Can your Homebuilt Aircraft have Too Much Power?

Experimental Aircraft designers specify guidelines for the size of the aircraft engines to be used. What happens if you use a larger (more HP) engine than is normally used? What effect does this have on flight characteristics? In this video, we show how 3 builders of the same homebuilt aircraft ( Zenith CH701) have installed larger engines and examine the results of their choice. (ULPower, Aeromomentum, Viking Aircraft).

More about engines for the STOL CH 701: http://www.zenithair.com/stolch701/7-engine.html

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Comment by Perry delano on December 10, 2019 at 10:47pm
Thanks for the video Jon, It was exactly what I was looking for, and Thanks for your comments Jonathan.
Comment by Jonathan Porter on December 9, 2019 at 6:05pm

Great Video - BUT there are more factors than just HP.... Pulse power, stress on firewall bolt points .... torque.... fuel burn... engine mount strength.... load on the nose gear... W&B.... etc.... Weight is a big factor, as mentioned, but I do believe that some of those airframes were considerably modified (gauge increases, etc) as part of the Experimental builders flexibility in moving to higher horses.... One area to watch is the tail feathers - because they are going to get a lot more propwash over them!  In some countries, there will not be authorisations to increase beyond the suggested HP (or maybe + 10 to 15%) .... In some places, the extra power is essential - but there is so much to take into account - and without understanding it and embracing it more power may mean more headaches!  Oh, and remember the VNE won't suddenly move up - so watch the risks of stress during straight and level at higher speeds.... surprises happen!  Think twice, and if you go the route.... having operated the 701 in Africa at 40C (104F) and over rain forest, with the 80 and 100hp engines, we never found they lacked performance for the missions we needed.... Our next 701 is going to be with the Direct Drive 107Hp UL260iS, and we will be working on the prop setup to get the most out of the engine... No it won't be the same as a geared engine, but it will still perform and do what it says on the tin!  Enjoy!

Comment by Sebastien Heintz on December 9, 2019 at 4:32pm
Thanks for another great video Jon! I do need to point out that, contrary to the end note, the designer does not "bless" engine selections. As you note, we recommend a power range for the aircraft (in this case 65 - 100 hp, up to 185 lbs. installed) as a guide for builders to help them choose an engine for the aircraft they are building. As pointed out by others in the YouTube comments, the size (hp and weight) of the engine will affect performance, specifications and flight characteristics of the aircraft. Also, the weight and balance of the aircraft may be adversely affected by different engines, and the original fuel system may not be adequate or suitable for some engines and installations, and most alternative engines will require a custom engine mount and cowl. It is the owner's responsibility to operate the aircraft within its design limitations (most notably gross weight and Vne when adding a bigger engine). As an airframe kit manufacturer, Zenith Aircraft Company does not manufacture or directly support engines nor their firewall-forward installations.
Remember to keep it light! Remember too that the high-lift features of the design give the STOL CH 701 its excellent short take-off and landing capability, and not just power. More about alternative engines for the Zenith STOL: http://www.zenithair.com/stolch701/7-engine.html
Comment by Zenith Aero on December 9, 2019 at 4:12pm

Zenith builders and owners: What's your experience using alternative engines? The GOOD, the BAD?

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