One way to mount your new or replacement engine in a model is to use a ladder! Yes, that’s right, an ordinary step-ladder you likely have around your shop!
To mount an engine at the very first point of adding the engine, or adding a new engine to an old model, you have very little way to support your plane while you try to calculate the final position while horizontal on the workbench. You need to determine proper clearance for the prop and/or spinner in front of the cowl. I have found that the best way to do this is to vertically mount your project-in-progress on a step-ladder!
Figure 1. Not to keep you wondering: a step-ladder, three clamps, and a 2×6 are the basics. Find the right height on the steps for your project.
Figure 2. But first, we’ll discuss that you may have a plane you picked up at a swap meet that needs a new engine and a lot of TLC (Tender Loving Care). This P-40 needed a new engine that was more in line with the power it deserved, a DA-60. To fit the new engine, this required the front end of the fuselage/firewall to be pushed back about 3 inches. This required carefully marking and then sawing off the original mounting flange. It takes a bit of courage and you need to be able to make some critical measurements before tackling this job! In this example, I snagged a fairly rare Troy Built 93-inch P-40E that was in need of rescue!
Figure 3. I’m committed now! Definitely left a gaping hole there!
Figure 4. Beginning of the solution. A new inner, 1/4-inch firewall, is cut to fit inside the fuselage and the outer firewall will be epoxied in front. On a large RC warbird like this 93-inch P-40, it is mandatory that you have a sufficient firewall and doubling the thickness in this case adds that extra security.
Figure 5. Once the inner firewall is epoxied into position, the outer firewall is epoxied in front. Use 30 minute epoxy, not 15 minute as you need good penetration into the plywood. Z-Poxy finishing resin can be used as well, but make sure to brush the resin on BOTH halves of the firewall, not just one half.
Figure 6. A sneak-peek before going forward. We are getting somewhere now. But mounting this engine with the fuselage horizontal on the bench will be difficult. This is where you may find yourself with a brand new model or a re-engining an older model – mounting the engine square and true to the firewall, and at the same time in line with the cowl and spinner. This is where you need to go vertical!
Figure 7. But first, the new firewall is glassed to the nose with 2 inch glass tape and Z-Poxy resin. Take the time to give the new plywood 2 coats of Z-Poxy resin to fuel-proof and improve appearance.
Figure 8. Now, with the new firewall completed, back to the step-ladder and carefully setting the P-40 as plumb and level as possible on the 2×6 with padding. Note the tape holding the tail-end plumb.
Figure 9. With the P-40 secure, the DA-60 is set on the firewall. Once you are confident it is not going anywhere, set the cowl over the engine.
Figure 10. First thing to check is to see if my calculations were correct on how much to cut off the nose back in Figure 2. Seems about right with the prop mounting back plate standing proud of the cowl by 1/4 inch. And now you can see how this type of practical testing would not be possible with the plane horizontal on the work bench. This isn’t guesswork, it’s the real deal, short of bolting it to the firewall. Now, not to panic, if your previous calculations in Figure 2 are not quite right, you can either shorten or lengthen your standoffs to set the record straight.
Figure 11. With the spinner and backplate on, looks like a good vertical alignment. This is also the time to make sure the horizontal positioning for the spinner is properly centered on the cowl.
Figure 12. Let me interject here with a photo or two of setting up a brand new model with an engine. This is a 1/4-scale SE5a build and the setup is basically the same as for the P-40. However, you have to be very careful with the fuselage at this stage of the build as it is a bit fragile. Make sure all your balsa joints are well glued! If you take your time and are careful you will be OK.
Figure 13. Here is the fuselage with the engine and standoffs in place sitting on the engine box. It is centered with the prop shaft 1/4 inch past the front of the “radiator” shell louvers and centered in the opening. The engine is a DLE-35A. This time, I used a fine point pen to mark the standoff points. Also, the sliding engine box should be marked to denote how far forward/aft it is to complete the alignment. On the work bench, once you have the engine bolted to the firewall and the engine box tack-glued to the former, you can put it back on the step ladder to recheck the engine positioning before the final gluing.
Figure 14. Back to the P-40. Carefully lift off the spinner, remove the cowl, (leave the engine on there so as not to disturb the alignment) and use CA to tack the standoffs where they sit! Don’t worry, you are using thick CA and it won’t adhere permanently. Then remove the engine leaving the standoffs tacked in place.
Figure 15. With the P-40 back on the bench, take a transfer punch and mark all 4 standoffs points with a light tap. You do this in case one of the standoffs pops off before you can drill a pilot hole.
Figure 16. Go ahead and drill a pilot hole if the standoffs are hollow as in this case.
Figure 17. Simply tap off the standoffs and drill for the T-nuts. Sand off the dried CA.
Figure 18. You can now add T-nuts on the backside of the firewall and mount your engine with long cap screws. I normally use 1/4-20 cap screws on a large, powerful engine like the DA-60cc.
Figure 19. Now that you have the engine completely bolted on, you can see the spinner and cowl fitting perfect, which would have been very difficult without a vertical engine mock-up using a common step-ladder.
Figure 20. Can’t leave you hanging, this is the P-40 after the engine replacement and plenty of TLC! Engine running full tilt! But realize that I have the P-40 well lashed down to the run-table at 5 points and 60 pounds of weight on the base of the table! Always consider your personal safety as the highest priority.
TEXT & PHOTOS BY LANE CRABTREE
4 CommentsAdd a Comment
Awesome. Will do this when I need. I’ll chanfe the engine of my old Dyna Flite PT-19 very soon.
Well written and well done! Thank you for a very useful building technique!
Unique ideas like this are extremely helpful — and it was wonderfully described and illustrated.
Thank you for the insight and a way to help in the shed. Great job