flat. After the shear webs are installed it will stay dead straight. Don’t skip the shear webs, they really strengthen the wing.
Dec 09, 2015, 11:23 AM
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If the spars are indeed balsa, they need to be hard balsa. And the sheer web would be a must. Personnally I would swap them out for spruce spars.
Dec 09, 2015, 11:58 AM
Bret Martin
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Spars


Quote:
Originally Posted by Appowner
If the spars are indeed balsa, they need to be hard balsa. And the sheer web would be a must. Personnally I would swap them out for spruce spars.
You are absolutely right. The ones in the kit are medium/hard balsa. I did use spruce for the bottoms but for the top went with the 2 hardest balsa from the kit. They were a little easier to bend down at the tips than the hardwood. I think with the shear webs they will be OK. They are much harder/stronger than the ones in the original kit.
Dec 10, 2015, 11:13 AM
Bret Martin
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Rear wing spars


I used pieces of 1/4 x 3/8 balsa and added them to the top of the rear spar in the 5 bays shown in the picture. This doubles the height of rear spars adding strength and reduces flex.
Dec 11, 2015, 07:59 PM
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Last edited by ARUP; Nov 09, 2016 at 09:48 PM.
Dec 11, 2015, 11:13 PM
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EloyM's Avatar
INTERESTING FACT! The Bristol M1 was the first airplane to fly the Andes, doing so in Dec 1918, from Chile to Argentina. It did so flying "through" the Andes, not over them as it was unable to reach the higher altitudes , the highest peak being Aconcaqua at 18-something thousand feet high. Of course no radio beacons, no weather reports, etc, probably just pointing east through every cloud opening visible.
Been there, done that - in the late 40's, but even in a C-47 we could not fly over - we went one pass at a time, and turned back more than once. Bristol flyer were indeed "Those Magnificent Men..... Eloy Marez USAF Ret
Dec 12, 2015, 02:00 PM
Bret Martin
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Quote:
Originally Posted by ARUP
These are fun airplanes! I had one but crashed it when the loop continued about 6" below ground level! lol If I were to build another I'd raise the LE of the stab 1/8". It had a tail low posture when flying straight and level. I would also 'stick build' the stab/ elev and fin/ rudder to save some weight at the rear end. I added hard points in the wing to attach flying wires (they were stranded cables but looked good to me) and I had the 'window' cut outs in the wing roots that I covered with clear acetate. Doing that made it fly just a bit better. Good luck with yours!
We did have fun with the original one. I could be wrong but changing the angle of the stab will just make it climb or dive. Like when you have a flying stab that the whole thing moves. To change the attitude of the fuse (plane) you change the wing incidence.
Last edited by SlickZERO; Jan 19, 2016 at 04:38 PM.
Dec 12, 2015, 07:01 PM
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Last edited by ARUP; Nov 09, 2016 at 09:48 PM.
Dec 17, 2015, 03:31 PM
Bret Martin
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Instructions Error


Going back to the beginning. Since there are many die cut parts that are similar I use the Key To Die Cut Parts and label them. Then remove them in groups as needed. In assembling the wing I found 2 miss labeled. On page 4 the bottom sheet in the top right corner shows it as W-2A. That should be W-3A. On the second to bottom sheet in the top right corner it shows it as W-3A and should be W-2A. At first it looks like you don't have enough W-2A. However since they only fit in their respective places it is not hard to figure out. Just a heads up.
Dec 18, 2015, 09:01 AM
Bret Martin
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Cross bracing wings


Might be overkill but I added cross braces in the 5 bays between ribs 2 and out to rib 3. The braces are not as tall as the ribs so they don't touch the covering. This does help the wing from twisting. If you elect to do this make sure you don’t cover the holes for the servo leads.

I know the addition of hard wood spars, rear spar fillers, and cross braces add a couple ounces to the weight but I feel it is worth it for the added strength.
Dec 30, 2015, 10:25 AM
Bret Martin
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Aileron hinges


For aileron hinges I am using Du-Bro Nylon Hinges #117. To prevent binding they must be at the top of the wing/aileron. I cut notches so they are flush with the top. After covering and painting they are glued in a slot cut in the covering. This worked fine on the original Bristol. If you are worried about them just being glued to the wood on one side and the covering on the other you can pin them with a 1/16” dowel. Cut the dowel flush with a sprue cutter and a dab of paint makes them nearly invisible.
Dec 30, 2015, 10:58 AM
Bret Martin
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Aileron servo horn mount


I installed the aileron horn mount per instructions. It is relatively thin and doesn’t give much “meat” for the screws to hold. On the top side I added a piece of 1/32” plywood to bring the mount up to the thickness of the trailing edge. After beveling the front to fit against the aileron spar I glued the 1/8” piece of plywood to the spar, rib, and trailing edge. This gives more wood for the screws to bite into and makes a stronger mount.
Jan 06, 2016, 12:59 PM
Bret Martin
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Motor mount and linkage


When building a plane I like to install the motor/electronic as I go. It is easier to work on and when done there a just a few final adjustment and ready to go. For the Bristol I am installing everything in the fuselage before the outside formers and stringers. It is easier to work on while it is still a square box.
I installed the motor inverted so the cylinder and exhaust will exit through the opening in the bottom. Using a shim under the left side of the mount makes the motor have right thrust as per the plan. The mount is bolted slightly off center to the left so the shaft is in the middle of the cowl.
For throttle linkage I am using a Dubro 4 stroke kit. I did substitute captured ball links for the snap on ones in the kit. To mount it I drilled and tapped for a 4-40 bolt. These work very well and have no slop.
The servo rails are installed level for the elevator and rudder. I know this is basic stuff but just a tip. Since the throttle linkage comes through the firewall lower than the servo I installed a spacer under the front of the servo so the horn lines up with the linkage. I temporarily plugged in the receiver and adjusted the linkage/end points. After it is finished I will re-install the motor, hook up the linkage, and good to go.


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